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Concrete Technology for Transportation Applications (2019)

Chapter: Chapter 2 - Overview of Concrete Technologies

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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
×
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
×
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
×
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
×
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
×
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
×
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
×
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
×
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Suggested Citation:"Chapter 2 - Overview of Concrete Technologies." National Academies of Sciences, Engineering, and Medicine. 2019. Concrete Technology for Transportation Applications. Washington, DC: The National Academies Press. doi: 10.17226/25701.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

10 Introduction This chapter includes an overview of established, emerging, and new concrete technologies and materials used by state highway agencies in construction, rehabilitation, and repairs of pavements, bridges, and other structures. The technologies include the following: • High-strength concrete (HSC); • Self-consolidating concrete (SCC); • Internally cured concrete (ICC); • Ultrahigh-performance concrete (UHPC); • Temperature control of mass concrete (TCMC); • Precast concrete pavement (PCP); • Roller-compacted concrete (RCC); • Pervious concrete (PC); • Recycled concrete aggregate (RCA); • High early strength concrete (HESC); • Very high early strength concrete (VHESC), repair materials, and alternative cementitious materials; and • Performance-engineered concrete mixtures (PEM). Most technologies listed above have been developed for some time and many are being specified and used by state DOTs. However, technologies such as ICC and PCP may be con- sidered as emerging technologies. In recent years, there has been growing interest by some state DOTs in PCP and ICC technologies. Some states have constructed and are evaluating the technologies in demonstration projects. Some states have even developed specifica- tions and construction guidelines and have implemented these technologies in roadway and bridge projects. PEM is a new concept in specifying concrete. A number of states in conjunction with FHWA and academia are developing performance criteria for acceptance based on spe- cific tests that measure or evaluate performance indicators rather than specific material properties. In discussing each technology an introduction is provided to briefly describe the technology. This is followed by benefits and needs for the technology. Also, information is provided on materials, mixture parameters, construction, tests and/or basic properties, a brief dis- cussion of specifications and implementation examples, and technology limitations and challenges. C H A P T E R 2 Overview of Concrete Technologies

Overview of Concrete Technologies 11 High-Strength Concrete Introduction HSC is defined by ACI 363R-10 (1) as concrete having a specified compressive strength of 8,000 psi (55 MPa) or greater, and it does not include polymer-impregnated concrete, epoxy con- crete, or concrete made with artificial normal-weight and heavyweight aggregates. ACI recognizes that as technology improves and higher compressive strengths are successfully demonstrated, it is likely that the definition of HSC will continue to be revised. Compared with normal-strength mixtures, HSC requires higher quality materials, the use of water-reducing admixtures, and more rigorous specification requirements for QA/QC tests and procedures to ensure that the mixture consistently meets the required workability, volume stability and strength development. The highest specified concrete compressive strength, as reported by ACI, is 14,700 psi (101 MPa) in Texas (1). In fact, a survey of state DOTs conducted in conjunction with this syn- thesis study showed that 15 of the 40 DOT responses indicated specifying UHSC with strengths exceeding 10,000 psi (69 MPa) (Appendix B). (UHSC is defined in this synthesis as concrete with compressive strength exceeding 10,000 psi.) Benefits HSC has demonstrated significant benefits in transportation projects in terms of optimizing structural design and accelerating construction and repairs of structures and pavements. With respect to design, the use of HSC allows the design of thinner and longer bridge girders (Figure 1) placed at wider spacings and/or requiring less steel reinforcement. Pavements constructed with HSC can also be optimized to handle heavier traffic volume over an extended service life without increasing their thicknesses. HSC may be specified in other concrete technologies such as SCC, UHPC, HESC, and ICC. These technologies are used in accelerated construction and repairs. SCMs such as fly ash, slag, and silica fume are often included in HSC mixtures. Their addition in conjunction with the use of water-reducing admixtures and low water–cement ratio not only produces high strength but also enhances concrete durability and longevity of the structure. Applications Since the 1990s, the use of HSC in prestressed concrete bridge girders has significantly increased (12). In the mid-1990s, many demonstration projects were constructed as a result Figure 1. Eighty-foot high-strength concrete prestressed girder.

12 Concrete Technology for Transportation Applications of the FHWA initiative to implement the use of HSC in bridges. Since then, the use of HSC has been expanded in all states as well as in more diverse applications such as bridge and tunnel components that are cast-in-place, precast/prefabricated, and prestressed and in pavement construction and repairs. HSC Mixture Materials Cementitious Materials Type II cement and SCMs such as slag or fly ash (Classes F and C), or blended hydraulic cements incorporating slag or fly ash, can be used in the production of HSC, provided they are in appropriate quantities that meet the strength and heat-of-hydration requirements (1). The type and amount of cement and SCMs can have a significant effect on temperature development within the concrete. Unless high early strength is required, such as in prestressed concrete, there is no need to use Type III HESCs that generate high heats of hydration. SCMs such as fly ash (Classes C and F), slag, silica fume, and metakaolin are widely used in binary or ternary concrete mixtures to produce HSC. In finely divided form and in the presence of moisture, they will chemically react with calcium hydroxide released by cement hydration to form additional calcium silicate hydrate gel and thus contribute to the high-strength properties (1). It is important that all cementitious materials be tested for acceptance and uniformity and be carefully investigated for strength-producing properties and compatibility with the other materials in the mixture, particularly chemical admixtures, before they are used in the work (1). Admixtures Chemical admixtures are widely used in the production of HSC. Selection of type, brand, and dosage rate of all admixtures needs to be based on performance with the other materials being considered or selected for use on the project. Significant increases in compressive strength, con- trol of rate of hardening, accelerated strength gain, improved workability, and durability can be achieved with the proper selection and use of chemical admixtures (1). A reliable track record of good performance in previous work and compatibility with the pro- posed cementitious materials and between chemical admixtures needs to be considered when selecting admixtures. Specifications for chemical admixtures and air-entraining admixtures are covered under ACI 212.3R, ASTM C494/C494M, and C260. The most commonly used admix- tures (1) are discussed. Retarding Admixtures (ASTM C494/C494M, Types B and D). Retarding admixtures are highly beneficial in controlling early hydration, particularly as it relates to strength (ACI 212.3R) (13). With all else being equal, increased hydration time results in increased long-term strength. Retarding admixtures are also beneficial in improving mixture workability. They can control the rate of hardening in the forms to eliminate cold joints and provide more flexibility in place- ment size and duration. The dosage of a retarding admixture can be adjusted to give the desirable rate of hardening under anticipated temperature conditions. Retarding admixtures frequently provide a strength increase proportional to the dosage rate, although the selected dosage rate is significantly affected by ambient temperature conditions (13). In hot weather, higher dosage of retarders in the mix- tures would mitigate temperature-induced strength loss. In winter months, lower dosage will prevent delayed setting time.

Overview of Concrete Technologies 13 Normal-Setting Admixtures (ASTM C494/C494M, Type A). These are water-reducing admixtures, commonly called normal-setting admixtures, that can provide strength increases while having minimal effect on setting time and hardening of concrete. High-Range Water-Reducing Admixtures (ASTM C494/C494M, Types F and G). High- range water reducers (HRWRs) reduce the mixture water and allow lower water–cement ratio, improve efficiency of the cement hydration and thus aid in developing HSC, particularly at early ages (24 hours) (14). The use of HRWRs tends to increase concrete strength through reduc- tion in the water–cement ratio while maintaining a consistent slump, or increasing slump while maintaining equal water–cement ratio, or a combination of both effects. HRWR admixtures frequently perform better in HSC mixtures when used in combination with conventional water-reducing admixtures or water-retarding admixtures. This is because of the increased slump retention and control of the hydration (1). Accelerating Chemical Admixtures (ASTM C494/C494M, Types C and E). Accelerating admixtures are not normally used in HSC unless early form removal or early strength development is absolutely critical. HSC mixtures can usually be proportioned to provide strengths adequate for vertical form removal on walls and columns at an early age. In pavement repair applications they contribute to rapid strength gain in HESC to allow opening the pavement to traffic (1). Air-Entraining Admixtures (ASTM C260). Air entrainment is needed to enhance mixture workability in the plastic stage and the freeze-thaw resistance in hardened concrete. However, entrained air can significantly reduce the strength of HSC mixtures and increase the potential for strength variability. This means that extreme caution needs to be exercised with respect to the use of air entrainment in HSC. Even though many DOTs require entrained air in prestressed precast HSC bridge girders, their use needs to be carefully evaluated for cast-in-place applications (1). Chemical Admixture Combinations. Water-reducing, set-retarding, and HRWR admixtures, or a combination of these types, have been used effectively to control water demand, rate of hydra- tion, slump loss, and strength increase. Combining HRWRs with water-reducing or -retarding chemical admixtures has become common practice to achieve optimum performance at lowest cost. Self-consolidating HSC mixtures are frequently produced using HRWRs in conjunction with viscosity-modifying admixtures. With optimized admixture combinations, improvements in strength development and control of setting times and workability are achievable (1). Aggregates Production of HSC requires proper selection of quality aggregates for the specific application. Coarse aggregate mineralogical characteristics, grading, shape, surface texture, elastic modulus (stiffness), and cleanliness can influence concrete properties. Both fine and coarse aggregates used for HSC need to, at a minimum, meet the requirements of ASTM C33/C33M. HSC often uses higher strength and higher quality aggregates to generate the targeted com- pressive strength level. Using normal-strength or low-quality aggregates will result in fracture of the aggregate before fully developing the strength potential of the paste matrix or bond strength of the aggregate–paste transition zone. Coarse aggregate may have a more significant effect in HSC than in conventional concrete (15). In conventional concrete, compressive strength is typically limited by the cement paste capacity or by the capacity of the bond between coarse aggregate and cement paste. In HSC, where the cement paste and coarse aggregate–cement paste bond are enhanced by the use of SCMs and low water–cement ratio, ultimate strength potential may still be limited by the strength of the aggregate particles (16).

14 Concrete Technology for Transportation Applications Maximum aggregate sizes of 1/2 in. (13 mm), or smaller sizes of coarse aggregate and crushed coarse aggregate, are needed for use in HSC. Smaller sizes of coarse aggregate have greater sur- face area for a given aggregate content, which improves bond between coarse aggregate and cement paste and thus enhances the ultimate strength of concrete. Mixture Proportioning Concrete mixture proportions for HSC have varied widely. Factors influencing mixture pro- portions include the required strength level, material characteristics, and type of application. Mixture proportioning of HSC is a more critical process than proportioning normal-strength concrete mixtures. The use of SCMs, admixtures, and low water–cement ratio are considered essential in high-strength mixture proportioning. Many trial batches are often required to generate and enable optimum mixture proportions to be identified (1). HSCs made with SCMs may gain considerable strength at later ages. Therefore, they may be evaluated at later ages, such as at 56 or 90 days, when construction requirements allow the concrete more time to develop strength before loads are applied. Water–Cementitious Material Ratio Higher cementitious material contents and lower water contents have produced higher strengths. In many cases, however, using larger amounts of cementitious material increases water demand. The use of HRWRs has enabled concrete to be placed at flowing and self- consolidating consistencies with lower water–cement ratio. Water–cementitious material ratios by mass for HSCs have typically ranged from 0.25 to 0.40. Supplementary Cementitious Materials Typical SCMs include fly ash, slag, silica fume, and metakaolin and other pozzolans and cementitious materials. The total cementitious content, including cement and SCMs, in HSC has ranged from 650 to 1,000 lb/yd3 (386 to 593 kg/m3). Incorporating SCMs and admixtures can significantly increase concrete strength and durability (17). Today, UHSC with specified compressive strengths up to 16,000 psi (110 MPa) at 56 days have been produced successfully. Another important benefit of the SCMs in HSC is their impact on reducing the heat gener- ated by the cement hydrations. The rise in temperature and, subsequently, the peak temperature resulting from high cement content in HSC mixtures can be reduced by using slag cement and pozzolans. Reduction in the peak temperature also reduces the potential for cracking and loss of durability, especially in hot weather and mass concrete. Aggregate Low fine aggregate contents with high coarse aggregate contents have resulted in a reduction in paste requirements and have typically been more economical. Also, such proportions have made it possible to produce higher strengths for a given amount of cementitious materials. However, if the proportion of fine aggregate is too low, there may be serious problems in mixture workability. In HSC, it has been found that the highest strengths for a given water–cement ratio are obtained by using smaller maximum size coarse aggregate. However, the selection of coarse aggregate size and content for HSC may be influenced by mixture requirements such as modulus of elasticity, creep, shrinkage, and heat of hydration. For these cases, larger aggregate sizes may be more desirable. In general, the least amount of fine aggregate consistent with necessary workability gives the best strength for a given paste. Mixtures with objectionably high coarse aggregate contents,

Overview of Concrete Technologies 15 however, may exhibit poor pumpability or may be significantly more prone to segregation during placement and consolidation (1). Construction Batching and Placement HSC may be mixed entirely at the batch plant, in a central or truck mixer, or by a combina- tion of the two. Batching, mixing, transporting, placing, and control procedures for HSC are not essentially different from procedures used for normal-strength concretes. Special consideration, however, needs to be given to minimizing the length of time between concrete batching and final placement in the forms. Delays in concrete placement can result in a subsequent loss of long- term strength or difficulties in concrete placement (1). Curing The potential strength and durability of HSC will fully develop only if the concrete is properly cured for an adequate period. Cast-in-place HSC needs to be water cured because of the low water–cement ratio in the mixture. At a water–cement ratio below 0.40, the ultimate degree of hydration is significantly reduced if an external supply of water is not provided. ACI 308-16 “Guide to External Curing of Concrete” provides guidance for curing methods and materials, curing for different types of construction, and means for monitoring curing procedures and effectiveness (18). The most effective method of water curing is ponding the horizontal surfaces with water. In many projects, however, this is not feasible or practical. Other methods include fogging, misting, or spraying at very early ages. Lawn sprinklers, applied continuously, are effective where water runoff is of no concern. Soaker hoses are useful, especially on surfaces that are vertical. Burlap, cotton mats, rugs, and other coverings of absorbent materials will hold water on the surface, whether horizontal or vertical. Liquid membrane-forming curing compounds assist in retaining the original moisture in the concrete but do not provide additional moisture or completely prevent moisture loss. Monomolecular film-forming agents have been effectively employed for interim curing before deployment of final curing procedures for exposed surfaces susceptible to drying during finishing. These so-called “evaporation retarders” are not to be used as an aid to finishing (1). Tests and Properties Compressive Strength The compressive strength in HSC is usually much higher than 8,000 psi (55 MPa). Also, accord- ing to Florida DOT research, HSC of 8,000 psi or higher can also be considered high-performance concrete with respect to low permeability and corrosion resistance (19). This has been attributed to the low water–cement ratio and the use of SCMs. With compressive strength, some exceeding 10,000 psi (UHSC), the concrete is often sampled and tested using 4- by 8-in. (10- by 20-cm) cylinders, which are more compatible with loading limits of most testing machines than 6- by 12-in. (15- by 30-cm) samples. Also, proper grinding of the sample’s ends, or using capping compounds or rubber caps, will ensure plainness of the sample’s ends and reduce the variability in the compressive strength test results (20). HSC gains a higher rate of strength at early ages compared with lower-strength concrete. The typical ratios of 7- to 95-day strength average 0.60 for low-strength concrete, 0.65 for medium- strength concrete, and 0.73 for HSC (21). It seems likely that the higher rate of strength devel- opment of HSC at early ages is caused by an increase in the internal concrete temperature due

16 Concrete Technology for Transportation Applications to a higher rate of heat of hydration, tighter spacing between the hydrated cement, and a lower water–cement ratio. Resistance to Freeze-Thaw The use of air entrainment to increase resistance to freeze-thaw actions can contribute to lowering the strength of HSC. Research results are inconclusive about the role and the appro- priate dosage rate of air-entraining admixtures in HSC (1). Some studies have indicated that with the low water–cement ratio and the use of SCMs, the HSC will have very low permeability and high tensile strength, making the concrete structure more resistant to freeze-thaw actions. This may negate the use of a large dosage of air entrainment (22, 23). Shrinkage For normal-strength concrete with highwater–cement ratio, the change in volume due to evaporation of the unbound portion of the mixture water, commonly termed drying shrinkage, is the predominant mechanism. For HSCs that have a low water–cement ratio and high binder content, other volume-change mechanisms influence the overall magnitude and rate of shrink- age and possible cracking. Most important among these are chemical shrinkage and autogenous shrinkage. Chemical shrinkage refers to the reduction in absolute volume of solids and liquids in paste resulting from cement hydration (1). The absolute volume of hydrated cement products is less than the absolute volume of cement and water before hydration (24). Autogenous shrinkage is that portion of chemical shrinkage that starts at initial set and results in volume change in concrete. It has been reported that autogenous shrinkage can be significant for HSC with water– cement ratio less than 0.40 and silica fume content greater than 10% (1). Permeability Moist curing not only influences the strength development, but also contributes to lowering the permeability of concrete. As the moist-curing period is increased, the strength development will increase, and the permeability will be lower (25). The use of highly porous aggregates will increase the permeability of the concrete because substances can flow more easily through aggregate pores than through smaller pores of the cement paste (25). However, a Florida DOT research project showed that HSC mixtures using Florida limestone aggregate with high absorp- tion capacity, compared to dense limestone, river gravel, and granite, can achieve a similar low permeability, using mixtures that include a combination of fly ash, slag, and silica fume and low water–cement ratio (26). Another study by the Virginia DOT (27) demonstrated the effectiveness of using silica fume, fly ash and slag to reduce concrete permeability and increase its durability. Specifications Most state DOTs have specification requirements for classes of concrete that are considered high strength and high performance (28). The specifications apply mostly to bridge structural members. The strength requirement is not necessarily set at 8,000 psi, but rather, at lower strengths, with no limits on how high the concrete strength may reach during trial batches or production. The specification requirements for the concrete generally include allowable cement types and quantity, minimum water–cement ratio, SCM types, and proportions. Also included are plastic properties such as slump and air content as well as hardened properties such as strength and durability. Some states provide special requirements for mass concrete and environmental con- ditions with respect to temperature control, monitoring, and testing needs.

Overview of Concrete Technologies 17 Challenges of HSC The initial cost of HSC is higher than that of normal-strength concrete. This is due to the use of higher quantities of cementitious materials and admixtures in the mixture as well as higher cost of QA/QC to achieve a higher and more consistent quality of concrete during production and in various stages of construction from placement to curing. Another challenge is personnel experience in producing HSC and maintaining the speci- fied concrete properties such as workability, strength, and durability. This requires more training and greater availability of experienced personnel at the project site and in the con- crete plants. Also, with the use of high cement content, the heat generated from cement hydration can result in significant rise in concrete temperature, causing cracks and delamination in new struc- tures, pavements, overlays, and repairs. However, the benefits of optimizing the design and accelerating construction tend to offset the disadvantages of higher initial cost and other challenges with HSC. Also, using HSC with its enhanced durability will most likely result in less maintenance and longer service life. Self-Consolidating Concrete Introduction SCC (Figure 2) is a highly flowable, nonsegregating concrete that can spread into place, fill the formwork, and encapsulate the reinforcement without mechanical consolidation (2). SCC is used primarily in cast-in-place or precast structural members with highly congested reinforcement. In general, SCC mixtures are produced with conventional concrete materials, and incor- porate admixtures such as high-range water reducers, viscosity modifiers, set retarders, and workability retainers to achieve a high workability maintained for an extended period of time. SCC has normal setting time and develops strength similar to that of conventional concrete (29). Figure 2. Self-consolidating concrete mixture— VSI rating 1 (30, pp. 37–38).

18 Concrete Technology for Transportation Applications Benefits SCC mixtures have become more widely used in construction due to their favorable char- acteristics, which include increased construction productivity, improved work environment and safety, and higher strength and durability (2). With its high flow rate, the SCC mixture is discharged in narrow and/or deep forms with congested reinforcement. The concrete mixture rapidly fills the form without leaving voids and fully encapsulates the reinforcing bars and self- consolidates without the need for external vibration. In precast plants, SCC mixtures can be dis- charged from one point and allowed to travel some distance to fill a large portion of the precast member without segregations. The SCC mixture is likely to include SCMs, a blend of workability and water-reducing admix- tures and low water–cement ratio. This mixture would produce HSC with enhanced durability suitable for use in structures subjected to highly aggressive environments. Also, in precast plants, the SCC mixture can be designed to achieve the necessary strength in less than 24 hours to allow early stripping of the forms and release of the prestressing strands in the cast member. Applications Among precast applications for SCC are prefabricated bridge construction, including decks and girders, and tunnel-lining segments and building structures (31). Cast-in-place applications include columns, walls, and bridge piers and girders. Virginia recently used SCC for bridge sub- structure repairs (32). Application of SCC in pavements has been limited to research and small experimental projects. In Iowa, SCC was used in an experimental project to evaluate its applica- tion in concrete pavement using slipform paving, and in Florida, research was conducted on the use of high early strength SCC mixtures for accelerated slab replacement (30, 33, 34). Materials SCC mixtures include the same basic ingredients used in conventional concrete mixtures. However, the SCC mixtures must achieve three important characteristics: (1) sustained fluidity over a long period, (2) stability to travel without segregation, and (3) ability to consolidate and self-level in the form without the aid of external vibration. Cementitious Materials In addition to portland cement, other cementitious materials such as fly ash, silica fume, and ground-granulated blast-furnace slag (GGBFS), and fillers such as limestone powder, can be incorporated in the mixture as partial replacement of the cement content to produce high- performance and durable SCC (35, 36, 37). These cementitious materials benefit the SCC by enhancing both its plastic and hardened properties, as well as controlling the heat of hydration. For example, silica fume and GGBFS with their finer particles (compared to cement) tend to increase the stability of SCC mixtures. Fly ash, with its spherical and smooth particles, can act as a ball bearing in the mixture to enhance SCC workability, facilitate its spread in forms, and improve the compressive strength (35, 36). The replacement of a portion of cement with finely ground limestone filler has also been shown to improve packing density and stability of the mixture. The concrete may exhibit up to 10% lower 28-day strength compared with similar concrete without the filler, according to ACI Report 237R-07 (2). However, a recent study showed slightly different results. SCC mixtures with 15% ground-limestone filler produced similar or marginally higher compressive strengths at 28, 90, and 180 days than those of the reference concrete (37). These slight improvements, which ranged between 2% and 8%, were partially attributed to the limestone powder’s filler effect, which improved the packing density of the studied SCC mixtures. The replacement of

Overview of Concrete Technologies 19 part of the cement with a less reactive powder may prove beneficial when project requirements limit the heat of hydration. Aggregate The intended type of application of the SCC mixture dictates the appropriate shape, nominal maximum size, and gradation of coarse and fine aggregates (2). The nominal maximum size of the coarse aggregate needs to be chosen to achieve an acceptable spread within the form, a pass- ing ability around the congested reinforcement, and a stability to resist segregation of the SCC mixture. ACI 237R-07 (2) suggests that the nominal maximum size of the coarse aggregate be one size smaller than that recommended by ACI 301, “Specifications for Structural Concrete,” to improve the passing ability. If the coarse aggregate is greater than 1/2 in. (12.5 mm) nominal maximum size, then the absolute volume of coarse aggregate needs to be in the range of 28% to 32% of the volume. For slab placements without reinforcement to obstruct the flow, the nominal maximum size and percentage of total volume of coarse aggregate in the SCC mixture may be increased (38). The particle shape of the coarse aggregate will affect the workability of SCC. For the same water content, a rounded coarse aggregate will provide greater mixture workability to fill and consolidate within the formwork compared with a crushed stone of similar size. Also, blending of different aggregate sizes can often improve the overall characteristics of the mixture. The fine aggregate component needs to be well graded and preferably prepared from a blend of natural and manufactured sand to improve the mixture’s plastic properties (2). Admixtures Polycarboxylate-based HRWRs are the most typical admixtures used for developing and proportioning SCC mixtures. They tend to maintain workability of SCC mixtures to allow longer transportation and construction time, as well as allowing the reduction of mixture water to produce concrete with higher strength and lower permeability. Additionally, some, but not all, HRWRs enhance stability and cohesiveness of the mixture (2). Viscosity-modifying admixtures (VMAs) are used to adjust the viscosity and to improve the ability of SCC mixtures to resist segregation. A VMA used with a compatible HRWR improves the viscosity of the mixture and increases its ability to tolerate water adjustments between batches. The use of a VMA is not always necessary, but a VMA can be advantageous when using lower powder content and gap-graded aggregates (2). In addition to HRWRs and VMAs, other admixtures and additives are often utilized in SCC. These may include air-entraining admixtures, normal and mid-range water reducers, accelera- tors, retarders, extended set-control admixtures, corrosion inhibitors, shrinkage reducers, and liquid and dry color. Fibers can also be specified for use in SCC (2). Guidelines have been developed for the use of SCC in precast and prestressed concrete bridge elements (39). These guidelines address the selection of constituent materials, proportioning of concrete mixtures, testing methods, fresh and hardened concrete properties, production and quality control issues, and other aspects of SCC. Many of these recommendations can be adopted for cast-in-place applications of SCC. Mixture Proportioning SCC mixtures need to be both fluid and stable to be successfully cast to achieve the desired structural characteristics and durability performance. The required level of fluidity is greatly influenced by the specific application. The fresh properties of SCC have a much higher degree of workability and self-consolidation than any conventional concrete. The workability

20 Concrete Technology for Transportation Applications characteristics of SCC include filling ability, passing ability, and stability (segregation resistance). These characteristics need to be present in concrete mixtures to be considered SCC. To achieve these characteristics, the SCC mixture needs to be carefully proportioned to account for the application type and placement technique. Combining finely divided cementitious and filling powders with portland cement and incorporating a blend of admixtures can enhance the behavior of fresh SC in terms of its form filling ability, passing ability, and stability (2). The intended application of the SCC can significantly affect the appropriate mixture propor- tions. The proportions of fine and coarse aggregate and powder content (cement, SCMs, and finely divided powders) for SCC need to be balanced to achieve the desired fresh and hardened properties. For noncongested footings and in plain slab applications, SCC mixtures can include a larger size and higher percentage of coarse aggregate and lower slump flow compared to an SCC being used in a congested girder or column applications (2, 30). Columns and wall forms congested with reinforcing steel will require an SCC mixture with greater passing ability to fully encapsulate the reinforcement, enhanced stability to minimize segregation, and a well-balanced ingredient to develop sufficient strength to meet the load requirement (2). The quantity, size, and spacing of steel reinforcement in a structure, if any, and method of SCC delivery and discharge play a major role in determining the filling ability, passing ability, and stability requirements (29). Examples of successful SCC mixture designs, as suggested by ACI 237 (2), are shown in Table 1. ACI emphasizes that the mixture proportions in Table 1 should not be copied or used in a project without first performing field trials, because local materials may have a considerable effect on the proportioning of SCC mixtures. The desired SCC performance needs to be verified for local materials and admixtures, application type, construction methods, and weather condi- tions. Table 1 mixtures can be used as a starting point, but then adjusted for the local condi- tions. It is important to perform trial batches of the candidate SCC mixture to make any needed adjustments in water and admixture contents to arrive at the proper slump flow and stability for the specific application. Construction Mixture Production Similar to other types of concrete, strict control of the materials characteristics and moisture conditioning of the aggregates is paramount for successful production of SCC mixtures. It is important that a consistent source of raw materials be used throughout the duration of a project. Causes of variability in performance among the batches of the SCC production mixture are changes in material characteristics and moisture condition of aggregates. Also, controlling the mixing temperature and using appropriate dosage of admixtures have been found to be important factors in controlling mixture set time and heat of hydration (40). Transport. SCC can be delivered to a job site by truck mixers. A concrete truck is an effective method of transporting and placing SCC mixtures with slump flow levels of 18 to 30 in. (455 to 760 mm) (41). However, because of the fluidity of SCC mixtures, the volume of SCC placed into a truck should not exceed 80% of the capacity of the drum in areas where the truck travels on steep inclines to avoid spilling the fluid concrete. Also, to avoid drastic loss of fluidity, it is advised that the revolving drum be turned in the mixing mode direction while in transport. Note that use of some HRWRs will result in slump flow loss more rapidly than others during transportation. This needs to be taken into consideration when preparing the production mixture to ensure proper fluidity and stability upon arrival of the concrete truck to the casting site. Alternatively, some suppliers have delivered the mixtures to the project at a conventional concrete consistency and then added an HRWR to bring the mixture to an SCC consistency prior to placement (2).

Overview of Concrete Technologies 21 Placement. SCC is placed in the forms by concrete truck, pump, hopper, bucket trans- porters, or other specialized devices such as tremies. A properly designed SCC mixture can easily be pumped into place without segregation. The height of discharge in tall walls and columns needs to be shortened to avoid mixture segregation. The fluid SCC mixture can flow long dis- tances without any mechanical consolidation. In practice, the flow distance is typically limited to 33 ft (10 m) to mitigate segregation of the concrete while ensuring self-consolidating properties. When used in cast-in-place slabs and precast forms (Figures 3 and 4), the SCC flow and space filling of the open pit, mold, or formwork is affected by the placement method and the concrete fluidity and stability. These characteristics need to be considered when designing SCC mixtures for slabs and precast elements. Trial batching is imperative to ensure successful placement characteristics. When placing SCC, the formwork needs to be watertight (nonleaking) and grout-tight, espe- cially when the mixture has relatively low viscosity. Also, there is a need to design the formwork for water tightness compared to conventional formwork so as to avoid honeycombs and sur- face defects. Also, the highly fluid nature of SCC may lead to higher formwork pressure than Slump flow 26 in. 26 in. 26 in. 33 in. 27 in. 26 in. Polycarboxylate Yes Yes Yes Yes Yes Yes Air entraining Yes Yes Yes Yes Yes Yes Water reducer Yes — — Yes — — VMA — — — Yes Yes Yes Total cementitious material, lb/yd3 750 680 780 797 700 700 Cement 600 680 620 345 700 600 Fly ash 150 — — 140 — 100 GGBFS — — 160 312 — — Water–cement ratio 0.37 0.42 0.39 0.34 0.41 0.40 Paste fraction (%) 37.1 36.5 38.1 36 34.7 35 Mortar fraction (%) 64.6 68.3 63.4 64 59.5 65.6 Volume of coarse aggregate (%) 35.6 31.7 36.6 36 31 33.5 Total gradation (sieve size), % retained 1.0 in. (25 mm) — — — — — — 3/4 in. (19 mm) 2.3 — 0.7 0.75 3 9 1/2 in. (12.5 mm) 9.2 — 11.3 5.6 15 19 3/8 in. (9.5 mm) 5.1 — 6.5 11.8 14 8 No. 4 (4.75 mm) 25.4 26.6 23.6 26.2 15 14 No. 8 (2.36 mm) 14.4 23.3 16.9 12.4 16 4 No 16 (1.18 mm) 9.5 10 5.7 12.5 14 12 No. 30 (600 µm) 11.1 12.5 8.2 20.1 10 13 No. 50 (300 µm) 12.2 14.2 18.4 8.5 8 14 No. 100 (150 µm) 7 11.2 7.1 1.5 3 6 Pan 3.9 2.3 1.4 0.24 1 1 Note: 1 lb/yd3 = 0.593 kg/m3. Dash = no information provided in reference to indicate that the item aMust perform trial batches to verify properties and performance for local materials, application, construction methods, and weather conditions. was not used or applied. Table 1. Examples of successful SCC mixturesa (2).

22 Concrete Technology for Transportation Applications conventional concrete, especially when the casting rate is high. Therefore, the formwork designs must accommodate the expected liquid head pressures. This will allow unrestricted placement rates and permit the contractor to take full advantage of a fast casting rate of the SCC. During construction, SCC needs to be discharged at one point and allowed to flow into place before moving the point of placement. Also, when possible, SCC needs to be discharged in the direction of desired flow to maximize the distance of travel. A fresh layer of SCC can be placed onto recently placed SCC that has not yet achieved initial set. In this case, it is acceptable to use an internal or external vibrator for a 2- to 3-second duration. However, the concrete needs to be deposited continuously and in layers of such thickness that no fresh layer is placed on concrete that has hardened enough to cause a seam or plane of weakness. If a section cannot be placed continuously, construction joints need to be provided (2). For casting new or replacement slabs using SCC, it is advised to have sufficient workers avail- able to accomplish surface strikeoff and finish in a timely manner. This is due to faster SCC placement that yields a larger concrete surface area at a given time interval ready to be finished as compared to conventional concrete (2). Also, research at FAMU-FSU College of Engineering showed that when using accelerators in high early strength SCC for slab replacements, surface Figure 3. Placement of SCC in a slab pit (38). Figure 4. Placement of SCC in precast member (courtesy of Dura-Stress, Florida).

Overview of Concrete Technologies 23 strikeoff and finish need to be executed simultaneously with concrete placement because the mixture tends to set much faster when stationary than conventional concrete (38). Curing. There should not be a difference in curing requirements for SCC compared with curing for conventional concrete mixtures. Curing is essential, and early protection of exposed surfaces is key to preventing rapid moisture loss that could lead to plastic shrinkage cracking. Tests and Properties Quality Assurance/Quality Control Tests The four main characteristics of SCC are ability to fill the form under its own weight, resist segregation, flow through reinforcing bars or other obstacles without segregation and without mechanical vibration, and achieve a quality surface finish (2). To evaluate these characteristics of SCC, the following tests can be performed. Slump Flow. This test is based on ASTM C143/C143M and is used to determine the hori- zontal free-flow or spread characteristics of SCC in the absence of obstructions (Figure 5). The common range of slump flow for SCC is 18 to 30 in. (450 to 760 mm). The higher the slump flow, the farther the SCC can travel under its own mass from a given discharge point and the faster it can fill a form or mold. Visual Stability Index. The VSI test involves visual evaluation of the SCC slump flow spread resulting from performing the slump flow test. It is used to evaluate the relative stability of batches of the same or similar SCC mixtures. A VSI rating of 0 or 1 is an indication that the SCC mixture is stable and should be suitable for placement. A VSI rating of 2 or 3 indicates possible segregation potential and that the SCC mixture materials and/or proportions need to be adjusted to ensure stability. An example of VSI rating of 1 (stable mixture) is shown in Figure 2. Figure 5. Slump flow test.

24 Concrete Technology for Transportation Applications J-Ring. This test (ASTM C1621) is used to characterize the ability of SCC to pass through reinforcing steel (Figure 6). The higher the J-ring slump flow, the farther the SCC can travel through a reinforcing steel obstacle under its own mass from a given discharge point, and the faster it can fill a form or mold with steel reinforcement. The difference between the J-ring slump flow and the unconfined slump flow is an indication of the degree to which the passage of SCC through reinforcing bars is restricted. T50. The flow rate of an SCC mixture is influenced by its viscosity. When developing an SCC mixture in the laboratory, a relative measure of viscosity is useful. The time it takes for the outer edge of the concrete spread (resulting from the procedure described in the slump flow test) to reach a diameter of 20 in. (500 mm) from the time the slump cone is first raised provides a rela- tive measure of the unconfined flow rate of the concrete mixture (see Figure 2). This time period, termed T50, gives an indication of the viscosity of the SCC mixture. T50 time of 2 seconds or less typically characterizes a low-viscosity SCC mixture, and a T50 time of greater than 5 seconds is generally considered a high-viscosity SCC mixture. Column Segregation. This is a laboratory test (ASTM C1610) to evaluate SCC mixture stability and resistance to aggregate segregation. The test is used to develop SCC mixtures with segregation not exceeding specified limits. The degree of segregation can indicate if a mixture is suitable for the application. The static segregation of SCC is determined by measuring the coarse aggregate content in the top and bottom portions of a cylindrical specimen (or column). This test consists of filling a 26-in.-high (610-mm-high) column with concrete (Figure 7). After 15 minutes from casting the sample in the mold, the concrete is removed in top and bottom sections and is washed over a No. 4 (4.75 mm) sieve. The retained aggregate in both sections on the sieve is weighed. A non- segregating mixture will have consistent aggregate mass distribution between the top and bottom sections. A segregating mixture will have a higher concentration of aggregate in the lower section. Strength Quality SCC mixtures are required to be highly flowable yet stable and cohesive enough to resist segregation. To achieve such characteristics, the mixture proportioning would include cementi- tious materials, low water–cement ratio, and the use of a combination of high water-reducing Figure 6. J-ring test (courtesy of A. Schindler, Auburn University).

Overview of Concrete Technologies 25 and viscosity-retaining admixtures. As a result of a low water–cement ratio and efficient cement hydration process, much higher compressive and flexural strengths are achieved compared to conventional concretes. SCC mixtures typically used for fabrication of high-strength precast members are proportioned with a water–cement ratio of 0.32 to 0.40. Mixtures with water– cement ratio higher than 0.40 are sometimes employed for cast-in-place and repair applications, and have strength characteristics similar to conventional concrete (2). Shrinkage Autogenous Shrinkage. Autogenous shrinkage can be high in SCC mixtures made with a relatively low water–cement ratio, high content of cement, and SCMs that exhibit a high rate of pozzolanic reactivity at an early age. In particular, the fineness of the cementitious materials can impact the rate of autogenous shrinkage for the first 28 days. For example, the finer the slag particles, the larger is the surface area for pozzolanic reaction. This leads to a faster reaction and greater autogenous shrinkage from loss of moisture and self-desiccation. Special attention needs to be given to moist-cure SCC at early ages to minimize autogenous shrinkage (2). Drying Shrinkage. Drying shrinkage is related to the water and paste contents as well as aggregate volume, size, and stiffness. High paste volumes and reduction in aggregate content can lead to greater potential for drying shrinkage. Paste volumes can be optimized during the SCC mixture-proportioning process (2). Plastic Shrinkage. SCC can be prone to plastic shrinkage cracking given the fact that these mixtures may exhibit little or no surface bleeding. SCC needs to be protected from rapid moisture loss, similar to conventional concrete that exhibits little or no surface bleeding, by using external curing techniques such as fogging, misting, and other curing provisions. Figure 7. Column segregation test tube (42).

26 Concrete Technology for Transportation Applications The higher the water–cement ratio of the mixture, the lower the autogenous shrinkage, and the higher is the drying shrinkage. Proper engineering and proportioning of the SCC mixture and early curing would minimize shrinkage at the fresh and hardened stages. Bond to Reinforcing Steel and Prestressed Strand The bonding characteristics of properly designed SCC are equal to or better than conven- tional concrete. SCC flows easily around reinforcing steel and generally bonds well to the reinforcement. In fact, the bond strength of reinforcing bars in SCC may be up to 40% higher when compared with conventional concrete (43). This may be due to the lower water content and the higher powder volume in the SCC mixtures relative to the conventional concrete mixtures, which reduces the accumulation of bleed water under horizontally embedded reinforcing bars. However, this bond can be reduced by excessive bleeding and segregation in poorly designed SCC mixtures, especially in upper sections containing reinforcement (44). Long-Term Durability SCC mixtures with SCMs, and low water–cement ratio, are dense and relatively impermeable, providing long-term durability and resistance to corrosion (20). Also, when a proper air-void system is developed in the mixture, SCC can exhibit excellent resistance to freezing and thawing and to deicing salt scaling (45). SCC is also expected to have the same resistance to carbonation as conventional concrete. With appropriate design and construction provisions, the durability performance of SCC is not expected to differ from other types of concrete mixtures. Issues and Challenges Cost of materials and production of SCC is higher than in conventional concrete mixtures. This is due to the fact that higher quantities of cementitious materials may be used, specific aggregate size may be required, and several types of admixtures may be incorporated in the mix- ture to attain favorable SCC plastic and rigid properties. Also, level of experience and training could make a difference in the quality of the SCC mixtures and structures. Mixture segregations can be a major challenge during construction. This may be due to poor mixture design or variation in the mixture properties among different batches. Poor quality con- trol during various construction activities may cause cracking and other surface blemishes such as “bugholes.” Unstable SCC mixtures that are prone to segregation can also exhibit poor surface quality and surface durability problems when excessive bleeding and surface foaming occur. With the power of SCC discharge and high rate of flow inside the form, there is a concern that the reinforcing cage may be shifted from its original position or pushed against the sides of forms. Also, with the high SCC fluid pressure, the forms may yield or collapse. It is important that reinforcement be well secured to prevent any shifting and the formwork be designed to handle SCC pressure during discharge. It is important to provide training to the agency pro- fessionals and utilize experienced project and concrete producer personnel to make a positive impact on quality of SCC mixtures and structures. Internally Cured Concrete Introduction Adequate curing using external curing methods will improve concrete strength, volume sta- bility, permeability, abrasion resistance, and durability (46). Loss of water due to inadequate curing can slow or end hydration, resulting in lower strength development, more permeable

Overview of Concrete Technologies 27 concrete, and shrinkage that may lead to cracking (47). The objectives of external curing include preventing loss of moisture through evaporation and hydration, replenishing the moisture lost to evaporation, and maintaining favorable heat to allow continuation of the hydration process (46, 47). Because of the need to meet construction schedule requirements, external curing is often discontinued prematurely, resulting in a negative impact on the concrete quality. Internal curing is another method of providing moisture inside the concrete to support hydration without increasing the water–cement ratio and also has the benefit of reducing self- desiccation and the accompanying stresses that can result in early age cracking (3, 48, 49, 50). ICC mixtures include prewetted lightweight aggregate, superabsorbent polymers (SAPs), or other agents that release moisture to the concrete paste to facilitate hydration after traditional curing measures have been terminated. An illustration of the differences between internal curing and external curing is shown in Figure 8 (51). As illustrated in Figure 8, conventional curing methods provide moisture only to a limited zone of paste within the upper few millimeters of the concrete surface. The distribution of the prewetted agents throughout the concrete allows for wide dispersion of the additional moisture to facilitate curing. Note that internal curing does not provide enough moisture to counter- act loss of moisture through evaporation and therefore is not a substitute for external curing. Appropriate provisions for external curing need to always be utilized for ICC mixtures (52). Need for the Technology The need for longer lasting, more durable transportation infrastructure requires design and construction of concrete components with low permeability and more resistance to cracking. In recent decades, concrete mixtures have been increasingly utilizing lower water–cement ratio and SCMs. HSC mixtures often combine a low water–cement ratio with high cementitious materials contents. These concrete mixtures are ideal candidates to benefit from the additional moisture provided by internal curing, since mixtures with lower water–cement ratio tend to be more susceptible to autogenous shrinkage due to less water available to support the hydration Figure 8. Illustration of the mechanisms of internal and external curing (51).

28 Concrete Technology for Transportation Applications (52, 53, 54). In fact, research suggests that mixtures with water–cement ratio less than 0.42 do not have adequate water to fully hydrate the cementitious materials (25). Cementitious binder systems that utilize SCMs can also benefit from increased hydration provided by the longer curing durations supported by internal curing (52). The additional hydration supplied by internal curing moisture has been shown to provide further benefits that include reduced cracking potential, enhanced durability, and sometimes increased strength (3, 49, 56, 57). Mechanisms of Internal Curing Internal curing can be accomplished using a number of materials that have a high absorption, including prewetted crushed concrete fines, SAPs, perlite, prewetted wood fibers, and light- weight aggregates (52). Lightweight aggregates provide structural strength to a mixture, while many other materials capable of providing internal curing benefits do not (49, 55), and have therefore been the material most commonly used in research and implementation of internal curing. For these reasons, use of prewetted lightweight aggregates to support internal curing is the focus of this report. To provide internal curing moisture, prewetted lightweight fine aggregate can replace a por- tion of the mixture fine aggregate, and/or prewetted coarse lightweight aggregate can replace a portion of natural coarse aggregates. The effectiveness of lightweight aggregates in facilitating internal curing is dependent on several factors, including (1) the amount of water included in the prewetted lightweight aggregate, (2) the spacing of the aggregate particles, (3) the character- istics of the pore structure of the aggregates, and (4) the strength and shape of the lightweight aggregate (54, 58). Lightweight fine aggregate has been demonstrated to be more effective in promoting inter- nal curing than lightweight coarse aggregate because [according to ACI (308-213)R-13] “it is distributed more fully throughout the concrete mixture and, therefore, the particle surfaces are closer to the hydrating cement particles” (52). In Figure 9, a representative image from an internal curing simulation model shows schematically the paste volume potentially protected via internal curing using prewetted lightweight fine aggregate. As cement hydrates, the products of hydration occupy less volume than the reacting materials, resulting in a net chemical shrinkage. This chemical shrinkage, which increases proportionally Figure 9. Example of two-dimensional image from internal curing simulation program showing predicted protected paste, using 70% aggregates by volume and 20% replacement of the fine aggregate with prewetted lightweight aggregate (54).

Overview of Concrete Technologies 29 with the degree of hydration, results in self-desiccation as pores within the microstructure lose water below the level of saturation (52). If curing water is not available, these pores in the cement paste will instead be filled with vapor. Curing water supplied internally from the pores in the lightweight aggregates provides moisture to support the cement hydration until the equilibrium point is reached between moisture in the lightweight aggregates and the surrounding paste (59). Key to ensuring that water delivered into the concrete by the prewetted lightweight aggregate is that the water release is delayed. The characteristics of the internal pore structures of manu- factured lightweight aggregates vary based upon source geology and manufacturing process. However, in general, the pores of lightweight aggregates are of a size that will allow water to be held within the aggregate during mixing (absorption) but released from the aggregate back into the paste after setting (desorption) (60). If reservoirs of water within the lightweight aggregates are available and well dispersed, the water within the reservoirs will be desorbed into the cement paste via capillary suction, restoring the internal humidity of the concrete to saturated condi- tions (61). Progression of hydration will continue to narrow the capillary pores as new hydra- tion products are formed. This will result in increased capillary suction from the lightweight aggregate reservoirs, allowing the internal curing to progress until all cement is hydrated or equilibrium relative humidity is reached between the capillary pores and the lightweight aggre- gate reservoirs (61). Mixture Proportioning of Internally Cured Concrete ACI (308-213)R-13, “Report on Internally Cured Concrete Using Prewetted Absorptive Lightweight Aggregate,” provides extensive guidance on development and implementation of ICC mixtures (52). The quantity of lightweight aggregates utilized to provide adequate moisture to effectively support internal curing is a function of the type of lightweight aggregates utilized (size, degree of saturation, desorption characteristics), the amount of lightweight aggregates utilized, the concrete water–cement ratio and type of binders utilized, and the type and extent of external curing provided (52). When proportioning concrete mixtures, an equation for the mass of lightweight aggregates or nomographs provided in the document can be used. Studies have indicated that virtually all lightweight aggregates produced in the United States demonstrate adequate desorption characteristics to support internal curing (60), and informa- tion such as desorption can be obtained from the manufacturers. A review of the literature indicates that most internally cured mixtures used in the laboratory and field utilize substitution percentages less than 50%, with most field studies tending to utilize volumetric substitution per- centages ranging from 20% to 35%. Regardless of the proportioning approach, ACI (308-213) R-13 emphasizes preparing trial batches and performing tests to verify that the required concrete properties can be obtained using the selected absorptive material and mixture proportions (52). Construction Prewetting of the Lightweight Aggregates Batching, mixing, transporting, and placing of ICC do not differ significantly from the pro- cess used for conventional concrete mixtures (52). Key to successful implementation of ICC is adequate prewetting of the lightweight aggregates prior to batching. Most lightweight aggregates with open textured surfaces can be prewetted by sprinkling stockpiles with water for a sufficient duration of time. The rate at which the lightweight aggregates will absorb the water will depend on a number of factors including the characteristics of the lightweight aggregates (in particular, aggregate absorption), the water application rate, stockpile characteristics, and environmental conditions including temperature and humidity (52). Prewetting needs to be performed for a duration to ensure that the lightweight aggregate has exceeded the saturated-surface-dry (SSD)

30 Concrete Technology for Transportation Applications condition. Use of lightweight aggregate that has not achieved the SSD condition in the concrete mixture may have adverse effects, including slump loss and placement issues during pumping and finishing (62). The SSD state is difficult to define for lightweight aggregates, and it is therefore consid- ered “best if the lightweight aggregates can be provided in a known and maintainable state of moisture equilibrium” (3). Similar to use of other types of aggregates in concrete, the moisture content and absorption of the prewetted lightweight aggregate needs to be accounted for during the batching process. Provisions to adequately prewet the lightweight aggregates will ensure that variability with slump loss and unit weight as well as issues with pumpability, segregation, and finish quality will not occur (62). In the laboratory, methods to prewet and drain the lightweight aggregate include submerging lightweight aggregate in a container of water and allowing it to soak for at least 24 hours (63, 64, 65). In the field, various methods have been used to prewet the aggregate, with most suppliers choos- ing to stockpile the material and provide sprinklers for the specified duration of time. The stock- pile needs to be configured in a manner that allows adequate drainage (Figure 10), and a uniform moisture state needs to be achieved by turning the stockpile. Testing needs to be performed to ensure that moisture corrections can be made to the batch weights. Historically, ASTM C1761 has been utilized to define the SSD state for lightweight aggregate and to compute moisture corrections. This method, also known as the “paper towel method” is time-consuming and can be subject to variability due to differences in paper towel characteris- tics and operator inconsistency (Figure 11). An alternative method to characterize the moisture state of prewetted lightweight aggregate is the centrifuge method, in which a sample of the material is spun in a centrifuge for 3 minutes at 2,000 rpm (Figure 12). This method has been shown to provide rapid, accurate results that correlate well with ASTM C1761 (66). Performance Properties Fresh Concrete Properties When proper proportioning considerations have been made and the lightweight aggregate adequately prewetted, fresh concrete properties tend to be relatively unaffected by internal curing. Impact on slump is generally negligible, although some studies have indicated increased work- ability when prewetted aggregate was used (67). It has been suggested that a portion of absorbed water may leave the aggregate and become integrated into the concrete mixture during mixing, Figure 10. Lightweight aggregate being prewetted by sprinkler (circled), with floor sloped to drain water from the stockpile.

Overview of Concrete Technologies 31 Figure 11. Paper-towel drying method. Figure 12. Centrifuge drying method (66). hauling, and placement, thus aiding in maintaining workability and surface finish quality (62). Field studies have not reported any complaints from placing or finishing personnel (68, 69). Hardened Concrete Properties The most significant improvement in performance of hardened concrete with the use of ICC is in the reduction of autogenous shrinkage at early ages (59, 61, 65), as shown in Figure 13. In some mixtures, use of prewetted lightweight aggregates for internal curing was shown to virtually eliminate autogenous shrinkage (49).

32 Concrete Technology for Transportation Applications An important benefit of ICC is the reduced shrinkage and the associated internal strains, which, in turn, reduce the early age cracking potential (48, 52, 56, 58, 70). A study for the Colorado DOT indicated that the reduced autogenous and drying shrinkage reduced residual stress buildup in restrained shrinkage testing of mixtures with low water–cement ratios, although this effect was decreased in mixtures with higher water–cement ratios (71). Using the ASTM C1581 restrained ring test, Henkensiefken et al. (63) found that cracking was essentially eliminated when prewetted lightweight aggregate was used at replacement rates greater than 23.7% (Figure 14). Use of prewetted lightweight aggregates for internal curing has been shown to reduce the permeability of concrete, enhancing resistance to deleterious substances such as chlorides and sulfates. Although improvements in permeability may not be observed at early ages, increased hydration of cementitious materials at later ages, likely supported by the internal curing moisture, improves the quality of the interfacial transition zone (ITZ) between paste and aggregate, leading to lower permeability (47, 67, 70). Overall, the potential durability of ICC using prewetted light- weight aggregates has been shown to be improved due to the increased hydration of cementitious materials, reduced shrinkage, and potentially increased compressive strength (3). An increase in compressive strength is typically not the goal of using ICC. However, some researchers have found slightly higher compressive strengths in ICCs and mortars (49, 56, 72). The 33.0%k 29.3%k 23.7%k 18.3%k 14.3%k 11.0%k 7.3%k 0.0% Sealed Figure 13. Reduction in autogenous shrinkage for internally cured mortars (50). 23.7%k Sealed 14.3%k 11.0%k 7.3%k 3.8%k 0.0%k Figure 14. ASTM C1581 restrained shrinkage test results, showing a correlation between age at cracking and prewetted lightweight aggregate replacement rate (63).

Overview of Concrete Technologies 33 potential for increased strength will depend on factors including strength and degree of saturation of the lightweight aggregates and improved strength of the paste surrounding the lightweight aggre- gates that has benefited from the internal curing moisture. Use of prewetted absorptive materials other than lightweight aggregates has been shown to decrease compressive strength (49). Flexural strength has been shown to be improved by internal curing (73, 74). The modulus of elasticity of lightweight aggregates is typically lower than that of natural aggregates. However, when using prewetted lightweight aggregates for internal curing, the change in concrete’s modulus is not linear. At low replacement percentages, the modulus of elasticity has been shown to increase slightly. However, at higher replacement levels [greater than 100 lb/yd3 (59.3 kg/m3)], a reduction in concrete’s modulus of elasticity has been demonstrated (75). Studies on creep behavior of concrete internally cured with lightweight aggregates have not been conclusive. A study found that creep often decreases but could potentially increase (76). ACI (308-213)R-14 recommends trial batching and testing of mixtures for creep when creep is a critical performance criterion (77). The unit weight of ICC will generally be slightly lower than that of conventional mixtures. However, at replacement levels typically used in internal curing applications, the unit weight does not fall below 135 lb/ft3 (2,160 kg/m3), the density at which the mixture is no longer classified as normal-weight concrete and additional structural considerations are generally required (77, 78). With respect to freeze-thaw resistance, a study by the Colorado DOT on ICC mixtures focused on evaluating the potential for enhanced freeze-thaw durability (71). Findings of this study indi- cated that ICC can exhibit freeze-thaw performance comparable to that of conventional mixtures, provided that excessive internal curing water and high water–cement ratios are avoided (69). Implementation A number of state agencies are moving forward with implementation of ICC for bridge decks. Internally cured pavements have been constructed on several municipal streets (primarily in Texas) and, perhaps most notably, the Dallas Intermodal Terminal constructed in 2005 (75), which has been cited as providing excellent performance (79). Interest has also been shown in the use of ICC for overlays (80, 81) and cementitious repair materials (82). To date, ICC has been used on bridge decks in New York, Indiana, Utah, Virginia, Georgia, Ohio, Colorado, and North Carolina (Figure 15) (68, 69, 71, 72, 80, 83). Studies of field installations Figure 15. Internally cured concrete bridge deck in Durham, North Carolina, being placed by pumping.

34 Concrete Technology for Transportation Applications of ICC bridge decks largely report success. The Indiana DOT constructed four bridges utiliz- ing prewetted lightweight aggregates to internally cure high-performance concrete mixtures and found that early-age autogenous shrinkage was reduced by 80% compared to non-ICC mixtures (69). Two internally cured bridge decks were constructed in northern Utah, along with two com- panion conventional bridge decks. At 28 days, the two types of concretes had similar compressive strengths; however, the ICCs exhibited lower permeability when tested using the rapid chloride permeability test. After several months, cracking was observed in the conventional decks while no visible cracks were found in the internally cured bridge decks (72). Most laboratory studies indicate that ICC members would have the potential to require less maintenance and provide extended service life compared to conventional concrete. However, a more complete assessment of its true potential will become evident over time as field imple- mentation sites age. Remember that although internal curing is a promising tool that can improve concrete properties, it cannot be expected to compensate for deficiencies in design and construction that result in cracking and other issues (68). Specifications and Guidelines Extensive guidance on development and implementation of ICC mixtures using prewetted lightweight aggregates is presented in ACI (308-213)R-13 (52). This document provides infor- mation on the materials, mechanisms, and benefits of internal curing, along with recommenda- tions for mixture proportioning and batching procedures. Sustainability benefits associated with ICC are also discussed. The National Institute of Standards and Technology maintains a robust online database of resources on internal curing. An extensive bibliography is provided, along with resources including mixture proportioning tools and internal curing simulation results (84). The Expanded Shale, Clay, and Slate Institute (ESCSI) has published a guide specification for ICC (85). This guide specification, prepared by the industry, suggests the need for prequalifica- tion of the lightweight aggregate (meeting ASTM C330 and ASTM C1761), provides guidance on prewetting and testing of the lightweight aggregate, and outlines a procedure for computing the quantity of prewetted lightweight aggregate required for internal curing. Construction require- ments outlined in this guide specification typically refer the reader to the contract documents. Some states have developed specifications for internal curing. The New York State DOT has had extensive experience in implementing ICC mixtures in bridge decks and has prepared several spec- ifications as well as a specified procedure for determining the moisture content of the fine aggre- gate on site (Test Method No. NY 703-19, “Moisture Content of Lightweight Fine Aggregate”). New York State DOT Specifications 557.51XX0018, 557.52XX0018, and 557.54XX0018 cover ICC for superstructure slabs as well as approach slabs (86). A consistent substitution proportion of 30% prewetted lightweight aggregates has worked well for the many ICC bridge decks constructed in New York, as has the stockpile prewetting provisions provided in the specifications (70). The West Virginia DOT has a special provision “Structural Concrete Internal Curing,” which provides guidance on material properties as well as guidance for mixture proportioning and use of shrinkage-reducing admixtures to enhance performance of these mixtures (Appendix C). Modified procedures for determining the absorption of the lightweight fine aggregates include testing from an independent laboratory to prequalify an aggregate for use. Procedures for com- puting the amount of dry lightweight fine aggregate are provided in the special provision, as well as the target cement factor, maximum water content, and entrained air content. Requirements for handling, measuring, and batching of materials are also provided, including detailed guid- ance on stockpile management of the lightweight fine aggregate (87).

Overview of Concrete Technologies 35 Requirements for use of internal curing in the Virginia DOT’s bridge concrete are provided in a Special Provision entitled, “Low Cracking Bridge Deck Concrete.” ICC mixtures can be used in both bridge decks and substructures. The Virginia DOT special provisions’ guidance and requirements are minimal and allow for input from the manufacturer of the lightweight aggregate. Issues and Challenges Availability of lightweight aggregate locally is a challenge in many states, because the lightweight aggregate is primarily a manufactured material. This will affect the price of the aggregate and will result in a higher cost to implement ICCs. From a concrete producer’s standpoint, internal curing requires introduction of an additional material to their operations, often requiring addi- tional space, storage bins, and handling equipment. This may influence the capability of some producers to supply ICC without some modifications to their plant or operation. Additional QA/QC associated with development and control of mixtures may also affect the cost of ICC. Agency awareness, experience, and guidance on the proper prewetting of the lightweight fine aggregates can be seen as an issue requiring additional training and oversight. Development of material handling guidelines by state agencies to assist concrete producers and project personnel would be helpful. Ultrahigh-Performance Concrete Introduction UHPC is a portland cement–based product that includes SCMs, well-graded fine sand, a high dosage of fiber reinforcement (usually steel) as well as superplasticizers and other admix- tures, and a very low water–cement ratio (4). Some mixtures may also include coarse aggregates, with small particle sizes, in quantities that are much less than that those used in conventional concrete. The ingredients may be mixed on site or batched and delivered using truck mixers. Benefits UHPC is highly flowable and self-consolidating when discharged, develops very high com- pressive and tensile strengths, and exhibits durability. UHPC mixtures have developed ultra- high compressive strengths greater than 21,700 psi (150 MPa) and have exhibited postcracking tensile strengths as high as 720 psi (5 MPa). These mixtures also have very low permeability, which reduces penetration of harmful liquids and greatly enhances durability compared to conventional concrete (88). Such favorable mechanical and durability properties have made UHPC an ideal product for use in joints connecting prefabricated components of bridges in ABC projects (Figure 16) and in bridge deck construction, overlay, and repairs (4). Field casting of UHPC connections results in stronger and more durable connections and provides better long-term performance compared to connections cast with conventional con- crete. The superior mechanical properties of UHPC allow more optimized design of connection dimensions and reinforcement that promotes both speed and ease of construction. Applications UHPC became commercially available in the United States in 2000. Since that time, research projects and field deployment have demonstrated the material capabilities in many applica- tions related to bridge construction, replacement, and overlays (88). These applications included

36 Concrete Technology for Transportation Applications connections between precast or prestressed bridge elements including girders, pile cap closure pours, and prefabricated deck components (Figures 17 and 18). Other applications included thin overlays of deteriorated bridge decks and fabrication of precast structural elements. The majority of applications have been in connection joints between prefabricated bridge components during construction or deck replacement, as shown in Figures 17 and 18. In these applications, UHPC mixtures have demonstrated superior mechanical and durability properties compared to conventional concrete mixtures. UHPC mixtures are used in joints as closure pours to accelerate connection of bridge com- ponents. They require shorter splicing of reinforcing bars of adjoining elements, develop high early strength for early form removal, and allow minimum shrinkage for long-term durability. The connection design using UHPC includes simple lap splicing of reinforcing bars where the tension development length of the reinforcement is much shorter than in conventional concrete connections, as shown in Figure 19 (4). In this application, the overall cost of using UHPC is relatively small because of the small quantity of material needed to cast the connections (88). This is important when considering that the cost of UHPC mixes is very high compared to con- ventional or HSC mixes (89). Materials and Mixtures The dry ingredients of UHPC include a large quantity of cementitious materials which may exceed 1,500 lb/yd3 (890 kg/m3), a blend of well-graded fine and coarse sand, and, in some mixtures, a small quantity of coarse aggregate of small particle sizes (88). A very high volume Figure 16. UHPC placement in connections between prefabricated bridge components (courtesy of New York State DOT) (4). Figure 17. Schematic showing cross section of precast beams with UHPC closure pours (4).

Overview of Concrete Technologies 37 of steel fibers (1% to 2% of mix volume) is an essential ingredient to provide the necessary reinforcement for enhanced compressive and tensile strengths and reduced shrinkage (4, 89, 90, 91). HRWRs and a variety of other admixtures are included to produce a highly flowable and self-consolidating mixture capable of filling narrow forms with congested reinforcement. The water–cement ratios for UHPC mixtures are typically not greater than 0.25 (4). Most of the UHPC mixtures are proprietary with the dry ingredients prepackaged by the pro- ducers. At the project site the dry ingredients are mixed with water, fibers, and admixtures using a portable mixer. The mixture ingredients may also be batched in truck mixers and transported to the project site. The cementitious contents of most mixtures include more than 1,000 lb/yd3 of portland cement with low tricalcium aluminate (C3A) (to control the mixture temperature) and silica fume powder at 10% or more by weight of the portland cement (4). Other pozzola- nic materials, such as slag, metakaolin, fly ash, and limestone powder, have also been used in addition to or as a replacement of silica fume and cement to control the mixture temperature, enhance durability and sustainability, and reduce cost (4, 89, 90, 91). Figure 18. Prefabricated bridge deck components with UHPC connections (4). Conventional Detail UHPC Detail Figure 19. Conventional and UHPC connections between prefabricated deck elements (4).

38 Concrete Technology for Transportation Applications Fine aggregates including quartz, limestone, and basalt aggregates are proportioned and sized in the dry constituents to facilitate the flowability of UHPC mixtures and increase the compressive strength. As mentioned previously, coarse aggregates are sometimes included in UHPC mixes to provide cost savings. The coarse aggregate tends to be relatively small [0.25 in. (6 mm) or less] (4). However, in a recent study of fiber balling in a nonproprietary UHPC mixture, 0.5-in. (13-mm) coarse aggregate was used to break up fiber balling in the mixture with good results (91). The steel fiber most commonly used in UHPC applications is fine fiber with 0.008-in. (0.2-mm) diameter and a 0.5-in. (19-mm) long straight fiber (4). However, it has been reported that a high volume of fine fibers can create high potential for fiber balling in UHPC mixtures (91). This challenge can be more pronounced in large-volume mixtures produced using drum mixers in concrete trucks. The proposed solution to the balling problem was to use a blend of 50% each of fine and medium-size fibers when batching large UHPC mixtures in concrete trucks. This solution does not seem to have had an effect on fresh and hardened properties of the mixtures. A variety of admixtures are used in UHPC mixtures to provide favorable fresh and hardened properties. These admixtures commonly include accelerators, polycarboxylate, and phosphonate- based superplasticizers (4). These and other admixtures provide the mixture’s high flowability, self-consolidation, and early strength properties. Construction Mixing and Placement UHPC mixtures can be batched in conventional rotary pans or drum mixers, including con- crete truck mixers. However, in most applications, UHPC mixtures are field-batched in a rotary pan mixer (Figure 20) (4, 88). Prepackaged dry components are first discharged into the mixer. Then water, admixtures, and fibers are added to the rotating mixer until the proper UHPC for- mulation is produced that meets the specific project requirement. This is a process similar to that of many of the proprietary grouts and patching materials used in bridge repairs and overlays (4). The high cementitious material contents and longer mixing time, compared with those of conventional concrete mixtures, will cause the temperature of the UHPC mixture to rise during mixing and placement. This temperature increase may require the use of chilled water or ice cubes to control the mixture temperature (4). Lowering the mixture temperature increases the flow rate and self-consolidation of UHPC during placement. Nonproprietary UHPC mixtures have been developed and deployed in the field in Michigan and New Mexico (89, 90, 91). These were engineered mixtures that used materials and products com- monly available to the concrete producers and contractors. The UHPC mixtures included portland cement with low C3A contents, silica fume, slag, and fly ash, as well as a blend of well-graded fine Figure 20. On-site mixing (92).

Overview of Concrete Technologies 39 quartz sand. In some mixtures, a small quantity of coarse aggregate, small and medium-size fibers, and HRWR admixture were also added. Prior to their deployment in the field, trial batches were prepared to optimize the mixture ingredients and ensure proper flow characteristics when placed, and also to verify that the specified strength and durability could be achieved (91). Tests and Properties Flow Characteristic QC tests for UHPC are similar to those used for conventional concrete or mortar. Both fresh and hardened concrete properties are measured (93). The flow of UHPC mixtures is frequently measured using ASTM C1437, Standard Test Method for Flow of Hydraulic Cement Mortar (94). The test is performed immediately after mixing to assess UHPC mixture appropriateness for casting. The favored flow range for UHPC mixtures used in bridge applications is 7 to 10 in. (178 to 254 mm) (4). Dryer UHPC mixes used in pavement overlays would be tested using the conventional concrete slump test according to ASTM C143. Strength Similar to most other concrete mixtures, compressive strength testing is used to evaluate the quality of hardened UHPC. The test is performed according to a modified version of ASTM C39, “Standard Test Method for Compressive Strength of Cylindrical Concrete.” Because of the high compressive strength of UHPC, the test method is modified to include an increased load rate of 150 psi/s (1 MPa/s). Also, since higher failure loads are anticipated for these high-strength mixtures, 3-in. by 6-in. (75-mm by 150-mm) test cylinders are used to accom- modate capabilities of most testing machines (88). Based on FHWA assessment, preblended UHPC mixtures with 2% fibers and cured in field-type conditions have exhibited compressive strengths exceeding 14,000 psi (97 MPa) after 4 days and 21,000 psi (145 MPa) after 28 days (4). ASTM C109 “Standard Test Method for Compressive Strength of Hydraulic Cement Mortars” [using 2-in. (50-mm)-cube specimens] can also be applied to UHPC. For UHPC qualification, the New York State DOT requires compressive strength test results for a minimum of sixty- four 2-in. (50-mm) cubes, tested at 4, 7, 14, and 28 days. The minimum compressive strength requirements are 14,300 psi (100 MPa) at 4 days and 21,800 psi (150 MPa) at 28 days (95). Durability and Shrinkage Durability and shrinkage tests are also performed during the mixture verification stage but are not necessarily required by the highway agency as QC tests (84). These tests include chloride ion penetration (ASTM C1202), freeze-thaw resistance (ASTM 666, procedure A) and shrink- age (ASTM C 157) tests. In bridge applications, the acceptance criteria are as follows: chloride penetration of 250 coulombs or less after 28 days; freeze-thaw resistance durability factor of at least 95% after 300 freeze-thaw cycles; and shrinkage of 800 macrostrain or less after 28 days (4). DOT Implementation As of December 2016, five states including Idaho, Iowa, New Jersey, New York, and Pennsylvania have made UHPC a standard practice on bridge projects for connections between pre fabricated components. Nineteen other states and Washington, DC, are either using UHPC in bridge construction projects or making plans to standardize the use of the technology (93). States in which UHPC connection projects are in various application stages, from research to deployment, include California, Connecticut, Florida, Idaho, Iowa, Massachusetts, Ohio, Oregon, and South Carolina. In addition to the United States, UHPC has been used in high- way infrastructure in Australia, Austria, Croatia, France, Germany, Italy, Japan, Malaysia, the Netherlands, New Zealand, Slovenia, South Korea, and Switzerland (88).

40 Concrete Technology for Transportation Applications Specifications Use of UHPC requires the development of material and construction specifications. The material specifications define the constituent properties, testing protocol(s), testing frequen- cies, performance criteria, and unit of payment. It is important that construction specifications provide guidance on field-related activities that may affect the performance of UHPC, including considerations such as material storage, adequacy of form work, mixing, and in-field testing, placement, and curing (4). Issues and Challenges Issues The joint faces of precast concrete components must be intentionally roughened to a 0.25-in. (6.4-mm) amplitude prior to filling with UHPC. Roughening of precast concrete allows increased UHPC bond at the joints and reduces the shear stresses carried by the discrete steel reinforce- ment crossing the interface (4). It is important that flow distances of field-cast UHPC mixtures in long joint connection be limited to 10 ft (3 m). Long flow distances around the reinforcement can interrupt the disper- sion of the fiber reinforcement, which could reduce the mechanical resistance of the UHPC (84). Also, to avoid possible mixture segregation, adjustments to length of casting must be made when coarse aggregate is used. A proprietary-based product can only be used if it undergoes the highway agency’s appro- priate acceptance testing protocols and is placed on a preapproved materials/products list. Sometimes an “approved equal” provision is included in the contract plans to allow unidentified suppliers an opportunity to demonstrate whether their product meets the criteria of the contract plans and specifications (4). Successful performance of UHPC connections requires that each stage of construction be completed in a timely and appropriate manner. The owner, the material supplier, the inspectors, and the contractor must work together to ensure success (4). At present, very few producers have experience with UHPC for precast or cast-in-place appli- cations. Information needs to be made available so that they become aware of the issues involved in dealing with UHPC mixtures and construction. For example, precast plant personnel need to be aware that longer mixing times than in conventional concrete mixers are necessary due to the high cementitious materials content and low water–cement ratio, longer set times due to high admixture dosage, and modified curing treatments (4). Challenges In an international conference on UHPC in 2016, a poll was conducted to gauge partici- pants’ responses to a question related to obstacles that were preventing wider implementation of UHPC. The responses included lack of design guidance, industry resistance to change or lack of understanding of the technology, high cost compared to conventional concrete, and other minor issues (96). To encourage greater implementation of UHPC in the highway infrastructure, the following have been identified as needs: • Studies showing the cost-effectiveness of UHPC in various applications, • Design and construction guide specifications for structures made with UHPC, • Research to address some of the missing information needed in the structural design, • Standard test methods and material specifications for UHPC,

Overview of Concrete Technologies 41 • Production procedures for precast and cast-in-place construction, • Broader geographic distribution of demonstration projects, and • Wider distribution of technical information. Temperature Control of Mass Concrete Introduction Mass concrete is defined as any volume of concrete with dimensions large enough to require that measures be taken to manage the generation of heat from hydration of the cement and associated volume change to minimize cracking (97). Mass concrete is used in dams, navigation locks, nuclear plants, and power houses. In transportation structures, mass concrete is used in large footings, mat foundations, bridge piers and columns, and some maritime structures (98). The generally large size of mass concrete structures creates the potential for significant rise in internal concrete temperature in the structure and significant temperature differentials between the interior and the outside surface of the structure during the early stages of hydration. The accompanying volume-change differentials and restraint result in tensile strains and stresses that may cause cracking that is detrimental to the integrity and durability of the structure and thus can shorten its service life (99). A mass concrete temperature control plan is required by many state DOTs for massive structural members in bridges and other transportation structures, and by specifiers of other mass structures such as dams, power plants, and navigation locks. The TCMC is developed and implemented during construction to control the core temperature and temperature dif- ferential in the mass concrete structure to avoid the negative consequences of mass concrete heat (28, 98). Objective The objective of temperature control plans in mass concrete members is to control the rise in internal temperature of concrete and maintain the temperature differential between the interior and outside surface below threshold levels that may cause cracking (28). To accomplish such objective, these plans address the selection of type and quantities of cementitious materials, admixtures, and aggregates; precooling mixture ingredients; cooling during the mixing process; postcooling of in-place concrete by embedded pipes; and surface insulation (5). Applications TCMC is used in dams, navigation locks, nuclear and other power plants, and foundations for large building structures. In transportation projects, a TCMC plan is developed and executed during construction of large footings, mat foundations, and bridge piers and columns that meet the definition of mass concrete. The purpose of the plan is to ensure that the core tempera- ture and temperature differential between the core and edges of the structure remain below the thresholds specified by the state DOT. Most state DOTs require that a TCMC plan be developed for projects that involve construc- tion of mass structural members. This is based on the survey responses by DOTs (Appendix B). The Florida DOT, for example, requires that the plan be administered by a specialty engineer to ensure proper execution of the TCMC plan in mass concrete projects (28).

42 Concrete Technology for Transportation Applications Elements of TCMC Plan The TCMC plans may achieve effective temperature control by incorporating four elements: (a) proper selection and proportioning of mixture materials, (b) precooling of aggregates and mix water, (c) cooling of the concrete during the batching process and placement, and (d) postplacement cooling and insulation (5). These elements may be used collectively, or, in many cases, only a select number of these elements may be chosen to accomplish the tem- perature control. The extent and duration of the plan depends on the member shape and dimensions, ambient weather conditions, aggressiveness of the surrounding environment, and specification provisions. The elements of TCMC include but are not limited to, the following details: • Selection of cement type and content to avoid high heat of hydration. The mixture is also likely to incorporate SCMs such as fly ash and slag to replace portions of the cement to lower heat generation in the mass concrete structure. • Precooling of aggregates and mixture water to achieve a lower concrete temperature when cast in the structure. • Construction management and controls, whereby concrete placement timing, scheduling, and procedures are adjusted and construction actions and equipment that introduce addi- tional heat in the freshly placed concrete are avoided. • Postcooling, where embedded cooling tubes and coils are installed to limit the temperature rise in the structure core, and insulation is applied on the edges and exposed surfaces to pre- vent rapid heat escape and steep decrease in surface concrete temperature thereby controlling the temperature differential. Materials and Mixture Proportioning Mass concrete (MC) is composed of the same ingredients as conventional concrete. The objective of the MC mixture design is to produce concrete that results in low temperatures during early ages while achieving the agency-required strength at the specified ages and durability. Cement Portland cement Types I, II, I/II, and V (ASTM C150), and blended cement Types P, IP, S, IS, I(PM), and I(SM), covered by ASTM C595 are commonly used in MC mixtures. One effec- tive measure to lower the heat of hydration is to limit the quantity of cement to a relatively low amount. This will result in lower heat of cement hydration and will contribute to lower rise in concrete temperature. Supplementary Cementitious Materials The use of SCMs such as Class F fly ash and GGBFS in MC mixtures as partial replacement of portland cement not only contributes to low permeability and long-term durability but also lowers the amount of heat liberated during hydration of the cement. This requirement of SCMs in MC is illustrated in DOT specifications. For example, Florida DOT Specification 346 requires that MC mixtures include up to 50% fly ash or 70% GGBFS as replacement by mass of the cement quantity (28). Class F fly ash with high silica content and low calcium content reacts chemically with the calcium hydroxide liberated during the hydration of cement. This is a very slow pozzolanic reaction that produces more hydration products, but at a lower rate of heat liberation, and thus contributes to a lower overall concrete temperature (14). However, Class C fly ashes contain

Overview of Concrete Technologies 43 high calcium content and tend to react in a manner similar to that of cement, and thus contribute to early concrete strength gain, but they are not as effective as Class F ash in lowering concrete temperature (5). Slag added to MC mixtures in large quantities as cement replacement reacts similarly to cement but at a slower rate. The slower hydration of slag reduces the rate of heat generation. Also, by substituting a large proportion of the cement, the use of slag further contributes to reducing the rise in overall temperature of the concrete (5, 14). Chemical Admixtures Admixtures provide important benefits to mass concrete in its plastic state by increasing workability, reducing water content, or both. Also, chemical admixtures can be used for retard- ing initial setting by slowing the hydration process and thus lowering rate of heat generation. However, their impact in heat reduction is minimal and is limited to early hours prior to final setting of the concrete. Construction Practices for Temperature Control Temperature control measures for a small structure may be as simple as restricting placement operations to cool periods at night or during cool weather. At the other extreme, some projects can be large enough to justify a wide variety of separate, but complementary, control measures in a well-prepared and -executed temperature control plan. Practices that have evolved to con- trol temperatures and consequently minimize thermal stress and cracking are listed below (98): • Cooling batch water; • Replacing a portion of the batch water with ice; • Shading aggregates in storage and in conveyors; • Spraying aggregate stockpiles for evaporative cooling; • Injecting liquid nitrogen into the mixture; • Scheduling placements when ambient temperatures are lower, such as at night or during cooler times of the year; • Controlling rapid surface cooling of the concrete with insulation; • Avoiding thermal shock during form and insulation removal; • Protecting exposed edges and corners from excessive heat loss; and • Effectively monitoring concrete and ambient temperatures. Precooling Mixture Materials Minimizing the temperature of the fresh concrete at placement is one of the most important and effective ways to minimize the maximum core and differential temperatures and reduce thermal stresses and cracking. In mass structural members, each 10°F (6°C) reduction of the placing temperature below average air temperature will lower the peak temperature of the hard- ened concrete by approximately 4°F to 6°F (2°C to 3°C) (99). The temperature of the mixed concrete is influenced by each component of the mixture, and the degree of influence depends on the individual component’s temperature, specific heat, and proportion of the mixture. Because the amount of cement in a typically lean mass concrete mix- ture is relatively small, cooling it may not be significant in a temperature control program (98). With respect to aggregates, which comprise the greatest part of a concrete mixture, a change in their temperature will produce the greatest change in the temperature of the concrete. Methods for cooling coarse aggregates can include sprinkling stockpiles with water to pro- mote evaporation, which helps to cool the aggregate. The moisture condition of the aggregates

44 Concrete Technology for Transportation Applications needs to be considered not only for adjustments in amount of batch water, but also in the heat balance calculations for control of the placing temperature (98). If stockpiles are sprinkled, adequate drainage needs to be provided beneath the stockpiles to assist in achieving a more uniform moisture throughout the stockpile. With respect to the batch water, a unit change in the temperature of the batch water has approximately five times the effect on concrete temperature as a unit change in the temperature; ice chips can be added to substitute for a portion of the batch water. The use of ice is one of the basic and most efficient methods to lower the concrete placing temperatures. It is important that all of the ice melts before the conclusion of mixing and that sufficient mixing time is allowed to adequately blend the last of the ice meltwater into the mixture. Liquid nitrogen is another effective method used for cooling batch water and creating an ice–water mixture. It can be injected into the water in a specially designed mixer just before the water enters the concrete mixer, whereby the liquid nitrogen causes a portion of the water to freeze. Liquid nitrogen has also been injected directly into mixers. This approach typically requires that the mixing time be prolonged and, preferably, that the mixer is at least partially sealed to minimize the loss of gas to the atmosphere. Placement Area During hot weather, precooled concrete can absorb ambient heat, mechanical heat, and solar radiation during placement, which will increase the effective placing temperature and the resulting peak temperature. This increase in temperature can be minimized or eliminated by reducing the temperature in the immediate placing area using fog sprayers, shading measures, or both. Placing concrete at night can also reduce the impact of hot weather and radiant heat. Scheduling In many parts of the United States, the temperature of concrete placed during the spring and early summer will be cooler than the average daily ambient temperature. Conversely, the temperature of concrete placed during the fall and early winter will often be warmer than the average daily ambient temperature. Scheduling placements during nighttime in the summer and during the daytime in the winter can take advantage of cooler and warmer temperatures and supplement other methods of reducing concrete temperature. Temperature Modeling and Measurement For critical projects, thermal modeling, using the Schmidt’s method (ACI 207.2R) (99) or finite element models (FEM), has been performed during design and planning stages to predict concrete temperatures and evaluate different control strategies. However, the prediction accu- racy is not very good due to multiple assumptions made in the calculations. Modeling accuracy can be greatly improved by measuring the adiabatic or semiadiabatic heat from the cement or cementitious materials used in the concrete mix. ASTM 1702 is the test method used to measure the heat of hydration of cementitious materials using isothermal calorimetry. Results of this test can then be used as input values in models. The modeling can aid in the optimization of mixture proportions, determining proper cooling and insulation needs, accommodation of predicted ambient conditions, and test- ing the effectiveness of construction provisions (100, 101). During construction, monitoring of the early age temperature of mass concrete is often required for QA/QC purposes. Temperature measurements can be obtained using a variety of embedded temperature sensors, including commercially available maturity measurement systems. In addition to monitoring internal and

Overview of Concrete Technologies 45 surface temperatures, embedded sensors can also be used to apply the maturity method to predict concrete strength (102). After Concrete Placement Thermal and Stress Development After Placement Once cement and water interact during mixing, the hydration process starts and the mixture temperature begins to rise. At placement with lifts of 4 ft (1.2 m) or higher and lateral form dimen- sions of more than 5 ft (1.5 m), the temperature will start to rise in the central part of the mass of fresh concrete without the opportunity to dissipate. In contrast, the heat generated at the exposed surfaces (formed or unformed) is dissipated into the surrounding air at a rate dependent on the temperature differential with surrounding temperature. The net temperature increase in concrete adjacent to the surface (or forms) is less than in the interior (99). Before initial set of concrete, the rise of the interior temperature of the structural member causes little or no stress or strain. Also, the development of steep thermal gradients near exposed surfaces during early ages while the modulus of elasticity is very low is usually not a serious con- dition. After the concrete hardens and acquires elasticity, decreasing ambient temperatures and rising internal temperatures work together to increase the temperature gradient and widen the stress difference between the interior and the surface. This results in a high tensile stress in the region of the exposed surfaces and a comparatively low compressive stress over the extensive interior areas. Also, changes in the temperature gradient result in length and volume changes that are partially restrained due to reinforcement and boundary effects, causing cracks that may affect structural integrity, durability, and long-term service life of the structure. This necessitates executing a plan for deploying postcooling systems to limit the rise in the concrete interior and the temperature differential with the exposed surfaces. Postcooling Systems The postcooling systems described below require installation of temperature-sensing devices (thermocouples or resistance thermometers) at key locations within the massive member to provide special information for the control of concrete cooling rates. Internal Cooling. An effective system to reduce the peak temperature of mass concrete placements is by circulating cool water through small-diameter aluminum or PVC pipes embedded in the concrete (Figure 21). Water circulated through cooling pipes in concrete sections such as massive mat foundations, piers, columns and beams can reduce the core temperatures and differential temperatures between the core and surface. This can sometimes be an economical alternative to pre-cooling the concrete during hot weather. After the cooling period is completed, the embedded pipes must be pressure grouted (103). Surface Insulation. Applying insulation to formed and exposed concrete surfaces is an effective method to maintain a manageable thermal differential between the core and surfaces of the concrete. An insulation factor (R-value) of –2.0 or higher will be necessary in many cases. Rigid synthetic cellular material in sprayed, board, or sheet form as well as thermal blankets containing closed-cell material can be practical methods of insulating. For example, a minimum 3-in (75-mm) wood form may be necessary to provide the desired level of protection while the forms remain in place. Steel forms offer virtually no insulation protection and need to be supplemented with suitable insulation materials before concrete is placed. Another practical solution is to coat the exterior of reusable steel forms with a spray-on synthetic foam of the necessary thickness.

46 Concrete Technology for Transportation Applications Also, delaying the removal of forms until a balance of temperature is reached between the concrete and ambient temperatures that meets the specification requirements may save additional efforts and cost of additional monitoring and insulation. However, if construction scheduling requires early removal of forms, insulation needs to be promptly installed against the exposed concrete surface. When practical, form removal and insulating activities need to be planned for the warmest time of the day. For unexposed formed surfaces, an alternative procedure is to install insulation on the inside of the forms before concrete placement. The insulation then is held in place against the concrete surface when the forms are removed. This method has not been successful on exposed concrete because of surface imperfections caused by the relatively flexible insulation. It is also suggested that insulation be increased along the edges and at corners of massive concrete structures. This action has effectively reduced the rate and magnitude of heat escape and temperature decline during the cold-weather season (98). In no event should the gradual surface temperature drop when protection is removed exceed the values recommended in ACI 306R or specified by the highway agency. Specifications The negative impact of temperature rise in mass concrete necessitates executing a TCMC plan to limit the rise in the concrete interior and the temperature differential with the exposed surfaces. Thirty of the 40 states that responded to the synthesis survey indicated that they have implemented TCMC. Also, 23 of the 40 states have developed specifications and/or construction guidelines (Chapter 3). For example, the Florida DOT Specification 346 requires the development of a mass concrete control plan in accordance with ACI 207 to ensure that concrete core temperatures for any mass concrete element do not exceed the maximum allowable core temperature of 180°F and that the temperature differential between the element core and surface do not exceed the maximum allowable temperature differential of 35°F (28). It needs to be emphasized that the tempera- ture requirements and temperature control plans may vary among the DOT specifications. In some cases, the maximum allowed temperature is 160°F. However, the common goal among all specifications is to control the core and differential temperatures to mitigate cracking and loss of durability in massive concrete structures. Figure 21. Cooling pipes in mass concrete sections such as piers, beams, and mat foundations (103).

Overview of Concrete Technologies 47 Issues and Challenges Experience and cost are two major challenges when implementing TCMC plans. Training of construction personnel and utilization of knowledgeable professionals to prepare the TCMC and supervise its execution will produce an optimized plan and minimize failures in meeting the specification requirements. Proper execution of the TCMC plans will ultimately save cost and construction time and will produce quality and highly durable structures. Also, it is critically important that the agency designer or the project specifier identify in the project plans those members that are considered mass concrete. This will allow contractors to account for the additional cost in their bids and plan ahead for construction of the mass members (104). The agency may also set the required strength at 56 days instead of the traditional 28 days for foundation members that will not be loaded before 6 months after construction (104). This provision will allow the increased use of SCMs and lower the cement content in the mixture, which will limit the rise in concrete temperature without affecting the structural integrity and long-term durability of the member. Precast Concrete Pavement Introduction Traditional slab replacement in concrete pavement rehabilitation projects involves several intense and time-consuming construction activities that must be completed in a short lane- closure time. In most urban areas the nighttime lane closure is limited to 8 or 9 hours, although some daytime and weekend closures may be possible if traffic conditions permit. This results in reduced productivity, early age distresses, and possible shorter service life of the replacement slabs compared to normal paving (105). One solution to increase production and to maintain good quality and longevity of replaced slabs is to use PCP instead of cast-in-place (CIP) panels or slabs. Precast concrete technology in pavement construction and rehabilitation is relatively new when compared to its tradi- tional use in structural members (106). In fact, most U.S. projects have been in service for less than 20 years. However, PCP systems are gaining wider acceptance in the United States for rapid repair and reconstruction of concrete and asphalt pavements in highways, roads, and intersections. Benefits and Advantages PCP systems are used in roads and highways with high traffic volume and where lane closures are problematic. The work is performed during the night, typically from about 8 p.m. to 6 a.m., or when short closures during daytime are possible. The production rate per lane closure is 15 to 20 segments or slab replacements or 300- to 600-feet-long sections of continuous slab replacements (6). Below are benefits and advantages of PCP as compared with CIP pavements (6): • Better quality concrete—Panels are prepared, cast, and cured in a precast plant under more controlled conditions. This eliminates potential CIP construction problems such as concrete delivery issues, paving equipment malfunction, early setting and poor mix consolidation, and poor surface finish. • Minimum weather restrictions on placement—Construction may continue during very cold nights or in rainy conditions that would otherwise restrict CIP construction.

48 Concrete Technology for Transportation Applications • Reduced delay before lane opening to traffic—PCP can be installed during nighttime lane closures and be ready to be opened to traffic in early morning. • Elimination of premature cracking or joint raveling—Early age distresses due to shrinkage and thermal stresses or raveling sawed joints are almost eliminated when PCP is used. • Control of structural cracks by panel reinforcement or prestressing—During its service life, any fatigue cracking will be maintained tight and confined by the reinforcement, simi- larly to bridge decks. This will allow the slab to function for a long time before replacement will be needed. Applications PCP technology is being applied in intermittent repairs of full slabs and for continuous paving of long uninterrupted road sections in rehabilitation projects. The service life is pre- dicted to be at least 20 years for individual slab replacements and 40 years for continuous paving projects. Dozens of projects have been constructed using different PCP systems and designs. Cali- fornia (107, 108), Florida (109), Missouri (110), New York (106), Texas (111), Virginia (112), and Illinois Tollway (113), among other state agencies, have constructed PCP on sections of their roads and highways. Progress continues to be made through research and demonstration projects in all aspects of the technology, including panel design, fabrication, installation, and performance (106, 109). Implementation of PCP Systems The implemented PCP systems include proprietary as well as nonproprietary systems (106). The panels are prepared in precasting plants, and then transported to the project site to be placed individually on prepared surfaces to replace the distressed slabs. They can also be assembled in groups of multiple adjoining panels to form a continuous pavement. Depend- ing on the pattern of the pavement assembly, the PCP fabrication may include prestressing the panels at the precasting plant and posttensioning them in groups of multiple slabs during the pavement reconstruction. The applications of PCP technology can be classified as follows: • Intermittent segment or full slab replacements—This application is for isolated individual segments or full slabs. The segment replacements are made by installing a precast panel on a prepared leveling course to replace a removed area of the slab. Full-slab replacements with precast slabs are also made to remove severely cracked, settled, or shattered single slabs or several consecutive slabs. The process is similar to CIP slabs. The precast panels are typically a full single lane or two lanes wide. • Continuous paving—In this application, a long and uninterrupted section of the road or highway is overlaid or reconstructed on a prepared leveling course. Prestressed precast con- crete panels or slabs are transported to the project site, assembled in groups of several panels, and then posttensioned at expansion joints between adjoining groups. PCP for Intermittent Replacements The two precast systems that have often been used in the United States for individual seg- ments or full slabs, or short sections of jointed slabs, include the Illinois Tollway PCP generic system (106, 112, 113), and the Fort Miller Super-Slab® system (112, 113). Illinois Tollway PCP System. In 2007 and 2008, Illinois Tollway implemented the Super- Slab® system on a section of I-294 and I-88 ramps. However due to the proprietary nature of

Overview of Concrete Technologies 49 the Super Slab® system and to encourage competition, the Tollway worked with local industry to develop their own generic precast system (112, 113). The generic system was developed in 2009 and has been used for intermittent replacement of individual segments or full slabs in their tollway system. The generic PCP system uses precast slabs with preformed dovetail slots that are fitted with loosely positioned dowel bars ready to be pushed in the holes in the adjacent slab, as shown in Figure 22. The panels have been designed and fabricated in preset dimensions to fit in the slab- replacement pit dimensions with respect to length, width, and thickness. The most widely used panels are 6 ft (1.8 m) long and a lane-width wide. The panel thickness equals the average thick- ness of the existing slabs in the project as determined from average thickness of multiple core samples from the project The dowels are concentrated at the wheel path zones, with four dowels in each zone. During installation, the precast panel is lowered into the replacement pit, ensuring that slots in the panels match the dowel holes in the opposing side to facilitate insertion of dowel bars in sockets in the opposing side. The dowels are pushed from each slot into the opposite epoxied hole (Figure 22). The slots are then filled with fast-setting nonshrink grout. The PCP surface is later diamond- ground to achieve the required surface smoothness. Fort Miller Super-Slab® System. The Super-Slab® fabricated concrete slab system is a pro- prietary product developed by the Fort Miller Co., Inc., with assistance from the New York State Thruway Authority and New York State DOT (106). This system was designed as a precast, non- prestressed concrete slab with prepared slots at the edges for housing tie bars and dowels across the joints as shown in Figure 23. Foam gaskets are placed underneath the slab to aid in proper grout distribution beneath the slab. The design of the system is most suitable for intermittent replacement of segments and full slabs. The precast panels can be fabricated to the specific project-designed dimensions. Installation involves unique construction methods, including the use of special bedding material (leveling course), a laser-guided grader for proper finishing of the bedding material, and grout to anchor the dowels and tie bars and provide proper slab support. The super-slab system includes grouting the dowel bar slots and the interface between the slab and the bedding layer (leveling course). Grout ports are provided on the top of the slab Figure 22. Illinois Tollway PCP system for individual slab replacement (113).

50 Concrete Technology for Transportation Applications for the dowel grout and the bedding grout. Additionally, for even distribution of the bedding grout, grout distribution channel and foam gaskets are provided underneath the slab as shown in Figure 23. Key requirements for successful intermittent PCP applications include • Good and uniform support condition under the panels; • Adequate load transfer at transverse joints; • Ensuring minimum, if any, elevation differences between the panel and the surrounding pavement; and • Acceptable long-term performance of the PCP replacement panels (112). PCP for Continuous Paving The PCP systems have been used to pave continuous short and long sections of roads and highways as part of pavement rehabilitation and reconstruction. The most common system used by several states is the FHWA generic prestressed precast concrete pavement (PPCP) system, originally developed at The University of Texas at Austin (111). The PPCP system has been modified in recent projects. The Florida DOT adopted a slightly different PPCP design for the reconstruction of a section of US-92 in central Florida (109). The continuous PCP sections have generally been longer than 500 ft (150 m), covering a single or multiple lane, including shoulders. The technology has been implemented on ramps, intersections, as wells as on highways in states such as California, Florida, Illinois, Missouri, Texas, and Virginia (107, 108, 109, 110, 111, 112). The PCP is designed using procedures similar to those used in design of CIP pavements. The Super-Slab and Illinois Tollway Generic Precast systems have also been used for continuous paving. The paving involves preparing a well-profiled base, using laser-guided grading equipment. The precast panels are transported to the project site and installed according to the design plans in a single lane or tied multiple lanes (106). A typical installation of the Super-Slab system for continuous paving is shown in Figure 24 (114). FHWA Prestressed and Posttensioned Concrete Pavement. The prestressed and postten- sioned concrete pavement design simulates the design of CIP paving with respect to traffic loads and jointing requirements, and type of base. One of the most common posttensioning designs is shown schematically in Figure 25. The panels are fabricated in special forms at a precasting plant. Reinforcement is placed in the forms. In addition, prestressing strands are also fitted in the Figure 23. Super-Slab® precast system and its installation (111, 112).

Overview of Concrete Technologies 51 forms and tensioned. The forms also include posttensioning ducts. After casting the panels, the prestressing strands are released when the concrete reaches the required strength. Some panel designs also include keyway edges to facilitate interlocking the joints between adjacent panels (115). In other designs, the ends are flat but are coated with epoxy to bond to adjacent panels during the pavement assembly to maximize load transfer across the joints. The fabricated prestressed panels are transported and installed at the project site in segments composed of 10–15 consecutive panels. Posttensioning strands are inserted through the ducts in the panels, and then posttensioned with sufficient force to press the panels against each other to establish good load transfer across the joints (Figure 26). The ends of each segment are connected to the next segment at a doweled expansion joint to maintain continuity for the intended pavement. The length of a segment may vary from 150 to 250 ft (46 to 76 m). The individual panel width may extend across single or multiple lanes. The panel length can vary from 8 to 12 ft (2.4 to 3.6 m), and the width can vary from 12 to 36 ft (3.6 to 10.8 m) for single or multiple lanes with shoulders. Florida’s US-92 PPCP Project. In 2012, the Florida DOT constructed a 793-ft demonstra- tion PPCP section on a US-92 rehabilitation project near Deland (109). It was part of an 8.2-mile concrete pavement rehabilitation project, which also included concrete overlay and other conventional rehabilitation such as slab replacement, grinding, joint resealing, and crack sealing. PPCP panels were fabricated in a precasting plant and then transported, installed, and posttensioned into a pavement structure. Figure 24. Installation of Super-Slab for continuous paving (114). Ducts for Posttensioning Ducts for Posttensioning Ducts for Posttensioning Pretensioning Strands Pretensioning Strands Expansion Joint Detail Pretensioning Strands Stressing Pockets Continuous Shear Key Continuous Shear Key Continuous Shear Key (a) (b) (c) Figure 25. Schematic of the FHWA prestressed and posttensioned concrete pavement system (115).

52 Concrete Technology for Transportation Applications The design included an asphalt interlayer to change the transverse profile of the pavement from a centerline crown to a 2% cross slope toward the outside edge and also to provide a smooth base to place the PPCP panels, as shown in Figure 27. Plastic sheet was used to cover the asphalt layer prior to placement of the PPCP panels to minimize friction during the post- tensioning process. The panels were 12 ft long, 24 ft wide, and 9 in. thick (3.65 m × 7.3 m × 23 cm) and included a keyway-pattern transverse joint. The PPCP panels were reinforced, fitted with six posttensioning ducts, and then cast and cured; they were prestressed transversely in four locations at a precast- ing plant. After fabrication, the panels were transported and placed along the paving track, where they covered two 11-foot lanes (3.35 m) and a 2-foot (0.6 m) shoulder, as shown in Figure 27. The PPCP panels were grouped in three 264-ft (80-m) segments. Each segment comprised 22 PPCP panels that where placed with the posttensioning ducts of adjacent panels, aligned, and connected at the joints (109). Panels of each full segment were posttensioned at the end panel. The ends of two consecutive segments were connected at a doweled expansion joint (Figure 28). The posttensioning was performed at the end panels and were patched with a quick-set patch- ing material. The posttensioning ducts were grouted through ports at the end panels. Also, the intermediate joints between adjoining panels were patched using the quick-set patching material, as shown in Figure 29. Figure 26. Posttensioning panels on site (110). Figure 27. Placement of PPCP panel. Notice the six posttensioning ducts.

Overview of Concrete Technologies 53 The expansion joints were sealed, and dowel slots and posttensioning blocks were patched. The pavement was later diamond-ground to establish a smooth riding surface (Figure 29). The PPCP section was constructed in 14 days. The pavement has been in service for 4 years under local traffic. It provides a smooth ride and has performed well structurally with no signs of distress (116). Limitations and Challenges Note that because of the short experience with the use of PCP technology in the United States, information and guidance on PCP design, practices, and in-service performance are continu- ously evolving with every demonstration project and performance study. At this time, there are not sufficient PCP projects available with long service time to allow direct field validation. As a result, the design of PCP systems needs to be based on current design procedures for conven- tional CIP jointed concrete pavement, such as the AASHTO Maine software (107). Figure 28. PPCP unit end panel with prefabricated dowel slots, posttensioning end blocks, and duct grouting ports. Figure 29. All PPCP joints were patched with quick-set patching material and the pavement was diamond-ground.

54 Concrete Technology for Transportation Applications It must be emphasized that PCPs are not “super pavements” and are not be expected to perform significantly better than CIP concrete pavements. Once installed, precast concrete pavements can be expected to behave similarly to CIP pavements under traffic loading and environmental effects. The primary difference between the two technologies is how each system is constructed (6). Some key limitation and disadvantages of PCP are the following (6): • Higher cost compared to CIP; • Lack of adequate long-term performance history for PCP; • Lack of experience of local contractor and precasting operators with the technology; • Proprietary products; • Newness of the PCP technology to DOT designers and consultants; • Construction delays and challenges, including – Establishment of standard dimensions for the slab replacement pit, – Panel dimension tolerances to fit the standard replacement pit with acceptable joint openings that must be sealed, – Preparation of the bedding layer (leveling course) and its proper grading to ensure even surface grade of panels with surrounding pavement, – Space limitation in the closed lanes to accommodate the PCP transporting trucks as well as cranes and other lifting equipment, which will require special maintenance of traffic plans, – Ensuring the patching of wide dowel slots prior to lane opening to prevent accidents involving motorcycles, – Treatment of special pavement areas such as gores, horizontal curves, or turning at inter- sections that would require either the use of CIP concrete or special precast panels that would fit in these areas; • Long-term performance of expansion joints; • Lack of national well-developed selection criteria for use of precast concrete technologies (criteria are generally based on desire of a highway agency to experiment with PCP); and • Lack of knowledge about maintenance needs and repairs, considered a gap in the PCP technology. Roller-Compacted Concrete Introduction RCC is a stiff concrete mixture with very low or no slump. In recent years, RCC pavements have been used for roads and highways. They are designed similarly to conventional concrete pavements, but are constructed without the use of forms, dowel and tie bars, or other steel reinforcement. RCC pavements use conventional asphalt or high-density paving equipment instead of slipform paving machines. The pavement is compacted into its final form using a combination of heavy vibratory steel-drum and rubber-tired rollers (7, 117). Benefits RCC pavements are typically more cost-effective compared to conventional concrete pave- ments (7). The cost savings are due to reduction in cement content, lack of forms, lower placement costs, faster construction, as well as absence of dowels and tie bars. RCC can also be constructed rapidly without the need to set up forms or stringlines or to install dowel baskets ahead of the paving operation. After placement and compaction, RCC pavements are well consolidated, where stable aggregate interlock develops to support movement of workers and occasional light vehicle traffic without damaging its fresh surface (Figure 30). Cement hydra- tion and strength gain continue in a manner similar to that of conventional concrete.

Overview of Concrete Technologies 55 With well-graded aggregates, proper cement and water content, and dense compaction, RCC pavements can achieve strength properties equal to those of conventional concrete, and with low permeability. In fact, a key advantage to this type of concrete paving is that the pavement may be opened to traffic shortly after construction, as soon as the strength reaches 3,000 psi (21 MPa) (7). Applications The modern use of RCC started in the 1970s in Canada when the logging industry switched to RCC as a heavy-duty paving material for log-sorting yards to sustain the massive loads and heavy equipment (117). Since then, RCC has been used in many other types of applications throughout North America. One of the main applications of RCC in the United States is in the construction of dams (118). Other primary applications of RCC include ports, industrial park- ing and storage areas, intermodal and military facilities, and low-speed roads and intersections carrying heavy truck traffic (119). In recent years, RCC pavement has been used in commercial areas, on local streets and roads, and on highway shoulders (Figure 31), as well as in base layers in two-lift concrete or asphalt Figure 30. Freshly placed RCC pavement (courtesy of G. Dean, American Concrete Pavement Association). Figure 31. RCC shoulder next to existing concrete pavement (courtesy of G. Dean, American Concrete Pavement Association).

56 Concrete Technology for Transportation Applications pavements (120, 121, 122). Success of these applications has been a result of improvements in RCC mixtures, paving equipment, and construction practices, as well as an increase in the availability of specialty admixtures that improve RCC placement speed and surface smoothness (7, 123, 124, 125). RCC Mixtures RCC mixtures consist of the same basic ingredients as conventional concrete mixtures, but with less cementitious material, lower water–cement ratio and coarse aggregate contents, and higher percentage of fine aggregates to allow for tight packing and compaction (7). A typical RCC mixture includes coarse and fine aggregates as well as cementitious materials including cement, fly ash, water, and, when appropriate, chemical admixtures. Aggregates make up to 85% of the volume of RCC. Proper attention to aggregate gradation will help ensure concrete workability at placement, proper compaction, and good surface finish. Fresh RCC mixtures have low or no slump and are stiff enough to remain stable under vibra- tory rollers yet wet enough to permit adequate mixing without segregation. RCC mixtures typi- cally provide similar strength properties and less shrinkage compared to conventional concrete mixtures in similar supplications (117). RCC mixtures are stiffer than conventional concrete mixtures because of their higher fines content and lower cement and water contents. The mixtures are placed with a heavy-duty, self- propelled asphalt paving machine, using a high-density single or double tamper bar screed to initially consolidate the mixture to a slab of uniform thickness. This is followed by a combina- tion of passes with rollers for proper compaction and fine surface texturing (7). Mixture Production The RCC mixtures are prepared in rotary concrete mixers at concrete batch plants or in pug- mills at plants or project sites (Figures 32 and 33). The RCC is then charged into dump trucks to be transported to the placement site. Pavement Construction Placement RCC pavements are constructed without forms or reinforcing steel because the mixture is dry and stiff. Dowels, tie bars, and reinforcement bars are not incorporated into RCC pavements Figure 32. RCC drum mixer (126).

Overview of Concrete Technologies 57 because the dry consistency of the mixture does not allow bonding with steel and the roller com- paction will result in dowel/tie bar misalignment (7). This fact must be considered in pavement design, since load transfer at the joints would be dependent on aggregate interlock with aid from a firm base support to minimize deflections under heavy vehicles. RCC is typically placed with an asphalt paver. The pavements are usually placed in lifts of 6 to 8 in. (150 to 200 mm) with 4 in. (100 mm) as a minimum and 10 in. (250 mm) as a maximum thickness (7). Conventional asphalt machines may be used for lifts that are 6 in. (150 mm) thick or less. High-density asphalt paving machines have been used successfully for pavements up to 10 in. (250 mm) thick, although 6- to 8-in. (150- to 200-mm)-thick lifts are more common (117). When placing multiple lifts, the top lift needs to be placed within 60 minutes of the lower lift to allow for adequate bonding between the layers (7). Compaction RCC is typically compacted with a 10-ton (9-metric ton) dual-drum vibratory roller imme- diately after placement. Typically, four to six passes of a dual-drum 10-ton vibratory roller will achieve the desired density of at least 98% for RCC lifts in the range of 6 to 10 in. (150 to 250 mm). Rubber-tired rollers or lighter steel rollers (4 tons) have also been used successfully, especially for a final pass, to remove surface cracks and tears and to provide a smooth and tight surface. The RCC pavement density is tested and verified using the field nuclear density gauge (Figure 34), according to ASTM C1040/C1040M. Figure 33. RCC pugmill (courtesy of Morgan Corp.). Figure 34. Field density test.

58 Concrete Technology for Transportation Applications RCC needs to be placed and compacted while it is still fresh and workable, usually within 60 minutes of delivery. If the RCC is too dry, the surface will appear dusty or grainy and may even shear (tear) horizontally. Excessive vibration can lead to edge collapse, which will disturb the profile of the road and its riding quality. Longitudinal construction cold joints are formed when a lane is placed more than an hour after the placement of the adjacent lane. Construction joints are formed by trimming away the outer uncompacted edge of the paving lane with a concrete saw and then paving against the resulting clean vertical edge (7). Curing Curing of RCC pavements is as important as in conventional pavements. Application of a heavy dosage of curing compound on the pavement surface and sides will preserve the mixture water to sustain the hydration process and achieve proper strength and a durable surface (7). Applying a fine mist or fogging prior to curing will prevent evaporation from the dry pavement surface. Also, using intermittent water spray in addition to the application of curing compound may add surface durability. Joints The joint saw cut is one-third of the slab thickness to minimize uncontrolled cracks (125, 127, 128). Early entry “green” saws have been used to initiate a 1-in. (25-mm) deep joint cut in the freshly compacted RCC pavement to prevent uncontrolled cracks. That is followed by a deeper cut to the proper depth using conventional saw machines (124). The joints are later cleaned and sealed similarly to conventional pavements. Texture RCC pavement has an open surface texture similar to that of asphalt pavement. The surface may have a rough texture and may exhibit poor ride quality in higher-speed roadways. The use of smaller aggregates, adding more cement, or using specialty admixtures can produce a denser and more favorable surface texture (123). Surface smoothness is further improved with diamond grinding (124). Opening to Traffic The pavement can be opened to traffic within hours after construction. Compressive strengths of 2,500 to 3,000 psi (17 to 21 MPa) are used as criteria for opening the pavement to traffic (7). Properties Strength In general, RCC pavement mixtures can have compressive and flexural strengths compara- ble to those of conventional concrete mixtures. RCC compressive strengths at 28 days typically range from 4,000 to 7,000 psi (28 to 48 MPa) (129). The densely graded aggregates and the use of low water–cement ratio in the mixtures help to achieve higher compressive strengths in the concrete (7). Although strength tests for RCC are similar to those used for conventional concrete, unlike in conventional concrete mixtures, cylinders and beam samples used for RCC strength tests are compacted using a vibrating hammer (Figure 35). Bond Strength and Multiple Lifts When placing RCC in multiple lifts, bond strength at the interface of RCC layers becomes a critical engineering property. Good bond strength must be achieved to produce a monolithic pavement that supports the designed traffic loads. Insufficient bond or bond failure will result in delamination and premature failures.

Overview of Concrete Technologies 59 Freeze-Thaw Performance RCC is not typically air entrained from conventional air-entraining admixtures. However, field performance studies in freeze-thaw environments have indicated that RCC performed well for more than three decades, whether air entrained or not (112, 130). Test data clearly demonstrate that very little entrained air is required to adequately protect RCC against frost- induced microcracking and deicing-salt scaling (7). Specifications ACPA has published a guide specification (124) useful for developing project specifications for RCC pavements. The guide specification includes materials and mixture requirements as well as recommendations for construction and QC processes and procedures. Implementation Examples in Streets and Highways RCC has been used in pavements for local streets and roads and for highway shoulders. Speed of construction, economy, and early opening to traffic are key reasons to use RCC for local streets and roads (7, 124). For example, RCC may be used for inlays to replace rutted asphalt pavements. In some cases, light traffic has been allowed on the RCC pavement within 24 hours after construc- tion to accommodate local traffic, or when concrete reaches the strength of 2,500 psi (7, 120). Because of the tendency of RCC to produce a rough surface texture, advancements have been made to improve this aspect of RCC paving. Most projects use high-density pavers, mixtures with smaller top-size aggregate, and workability-aiding admixtures to improve surface smoothness (123). In streets with speed limits exceeding 30 mph (48 km/h), diamond grinding has often been applied to improve surface smoothness (124). Applying a thin asphalt surface course on top of the RCC is another option to improve surface smoothness. For roadways carrying traffic at highway speeds, RCC is currently used primarily as a base that is overlaid with a thin asphalt wearing course for better rideability. Another possibility for high- ways is the use of RCC as a base for conventional concrete pavement. RCC provides an excellent construction platform in unbonded concrete overlays. This allows for the conventional concrete Figure 35. Preparing RCC field-test cylinders (courtesy of Georgia DOT).

60 Concrete Technology for Transportation Applications pavement surface thickness to be reduced. A separation layer (generally asphalt) between the RCC base and concrete overlay is required as a bond breaker to allow for separate movement of the layers and to prevent cracks from reflecting upward from the base into the conventional concrete pavement. In all applications, joint spacings similar to those used in conventional pave- ments have been used in RCC pavements. In unbonded concrete overlays on RCC, the joints must coincide to prevent reflective cracking (121, 126, 127). Some examples of street and road applications include reconstruction of a street in Columbus, Ohio. This four- to six-lane project was constructed under traffic. It consists of 8 in. (200 mm) of RCC overlaid with 3 in. (75 mm) of asphalt to provide smoothness for the higher traffic speeds. Another example is US-78 in Aiken, South Carolina, where a 10-in. (250-mm) RCC pavement replaced an existing full-depth asphalt pavement. The RCC surface was diamond ground for this four-lane section to improve its surface smoothness and rideability (128). RCC has also been used in highway shoulder applications. For example, the Georgia DOT used RCC to reconstruct a 34-mile (55-km) shoulder on I-285 (121, 122) (Figure 36). The exist- ing shoulder was milled and replaced with a 10-ft (3-m)-wide RCC pavement at a thickness of 6 to 8 in. (150 to 200 mm). Rumble strips were ground into the RCC surface to conform to highway safety requirements. No surfacing was placed on the RCC. The transverse joints were sawed to align with the joints in the mainline pavement. A directory of RCC pavement projects in the United States is available from the ACPA (131). Also, the ACPA recently developed pavement design software, called Pavement Designer, that includes provisions for design of RCC pavements (132). The software is a web-based pavement design tool that can be used for design of roadways, overlays, parking areas, and industrial and intermodal pavements. RCC Pavement Issues and Challenges Possible limitations and challenges associated with RCC pavements include the following: 1. Surface profile and smoothness. An RCC pavement may not meet the rideability require- ments for roads and streets carrying high-speed traffic. Surface grinding has significantly Figure 36. RCC paving on an Interstate shoulder (courtesy of G. Dean, American Concrete Pavement Association).

Overview of Concrete Technologies 61 improved the ride quality of RCC pavements (127). Also, recent advances in specialty admix- tures and surface finishing aids have produced smoother RCC surfaces (123). The use of smaller coarse aggregates and modifications in roller compaction patterns and weights have also helped contractors to achieve better surface smoothness. 2. Paving in multiple lifts and adjacent lanes. Placing multiple lifts of RCC must be accom- plished within 1 hour of each other to ensure good bond between the layers. Also, the ini- tially paved layer must be clean and kept damp prior to placement of the next lift. In case of multiple lane construction, if adjacent lanes are not placed within 1 hour of each other, a longitudinal joint must be formed between lanes (7). 3. Pavement edges are more difficult to compact. It is suggested that the specifications allow 96% modified Proctor density along pavement edges instead of the 98% required on pave- ment interior. History has shown that properly prepared and consolidated edges compacted to lower density perform very well (7). 4. Hot-weather paving. Precautions and good practices followed when paving RCC in hot weather are not much different than those used in conventional pavement. In hot paving environments, extra attention is required to minimize loss of RCC mixture water by evaporation. Use of admixtures and misting, fogging, or spraying of newly placed pavement can minimize water loss and protect its surface integrity (7). Timely curing with application of a heavy dose of curing compound on pavement surface and edges as well as intermittent water spraying will provide the necessary curing for strength development and produce a durable surface. Pervious Concrete Introduction Pervious concrete (PC) is an open-graded concrete mixture with a near-zero slump, comprising portland cement, coarse aggregate, a small amount or no fine aggregate, admixtures, and water. In its hardened state, it contains high percentages (20% to 35%) of interconnected voids, which allow rapid passage of water through the body of the concrete (Figure 37). The typical compressive strengths of PC are from 400 to 4,000 psi (2.8 to 28 MPa). The drainage rate of PC pavement will vary with aggregate size and mixture density from 2 to 18 gal/min/ft2 (81 to 730 L/min/m2) or 192 to1,724 in./h (0.14 to 1.22 cm/s) (8). Figure 37. PC parking during a rainstorm.

62 Concrete Technology for Transportation Applications Applications and Benefits PCP is often used as a surface layer in streets and parking areas to reduce or eliminate storm- water runoff (133). It is also used as a rigid subbase beneath concrete pavements in roads and highways (Figure 38) to drain surface water and provide stiff support for the pavement (134). PC is also commonly used in edge drains of pavements (Figure 39) to collect and pass the drained water into a perforated pipe and discharge it at specific distances to the side trenches (135). Materials A PC mixture is composed of cement or a combination of cement and other cementitious materials, coarse aggregate, water, and admixtures. A limited quantity of fine aggregate may be added to increase the compressive strength and density of the mixture and achieve higher Figure 38. PC base for concrete pavement. Figure 39. PC edge drain.

Overview of Concrete Technologies 63 load-carrying capacity of PC pavements. However, the flow rate of water through the pavement is reduced with increase in the amount of fine aggregate (8). Color may also be included in the mixture for enhanced esthetics and/or to distinguish the surface from adjacent conventional concrete or asphalt surfaces. Portland cement is used as the primary aggregate binder. However, SCMs such as fly ash, GGBFS, and silica fume can also be used in PC mixtures as partial replacements of the cement content. Use of SCMs has been, in some cases, shown to improve the strength and durability of PC, although the results vary depending on SCM type used and replacement rates (135, 136, 137). Rounded and crushed aggregates, meeting requirements ASTM C33/C33M, have been used in PC mixtures. Aggregate sizes No. 7 (1/2 in. to No. 4), No. 8 (3/8 in. to No. 8), No. 67 (3/4 in. to No. 4), and No. 89 (3/8 in. to No. 16) have been used in PC mixtures. Aggregates in PC mixtures can be normal-weight or lightweight aggregates. The aggregate must be clean and free from dust or clay that might adversely affect bond with the cementitious paste. Prior to mixing the PC ingredients, the aggregate must be in a saturated-surface-dry (SSD) moisture condition. This is achieved by applying water sprinklers on the aggregate stockpile. Dry porous aggregate will absorb mixture water and reduce the workability necessary for proper placement and compaction (8). With respect to admixtures, water-reducing admixtures (high range or medium range) are commonly used to achieve proper workability. Also, the use of cement hydration stabilizers and VMAs aids in extending the placement and compaction time of the mixture. The three admixtures are also helpful in producing and maintaining proper consistency of the PC mixture during transport, placement, and compaction, and also to mitigate segregation (138, 139). Retarding admixtures may be used to stabilize and control the cement hydration to allow longer transport and to extend the compaction window of the PC mixture. They can also act as lubricants to help discharge concrete from a mixer and improve placement and compaction, especially in hot weather. Accelerators can be used when PC is placed during cold weather (8). Air-entraining admixtures are not commonly used in PCs but may be included in pavement susceptible to freezing and thawing (8). Also, incorporating fibers in mixtures exposed to freez- ing and thawing has shown success in improving durability and abrasion resistance in cold climates. However, fibers do net seem to improve compressive strength and may reduce PC permeability and infiltration (140, 141). Dry and windy conditions create high evaporation rates that reduce PC workability during placement and compaction and may case raveling of surface aggregates. The use of evaporation retarders and other chemicals is beneficial in windy and dry paving conditions to maintain sur- face moisture prior to applying plastic sheet cover (8). Mixture Proportioning The goal of mixture proportioning for PC is to achieve balance between permeability, strength, and workability. The mixture has to be proportioned to meet the main objective of the application type. For example, to maximize the water percolation rate, the PC mixture has to be proportioned to produce high void content including the use of gap-graded aggregate and lower paste content. Conversely, to maximize a pavement load-carrying capacity, the PC mixture may include higher cement content, lower water–cement ratio, well-graded coarse aggregate, and possibly, the addi- tion of some fine aggregate. The Virginia DOT has developed special provisions for PC parking areas that include provisions for materials, mixture design, and construction (142, 143). The Florida DOT has specifications for pervious base layers and pavement edge drains (134, 135). Higher voids in PC will lead to a higher percolation rate and lower strength. In contrast, lower void content results in a reduced percolation rate but higher PC strength. The addition of fine

64 Concrete Technology for Transportation Applications aggregate will decrease the void content and increase strength (135). Density and void content of freshly mixed PC mixtures can be determined using ASTM C1688/C1688M-14a “Standard Test Method for Density and Void Content of Freshly Mixed Pervious Concrete.” The infiltration rate of water determined using 4-in. × 6-in. (10-cm × 15-cm) samples obtained from trial batches or field core samples may be tested using ASTM D5084—Method B, “Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter,” as shown in Figure 40 (143). Experience has shown that a water–cement ratio in the range of 0.26 to 0.45 will provide paste with a consistency supporting the best aggregate coating, paste stability, and overall mix- ture cohesiveness. The conventional relationship between water–cement ratio and compressive strength for normal concrete does not apply to PC (8). This is because other factors may also affect compressive strength development such as paste–aggregate bond strength, void content, and strength of the aggregate particles. A necessary range of quantities for the main PC mixture ingredients is shown in Table 2. Admix- tures are also used in dosage rates recommended by the manufacturer or concrete producer. Figure 40. Virginia DOT’s falling head permeameter (143). Cementitious materials, lb/yd3 (kg/m3) 450 to 700 (270 to 415) Aggregate, lb/yd3 (kg/m3) 2,000 to 2,500 (1,190 to 1,480) Water–cement ratio, by mass 0.27 to 0.34 Aggregate–cement ratio, by mass 4:1 to 4.5:1 Fine aggregate–coarse aggregate ratio, by mass 0 to 1:1 Component Proportions Table 2. Necessary quantities of basic PC ingredients [adapted from ACI 522 (8)].

Overview of Concrete Technologies 65 Experience of local PC producers and paving contractors with track records of successful PC projects will be helpful in designing appropriate PC mixtures for the application. Design and Construction Pavement Design For thickness determination of a pervious pavement, structural adequacy and drainage efficiency are two important design considerations. These two characteristics influence each other so both need to be addressed with care. The modulus of elasticity and flexural strength of PC are typically lower than those of conventional pavement concrete. However, with prop- erly designed PC thickness on a thick and stiff base layer, PC pavements have demonstrated acceptable structural capacity for low truck traffic (144). ACPA’s design software for concrete pavements, Pavement Designer (132), includes PCP design as one of the software modules. Pavement Designer software pertains to the structural requirement of the pavement. However, the pavement designer must also be concerned with the drainage aspect of the pavement, including pavement storage capacity, need for any backup stormwater drainage system, and the percolation efficiency of the pavement and its support layers (145). Construction The construction process needs to result in a PC pavement possessing both adequate strength and efficient percolation. It is paramount that the agency be assured that the contractor and concrete producer are adequately qualified and experienced to construct, provide construction QC, and produce successful mixtures for PC pavement projects. Variability in PC pavement performance can be attributed to poor construction practices, inadequate QC and/or lack of consistency in the properties of PC mixtures among the production batches (142, 146). The PC mixture is batched and/or transported to the construction site in truck mixers. The mixture is discharged in stationary forms, distributed with steel rakes and struck off, with some compaction, using low-frequency vibratory screeds. This is followed closely with final compaction and surface finishing using a heavy-pipe roller, roller screed, or frame-mounted roller (Figure 41). The necessary average roller weight is approximately 500 lb (227 kg). Over- compaction needs to be avoided to prevent paste from migrating to the surface and closing the Figure 41. Placement, compaction, and finishing of PC pavement.

66 Concrete Technology for Transportation Applications surface voids (145). Also, because of the nature of the surface compaction, some variation in strength, void ratio, and permeability can be expected (146, 147, 148). PC placement needs to be completed as quickly as possible, because the mixture has almost no excess water. Exposure to adverse weather conditions such as high wind and/or high ambient temperature for a significant time period will result in rapid loss of hydration water, which will reduce the final strength and my also cause surface raveling (8). The pavement surface needs to be covered as soon as the final compaction is completed. Plastic sheets are generally used to cover the surface and edges of the freshly placed pavement. Applica- tion of the plastic sheets must be within 20 minutes after compaction and surface finish. This time may be significantly reduced depending on ambient temperature and wind velocity. Curing compounds need to be avoided because they may seal the surface voids. For proper curing, the pavement typically needs to remain covered for at least 7 days. Poor curing practices will result in surface raveling. No traffic should be allowed on the pavement during curing (8). Contraction joints need to be installed in the fresh PC pavement using special grooving tools. Saw cutting the pavement is another method used to form the joints. Saw-cut depths need to be one-fourth to one-third of the pavement thickness. The saw-cutting procedure needs to begin as soon as the pavement has hardened sufficiently to prevent surface raveling and damage. The exposed area around the sawed joint must be recovered with a plastic sheet as soon as saw cuts have been made (8). The sawed joint must be flushed out with water to remove fines and debris. However, no sealant is required to fill the joint grooves. In cold weather conditions, PC construction may be suspended and curing blankets be used when ambient temperature is expected to fall below 40°F (4°C) during and 24 hours after place- ment. The PC pavement must be protected from freezing conditions during the curing period. In hot weather, transporting, placing, and compacting need to be handled as quickly as possible. An evaporation retarder may be applied to the surface of the concrete follow- ing the strike-off process to retard loss of moisture from the surface. After consolidation and before placing the plastic sheet, the surface may be lightly misted, fogged, or sprayed with an evaporation retardant if the surface appears to be losing its sheen appearance. Properties Strength of PC is a function of the aggregate strength, aggregate-paste bond strength, and strength of the cement paste. Compressive and other strengths increase as the paste proportion in the mixture increases, the size aggregate decreases, and when the aggregate is well graded. Adequate compaction and effective curing techniques, which preserve mixture moisture for more efficient hydration, are important construction-related factors that produce higher compressive and tensile strengths. Four-inch (10-cm)-diameter core samples are obtained from the pavements and tested for compressive strength using ASTM C39 (143). It is also suggested that laboratory test cylinders for compressive strength be prepared with a shape factor of 1:1 (diameter to length). This shape factor produces test results more representative of the composition of the PC structure than the cylinder samples with a 1:2 shape factor used in conventional concrete. Issues and Challenges Infiltration Capacity The performance of PC pavements is affected by changes in infiltration rates, structural distress, surface erosion, and degree of resistance to freeze-thaw cycles. Also, dust, sand, clay, and other debris will gradually clog the voids in the surface of PC pavements. By reducing the

Overview of Concrete Technologies 67 permeability of the PC in order to increase its strength, the risk of surface clogging is further increased (141). To avoid surface clogging and loss of drainage capacity, PC pavements in streets and parking areas require frequent vacuum sweeping or power washing (146). Vacuum sweeping seems to be the preferred method to dislodge and remove accumulated debris from the surface voids and to restore or maintain good percolation rate (149). Also, a backup stormwater drain system may be required in areas of high potential for surface clogging. Infiltration rate at the project site can be measured using ASTM C1701/C1701M-17, “Standard Test Method for Infiltration Rate of In Place Pervious Concrete.” Joint Raveling Raveling and erosion of the pavement surface and especially along the joints is a major problem in PC pavements (133). This functional distress may due to poor construction prac- tices or deficient mixtures. Surface abrasion and erosion may also be caused by heavy traf- fic wheels exerting repeated pressure on the pavement surface upon breaking and turning. A useful test to evaluate the abrasion resistance of PC samples is ASTM C1747, “Standard Test Method for Determining Potential Resistance to Degradation of Pervious Concrete by Impact and Abrasion.” Selection criteria for PC streets have to consider traffic including volume of truck traffic. In general, PC pavements are suitable for streets with light truck traffic only. Compaction The compaction energy during PC pavement construction affects the pavement load-carrying capacity, infiltration efficiency, and durability of the pavement. Undercompaction of the pave- ment will cause low unit weight, high void ratio, and low strength and durability. Overcompac- tion tends to push the cement paste up to the surface and cause clogging of the voids. A useful test to determine density and void content of PC is ASTM C1754. A study was conducted to evaluate the effects of compaction energy on PC void ratio, compres- sive strength, tensile strength, unit weight, and freeze-thaw durability (150). The study concluded that low compaction energy reduces PC compressive and split tensile strengths and unit weight and reduces the freeze-thaw durability of the pavement. Another study evaluated the laboratory performance of polymer-modified PC with a focus on the abrasion and freeze-thaw durability (151). Various laboratory tests were conducted to evaluate the physical properties (air voids, permeability), mechanical properties (compressive and split tensile strengths), and durability performance (abrasion and freeze-thaw resistance) of PC mixtures. The test results showed that the use of polymer in PC improves the strength and abrasion resistance of the PC. Structural Distresses Structural distress includes cracking or subsidence due to loss of subgrade support. Sources of the distress include materials and mixture problems, weak subgrade or voids beneath the pave- ment, and heavy traffic loads. Proper attention to pavement design, good QC of materials and mixtures, and following good construction practices will reduce the rate of structural distresses and surface erosion (8). Improved test methods to support QC/QA of PC are the focus of a recently published study (152). Freeze-Thaw When the PC is completely saturated and subjected to freezing, excessive stresses from frozen water may rupture the thin cement paste coating the aggregates and cause deterioration of the pavement. It has been recommended that PC pavements not be used in freeze-thaw environments where the groundwater table rises to less than 3 ft (0.9 m) from the surface of the subgrade (8).

68 Concrete Technology for Transportation Applications Fibers seem to improve resistance to freeze-thaw. A study in Maryland concluded that using cellulose fibers in PC mixtures resulted in a significant improvement in freeze-thaw durability, increase in abrasion resistance, and improvement in tensile strength (138). Recycled Concrete Aggregate Introduction RCA is produced by crushing and processing demolished concrete infrastructure. In trans- portation applications, RCA is typically sourced from highway bridges and pavements, but is also available from commercial crushing of concrete buildings, parking areas, and drainage facilities. In addition, returned concrete from ready-mixed concrete trucks can also be crushed and used as RCA. As existing transportation infrastructure is decommissioned, pavements, bridges, and other concrete elements are becoming increasingly available for and utilized as RCA. Although there are some limitations, RCA is commonly used in new concrete pavements and drainage structures. The most popular use of RCA by state highway agencies is in unbound applications such as pavement base material, fill, or for erosion control at bridges and drainage structures (9, 153). Agencies have also used RCA from crushed concrete as partial or complete replacement of aggregates in bound applications including concrete mixtures for pavements and lean concrete bases (154, 155). Use of RCA in concrete for bridges and other nonpave- ment structural applications is still rare. However, in recent years, driven by economic and sustainability factors, as well as the success of research studies and field implementation, concrete recycling has become more desirable and has been gaining greater acceptance in light structures. Need for the Technology Recycling is generally viewed as one of the most sustainable end-of-life alternatives for existing concrete infrastructure (156). Sustainability benefits associated with use of RCA include reduc- tion of landfill space, energy savings, fewer impacts from quarrying activities, and a reduced carbon footprint associated with the production of the new infrastructure. If RCA is produced on site (or near the site), haul times can be reduced, providing environmental and social benefits including fuel savings, reduced air emissions, and lower community impacts such as traffic and noise (155, 156, 157). Agencies are increasingly pressured to build transportation infrastructure more rapidly, at reduced cost, and with minimal impact to the traveling public. Use of RCA has been shown to provide savings in both cost and time. Economic benefits associated with reuse of RCA include reduced unit cost per ton, time and fuel savings (with reduced hauling), elimination of landfill tipping fees, and improved contractor production efficiencies (155, 157). Availability of a wide range of stationary and movable recycling equipment has made concrete recycling an economi- cal, time-saving option for many projects (155). Depletion of aggregate resources in existing quarries, difficulty commissioning new quarries, and reduced availability of an ample supply of high-quality aggregates are also viewed as drivers of RCA use (153). A recent survey of state highway agencies indicates that the most common use of RCA is in unbound base material for pavements. This decision appears to result from considerations including specification provisions, risk, and contractor advantages associated with use of on-grade recycling (9). When used as an unbound base material in pavements, RCA has demonstrated performance superior to that of virgin aggregates, primarily due to increased stiffness associated with RCA’s angular particles and the secondary cementing action of unhydrated cement (158). However, economic and sustainability factors may increasingly support the

Overview of Concrete Technologies 69 use of RCA in new concrete mixtures. With proper design considerations and testing, concrete containing RCA has been shown to provide performance equivalent to concrete containing conventional aggregates (154, 155, 159, 160). For the purpose of this report, further discussion will primarily focus on use of RCA in new portland cement concrete (“RCA concrete”), and the reader is referred to other resources for guidance on use of RCA in other bound and unbound applications (153, 155, 161, 162, 163). Materials, Mixture Parameters, and Common Test Procedures Source Concrete and RCA Properties RCA can be used as a full or partial replacement of coarse aggregate or fine aggregate in a concrete mixture. Concrete produced using RCA needs to meet the same performance require- ments as concrete produced using conventional (virgin) aggregates. Mindful of this goal, some specifications treat RCA the same as other types of aggregates. Other agencies have developed a separate specification for RCA or have modified requirements to accommodate RCA (155). Regardless of approach, it is important to bear in mind that RCA can have different properties than conventional aggregates, and the effect of these differences needs to be considered during design and proportioning of concrete mixtures. Effective characterization of RCA will support successful use in new infrastructure (153, 155, 162). Characteristics of RCA will be influenced by (1) the characteristics and quality of the source concrete and (2) the production process. Most concrete that has demonstrated satisfactory durability performance can be used to produce RCA for use in new concrete (162). Concrete sourced from projects with known materials and performance history, such as existing highway infrastructure, to produce RCA generally brings less risk than use of concrete from unknown sources or RCA-sourced construction and demolition waste, which may include material from a variety of sources within a single stockpile (155). Existing infrastructure generally comprises known materials, and the concrete will have met agency specifications for acceptance. Source concrete affected by materials-related distress, such as alkali-aggregate reactivity and D-cracking, needs to receive additional scrutiny prior to making the decision for use as RCA in new concrete. The potential for alkali-silica reactivity (ASR) due to RCA produced from ASR-affected source concrete in new concrete is a function of the potential reactivity remain- ing in the RCA as well as the alkali contents of both the source concrete and the new concrete mixture. However, ASR damage in new concrete produced using RCA from ASR-affected source concrete has been shown to be mitigated using the same techniques typically utilized for other reactive aggregates. These techniques include the use of low-alkali cements, SCMs, admixtures, low water–cement ratio, and other measures to reduce permeability and moisture exposure (162). In fact, several case examples exist of concrete pavements produced using RCA from D-cracking and ASR-affected source concrete, where the pavement performed satisfactorily for several decades (154, 155, 160, 162). RCA is often produced from pavements and bridge components that have been exposed to chlorides and other deicing or anti-icing chemicals. The presence of chlorides may cause concerns related to potential accelerated set time and corrosion. However, field studies of RCA concrete have shown no problems attributable solely to chloride content of RCA (162). Nevertheless, the chloride content of the RCA that may have been exposed to excessive salt needs to be evaluated, and epoxy-coated reinforcing steel needs to be used if the predicted chloride content of the new concrete mixture is high enough to cause concern. Since chlorides are typi- cally contained in the fine RCA particles produced from the near-surface portions of the source concrete, reducing or eliminating the fines or washing the RCA to remove material passing a No. 200 sieve is also an option (162).

70 Concrete Technology for Transportation Applications During the recycling process, provisions need to be made to reduce the amount of contami- nant material included in the RCA (155, 162). Reinforcing steel and other materials such as joint sealant need to be removed. Concrete containing low amounts of asphalt cement con- crete patching material has been utilized to produce RCA, but limiting its presence is advisable. Crushing and processing equipment (particularly the type of crusher) used to produce RCA will influence the yield, properties, and characteristics of RCA produced (155). RCA needs to be generally free of contaminants, and provisions to protect stockpiles from contamination need to be implemented (162). A typical on-site crushing and grading process is shown in Figure 42. RCA particles comprise aggregates and reclaimed cement mortar from the source concrete (Figure 43), and therefore properties of RCA will be a function of both components. Relative proportions depend on the source concrete materials, mixture proportions, and properties, as well as the crushing and processing methods. The properties of the coarse aggregates contained in the source concrete, the aggregate–paste bond, and the type(s) of crusher(s) used have been shown to influence the ultimate composition of RCA (155, 162). Particle composition will also Figure 42. Typical crushing and grading operation for producing RCA on site (courtesy of G. Fick, Trinity CM Services). Figure 43. Coarse RCA (courtesy of M. Adams, New Jersey Institute of Technology).

Overview of Concrete Technologies 71 vary by size, with larger sizes of RCA containing more aggregates from the source concrete, and finer sizes of RCA containing a greater fraction of mortar. The crushing process will also influ- ence the shape, texture, and gradation of RCA particles. In general, RCA particles tend to be angularly shaped with a rough surface texture (162). RCA typically has a higher absorption than conventional aggregate. This is driven by the absorption of the reclaimed mortar, which is more porous and has additional surface area. Smaller RCA particles tend to contain a greater mortar fraction with higher impact on absorp- tion (164). The porosity of the reclaimed mortar also results in a relatively lower specific gravity and unit weight of RCA concrete (162). RCA also tends to have a slightly higher abrasion loss than conventional aggregates, attributed to the adhered mortar fraction and partially fractured particles (155). The presence of fines (or crusher dust) on RCA particles can increase water demand in new concrete mixtures and, in unbound base applications, the potential for pre- cipitate formation in drain systems. Washing RCA will aid in reducing fines and the associated issues (162). Field studies of pavement applications have shown that RCA concrete that includes higher mortar content often exhibits more distress, and the reclaimed mortar content needs to be considered and accounted for during mixture proportioning and trial batching (160). RCA Concrete Production and Properties In research and in practice, it has been shown that concrete mixtures containing RCA can meet performance expectations for strength and durability (154, 155, 162, 165). The fundamen- tals of mixture design and proportioning for RCA concrete mixtures do not differ from those used for a conventional concrete mixture, and production of RCA concrete, including batch- ing, mixing, placement, and finishing can also be very similar to production of conventional concrete. However, certain characteristics of RCA that differ from conventional aggregates can affect the properties of fresh and hardened RCA concrete differently, and these differences need to be considered and accounted for in the design process (155, 162, 165). Mixture proportioning procedures for RCA concrete mixtures can follow the same methodol- ogies used for conventional mixtures. Guidance on the effects of RCA on the properties of fresh and hardened concrete is presented in subsequent sections of this report as well as in a number of guidance documents (155, 162, 165). General needs include ensuring that proper test- ing to characterize RCA be performed, admixtures be used to address increased water demand without adding water, mixture proportions be adjusted to accommodate the potential higher variability in strength, and air content be adjusted to account for air voids in RCA mortar fraction. Trial batching and adequate testing are key to achieving the desired performance (155). Impact of RCA on Fresh Concrete Properties Typical concerns associated with use of RCA are increased water demand and premature stiffening, driven by the increased absorptivity of RCA. The angular particle shape and rough texture of the crushed RCA can also result in reduced workability of a concrete mixture. ACI 555 indicates that for a given slump, RCA concrete will have a 5% additional free water requirement, although an even greater increase in water demand can be expected if fine RCA is used (165). Without the need to add water, workability and premature stiffening issues can generally be addressed by using chemical and mineral admixtures, prewetting or presoaking the RCA, adjusting past content, optimizing aggregate gradations, and limiting or eliminating use of RCA as fine aggregate (155, 162, 165). ACPA recommends limiting inclusion of RCA as a fine aggregate to 30% replacement level in order to reduce the potential for loss of workability (162). Use of RCA in high amounts can result in mixtures that are difficult to finish by hand, although mechanical finishing equipment is generally not affected (155, 164). When used as coarse aggregate, RCA has minimal effect on bleeding, although bleeding is often reduced in mixtures

72 Concrete Technology for Transportation Applications using RCA as fine aggregates (162). Also, the setting time of RCA concrete could be shorter than that of a conventional concrete mixture, particularly when RCA fines are included (155, 166). Although RCA should not affect the action of air-entraining admixtures, the air content of a new mixture containing RCA will be affected by the air void system introduced to the new con- crete through the RCA’s reclaimed mortar. Air content tests of fresh RCA-concrete mixtures will be influenced by the air void system of the RCA, and thus the results need to be adjusted using the aggregate correction factor in ASTM C231. Alternatively, the volumetric method (ASTM C173) could be utilized (162). Effect of RCA on Hardened Concrete Properties The effect of RCA use on concrete mechanical properties and durability performance will depend on the characteristics of the source concrete, RCA characteristics as produced, the type of RCA used (coarse RCA, fine RCA, or both), and the level of replacement of conventional aggregate. Use of RCA as coarse aggregate in a concrete mixture will generally reduce the com- pressive strength, tensile strength, and modulus of elasticity compared to equivalent mixtures using conventional aggregates (up to 24%, 10%, and 33%, respectively). When RCA is used as fine aggregate, greater reductions in test values for these properties can be observed (up to 40%, 20%, and 40%, respectively), compared to use of RCA as coarse aggregate only. However, decreases in strength and the potential for increased variability can be accommodated by reducing the water–cement ratio, use of admixtures, and other mixture proportioning considerations (162, 165). RCA concrete tends to have higher values of the coefficient of thermal expansion (CTE), drying shrinkage, creep, and permeability than equivalent conventional concrete mixtures. The effects will be highly influenced by the characteristics of the RCA and the replacement type (coarse aggre- gate only or coarse and fine aggregate), and percentage replacement of natural aggregate. Use of RCA as fine aggregate tends to result in up to 15% reduction in unit weight, and significantly affects shrinkage and permeability. This is a result of the increasing amount of paste needed with the fine RCA (158, 159, 162, 167). The permeability of RCA concrete can be higher than equivalent conventional concrete mixtures, but the impact can range from negligible to very large (162). Use of RCA produced from high-quality, low-permeability source concrete has been shown to mitigate this predicted increase in permeability, along with measures to reduce water content and paste volume dis- cussed in the previous section (165). Limiting RCA use as a coarse aggregate replacement can significantly limit the anticipated increase in shrinkage of the concrete (162). Similar to conventional concrete, a properly entrained air void system has been shown to sup- port freeze-thaw durability of RCA concrete, and use of sulfate-resistant cements should aid in prevention of issues with sulfate environments (165). The increased permeability of RCA concrete can lead to a higher potential for carbonation, although this can be offset by use of a lower water– cement ratio for the new mixture (165). ACPA (162) indicates that this increased permeability can be “offset by reducing the water–cement ratio by 0.05 to 0.10” and/or by replacing some portion of cement with SCMs. Also, effect of ASR in the RCA can be mitigated in the new concrete by conventional mitigation approaches such as the use of SCMs and low-alkali cements (165, 168). Overall, research has shown that “RCA concrete can be highly durable, even when the RCA is produced from concrete with durability problems, provided that the mixture proportioning (including chemical and mineral admixtures) is done properly and the construction (including concrete curing) is of good quality” (162). The RCA user needs to be mindful that the impact of RCA use on the durability performance of concrete is dependent on the characteristics of the RCA source concrete, the RCA as produced, other mixture materials, and mixture proportions (162, 167). In fact, some research has shown favorable changes in RCA concrete performance (169).

Overview of Concrete Technologies 73 Construction Practical and economic factors determine whether a project is a candidate for use of RCA. A key consideration is whether the potential amount of RCA produced and utilized on a project warrants the mobilization of a mobile crushing and grading plant to the site. The cost of conventional aggregates, the project’s proximity to available stationary crushing and grading plants, the amount of RCA to be utilized on the project, permitting requirements, project phas- ing, and the space requirements of a mobile plant on the site (public vs. private right-of-way land) each play a role in project scoping and determination of the potential use of RCA (153, 155, 157, 167). Alternatively, if RCA is to be utilized, the project costs and the environmental impact of hauling material to a stationary crushing plant are also considerations (153). Technologies to support in-place or on-site recycling, such as crack-and-seat, rubblization, and on-grade crushing and processing are available, and economic and time-saving benefits have supported increasing use of RCA in unbound applications or as a stabilizer in full-depth reclamation techniques in recent years (155). Other commonly utilized unbound applications for RCA include fill material, erosion control, and embankments. Despite the fairly widespread use of RCA in unbound applications, use of RCA concrete in pavement applications is relatively uncommon in the United States, and use of RCA concrete in other structural applications in transportation, such as bridge components, is quite rare. Concerns with the consistency or quality of the RCA, the increased water demand of the RCA due to high absorption, the potential for chemical contamination, and the possibility of introducing preexisting durability issues into the new concrete components are often cited (155, 157, 165). Because of risk aversion, structural considerations, and other concerns, pavement applica- tions appear most promising for increased use of RCA concrete. However, RCA can and has been successfully used in new concrete pavements, and over 100 field sites exist where RCA concrete has been utilized. Reza and Wilde (154) present an extensive list of existing RCA con- crete projects, with supporting information on type of RCA, how RCA was used in the mixture, pavement design, and performance. Field performance of RCA pavement projects is reported by Gress and coworkers (160). One successful project where RCA was used as a 100% replacement for both coarse and fine aggregates is a section of I-10 near Houston, Texas (Figure 44). In 1995, 5.8 miles of continu- ously reinforced concrete pavement (CRCP) were reconstructed using RCA concrete. RCA was required to meet the same specifications for virgin fine and coarse aggregates. During a 2013 inspection, with the pavement approaching 20 years of age, no punchouts were present and crack widths appeared tight (170). Figure 44. CRCP RCA pavement near Houston, Texas (courtesy of A. Naranjo, Texas DOT).

74 Concrete Technology for Transportation Applications Use of RCA in concrete for structural applications such as bridges continues to be rare, with concerns often expressed about issues affecting structural performance, including durabil- ity and corrosion potential (171, 172). However, many research studies have been performed demonstrating the potential for RCA concrete to perform satisfactorily in structural members (165). These studies have provided strategies for mitigating the risks (perceived or real) in use of RCA and have offered guidance and strategies to support increased use in structural appli- cations. Economic and sustainability drivers may result in the increased appeal of RCA for structural applications. In one notable recent example of use of RCA concrete in a transporta- tion structure, RCA sourced from a demolished temporary detour bridge has been used as a 30% replacement of conventional aggregate in a portion of the foundations (mass concrete shaft caps) of the new Willamette River bridges (173). Performance Properties For successful use in bound or unbound applications, RCA needs to be treated as an engi- neered material (155). From a specification standpoint, some state agencies treat RCA similarly to conventional aggregates, with specification requirements for RCA identical to those for other aggregates. Several states have separate specifications for RCA or require additional test- ing if material is not sourced from agency infrastructure. QC/QA tests for RCA are generally the same as those used for conventional aggregates, and appropriate specification provisions often include gradation, limits on deleterious substances, abrasion resistance requirements, absorption, and specific gravity. For unbound uses, specifications for RCA are provided in AASHTO M 319-02, which provides guidance for use of RCA sourced from both agency infrastructure and from construction and demolition debris. Additional guidance is provided by ACPA (162). Of note, use of the sodium and magnesium sulfate soundness tests is not appropriate for testing RCA because of inconsistencies in the tests. Other soundness testing procedures have been found appropriate by other agencies, some of which are described in AASHTO M 319 and by Snyder et al. (155). Specific gravity and absorption tests can be performed according to AASHTO T 85. How- ever, since the specific gravity and absorption of RCA can be more variable than conventional aggregates, AASHTO MP 16 provides limits on total variability for both of these tests, along with additional guidance. AASHTO MP 16 presents limits for soundness tests, but also states that alternative tests can be used. Testing for alkali-aggregate reactivity is suggested in accordance with AASHTO T 303 and ASTM C586 for ASR and ACR, respectively, with alternative methods also discussed in an appendix. Testing of RCA for D-cracking is suggested using AASHTO T 161. Implementation Conclusions of many field studies indicate that RCA concrete can be used to construct pave- ments capable of providing performance equivalent to pavements constructed with conven- tional aggregates. Appropriate design considerations, such as the use of load transfer devices, shorter joint spacing to account for the increased CTE and other thermal properties, and con- sideration of RCA properties in mixture proportioning have been recommended (154, 160). Use of production processes that reduce the amount of reclaimed mortar in the RCA would ensure that the RCA performs close to conventional aggregates in pavements (160). RCA con- crete pavements demonstrating undesirable performance have failed due to mid-panel cracks and design issues such as poor support layers, excessive slab lengths, and undoweled joints (159, 160). Implementation of RCA concrete in the lower lift of two-lift pavements has been a practice in Europe, with RCA concrete in the lower lift and virgin aggregate in the upper lift. Several two- lift concrete pavements with RCA concrete in the lower lift have been constructed in the United

Overview of Concrete Technologies 75 States (174). These include a reconstructed section of US-75 in Iowa that provided over 40 years of service, and more recently a section of I-70 in Kansas (155). In these applications, use of RCA in the lower lift was found to be a viable alternative to conventional pavement construction from both economical and sustainability standpoints, with cost savings associated with the RCA in the lower lift helping to offset expenses associated with construction of a two-lift pavement. Specifications and Guidelines Specifications for use of RCA in new concrete mixtures is presented in AASHTO MP 16 and in ACPA (162). AASHTO MP 16 states that when using RCA for new concrete, enhanced QA/QC procedures should be followed to ensure that deleterious materials are not present in the RCA. The standard provides limits for deleterious substances as well as requirements for physical property. The specified maximum Los Angeles (LA) abrasion for RCA is 50%, which is slightly higher than the LA abrasion specified for virgin aggregates by some agencies. Gradation requirements for RCA are typically the same as those required of conventional aggregates for the same use. Guidance on use of RCA for concrete mixtures has been published by a number of organizations (155, 162, 165, 166, 167). Many state specifications also address construction-related concerns associated with RCA. Appropriate and attentive aggregate stockpile management is necessary when using RCA, because stockpiles must be protected from contamination and moisture application must be monitored. Stockpile management has been developed for several states, including Michigan (153, 155). Environmental concerns related to use of RCA include high pH and potential pol- lutants in stockpile runoff and air quality and community impacts associated with crushing and handling (155). In unbound base applications, drainage structures can be clogged by precipi- tates, but can be mitigated by minimizing RCA fines and use of effective drainage designs (158). Guidance on mitigating environmental concerns associated with RCA use during planning, design, and construction is presented by Snyder et al. (155). Limitations and Challenges RCA is produced from crushed concrete that can be obtained from a variety of sources, where the parent concrete may have been of high, medium, or low quality. Variation in the quality of the parent concrete can produce RCA with unacceptably variable properties with respect to strength, absorption, and particle stability. Low- or nonuniform-quality source concrete will produce RCA that may not be suitable for reuse in concrete mixtures for pavements and structures (155, 165). State agencies need to use RCA only in new concrete mixtures for pavements and structures if they can be assured that the properties of the source concrete will support production of RCA of acceptable quality. Concrete sourced from agency projects with known, acceptable performance history is typically recommended for use as RCA. Properties of the source concrete can be tested and verified to be adequate, if characteristics are not already known from historical records of the source concrete. RCA sourced from a variety of projects or from unknown projects needs to be used only as subgrade or fill material, and only if QA/QC testing indicates sufficient performance characteristics and an acceptable amount of contaminant material. A detailed discussion of project selection and scoping for concrete recycling in pavement applications, including a flowchart to aid in characterization of the source concrete for use as RCA, is presented by Snyder et al. (155). Using RCA in new concrete mixtures as a partial or full replacement for virgin coarse aggre- gate typically requires prewetting the RCA, since its absorption can be high due to the paste com- ponent of the aggregate particle. Without prewetting, the RCA can make it difficult to control mixture workability and strength.

76 Concrete Technology for Transportation Applications When using RCA in jointed concrete pavements, the designer needs to include dowel bars at transverse joints to provide adequate load transfer between adjoining slabs. In pavements with undoweled joints, the recycled coarse aggregate can deteriorate due to the friction between interlocking slabs at the transverse joint, leading to loss of load transfer and joint failure issues. High Early Strength Concrete Introduction HESC is a concrete mixture that is designed to achieve a specified high early strength within 24 hours, and in many cases, in less than 12 hours (10, 175). HESC is commonly used to accel- erate construction and repair of highway pavements (Figure 45) and repair of airport runways to allow early opening of the facility to traffic (10, 176). In precasting plants (Figure 46), HESC mixtures are used to achieve the required strength for early release of the prestressed strands (177) and removal of forms in non-prestressed members. HESC uses materials similar to those used in conventional mixtures. However, for the mixture to achieve high early strength, several changes in the mixture design are required based on the specified strength to open the pavement to traffic or to release the prestressed strands. Among mixture ingre- dients and proportions that produce rapid strength gain are higher quantities of Type I/II cement, lower water–cement ratio, high dosage rate of accelerating admixtures and HRWRs, and the use of Figure 45. HESC for slab replacement. Figure 46. High early strength SCC placement in prestressed beam (courtesy of Dura-Stress, Florida).

Overview of Concrete Technologies 77 Type III cement instead of Types I/II (175). Insulating blankets may be required to aid in developing high early strength in cold weather or to accelerate strength gain (10, 178). For pavement projects in cold environments, HESC must not only gain strength rapidly but must also achieve long-term durability (175). In all projects requiring HESC, design of the pave- ment and the concrete mixture, as well as construction methods must be compatible to ensure that premature distresses including cracking and spalling are mitigated. Concrete Materials and Mixtures Mixture Proportioning In proportioning HESC mixtures for accelerated paving, factors such as cement type and content, aggregate size distribution, use of entrained air, concrete, and ambient tempera- tures may influence early and long-term concrete strength, durability, and performance (178). Table 3 shows combinations of mixture materials utilized for projects with different lane- opening times (179). Table 4 shows a mixture design for high early strength SCC used to cast a prestressed member (177). The 14-hour strength gain allows release of the tensioned strands in prestressed beams. A thorough laboratory investigation using trial batches and performing tests of key perfor- mance characteristics is critical before utilizing an HESC mixture. The laboratory work needs to determine plastic and hardened concrete properties using project materials and needs to aim to verify the compatibility of all chemically active ingredients in the mixture. For example, not every cement will gain strength rapidly (14). Also, with respect to the compatibility issue, an NCHRP study concluded that it might be difficult to control the air content in a HESC mix- ture that contains a large quantity of Type III cement, low water–cement ratio, and multiple Mix Characteristic 4- to 5-Hour Concrete 6- to 8-Hour Concrete 20- to 24-Hour Concrete Cement type I or III I or III I or III Cement content, lb/yd3 (kg/m3) 560–895 (333–532) 715–885 (425–525) 675–800 (400–475) Water–cement ratio 0.38–0.40 0.36–0.40 0.40–0.43 Accelerator Yes Yes None to Yes Table 3. Common ranges of mixture ingredients for HESC in accelerated pavements (179). Material Quantity Cement, lb/yd3 (kg/m3) 740 (440) Class F fly ash 175 (104) Water–cement ratio 0.27 HRWR As necessary Table 4. High early strength SCC mixture design for a prestressed member (177).

78 Concrete Technology for Transportation Applications admixtures (175). Therefore, proper testing of laboratory samples is needed not only to verify strength, but also to evaluate the concrete’s performance using other appropriate tests such as the test for resistance of concrete to rapid freezing and thawing (AASHTO T 161). Cement With proper proportioning, concrete mixtures using Type I, Type II, or AASHTO I/II, and Type III portland cements can produce the required high early strength and durability perfor- mance for accelerated concrete paving and precast members. The HESC mixture often requires multiple admixtures such as HRWR, air entraining, and accelerating admixtures to provide the needed fresh and hardened properties. Use of cement with high levels of tricalcium silicate (C3S) and finely ground cement particles will result in rapid strength gain. Tricalcium aluminate (C3A), although not contributing to strength gain, is a catalyst to enhance the rate of hydration of C3S. Cement with high fineness has an increased surface area, allowing more cement contact with mixing water and, consequently, contributing to faster hydration and rapid strength gain (14). Fly Ash Classes C and F fly ash have been used in HESC with the purpose of improving workability and flow, as well as contributing to long-term strength and durability. Class F fly ash has been used in high early strength mixtures for prestressed members, while Class C ash has been mostly used in accelerated pavement construction (14). Strength evaluation of HESC with Class F fly ash must be performed using trial batches to verify achieving early strength development. This is due to the lower heat of hydration generated from the pozzolanic reaction which can delay early strength gain. Use of accelerators needs to be considered when the strength of concrete is below that specified for lane opening (10). Ground-Granulated Blast-Furnace Slag Because of its cementitious properties and contribution to long-term strength and durability, the use of GGBFS (slag) in accelerated paving is generally acceptable (10). However, the slow nature of the cementitious reaction generates lower overall heat not conducive to very rapid strength development. Therefore, in designing HESC mixtures with slag, tests must be performed on trial batches to determine the optimum dosage of slag and the needed accelerating admixture to ensure early strength development that meets agency specifications. Also, use of curing blankets may be needed to aid in rapid strength development. Admixtures Air-entraining admixtures meeting ASTM C260 requirements are necessary for HESC mixtures in freeze-thaw environments. However, care needs to be exercised when selecting the dosage rate of the admixture. A high dosage of air entrainment will reduce the rate of strength development and a low dosage may reduce the resistance to freeze-thaw action. Therefore, control of air content is necessary for successful projects. According to ACPA, the concrete mix should have between 4.5% and 7.5% entrained air, depending on the maximum coarse aggregate size and the local climate (178). Normal and high-range water-reducing admixture Types A, E, and F (ASTM C494) generally provide the necessary properties for accelerated concrete paving. These admixtures tend to reduce mixture water and increase efficiency of the cement hydration, thus contributing to workability at placement and early strength gain. However, laboratory testing is essential to determine if a concrete containing the admixture will develop the desired properties. For example, using excessive dosage of high-range water-reducing admixtures may delay concrete setting and strength gain (10).

Overview of Concrete Technologies 79 Accelerating admixtures aid in early strength development and reduce initial setting times by increasing the reaction rate of C3A. Energizing this reaction generates additional heat to increase the cement hydration to form more hydrated gel and achieve high early strength. Accelerating admixtures generally consists of soluble inorganic salts or soluble organic compounds and needs to meet requirements of ASTM C494, Type C or Type E (10). Cal- cium chloride is used as an accelerator in pavement repairs and slab replacement when no reinforcement is present. However, in reinforced pavements the use of calcium chloride may be prohibited due to its corrosive effect. Agencies generally specify the noncorrosive or corrosion-inhibiting accelerators such as calcium nitrite in patching or replacement of reinforced slabs or in bridge repairs. Construction Curing and Temperature Management The key to achieving rapid strength gain in HESC is to have an efficient cement hydration that is continuously energized by internal and external heat. Therefore, it is important to con- trol and reduce heat loss, especially in cold weather, and to mitigate moisture loss in hot and windy weather conditions. This is accomplished by implementing effective curing provisions to maintain satisfactory moisture and temperature conditions in concrete for a period sufficient to ensure proper hydration and rapid strength development (10). The most effective and practical curing provisions for concrete pavements and replacement slabs are curing compounds and the use of curing and insulating thermal blankets (176). In precast plants the use of an external heat source or steam curing of forms has proven effective in achieving the required high concrete strength to allow for early release of the tensioned strands and/or removal of the formwork (175, 180). Curing Compound. Liquid membrane-forming curing compounds for HESC need to meet ASTM C309 requirements. Typically, a white-pigmented compound (Type 2, Class A) is applied to the surface and exposed edges of the concrete pavement. In mountainous and arid climates, agencies often specify a slightly heavier dosage rate of resin-based curing compound meeting ASTM C309, Type 2, Class B requirements (10). The recommended application rate of curing compound for accelerated paving projects ranges from 100 to 150 ft2/gal (2.5 to 3.75 m2/L). Thinner pavement requires a thicker coating of the curing material (181). To reduce loss of mix water from the paved surface, the curing com- pound must be applied as soon as the final surface finish is completed. Evaporation retarders may also help to prevent very early loss of mix water when applied immediately after concrete placement and initial strikeoff. Curing and Insulating Blankets. Some states also require the use of curing or insulating blankets to supplement the action of the curing compound. Curing and insulating blankets reduce the heat loss and moisture evaporation from the finished pavement surface (182). The purpose of the insulation is to aid early strength gain in cool ambient temperatures by reducing heat loss from the concrete. The insulating blanket needs to consist of a layer of closed-cell poly- styrene foam with another protective layer of plastic film. Additional blankets may be necessary for temperatures below about 40oF (4oC). In warm weather with mild cool nights, thinner curing blankets are sufficient to aid in pre- serving heat and moisture in the pavement. Florida, for example, requires the use of one and, if necessary, two layers or more of white burlap-polyethylene blankets (183).

80 Concrete Technology for Transportation Applications Joint Sawing HESC sets fast and gains strength early and rapidly. Therefore, there is a short window for saw cutting joints in an accelerated pavement project. Timely joint sawing is important to avoid uncontrolled cracks that develop due to tensile stresses induced by drying shrinkage and thermal effects (10). Concrete placed in early morning often reaches higher maximum temperatures than con- crete placed in the late morning or afternoon, because the former receives more radiant heat throughout the day. This suggests that concrete placed early in the morning will generally have a shorter sawing window. Nighttime paving allows a longer window for joint sawing in the early morning since the maximum concrete temperature will not coincide with the maximum ambi- ent temperature (10). Proper timing of joint sawing is important to avoid joint spalling when sawing prematurely or uncontrolled cracking when sawing too late. A sacrificial slab placed at the project site and then sawcut at different time intervals may determine proper timing of the sawcut for the paving project. The nondestructive maturity test (ASTM C1074 and C918), which is normally used to determine strength of concrete in pavements and structures, may be performed at different time intervals to identify the beginning and end of the joint sawing window. Strength Requirement for Lane Opening The critical issue in accelerated pavement construction is determining the lane opening time when traffic is allowed to use the newly placed pavement. This decision needs to be based on achiev- ing a specified concrete strength and not arbitrarily on a set time from concrete placement (184). Some state highway agencies use flexural strength test results and requirements for lane opening, but most states use compressive strength (10). There is no clear consensus on what strength is required for opening accelerated concrete pavements to traffic. Factors such as expected traffic loadings, edge conditions, pavement geometry and project type, new construc- tion or rehabilitation affect the pavement strength required for traffic (179). A review of state highway practices suggests that a range of values is often specified for lane opening of accelerated pavements. Compressive strength values of 2,000 to 3,000 psi (13.8 to 20.7 MPa) and flexural strength values of 290 to 400 psi (2.0 to 2.8 MPa) have been reported (185). These values are conservative and represent the minimum strength needed to open the repaired/replaced slabs to traffic. The required ultimate strength of the HESC would normally be reached from 24 hours to several days. In Table 5 minimum opening-strength requirements for various slab thicknesses are shown (186). Thicker slabs require lower strength. Slab Thickness in. (mm) Strength for Opening to Traffic, psi (MPa) Repair Length < 3 m (10 ft) Slab Replacements Compressive 3rd-Point Flexural Compressive 3rd-Point Flexural 6 (150) 3,000 (20.7) 490 (3.4) 3,600 (24.8) 540 (3.7) 7 (175) 2,400 (16.5) 370 (2.6) 2,700 (18.6) 410 (2.8) 200 (8.0) 2,150 (14.8) 340 (2.3) 2,150 (14.8) 340 (2.3) 225 (9.0) 2,000 (13.8) 275 (1.9) 2,000 (13.8) 300 (2.1) 250+ (10.0) 2,000 (13.8) 250 (1.7) 2,000 (13.8) 300 (2.1) Table 5. Minimum opening strength for full-depth slab replacements (186).

Overview of Concrete Technologies 81 A few highway agencies, including Florida and Georgia, have revised their required opening strengths to values lower than 2,000 psi (13.8 MPa). Florida specifies 1,600 psi as a minimum opening strength requirement for replacement slabs (183). However, state DOTs are encour- aged to evaluate the appropriateness of using lower opening strength values that are suitable for their climatic conditions and project types (179). The use of maturity meters or pulse-velocity devices for monitoring the in-place concrete strength is recommended as part of that process (178, 182). Also, HIPERPAV computer software (www.hiperpav.com) may be helpful in identi- fying conditions that may be potential contributors to random cracking in HESC mixtures used in accelerated paving (187). Very High Early Strength Concrete Repair Materials and Alternative Cementitious Materials Introduction The demand to maintain and extend the service life of existing infrastructure has driven devel- opment of a wide variety of VHESC or cementitious repair materials that gain the required strength (often to support lane opening) from 1 to 4 hours. Selection of the most suitable approach will depend on many factors, including the condition of the existing facility, the type and extent of pavement deterioration, service life goals, and other site-specific and agency con- siderations. Although identification of the appropriate approach is beyond the scope of this synthesis, this section presents a basic overview of the cementitious materials often utilized for such purposes. Need for Technology In transportation applications, cementitious repair materials are utilized in pavements and bridges subjected to heavy traffic with challenges in closing lanes to perform repairs with con- ventional concrete that requires longer cure time. Typical application of such materials includes rapid repair of pavements in highways and airports and in bridge deck patching, as well as other structural and nonstructural applications. In airfield applications, rapid repairs of distressed areas are necessary to reduce the potential damage to aircraft from concrete debris and/or to allow quick opening of runways to resume military flights (188). Repairs to concrete infrastructure can be performed with conventional concrete mixtures, pro- vided that time, weather, traffic, and construction conditions allow for batching, mixing, place- ment, surface finish, and early strength gain. However, transportation agencies, airports, and the military are increasingly required to perform the repairs more rapidly and open the pavement, bridge, or runway to traffic much sooner to keep the traffic disruption period to an absolute mini- mum (4 hours or less). Very often, the most optimal lane closure window to perform the work is during nighttime. The short time frames allowed for work generally require that repairs be per- formed using VHESC materials that cure and gain strength very rapidly, often in less than 1 hour. Materials, Mixture Parameters, and Common Test Procedures Concrete repair often requires addressing a variety of engineering challenges. For example, repairs may need to be performed in cold or hot weather, which affects the fresh and hardened properties of the repair materials with respect to setting time, strength gain, shrinkage, bonding to substrate, and overall longevity of the repair. In addition, construction challenges associ- ated with the repairs need to be addressed. These include achieving proper installation condi- tions, such as adequate removal of existing materials and achieving the appropriate substrate

82 Concrete Technology for Transportation Applications conditions (clean, dry, appropriate bonding texture and/or bonding agent) to achieve adequate bonding of the repair material (189, 190, 191). Concrete repair has been called “as much an art as a science,” and engineers and contractors traditionally receive minimal formal training, relying more upon experience and lessons learned from previous trials (189). The conditions associated with repairs often require rapid setting and very high strength gain of the materials, while allowing adequate time and workability for proper placement and finish. Because of the rapid and often high strength gain of many repair materials, durability performance can be compromised. Many cementitious repair materials have historically been associated with high heat of hydration, issues with dimensional stability or shrinkage, bond failure, and distresses resulting from high stress concentrations due to the high stiffness of the hardened material (190). In fact, the rapid hydration of early strength cements using latex admixtures has been linked to significant shrinkage (up to 80% of the total volume change) during the first several hours of curing (191). Preferred performance criteria for repair materials for bridge decks and pavements are sum- marized as follows (190): • Very high early strength, • Long-term durability, • Installation efficiency, • Exhibiting no surface damage, • No internal cracking, • No separation from underlying pavement or bridge deck (debonding), and • No other indications of distress. Repair materials can be classified into the following general types (179, 189, 190, 192): • Cementitious concrete including Type III portland cement, ultrafine portland cement, high-alumina cement, and expansion-producing grouts; • Polymer-modified concrete including additives such as styrene butadiene rubber, vinyl acetate, acrylic, and magnesium phosphate; and • Polymer concrete and resinous mortars including epoxy, polyester, acrylic, and polyurethane compounds. As can be surmised from the above list, the variety of types and formulations for concrete repair material presents a wide range of fresh, early age, and late age performance character- istics. These repair materials can have proportions and early age performance characteristics that are (1) similar to conventional concrete, (2) gain early high strength during the first day or over several days, or (3) set very quickly and gain strength early and rapidly to levels that can support traffic within a few hours (such as high-alumina cements and magnesium phosphate materials). For rapid-hardening repair materials, traffic opening times vary by product and installation conditions, but can range from 0.5 hour to 24 hours (179, 190). The rapid hard- ening of some materials requires expedient placement, since hardening and set can occur as quickly as 10 to 30 minutes (193). Recent initiatives to support improving the sustainability of construction have resulted in increased interest in the use of alternative (non-portland) cements, which can provide early age properties and good to superior durability performance in a variety of applications while also reducing environmental impacts associated with their production (194). ASTM C1600/C1600M-17, “Standard Specification for Rapid Hardening Hydraulic Cement,” provides the requirements for strength, volume stability, and durability properties of rapid- hardening hydraulic cements, as shown in Tables 6 and 7. Rapid-hardening hydraulic cement is defined according to ASTM C1600 as a hydraulic or blended hydraulic cement that exhibits

Overview of Concrete Technologies 83 rapid strength gain during the first 24 hours of hydration, with or without other constituents, processing additions, and functional additions. The specification covers four types of rapid-hardening cement, shown in Tables 6 and 7. They are as follows: Type URH. Ultrarapid hardening for use where ultrahigh early strength is desired. Type VRH. Very rapid hardening for use where very high early strength is desired. Type MRH. Medium rapid hardening for use where mid-range rapid-hardening high early strength is desired. Type GRH. General rapid hardening for use when the higher strength properties of a Type VRH or a Type MRH cement is not required. Property Age Cement Type URH VRH MRH GRH Compressive strength (ASTM C109), minimum psi (MPa) 1½ hours 3,000 (21) 1,700 (12) — — 3 hours 4,100 (28) 2,200 (15) 1,500 (10) 1,000 (7) 6 hours — — 2,000 (14) 1,500 (10) 1 day 5,100 (35) 3,500 (24) 2,500 (17) 2,000 (14) 7 days 6,000 (41) 4,100 (28) 4,100 (28) 3,500 (24) 28 days 8,300 (57) 5,100 (35) 4,500 (31) 4,100 (28) Drying shrinkage (ASTM 596), max % 7 days 0.06 0.06 0.08 0.10 28 days, air storage 0.07 0.07 0.09 0.12 Minimum time of final set (ASTM C191),a apparatus (min) 10 10 10 10 Autoclave (ASTM C151), max expansion (%) 0.8 0.8 0.8 0.8 aThe initial setting time typically ranges from 10 to 45 minutes for and composition. rapid-hardening cements of various types Note: Dash = no information provided in reference to indicate that the item was not used or applied. Table 6. Standard physical requirements for rapid-hardening cements (from ASTM C1600). Property Age Cement Type URH VRH MRH GRH Sulfate expansion (ASTM C1012)a 6 months, max % 0.05 0.05 0.05 0.05 1 year, max % 0.10 0.10 0.10 0.10 ASR expansion (ASTM C441)b 14 days, max % 0.020 0.020 0.020 0.020 56 days, max % 0.060 0.060 0.060 0.060 Heat of hydration (ASTM C186) 7 days, max kJ/kg (kcal/kg) 250 (60) 250 (60) 250 (60) 250 (60) 28 days, max kJ/kg (kcal/kg) 290 (70) 290 (70) 290 (70) 290 (70) Expansion in water (ASTM C1038) 14 days, max % 0.10 0.10 0.10 0.10 aIn the testing of these cements, testing at 1 year shall not be required when the cement meets the 6-month limit. Cement failing the 6-month limit shall not be rejected unless it also fails the 1-year limit. bThe test for mortar expansion is an optional requirement to be applied only at the purchaser’s request and is not required unless the cement will be used with alkali-reactive aggregate. Table 7. Optional requirements for rapid-hardening cements (from ASTM C1600).

84 Concrete Technology for Transportation Applications Alternative Cementitious Materials There has been increasing interest in use of alternative cementitious materials (ACMs) for a variety of sustainability and performance-related reasons (194). The rapid hardening and strength gain of several types of ACMs such as calcium sulfoaluminate cements (CSAs), calcium aluminate cements (CACs) and alkali-activated (AA) binders has generated interest for use in slab replacements and accelerated concrete pavements (195). Several ACMs have been linked to enhanced durability performance, although limited field studies exist, and claims of supe- rior durability have not been investigated to a full extent (196). Although recent studies have provided insight into the mechanisms and performance of ACMs, only limited use has been observed to date (194, 195, 196). Guidance on use of ACMs is presented in ACI ITG-10R-18, “Practitioner’s Guide for Alternative Cements,” which presents an introduction to ACMs, provides information on the properties and applications of these materials, presents selected case studies, and provides guidelines for use (194). Performance measures discussed as part of ACI ITG-10R-18 include the environmental impacts of ACMs, life-cycle cost considerations, initial cost considerations, and functional performance. A comparison of commercially available alternative cement tech- nologies, including CAC, CSA, AA, and several other types of ACMs, is provided in Table 8, as presented in ACI ITG-10R-18 (194). The publication provides a detailed description of selected types of ACM technologies, along with testing requirements to support specifications and QA/QC. Construction As can be surmised from the above list, the variety of types of concrete repair material for- mulations present a wide range of fresh, early age, and late-age performance characteristics, which can also affect construction. Project characteristics drive selection of materials that provide the required strength (within the required time to opening) and durability perfor- mance, while also addressing constructability and cost constraints. Many cementitious repair materials are sold in packaged form that requires preparation of small batches on site. For larger quantities of repairs, some materials can be batched in mobile volumetric mixers or at ready-mix plants. ACI provides a summary of repair and overlay material properties, selection, and a list of essential steps for repair in ACI 546.3R-14, “Guide to Materials Selection for Concrete Repair” (189). Guidance specifically on polymer-modified concrete mixtures is available in ACI 548.3R-09, “Report on Polymer-Modified Concrete” (197). This report provides mixture proportioning guidance for these types of concretes, which are a common choice for larger repairs where cementitious ready-mix repair material can be batched (197). Guidance for materials used for pavement maintenance and preservation activities, as well as approaches for different repair types including slab stabilization or jacking, partial-depth repairs (patches), and dowel bar retrofitting, is presented in the “Concrete Pavement Preservation Guide” (179). Use of bonding agents for partial-depth repairs is also discussed in ACI 546.3R-14 and in other publications (179, 198). Other references on partial-depth repairs include those published by FHWA, the National Highway Institute (NHI), and ACPA (198, 199, 200). Performance Properties Mechanical properties and durability performance characteristics vary by formulation, place- ment conditions, and for prepackaged products, whether the material is extended with fine aggregate or small-size coarse aggregate (often “pea gravel”). For larger repairs, some materials

Overview of Concrete Technologies 85 can be provided in “super sacks” of several thousand pounds of preblended material. Agencies typically require prequalification of prepackaged products in order to appear on an approved materials list, which can be developed independently and/or with the support of documentation from the National Transportation Product Evaluation Program (NTPEP). The cost of repair materials varies greatly, and some products can be quite expensive and cost-prohibitive for larger repairs (179, 190). For economic and performance reasons, high- quality conventional concrete is generally the most appropriate material for repairs when given reasonable time to cure and gain the lane opening strength (179). However, in many cases the lane closure time is limited to less than 4 hours and thus requires very high early strength repair products. Because of the variety of repair conditions and products that exist, specifiers can find it challenging to identify the appropriate performance criteria and tests to ensure good results CAC CSA MOC MPC AAFA AAS SCC Hydraulic Yes Yes No No No No No Main hydration or reaction products Calcium aluminate hydrates C3AH6 and AH8 Ettringite, C- S-H, CH Hydro- magnesite Insoluble ammonium and phosphate phases Variable, C- A-S-H, N-A- S-H Variable, C- A-S-H Ettringite, C-S-H Set time relative to portland cement Rapid Rapid and expansive Same or longer Rapid Rapid Same or faster Same or faster Strength High early, late strength comparable to portland High early, slower rate of late strength gain compared to p o r t l and High early, late strength comparable to portland Low early, moderate late strength compared to p o r t l and High early, late strength comparable to portland Low early, late strength comparable to portland Low early, late strength comparable to portland Key durability attributes Good sulfate, ASR resistance Abrasion resistant Good sulfate resistance Carbonation rates high Good fire, abrasion, ASR resistance Good freeze-thaw resistance Good sulfate, ASR performance Good fire resistance Good sulfate, acid, ASR resistance Good fire resistance Good sulfate, corrosion, acid, ASR resistance Good fire resistance Good sulfate resistance Concerns Conversion reactions increase porosity and reduce strength over time Significant heat evolution Carbonation affecting corrosion resistance Possible thaumasite formation Loses strength when exposed to water at early ages Significant heat evolution Significant heat evolution Performance varies with fly ash source Performance varies with slag source Limited field experience Applications Refractory concrete, sulfate and acid resistance Structural, precast, cold-weather Patching, wallboard Fireproof coatings, patching Same as portland cement Same as portland cement Same as portland cement Note: C-S-H = calcium silicate hydrate, C-A-S-H = calcium aluminate hydrate, N-A-S-H = sodium aluminate hydrate, CH = calcium hydroxide, ASR = alkali-silica reactivity. Table 8. Comparison of commercially available alternative cement technologies (from ACI ITG-10.1R-18).

86 Concrete Technology for Transportation Applications (179, 197). Testing of these materials will provide confidence to the design engineer that the material will meet performance needs. ACI 548.3R-09 provides an extensive table of information on the performance require- ments of repair materials replacing portland cement, including a summary of available test methods and test values (197). Also provided in this document is a summary of the changes in material properties of cementitious repair materials when a variety of modifications are performed, such as addition of a variety of chemical and mineral admixtures, SCMs, and fibers (197). The U.S. Army Corps of Engineers Engineer and Research Development Center (ERDC) recommendations for QA/QC testing for cementitious materials includes compres- sive strength, bond strength, modulus of elasticity, volumetric expansion, shrinkage poten- tial, CTE, and time of setting (201, 202). Other testing recommendations have been suggested by the NTPEP and Delatte et al. (190), Lesak (203), and Susinskas (204). Although many types of repair materials have been successfully utilized for several decades, relatively few studies on performance of repair materials exist, and a better understand- ing of the long-term performance of repair materials has been cited as a need by several researchers (190, 194, 201). For proprietary products, issues have been caused by changes in their formulation, and occasionally procurement difficulties have been encountered (188). Other challenges include the inability to batch large quantities of the products at one time, resulting in the potential for cold joints to form in the patch between consecutive batches (190, 201, 202). Issues facing the industry, including test methods and reporting, curing procedures, product limitations and warnings, standardized industry acceptance, bond to substrate material, corrosion potential, and structural repairs, are discussed in Appendix A of ACI 546.3R-14 (189). In recent studies, ERDC performed laboratory and field testing of products for mechani- cal properties and durability performance to evaluate their use in rapid repairs for airfield pavements. This project resulted in development of a recommended testing protocol to guide specifications, including a table of proposed test requirements and performance thresholds for emergency (temporary) repairs and permanent repairs for airfield pavements (201, 202). Results of field studies using full-scale traffic tests indicated that a wide variety of repair material types provided suitable performance for rapid repair of small, full-depth sections of PC (188, 193). To address concerns about changes in material properties due to product reformulations, periodic retesting is suggested (188). Additional requirements for polymeric repair materials have been published by the Department of Defense (205). A study for the Ohio DOT (190) found that all materials selected for the study (includ- ing the lowest cost material) performed quite well, indicating that the use of the higher cost materials may not be necessary for most installation conditions. A 2-year field study revealed that measured and observed distresses tended to be attributable to substrate conditions, and not to the repair materials (203, 204). Laboratory testing indicated that there may be perfor- mance differences between the materials, but this was not observed in the field (206). Materials investigated in that study did not perform well when used to repair asphalt pavements, and therefore bituminous repair products were recommended for this application (190). Specifi- cation recommendations and a draft specification based on this work are presented in Delatte et al. (190) and Woods (207). Project descriptions and findings of field studies of highway infrastructure constructed using ACMs is presented in Burris et al. (195). Case studies include two Los Angeles, California, installations of pavement constructed using CSA and CSA–portland cement blend (85% CSA/ 15% PC) which have shown good performance, and a CAC concrete pavement repair in Chicago, Illinois, that also appears to be performing well.

Overview of Concrete Technologies 87 Performance-Engineered Concrete Mixtures Introduction State highway agencies are faced with the challenge of maintaining an aging infrastructure with increasingly limited resources. A key to ensuring the integrity of concrete highway infra- structure includes construction of new infrastructure and repairs with concrete mixtures that provide durable performance and extended service life. Historically, concrete has been speci- fied using three criteria (slump, air content, and compressive strength) which are only loosely correlated with successful, long-term performance. Highway engineers are focusing more on enhanced concrete durability as a means of reducing maintenance and replacement costs. Enhancing durability can be achieved and assured by careful selection of concrete ingredients as well as utilizing advanced performance testing for meaningful acceptance criteria. Although concrete science and testing technology has advanced over the past decades, state specifications have often not been modified to reflect these advancements (11). Consistent with the focus of Moving Ahead for Progress in the 21st Century (MAP-21) legis- lation on performance, as well as increased interest in use of performance specifications, there is a desire by FHWA, public agencies, and industry to move toward performance-engineered construction materials. One area of focus on materials performance is the work toward the development of performance-engineered concrete mixtures. PEMs include optimized mixture designs (materials selection, gradation, cement content, etc.) that are engineered to meet or exceed design requirements, and are predictable, durable, and have increased sustainability (208). The key features of PEM include (209): • Design and field control of concrete mixtures around engineering properties related to performance; • Development of practical, performance-based specifications; • Incorporation of this knowledge into an implementation system (Design/Materials/ Construction/Maintenance); and • Validation and refinement by performance monitoring. Concept and Benefits In the past century, many changes have been made to concrete mixtures and materials. Concrete materials have become more complex, using a wide variety of admixtures and SCMs, sometimes in combinations (210). Exposure conditions, including increased traffic, adverse chemical reactions from chlorides in sea environments, and increased use of deicing chemicals in winter environments have affected long-term durability and service lives of many concrete structures (211). Advances in construction technologies have resulted in changes in the way concrete is batched, placed, consolidated, and finished. Also, accelerated schedules are placing increased demands on the early age performance of concrete. Because of impacts of these various factors on long-term concrete performance of concrete infrastructure, FHWA, state highway agencies, and many industry stakeholders agree that there is a need to re-address the way that concrete mixtures are specified and tested. Extensive research in recent decades has led to new understanding of concrete deteriora- tion mechanisms, advancements in concrete mixture design, and development of better field and laboratory tests for QA/QC. With this new knowledge, an FHWA initiative is under way to improve performance of concrete infrastructure through PEMs. This initiative has resulted in development of AASHTO specification and commentary, AASHTO PP 84, “Standard Prac- tice for Developing Performance Engineered Concrete Pavement Mixtures,” which provides

88 Concrete Technology for Transportation Applications a framework and guidance for state highway agencies to develop a specification for PEMs that focuses on measurement and acceptance of concrete based on characteristics that have been linked to satisfactory long-term durability performance of the concrete (212). Although developed for pavement concrete mixtures, the approach outlined in AASHTO PP 84 could be extended to include specifications for PEMs utilized for other infrastructure, such as bridges, barriers, and lower-grade uses, as well. Performance-related specifications provide agencies the ability to obtain the desired con- struction quality while allowing contractors greater control and flexibility (208). For instance, current prescriptive specifications for minimum cement content and rate of strength gain may preclude the acceptance of mixtures that have superior economy, durability, and satisfactory mechanical performance, but contain high proportions of SCMs. The provisions included in AASHTO PP 84 are presented in a format that allows state agencies flexibility in selecting the tests and requirements most applicable to their states. Recommended uses of the PEM tests, such as for mixture qualification or for acceptance, are also suggested. An appendix to the standard provides additional context, technical information, and guidance. Performance-related specifications require measurement of key properties and perfor- mance characteristics. For performance specifications to be successfully utilized, QA/QC tests need to be performance related, rapid, effective, reliable, and inexpensive (209). Recent advancements in testing technologies have provided means of more directly measuring the properties of concrete mixtures that have been linked to successful field performance (210). A number of state agencies are using and evaluating new, rapid, early age testing technologies such as resistivity, sorptivity, and air void system analysis that support development and use of PEMs. Ongoing concrete materials research is providing state highway agencies data to support the use of PEMs. However, additional work is needed to identify appropriate per- formance measures, performance goals, and QA/QC protocol. The capabilities of these tests to evaluate the durability performance of concrete mixtures is improving as state highway agencies build sufficient data to correlate the test results with field performance. Materials, Mixture Parameters, and Specifications As mentioned earlier, tests used for specification and acceptance of concrete mixtures have typically been tests for slump, air content, and strength. It has generally been believed that strength could be used as a “quasi-indicator of durability” (210). However, research and field experience has shown that slump, air, and strength are not reliable predictors of long-term performance (212). To endure stresses related to field exposure, concrete needs to exhibit characteristics that indicate good resistance to freezing and thawing and to chemical attack from the corrosive deicing salts and chlorides to the extent to which it will be exposed during its service life (211). Additionally, the concrete cannot be susceptible to deleterious alkali–aggregate interaction (such as ASR) (213). Although none of these characteristics is easily measured directly, it has long been known that durable concrete is associated with several performance characteristics measurable in a labora- tory setting. Low permeability, resistance to cracking and transport of deleterious substances, aggregate stability, and an adequate air void system are examples of these performance charac- teristics (11, 214). Additionally, to mitigate placement defects that result in the poor durability of what would otherwise be a satisfactorily performing concrete mixture, workability needs to be considered (11, 209). Conventional mixture designs using ordinary portland cements and quality aggregates can provide good durability performance if they are properly proportioned with low water–cement

Overview of Concrete Technologies 89 ratio, have good workability, and take advantage of admixtures to create an adequately dispersed air void system (214). Additionally, SCMs such as fly ash and slag have been shown to provide enhanced durability performance (reduced permeability and mitigation of ASR). Established and emerging mixture proportioning and test methods included in AASHTO PP 84 (212) will help to ensure that mixtures will meet performance expectations. A key feature of the AASHTO PP 84 specification is that it provides a menu of potential speci- fication provisions that address six key performance-related properties (shown below), with rec- ommended test methods that state highway agencies can select (or omit) as they desire. This approach allows state highway agencies to incorporate knowledge of local historical performance, risk tolerance, and agency preference into a durability-based specification. For many performance requirements, an agency can select from either a prescriptive or a performance approach. The six key performance requirements included in AASHTO PP 84 (212) include: 1. Concrete strength. Despite not always being directly indicative of long-term performance, the strength of concrete continues to be an important specification parameter. AASHTO PP 84 suggests use of either flexural or compressive strength (or both) for mixture qualification and for acceptance. 2. Reducing cracking due to shrinkage. AASHTO PP 84 suggests several specification provi- sions to reduce cracking, including a prescriptive measure of limiting the volume of paste in a paving mixture to 25%. A performance test that could be selected includes the unrestrained volume change (AASHTO T 160). Other conventional and emerging test methods such as the restrained ring tests and a probability of cracking method are discussed in the appendix of AASHTO PP 84. 3. Durability of hydrated cement paste for freeze-thaw durability. AASHTO PP 84 suggests the use of a prescriptive water–cement ratio limit (0.45) or acceptable performance using one of several other currently utilized or emerging rapid test methods. These methods include fresh air content using the conventional pressure or volumetric air meter (AASHTO T 152 and T 196), the Super Air Meter (SAM) (AASHTO TP 118), and tests related to time of critical saturation (ASTM C1585) and deicing-salt damage (215). Other prescriptive specification provisions suggested for protecting concrete from deicing salts include use of SCMs at a sug- gested replacement rate of 30%, and application of sealers (AASHTO M 224). Measures to protect joints from damage caused by calcium oxychloride formation include tests to quantify the amount of calcium oxychloride in the cement paste (AASHTO T 365) (216, 217). 4. Transport properties. A prescriptive measure of maximum water–cement ratio (limiting to less than 0.45 or 0.50) is suggested, based upon freeze-thaw conditions. Results from several research projects showed that test results of the surface resistivity meter (AASHTO T 358) correlate with the well-established but time-consuming rapid chloride ion permeability test (ASTM C1202) (218). However, both of these electrical tests have limitations associated with pore solution ionic concentration, temperature effects, sample geometry, degree of satura- tion, and storage. AASHTO PP 84 extends the use of resistivity meter by suggesting use of a formation factor (F-factor) to assist in normalizing the results of surface resistivity testing. 5. Aggregate stability. Prevention of deleterious aggregate-related issues such as D-cracking, ASR, and ACR are addressed in AASHTO PP 84. ASTM T161 and ASTM C1646 are suggested for screening aggregates for D-cracking. AASHTO PP 84 suggests use of the approaches out- lined in AASHTO R 80 to prevent and mitigate ASR and ACR. 6. Workability. Although not a measure of durability performance, considerations for assessing workability are included in the AASHTO PP 84 guide specification due to the linkage between inappropriate workability and construction-induced issues such as poor consolidation, edge slump, segregation, and degraded air void system quality. Two emerging methods of assessing concrete workability of low-slump paving mixtures suggested in AASHTO PP 84 are the Box test (219) and the Modified V-Kelly test (AASHTO TP 129) (220).

90 Concrete Technology for Transportation Applications Construction AASHTO PP 84 provides mixture proportioning guidance to assist in developing PEMs. Commentary provided within the standard and appendix provide insight into strategies to meet performance goals, such as optimizing aggregate gradation to assist in reducing paste volume, and meeting strength requirements while simultaneously economizing the mixture. Requirements for mixture qualification and mixture acceptance are also presented in AASHTO PP 84 (212). Performance specifications tend to shift risk from the agency to the contractor, with the contractor in turn benefiting from the opportunity to innovate. AASHTO PP 84 details the required QC activities to be performed by the producer, which include development, approval, and implementation of a QC plan. This QC plan needs to include details on the methods and frequency of monitoring and testing as well as data management and reporting tools such as control charts. The QC plan will communicate to the agency how the contractor intends to meet the specification requirements (210). A QC plan to support PEMs will reduce risk for all parties and can maximize the economic and performance benefits associated with the mixture. Education and training (of both agency and contractor personnel), use of shadow and pilot projects, a mixture qualification/verification procedure, and QC tools such as control charts are important parts of a QA program for PEMs (210). With proper mixture design, control, and testing, construction considerations for use of PEMs in transportation infrastructure components need not differ significantly from con- struction considerations for conventional concrete mixtures. As with other types of concrete, appropriate construction techniques must be utilized and adequate curing must be performed in order to ensure development of the desired properties. Performance Properties Properties of interest for PEMs will depend on the agency’s goals, preferences, and risk tolerance, as well as the project constraints. Performance specifications allow the contractor flexibility to meet contract requirements, encouraging innovation and potential cost savings for the owner (210). Agencies will need to continue to review and approve PEMs as they would other types of concrete. Guidance for establishing a QA program for PEMs is outlined in Cackler et al. (210). This publication also describes the importance of development and use of contractor QC plans, which serve as a means for the contractor to alert the agency about how specification provisions will be met. Implementation The approach outlined in AASHTO PP 84 was developed for pavement concrete mixtures. However, PEMs could be extended to include mixtures of other classes of concrete as well. For example, use of PEM specifications could be used to ensure placement of low-permeability concrete in bridge decks, girders, piers, and foundations, if desired. Development and implementation of PEM specifications is an extensive undertaking, and the shift will affect all stakeholders in the construction process. The menu of specification pro- visions suggested by AASHTO PP 84 has provided guidance for a number of state agencies to make initial movement toward PEMs in a variety of means (examples include shadow testing using emerging test methods, pilot projects, and enhanced QC plans). At the time of publica- tion of this report, a number of states, including Colorado, Indiana, Iowa, Michigan, Minnesota, New York, North Carolina, South Dakota, and Wisconsin, were performing PEM tests.

Overview of Concrete Technologies 91 Although some states are currently utilizing some performance-related or performance- based specification provisions, implementation of PEMs is an ongoing effort to improve specifications. Research is being performed at a number of universities and DOTs to enhance the knowledge of the basic science, emerging tests, and field performance data to support the specification. Evaluation of new technologies and equipment under field working conditions is ongoing, with a goal of providing feedback to researchers and agencies, as well as refining the technologies (221). Challenges facing agencies interested in moving toward PEMs include ensuring that stake- holders are aware of and capable of performing the new tests as well as properly interpreting the results. Some tests require purchase of new testing equipment by both agencies and contrac- tors. Ongoing technology transfer efforts are focused on preparing guidance for specification approaches, tests, and QC (221). AASHTO PP 84 also requires an approved QC plan. This provision, although likely to improve the quality of concrete produced, may be viewed as an additional burden by some contractors. Overall, implementation of PEMs should result in “higher quality concrete and more efficient construction practices, reducing long-term costs to the agency” (210). AASHTO PP 84 is the specification for PEMs. Additional guidance is presented in Cackler et al. (11, 210).

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The past few years have seen some significant advances in concrete technology. For example, newer concrete incorporating advances in admixtures and cementitious materials has emerged.

The TRB National Cooperative Highway Research Program's NCHRP Synthesis 544: Concrete Technology for Transportation Applications documents how state departments of transportation select and deploy concrete technologies in the construction of transportation facilities.

Concrete technology is also facing some emerging challenges that need to be addressed. These challenges include the present or future depletion of high-quality aggregates in some parts of the country, changes to power generating plants that will reduce the supply and consistency of acceptable fly ashes, and the incorporation of reclaimed or traditionally landfilled materials such as recycled concrete aggregate (RCA) into concrete.

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