High Performance Concrete Specifications and Practices for Bridges (2013)

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3 BACKGROUND In 1993, FHWA initiated a national program to implement the use of high performance concrete (HPC) in bridges (Rabbat and Vanikar 1999). As part of this initiative, FHWA developed quantifiable definitions for eight concrete perfor- mance characteristics—four relating to durability and four relating to structural design (Goodspeed et al. 1996). Details about these characteristics are provided in chapter two. The program included the construction of 19 demonstra- tion bridges by state departments of transportation (DOTs) and dissemination of the technology and results at showcase workshops. Information about each bridge was compiled into a single compact disc (Russell et al. 2006a), which included a description of the bridge, benefits and costs of HPC, structural design details, specified properties, concrete mix proportions, measured concrete properties, research data, sources for the data, and the HPC specifications. After the bridges had been in service for several years, the bridge decks were inspected and their performance evaluated relative to the previously compiled data (Mokarem et al. 2009). The inspection indicated that cracking in the reinforced concrete bridge decks ranged from none to more than expected. Other observations also suggest that the use of HPC has resulted in more cracking of concrete bridge decks (Russell 2004). A survey of highway agencies in 2003/2004 by FHWA showed that almost every agency had either incorporated HPC into their standard specifications, or had tried it at least during the previous 10 years (Triandafilou 2009). However, results were inconclusive as to the extent of HPC usage by each agency. A follow-up survey in 2006/2007 solicited informa- tion as to the number of bridges constructed with an HPC element (Triandafilou 2009). The results of the survey indi- cated a wide range of usage between agencies. The survey also revealed that agencies use three different methods to specify HPC. Twenty-two agencies reported using special provisions for individual projects, 22 reported using a combination of special provisions and general specifications, and eight used only general specifications. Also, HPC specifications were usually prescriptive or used a combination of performance and prescriptive provisions. Little use was being made of end-result performance specifications. As a result of these activities, the use of HPC has increased but its success has been variable. At the same time, highway agencies have developed a wide range of specifications for HPC. HIGH PERFORMANCE CONCRETE DEFINITIONS Ever since the term “high performance concrete” was intro- duced into bridge industry terminology, numerous definitions have been created and published (Russell 2011). Strategic Highway Research Program Definition The first definition was developed as part of the first Strategic Highway Research Program (SHRP). It defined HPC by the following three requirements (Zia et al. 1991): 1. Maximum water-cementitious materials (w/cm) ratio of 0.35, 2. Minimum durability factor of 80% as determined by ASTM C666 Method A, and 3. Minimum compressive strength of a. 3.0 ksi within 4 hours after placement, b. 5.0 ksi within 24 hours, or c. 10.0 ksi within 28 days. Federal Highway Administration Definition In 1996, Goodspeed et al. published a definition for HPC that FHWA adopted for bridges. The definition consisted of four strength-related performance characteristics (com- pressive strength, modulus of elasticity, drying shrinkage, and creep) and four durability-related performance characteristics (freeze-thaw resistance, scaling resistance, abrasion resistance, and chloride penetration). For each characteristic, a standard test method was listed and various performance grades established. Consequently, the selection of performance characteristics and performance grades became a decision to be made by the owner for the intended application. For example, a pre- cast, prestressed concrete bridge beam could be required to have a high concrete compressive strength and normal chloride permeability, whereas a bridge deck could have a low chloride permeability and normal concrete compressive strength. Both concretes would be HPC but with different requirements. More details of the FHWA definition are given in chapter two. The intent of the FHWA definition was to stimulate the use of higher quality concrete in highway structures. Based on lessons learned from the implementation of HPC in bridges, the characteristics of alkali-silica reactivity (ASR), sulfate resistance, and workability were added to the previous eight chapter one INTRODUCTION

4 performance characteristics (Russell and Ozyildirim 2006). The last characteristic became important with the introduction of self-consolidating concrete. American Concrete Institute Definition Although not intended specifically for bridges, the American Concrete Institute (ACI) defines HPC as “concrete meet- ing special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents, and normal mixing, placing, and curing practices” (ACI 2010). ACI has a separate definition for high strength concrete; that is, concrete that has a speci- fied compressive strength for design of 8000 psi or greater (ACI Committee 363 2010). American Association of State Highway and Transportation Officials Bridge Specifications AASHTO LRFD (Load and Resistance Factor Design) Bridge Construction Specifications (AASHTO 2010a) includes two classes of HPC designated as P(HPC) and A(HPC). Class P(HPC) is intended for use in prestressed concrete members with a specified concrete compressive strength greater than 6.0 ksi. Class A(HPC) is intended for use in cast-in-place (CIP) construction with a specified concrete compressive strength less than or equal to 6.0 ksi and where performance criteria in addition to concrete compressive strength are specified. The Commentary to the AASHTO LRFD Bridge Design Specifi- cations (AASHTO 2010b) includes a Class P(HPC) concrete intended for use when concrete compressive strengths in excess of 4.0 ksi are required. OBJECTIVES AND SCOPE The two primary objectives of this synthesis are as follows: 1. Document the specifications and practices for HPC used by state agencies, and 2. Identify specifications and practices reported as having improved bridge performance and those that have been less successful. This synthesis is intended to help bridge owners, designers, contractors, and material suppliers determine the appropriate specification requirements for the use of HPC in bridges by providing information about current practices. For purposes of this synthesis, HPC includes FHWA’s 11 performance characteristics of permeability, freeze-thaw resistance, deicer scaling, abrasion resistance, workability, resistance to ASR, sulfate resistance, compressive strength, modulus of elasticity, creep, and drying shrinkage. It does not include ultra-high performance concrete (UHPC). UHPC is generally defined as a cementitious-based composite material with fiber reinforcement and having a compressive strength greater than 20 ksi and enhanced durability by means of a discontinuous pore structure (Graybeal 2011). The synthesis does not include information on bonded overlays, internally cured concrete, lightweight concrete, self-consolidating concrete, and substructure concrete unless such information was supplied in response to the survey. The synthesis describes the evolution of HPC for bridges in the United States. It then reports on current specifications for CIP and precast, prestressed concrete with primary emphasis on CIP bridge decks; precast, prestressed concrete beams; and precast, prestressed concrete deck panels. Information gathered for this synthesis includes the following: • State DOTs’ approaches for incorporating HPC in their specifications and implementation in construction practices; • State specifications and practices addressing materials, construction, testing, acceptance criteria, and perfor- mance of HPC; • Testing requirements for the acceptance of a new HPC mixture’s performance (e.g., structural or durability); • Specification types used by states (e.g., prescriptive, performance, or hybrid); • Practices for evaluating short- and long-term HPC per- formance of in-service structures; and • Specifications and practices reported as successful or unsuccessful. RESEARCH METHODOLOGY Information for this synthesis was obtained from a review of published literature, review of state agencies’ specifications, and a survey of highway agencies through the AASHTO Highway Subcommittee on Bridges and Structures. The pur- pose of the survey was to obtain information about actual state practices, both successful and unsuccessful, that could not be learned from reviewing the specifications. Specifica- tions include a range of options, some of which might not be used in practice. Forty-two agencies (an 82% response rate) returned the survey. Following completion of the survey, six states were selected for a more in-depth report on their specifications and practices. TERMINOLOGY Many state specifications originated when cement was the only cementitious material used, most cement was shipped in bags, and water quantity was measured in gallons. Consequently, many specifications still refer to cement content rather than cementitious materials content, bags of cement rather than

5 lb/yd3, and gallons/bag rather than w/cm ratio (ACI 2010). This synthesis uses the current terminology. For purposes of the survey and reviewing the state specifications for this synthesis, it has been assumed that “cement” when used in specifications refers to cementitious materials content unless stated otherwise. Also, a bag of cement is assumed to weigh 94 lb and a gallon of water to weigh 8.33 lb. In some speci- fications, fly ash, silica fume, and slag cement are referred to as mineral admixtures. In this synthesis, they are called “supplementary cementitious materials” (SCMs). Specifica- tions also refer to ground granulated blast-furnace slag. The terminology “slag cement” is generally used in this synthesis. The terms water curing, wet curing, and moist curing are used in specifications to describe the means by which the sur- face of the concrete is kept continuously wet for a specified time period. This synthesis uses the terminology “wet curing.” The terminology “rapid chloride permeability” as used in this synthesis refers to measurements made using the AASHTO Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration (AASHTO T 277 or ASTM C1202). In this test method, concrete with a perme- ability less than or equal to 2000 coulombs and greater than 1000 coulombs is defined as having low chloride ion pene- trability and is frequently called low permeability concrete. However, other test methods exist that can be used to measure permeability. REPORT ORGANIZATION The text of the synthesis is organized as follows: • Chapter two addresses the evolution of HPC for bridges beginning with the first strategic Highway Research Program in the 1980s. It describes the various initiatives undertaken by FHWA and AASHTO to promote the use of HPC with the state agencies. • Chapter three addresses how states are currently incor- porating HPC in their specifications and in their con- struction of CIP concrete with emphasis on bridge decks. This includes information about materials, construction, testing, acceptance criteria, and short- and long-term performance of in-service structures. Most of the infor- mation for chapter three came from the survey of state DOTs and review of state bridge specifications. • Chapter four addresses how states are currently in- corporating HPC in their specifications and in their construction practices for precast concrete with em- phasis on precast, prestressed concrete beams and deck panels. This includes information about materials, construction, testing, acceptance criteria, and short- and long-term performance of in-service structures. Most of the information for chapter four came from the survey of state DOTs and review of state bridge specifications. • Chapter five provides a more in-depth discussion of the development and usage of HPC in the states of Kansas, Louisiana, New York, Virginia, Washington, and Wisconsin. • Chapter six summarizes the current status of specifica- tions with regard to HPC and the practices and details that have proven to enhance the performance of concrete bridges. Practices that have not been successful are also identified, and some knowledge gaps that could be filled by research are listed. • Appendices provide the survey questionnaire (Appen- dix A), a summary of the responses to the questionnaire (Appendix B), and a listing of websites for state speci- fications (Appendix C).