Self-Consolidating Concrete for Cast-in-Place Bridge Components (2016)

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1 Self-Consolidating Concrete for Cast-in-Place Bridge Components Research Significance Self-consolidating concrete (SCC) is a specially proportioned hydraulic cement concrete that enables fresh concrete to flow easily into the forms and around steel reinforcement without segregation and without any mechanical consolidation. Use of this type of concrete in precast, prestressed bridge elements has increased in recent years because of the increased rate of pro- duction and safety, reduced labor needs, and lower noise levels at manufacturing plants. How- ever, use of cast-in-place SCC has had limited application in bridge construction because of the lack of design and construction guidelines and concerns about certain design and construc- tion issues that may influence the structural integrity of the bridge system. NCHRP Report 628 (Khayat and Mitchell, 2009) focused on the application of SCC in precast, prestressed bridge elements; some of the findings are applicable to cast-in-place concrete bridge components, but use of SCC in cast-in-place applications requires the consideration of conditions other than the controlled conditions existing in precast concrete plants. NCHRP Project 18-16 was conducted to address the use of SCC in cast-in-place bridge applications. Project Objectives and Scope The objectives of this research were to develop guidelines for the use of SCC in cast-in-place concrete in highway bridge components and recommend relevant changes to the AASHTO LRFD Bridge Design and Construction Specifications. The research included the following: • Identifying the properties of fresh, early-age, and hardened SCC that are relevant to cast-in-place bridge components and the factors that have significant influence on these properties. • Developing criteria for evaluating the performance of SCC used in cast-in-place bridge substructure and superstructure components. • Identifying quality control and quality assurance test methods for fresh SCC (at the ready-mixed plant and on site) and for hardened SCC. • Evaluating the constructability of a full-scale, cast-in-place bridge pier and a post-tensioned box girder using SCC. • Developing guidelines for the use of cast-in-place SCC in bridge construction. • Proposing relevant changes to the 2014 AASHTO LRFD Bridge Design Specifications (7th edition) and the 2010 AASHTO LRFD Bridge Construction Specifications (3rd edition). The project considered the use of SCC for cast-in-place concrete bridge substructure components (e.g., piers, pier caps, footings, abutment walls, and wing walls) and superstructure S u m m a r y

2components (e.g., girders, stringers, floor beams, arches, diaphragms, connections, closure pours, rails, and concrete filled tubes) but not for other bridge components (e.g., deep foundations, drilled shafts, bridge decks, and approach slabs). Organization of the Report This report includes this summary, three chapters, and two attachments. Appendices A through F are available on the TRB website at http://www.trb.org/Main/Blurbs/174472. aspx. This summary presents an overview of the project and its major findings. Chapter 1 summarizes the approach used in conducting the literature review, experimental investiga- tions, and full-scale testing; Chapter 2 discusses test results and their appraisal and interpreta- tion; and Chapter 3 presents the research findings and recommendations for future research. Attachment A presents proposed changes to AASHTO LRFD Bridge Design and Construction Specifications and Attachment B presents proposed guidelines for use of SCC in cast-in-place bridge components. Appendices A through F provide further details on the reviewed literature and survey of state departments of transportation; material properties; fresh, early-age, and hardened concrete properties; and testing of full-scale bridge components. Overview of the Project An extensive literature review and a survey of U.S. transportation agencies were con- ducted to determine the properties of SCC that are relevant to the design and construction of cast-in-place bridge components, the appropriate test methods to evaluate these proper- ties, and the associated target values/ranges. The SCC properties included fresh SCC proper- ties (rheology, filling ability, passing ability, static stability, dynamic stability, and workability retention); early-age SCC properties (formwork pressure, heat of hydration, and time of set- ting); mechanical properties (compressive strength, modulus of elasticity, tensile strength, modulus of rupture, bond strength, and shear resistance); visco-elastic properties (drying shrinkage, restrained shrinkage, and creep); and durability properties (air void system characteristics and surface resistivity). Fresh, early-age, and hardened concrete properties were evaluated in a laboratory investi- gation of forty SCC mixtures and six conventionally vibrated concrete (CVC) mixtures for comparison. The SCC mixtures were proportioned using two types of coarse aggregate: crushed limestone and natural gravel; three nominal maximum sizes of aggregate (NMSAs): ¾, ½, and 3⁄8 in.; three supplementary cementitious materials (SCMs) and one filler: 25% Class F fly ash, 25% Class C fly ash, 30% ground granulated blast-furnace slag (GGBFS), and 20% Class F fly ash plus 15% limestone powder (LSP); and two levels of slump flow: low (22 to 26 in.) and high (26 to 30 in.). The CVC mixtures were proportioned using the same two types of coarse aggregate and three NMSA used in the SCC mixtures. All CVC mixtures were proportioned with the same SCM (25% Class F fly ash) and medium slump (2 to 4 in.). All SCC and CVC mixtures were air-entrained and contained portland cement Type I/II. The laboratory tests were conducted according to AASHTO or ASTM methods or accord- ing to methods reported in the literature when AASHTO or ASTM procedures were not avail- able. Available test methods were adequate for characterizing SCC properties; no new test methods were developed. Measured properties of SCC mixtures were compared to AASHTO LRFD predicted values/ranges for CVC (current AASHTO LRFD Bridge Design and Con- struction Specifications do not address SCC) to determine whether AASHTO LRFD provi- sions for CVC would apply to SCC or whether changes should be proposed to accommodate SCC applications. Constructability and structural performance of SCC mixtures were evaluated by fabri- cating and testing two full-scale bridge components (a bridge pier and a post-tensioned

3 box girder) using four ready-mixed SCC mixtures to simulate field applications. Several SCC properties (e.g., formwork pressure, formed surface quality, and air void system) were evalu- ated when different placement methods and rates were used. Uniformity of SCC consolidation was evaluated by examining cores extracted at different locations in each component. Research Findings The following is a summary of the research findings. These findings were obtained for the materials and mixtures used in the project; other materials or mixtures may result in different findings. • SCC mixtures with satisfactory properties for cast-in-place bridge construction could be pro- portioned with natural gravel or crushed limestone aggregates (NMSA of 3⁄8, ½, or ¾ in.), SCMs (Class F fly ash, Class C fly ash, or GGBFS), and fillers (limestone powder). • Standard test methods, such as slump flow, T50, J-ring, caisson test, visual stability index (VSI), hardened visual stability index (HVSI), penetration, and column segregation were adequate for characterizing the key workability properties of SCC. Slump flow, T50, J-ring, VSI, and penetration tests were suited for job site quality assurance because of their sim- plicity, rapidness of assessment, and ability to be conducted with a single operator. Caisson, column segregation, flow trough, and HVSI tests were suitable for evaluating trial batches. • Modifications were made to the flow trough test method used to evaluate the dynamic stability of cast-in-place SCC mixtures to enhance test reliability and ease of use. • The rate of workability loss of SCC mixtures ranged from 3 to 9 in. per hr and was directly proportional to the initial slump flow but varied widely depending on the mixture com- position, temperature, and type of chemical admixtures used. • Time of initial setting of SCC mixtures ranged from 4 to 11 hr depending on the type of SCM/filler, temperature, and slump flow. SCC mixtures with high slump flow had a longer time of initial setting due to the retarding effects of the high-range water-reducing admixture (HRWRA). SCC mixtures that contained Class C fly ash had the longest time of setting, and those that contained Class F fly ash had the shortest time of setting. • Temperature rise due to heat of hydration of SCC mixtures ranged from 20 to 40°F (not significantly different from that of CVC mixtures). A slight delay was observed in reaching the peak temperature of SCC mixtures depending on the type of SCM/filler; the longest delay was observed in SCC mixtures containing the Class C fly ash. • The formwork pressure of SCC mixtures was slightly less than full hydrostatic pres- sure. The rate of SCC placement, thixotropic effects, and yield stress had significant effect on the maximum formwork pressure and its reduction with time. • The ratios of compressive strength of SCC at 7, 14, and 56 days to the 28-day compressive strength was accurately predicted using the ACI 209 model developed for CVC. • The modulus of elasticity (MOE) of SCC was slightly lower than predicted by AASHTO LRFD for CVC. Also, mixtures containing limestone aggregate showed a slightly higher MOE than mixtures containing gravel aggregate. • The modulus of rupture (MOR) of SCC was within the range predicted by AASHTO LRFD for CVC. However, the splitting tensile strength of SCC was lower than predicted by AASHTO LRFD for CVC. • The bond strength of deformed steel bars in SCC was lower than that in CVC for vertical bars, but comparable to that in CVC for horizontal bars. Also, the top-bar effect of hori- zontal bars in SCC decreased as the slump flow of SCC increased. • The nominal shear resistance of SCC was accurately predicted by AASHTO LRFD for CVC, but the interface shear resistance of SCC with compressive strength less than 6 ksi was lower than predicted by AASHTO LRFD for CVC.

4• Drying shrinkage of SCC was significantly higher than predicted by AASHTO LRFD for CVC. The type of SCM had a significant effect on drying shrinkage (e.g., SCC containing Class C fly ash or GGBFS exhibited higher drying shrinkage than SCC containing Class F fly ash). • Restrained shrinkage of SCC depends on the type of SCM and NMSA (e.g., SCC contain- ing Class C fly ash and/or NMSA of 3⁄8 in. exhibited higher cracking potential than that for SCC containing Class F fly ash and NMSA of ½ or ¾ in.). • The creep coefficient of SCC was accurately predicted by AASHTO LRFD provisions for CVC (except for SCC containing 15% limestone powder as a filler, which showed higher creep strains). • Surface resistivity and air void system parameters of SCC were within the ranges reported in the literature. • SCC mixtures proportioned with high segregation resistance did not show signs of seg- regation under a free-fall height of 15 ft and free-flow distance of 20 ft in complex/highly congested sections. • The formed surface of full-scale bridge components made of SCC has shown low sur- face void ratio and small surface void diameter. Flow direction during placement influ- enced the surface voids (e.g., flowing in a bottom-up direction resulted in less and smaller surface voids than flowing in a top-down direction). • Limited testing of full-scale bridge components fabricated using SCC mixtures yielded structural capacities (i.e., flexure and shear resistance) that are different from those predicted by AASHTO LRFD specifications for CVC. The deformations and cracking patterns of these components appeared comparable to those reported in the literature for similar CVC components.