Evaluation of Self-Consolidating Concrete for Use in Prestressed Girder Applications
Type of DegreeThesis
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Self-consolidating concrete (SCC) is a highly flowable, yet cohesive, concrete that is able to fill formwork and completely encapsulate any reinforcement without the need for external vibration. The use of SCC may help prestress plants to produce high-quality prestressed concrete elements at reduced labor costs. An evaluation of SCC mixtures for use in prestressed concrete applications is presented in this thesis. Twenty-one SCC mixtures were made with varying water-to-powder ratios of 0.28, 0.32, 0.36, and 0.40, varying sand-to-aggregate ratios of 0.38, 0.42, and 0.46, and different powder combinations that included Type III cement, Class C fly ash, ground granular blast-furnace (GGBF) slag, and silica fume. The inverted slump flow, VSI, T-50, J-Ring, and L-Box were used to evaluate the fresh properties of the twenty-one SCC mixtures. Cylinders were match-cured to a time-temperature profile that is typical of prestressing operations. SCC mixture properties were compared to those of two conventional-slump prestressed concrete mixtures. The SCC mixtures achieved 18-hour (prestress transfer) compressive strengths between 5,470 and 9,530 psi. Compressive strengths at prestress transfer and at later ages were not sensitive to changes in the sand-to-aggregate ratio. All SCC mixtures had lower 18-hour moduli of elasticity than the control mixture with a water-to-powder ratio of 0.37. The moduli of elasticity at prestress transfer and at later ages were not significantly affected by changes in the sand-to-aggregate ratio. The moduli of elasticity of the SCC mixtures are in reasonable agreement with the elastic stiffness assumed during the design of conventional-slump concrete structures. The AASHTO LRFD formulation generally underestimates the modulus of elasticity of the SCC mixtures. The ACI 363 formulation also underestimates the modulus of elasticity for SCC mixtures but on a higher order of magnitude than the AASHTO LRFD formulation. The 112-day drying shrinkage strain for all the SCC mixtures are of the same order of magnitude or less than those measured for the control mixtures. A change in sand-to-aggregate ratio from 0.38 to 0.46 had no significant effect on the 112-day drying shrinkage strain of the SCC mixtures. At later ages of 56 and 112 days, the AASHTO LRFD procedure overestimated the measured drying shrinkage of the SCC mixtures, while the ACI 209 procedure corresponded reasonably well with the measured drying shrinkage of the SCC mixtures. The use of SCC in prestressed applications appears favorable and full-scale evaluations of the mixtures developed in this study should be undertaken.