High Strength Concrete Prestressed Bridge Girders: Evaluation and Modification of the Allowable Stresses

High strength concrete (HSC) is regularly used for prestressed bridge girders in Texas and other states. The American Concrete Institute (ACI) Committee 363 (1997) defines HSC as concrete with a compressive strength exceeding 6,000 psi (41 MPa) produced without using exotic materials or techniques. The design provisions for the design of prestressed concrete members according to the AASHTO Standard and LRFD Specifications are based on mechanical properties determined for normal strength concrete (NSC). Therefore, there is a need to evaluate these specifications based on the properties of HSC. The main objective of this research is to evaluate the allowable tensile stresses for HSC prestressed bridge girders. The effects of field curing conditions on the compressive strength and the flexural tensile strength of HSC were determined. The HSC mixtures tested in this study are representative of mixtures used in Phase 1 of this research program (Chompreda 2001). The plant-produced samples from the earlier study were lab cured after the first day (approximately 24 hours). Necessary strength adjustment factors are needed to account for the effect of field curing conditions.