Development Length of 0.6 in. Prestressing Strands in Precast, Prestressed Calcium Sulfoaluminate Cement Concrete
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Calcium sulfoaluminate cement is a very rapid setting, hydraulic cement that releases approximately half as much carbon dioxide during production as conventional portland cement. Calcium sulfoaluminate cement produces concrete with high early strength, excellent durability, and limited shrinkage. These properties have the potential to substantially improve the speed of production and performance of precast products. The compressive strength typically required for prestress release at an age of 18-24 hours can be reached in just a few hours, without the need for heat curing. Three series of 6.5 in. by 12 in. by 18 ft long rectangular beams prestressed with 0.6 in. prestressing strands were cast to evaluate the effect of calcium sulfoaluminate cement concrete age at the time of prestress release on bond behavior and prestress losses. One series of calcium sulfoaluminate beams was cast with prestress release targeted for a compressive strength of 3500 psi at approximately 2 hours of age and a second set with prestress release at 24 hours of age, at which time the compressive strength was significantly higher. A series of conventional concrete beams with a similar compressive strength at release was also cast for comparison. Surface strain and strand end slip were measured to evaluate transfer length and vibrating wire strain gages were embedded to evaluate prestress losses. The CSA specimens with vibrating wire strain gages yielded reduced prestress losses compared to conventional concrete. The specimens also showed no significant detrimental effects of early age prestress transfer and similar transfer lengths for rapid setting and conventional concrete. Code predicted transfer and development lengths proved reasonable for the CSA specimens.
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