The effects of high strength concrete curing temperatures on compressive strength development and force levels in straight, bonded pretensioned strands were investigated. Concrete temperatures and prestressing strand forces were monitored during the fabrication of five AASHTO Type Ill bridge girders with a specified design concrete compressive strength of 10,000 psi (69.0 MPa). After casting, hydration-induced concrete temperature increases resulted in an 11 percent reduction in the average prestressing strand force level due to thermal expansion. Measured concrete temperatures within the instrumented girders varied by as much as 30°F (17°C). Peak concrete temperatures measured in standard field-cured 6 x 12 in. (152 x 305 mm) cylinders cured alongside the girders were as much as 26°F (14°C) less than the peak temperature within the girder. Measured compressive strengths of the standard field-cured cylinders were consistently less than the strength of cylinders that were match-cured using a reference thermocouple installed in the girders. Based on the measured strength data, it was concluded that field-cured cylinders may underestimate the compressive strength of the girder concrete by as much as 10 percent.
