Expected compressive strength in precast, prestressed concrete design: Review and discussion of regional practice

Accurate estimates of expected concrete compres­sive strength are critical for designers to predict the deformational behavior of precast, prestressed concrete elements such as camber, deflections, and prestress losses. To explore the difference between specified and expected concrete compressive strength for Alabama bridge girders, a compressive strength data set repre­senting 1887 girder production events was collected. The average measured concrete compressive strength for Alabama girders was 33% greater than the specified strength at prestress transfer and 59% greater than the specified 28-day strength. Available empirical strength prediction methods derived for other U.S. regions did not accurately represent the Alabama data. The most promising candidates for prediction methodologies for expected compressive strength were models based on guidance from the American Concrete Institute Committee 214 for the prediction of expected strength at prestress transfer and models based on concrete strength-growth modeling to predict 28-day strength.