Life-prediction

To determine the expected long-term performance of concrete in a sulfate-rich environment, a reliability analysis is performed using a previously developed model and data collected over a 40+ year period by the U.S. Bureau of Reclamation (USBR). The reliability analysis contains three main phases: (1) an expected time to failure analysis, (2) a probability of failure analysis, and (3) a sensitivity analysis. This analysis demonstrates that the concrete mixes of the USBR program subjected to a severe sulfate environment have expected times to failure of 19 to 89 years, depending on the concrete mix proportions and the portland cement composition. Probability of failure increases with increasing exposure time, water-to-cement ratio, and C3A content, although at different rates. Through the use of probability sensitivity analysis, it is found that uncertainty in the water-to-cement ratio is the most influential parameter in the reliability model, roughly twice as important as exposure time. Also, the influence of water-to-cement ratio is roughly one order of magnitude larger than the influence of the C3A content, for cements with C3A content less than 8%.