Reliability of service life predictions for concrete under sulfate attack

This paper presents a reliability analysis for sulfate attack of concrete, an expansive durability problem that causes degradation of concrete structures in the presence of sulfate ions. This work is based on data collected by the U.S. Bureau of Reclamation (USBR) from 1948-1991 and previously developed empirical and reliability models. The previous reliability model treats the material and exposure parameters as deterministic. In this work, uncertainty in the material and exposure parameters is incorporated into the model. Also, the exposure time parameter is separated into an up-to-present exposure parameter and a remaining time to failure parameter. The focus of the analysis is the remaining time to failure parameter and the reliability of assuming deterministic increases in that quantity. Three scenarios are presented, corresponding to varying levels of uncertainty in the material and exposure parameters: (1) general uncertainty, (2) uncertainty in materials and workmanship, and (3) uncertainty in exposure. Each scenario corresponds to a field situation in which there are specific uncertain conditions. Analysis of the scenarios yields the expected remaining service life and reliability of the system to assumed remaining service lives. Reliability sensitivity analysis is also performed, which allows for the most influential model parameters to be identified.