Modeling and Projecting the Onset and Subsequent Failure Rate of Corroding Bridge Post-Tension Tendons Arising from Deficient Grout

Post-tensioning (PT) has become an important approach to affecting integrity of large reinforced concrete structures, including bridges. While there are a number of advantages to PT construction compared to conventional reinforcement, corrosion caused bridge tendon failures have recently been reported, in some cases within but a few years of construction, as a consequence of either chemically or physically deficient grout (or a combination of the two), where the former involves elevated concentration of chlorides or free sulfates (or both) and the latter voids with free water, and soft, chalky, segregated, separated grout. The present paper reviews a predictive model that was developed to project the onset and subsequent rate of wire and strand fractures and tendon failures as a function of time, given information regarding the present extent of corrosion. Inputs to the model are the mean and standard deviation of, first, remaining cross-section area at the most corroded location on individual wires and, second, an experimentally determined relationship between residual fracture stress and remaining cross-section area of corroded wires, both of which are represented as distributions. Particular emphasis is placed upon fracture and failure rates subsequent to first occurrence, because these can provide useful information for assuring timely intervention and integrity assurance of PT structures with corrosion issues. The results indicate that tendon failures, once initiated, can occur at an unmanageable rate even for relatively modest rates of corrosion.