Characterization of segregated grout promoting corrosion of posttensioning tendons

Segregation of grout applied for the protection of posttensioning steel may cause corrosion of steel wires, leading to serious hazards to the safety of posttensioned structures. Several cases of failure of external tendons of bridges have been documented arising from heavily corrosion attacks initiated and propagated in the presence of an unhardened (soft) whitish paste generated by segregation. The reasons for this aggressive corrosion attack are not clear, and improving the knowledge on the properties of the segregated grout would help in clarifying this phenomenon. Chemical, physical, and microstructural properties of grouts collected from the ducts of a bridge where segregation occurred are investigated. Results describe the different stages of segregation of the grout and show that the aggressiveness of the whitish grout could be associated with the high content of soluble compounds produced by early hydration of cement, especially alkalis, which lead to pH values exceeding 14.