GROUTS FOR BONDED POSTTENSIONED CONCRETE CONSTRUCTION - PROTECTING PRESTRESSING STEEL FROM CORROSION

Currently, there is a serious problem with the deterioration of concrete bridges due to corrosion induced by chloride intrusion into the concrete. Historically, the problem has been associated with conventionally reinforced concrete bridge structures as opposed to prestressed or post-tensioned structures. However, corrosion of steel tendons in prestressed concrete structures is potentially of even greater concern, since the structural integrity of the bridge relies on the high tensile strength of the tendons. Corrosion-induced cracking of the tendons could lead to catastrophic failure of the structure. Grout is the final line of defense against corrosion of the steel tendons. Modifiers and additives for grouts were evaluated regarding their effect on relevant engineering properties of grouts in this application, including the ability of the grout to protect embedded tendons from corrosion. The beneficial effect of various additives and modifiers on grout fluidity, open time, bleeding/segregation, chloride ion permeability, and mechanical properties was demonstrated. An accelerated corrosion test (ACT) method was developed that evaluates the corrosion performance of steel tendons embedded in grout.