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

Currently, there is a serious problem with the deterioration of concre te bridges due to corrosion induced by chloride intrusion into the con crete. Historically, the problem has been associated with conventional ly reinforced concrete bridge structures as opposed to prestressed or post-tensioned structures. However, corrosion of steel tendons in pres tressed concrete structures is potentially of even greater concern, si nce the structural integrity of the bridge relies on the high tensile strength of the tendons. Corrosion-induced cracking of the tendons cou ld lead to catastrophic failure of the structure. Grout is the final l ine of defense against corrosion of the steel tendons. Modifiers and a dditives for grouts were evaluated regarding their effect on relevant engineering properties of grouts in this application, including the ab ility of the grout to protect embedded tendons from corrosion. The ben eficial effect of various additives and modifiers on grout fluidity, o pen time, bleeding/segregation, chloride ion permeability, and mechani cal properties was demonstrated. An accelerated corrosion test (ACT) m ethod was developed that evaluates the corrosion performance of steel tendons embedded in grout.