A serious problem in the United States and elsewhere is the deterioration of concrete bridges as a result of corrosion induced by chloride (Cl-) intrusion into the concrete. Historically the problem has been associated with conventionally reinforced concrete bridge structures as opposed to prestressed or posttensioned structures. However, corrosion of steel tendons in prestressed concrete structures is of greater concern because the structural integrity of the bridge relies on the high tensile loading of the tendons. Any corrosion or corrosion-induced cracking of the tendon could lead to catastrophic failure of the structure. In bonded posttensioned construction, grout is the final line of defence against corrosion of the uncoated steel tendon. The purpose of this research was to develop and test new mixture designs for grouts, develop and perform accelerated corrosion test methods on the new grouts, and compare the corrosion performance of the new grouts with the standard grouts. A variety of modifiers and additives for grouts were examined, including high-range water reducers, fly ash, silica fume, latex polymer modifier, expansive agents, antibleed additives, and corrosion inhibitors. It was shown that these additives can favourably influence grout fluidity, open time, bleeding and segregation, Cl- permeability, mechanical properties, and the resistance to corrosion of steel tendons embedded in the grout. Several experimental grouts were designed that provided improved properties compared with the grouts used currently. (Author/publisher)
Abstract