Research On The Corrosion Of Post-tensioned Strands Under Grouting Deficiency

Due to economic and structural advantages, post-tensioned bridge type is a widely used structural type in bridge. In practice, post-tensioned bridge has a problem: the duct is often not compact. In coastal and the region where it needs deicing salt to melt snow, post-tensioned bridge which has grouting deficiency will suffer the erosion of chloride ion. As a result, the tendons are corrosive, shortening the life of the structure. Considering the above background and basing on the common grouting deficiency of post-tensioned bridge, this article studied the corrosion of strands under condition of grouting deficiency(empty grouting,parallel grouting, vertical grouting).The strand immersed in sodium chloride solution was on behalf of the condition of strands in empty grouting. By testing the strand’s polarization resistance, mass loss and other parameters, we studied the influence of chloride ion’s concentration on corrosion rate. Studies have shown that as chloride ion’s concentration increased, so was the corrosion rate of strand. In parallel and vertical grouting types, part of strand was protected by grouting and the other part was exposed to erosion environment, by testing the corrosion potential, AC impedance spectroscopy of both strands before the strand embedded in sodium chloride solution and cement paste were connected and the coupling potential, coupling AC impedance spectroscopy, corrosion morphology, mass loss and galvanic current of the strand after they were connected, we studied the corrosion mechanism of the strand and the influence of the chloride ion’s concentration and area ratio of cathode to anode in the two defect grouting types on the corrosion rate. Studies have shown that after strand embedded in sodium chloride solution and cement paste were connected, the macro-cell was formed that the former was macro-cell anode and the latter was macro-cell cathode and the corrosion rate of anode increased after macro-cell was formed. When the chloride ion’s concentration and the area radio of cathode to anode increased, so was the corrosion rate of macro-cell anode. When the concentration of chloride ion is 0.1% and the area radio of cathode to anode is 60:1, the fastest corrosion rate of grouting type was parallel grouting, and then was vertical grouting, empty grouting.Using mixed potential theory and numerical methods to predict corrosion rate of macro-cell anode in parallel and vertical grouting type, research showed that there were large deviations between predictions of mixing potential theory and experimental values and the deviations between predictions of numerical methods and experimental values were small. Based on this, we built the practical model using the numerical methods and studied the influence of the variety of the duct voids on the corrosion of strand. Studies showed that when parallel grouting appeared, the smaller voids caused the faster corrosion rate of strand and when vertical grouting appeared, the fastest corrosion rate point was the intersection of cathode and anode.