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Laboratory corrosion assessment of post-Tensioned tendons repaired with dissimilar grout
Lau, K; Rafols, J; Lasa, I; Paredes, M
Recently, corrosion problems have occurred with new formulation grouts in post-Tensioned tendons that were specified to meet low bleed-water requirements. Severe material deficiencies were observed in external post-Tensioned tendons of several bridges in Florida, one of which had tendon failures after only ~8 years in service. The deficient grout there was typically characterized as having high moisture content, high pore water pH, low total chloride concentrations, and enhanced sulfate concentrations. There was interest in gauging the extent to which corrosion may develop for repaired PT systems in which void spaces have been re-grouted with dissimilar grouting materials and where differences in pore water chemistry may contribute to corrosion development. In laboratory testing, there was no evidence of significant corrosion development in PT tendons with voids repaired with dissimilar grout when the base and repair grouts were properly cast and conditions were free of tendon material deficiencies. The cause of the lack of steel passivation in the deficient grout that led to corrosion activity and enhanced macrocell corrosion was thought to be due to the presence of high moisture content that contained enhanced levels of sulfate ions. If steel was allowed to develop a stable passive layer, later exposure to sulfates at levels tested may not be sufficient in high pH environment to cause local depassivation of the steel and corrosion development. But, results suggest that if there is early exposure to sulfates in the deficient grout, development of a stable passive layer may be impaired. © 2013 by NACE International.
September 2, 2013