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Results
ABSTRACT 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.
- Research Report > Experimental Study (0.54)
- Research Report > New Finding (0.34)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT The assessment of recently failed external post-tensioned tendons from a bridge in Florida provided some insight on the material and environmental conditions of the tendon components leading to the failure. Segregated grout material was observed in the vicinity of the corrosion failure. The segregated grout was manifested as wet plastic grout, white chalky grout, and sedimented grout. The deficient grout material has been attributed to segregation of the grout as evidenced by differences in texture and color of the grout, high moisture content, and apparent accumulation of chloride, sulfate, and other ionic species. No evidence of significant carbonation was detected by pH measurement. Accelerated corrosion was evidently caused by macrocell coupling of local anodes in the strand embedded in segregated grout and extended cathodes throughout the tendon. Due to grout segregation, part of the upper region of the tendon contained high water content which carried higher concentrations of ionic species including sulfates and chloride ions. The segregated grout material provided poor corrosion protection due to its high porosity, enhanced sulfate concentration, and possible enhanced carbonation and their associated deleterious effects on pore water chemistry and steel passivation. Differential aeration due to easy access to oxygen at vent caps, vastly different moisture contents in localized tendon regions, and strand interstitial spaces that created crevices allowed greater extent of macrocell polarization whereby corrosion failure occurred within a short time frame. Keywords: Corrosion, Grout, Segregation, Sulfate, Macrocell, Tendons INTRODUCTION Corrosion failure of longitudinal external post-tensioned (PT) tendons was identified in 2011 in a Florida bridge after being in service for 8 years. The bridge was a PT segmental bridge with internal and external tendons.
- North America > United States > Florida (0.46)
- North America > United States > Texas (0.32)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Reservoir Description and Dynamics (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)