51313-02600-Corrosion Failure of Post-Tensioned Tendons in Presence of Deficient Grout

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Product Number: 51313-02600-SG

ISBN: 02600 2013 CP

Author: Kingsley Lau

Publication Date: 2013

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Corrosion protection of post-tensioned (PT) steel strand consisted of embedding the strand in grout material (with highly alkaline pore water) within a high density polyethylene (HDPE) duct. The highly alkaline environment ideally would promote steel passivation and the HDPE duct would prevent intrusion of external moisture and aggressive chemical species into the tendon. However corrosion development of PT tendons has occurred. In early tendon failures in Florida corrosion had in part been attributed to void space formation in the grout due to bleed water accumulation or improper grouting procedures. Subsequently new grout material requirements for PT systems specify minimal bleed water formation. Yet recently corrosion problems have occurred with these new formulation grouts as well.

Some of the first PT bridges to be constructed in Florida with the low bleed water grouts were recently found to have severe material deficiencies in the grout of post-tensioned tendons and tendon failure due to corrosion had occurred after only ~8 years in service. The deficient grout was typically characterized as having high moisture content high pore water pH low total chloride concentrations and enhanced sulfate concentrations. Large voids were not consistently associated with the corrosion and deficient grout. Accelerated corrosion occurred in regions with severe grout segregation and was aggravated by macrocell formation between regions of dissimilar aerated conditions caused by varying moisture content distance from vent ports and strand interstitial crevice environments.