Corrosion of post-tensioned tendons with deficient grout : final report.
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2016-10-20
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Edition:Final report
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Abstract:Recent corrosion failures of post-tensioned (PT) tendons in the Ringling Causeway Bridge (and corrosion development of PT tendons elsewhere in Florida) utilizing pre-packaged low-bleed specified grout products have spurred the need to evaluate what mechanisms were involved to cause the failure and to determine to what extent the problem is in PT tendons with similar materials. Severe corrosion was accommodated by segregated grout that was characterized as having high moisture content, low total chloride content, high free sulfate concentrations and high pore water pH. Accumulation of bleed water and grout void formation, considered sometimes as the cause of PT strand corrosion, were not consistently present with corrosion formation in the recent tendon failures. Furthermore, in addition to grout segregation with enhanced sulfate concentration, another separate issue of enhanced chloride content in PT grouts had garnered significant attention. Initial testing and chloride limit recommendations did not directly address the possible combined effect of enhanced chlorides in deficient grout. Elucidation of the role of the pore water chemistry of these deficient grouts in the corrosion mechanism is needed so that appropriate inspection and management decisions can be made.
The objective of the research is to identify criteria of deficient grout properties that may cause active corrosion of strand in post-tensioned tendons. Important material and corrosion parameters that may need to be more comprehensively studied as well as refinement in the proposed set of criteria is to be identified in this phase of research. The following approach was followed: 1). Identify the characteristics of deficient grout associated with steel corrosion including grout conditions formed when cast in presence of enhanced moisture presence, 2)
Identify the role of sulfates in alkaline solutions and its possible adverse effects on steel corrosion activity, 3) Identify the behavior of steel in deficient grout with enhanced sulfate concentrations, and 4) Identify combined effect of enhanced chloride content and free sulfate content in deficient grout on corrosion initiation and identify practical threshold limits.
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