An FHWA Special Study: Post-Tensioning Tendon Grout Chloride Thresholds

Since the 1970s, the number of pre-tensioned and post-tensioned (PT) concrete bridge structures utilizing high-strength seven-wire strands has increased steadily. For bonded PT tendons, the grout functions as the last layer of corrosion protection for the highly stressed seven-wire strands by providing a high pH environment to form a protective oxide film on the strand surface and also acting as a physical barrier to water, oxygen, and chloride ions. Corrosion of strands initiates when the protective oxide film is compromised due to chloride attack or carbonation of the surrounding grout upon exposure to water and air. A recent discovery of a grout product with elevated levels of chloride used in a PT concrete straddle cap located in Corpus Christi, Texas, resulted in a full investigation of a potential corrosion problem. There is limited information reported in the literature pertaining to the chloride threshold of the PT tendons. As chloride information is needed to assess corrosion risk of the PT bridges containing the chloride contaminated grout, the Federal Highway Administration sponsored a 6-month accelerated corrosion testing program to determine chloride threshold(s) of PT strands exposed to chloride-contaminated grout. This TechBrief explains how two chloride threshold values of 0.4 and 0.8 percent by weight of cement were determined for corrosion initiation and corrosion propagation, respectively, using supporting test results.

• Record URL:
  http://www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/14040/14040.pdf
• Summary URL:
  http://www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/14040/index.cfm
• Record URL:
  https://rosap.ntl.bts.gov/view/dot/38206
• Publication Date: 2014-3

Language

• English

Media Info

• Media Type: Digital/other
• Features: Figures; Photos; References;
• Pagination: 8p
• Serial:
  • TechBrief
  • Publisher: Federal Highway Administration
• Publication flags:

  Open Access (libre)

Subject/Index Terms

• TRT Terms: Chloride content; Concrete bridges; Corrosion; Corrosion tests; Grout; Posttensioning; Tendons (Materials)
• Subject Areas: Bridges and other structures; Design; Highways; I24: Design of Bridges and Retaining Walls;

Filing Info

• Accession Number: 01520473
• Record Type: Publication
• Report/Paper Numbers: FHWA-HRT-14-040
• Files: NTL, TRIS, ATRI, USDOT
• Created Date: Mar 29 2014 11:15AM