Thresholds

Details

• Alternative Title:
  FHWA Special Study: Post-Tensioning Tendon Grout Chloride ; Thresholds
• Creators:
  Lee, Seung-Kyoung ; Zielske, James
• Corporate Creators:
  Rutgers University. Center for Advanced Infrastructure and Transportation
• Corporate Contributors:
  United States. Department of Transportation. Federal Highway Administration. Office of Infrastructure Research and Development
• Subject/TRT Terms:
  Chloride Threshold, Chloride, Corrosion Initiation, Corrosion Propagation, Seven-wire Strand, Post-tensioning, Grout, Accelerated Corrosion Testing, Sulfate Ions Grout Grouting Posttensioning Tendons (Materials)
• Publication/ Report Number:
  FHWA-HRT-14-039
• Resource Type:
  Tech Report
• Geographical Coverage:
  United States
• Corporate Publisher:
  United States. Department of Transportation. Federal Highway Administration. Office of Infrastructure Research and Development
• Abstract:
  "Elevated levels of chloride were recently discovered in a commercially available pre-bagged grout product made for
  
  post-tensioned (PT) tendons. Chloride concentrations were reported to be as high as 5.27 percent by weight of cement.
  
  These numbers exceed the current limits set by all of the domestic and international regulatory committees. For
  
  example, the chloride limits for prestressed concrete imposed by American Concrete Institute committees are either
  
  0.06 percent water-soluble chloride by weight of cement or 0.08 percent acid-soluble chloride by weight of cement.
  
  Chloride threshold is defined as a minimum chloride concentration needed to induce corrosion. However, there is
  
  limited information reported in the literature pertaining to actual chloride threshold of seven-wire PT strands. For this
  
  reason, 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.
  
  Based on the test results obtained through the 6-month accelerated corrosion testing program and subsequent autopsy
  
  of the specimens, two chloride threshold values were determined for the PT strands fully encased in normal grout. The
  
  first threshold is 0.4 percent chloride concentration by weight of cement, which is the lowest amount needed to initiate
  
  corrosion of strands. At this threshold, rust spots can be formed, and a small number of pits start to form beneath some
  
  of the rust spots. The second critical chloride threshold is found in association with corrosion propagation. At this
  
  threshold, corrosion starts to intensify in terms of the number of pits and pit depth. Test data and autopsy results
  
  obtained in this study indicated that 0.8 percent chloride by weight of cement is the critical threshold. Once chloride
  
  concentration exceeds the critical threshold, significant corrosion damage can occur rapidly, and structural integrity of
  
  the PT bridges may be compromised in the near future. The actual deterioration rate will be influenced by many
  
  factors. These threshold values are applicable to normal grout condition only. They may not be adequate in other
  
  conditions such as carbonated grout, segregated grout, duct cracks, grout voids filled with water with or without
  
  chloride ions, or free sulfate ions in contact with the strands. In these circumstances, corrosion should start below the
  
  proposed threshold values."
  
  
• Format:
  PDF
• Funding:
  DTFH61-08-C-00005
• Collection(s):
  US Transportation Collection Federal Highway Administration
• Main Document Checksum:
  urn:sha-512:72d8e5eca5b0fbfd38d3e1b1fa69bb78277510cf334dae6982a2d7a1e01feb00c9497a7c1f02c8440e9c38906d38c2c305518a177367ef9beb16fdd2d2862293
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/27468/dot_27468_DS1.pdf
• File Type:
  [PDF - 14.00 MB ]