Development of a Standard Accelerated Corrosion Test for Acceptance of Post-Tensioning Grouts in Florida

Recent corrosion problems found in Florida’s post-tensioned bridges have shown how important quality grouting materials and proper grouting techniques can be to the longevity of State bridges. Portland cement grout is commonly used to fill the voids in post-tensioning ducts after the tendon is stressed. Portland cement grout provides a protective barrier, high alkaline environment, and bonds the tendon to the duct to allow higher tendon stresses to be developed in the tendon. Current Florida Department of Transportation (FDOT) specifications currently require that prepackaged grouts proposed for use in filling post-tensioning ducts must be tested using the accelerated corrosion test (ACT) method as outlined in Appendix B of the “Specification for Grouting of Post-Tensioning Structures” published by the Post-Tensioning Institute. The qualifying grout must show a shorter average time-to-corrosion than the control sample that is fabricated using 0.45 w/c. Furthermore, the time-to-corrosion must not exceed 1,000 hours. The ACT is an anodic polarization test of a “lollipop” specimen formed from a single strand and grout. Although already in use, the ACT is not fully developed and was in need of further development including studying the influence of using IR compensation during the ACT test because this phenomenon is likely to skew results for grouts of significantly different resistivities. Tests with four different types of grout (plain, with corrosion inhibitor, with silica fume, and with fly ash) at three different ages (7, 28, and 56 days) were conducted with and without IR compensation. On average, the reduction in time-to-corrosion when IR compensation was used was 11 to 46%, but reached values as high as 149%. Test specifications are presented for the ACT. The most significant of the recommendations is that the test results be compared to the results from a qualifying grout tested using the same equipment and strand. The current minimum 1,000 hour requirement should be eliminated. The ACT test can take several months to run for a good quality grout, so an alternate method was developed that can provide initial results immediately after the grout has cured. Linear Polarization Resistance provides a method by which the grout can be qualified more quickly than waiting for the time-to-corrosion results. A polarization resistance value of 700 kΩ-cm² is suggested until further LPR and ACT direct correlations are done. While a set limit would not be recommended as a single pass-fail criterion, in this case it provides a restrictive first level of testing so that the ACT can be avoided for some grouts. Grouts that do not meet this criterion, but then pass the ACT should not be penalized. The LPR method also is useful during new mix grout development as a quick evaluation technique. Bleed in grouts is also a significant problem and may lead to susceptibility of the prestressing strand to corrosion. A new method, the Wick Pressure test, was also developed in this study that combines the positive attributes of the other two test methods.

Language

  • English

Media Info

  • Media Type: Print
  • Edition: Final Report
  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 108p

Subject/Index Terms

Filing Info

  • Accession Number: 01044259
  • Record Type: Publication
  • Report/Paper Numbers: 00026900
  • Contract Numbers: BD535
  • Files: TRIS, STATEDOT
  • Created Date: Mar 3 2007 6:05AM