Revisions to accelerated corrosion test method for post-tensioning grout

Along with requirements related to placement, post-tensioning grouts should confer a minimum degree of corrosion protection to the embedded prestressing strand. In the U.S., this degree is currently being measured with the use of an anodic polarization test procedure known as the accelerated corrosion test (ACT). Two conditions for approval of a specific grout are currently in use: a) an ACT time-to-corrosion result greater than or equal to one from a 0.45 water-cement ratio (w/c) standard mixture (only portland cement and water) tested under the same conditions; and b) a minimum result of 1000 hours average ACT time-to-corrosion. Various specifications use different combinations of these two approval conditions. The ACT test procedure has been criticized because it does not currently require that the applied voltage account for the variations in the resistance of the grout (IR drop) when selecting the appropriate applied voltage. Grout resistance can vary significantly with the addition of pozzolans and admixtures, perhaps adversely affecting the results of the test. The research reported in this paper investigated different post-tensioning grout mixtures in ACT tests with varying levels of admixtures and the option of compensation for the effects produced by resistivities that are inherent to electrochemical systems. Testing confirmed that variation in the type of test is significantly affected by variation in these resistivities, allowing grouts of potentially lower quality to pass the test when IR compensation is not available in the equipment used to conduct the tests.