Effect of Calcium Chloride and Initial Curing Temperature on Expansion Caused by Sulfate Exposure

Previously unpublished U.S. Bureau of Reclamation (USBR) investigations conducted over a 40-plus year period examined the influence of calcium chloride (CaCl2) addition rate and mixing temperature on the sulfate resistance of concrete. Herein, those data are analyzed and compared with predictions from an existing model, as well as with results from accelerated tests performed in parallel by the USBR to better understand the individual and combined effects of these parameters. Because CaCl2 is more likely to be used during lower temperature construction, the combined effects of these parameters are important to consider. The addition of 1% calcium chloride by weight of cement can significantly decrease the sulfate resistance of samples made using Type V and II cements. Mixing and initially curing at 21.1 degree C (70 degree F) resulted in significantly lower sulfate resistance than when mixing at 4.4 degree C (40 degree F). Within the ranges considered, both the initial curing temperature and the CaCl2 addition appear equally important to sulfate expansion. Together, these results indicate that higher overall heat generation during the early hydration reactions can significantly decrease the long-term sulfate resistance of concrete.