The Influence of Calcium Chloride Deicing Salt on Phase Changes and Damage Development in Cementitious Materials.

The conventional CaCl-HO phase diagram is often used to describe how calcium chloride behaves when it is used on a concrete pavement undergoing freeze-thaw damage. However, the chemistry of the concrete can alter the appropriateness of using the CaCl-HO phase diagram. This study shows that the Ca(OH) present in a hydrated portland cement can interact with CaCl solution creating a behavior that is similar to that observed in isoplethal sections of a ternary phase diagram for a Ca(OH)-CaCl-HO system. As such, it is suggested that such isoplethal sections provide a reasonable model that can be used to describe the behavior of concrete exposed to CaCl solution as the temperature changes. Specifically, the Ca(OH) can react with CaCl and HO resulting in the formation of calcium oxychloride. The formation of the calcium oxychloride is expansive and can produce damage in concrete at temperatures above freezing. Its formation can also cause a significant decrease in fluid ingress into concrete. For solutions with CaCl concentrations greater than about 11.3 % (by mass), it is found that calcium oxychloride forms rapidly and is stable at room temperature (23 °C).