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

The conventional CaCl₂-H₂O 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 CaCl₂-H₂O phase diagram. This study shows that the Ca(OH)₂ present in a hydrated portland cement can interact with CaCl₂ solution creating a behavior that is similar to that observed in isoplethal sections of a ternary phase diagram for a Ca(OH)₂-CaCl₂-H₂O 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 CaCl₂ solution as the temperature changes. Specifically, the Ca(OH)₂ can react with CaCl₂ and H₂O 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 CaCl₂ concentrations greater than about 11.3 % (by mass), it is found that calcium oxychloride forms rapidly and is stable at room temperature (23 °C).