The anhydrous form of calcium chloride is very hygroscopic. It is used as a desiccant. Calcium chloride also exists as dihydrate and hexahydrate crystals. These crystalline forms are used in antifreeze solutions, fire extinguishers, fireproofing solutions, wood preservatives, as a gelling agent for starch size and to melt snow and ice from roads. Calcium chloride was used to speed up the rate of cure in mortar, shotcrete, and dry-mix concrete until 1973 when it was replaced by a non-chloride accelerator because it corroded steel reinforcements.
