Calcium Chloride — Frequently Asked Questions

Because it releases heat as it dissolves rather than absorbing it. Sodium chloride depresses the freezing point but takes heat from its surroundings to dissolve, so it becomes sluggish as temperature falls and is largely ineffective below about minus 9 degrees Celsius. Calcium chloride's exothermic dissolution accelerates melting and keeps it working to around minus 25 or lower.

By keeping the surface damp. It is strongly deliquescent, so it draws moisture from the air and holds it in the road surface long after applied water would have evaporated. That moisture binds the fine particles into the surface rather than letting them become airborne, and a single application can control dust for weeks.

Because chloride corrodes embedded steel. It is the classic and most effective set accelerator, but chloride ions penetrate the concrete and break down the passive film on the reinforcement, causing rust that expands and spalls the concrete. Chloride-free accelerators such as calcium nitrate or calcium acetate are used where steel is present.

As anhydrous flakes, prills or powder at around 94 to 97 percent, as the dihydrate, and as a solution typically around 32 to 38 percent. The anhydrous form carries the most active material per tonne and generates the most heat on dissolution; the solution avoids handling a deliquescent solid. The form should be specified with the application.