Calcium chloride is commonly used during cold weather to accelerate setting and early strength gain - but not without potentially harmful side effects. A survey conducted in Illinois found that few concrete plant operators have specific guidelines for controlling the amount of calcium chloride that's added to concrete. Several American Concrete Institute (ACI) documents reference an upper limit on the addition of calcium chloride - 2 percent by weight of cement. But the 2 percent figure may be confusing because solid calcium chloride can be purchased in varying concentrations. Calcium chloride should always be added to the concrete in solution form.
Some admixture companies, as a courtesy, provide dispensing equipment for calcium chloride solutions. However, they don't perform maintenance on the equipment or calibrate it periodically for the concrete producer. Few of the concrete producers interviewed for this article checked calcium chloride solutions to make sure the concentration was correct. Concentration of a calcium chloride solution can be verified by measuring the density of the solution. This procedure, however, is not exact because the solution density is affected by up to 23 percent impurities in the Grade 1 calcium chloride. The percentage of calcium chloride in the solution can also be estimated by measuring the specific gravity of the solution.