An admixture is an additional substance added to the concrete during mixing to include a unique feature.
Admixtures used to accelerate the hardening of concrete are accelerators; these do not have to affect the setting time of the concrete.
During early hydration, an accelerating admixture should enhance the dissolution of the slowest-dissolving cement components, like silicates.
The most prevalent among the accelerators is calcium chloride. This admixture is often applied in cold weather at 35 to 40 degrees Fahrenheit or when rapid repair requires high early strength post-mixing.
Adding anhydrous calcium chloride at 1 percent of the cement's mass can accelerate the hardening process as effectively as an 11 degrees Fahrenheit increase in temperature.
Uniform distribution of calcium chloride throughout the concrete mixture is critical, and is most effectively accomplished by dissolving flakes instead of granule admixtures in the mixing water.
Calcium chloride may reduce cement's sulfate resistance and increase alkali-aggregate reaction risks, as well as shrinkage and creep, but enhances resistance to erosion and abrasion.
