Accelerators in concrete serve as admixtures to speed up the hardening process, enabling the concrete to achieve early strength faster. Although accelerators do not necessarily impact the time it takes concrete to set, they reduce this time in practice. A common accelerator is calcium chloride, which is particularly useful for hastening early strength development in cold weather or for rapid repair jobs that require quick heat generation after mixing.
The effectiveness of calcium chloride can be compared to raising the temperature of the concrete by 11 degrees Fahrenheit, with a typical addition amount being 1 to 2 percent of the cement's mass. The distribution of this admixture must be uniform within the mix, achieved by dissolving it in the mixing water.
However, using calcium chloride has drawbacks. It may reduce concrete's resistance to sulfate attack and increase the risk of alkali-aggregate reaction. Furthermore, it can enhance shrinkage and creep and lower the durability of air-entrained concrete against freeze-thaw cycles. There is also a potential for embedded metal corrosion, such as reinforcing steel. As a result, other chloride-free admixtures like calcium formate are considered for acceleration as they are less likely to cause corrosion. However, their long-term effects on concrete are still being evaluated.
