Calcium formate and Calcium Chloride can accelerate cement hardening speed, shorten the setting time.

Accelerating admixtures are added to concrete either to increase the rate of early strength development or to shorten the time of setting, or both. Chemical compositions of accelerators include some of inorganic compounds such as soluble chlorides, carbonates, silicates, fluosilicates, and some organic compounds such as triethanolamine.

Among all these accelerating materials, calcium chloride is the most common accelerator used in concrete. Most of the available literature treats calcium chloride as the main accelerator and briefly discusses the other types of accelerators. However, growing interest in using “chloride-free” accelerators as replacement for calcium chloride has been observed. This is because calcium chloride in reinforced concrete can promote corrosion activity of steel reinforcement, especially in moist environments. However, the use of good practices, i.e. proper proportioning, proper consolidation, and adequate cover thickness can significantly reduce or eliminate problems related to corrosion.

Calcium chloride has been used in concrete since 1885?and finds application mainly in cold weather, when it allows the strength gain to approach that of concrete cured under normal curing temperatures . In normal conditions, calcium chloride is used to speed up the setting and hardening process for earlier finishing or mold turnaround.

Calcium formate?is type of nonchloride accelerator used to accelerate the setting time of concrete. At equal concentration, calcium formate (Ca[OOOCH] 2) is less effective in accelerating the hydration of C3S than calcium chloride and a higher dosage is required to impart the same level of acceleration as that imparted by CaCl2 (Ramachandran 1984). An evaluation study of calcium formate as an accelerating admixture conducted by Gebler (1983) indicated that the composition of cement, in particular gypsum (SO3) content, had a major influence on the compressive strength development of concretes containing calcium formate. Results showed that the ratio of C3A to SO3 should be greater than 4 for calcium formate to be an effective accelerating admixture; and that the optimum amount of calcium formate to accelerate the concrete compressive strength appeared to be 2-3% by weight of cement (Gebler 1983). Calcium nitrate and calcium thiosulfate are also considered accelerators.