Accelerators increase the rate of reaction between cement and water, thus increasing the rate of set and development of strength. This can be advantageous in precasting, where early removal of the formwork is required, and in cold weather when the heat generated speeds up the hardening processes and reduces the risk of frost damage. Only chloride-free accelerators, such as calcium formate, should be used in concrete, mortar or grout where metal will be embedded, because calcium chloride accelerators can cause extensive metallic corrosion. Accelerators producing a rapid set are not normally used within structural concrete.

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