Which chemical is commonly used as an accelerator in concrete mixes?

Calcium chloride is commonly used as an accelerator in concrete mixes due to its ability to enhance the rate of hydration in cement. When added to concrete, calcium chloride increases the speed at which the concrete sets and gains strength, which is particularly useful in cold weather conditions. This accelerative effect helps in reducing the time needed for forms to be removed and for the concrete to reach its design strength, facilitating faster project completion.

The use of calcium chloride is preferred because it is effective at low dosages and does not significantly impact the workability of the concrete mix. It can also help to prevent issues associated with delayed setting times, such as freezing of freshly placed concrete, which is critical in ensuring structural integrity.

The other chemicals mentioned, while they may serve various purposes in construction, do not function as accelerators in the same manner as calcium chloride. Lime is usually used to alter soil properties or improve workability, sodium chloride can be detrimental to concrete durability if used excessively as it promotes corrosion of reinforcing steel, and potassium sulfate is primarily used as a fertilizer and does not effectively serve as a concrete accelerator.