Accelerators are substances that can enhance the initial rate of chemical reaction between cement and water in concrete, resulting in faster stiffening, hardening, and strength development. These admixtures are known to have a negligible impact on the consistency of the concrete mixture, and their use rarely affects the 28-day strength of the hardened material.
One of the primary applications of accelerators is during cold weather when low temperatures can significantly slow down the chemical reaction between cement and water. The use of accelerators can counteract this effect by increasing the reaction rate, thereby ensuring timely strength development. However, it’s worth noting that the impact of accelerators on the strength of concrete is typically limited to the early stages of curing.
Calcium chloride has been the most commonly used accelerator for concrete for quite some time. However, the presence of chlorides in concrete, even in small amounts, can increase the risk of corrosion, especially in embedded metal components. As a result, the use of admixtures containing chlorides is now prohibited in all concrete containing embedded metal, and alternative accelerators are being explored to meet the growing demand for safe and durable construction materials.
The paragraph discusses the use of accelerators in concrete and how they are sometimes marketed under different names such as hardeners, anti-freezes, and frost-proofers. However, the paragraph clarifies that accelerators are not true anti-freezes and cannot fully protect the concrete from the cold. Insulation is still necessary to keep the concrete warm after it has been placed. Additionally, the paragraph notes that accelerators are ineffective in mortars because the thickness of the mortar quickly dissipates any heat generated by the faster reaction.