Accelerators

Different means to accelerate concrete hardening and initial strength can be used, such as the use of high-strength cement, cement with low water–cement or water–binder ratios, external heat, or insulated forms. If any of these options cannot provide an initial strength high enough, it is appropriate to use an accelerator, usually calcium chloride if the local codes permit it. It is important to check in what cases its use is permitted and what is the maximum dosage permitted. Despite its potentially negative secondary effects, calcium chloride remains the most efficient and cheapest accelerator used in the concrete industry. Accelerators for shotcrete are completely different products based on silicates or aluminum salts. Some commercial products may contain alkalis, which make their handling dangerous. Usually, their use results in a reduction of the long-term compressive strength.