Which is the Best Accelerator for Concrete, and How Do They Work?
A concrete accelerator is an additive that reduces the set time or increases the strength development/ hardening rate when added to concrete, grout, or mortar. Common accelerators include inorganic compounds such as silicate, triethanolamine, carbonates, soluble chlorides, and fluorosilicates.
Classifications of Concrete Accelerators
Depending on their performance, concrete accelerators are divided into various groups. They include:
A set accelerator is a mortar or concrete admixture used to shorten the setting time of cement by enhancing its hydration. They act as catalysts during the hydration process. The hydration reaction products accumulate continuously until all of the water or the cement in the mixture is exhausted.
Hardening accelerators increase the early strength of mortar and concrete without changing the final strength and the initial workability. These accelerators are typically used in construction projects where very early access to pavements or early stripping of shuttering is required. They are typically used with water reducers, mainly in cold conditions.
Examples of Concrete Accelerators
Calcium chloride (CaCl2) is one of the most popular and effective concrete accelerators. CaCl2 can enhance cement hydration, shorten the setting time and exhibit hardening properties.
Some of the benefits of calcium chloride include the following:
- Improved workability- Regardless of the design of the mixture, less water is needed to create a slump when CaCl2 is used.
- Reduced bleeding- The early stiffening created by the acceleration and final finishing reduces bleeding.
- Enhanced strength of air-entrained concrete- CaCl2 uses a higher cement factor concrete to compensate for the strength reduction.
These benefits help produce high-quality concrete within a short turnaround time. Using Calcium Chloride for concrete acceleration significantly facilitates job completion as economically and quickly as possible. Calcium chloride is the quickest and cheapest accelerator, but it is not ideal for reinforcements since it can easily corrode.
Calcium nitrate is used in concrete and mortar as a multipurpose additive: a long-term strength enhancer, antifreeze admixture, plasticizer, and set accelerator. The effectiveness of calcium nitrate as a set accelerator depends on the cement type. Typically it works effectively on liquid ordinary Portland cement (OPC) systems.
Calcium formate is in dry mix systems as a setting accelerator. It has two main benefits; reducing setting time and avoiding slowing down condensation speed in winter constructions. It also contributes to the early strength development in dry mix systems.
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