Admixtures are materials that are added to concrete to alter the mix’s properties. They improve the strength, workability, and durability of the concrete. Admixtures can be used before or during the mixing process. The effectiveness of admixtures depends on the type of cement, water content, and the amount of time the concrete is exposed to high temperatures.
There are several common types of admixtures, including air-entraining admixtures, retarding admixtures, water reducers, and mineral admixtures. Each of these has different strengths and can be used for different purposes.
Water-reducing admixtures reduce the amount of water in the concrete. Using these admixtures can help create a slump at a lower water-cement ratio, reducing the need for energy.
Air-entraining admixtures help to entrain micro-air bubbles in the concrete, which act as a physical buffer against stresses. These admixtures are compatible with almost all types of concrete admixtures.
Retarding admixtures help to delay the initial set of the concrete. They usually use metal oxides. It is important to note that most retarders will entrain air into the concrete. However, too much air will decrease the compressive strength of the concrete.
Accelerating admixtures speed up the setting and finishing operations of the concrete. This means less time to get the job done and can save money.
Various new types of admixtures have been developed to meet the needs of the construction industry. These new admixtures have the ability to reduce the production of Portland cement and can also provide environmental benefits.