The chemical admixtures are added to concrete to enhance the durability, workability and strength of the concrete mixtures. It makes the concrete hard and fresh thereby aiding in all the types of construction situations regardless of how difficult it is. The penetration of water and water-borne chemicals are mainly the reasons that lead to damage in the concrete.
Types of Chemical Admixtures
Superplasticizers – The Superplasticizers when putting into the concrete mixture helps in reducing the water content between 12% and 25% thereby increasing the strength and performance and decreasing the permeability of the concrete. These admixtures provide the highest level of water resistance and are suitable for enduringly damp and waterlogged environments.
Air-Entraining Admixtures – Microscopic air bubbles called entrained air is produced when certain liquid chemicals are mixed with the concrete. These air bubbles help in improving the concrete’s resistance to damage, improve workability and reduce bleeding and segregation of concrete mixtures. Air entrainment is mainly used to protect that concrete which is constantly exposed to freezing and thawing. Higher dosages should be used for concretes placed at temperatures above freezing.
Water-Reducing Admixtures – The water reducers are used to increase the strength of the water concrete and to decrease the water content in it. It also aids in obtaining a higher slump without adding water. The type and amount of active ingredients in the admixtures determines the dosage rate of the water-reducing admixtures. The dosage levels may also vary depending on the different manufacturers. It is best to test it, in the beginning, to ensure that the resultant concrete meets the requirements you need.
Retarding Admixtures – The chemical retarders are used to delay the initial setting of the concrete. In hot weather, the concrete sets rapidly because of the high temperatures. So the retarders are used here which helps in delaying the setting by an hour or so. Retarders also perform the function of reducing the water content. Admixture concentration, dosage rate, concrete proportions, and ambient and concrete temperatures are some of the factors on which the amount of retardation depends upon. The dosage rates are based on the number of cementitious materials in the concrete mixture.
Accelerating Admixtures – The accelerators are an advanced version of the retarders. It not only helps in delaying both the initial and final setting time of the concrete but also gives the concrete a higher strength during the initial period itself. It also makes the concrete stronger to resist damage from freezing in cold weather. Accelerating Admixtures also helps in reducing the bleeding, completing the project earlier than the set time, improving protection against early exposure to freezing and thawing and reducing the protection time to achieve the quality.
Admixtures are in fact a great solution for both plastic as well as hardened state of the concrete. It helps in making the concrete more reliable, durable and delivers high in performance. There is also admixture dispensing equipment’s available and it helps in producing quality concrete.
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