2023-05-19 14:15:01
Types of Admixtures Used In Concrete
Admixtures are natural or manufactured chemicals which are added to the concrete before or during mixing. The most often used admixtures are air-entraining agents, water reducers, water-reducing retarders and accelerators.
We'll discuss The Types of Concrete Admixtures in the following Posts.
1- Water Reducing Admixtures
Water reducing admixtures, the name itself defines that they are used to minimize the water demand in a concrete mix. Workability is the important property of concrete which is improved with the addition of water but if the water is added more than required the strength and durability properties of concrete gets affected.
In addition, to increase in workability it also improves the strength of concrete, good bond between concrete and steel, prevents cracking, segregation, honeycombing, bleeding etc. Water reducing admixtures are also called as plasticizers and these are classified into three types namely plasticizers, mid-range plasticizers and superplasticizers. Normal plasticizer reduces the water demand by up to 10%, mid-range plasticizers reduce the water demand by up to 15% while superplasticizers reduce the water demand by up to 30%.
2- Retarding Admixtures
Retarding admixtures slow down the rate of hydration of cement in its initial stage and increase the initial setting time of concrete. These are also called as retarders and used especially in high-temperature zones where concrete will set quickly. The quick setting in some situations may lead to discontinuities in structure, the poor bond between the surfaces creates unnecessary voids in concrete etc. Retarders are useful to eliminate this type of problems. Commonly used retarding admixture is calcium sulphate or gypsum. Starch, cellulose products, common sugar, salts of acids are some other retarders. Most of the water-reducing admixtures are also acts as retarding admixtures and they are called as retarding plasticizers.
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