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In continuation with Admixtures article, let us understand the functions
Functions of Admixtures
Concrete admixtures have various functions and they are as follows:
(a) To increase the rate of strength development at early ages – calcium chloride is the most widely used accelerator,
(b) To retard the initial setting time while pumping concrete over a long distance,
(c) To increase the workability without changing the water content – pozzolana such as fly ash is used,
(d) To increase the strength,
(e) To increase the resistance to freezing and thawing – vinyl resin is an air entrainment admixture which is used for this purpose,
(f) To decrease heat evolution,
(g) To increase water tightness,
(h) To decrease capillary flow of water, and
(i) To decrease rate of bleeding and segregation.
Chemical admixtures are various types and they are:
(a) Accelerating admixture – A substance that increases the rate of hydration of hydraulic cement, reduces the setting time, or in other words, increases the rate of strength development.
(b) Retarding admixture – A substance which delays the setting time of cement paste.
(c) Water – reducing admixture – A substance which either increases the workability of freshly mixed mortar or concrete without increasing water-cement ratio or maintains workability with reduced water-cement ratio.
(d) Air – entraining admixture – A substance that causes air to entrap/Cd in the form of tiny bubbles in mortar or concrete during mixing to increase its workability and resistance to freezing and thawing.
(e) Super plasticizing admixture – A substance that has very high workability with a large decrease in water content (at least) for a given workability. High range water reducing admixture (HRWRA) is also referred to as a superplasticizer.
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