Chemical admixtures are those, which are added after batching of concrete so that every separate admixture gives some important functions to the properties of concrete. Chemical admixtures can be used for many purposes like strength of concrete, retarding setting of concrete, as to replace air in concrete, used for improvement in freeze thaw effect etc…
Chemical admixtures also functions as in the increment in slump value, improves the workability of concrete and to reduce the water amount for same workability. Chemical admixtures have functionality of either fasten setting of concrete or delaying its setting (as a retarder).
Chemical admixtures are also used for the early strength in concrete. In case when early strength is required than admixtures with particular functionality will be used which fastens the hydration rate. When admixtures being used for early strength than high amount of heat evolve and that indicates the rapid hardening of concrete.
Chemical admixtures when used for functionality of set retarding than what admixtures do, admixtures simply lengthen the second phase of hydration of C3S. 2nd phase is also known as dormant phase (when there will be no reaction).
AS the initial setting starts after the dormant period so when chemical admixtures will be adding up than time to reach the start of initial setting line will be more and due to which workability of concrete will not loss up to longer time, so it is easy to use concrete for longer durations before hardening of concrete and when concrete harden than work-ability of concrete vanishes.
