A type of chemical admixtures that are used as a replacement of water is known as water reducing admixtures. By using that kind of admixtures, amount of required water for a workable concrete will be reduced and hence improved the strength of concrete by attaining a given value of slump at less amount of water.
When water content decrease, then impermeability of concrete increases and hence concrete become safe against freeze-thaw effect. When required weight of water become less then in the same manner required amount of cement will also be less. And as we all know, that if concrete became an expansive than it is only due to cement. Because in concrete cement is the most expensive content.
By the use of water reducing admixtures cracking index of concrete increases. This is due to very fast hydration. When early hydration occurs then large amount of heat releases at the start of reaction in return which cause cracking in concrete.
Water reducing admixtures overcome this effect and increase the cracking index by reducing high amount of early heat. These admixtures also lessen the shrinkage (reduction in volume of concrete) in concrete.
Water reducing admixtures also increases the value of slump. This slump value increase the workability (how easy a concrete can be handled) of concrete. Without admixtures increasing slump value is not simply possible, to increase slump value without admixtures, we must require a change in water to cement ratio. So as we know cement is the most expansive, therefore concrete not remains cost-effective.