A place where weather is not normal (abruptly changing), air entraining admixture is used that protects concrete from different weather actions. Concrete is very weak against frost action in this water penetrates into concrete and damages the concrete. Basically when freeze thaw cycle occurs with time than deterioration of concrete occurs. This case is mostly found in dams, slabs, foundations of a structure, bridges etc… In these cases to protect concrete against deterioration, air entraining admixtures are used that increases resistance against freeze thaw effects. Air entraining admixtures during severe conditions protect concrete by closely packed air voids and these voids provides storage of water, which releases when paste in the concrete freezes.
Amount Of Air-Entraining Admixtures
When air entraining admixtures are used in concrete during homogenous mixing, then these admixtures increase the quantity of air in concrete. The quantity of air that is required in concrete depends on the number of Fines modulus (maximum coarse aggregates). If entraining admixtures are added by weight of mortar, then almost 8-10% air is being inserted by volume of mortar not by volume of concrete. There is also some amount of natural air contents.
Advantages of Air Entraining Admixtures
Air entraining admixtures increase the slump of concrete by using less amount of water. As we all know strength of concrete is very widely affected by water now when water will be less than concrete strength will be more without any effect on workability of concrete. If air entraining admixtures are added about 3-4% then it increases the slump value of concrete by 50-60%.