Air Entraining Agents (Admixture)

Concept

Air entrainment is the international creation of tiny air bubbles in concrete. The bubbles are introduced into the concrete by the addition to the mix of an air entraining agent, a surfactant. The air bubbles are created during mixing of the concrete, and most of them survive to be part of the hardened concrete. The primary purpose of air entrainment is to increase the durability of the hardened concrete, especially in climates subject to freeze-thaw; the secondary purpose is to increase workability of the concrete while in a plastic state.

While hardened concrete appears solid, it is porous, having small capillaries resulting from the evaporation of water beyond that required for the hydration reaction. A water : cement ratio (w/c) of approximately 0.30 required for all the cement particulars to hydrate. Water beyond that is surplus and is used to make the plastic concrete more workable or flow able, which means there is substantial excess water that will not react with cement. Eventually the excess water evaporates, leaving little pores in its place. Environmental water can later fill these voids. During freeze-thaw cycles, the water occupying those pores expands and creates stresses which lead to tiny cracks. These creaks allow more water into the concrete and the cracks enlarge. Eventually the concrete spells - chunks break off. The failure of reinforced concrete is most often due to this cycle, which is accelerated by moisture reaching the reinforcing steel. Steel expands when it rusts, and these forces create even more cracks, letting in more water.

It is generally observed that a.e.a. Containing heavy sodium ions cause excessive foaming larger size air bubbles & high ph unlike non-sodium based a.e.a. Addition of ixxona a.e.a. In construction mixture helps in achieving this desired property.