Air entrainment makes concrete more workable[1] during placement, and increases its durability when hardened, particularly in climates subject to freeze-thaw cycles.
Therefore, adding air to concrete when it's being made makes it easier to handle at first, but then later helps it stay strong even under tough conditions like freezing temperatures or fire exposure.
Additionally, the air voids, acting as pressure relief zones, allow water or moisture expansion during freeze-thaw cycles without causing internal stresses and subsequent cracking.
Fly ash, a supplementary cementitious material, improves paste packing due to its smaller particles, resulting in better flow and finishing of the concrete.
Fly ash's lower specific gravity increases the paste content for a given water-to-cementitious material ratio (w/cm) compared to ordinary Portland cement.
Different types of fly ash require adjustments in air-entraining admixture dosage due to variations in their chemical compositions and air loss characteristics.
[12] Including natural pozzolans like rice husk ash or metakaolin affects fineness and composition, which further influence the required dosage of air-entraining admixtures in mixed concretes containing these materials.
Using fly ash, a byproduct of coal combustion, as an additive in concrete production, is a common practice due to its environmental and cost benefits.
Still, residual carbon in fly ash can interfere with air-entraining admixtures (AEAs)[13] added to enhance air entrainment in concrete for improved workability and resistance against freezing and thawing conditions.
Specifically, they observed that the concrete contained tiny, dispersed air bubbles throughout its structure, significantly improving its durability and resistance to freezing and thawing.
Further investigations and research were conducted to understand this phenomenon, leading to the realization that the grinding aid was responsible for entraining air into the concrete.
[16][17] Air-entraining agents (AEAs) have been developed and extensively studied to improve resistance against freezing and thawing damage caused by both internal distress and salt scaling.
Unlike AEAs, which may lose a portion of entrained air due to factors like long hauling durations or high ambient temperatures, SAP's pore system remains stable regardless of consistency, superplasticizer addition, or placement method.
Using SAP instead of traditional AEAs, construction practitioners can enhance freeze-thaw resistance without worrying about losing a significant portion of entrained air bubbles during mixing or placement processes.