A major advancement in concrete technology in recent years is the creation of tiny disconnected air bubbles called air entrapments in concrete. Using either an air-permeable cement or an air-penetration mixture during mixing results in an air-in concrete.
Adding permeated air to concrete offers significant advantages over both plastic and hard concrete, such as resistance to freezing and thawing in saturated environments. Trapped air in non-air-penetrated concrete fills relatively large voids that are not evenly distributed throughout the mix.
Following are the properties of air entrained concrete:
The improved workability of air-entrained concrete greatly reduces water and sand requirements, especially in lean mixes and mixes with angular and poorly graded aggregates. In addition, disconnected air bubbles reduce separation and bleeding of the plastic concrete.
2. freeze-thaw durability
The expansion of water in concrete when it freezes can create enough pressure to break the concrete. However, the trapped air bubbles serve as reservoirs for the expanding water, thereby relieving the expansion pressure and preventing concrete damage.
3. de-icers resistance
Because permeated air prevents scaling caused by de-icing chemicals used for snow and ice removal, air-impregnated concrete is recommended for all applications where concrete contact is with de-icing chemicals.
4. sulfate resistance
Entered air improves concrete’s resistance to sulfate. Concrete made of cement with a low W/C ratio, permeable air, and low tricalcium-aluminate content is most resistant to sulfate attack.
The voids to cement ratio basically determines the strength of air-permeable concrete. For this ratio, voids are defined as the total volume of water and air (both entangled and trapped). When the amount of air remains constant, the strength changes inversely to the W/C ratio. As the amount of air increases, you can usually maintain a given strength by keeping the voids to cement ratio constant. To do this, reduce the amount of water added, increase the amount of cement, or both. Any strength loss that occurs with air entrainment is minimized because air-entrained concrete has a lower W/C ratio than non-air-entrained concrete with similar deceleration.
However, it is sometimes difficult to achieve high strength with air-entrained concrete, such as when the temperature of the concrete rises while using certain aggregates, so the deceleration remains constant.
6. abrasion resistance
Air-entrained concrete has the same abrasion resistance as non-air-entrained concrete of similar compressive strength. The frictional resistance increases as the compressive strength increases.
7. water tightness
Air-entrained concrete is more watertight than non-air-entrained concrete because the entrained air prevents the formation of interconnected capillary channels. Therefore, use air-tight concrete where water tightness is required.