What is the role of air – injection agent?

The Purdue OWL: General Writing
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Action one: improve and ease
In the mixture, the small independent bubble can play a role of ball bearing, reduce the friction resistance between the particles, so as to greatly improve the mobility of the mixture. If a constant flow of reduction of about 10% of water, due to the existence of a large number of tiny air bubbles, uniform water distribution on the surface of the bubble, the mixture has good water retention and cohesiveness.
Function two: improve durability
After the concrete has hardened, due to the bubble partition the concrete capillary leakage passage, improve the space characteristics of concrete, which can significantly improve the concrete impermeability and frost resistance, erosion resistance is also improved.
Influence on strength and deformation
The existence of bubbles makes the elastic modulus of concrete decrease slightly, which is beneficial to the crack resistance of concrete, but the air bubble also reduces the force area of concrete, so as to reduce the strength and wear resistance of concrete. In general, each increase in gas content of 1%, the concrete strength decreased by about 3%-5%.
At present, the most widely used rosin and rosin soap and so on, the appropriate dosage of 1.20. per 1000 0.50- of air entrained agent used in roads, dams, bridges and other concrete projects.