An air entraining agent is an additive for concrete which allows for the forming of a controlled amount of finely dispersed air bubbles during the mixing process. These little air bubbles continue to remain present after the hardening of the concrete mixture. When the concrete has hardened, the remaining air bubbles interrupt the capillary action of the small air ducts of the concrete. This decreases the water adsorption. When water in the concrete freezes the ice can expand in air cavities that are formed by the air bubbles. Hence the frost-thaw resistance increases.