What is the function of air-entraining agents in concrete?

Air-entraining agents play a crucial role in enhancing the durability of concrete, particularly in environments susceptible to freeze-thaw cycles. By introducing microscopic air bubbles into the concrete mix, these agents help create air voids within the hardened concrete. These voids are essential for accommodating the expansion of water as it freezes, which prevents internal cracking and spalling of the concrete. In essence, the presence of these air voids enhances the concrete's resistance to degradation caused by repeated freeze-thaw cycles, ultimately contributing to the longevity and performance of the concrete structure in adverse weather conditions.