Studying AEA interaction in cement systems using tensiometry

Tensiometry measurements reveal the behavior of air-entraining agents (AEA) in solutions that isolate features of the pore solution that control the impact on the surface tension of four anionic commercial AEAs. The degree to which each surfactant is affected by ionic strength and calcium coagulation is related to its molecular structure and critical micelle concentration. At the concentration recommended by the AEA manufacturer for use in concrete, two of the AEAs show no reduction in surface tension when exposed to a synthetic pore solution, but show strong interaction with Ca^{2 +} ions. This suggests that some AEAs rely more on surface tension reduction to stabilize bubbles and others rely primarily on calcium interaction. AEAs that self-associate more easily (and interact with calcium more strongly) offer better frost protection for mortars at lower AEA concentrations, which is the focus of a future publication.