Synergism effects of coconut diethanol amide and anionic surfactants for entraining stable air bubbles into concrete

•The interactions between the anionic and nonionic surfactants were studied.•There are strong interactions on the interfaces of the mixed surfactants.•The mixed surfactants have higher foaming stability in aqueous solutions.•They also have higher air content stability in both cement mortars and concretes.•The study shows great benefit to understanding the influence of mixed surfactants on the interfaces and stability of air bubbles in concrete. Entraining tiny and stable bubbles into cement and concrete is becoming more and more important with the complex composition of cement and concrete. In this work, multi-component surfactants are compounded to improve the air-void stability in fresh concrete. The surface tensions, foam properties of their solutions, and the air contents and air-void parameters of the fresh and hardened cement mortars were tested. The results show that there are strong interactions on the interface of multi-components by calculating the important parameters of surface activity. When coconut diethanol amide molecules are introduced into the interface for co-assembly, the electrostatic repulsion between the anionic surfactant molecules is effectively diminished, thereby decreasing the interfacial free energy and making the interface more stable. The multi-component surfactants induced smaller bubbles with larger amounts in aqueous solutions, which also have higher stability of air bubbles in both cement mortars and concretes. So it is of great practical significance to compound nonionic and anionic surfactants to improve the air-void stability in concrete.