Effect of fly ash on the air void size distribution entrained by selected anionic, cationic and nonionic surfactants in hardened cement mortars

In this study, three types of surfactants, as anionic (mainly SDS), cationic (DTAB) and nonionic (AEO-9), were selected as the air-entraining agent (AEA). Air void size distributions of air-entrained mortars with or without fly ash were measured. The surface tension, the zeta potential of solid particles, and rheological properties were examined. The zeta potential alteration is used to characterize the interaction between surfactants and solid particles, as larger zeta potential alteration represents stronger interaction. Results indicate that the overall airentraining behavior is governed by the surface tension, as lower surface tension leads to finer air voids. In addition, fly ash influences the air void structure by changing the interaction between surfactants and solid particles. Stronger interaction leads to finer small air voids and coarser large air voids, especially for the anionic and cationic surfactants. For the nonionic surfactant, this interaction is relatively weak, thus large air voids are affected by viscosity, as higher viscosity results in coarser large air voids.