Effect of mineral additives on the performance of air-entraining surfactants in materials based on Portland cement.

The effect of mineral additives of various composition and dispersive capacity (kaolin, metakaolin, microsilica, microcalcite, wollastonite) on the efficacy of ionic and nonionic air entraining agents (surfactants). The measurement of the entrained air content in the cement paste and mortar with mineral and air-entraining additives using air pressure compensation technique, and the electron microscopic study of the cement stone microstructure with these additives have shown that highly dispersed mineral additives (microsilica, kaolin and metakaolin) increase the volume of the air entrained by the agents (both ionic and nonionic), 2 or 3 times over. The study of active sites distribution on the surface of the particles of mineral additives by adsorption of acid-base indicators allows for the conclusion that the sorption of surfactants on the active sites of the additive particles (presumably Broensted acidic sites) provides additional stabilization of the entrained air in the form of bubbles with a 50-100 μm diameter.

Author: Yu.M. Kudla, A.S. Brykov, S.V. Myakin, E.A. Mikhailova

Section: Science and production

Keywords: concrete freeze-thaw resistance, air entrainment, air- entraining admixture, active mineral additives, active centres.