Ceramics-Silikáty 54 (1) 47-52 (2010)

THE INFLUENCE OF POZZOLANA TO THE TRICALCIUM ALUMINATE HYDRATION AND THE EFFECTS OF CHLORIDE IONS TO FORMED HYDRATES

R. Kaminskas, I. Barauskas

Influence of natural pozzolana additive to the hydration of tricalcium aluminate and the effects of chloride ions to formed hydrates was investigated. In the samples 25 % C₃A mass weight was replaced by pozzolana and they were hardened for 28 days at normal conditions, soaked in saturated NaCl solution, and stored there for three months at 20 °C. It is estimated that at normal conditions the additive of pozzolana has no substantial effect on the course of C₃A hydration, but a part of amorphous SiO₂ penetrates into the structure of aluminium hydrates. Regular C₃A hydrates and CO₃^2- - AFm affected by NaCl becomes unstable and takes part in reactions producing Friedel’s salt and a complex compound - hydrocalumite - Ca₈Al₄(OH)₂₄(CO₃)Cl₂(H₂O)_1,6·(H₂O)₈. Pozzolana additive reduces the penetration of Cl^- ions to the structure of C₃A hydrates and impedes the formation of aluminium chloride hydrates. In samples with pozzolana additive a part of cubic aluminium hydrates, CO₃^2- - AFm and C₃A hydrate substituted with Si⁴⁺ affected by chlorides remained stable.

Keywords: Tricalcium aluminate, Chloride, Pozzolana