INFLUNENCE OF HEATING ATMOSPHERE ON THE CHANGES IN CRYSTAL PHASE OF HARDENED CEMENT PASTE

Abstract

In this study, we discussed the influence of heating atmosphere on the chemical changes, such as crystal phase and carbonation of hardened cement paste. The decomposition of hydration products was accelerated by heating and related to the decrease of compressive strength of mortar. β-C₂S and C₄AF were reproduced under heating condition at 800℃. And we also investigated the change in crystal phase of cement paste under high temperature condition by using high temperature XRD in-situ analysis. In the case of heating with N₂, Ca（OH）₂ in hardened cement paste changed to CaO at 400～500℃. However, in the case of heating with CO₂, Ca（OH）₂ in hardened cement paste changed to CaCO₃ at 400～500℃. We can observed the decomposition of Ca（OH）₂ to CaO and reproduction of CaCO₃ with CO₂ gas by TG-DTA analysis. And CaO was directly reacted with CO₂ under this reaction. It is considered that this result is related to the carbonation of concrete under fire damage.