Modeling the instantaneous phase composition of cement pastes under elevated temperatures

Abstract

This paper models the instantaneous phase composition of cement pastes under elevated temperatures (up to 1200 °C). First, a hydration model was introduced. Then kinetics models for dehydration of cement hydrates, including C-S-H, CH and aluminate hydrates, and evaporation of free water were proposed. Subsequently, based on the kinetics models, the thermal decomposition model for cement pastes was proposed, which could predict the solid phase, porosity and water compositions of cement pastes under arbitrary temperature history. The thermal decomposition model was then validated by multiple experiments. Finally, a parametric study was conducted to investigate the effects of heating rate on the instantaneous phase composition of cement pastes. It was found that the phase compositions of cement pastes at the same temperature differ greatly from one another among different heating rate cases. This demonstrates the needs to consider temperature histories when analyzing real-world concrete structures under fires.