A study of thermal decomposition of phases in cementitious systems using HT-XRD and TG

Abstract

Significant variations have been reported on the temperature range of thermal decomposition of cementitious phases. Thus, this study identified temperature ranges on the phases in actual cementitious systems (portland cement (OPC) pastes, blended pastes of ground granulated blast furnace slag (GGBFS) with OPC, and Ca(OH)(2)-activated GGBFS) by simultaneously using thermogravimetry (TG) and high-temperature X-ray diffraction (HT-XRD) as follows: (1) 81 degrees-91 degrees C for dehydration of ettringite, (2) similar to 80 degrees-240 degrees C for major dehydration of C-S-H, (3) similar to 241 degrees-244 degrees C for hydrogarnet, (4) similar to 129 degrees-138 degrees C for Al2O3-Fe2O3-mono phase (AFm), (5) similar to 411 degrees-427 degrees C for Ca(OH)(2), and (6) similar to 648 degrees-691 degrees C for CaCO3. The CaO layers and SiO2 chains of C-S-H likely started to decompose from 615 degrees-630 degrees C, and eventually transformed to new crystalline phases. This study also demonstrated that (a) the quantity of calcite could be overestimated due to additional carbonation when Ca(OH)(2) is plentifully present in samples, and (b) the quantification of phases would be greatly affected by sample particle size when GGBFS is used in the system.