Study on the activity, phase, thermal decomposition characteristics, microstructure, and chemical element of hardened cement powder under heating temperature of 100°C~1200°C

Abstract The properties of thermoactivated hardened cement powder (HCP) are of great significance for the recycling and utilization of concrete waste. This paper focuses on heating activation of HCP under the temperature between 100 and 1200°C. The activity, phase changes and microstructure of thermoactivated HCP were analyzed. The results showed that HCP with heating temperature between 1000 and 1200°C showed high activity. Under the conditions of heating activation at 1200°C, water–binder ratio of 0.38 and curing time of 30 days, the compressive strength of the specimen made of HCP reached 17.56 MPa. When the heating temperature is between 700 and 1200°C, CSH gel is gradually decomposed into C 2 S and C 3 S. The chemical reaction products of cement and thermoactivated HCP are similar, both containing CaCO 3 , Ca(OH) 2 , AFt, Hydrotalcite, etc. Compared to the diffraction peaks of hydrated cement, the diffraction peaks of thermoactivated HCP are broadened and dispersed. The high Ca/Si and Al/Si ratios in the chemical reaction products of thermoactivated HCP are important reasons for the decrease in its mechanical properties.