Evolution of Microstructural Characteristics of Carbonated Cement Pastes Subjected to High Temperatures Evaluated by MIP and SEM

Journal article, 2022

The microstructural evolutions of both uncarbonated and carbonated cement pastes subjected to various high temperatures (30 degrees C, 200 degrees C, 400 degrees C, 500 degrees C, 600 degrees C, 720 degrees C, and 950 degrees C) are presented in this study by the means of mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). It was found that the thermal stabilities of uncarbonated cement pastes were significantly changed from 400 to 500 degrees C due to the decomposition of portlandite at this temperature range. More large pores and microcracks were generated from 600 to 720 degrees C, with the depolymerization of C-S-H. After carbonation, the microstructures of carbonated cement pastes remained unchanged below 500 degrees C and started to degrade at 600 degrees C, due to the decompositions of calcium carbonates and calcium modified silica gel. At 950 degrees C, both uncarbonated and carbonated cement pastes showed a loosely honeycombed microstructure, composed mainly of beta-C2S and lime. It can be concluded that carbonation improves the high-temperature resistance of cement pastes up to 500 degrees C, but this advantage is lost at temperatures over 600 degrees C.