Investigating Carbonation and Hydration of Reactive Magnesia Cement Using Advanced Characterization Methods

Reactive MgO cement (RMC) is an alternative, low-carbon binder to ordinary Portland cement (OPC). RMC reacts with water and absorbs environmental CO2 to precipitate hydrated magnesium carbonates (HMCs). Depending on CO2 curing conditions and RMC composition, various polymorphs of HMCs precipitate, which affects the strength of the final RMC-based composite. In this study, polymorphism in HMCs is studied by visualizing the hydration and carbonation reactions of RMC using a specialized in-situ gas cell with transmission electron microscopy (TEM). The first step of the experiments is sample preparation, which involves ball milling, centrifugation, and sonication to obtain the right particle size and distribution for the analyses. The in-situ experiments are then conducted by flowing gases into and out of the gas cells at the required concentrations and temperatures. Various mixtures of water vapor and CO2 gas are used to investigate their effects on the nucleation pathways during the precipitation of HMCs. The reactions are also conducted at different temperatures, from 25˚C to 300˚C, to investigate the effect of temperature on the formation of the different HMC phases. In addition, changes in the sample morphology and phases can be captured with videos and images taken using in-situ TEM. Diffraction patterns and lattice images collected from TEM can also provide information about the different phases of HMCs formed during the experiments. These results help provide valuable information on polymorphism in magnesium carbonates, which will, in turn, aid in evaluating and enhancing the properties of RMC.