Effect of the hydration temperature between 110 and 190 ^∘C on the microstructure of Class G cement: Phase composition, pore structure and C–S–H chemistry

This study examines the microstructural evolution and changes in the properties of C–S–H in a cement paste hydrated at elevated temperatures ranging from 110 to 190 ^∘C. Using a simple slurry formulation composed only of Class G cement and water, the material's evolution was quantitatively investigated through a multi-technique approach, including mechanical testing (UCT), microstructural analysis (MIP), and chemical characterization (TGA and XRD). The results reveal two key mechanisms driving the observed strength loss: (1) a significant increase in porosity and pore size over time, leading to microstructural coarsening, and (2) the formation of denser crystalline phases with higher C/S ratios (over 2). Estimations of the C/S ratio and density of the amorphous C–S–H indicate its progressive decalcification and densification, with the lowest C/S values observed at the highest curing temperatures. This work extends previous studies on the quantitative characterization of Class G cement paste hydrated between 7 and 90 ^∘C (Bahafid et al., 2017, 2018), offering a comprehensive understanding of microstructural evolution over a broad temperature range - from 7 to 190 ^∘C - during hydration.