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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. • Quantitative characterization of class G cement microstructure hydrated at 110–190 ∘ C . • Evaluation of C–S–H density, C/S and H/S ratios, composition of microstructure phases. • Porosity rises and pore sizes grow with time, leading to microstructural coarsening. • C–S–H densification and decalcification with time. • Extends previous studies (Bahafid et al. 2017, 2018) to broader 7–190 ∘ C temperature range.