A multiscale micromechanical model for high-temperature effects in cementitious materials: From microstructural evolution to macroscopic deterioration

This study introduces a multiscale micromechanical model linking microstructural evolution to macroscopic mechanical degradation for predicting high-temperature behavior of cementitious material. The framework integrates four key components: thermodynamic hydration modeling, thermo-chemical decomposition tracking, three-level homogenization from individual cement phases to microcracked cementitious material, and micromechanical analysis considering pore pressure effects. The model captures mechanical deterioration from 20 °C to 800 °C, including degradation of elastic modulus, tensile strength, and compressive strength. Validation against experimental data shows reasonable agreement for porosity evolution, elastic modulus degradation, and strength reduction. The validated model identifies six sequential deterioration stages, each governed by specific phase transformations. Quantitative analysis reveals that CEM III exhibits superior high-temperature resistance due to lower concentrations of thermally sensitive phases, whereas CEM I shows greater deterioration owing to higher contents of portlandite, ettringite, and AFm phases. This framework enables targeted cement formulation strategies and is valuable for fire safety assessment. • Framework links phase evolution to mechanical deterioration in cement paste. • Hydration, decomposition, homogenization, and microcracking are integrated. • Pore pressure evolution and micromechanics predict elastic and strength losses. • Six sequential deterioration stages are identified with phase-specific dominance.