Multiscale Micromechanical Modeling of Deterioration in Cementitious Materials due to High Temperatures
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This study presents a multiscale micromechanical model for predicting high-temperature behavior of cementitious materials, bridging microstructural evolution with macroscopic mechanical degradation. The framework integrates four key components: thermodynamic hydration modeling using CemGEMS[1], thermo-chemical decomposition tracking of major phases[2], three-level homogenization from individual hydrate phases to microcracked cement paste, and micromechanical analysis[3] incorporating 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 demonstrates reasonable agreement for porosity evolution, elastic modulus degradation, and strength reduction. Six sequential deterioration stages are identified, each governed by specific phase transformations: Stage A (100°C–165°C) dominated by ettringite and hydrotalcite decomposition, Stage B (165°C–280°C) controlled by AFm phase breakdown, Stage C (280°C–420°C) driven by bassanite decomposition, Stage D (420°C–525°C) accelerated by hydrogarnet decomposition, Stage E (525°C–700°C) controlled by portlandite decomposition, and Stage F (700°C–800°C) dominated by C-S-H transformation and calcite decarbonation. The model successfully captures distinct performance characteristics across different cement types. CEM III demonstrates superior high-temperature resistance due to lower concentrations of thermally sensitive phases, while CEM I shows greater degradation owing to higher portlandite, ettringite, and AFm phase contents. This framework enables targeted cement formulation strategies and is valuable for fire safety assessment of concrete structures.
