Tensile failure mechanism of C–S–H/SiO ₂ composite exposed to temperatures from 50 to 700K: reactive molecular dynamics and constitutive modelling

The temperature-dependent failure mechanism of the interfacial transition zone (ITZ) in concrete, a region that significantly influences macroscopic durability, remains inadequately understood at the atomic scale. Reactive molecular dynamics simulations have been conducted to investigate the tensile behaviours and structural evolutions of the calcium silicate hydrate and silicon dioxide (C−S−H/SiO₂) composite, which acts as a nanoscale analogue of the ITZ, over a temperature range of 50–700 K. The findings indicate that the ultimate tensile strength diminishes by 50.3% as the temperature rises from 50 to 700 K. Tensile failure consistently initiates at the C−S−H/SiO2 interface, particularly within the interlayer region of C−S−H adjacent to the interface. Furthermore, elevated temperatures result in a reduced number of interfacial hydrogen bonds, leading to a 64% decrease in interfacial binding energy. Additionally, a temperature-dependent tensile constitutive model has been proposed and parameterised based on atomic simulations. This study provides crucial nanoscale insights for multiscale modelling of concrete under extreme thermal conditions and enhances the fundamental understanding of thermal decohesion in hydrated cement composites.