Multiscale prediction of thermal damage for hybrid fibers reinforced cementitious composites blended with fly ash at high temperatures

Thermal damage assessment of cementitious composites is essential for evaluating post-fire health conditions of the engineering structures, as well as the basis for reinforcement and repair after fires. Fibers and fly ash are widely used in cementitious composites due to their excellent properties. However, quantifying and predicting the thermal damage of hybrid fibers reinforced cementitious composites blended with fly ash at high temperatures is still inexplicit. Hence, this study aims to realize multiscale prediction of thermal damage for hybrid fibers reinforced cementitious composites blended with fly ash at high temperatures. First, the volumes of the phase compositions during hydration and dehydration are calculated by the hydration of cement and fly ash and the dehydration of hydration products. Then, a multiscale model is established to predict the thermal damage of hybrid fibers reinforced cementitious composites and verified by the experimental data. At last, the temperature field of tunnel lining structure in fires is obtained by numerical modeling and employing it to predict thermal damage at different thicknesses and moments. Results show that the heating rate determines the dehydration degree of hydration products and the volumes of the phase composites at high temperatures. The proposed multiscale model can reflect the thermal microcracking of cement paste, the interfacial thermal damage between aggregates and the cement paste, and the deterioration of elastic modulus of fibers. After three hours of exposure to fires, serious damage appears at the surface and the thickness of 2 cm and 5 cm of the lining, while there is nearly no damage at a thickness of 30 cm or more.