Multi-physics modeling of fire-induced damage in high-performance concrete

Abstract

The response of high-performance concrete (HPC) to rapid heating due to exposure to fire with air temperatures exceeding 700°C is analyzed. The analysis focuses on coupled thermal-mechanical-transport processes at the mesoscale in the first 10 minutes of exposure during which heating rates on the order of 10 °C/minute and temperature gradients on the order of 15 °C/cm are involved. The driving forces for damage considered are thermomechanical stresses and internal pore pressure resulting from the expansion of water within the material. The HPC is modeled as a two-phase composite consisting of a cementitious matrix and a population of quartz aggregate particles. Mesostructures with aggregate sizes of 400-1600 μm and aggregate volume fractions of 10-30% are considered. To capture the development of stresses and pore pressure, the cementitious matrix is modeled using a coupled thermal-mechanical-transport formulation and the aggregate is modeled using a thermal-mechanical formulation. Simulations show that the composition of the mesostructures significantly influences the time and spatial distribution of damage. Materials with smaller aggregate sizes and the lower effective permeability are found to exhibit more rapid property degradation. The time to failure and depth of thermal spall are quantified as functions of structural variables. This framework and the mesostructure-response relations obtained serves as a tool for the design of HPC that are more resistant to fire-induced damage.