Model-based risk assessment of concrete spalling in tunnel linings under fire loading

Explosive spalling of concrete subjected to fire loading has been studied for more than 30 years. Many numerical models have been developed, attempting to simulate and predict the spalling phenomenon for specific concrete mixes, structural forms and fire-loading scenarios. In this paper, the authors propose a fully-coupled thermo-hydro-chemo-poro-mechanical model. In addition to the consideration of all essential processes including energy and mass transport, material degradation, thermal induced strain, the temperature-dependent Biot’s coefficient is introduced by means of a micromechanics approach. Employing an axisymmetric model representing plate-like concrete such as slabs, walls, and tunnel linings, the effect of material properties (intrinsic permeability, porosity) and environmental condition (saturation degree) on spalling is investigated. The obtained numerical results provide insight into the spalling risk for a wide range of material properties and environmental conditions. In fact, based on the acquired results, the spalling risk of an Austrian highway tunnel built in 1970s is assessed.