A New Approach in the Hygro-Thermo-Mechanical Analysis of Concrete at High Temperature

The prediction of concrete performance at high temperature is of great practical importance, in particular for safety evaluation of various concrete structures during fire or in the case of nuclear accident. In such conditions concrete may be subject to spalling phenomena which hazard the integrity of the construction and which may often lead to collapse of the structure. Designers are increasingly using High Performance Concrete (HPC) and Ultra High Performance Concrete (UHPC) for their significantly improved strength and durability compared to `normal' concrete. Anyway, the drawback of the HPC and UHPC is their higher tendency to experience explosive spalling because of their higher compactness and lower permeability than a `traditional' concrete. Spalling involves thermal, hygral and mechanical processes. Such complex coupled phenomena require numerical simulations implementing new mathematical models. An innovative mathematical model to analyse heat and mass transfer in concrete at high temperature and resulting mechanical behaviour including damage effects and some results of computer simulation of a UHPC structure are presented and discussed.