The present work deals with an innovative model for analyzing the behaviour of concrete in high temperatures conditions. In particular it is focused on High Performance and Ultra High Performance concretes which have been often used in the last decade…
The present work deals with an innovative model for analyzing the behaviour of concrete in high temperatures conditions. In particular it is focused on High Performance and Ultra High Performance concretes which have been often used in the last decade in nuclear engineering applications, tall buildings and in tunnels. In such cases prediction of concrete performance during and after fire exposure is of great practical importance, in particular as far as tunnels are concerned, as recent fires in major European tunnels have dem- onstrated. Nowadays, it is well established that phenomena which take place in concrete exposed to high tem- peratures, cannot be studied by means of purely diffusive models. In the model presented in this paper con- crete is treated as partially saturated porous material and allows to consider hydration-dehydration, evaporation-condensation, adsorption-desorption phenomena and non-linearities due to temperature and pres- sure. An application of this model to an HP concrete structure will be shown. I INTRODUCTION pores, vapour transport by diffusion, flow of liquid 1.1 General overvievv of concrete at high water due to diffusion, capillary action, or gravity, temperature and further complications associated with phase changes due to condensation/evaporation, freez- When concrete is exposed to high temperature a ing/thawing, ablimation/sublimation, and adsorp- rather complex analysis is required to deal with the tion/desorption. coupled heat and mass transfer that can occur, in- Movement of air and water through the concrete volving both liquid mass transfer and vapour mass is accompanied by significant energy transfer, asso- transfer and related mechanical effects (Bazant & ciated with the latent heat of water and the heats of Kaplan, 1996). hydration and dehydration.