Experimental and numerical studies of thermo-hydrous transfers in concrete exposed to high temperature

Abstract

The compressive strength of concrete can be as high as 80 MPa at 28 days. High strength concrete (HSC) can be obtained by decreasing porosity and lowering permeability. Concrete, especially HSC, performs poorly when subjected to fire. This is attributed to high thermal stresses and water vapour pressure. High thermal gradient induces high thermo-mechanical stresses in the concrete system. Low permeability prevents water from escaping and induces high water vapour pressure causing cracking and spalling. The aim of this study is both experimentally and numerically study the coupled heat and mass transfers in concrete exposed to elevated temperature. Five concrete mixtures with various cement contents and water cement ratios of a constant aggregate content were studied before and after heating–cooling cycles. The concrete cylindrical specimens were subjected to several tests: compression and splitting tensile tests, measurement of modulus of elasticity, heating–cooling cycles, thermal field and mass loss during the heating–cooling cycles, and permeability tests. Comparisons between the numerical and experimental results on the thermo-hydrous behaviour were reported. Parametric analyses were carried out in order to underline main parameters involved in concrete behaviour at high temperature. The numerical and experimental results included thermal gradient, water vapour pressure, relative humidity, concrete mass losses due to dehydration, and water content for concrete elements heated from 20 to 600°C. The results show the degrees of damage due to the concrete chemical transformations at high temperature.