New approach on thermal conductivity of concrete in case of fire

The design of concrete elements in case of fire by using fire safety engineering methods as described in Eurocode 2 is getting more and more common practice. An essential step within this calculation is to determine the cross-sectional temperature under transient thermal stress. DIN EN 1992-1-2 provides temperature-dependent curves for the thermal conductivity of concrete. As regulated by the national annex of DIN EN 1992-1-2 the so-called upper limit function of thermal conductivity has to be used in Germany. Thermal calculations using this limit function lead to results, for which the insulation criterion in case of fire is not complied with the tabulated minimum thicknesses of section 5 in DIN EN 1992-1-2. This paper presents a new approach on thermal conductivity of concrete, which was verified by comparison of numerical calculations to experimental determined temperaturetime curves. Experimental data of 15 different tests on wall, ceiling and column specimens, carried out at Institute of Building Materials, Concrete Construction and Fire Safety (iBMB) of TU Braunschweig and furthermore European Institutes, was used.