Thermal conductivity of gypsum plasterboards : at ambient temperature and exposed to fire

One of the more complicated thermal properties to calculate for gypsum plasterboard is the thermal conductivity. The thermal conductivity is important because it plays an important role in the fire behaviour of gypsum plasterboards. Plasterboard often protects steel structures of buildings, because it conducts heat slowly and absorbs the heat of the fire by its volumetric enthalpy. This paper will focus on the first role. The thermal conductivity becomes more complicated for porous media, which consist of different phases. Kaviany (1995) points out that the heat conduction through fully saturated matrix depends on the structure of the matrix and the thermal conductivity of each phase. The same principle applies for any heterogeneous material. One of the most difficult aspects of the analysis of heat conduction through a porous medium is the structural modelling. The thermal conductivity of the solid phase is generally larger then that of the fluid, the manner in which the solid is interconnected influences the conduction. Plasterboard consists of a solid phase and water/air mix in the voids. The thermal conductivity of the voids depends strongly on the amount of moisture (absorbed water) in the voids, since the thermal conductivity of water is 23 times the thermal conductivity of air. This article will try to solve this problem partly by assuming that gypsum plasterboards can be assumed to be a three-phase system consisting of two different two-phase systems. This concept is applied to various types of gypsum/limestone plasterboards. The models are validated by comparing the results of the models with experiments. Based on these results and models conclusions are drawn in regard to the amount of absorbed water. Finally the concept of thermal conductivity is applied on gypsum plasterboards under fire