Calculation of thermal conductivity of gypsum plasterboards at ambient and elevated temperature

Plasterboard often protects steel structures of buildings because it conducts heat slowly and absorbs the heat of the fire by its volumetric enthalpy. The most important property governing the heat transfer is the thermal diffusion. This property depends on the density, specific heat and thermal conductivity. The first two can be calculated based on the mass composition of the board. The thermal conductivity is more difficult to derive since it is a directional property. This paper will focus on the calculation of the thermal conductivity at ambient and elevated temperatures. It is shown that the thermal conductivity of gypsum plasterboard (i.e. a porous medium) can be assumed to be a three-phase system. Plasterboard consists of a solid phase and a water/air mix in the voids. The differences between different theoretical equations for both dry and moistured plasterboards are presented. The equation proposed by Zehner and Schlunder (Chem. Ing.-Tech. 1972; 44(23):1303-1308) with shape-factor C of 5 gave good agreement with experimental data of the different boards. Furthermore, the influence of the composition of the boards on the thermal conductivity is investigated. This has an influence, especially since the composition is also related to its moisture content. Regression analysis xpoints out that the moisture content depends only on the gypsum content. A value of 2.8% absorbed water on the mass of gypsum is found, and this water plays an important role in the thermal conductivity of plasterboard at ambient temperature. Finally, the thermal conductivity of board at elevated temperature is computed. A close fit between computed and experimental values derived from literature is found. Copyright 0 2009 John Wiley & Sons, Ltd.