Measurement and modelling of thermal and physical properties of wood construction materials

Abstract

Construction materials exposed to fire conditions may decompose resulting in a loss of strength as well as contributing to the growth and size of the fire. Predicting the behavior of timber and other construction materials during a fire exposure requires accurate thermal modeling of the material considering both the effects of elevated temperature and material decomposition state (virgin to char) on the thermal and physical properties. This paper evaluates the use of different techniques to measure the porosity, permeability and thermal diffusivity of wood construction materials at different levels of decomposition due to a high temperature exposure. The porosity and thermal diffusivity values of wood exhibit similar changes with decomposition level. It was found that virgin and char material properties can be used in conjunction with thermogravimetric data to estimate material properties at intermediate decomposition levels. The findings can be used to reduce the number of experiments required to characterize other materials. Permeability was observed to be dependent on the structure and composition of the material. Scanning electron microscopy images revealed that decomposition increased the space between the otherwise compact-arranged elements (grain, particles), resulting in an increase in permeability. Consequently, permeability should be measured at different decomposition levels and direction to quantify the material changes due to a high temperature exposure.