The performance of fire resistive materials (FRMs) for structural steel is based on their abilities to remain adhered to the steel substrate and to limit the substrate's temperature rise during a fire exposure. While this paper will focus on the microstructure and thermal conductivity of FRMs, measurements of their adhesion properties are also a critical component of the overall NIST research program for these materials. As with any energy transfer analysis, the thermophysical properties of the FRMs, such as their specific gravity, heat capacity, heats of reactions and phase changes, emissivity, and thermal conductivity, determine their effectiveness in limiting the transfer of energy from the fire to the steel. For simulating this performance using computer models, accurate values of these properties as a function of temperature over a quite large temperature range are necessary (1).
To date, efforts to relate these thermophysical properties to the underlying three-dimensional microstructures of these materials have been limited. This is somewhat surprising in that the potential payoffs of establishing quantitative relationships between microstructure and performance properties should be large, in terms of both optimizing existing products and developing new materials and protection strategies. This paper focuses on the linkages between microstructure and thermal conductivity. An experimental technique based on using a slug calorimeter to determine effective thermal conductivities as a function of temperature will be presented and two approaches for computing thermal conductivity from microstructural characteristics will be explored.