Microstructure and Thermal Conductivity of Hydrated Calcium Silicate Board Materials

The thermal conductivity of a porous material is controlled by the thermal conductivities of its components and their spatial arrangement within the composite structure, e.g., the material's microstructure. In this study, the relationships between thermal conductivity and microstructural parameters, such as porosity and pore size are examined for two calcium silicate boards of different densities. Thermal conductivities are measured from room temperature to 400°C using a transient plane source technique, for both the as-received boards and for a corresponding set of boards that were first heated to and held at 1000°C for at least 4 h. Microstructure is characterized by the measurement of the boards' bulk and powder densities and an assessment of pore size based on scanning electron microscopy. The experimentally measured thermal conductivities are then compared to those predicted by three previously presented theories for porous materials. A better agreement is observed between the experimental values and two of the three theories. Aging the boards at 1000°C has a small but significant effect on thermal conductivity, decreasing the room temperature values but increasing the 400°C ones.