A new composite based on gypsum matrix and mineral additives: Hydration process of the matrix and thermal properties at room temperature

• Plaster particles size has more influence than dehydrate on the kinetics of hydration.
• The matrix thermal conductivity decreases from 0.58 to 0.27 W m−1 K−1 with vermiculite.
• Numerical model is well suited for thermal conductivity until a porosity of 40%.
• Above 40% isolated porosity becomes open pores well described by Landauer model.

The present work aims to investigate a new composite used in building construction. The starting products are an industrial plaster, mica, vermiculite and water. The chemical characterization of the matrix reveals the presence of dihydrate (5 wt%) in plaster which modifies the setting time of the hydration process. This phenomenon is not observed with a pure plaster suggesting that another parameter modifies the kinetics: the particle size. Indeed, the setting time decreases of 30 min when the plaster is sieved from 150 to 10 μm. The evolution of the thermal properties versus the nature and the quantity of additives is also studied. Vermiculite proves to be well suited to decrease the thermal conductivity of the panel (0.58–0.27 W m−1 K−1) whereas mica tends to increase it. The analytical model of Hashin and Strikman well describe the evolution of the thermal conductivity until a porosity of 40%.