Fiber-Cement Extrudates with Perlite Subjected to High Temperatures

Short fiber reinforced cement composites with large volumes of perlite have been investigated for their resistance to high temperature exposures. The composites were manufactured by the extrusion technique. The extruded products, thin plates and cylinders, were subjected to different thermal treatments with the maximal exposure temperatures, $T_m\text{,}$ of 200, 300, 450, and $600°C\text{,}$ and exposure periods, $T_h\text{,}$ of 1 and 10 h. After that, the residual mechanical properties of those extrudates, such as flexural strength, $f_t\text{,}$ compressive strength, $f_c\text{,}$ and modulus of elasticity, $E$ were measured and normalized to the corresponding values obtained from specimens without thermal treatments. The weight loss ratios, ω, of the composites were also monitored during the thermal treatment process. In addition, the microstructure of these composites was studied using a scanning electron microscope and the pore structure was examined by mercury intrusion porosimetry. It was found that $f_t\text{,}$ $f_c\text{,}$ and $E$ significantly decreased as $T_m\text{,}$ $T_h\text{,}$ or both increased. The property deterioration could be attributed to fiber melting or softening, dehydration of cement hydrates, and porosity increasing during the heating process. Flexural strength, $f_t\text{,}$ decreased more remarkably than compressive strength, $f_c\text{,}$ and modulus of elasticity, $E\text{.}$ The thin sheets reinforced by polyvinyl acetate (PVA) fibers showed more significant reduction in flexural strength than those reinforced by glass fibers due to the much lower melting point of PVA fiber. The composites, incorporating silica sand as aggregates, showed greater degeneration of mechanical properties than those using perlite as aggregates. The improvement of thermal resistance of perlite specimens could be attributed to the greater specific heat, lower thermal conduction coefficient, and the better thermal insulation property of perlite.