BEHAVIOUR OF LIGHTWEIGHT EXTRUDED CONCRETE SUBJECTED TO HIGH TEMPERATURES

摘要

Lightweight concrete manufactured by extrusion technique has been investigated for resistance to high temperatures. The concrete contains a large amount of perlite and a small percentage of fibres. The samples, thin plates and cylinders, were subjected to different thermal treatment with maximal exposure temperatures T_m up to 600℃ and exposure periods T_h from 1 hour to 10 hours. The residual mechanical properties, flexural strength f_t, compressive strength f_c and modulus of elasticity E, were measured and normalized to the values of those without thermal treatments. The microstructure of these composites was studied by SEM while the pore structure by MIP. It was found that f_t, f_c and E significantly decreased as T_m and T_h increased due to fibres melting and softening, cement hydrates degenerating and porosity increasing during thermal heating. f_t decreased more remarkably than f_c and E. The thin sheets reinforced by PVA fibres showed a more significant decrease in f_t than those reinforced by glass fibres, due to PVA fibres having much lower melting point. Besides, the composites, incorporating silica sand as aggregates, showed systematically more significant degeneration of mechanical properties than those using perlite as aggregates, which could be attributed to the greater specific heat, lower thermal conduction coefficient, and the better thermal insulation property of perlite.