Investigation of the effect of autoclaving on foam concrete properties

Abstract

The physical, mechanical and thermal properties of foam concrete, one of the lightweight concrete types, are closely related to its density. A decrease in density leads to a decrease in volumetric stability in the fresh state on the one hand and an increase in drying shrinkage and weakening of mechanical properties on the other. In this study, it was aimed to determine the appropriate density for autoclaved foam concrete as a wall filling and thermal insulation material at the required standards. Water/binder (0.60), lime/cement (0.25) and binder/aggregate (0.62) ratios were kept constant in foam concretes produced at dry densities of 300, 400 and 500 kg/m3 using Portland cement, powdered quartz, hydrated lime and synthetic foaming agent. Half of the prism specimens (40 mm × 40 mm x160 mm) in each density class were cured in a climate chamber at 20 ± 5 °C and 95% relative humidity for 28 days, and the other half were autoclaved at 170 °C and 14 bar pressure for 12 h. In autoclaved foam concrete specimens, compressive strengths increased by 237, 323, 443%, flexural strengths increased by 116, 308 and 342%, while thermal conductivity coefficients decreased by 14, 15 and 17% due to increasing density. It was found that autoclaving significantly improved the mechanical and thermal properties of foam concrete and the standard requirements were met at a density of 300 kg/m3.