Microstructural, physical and mechanical properties of aerated concrete containing fly ash under high temperature and pressure

This study analyzed the effects of the use of fly ash as a replacement for the quartz sand on the compressive strength, dry density, moisture content and thermal conductivity of the aerated concrete. Based on the production of Class G2/04 aerated concrete, a commercially available wall construction element, aerated concrete samples were produced using the fly ash as a replacement for the silica sand (quartz sand) at additive ratios of 5%, 10%, 15%, 20%, and 25%. After steam curing the samples for 4 hours at 60 degrees C, they were cured in an autoclave for 6.5 hours at 180 degrees C under 11 bar pressures. As a result, the samples showed an increase in their dry density directly proportional to the fly ash addition ratio; and the highest dry density was found in the aerated concrete with 25% fly ash content. It was further observed that the moisture content increases as the fly ash addition ratio increases. Compressive strength was reduced with the fly ash addition. Thermal conductivity was found to be reduced up to fly ash addition ratio of 10%, however, it was then increased again up to fly ash addition of 25%. 25% fly ash replacement ratio is recommended in this study in terms of thermal conductivity, dry density, which are the most important properties of aerated concrete. Higher levels of fly ash replacement with sand can be actualized which can further enhance to the utilization of fly ash, raise awareness regarding waste minimization and reduce the overall costs of aerated concrete mixtures.