Thesis (M.Sc.)--Chulalongkorn University, 2007

The purpose of this research is to study and develop lightweight concrete using waste products; namely, rice husk ash and biomass fly ash. The wastes were obtained from a biomass power plant as replacement materials for main ingredient, Portland cement, to make lightweight concrete. Experimental programs involve determination of proper manufacturing method of autoclaved aerated lightweight concrete using blowing agent and duration of curing time based on density and compressive strength of lightweight concrete. Optimum amount of aluminium powder and water-to-binder ratio were investigated for all mixes throughout the experimental programs. Physical and chemical characteristics of biomass fly ash were also determined. The physical and mechanical properties of lightweight concrete samples evaluated include dry density, compressive strength, and water absorption. The testing results showed that the optimum duration of high pressure curing was 14 hours. While the optimal amount of aluminium content, water–to-binder ratio, and binder-to-aggregate ratio of lightweight concrete were 0.3% of aluminium powder by total solid weight, 0.472, and 55:45, respectively. The use of fly ash as the main ingredient to replace Portland cement resulted in decrease in density significantly. From main testing results, it can be used to noted that the optimal mix proportion be 30%RH, 30%B3 which used the highest amount of biomass fly ash replacement and did not compromise the aerated lightweight mortar properties as compared with control mix.. Finally, it can be concluded that fly ash from a biomass power plant can be sufficiently used as cement replacement for lightweight concrete block production. Beside the utilization of the wastes, biomass fly ash, pollution, and disposal problems can also be mitigated as a result.