A study on recycling of coal bottom ashes as the raw material for geopolymer mortars

There are about two million tons of thermal power plant ashes produced annually by Tai-Power Company in Taiwan. Around 80 percent of the unburned material is entrained in the flue gas and is captured and recovered as fly ash. The remaining 20 percent of the ash is dry bottom ash. Most of the researchers were concentrated in the application of coal fly ash, however, only few works had been done in recycling of the coal bottom ashes. The aim of this research work is using coal bottom ash as raw material to fabricate fire resistance geopolymer. The bottom ash-based geopolymers were manufactured by controlling different solution mole ratio of SiO2/Na2O and tried to compare the fire resistance and mechanical properties with standard silica sand geopolymer. Experiment results showed that the compressive strength of the geopolymer mortar was related to solution SiO2/Na2O mole ratio, and the lower the solution mole ratio of SiO2/NaO, the higher is the compressive strength. On the other hand, bottom ash-based geopolymer showed excellent performance in the characteristic of fire resistance properties. Therefore, the coal bottom ash-based geopolymer have great application potential for building materials in the future.