Development of porous fly ash-based geopolymer with low thermal conductivity

• Using industrial waste fly ash as main material to reduce its environmental endanger.
• Its synthetic process is simple and environmentally friendly and needs no sintering.
• Its thermal conductivity is as low as 0.0721 W/m K.
• It can be used as low cost insulation material in some conditions.
• The properties of samples made at various experimental conditions were discussed.

Porous fly ash-based geopolymer material was produced using fly ash and sodium water glass as original material and H2O2 as foaming agent. The changes caused by the geopolymerization and decomposition of H2O2 on the properties of the final products were investigated by applying curing on geopolymer mortars with different amounts of sodium water glass (60, 80 and 100 g) and H2O2 (4, 6 and 8 g) added at various curing temperatures. The samples were cured at two different temperatures (55 and 85 °C). Physical properties such as porosity, density and thermal conductivity and mechanical property were determined from the completely dried samples. As a result, this study confirmed that the amount of sodium water glass, H2O2 and curing temperature had effects on properties of the samples. Given the compressive strength obtained and the environmental and economic effect, the optimal thermal curing temperature and the amount of sodium water glass and H2O2 were 55 °C, 80 g and 6 g, respectively. Sample synthesized at this condition had porosity of 79.9%, thermal conductivity of 0.0744 W/m K and compressive strength of 0.82 MPa. Therefore, it shows promise as thermal insulation material in some situations.