Rice husk is a byproduct of rice production. Appropriate burning the husk produces the rice husk ash containing amorphous silica as a main component. Currently, the ash is expected as a biomass resource. In the present study, the rice husk ash was used to prepare potassium silicate solution. Geopolymer materials were synthesized by a reaction between the potassium silicate solution and metakaolin. In addition, Si powder and a dispersing agent were added to the geopolymer precursor paste to prepare a porous material, and its applicability as a heat insulating material was investigated. Assuming application to heat insulating materials, the effects of alkali concentration in the potassium silicate solution on the curing rate and density were investigated, and the thermal conductivity properties were evaluated. As a result, the curing rate of the geopolymer precursor increased with increasing alkali concentration of the potassium silicate solution. As the concentration increased, in addition, the bulk density and the thermal conductivity decreased. It was found that the heat insulation performance of the porous geopolymer is controlled by adjusting the alkali concentration in the potassium silicate solution.
