Fast microwave synthesis of high-silica natural soil based porous geopolymer

This study describes a simple microwave process for fabricating porous geopolymer-polymer based Shirasu soil. The porous geopolymer samples were synthesized using sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solution as alkaline solution in range of 0.5 M to 9 M. After mixing process, the geopolymer slurry was heated and stimulated geopolymerization reaction by different microwave powers at 200 W, 500 W and 700 W for 30 s, 60 s, 90 s and 120 s. The influence of NaOH concentration, microwave powers and heating times on the apparent bulk density, the water adsorption was focused. Results showed that the microwave powers and heating time affected the apparent bulk density, the water adsorption, and the densification of geopolymer matrix. Higher microwave power can promote higher water adsorption related to lower apparent bulk density. Moreover, the results revealed that the porosity and the nitrogen adsorption of geopolymers at 120 s of heating time increased with an increment of the NaOH from 1 M to 4 M. On the other hand, geopolymers activated by 200 W at 30 s could not be hardened. This work provides the feasibility of porous geopolymer synthesis based natural soil.