Experimental evaluation of rice husk ash for applications in geopolymer mortars

Rice husks obtained from upland and lowland rice varieties were characterized for composition and content of ash. Each of the rice husk varieties was fired at temperatures of 600, 800 and 900 degrees C for a soaking period of 3 h. The resultant rice husk ash was analyzed for oxide composition and crystallinity using X-ray fluorescence and diffraction techniques, respectively. The generated amorphous ash with the highest silica content, together with metakaolin, aggregate, water, and an alkaline activator was employed to formulate geo-polymer mortar prisms according to the standard EN 196-1. Results showed that the content of ash in the varieties ranged from 18.3% to 28.6% dry basis. Out of this, 89 wt%-96 wt% was silica, with amorphous and crystalline forms of silica obtained at 600 degrees C and 900 degrees C, respectively, regardless of the rice variety. However, at 800 degrees C, the silica in the generated ash exhibited both amorphous and crystalline forms. The amor-phous ash generated at 600 degrees C was used in formulation of geopolymer mortars. Compressive and flexural strength of the formulated mortar after 7 days of curing was 1.5 and 1.3 MPa, respec-tively. These results reveal the firing protocol to form pozzolanic ash, with potential applications in mortar production.

Automated summary

Different rice husk varieties were analyzed for ash content and composition, then fired at different temperatures to produce ash for geopolymer mortar formulation, with silica as the main component. The study found that the ash had potential applications in mortar production, indicating the effectiveness of the firing protocol for producing pozzolanic ash.