Mechanical strength and microstructure of metakaolin/volcanic ash-based geopolymer composites reinforced with reactive silica from rice husk ash (RHA)

The physical, mechanical and microstructural properties of metakaolin/volcanic ash-based geopolymer composites were investigated, as well as the influence of the incorporation of a reactive silica from rice husk ash (RHA) in their performance. The geopolymer composites were designed by replacing metakaolin with volcanic ash, VA (10–30 wt%) and RHA (0–20 wt%). Physical and mechanical testing, FTIR, XRD, optical microscopic and SEM were used to characterize the geopolymer composites. The results showed that the mechanical strengths and physical properties were mostly affected by the VA content as well as RHA content where the optimal mechanical strengths (19.3 and 60.73 MPa for flexural and compressive strength, respectively) were obtained with the composite sample containing 20 wt% of VA and 10 wt% of RHA. This was due to the additive that enhances the compactness and microstructure of geopolymer matrices obtained and also the increase of SiO2/Al2O3 ratio with the addition of RHA. Synergistic use of metakaolin, volcanic ash, and rice husk ash for construction materials through alkaline activation looks like the upcoming trend to valorize these materials.