Silica fume-induced phase and structural modifications in biomass-based geopolymer mortars

The study explores the influence of silica fume (SF) on the mechanical and microstructural properties of biomass-derived geopolymer mortars. Three pozzolanic precursors rice husk ash (RHA), palm shell ash (PSA), and laterite soil ash (LSA) were combined with SF at substitution levels of 0–20% by binder weight. Alkaline activation employed 6M NaOH and 2.65M sodium silicate. Compressive strength tests, XRD, FTIR, and SEM analyses were conducted. Results showed a substantial strength increase, particularly in RHA-based mortars, from 19 MPa to 52 MPa at 20% SF. XRD and FTIR analyses indicated enhanced gel formation with dominant amorphous phases and stronger Si–O–T and O–H vibrations. SEM images revealed denser microstructures with lower porosity. These findings demonstrate that SF significantly enhances geopolymerization and mechanical performance. The study offers new insights into the use of biomass-derived materials and SF for developing high-performance, sustainable construction mortars.