Upcycling municipal solid waste incineration fly ash with rice husk ash-derived activators for geopolymer composites

Abstract

This study investigates the feasibility of using rice husk ash (RHA) as a sustainable silica source for synthesizing sodium waterglass which serves as an activator in geopolymer composites based on municipal solid waste incineration fly ash (MFA). Six different mixes were prepared using RHA-derived activators and without activators. The activation moduli (Ms) ranged from 0.0 to 1.10. The mixes were evaluated for compressive strength, density, water absorption, porosity, capillary water absorption, and microstructural characteristics using scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). To compare the mechanical strength, total porosity, and water absorption of mixes, a one-way analysis of variance (ANOVA) was conducted at a significance level of 5%. The RHA30 mix (Ms = 1.0) obtained the highest compressive strength of 31.56 MPa at 28 days, compared to just 7.19 MPa for the NaOH-only mix (Ms = 0.0). Bulk density increased from 2265 kg/m³ (MFA-RHA0) to a peak of 2861 kg/m³ (MFA-RHA30) while total porosity and water absorption decreased to 16.83% and 4.51%, respectively. Capillary water absorption was also reduced with the sorptivity coefficient (k) dropping by 15.46% in the optimal RHA mix. Microstructural analyses confirmed the formation of dense N/C-A-S-H and C-A-S-H gels. XRD and FTIR results indicated successful polymerization and development of amorphous aluminosilicate networks with spectra shifts confirming improved cross-linking.