Valorisation of rice husk ash as an activator in the preparation of alkali-activated cements based on electric arc furnace slag

Abstract Rice husk ash (RHA) was employed as a silica source to produce an alternative sodium silicate solution through the dissolution of varying quantities of RHA in an 8 M NaOH solution. The solution was employed in the production of alkali-activated cements based on electric arc furnace slag (EAFS). Solutions were prepared with varying activator modules (Ms, molar ratio SiO₂/Na₂O) of 0.60, 0.85, 1.00, and 1.15. As control samples, slags were activated with 8 M NaOH (Ms = 0.0) and with 8 M NaOH in conjunction with commercial sodium silicate (Ms = 1.0). Mechanical, physical, mineralogical (XRD, FTIR), and microstructural (SEM/EDS) tests were conducted to characterize the obtained pastes. The results of the FTIR and SEM analyses indicated that the SiO₂/Na₂O ratio exerts a significant influence on the reaction products formed. At Ms values higher than 0.85, the predominant reaction product was observed to be a more cross-linked hybrid gel (N,C)-A-S-H. Lower modules resulted in the predominant formation of C-A-S-H gel and a more porous structure with lower mechanical properties. Pastes activated with the alternative RHA solution and Ms = 1.0 exhibited a composition, microstructure, and strength that was similar to or superior to those prepared with conventional commercial activators.