| Summary: | Rice husk ash (RHA), a byproduct of the rice industry, is the primary source of amorphous silica for producing sodium silicate solutions to replace standard commercial sodium silicate in geopolymer mixture design. The effect of various concentrations of NaOH used as an activator to produce epoxy-geopolymer cement was studied. Three initial concentrations of NaOH were used (8, 10, and 12M) to examine the optimum dissolution and formation of silica oligomers that can function as the activator during the geopolymerization. The result indicated the increase of NaOH concentration raises the silica yield strength. The silica yield found was 65.84%, 70.53% and 72.06% on NaOH use of 8, 10, 12 M, respectively. IR-spectra results showed silica functional groups and the sodium silicate were successfully synthesized. The IR spectra indicated the appearance of hydroxyl bonds, which strengthen the geopolymer matrix. SEM results showed the C-S-H and N-A-S-H bonds in the geopolymer. With 10M NaOH, the compressive strength of the geopolymer cement paste was optimal at 27.53 MPa. Thus, Rice husk ash (RHA) is feasible to be used as an activator in high calcium fly ash-based epoxy geopolymer cement. © Published under licence by IOP Publishing Ltd.
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