Impacts of silica modulus on the early strength of alkaline activated ground slag/ultrafine palm oil fuel ash based concrete

The alkaline activated ground steel slag/ultrafine palm oil fuel ash (AAGU) concretes were used to study effects of silica moduli (Ms = SiO₂/Na₂O) that varied from 0.915 to 1.635 on strength and microstructure of the product sythesized by using combined alkaline activators (CAA) − 10 M NaOH_aq and Na₂SiO_3aq with an initial silica modulus (Ms) of 3.3. The scanning-electron-microscope coupled with energy-diffractive-spectroscopy (EDS + SEM) showed that Ms had significant effects on the product compactness, elemental composition and density while Fourier transform infrared spectrometer indicated that Ms positively affected the product amorphousity, homogeneity and structural units due to the difference in Si–Al substitution. However, at the workable total-activators to prime materials ratio (CAA/PMs = 0.5) and the total Ms range of 0.915–1.635, there existed an insignificant range in concrete strength as the maximum and minimum strength were 69.13 MPa (Ms = 1.635) and 65 MPa (Ms = 0.915), respectively.