Effects of addition of Al(OH)3 on the strength of alkaline activated ground blast furnace slag-ultrafine palm oil fuel ash (AAGU) based binder

•This study investigated the effects of Al(OH)3 on the alkaline-activated-binder.•The possibility of formation of different distinctive products is established.•Al(OH)3 enhances Si–Al substitution, amorphousity and carbonation of the products.•The 3-day compressive-strength of 42–49.5 MPa with inclusion of 3–4 wt.% Al(OH)3.

Effects of Al(OH)3 content on the compressive-strength of alkaline activated ground blast furnace slag (GBFS)-ultrafine palm oil fuel ash (UPOFA) based mortar (AAGU) were investigated. The mortar was activated with combined activators (Na2SiO3aq of silica modulus (Ms = SiO2/Na2O) of 3.3 and 10 M NaOHaq). The Scanning Electron Microscope couple with energy dispersive X-ray (SEM + EDX) revealed the possibility of formation of distinctive products of calcium-silicate-hydrate (C-S-H) and Ca/Na-alumino-silicate-hydrate (C/N-A-S-H) while Fourier transform infra-red spectroscopy (FTIR) revealed the existence of higher degree of Si–Al substitution, amorphousity and carbonation as a result of inclusion of Al(OH)3 in the mixture. The 3-day compressive-strength of AAGUAl mortar increased with Al(OH)3 up to optimum value of 4 wt.% of PMs (GBFS + UPOFA) but started decreasing when the Al(OH)3 is outside the optimum. The strength of 42–49.5 MPa could be achieved at the Al(OH)3 dosage of 3–4 wt.% while the equivalent SiO2/Al2O3 molar-ratio ranged from 6.72 to 8.94.