Strength and microstructure of alkali-activated binary blended binder containing palm oil fuel ash and ground blast-furnace slag

In this study, combinations of ultrafine palm oil fuel ash (UPOFA) and ground blast furnace slag (GBFS) have been used to study the compressive strength and microstructure of the alkali-activated GBFS-UPOFA (AAGU) binary blended binder paste. GBFS (G) was added in varying percentages to alkaline activated UPOFA (AAU) such that the ratio of G/U + G varied from 0 to 0.3 at interval of 0.05. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) with a final silicate modulus (Ms = SiO2/Na2O) of 1.58 were used as activators. Pozzolanic materials (G + U), activators, and free water were combined by weight ratios as: 1/0.35/0.02. A 28-day compressive strength of 44 MPa was achieved for G/U + G of 0.2 cured for 24 h at 60 °C. Finally, characterization was done using X-ray diffraction, SEM and FTIR and the analyses revealed that GBFS contributes significantly to the mechanical strength by pore filling effects, and the formation of additional calcium (aluminate) silicate hydrate (C(A)SH).