Evolution of alkaline activated ground blast furnace slag–ultrafine palm oil fuel ash based concrete

•Alkaline activated palm oil fuel ash with blast-furnace-slag binder was developed.•The maximum 3-day compressive strength of 69 MPa was achieved.•The optimum slag content was found to be 20%.•The optimum alkaline activator to pozzolanic material (AAs/PMs) mass ratio is 0.5.•Optimum curing temperature and duration are 60 °C and 24 h, respectively.

The two locally available pozzolanic solid wastes (PMs) – ultrafine palm oil fuel ash (UPOFA) and ground blast furnace slag (GBFS) – have been used as base materials to develop high alkaline activated strength concrete. The samples were prepared with combined aggregate modulus of 3.66 and at constant GBFS/PM that varied from 0 to 0.3. The combined alkaline activators (CAA) (Na2SiO3 and NaOH) to PMs ratios (CAA/PMs), temperature and curing durations also varied as 0.45–0.55, 25–90 °C, and 6–24 h, respectively. The findings revealed that the strength at 3-day and 28-day were 69.13 and 71.2 MPa, respectively and the respective optimum GBFS/PM, CAA/PM, temperature and curing duration are 0.2, 0.5, 60 °C and 24 h. GBFS was found to contribute to the soluble Ca, heterogeneity, and amorphousity of the product. This eventually facilitated the formation of suspected calcium-silicate-hydrate and the geopolymer products of Ca/Na-aluminosilicate-hydrate (C/NASH) that enhanced the compressive-strength results.