Compressive Strength and Microstructural Characteristics of Binary Blended Cement Mortar Containing Palm Oil Fuel Ash

The use of non-traditional cement replacement materials such as POFA in concrete has attracted many researchers, likewise this study attempted to keep investigating the ability of utilizing the ultra-fine treated palm oil fuel ash (u-TPOFA) as supplementary cementitious materials (SCMs) in Portland cement mortar. The u-TPOFA was used as SCM to produce binary blended cement mortar (BBCM) at different replacement levels of 30, 40, 50 and 60 wt% of ordinary Portland cement (OPC). The compressive strength (CS) was evaluated for all the cured samples at various ages of 3, 7, 14, and 28 days. The test results showed that the CS development improved with curing age as expected in all cases and a clear influence of u-TPOFA replacement levels on CS of the BBCM was observed. The CS at early ages of the BBCM was lower than the control binder mortar (CBM). However, the CS started to increase after 7 days of curing. The highest CS among all the BBCM was observed with u-TPOFA replacement level of 30 wt% from OPC which achieves 81.7 MPa at 28 days, whereas the CBM registers the highest CS of 83.73 MPa. The results for the CS concur with the phase changes based on XRD and TG analyses. The changes in CS was as a result of the formation of more C-S-H and C-A-S-H gel binders and less Ca(OH)₂ content remained in the structure.