| Summary: | Palm oil fuel ash (POFA) has limited pozzolanic capability, only 10% can be used as cement replacement without decreasing concrete strength. Fly ash (FA) is known for low pozzolanic reactivity at early age. This study combines different ratios of hybrid POFA and FA to find an optimum combination that will produce optimum strength at early age. The fresh and mechanical properties were studied at ratios of POFA and FA at 60% replacing type II composite cement plus 2% silica fume (SF) addition. The experimental findings indicate that the highest and lowest slumps are POFA0FA60 and POFA30FA30, respectively. The compressive strength (7 days) of POFA30FA30 mix is the highest at 22 MPa and single replacement binders (POFA60FA0, POFA0FA60) are lowest at 12 MPa. However, at 28 days, mixes with higher ratios of FA shows higher increment of strength at 27 MPa, indicating that FA has started its pozzolanic activities and contributing to strength. The ratio of tensile and flexural strength POFA30FA30 to its corresponding compression strength is 25% and 61% lower than the control. For high early-age strength, POFA30FA30SF2 hybrid mix performs optimally, 7 days strength 80% of the 28 days and using a single material (60% POFA or FA), yields low early-age strength (50% at 7 days). © Published under licence by IOP Publishing Ltd.
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