Effect of palm oil fuel ash fineness on the microstructure of blended cement paste

This paper presents the effect of palm oil fuel ash fineness on the microstructure of blended cement paste. Palm oil fuel ash (POFA) was ground to two different finenesses. Coarse and high fineness palm oil fuel ash, with median particle sizes of 15.6 and 2.1 μm, respectively, were used to replace ordinary Portland cement (OPC) at 0%, 20% and 40% by binder weight. A water to binder (W/B) ratio of 0.35 was used for all blended cement pastes. The amorphous ground palm oil fuel ash was characterized by the Rietveld method. The compressive strength, thermogravimetric analysis and pore size distribution of the blended cement pastes were investigated. The test results indicate that the ground palm oil fuel ash was an amorphous silica material. The compressive strengths of the blended cement pastes containing coarse POFA were as high as that of OPC cement paste. Blended cement paste with high fineness POFA had a higher compressive strength than that with coarse POFA. The blended cement pastes containing 20% of POFA with high fineness had the lowest total porosity. The Ca(OH)2 contents of blended cement paste containing POFA decreased with increasing replacement of POFA and were lower than those of the OPC cement paste. In addition, the POFA fineness had an effect on the reduction rate of Ca(OH)2. Furthermore, the critical pore size and average pore size of blended cement paste containing POFA were lower than those of the OPC cement paste. The incorporation of high fineness POFA decreased the critical pore size and the average pore size of blended cement paste as compared to that with coarse POFA.