Effects of nano-SiO2 and different ash particle sizes on sludge ash–cement mortar

The effects of nano-SiO2 on three ash particle sizes in mortar were studied by replacing a portion of the cement with incinerated sewage sludge ash. Results indicate that the amount of water needed at standard consistency increased as more nano-SiO2 was added. Moreover, a reduction in setting time became noticeable for smaller ash particle sizes. The compressive strength of the ash–cement mortar increased as more nano-SiO2 was added. Additionally, with 2% nano-SiO2 added and a cure length of 7 days, the compressive strength of the ash–cement mortar with 1 μm ash particle size was about 1.5 times better that of 75 μm particle size. Further, nano-SiO2 functioned to fill pores for ash–cement mortar with different ash particle sizes. However, the effects of this pore-filling varied with ash particle size. Higher amounts of nano-SiO2 better influenced the ash–cement mortar with larger ash particle sizes.