Performance of rice husk ash under different two periods combustion conditions and effect of particle size on the strength of mortar

This study aims to investigate the effect of two periods burning conditions on the chemical properties of rice husk ash (RHA). Gray correlation theory analysis combined with a scanning electron microscope was used to precisely analyze the impact of RHA particle sizes on the mechanical properties and microstructure of mortar. The experimental results reveal that prolonging residence time at 600 ºC could significantly reduce the carbon content and boost the silica content in RHA. The potassium content of RHA could be reduced by burning at a low and then high temperature. Additionally, gray correlation analysis indicated that the particle sizes of 5 -10 μm in RHA could positively accelerate the gaining strength of mortar, followed by 10-15 μm and < 5 μm. At the micro-scale, incorporating RHA with a mean particle of 5.9 μm could accelerate the formation of calcium silicate hydrates having a low Ca/Si by secondary hydration reaction, subsequently leading to the increment of mortar strength.