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Controlled burning of rice husks at<700°C produced rice husk ash (RHA) which is predominantly amorphous silica (SiO2). RHA was used as a substitute for laterite and cement in proportions of 5%, 10%, 15%, 20%, 25% and 30% of concrete. The concrete was cured for 7 days, 14 days, 21 days, and 28 days respectively. It was observed that 20% of RHA provides the optimum strength. The effects of different particle sizes of 75, 150, 212, 300, 425 and 600 microns (µm) were tested using a compression test machine. A graph of average strength against particle size indicates 2.9 Nm-2 as the optimum strength at 75 µm and 1.2 Nm-2 as the minimum at 150 µm. From the ash size distribution, the presence of grains of several different sizes was observed. The grains were weighed using a weighing machine and a graph of particle size against percentage plotted to determine the particle size distribution. This showed that rice husk ash (RHA) is coarse grain material.