Evaluation of rice husk ash and Portland cement reinforced clay for use as road subgrade using the CBR test

The amount of rice husk waste generated in Nigeria is posing serious threat to the environment and the ecosystem. Utilizing these wastes for productive purposes has been of interest to government and researchers. This study evaluated rice hush ash (RHA) reinforced clay for use as road subgrade, using the California Bearing Ratio (CBR) as prescribed in ASTM D1883. The clay was mixed with RHA/Portland cement in the ratios of 0% (control), 2.5%, 5%, 7.5% and 10%. Results showed that the physical properties of the soil in its natural form did not meet the FMW&H guideline specification for subgrade road; thus there was a need to stabilize the soil. As the percentage of RHA increased, the strength of the soil increased, with the maximum strength observed at 5% RHA, beyond which there was decrease in the load bearing capacity of the soil. Optimal CBR ratio of 9.35% was obtained at 5% RHA, 5% Portland cement and 90% clay soil. Comparing this result with the soil at natural state (CBR=1.55%), it shows that RHA is a good improvement agent for the soil. This research can be beneficial to highway road construction in areas with similar soil conditions.