Strength Development by Rice Husk Ash With Partial Replacement of Cement

Rice husk ash is a byproduct of agriculture that has potential pozzolanic qualities that could increase the mechanical strength and durability of concrete. RHA is produced during the milling process and accounts for about 20% of the weight of rice; the world produces more than 649.7 million tons of rice annually. Burning this abundant byproduct at regulated temperatures produces ash that has a high silica content, which makes it a useful addition to cementitious materials. This research examines the impact of partially replacing Ordinary Portland Cement (OPC) with RHA (at 0%, 5%, 10%, 15%, 20%, and 25%) on the compressive strength development of concrete. The core contribution of this research is the development of a predictive model to estimate the 28-day compressive strength from early-age tests, thereby reducing the reliance on the standard 28-day curing period for strength assessment. Using linear regression analysis on experimental data from 7, 14, and 28-day tests, a set of unique equations was formulated for each RHA replacement percentage. The results indicate that a 20% replacement of cement with RHA yielded the highest 28-day compressive strength, demonstrating a significant improvement over the control mix. Furthermore, the predictive models showed a high coefficient of determination (R² > 0.82), confirming their validity and accuracy for estimating long-term strength based on early-age results for RHA-blended concrete. This work supports the use of RHA as a sustainable and performance-enhancing supplemental cementitious ingredient by offering a useful technique for accelerating strength measurement in concrete mixes containing it.