Agricultural Waste as a Cementitious Material — Rice Husk Ash

To reduce global CO2 emissions, researchers have been exploring various materials to replace Portland cement. Rice husk ash has been considered a promising alternative due to its widespread availability and increased production. However, the current process of using rice husk ash in construction involves burning the husks at high temperatures (700-900 °C), which is energy-intensive and generates CO2 emissions. In this study, we investigated the use of unprocessed rice husk ash, burnt at 400°C, as a replacement for Portland cement in concrete. We used rice husk ash at 10%, 20%, and 30% by mass and conducted tests to measure its reactivity, mechanical strength, and durability. Preliminary results indicate that the pozzolanic reactivity of unprocessed rice husk ash is similar to that of fly ash and other supplementary cementitious materials. However, the main peak of hydration is delayed compared to that of Portland cement. Mechanical strength and durability were found to be influenced by curing age, with samples cured for 90 days showing improved tensile strength. Furthermore, higher rice husk ash content at 90 days of curing resulted in lower chloride penetration, a parameter often used to describe the corrosion potential of cementitious matrices. Overall, our findings suggest that unprocessed rice husk ash can be a promising replacement for Portland cement in concrete, as it offers similar reactivity to other supplementary materials and has the potential to improve the durability of the resulting cementitious matrix.