Recycled aggregate concrete with the incorporation of rice husk ash: Mechanical properties and microstructure

This work investigates the effect of partial replacement Portland cement with rice husk ash (RHA) on the mechanical properties and microstructure of recycled aggregate concrete (RAC). The workability, compressive strength, and splitting tensile strength tests were conducted from specimens with different RHA content (0%, 10%, 20%, 30% of binder) and recycled concrete coarse aggregate replacement ratios (0%, 50%, 100%). The results reveal that adding RHA improves the concrete's compressive strength, adversely affecting the workability and splitting tensile strength. In addition, the microstructure of the cement paste was analyzed using an X-ray diffractometer (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and the pozzolanic reaction action mechanism of RHA particles was proposed. The results show that RHA particles consume the calcium hydroxide (CH) generated by cement hydration due to the pozzolanic effect, increasing CSH content. The additional CSH refines the interface transition zone (ITZ) and the pore structure, resulting in a denser microstructure by optimizing the pore distribution. The findings also indicated that the synergistic preparation concrete of 100% recycled coarse aggregate and 30% RHA satisfies the design requirements for engineering application and significantly reduces the production cost of concrete and lower carbon emissions.