Enhancing CO₂ uptake in concrete using activated rice husk ash and zeolite 13X: A performance evaluation on mechanical, durability and carbonation study

The more carbon footprint associated with cement manufacture has enhanced the search for sustainable alternatives capable of successful concrete performance while enabling carbon sequestration. This research work studies the combined effect of agricultural and mineral-based additives, namely rice husk ash (RHA), zeolite 13X (Z13X), and along with their activated forms, on the mechanical properties and carbon capture potential of concrete. Concrete mixtures with varying replacement levels of above materials were prepared and their mechanical properties were evaluated. In addition, the carbonation behaviour of hardened concrete was evaluated depth of carbonation and CO₂ uptake capacity were assessed using the mass gain method, while the compressive strength of carbonated concrete was determined and compared with non-carbonated specimens to evaluate the influence of carbonation on structural performance. The test results show that an optimum replacement level of nearly 10% gives the most favourable balance between strength and carbonation performance. Among the investigated materials, followed by RHA with 41.11 N/mm², primarily due to enhanced particle packing and pozzolanic reactions that promote the formation of additional C–S–H gel. Activated materials exhibited significantly greater CO₂ uptake and carbonation depth, with activated rice husk ash (AR-10) achieving the peak CO₂ absorption of 1.8%. However, excessive carbonation in highly reactive activated materials slightly reduced compressive strength. The test results indicate that an optimum replacement level of 10% provides the best overall performance. The AR-10 mix achieved the highest CO₂ uptake of 1.8%, while maintaining satisfactory mechanical properties. The RHA-10 mix exhibited the highest compressive strength of 41.11 MPa , attributed to improved particle packing and enhanced pozzolanic reactions that promoted the formation of additional calcium silicate hydrate (C–S–H) gel. Activated materials showed greater carbonation depth and CO₂ absorption than non-activated. Although increased carbonation in highly reactive activated mixes resulted in a slight reduction in compressive strength, the carbonated specimens retained measurable residual compressive strength, with the extent of strength retention varying according to the replacement material and dosage. Further, the results demonstrate that the integration of agricultural waste and mineral additives can simultaneously enhance mechanical properties and carbon sequestration capacity, offering a favourable strategy for the advancement of low-carbon and sustainable concrete systems.