Carbonation curing provides a practical route to reduce the carbon footprint of cement by converting CO 2 into stable carbonates while improving early-age performance. However, its efficiency is limited by moisture-controlled diffusion barriers and inconsistent curing protocols. This study couples process optimisation with waste-derived biochar to enhance CO 2 uptake and strength development in cement pastes. An L9 orthogonal design using rice husk biochar (RHB) identified water-to-cement ratio, preconditioning duration, and biochar dosage as the governing parameters. The optimal combination—W/C = 0.40, 5% RHB, and 3 h preconditioning—produced substantial improvements in CO 2 absorption, pore refinement, microhardness gradients, and both early and 28-day strengths. To evaluate the generality of this approach, two types of additional agricultural waste biochar, straw biochar (SB) and coconut shell biochar (CSB), were incorporated under the optimized curing regime. SB mainly acted as a filler, limiting CO 2 transport, whereas CSB introduced a favorable meso–macropore network that enhanced CO 2 transport, achieving carbonation degrees above 40% and early-strength gains of approximately 20 MPa at 5% dosage. These findings highlight the value of transforming bio-waste into functional porous additives that enable more efficient CO 2 curing, which supports scalable, circular-economy strategies for low-carbon cement production.
Lin et al. (Mon,) studied this question.