● 28-day strength reached 60.97 MPa with lime–biochar modification. ● Strength increased by 11.4% compared to conventional AAS. ● 1 wt.% biochar optimized pore structure and CO₂ uptake. ● Up to 86.8 kg CO₂ uptake per ton of binder achieved. This study investigated the synergistic effects of calcium oxide (CaO) and wood waste-derived biochar incorporation on the hydration behavior, microstructure, carbon sequestration capacity, and mechanical performance of CO 2 -cured alkali-activated slag (AAS) pastes. The proposed dual-modified system achieved a 28-day compressive strength of up to 60.97 MPa, representing an 11.4% increase over the control mixture. Vaterite and calcite were the main carbonation products, while the C–(N)–A–S–H, portlandite, monocarboaluminate, and hydrotalcite-like phases were the primary hydration products. CaO accelerated early hydration and facilitated the formation of Ca-rich phases, whereas biochar-enhanced CO 2 uptake resulted in portlandite consumption and subsequent carbonate formation. The 1 wt.% biochar sample exhibited the densest and most refined pore structure, while higher dosages increased the total porosity. Flowability reduced with the volume of biochar due to its large surface area. Overall, combining biochar and CO 2 curing in CaO-activated slag systems reduces CO 2 emissions during binder production for ordinary Portland cement (OPC) and enables the development of a low-carbon binder through biochar’s sequestration potential (∼3 kg CO 2 per kg biochar) and CO 2 uptake during curing (up to 86.8 kg CO 2 per ton of binder). These results demonstrate the feasibility of producing high-strength low-carbon binders suitable for practical structural and precast construction applications.
Kennedy et al. (Wed,) studied this question.