The role of amino nano silica in enhancing carbon capture and strength development in MgO-substituted MSWI fly ash blended mortars

The cement industry is a critical target for CO₂ mitigation, with carbon capture and utilization in cementitious materials offering a promising pathway. However, existing systems face limitations in balancing CO₂ sequestration efficiency, mechanical performance, and industrial waste valorization. This study addresses the gap in understanding synergistic interactions within multi-component binders by investigating a novel cementitious system (MMC) of reactive MgO, municipal solid waste incineration fly ash (MFA), cement and amine-functionalized nanosilica (NH2-NS) under accelerated carbonation. The NH2-NS acts as a CO₂ capture accelerator, while MgO and MFA provide complementary alkalinity and reactive phases for carbonate formation. The results reveal that increasing MgO substitution leads to higher alkalinity, which promotes carbonation reactions. MgO-substituted mixtures formed magnesium calcite and a denser morphology, which reduced pore volume and increased the strength of MMC compared to non-carbonated pastes. Accelerated carbonation significantly enhanced the compressive strength of MMC, particularly for samples containing 40 % MgO. NH₂-NS doping further enhanced CO₂ capture, increasing the carbonized area by 14.4 % and refining the pore structure by reducing harmful pores. SEM and thermodynamic simulations indicated that NH₂-NS promoted the formation of C-S-H and M-S-H gels, improved the carbonation products' morphology, and increased the Mg/Ca ratio, contributing to the enhanced mechanical properties of the material. These findings suggest that MMC containing MgO and NH₂-NS holds promise for sequestering CO₂ and enhancing the mechanical performance of cementitious materials, offering potential for use in negative emission technologies.