Synergistic enhancement of low-carbon cement-based materials and CO2 sequestration via graded carbonization and composite design of rice husk ash

Abstract

To achieve solid waste recycling and carbon emission reduction in the cement industry, this study proposes a graded carbonation and functional compounding strategy that utilizes rice husk ash (RHA) as CO₂-sequestration functional carrier capable of active CO₂ sequestration and structural regulation. The progressively refined RHA samples (S1, S2, S3) were subjected to activation-carbonation treatment and graded compounding (Scheme A, B, C) and subsequently incorporated into an alkaline composite cementitious system at contents of 4%–20%. CO₂ adsorption tests combined with the Avrami model were employed to quantitatively evaluate the CO₂ capture capacity, while FTIR confirmed the coupling of physical adsorption and chemical carbonation processes. MIP, TG-DTG and SEM-EDS were used to systematically characterize the influence of the compounding schemes on the workability and mechanical performance of the system. The results demonstrate that progressive refinement from S1 to S3 transforms the pore structure of RHA from a macropore-dominated system to one enriched in micropores and mesopores, with the specific surface area increasing from 21.49 to 104.19 m²/g. FTIR and CO₂ adsorption experiments confirm the concurrent enhancement of physical adsorption and chemical carbonation, with the maximum CO₂ adsorption capacity increasing from 3.21 to 16.21 cm³/g. RHA-S3 exhibits a higher density of high-energy adsorption sites and enhanced adsorption kinetics. The RHA20-C group achieved the highest compressive strength of 51.11 MPa. TG-DTG analysis indicates that appropriate gradation enhances the pozzolanic reaction, promotes CH consumption, and facilitates the formation of stable carbonate phases. Pre-carbonation with CO₂ further refined the pore structure and reduced the total pore volume, thereby increasing the proportion of harmless pores from 30%–34% to 34%–40%. Graded compounding counteracted structural degradation induced by macropores. The proposed system reduced carbon emissions by up to 11.16% and achieved a carbon sequestration capacity of 39.48 g CO₂/kg. These findings provide a feasible pathway for the high-value utilization of solid waste and the development of low-carbon alkaline cementitious materials with integrated carbon sequestration functionality.