IntroductionLarge amounts of CO₂ emissions have caused escalating challenges of global warming risk. The construction industry significantly contributes to global CO₂ emissions, prompting the need for sustainable building materials. Carbon capture, utilization, and storage (CCUS) technologies provide a promising solution by reducing emissions and integrating carbon storage capabilities into materials. To this end, foam concrete, a lightweight porous material (normally 500-1600 kg/m³), has gained increasing attention for its significant advantages in energy-efficient and low emission buildings. Traditional foam concrete is lightweight with good insulation properties but has low strength and limited environmental benefits. In contrast, CO₂ foam concrete offers the potential of reducing emissions during production and CO₂ sequestration, making it a more environmentally friendly alternative.The objective of this research was to develop a high-strength CO₂ foam concrete (HSCFC) that incorporates carbon capture and storage (CCS). By enhancing foam stability and optimizing the concrete mixture, this study firstly developed a new HSCFC product with assessing the CO₂ sequestration efficiency and micro/macro performance of the devloped material, thereby verifying its potential as both a sustainable building material and a solution for carbon reduction.MethodsThe design concept of HSCFC was based on integration of a CO₂ foam precursor into a high-strength cement-based paste, utilizing particle packing theory to optimize strength and density. The CO₂ foam was produced using a amphiphilic nano-silica modified sodium dodecyl sulfate foaming agent, enhancing the stability of the foam and preventing collapse of foam concrete. The HSCFC was prepared by mixing the CO₂ foam with a high-strength cement slurry, followed by curing and a series of micro and macro testing to evaluate HSCFC performance, including compressive strength, concrete density, pore structure and microstructures.Results and discussion1) The CO₂ foam exhibited a well-distributed pore size of 50-100 μm, which grew over time due to natural drainage and coalescence processes. The stability of the foam was attributed to the surfactant and nanoparticle interactions, which prevent CO₂ diffusion and enhance liquid film strength. The overal performance of CO₂ foam met the requirments of the Chinese standard for the concrete foam, which thus could be used to fabricate the foam concrete products. 2) The rheological behavior of HSCFC followed the Bingham model, with an increase in yield stress as CO₂ foam volume increases, up to 110% compared to the control group. However, excessive foam content led to a reduction in yield stress due to the weakening of the matrix from enlarged pores. The plastic viscosity was inversely proportional to foam content, enhancing workability by reducing internal friction. 3) The increase in CO₂ foam content led to the decrease in compressive strength of HSCFC. The compressive strength of HSCFC was found to be significantly higher than conventional foamed concretes, which is more than double that of typical foam concretes of similar density. Microhardness tests revealed values above 90 HV, close to ultra-high-performance concrete, despite the presence of foam. 4) X-ray computed tomography (XCT) analyses indicated that the pore structure of HSCFC became more complex as foam content increased, with the peak value of the pore size enlarging from 162.8 μm to over 1100 μm. This indicated the importance of balancing the compressive strength and density for the HSCFC. Additionally, using CO₂ foam improved the cement hydration degree and led to the in-situ growth of calcium carbonate (CaCO₃) on pore walls, enhancing pore wall strength. However, excessive foam amounts resulted in non-uniform pore distribution, leading to reduced material strength. 5) The thermal conductivity of HSCFC was lower than conventional concretes due to its porous structures. This property made the material suitable for energy-efficient buildings, where insulation is critical for reducing energy consumption. Therefore, the use of CO₂ foam could realize the synergy of active and passive carbon reductions by carbon mineralization and decreasing engergy uses respectively.ConclusionThis research demonstrated the successful design and development of a high-strength CO₂ foam concrete system with superior mechanical properties, enhanced carbonation, and thermal insulation capabilities. The use of CO₂ foam not only provided an effective CCUS solution but also significantly improved the performance. The synergistic effects of foam stability, internal carbonation, and matrix densification showed a promising pathway for the sustainable development of carbon-neutral building materials. Future research could focus on improving the overall performance of HSCFC and investigating its long-term service values. This material presents a novel approach for CO₂ capture and utilization, alongside advancements in foam concrete technology. The developed materials can be further optimized to improve carbon sequestration efficiency, facilitating their use in innovative structures like energy-efficient and floating buildings.