Preparation and carbon sequestration properties of supercritical CO₂ foamed concrete

Realizing green and low-carbon development will be a new requirement facing the coal industry. In order to address this problem, this paper proposed a method of preparing foam concrete using a supercritical CO₂ phase change foaming technology, and a Portland cement-based supercritical CO₂ foamed concrete with both high pore structure and carbon sequestration capacity was prepared. The effects of supercritical CO₂ on the dry density, pore structure and carbon sequestration capacity of the material and its mechanism were investigated. The experimental results revealed that the supercritical CO₂ phase change foamed concrete preparation process is a temperature-pressure dynamic coordination process considering Portland cement properties and its reaction properties with CO₂ mineralization. The mechanism of Portland cement-based foamed concrete prepared by the supercritical CO₂ phase change foaming technology may be divided into four stages: CO₂-cement slurry coexistence, CO₂-cement slurry co-solution, supercritical CO₂-cement slurry co-solution, and unpressurized foaming. Increasing the experimental pressure can increase the CO₂ concentration in the supercritical CO₂-concrete system and reduce the dry density of supercritical CO₂-foamed concrete, which varies from 787.14 to 993.52 kg/m³ with a range of 8.28% to 19.20%. The development of porosity of supercritical CO₂ foamed concrete was affected by the diffusion-dissolution behavior of CO₂ in the supercritical CO₂-concrete system, and its porosity was 47.87%-89.79%. Increasing the experimental pressure and optimizing the holding time are the development direction for preparing supercritical CO₂ foamed concrete with high porosity. The supercritical CO₂ foamed concrete has uniform, regular and independent circular pores with approximately the same pore diameter of 0.2 mm. Increasing the experimental pressure can promote the degree of CO₂ mineralization reaction and effectively optimize the structure and distribution density of the pores. Each tonne of supercritical CO₂ foamed concrete has a carbon sequestration capacity of 6.32%-10.36% in the skeleton and 0.98-2.27 kg in the pore, which has obvious carbon sequestration potential, but the preparation process and parameters still need to be further improved. The results show that the supercritical CO₂ foamed concrete is expected to be developed into a functional material with near-zero-carbon for mining, which is of great significance for realizing the carbon reduction at the source of coal power integration base.