Preparation and mechanism of Portland cement-based CO₂ foam concrete

The environmental problems caused by the large amount of CO₂ generated in the operation of coal-electricity integration base have attracted a great concern. The foam concrete material prepared from the CO₂ generated in the pithead power plant can be used for mine filling, and can realize the in-situ treatment of the CO₂ of the pithead power plant. Therefore, a CO₂ foam concrete material with high strength and carbon fixation characteristics was developed, and the preparation mechanism of CO₂ foam concrete (CFC) based on Portland cement was explored. The CO₂ foam concrete based on Portland cement was prepared by carbonation pretreatment cement and physical foaming. Scanning electron microscopy (SEM)and Fourier transform infrared spectroscopy (FTIR)were used for microscopic characterization. Universal testing machine was used to test mechanical properties. Thermogravimetric analysis (TG)was used to measure the carbon fixation capacity. The effect of CO₂ on the dry density, porosity, compressive strength and carbon retention of CFC was studied. The defoaming mechanism of CO₂ foam in Portland cement was analyzed, and the mechanism of CO₂ foaming Portland cement based concrete was discussed. The experimental results show that the compressive strength of CFC was significantly improved due to CO₂ curing. After carbonation pretreatment, the 7 d compressive strength of CFC increased by 44.6%, and the 28 d compressive strength increased by 27.7%. Carbonation pretreatment could significantly improve the cellular structure and foaming effect of CFC, and the porosity of CFC increased by 7.38% after carbonation pretreatment. The carbon fixation rate of CFC skeleton was 5.70%-8.08%, which has obvious carbon fixation potential. However, the preparation process and parameters of CFC still need to be further improved to meet the needs of mining. It was found that the mineralization reaction of calcium silicate mineral phase and CO₂ is the main reason for the defoaming of CO₂ foam. The key to the preparation of CFC is to reduce the content of calcium silicate mineral phase and its hydration products in the system by carbonation pretreatment of Portland cement slurry, and increase the content of calcium carbonate.