Mechanical, Thermal, and Microscopic Properties of Concrete Modified with CO2 Foams and Silica Fume

Abstract CO 2 curing represents an effective approach for sequestering greenhouse gases while improving the mechanical performance of cementitious materials. However, the limited permeability of CO 2 in the dense cementitious matrix restricts carbonation to the outer layers of the blocks when conventional external curing techniques are employed. In this study, a CO 2 foam modification technique was applied to enhance the curing process of foam concrete by premixing CO 2 into the pores, thereby increasing its contact surface with the cement paste. Silica fume (SF) was also integrated to densify the pore walls to further optimize performance. The CO 2 concentration ranged from 0%–40 vol%, and SF concentration ranged from 0%–8 wt%. Measurements were taken to assess the variations in pore characteristics, dry density, compressive strength, and thermal conductivity of foam concrete at different CO 2 concentration levels. The results indicated that the optimal strength-to-weight ratio of 6,985.6 N · m / kg was achieved at a CO 2 concentration of 30%, resulting in an improved compressive strength of 4.38 MPa. Furthermore, scanning electron microscopy (SEM), thermogravimetric (TG), and X-ray diffraction (XRD) analyses were used to investigate the modification mechanisms of carbonated foam concrete. The formation of calcium carbonates enhanced the compactness of the pore walls and contributed to the improved performance of the material.