Regulation of early accelerated carbonation behavior in nano-modified cementitious materials under low concentration CO2

Accelerated carbonation has emerged as a promising curing technique for cementitious materials, attracting increasing attention. However, the efficient utilization of low concentration CO 2 sources in cementitious systems remains a significant challenge. The present study systematically investigated the effects of reactive nano-silica (NS) and inert nano-titania (NT) on the early-stage accelerated carbonation behavior of cement mortars under 3% CO 2 concentration. Key parameters—including CO 2 uptake, carbonation depth, CaCO 3 crystallinity, calcium silicate hydrate (C-S-H) polymerization, and pore structure—were compared to elucidate the mechanisms by which nano-modification regulates carbonation.The results demonstrated that the incorporation of nanoparticles significantly enhanced early carbonation performance. Compared to the control group, the CO 2 uptake increased by approximately 120% and 54% in the NS and NT modified groups, respectively, with a substantial increase in CaCO 3 formation within the carbonation zone, predominantly in the form of highly crystalline calcite. In addition, nanoparticles promoted cement hydration, increased the degree of polymerization of C-S-H gels, and effectively inhibited their decalcification, thereby improving the pore structure of the matrix. Notably, the NS modified group exhibited the lowest total porosity and average pore size across all carbonation stages, with the proportion of large pores (>200 nm) reduced by approximately 69% compared to the control. Under low CO 2 concentration conditions, nano-modification enables the synergistic enhancement of both carbonation and hydration processes, offering technical support and theoretical insights for the green and low carbon transformation of construction materials.