Influences of titanium dioxide nanoparticles on regulation of crystalline growth and early carbonation of cementitious composites

As the major source of carbon emission in the construction industry, Cement has presented an urgent challenge that demands the resolution of its high carbon emission issue. Utilizing in-situ CO2 capture from plant sites for the carbonation curing of cementitious materials can be regarded as an effective carbon sequestration method. This study employs low-concentration CO2 curing to modify nano titanium dioxide (NT)-enhanced cementitious materials. By investigating the influence of highly homogeneous NT on the crystalline growth and microstructural evolution of hydration product Ca(OH)2, this research further explores the impact of low-concentration CO2 curing on the early-stage carbonation behavior of the surface layer of cementitious materials. The results of this study indicate incorporation of 2 wt% NT promotes the degree of cement hydration, particularly during the first three days, leading to a 31.11% increase in the generation of the hydration product Ca(OH)2 at 1 day and 20.82% increase at 3 days compared to the blank sample, and a significant reducing of the crystalline size and directional growth index of Ca(OH)2 to increase the specific surface area of Ca(OH)2, thereby promote early carbonation of the cementitious mortar surface. The carbon uptake of the specimens at 28 days reaches 0.94 kg/m2 after exposure to 3% CO2 concentrations, forming a dense protective layer of calcium carbonate on the surface. The gas permeability coefficient of the surface decreases by 79.57%, enhancing the resistance of long-term continuous carbonation. This study provides innovative ideas for the cement industry in terms of utilizing surface carbonation of the substrate to promote carbon sequestration technology.