Chelator-enhanced low-concentration CO₂ curing of cement paste: A pathway to improved sustainability and CO₂ sequestration in construction materials

To improve the microstructure and mechanical properties of cement-based materials under low-concentration CO₂ curing, effects of chelator on cement paste cured in simulated flue gas contained 20 % CO₂ and 80 % N₂ were investigated and compared to pure CO₂ curing. The results showed that chelator significantly increased the mineralization reaction degree of cement paste, reduced the total porosity, and promoted the transformation of larger pores into smaller ones, thereby improving the pore size distribution and microstructure of cement paste cured under simulated flue gas conditions. Nanoindentation tests showed that after 48 h of simulated flue gas curing, the CaCO₃ content in cement paste doped with chelator (CPC) within the 30–40 GPa range increased by 14.3 %, and the frequency density of elastic modulus increased by 33.3 %, which was comparable to the micromechanical properties of ordinary cement paste (OCP) cured in pure CO₂. X-ray diffraction and ²⁹Si magic-angle spinning nuclear magnetic resonance analyses demonstrated that chelator enhanced CaCO₃ formation, silicate gel polymerization and the development of bulk-structure mineralized products. These improvements brought the macro-mechanical properties of CPC cured in simulated flue gas closer to those of OCP cured in pure CO₂. Additionally, chelator was conducive to further purify flue gas by mineralization curing and reduced CO₂ emissions, offering a novel approach for carbon reduction in construction materials.