Effects of Pressurized CO2 Mixing on the Properties of Mortar (2025-10)¶

CO2 mixing is a promising technology to solve the inherent contradiction between workability and buildability in 3D printing concrete (3DPC), which also has the potential to sequester CO2. This study proposed a novel CO2 mixing technique called pressurized CO2 mixing. The properties of fresh and hardened mortar under pressurized CO2 mixing were investigated. The evolution of the microstructure and chemical composition induced by pressurized CO2 mixing were also studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and thermogravimetric analysis (TGA). The findings demonstrated that pressurized CO2 mixing enhanced the efficiency of CO2 absorption compared to normal CO2 mixing, and it also increased the buildability of mortar while slightly improving the compressive strength. This was because nano-sized CaCO3 was produced during pressurized CO2 mixing, which accelerated the hydration of cement clinkers. However, the accelerated hydration reaction resulted in an expansion of gel pore volume, which led to an increase in mortar shrinkage. Compared with normal CO2 mixing, pressurized CO2 mixing reduced setting time and workability more quickly and effectively because more nano-sized CaCO3 was produced during CO2 mixing, which indicated that pressurized CO2 mixing might be a better way to deal with the dilemma encountered by 3DPC.