Effect of CO2 mixing on the rheological and electrochemical properties of fresh mortar at the early age

The study aimed to elucidate the mechanism behind rheological modification due to CO2 mixing at the mixing and post-mixing stages from an electrochemical perspective. The results indicated that CO2 mixing reduced the flowability while increasing penetration resistance and static yield stress. The electrostatic attraction between particles with opposite surface charges and the bridging effect of calcium carbonate constitute the primary factors for influencing the rheological properties of mortar at an early age. The altered surface charge of carbonized cement particles, primarily resulting from CO2 injection lowering the pH and ion concentration, reversed the zeta potential of particles from the traditionally negative charge (-3.59 mV) to a positive value (+13.3 mV). Furthermore, CO2 mixing further enhanced the dissolution of cement particles and accelerated the hydration process, thereby increasing the rate of structural build-up. CO2 mixing was demonstrated to be a potential rheological modifier for 3D-printed concrete applications.