Effect of carbonation pressure on the chloride ion transport and redistribution in Portland cement pastes

Durability of reinforced concrete in marine environments is severely compromised by coupled effects of carbonation and chloride ingress, particularly under pressurized CO 2 conditions, as deep-sea engineering structures and performance enhancement of chloride-containing recycled aggregates. This study examines the influence of carbonation pressure (0–200 kPa) and chloride doping (0–0.36 % Cl⁻) in hardened cement paste. A combination of mercury intrusion porosimetry (MIP), microhardness measurements, and potentiometric titration was employed to investigate the microstructure evolution, chloride redistribution, and carbonation front progression. Results show that elevated CO 2 pressure produces dense calcium carbonate layers that increase surface density while restricting deeper penetration. Pressurization stabilizes internal relative humidity (∼70 %–80 %), shifting CO 2 transport from gas-phase diffusion to liquid-phase convection. Microcracking and amplifying ionic gradients generated by pressurized carbonation drive the inward transport of Cl⁻. Residual chlorides present long-term risks, with concentrations at corrosion-critical thresholds (∼0.30 %) persisting beyond 20 mm depth. The study addresses key limitations in current durability predictions for coastal infrastructure, and enhance the application of high-pressure CO 2 in the construction industry.