Charge-directed polymer engineering of carbonate crystallization and microstructure for enhanced transport resistance in cementitious materials

Early hydration studies are often interpreted to suggest that cationic polymers, which impose weaker hydration inhibition, should outperform anionic polymers in reducing permeability. We test this premise by comparing anionic and cationic latexes at 3, 6, and 9 % by binder mass, evaluating transport via non-steady chloride migration and intrinsic gas permeability using Klinkenberg extrapolation, and linking outcomes to MIP-derived pore fractions and tortuosity together with FTIR, XRD, and TGA. At about 6 %, the anionic system delivers larger permeability improvements than the cationic counterpart, with chloride decreasing from 1.15 × 10⁻¹ ² to 0.43 × 10⁻¹ ² m²/s (62.6 % reduction) and gas permeability from 4.86 × 10⁻¹ ⁷ to 1.18 × 10⁻¹ ⁷ m² (75.7 % reduction), while the cationic system shows 49.6 % and 68.1 % reductions at the same dosage. Higher dosages are associated with pronounced early-age strength penalties. Mechanistically, charge-driven interfacial complexation refines pore connectivity and increases tortuosity, with evidence of local carbonate densification, thereby decoupling early-hydration suppression from permeability gains. The contribution of this work is a directly actionable selection guideline: when permeability improvement is the primary objective, prioritize an anionic latex. Finally, a streamlined life-cycle assessment indicates that the optimized anionic system improves durability while lowering global warming potential (GWP).