Interfacial and nanoconfinement effects on electric field-driven chloride migration in C-(A)-S-H nanopores

The durability degradation of coastal reinforced concrete structures under chloride ion erosion is a key issue restricting the life span of marine engineering. Electrochemical chloride extraction (ECE) technology, which drives chloride ion migration via an electric field, has become an effective repair method. Its dechlorination efficiency is affected by the concrete micro-pore structure and the properties of hydration products. In this paper, molecular dynamics simulations were used to systematically investigate the chloride ion migration behavior in the nanopore channels of hydrated calcium silicate (alumina) (C-(A)-S-H) gels, and the mechanisms of the pore sizes, aluminum doping, and electric field strength on the transport kinetics were revealed. In aluminum-doped C-A-S-H, enhanced surface negativity and the stabilizing effect of Al-O-Si bonds inhibit chloride migration by strengthening Na⁺-Os bonding and promoting Cl⁻-Caw ion pair formation. Water molecule dynamics shows that the electric field weakens the stability of the Cl - hydration layer, which has a higher diffusion coefficient than that of Na⁺, and the hydrogen bonding network in C-A-S-H further restricts the ionic migration. The study reveals the synergistic mechanism of interfacial charge effect and pore size limiting domain in nanopore channels, which provides a theoretical basis for optimizing electrochemical remediation technology and the design of highly durable cementitious materials. • The mechanism by which electric field strengths ranging from 0 V/Å to 0.05 V/Å in C-(A)-S-H structures regulate the migration of corrosive ions has been elucidated. • Compared to the C-S-H matrix, the aluminum-doped C-A-S-H matrix exhibits a dual inhibitory effect on corrosive ions. • The study elucidates the confinement effect of different pore sizes in the C-A-S-H matrix upon application of an electric field.