Corrosion of steel reinforcement in concrete is largely caused by the ingress of chloride ions from deicing salts and coastal marine environments. Electrokinetic nanoparticle treatment [1] concurrent with electrochemical chloride extraction have been employed to minimize chloride attack and reinstate the passivity of embedded steel. Additionally, pozzolanic nanoparticles such as aluminum- and silicon-containing materials can be injected into concrete pores using externally applied electric fields in order to reduce permeability of chloride ions into concrete.[2]

In this work, molecular simulations are used to investigate solvated chloride anion (Cl^-) diffusion through nanoporous calcium silicate hydrate (the main binder phase in Portland cement), when alumina (Al₂O₃) and silica (SiO₂) nanoparticles are present inside the pore. First, equilibrium properties of the chloride-water system are explored as a gradual approach to obtaining a hydrated ion model using Density Functional Theory. Cl^- ion mobility in nanoparticle-reinforced, nanoporous, tricalcium silicate is investigated through calculations of diffusion coefficients for different electric field strengths using Molecular Mechanics and Molecular Dynamics simulations. Different nanoparticle sizes are tested for effective Cl^- blocking at different temperatures, pH, and Cl^- ion concentrations, and the results are compared to the those obtained using a stochastic mathematical model and with experimental observations.

[1] Cardenas, H. E.; Struble, L. J. “Electrokinetic Nanoparticle Treatment of Hardened Cement Paste for Reduction of Permeability,” Journal of Materials in Civil Engineering 2006, 554-560.

[2] Cardenas, H. E.; Kupwade-Patil, K. V. “Corrosion Mitigation using Nanoscale Pozzolan Deposition,” Journal of the American Concrete Institute Submitted January 2007.