Dynamics of Solvated Chloride Inhibition by Nanoparticle Treated Concrete

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.