Atomic diffusion of sulfate and chloride ions in the nanometer cavity of C-S-H/Nanoclay

Abstract

Concrete is notably vulnerable to aggressive ions such as sulfate and chloride penetrating its inner nanopores and damaging its microstructure or the reinforcements it encompasses. Nanoclay particles, being impermeable to sulfate and chloride ions are one of the candidates being considered for this role. In this study, we have evaluated montmorillonite (MMT) and layered double hydroxides (LDH) for linings inside the nanopores of the cementitious matrix against the encroachment of NaCl and Na2SO4 compounds. The results show that the chemical composition of the nanoclay particles plays an important part in trapping the passing ions. The ions released by dissolution of NaCl and Na2SO4 proved to be highly vulnerable to the charged surface of the both nanoclay linings. The relatively electrophile hydrogens on the surface of the LDH help absorb and trap the sulfate and chloride ions from the flow. In case of MMT surfaces, the abundant nucleophile oxygen atoms are better suited for trapping Na cations. Given the higher number of Na cations in Na2SO4 and the partial ionization of the compound, the adsorption of Na cations on the surface of the MMT nanoclay lining of the pores can create an effective barrier, slowing down the movement of ions further inside the pore. The results of this study shed light into the viability of using nanoclay particles for denying aggressive ions entering the nanopores, and provide insight for the development of sustainable robust cementitious composites.