Investigation of the Penetration of Water and Chloride into Unsaturated Concrete: An Experimental and Molecular Dynamics Study

Abstract

Unsaturated transport of water and chloride into concrete was investigated using capillary absorption tests and molecular dynamics (MD) modeling. Results showed that a linear relation between capillary absorption rate and saturation degree (SD) of concrete was significantly influenced by water to cement ratio (W/C) due to different pore-size distributions. Chloride penetration depth was reduced at high SD and low W/C. The relationship model of chloride diffusion coefficient with W/C and SD is proposed. MD modeling was conducted to simulate water molecules and ion transport in the nanopores of calcium silicate hydrate gel. The MD study indicated that the rapid capillary absorption of water and ions in the dry state followed the Lucas–Washburn equation, and the slow diffusion of solution species in the saturated state matched well with Fick’s second law. MD also attributed the slow transport rate of water and ions in cementitious materials with fine microstructures to the pronounced filter effect of nanometer confinement and the longer resident time on a hydrate’s surface as a result of the electrostatic trapping of surface silicate and calcium atoms.