Ab-initio modeling of chloride binding at hydrocalumite/sodium chloride solution interfaces

Understanding the energetics and kinetics of chloride in cement-based materials is critical to identify effective ways to control chloride diffusion. Here, we performed an ab-initio molecular dynamics (AIMD) simulation on interfacial activities to reveal the reaction mechanism and dynamic nature of chloride. Chloride ions mainly distributed in the electric double layer (EDL) of positively charged surface ([Ca2Al(OH)6]+) through electrostatic interactions with calcium ions and protons, while sodium ions were mainly confined within the interface region between the negatively charged surface ([Cl·2H2O]−) and hydrocalumite main layer, forming various ionic complexes. The above interactions are driven from the nucleophilic nature of bound chlorides and electrophilic nature of water hydrogen and calcium ions. These findings were further confirmed by dynamic analyses, local structures and electronic properties as well as comparing with experiments and classical molecular dynamics (MD) simulations. We finally inferred that the chloride binding properties can be tailored by regulating the Ca/Al ratio of hydrocalumite main layer.