Once the Cl -ion content reaches a certain level, the rebar undergoes depassivation, leading to localized pitting corrosion. Altarawneh et al. studied chlorine adsorption on the Fe(100) surface in detail using DFT calculations, in which a five atomic layer slab model was used to describe the Fe(100) surface with the bottom two layers fixed. Three main adsorption sites (top, bridged, and hollow) with various coverage of chlorine were investigated. The energies demonstrated that chemisorption at bridge and hollow sites are preferred over the top site while maximum chlorine coverage was observed at 0.5 monolayer coverage. This optimum coverage was found to be less than the experimental results of ~0.74 ML coverage. Given that the iron surfaces produce iron chlorides and oxychlorides in a chlorine containing environment, a comparison was made between surface chloride configurations and bulk FeCl2 and FeCl3