Study On Mechanical Properties And Interface Properties Of Reinforced Passivation Films Based On Molecular Dynamics Theory

A better adhesive property between reinforcing steel bar and concrete is the basis of the durability of reinforced concrete.In the service process of reinforced concrete,one of the main reasons of the concrete durability deterioration is reinforcement corrosion.In the strong alkalis condition of concrete,a compact oxidation film can be formed on the rebar surface,that is steel passivation film.This film can affect inevitably effect the properties of reinforcing steel bar.In this study,molecular dynamics approach was employed to investigate the main component of rebar(outer layer is ?-FeOOH and inner layer is ?-Fe2O3).The mechanics performances of different components were obtained.The interfacial bond property between ?-FeOOH and concrete surface and adsorption performance were analyzed.The results are listed as following(1)The uniaxial stretch properties of different components in steel passivation were investigated.Comparing the tensile strengths of Fe,?-Fe2O3 and ?-FeOOH,a significant mechanics difference between three components was found.This is mainly because that the connection between layers of ?-FeOOH is based on van der Waals forces,leading a week interaction between these layers,thus its mechanics property was decreased(2)The structural and dynamics properties and mechanics performance of the interface between reinforcing steel bar and C-S-H with different moisture contents were probed.Calcium atoms shows a bridging effect between C-S-H and ?-FeOOH surface,which is the main reason of the adhesive between rebar and concrete.However,free water molecules can weaken the interaction the interaction between Ca and ?-FeOOH by occupy the binding sites of Ca atoms,leading the dispersion of Ca atoms.As the water content increasing,the migration rate of Ca atoms increased,the adhesive property between rebar and C-S-H was further decreased.The results of uniaxial tension simulation show a good agreement with this conclusion(3)The adsorption behaviors of water and ions on the surface of reinforcing steel bar were characterized.A layered adsorption structure of water molecules on ?-FeOOH was found.The adsorption of water is mainly contributed to the bonding between Ow atom of water and H atom of surface hydroxyl.In the presence of Na+ and Cl-ions,the hydroxyl group of ?-FeOOH surface provides large number of O sites for ionic bond formation with Na+.While the adsorption of Cl-is mainly depend on the electronic interaction from Na+ cations.?-FeOOH shows an obvious affection on the penetration behavior of water molecules and ions in the solution.The diffusion coefficient of water molecule,Na+ and Cl-near ?-FeOOH surface account for 27.8%,27.5%and 29.5%of that in the solution.