Research On Coatings Corrosion Of Steel Bridge Deck And Its Ifluence On Decline Mechanism Of Asphalt Paved Layer

A plenty of application of long-span steel bridge pavement system and its current condition were investigated in this dissertation. The disease type and possible reason of the paved layers were analysed as well. The results indicated that the diseases are mainly shearing, cracking, rutting and breakage of asphalt binding coating, and the reasons for diseases are briefly rigidity shortage of steel bridge deck, poor asphalt concrete materials, overloading, disqualified paved technology and unresonable pavement system. It is proposed firstly and researched in this dissertation that the interface corrosion of asphalt binding and zinc antisepsis coatings under the paved layer on the deck has relevant influence on decline of the layer.The water penetrative mechanism was derived from the study under the conditions of different pressure or pressure cycles. The results showed that the water on the surface or in asphalt layer penetrates to interface between the asphalt binding coating and zinc antiseptic coating. Furthermore, the quantity of penetrated water is increased with process pressure, time and pressure cycles, and this trend is in evidence when the pressure is beyond 0.3Mpa.The corrosive performance of zinc coatings was systematically investigated through corrosive electricty potential, corrosion rate, polarization property, electrochemical impedance spectroscopy analysis, corrosion appearance and corrosive products on inorganic rich zinc coating, epoxy rich zinc coating and arc spraying zinc coating. The uniform corrosion mechanism for arc spraying zinc coating and dot corrosion mechanism for inorganic and epoxy rich zinc coatings are summarized. The corrosion rate is comparatively steady with time increasing for arc spraying zinc coating, but the corrosion rate for the other two coatings--inorganic and epoxy zinc coatings is increased initialy and then kept unchanged subsequently with time increasing. Moreover, the zinc corrosive products are mainly zinc oxides and zinc salts including CO32-,Cl-, SO42-,OH- ion.The corrosive characteristics of the asphalt binding and zinc coating systems under different breaking modes for binding coating were discussed. Both asphalt binding and zinc coating systems represent composite corrosion mechanism which has synchronously charge transportation and ions diffusion.The corrosive degree of the zinc coating inside the system which is composed of the zinc coating and asphalt binding coating and asphalt pavement layer , is poorer than the other zinc coating inside the system which is composed of the zinc coating and asphalt binding coating. The zinc coating corrosion process involves activation-oxidation-reactivation.The shear fatigue experiment of the two systems were carried out whether or no corrosion. The results showed that the shear fatigue strength of two systems decreases obviously, and the shear displacement increases apparently when the zinc coating is in corrosion condition, these phenomenon are more remarkable with increasing fatigue load.In this research, The distribution pattern of stress and strain of the paved layer was derived from ANSYS analysis. The computation results indicated that surface stress is bigger than interface stress when the zinc coating corrosive area is smaller than 500mm×500mm. Moreover, when zinc coating corrosive area exceeds 500mm×500mm, the paved layer surface stress is smaller than interface stress, and stress in transversal is bigger than longitudinal. Indeed, the surface stress is not consistent with interface with regard to paved layer, such as the longitudinal displacement in interface is converse absolutely to the transversal displacement in surface.A new type antisepsis coating was exploited. The results showed that the bond strength of this new coating is more than 30-40Mpa to steel deck, and 2-3Mpa to asphalt binding coating. Moreove, this new coating possesses excellent corrosion resistance, the corrosive current is lower to 50μA in 5%NaCl+Na2CO3+Na2SO4 solution, and is not more than 100μA in 5%NaCl solutin, and no interface corrosion occures.