Study On The Aging Failure Mechanism And Life Prediction Of Steel Bridge's Anti-corrosion Coating

As the main way of the anti-corrosion protection of bridge steel structure , organic coated has played an important role, however, organic coatings will be degraded in accordance with different mechanisms because of effects of sunshine(for example ultraviolet radiation), humidity, temperature etc. in atmosphere, and will produce powder, microcracks and break off,then coating will be failure, re-painting of bridge is need, in order to determine a reasonable time to re-painting, make the painting cost most economical, so study on corrosion failure mechanism of coatings and their service life in the outdoor atmospheric environment is essential.24 sets of coating system is used the research object in this paper, the system is constituted by 6 topcoat, including alkyd, polyurethane, acrylic polyurethane, rubber chloride, fluorocarbon and acrylic polysiloxane. Steels samples coated with above coatings are exposed outdoor in typical atmospheres that are warm temperate climate and urban atmosphere in sub-humid belt and semiarid atmosphere in Xi'an, and use them to do indoor artificial accelerated aging experiments at the same time. Based on the experiment results,the aging behaviors of organic coatings, the effect degree of aging of organic coatings on corrosion resistance and the formation mechanism of corrosion product can be gotten, coating aging failure mechanism, the correlation between outdoor exposure experiments and QUV accelerated experiments are discussed. According to mechanism, the coating life prediction equation which included metal substrate under atmosphere environment try to be given.From the results, conclusions can be obtained: under the artificial aging conditions, different coating system have the same aging failure form of external apparent, the rate of losing-gloss raise according to index equation y = a(1 ?exp(?bt)), but micro-failure modes and failure mechanism is different; in the UV/condensate accelerated aging test, besides the fluorocarbon coating, the aging behaviors of other several coating can better simulate to same coating in outdoor exposure better. With increasing aging time of indoor and outdoor, water absorption of coating system according increase by linear equations, and the combined strength between coatings and metal interface also drop by linear equations. The latter period of indoor artificial aging, the main corrosion product of carbon steel substrate is Fe3O4 and r-FeOOH.