Durability Design And Long Service Life Analysis Of Prestressed Concrete Box Girder Exposed To Marine Environment

The destruction of concrete structure has become a disaster of durability in the circles of civil engineering due to the chloride diffusion in the marine environment. And it has been the most concerned topic. To the box girder, because of the long-term erosion of sea salt mist,a lot of chloride will invade the concrete, which results in serious corrosion of the steels in the box girder. So the concrete box girder is difficult to reach the requirement of the designed service life of 100 years. The paper respectively predicts the service time when the cantilever slab,the inclined web and the bottom slab reach five percent or ten percent of the rusting probability. It also puts forward a series of solutions to postpone the rusting time of the steels and then enhance the durability of the box girder and ensure the structure can reach the service life of 100 years. Main results achieved are as follows:(1)In the condition of marine atmosphere, the durability of concrete box girder mainly depends on the reinforcing steels’ rusting time of the cantilever slab,the inclined web and the bottom slab. Its designed requirements of durability can be guaranteed if the reinforcing steels can not be rusted within 100years;(2)In the condition of marine atmosphere, the cantilever slab and the inclined web will be rusted within five years if the concrete box girder has no rust prevention. To the F0, F20, S30 and S60, the effects of rust prevention can be enhanced in turn. And the differences of such effects in F0 and F20 are not obvious. The service time of S30 and S60 can reach 50 years;(3)In the condition of marine atmosphere, the concrete box girder can reach the requirements of the designed service life of 100 years and even 120 years if the cantilever slab and the inclined web are painted with silane less than eight millimeters and the bottom slab of the box beam is painted with a small amount of silane;(4)To satisfy the requirements of the concrete box girder’s durability, we need to select high-performance concrete and take some additional measures, for example, increase the thickness of the concrete cover, use stainless steels and paint the surface of the box girder with silane and add some rebar inhibitors; The concrete box girder’s service life can reach 500 years in the following cases: the first one is that steels in the first rank are the stainless steels. The second one is that adding a certain amount of rebar inhibitors in the high-performance concrete. The last one is that cantilever slab and the inclined web are painted with silane less than eight millimeters.