Study On The Durability Of The Subway Concrete Structure And Service Life Prediction

The durability of concrete is an important subject in concrete research field. But how to transit it from qualitative analysis to fix quantitative analysis? How can the durability index reflect the actual state of the concrete construction? How to give a overall evaluation of the durability and service life of the concrete under multi- actions? How to decrease the steel corrosion induced by the stray current through the material design? All these problems need the further study.Combining the project of the experimental study on Nanjing subway HPC, the physical and mechanical properties of HPC (C30) are studied. The concrete carbonation, the chloride ions ingress, the stray current corrosion, the sulfate attack on concrete and so on are also studied. From the test results, several conclusions can be drawn as follow:Firstly, the analogical relation and test method of concrete carbonation are built. The test result shows that the carbonation speed increases with the addition of fly ash and mineral powder. The model of concrete carbonation can reflect the actual state very well.Secondly, considering the thickness of sulfate ions, water- cement ratio and other factors, the prediction model of sulfate resistance is built, which choose the flexural strength as the evaluation index. The prediction result shows that concrete of Nanjing subway construction has the strong ability of sulfate resistance.Thirdly, decreasing the water- cement ration is helpful to improve the ability of concrete to resist the chloride ions ingress. Adding fly ash or adding both fly ash and mineral powder can reduce the chloride diffusivity coefficient, and adding both fly ash and mineral powder is better to reduce the chloride diffusivity.Fourthly, adding fly ash or adding both fly ash and mineral powder can decrease the corrosion caused by stray current. Adding both fly ash and mineral powder can decrease the stray current to only one- fifth of the normal concrete with the same water- cement ratio, so the corrosion caused by stray current can be evidently decreased.Lastly, using the fuzzy various attribute decision-making theory, an overall evaluation of the durability life of the concrete can be made. The result shows that adding both fly ash and mineral powder is the best proportion and the subway C30 HPC's overall durability life is longer than 100 years.