Research On Design And Quality Control Of HPC Of Bridge Based On Durability

High performance concrete is used widely in bridge engineering, and the problem of durability is becoming more and more serious. In this paper, with reference to the construction practice of SuYang highway bridges, and based on the theory of concrete science, a systematic study of HPC was carried out from three aspects:mix proportion design, long-term performance and durability, and quality control.A new method for the optimization of aggregate gradation based on aggregate model is put forward, which is quick, easy and accurate. The reference mix is designed using semi-theoretical and semi-empirical calculation method, optimized through the orthogonal experi-ment. The results was analysed through function method, and the best HPC mix proportion with the best comprehensive properties was obtained.On the basis of optimal mix, research of shrinkage, carbonation and chloride ion perme-ability was carried out on HPC. The research of shrinkage consists of three aspects:early shrin-kage, autogenous shrinkage and drying shrinkage. Results show that the autogenous shrinkage of C50 HPC is bigger than normal concrete, and it's close to half of the drying shrinkage, the autogenous shrinkage increases with the decrease of water-cement ratio. Special drying shrin-kage prediction model for the concrete of special strength grade is more accurate than normal model. The fitting results show that the final value of drying shrinkage is inversely proportional to the strength when maintaining stopped.The chloride ion permeability of HPC was tested by electric flux and RCM method, the teat results of the two ways have good correlation. The influence of aggregate content on elec-tric flux is bigger than on the diffusion coefficient, the electric flux of slurry and mortar is bigger than concrete with the same water-cement ratio, but the diffusion coefficient has little difference. For the specimens with lage electric flux, RCM method is suggested to be used to test the chlor-ide ion permeability. The electric flux method was improved by measures such as reduce vol-tage by series, result correction and actual penetration depth test, which can expanded the test range and reduce the test error. The actual penetration depth of chloride ion has a good correla-tion with the electric flux, and the unsteady diffusion coefficient of concrete calculated by the actual penetration depth can be used for quantitative analysis. The steady diffusion model is used to the simulation of chloride ion's penetration in the concrete under the environment of marine and using de-icing salt, the results shows that C50 HPC recommended in this paper can meet the requirements of durability for 1 OOyears in the area of 6km and above far from the coastline, when used in the de-icing salt environment, the chloride ion concentration on the sur-face of concrete of main girder structure should be controlled below 0.06%.According to the test results of shrinkage, carbonation and chloride ion permeability, the C50 HPC mix proportion designed in this paper can well satisfied the requirements of durability, combining the engineering practice of SuYang highway bridege, proposed quality control method of HPC in the field to ensure the quality and durability of the bridge project.