Study On Mix Proportion Design And Permeability Of High Performance Concrete For Heavy-haul Railway

Heavy-duty railway concrete structures often have durability problems such as concrete cracking and steel corrosion during the service life,which seriously affects driving safety.The external factors that affect the durability of railway concrete can not be eliminated.Therefore,it is very important to improve the durability of railway concrete from the source,In addition,the electric flux method and the RCM method used to evaluate the permeability of railway concrete have many disadvantages.Especially for major projects such as heavy-duty railways,it is difficult to reach concrete For the purpose of quality pre-control,aiming at the above-mentioned problems,this paper applies the full calculation method to the mix ratio of heavy-duty railway concrete and proposes a test method to characterize the permeability of concrete with electrical resistivity.The main work and conclusions of the paper are as follows:(1)Complete the reference mix design of C60 heavy-duty prestressed sleeper concrete using the full calculation method,and on the basis of the mix ratio,analyze the types and amounts of mineral admixtures through the electric flux method and the RCM method(0,10%,20%,30%),mixing method and curing age change(28d,56d)on the influence of concrete electric flux and chloride ion diffusion coefficient.The test results show that the concrete’s electric flux and chloride ion diffusion coefficient With the extension of the curing age and the increase of the amount of fly ash and mineral powder,the concrete has the strongest resistance to chloride ion penetration when the fly ash and mineral powder are mixed in a ratio of 2:1.(2)Introduced the test principle of the four-electrode method,and the resistivity calculation formula is derived.Based on the AASHTO TP 95-14 specification,the concrete resistivity test process is specified,and the influence of water-binder ratio,mineral admixture type,dosage and age change on the evolution process of concrete resistivity is studied and analyzed,a multi-factor resistivity evolution model was established,through COMSOL software to solve the standard cube the shape of the concrete resistivity correction coefficient K,and established a three-dimensional random aggregate model,analysis the influence of aggregate content change of resistivity.The results show that there is a negative correlation between the resistivity and the water-cement ratio,fly ash and mineral powder can significantly improve the resistivity of concrete,and the composite mixing effect is obviously better than the single mixing effect,and the resistivity of concrete increases with the increase of aggregate content.(3)Through the electric flux and RCM tests,the effects of mineral admixture type,dosage,blending method and age change on the electric flux and chloride ion diffusion coefficient of sleeper concrete were studied and analyzed.The correlation analysis of the concrete resistivity,electric flux,and chloride ion diffusion coefficient under 28d and 56d curing ages found that there is a good power function relationship between the resistivity and the diffusion coefficient,and the correlation coefficient R~2 is 0.875.There is a good exponential function relationship between the power rate and the electric flux,and the correlation coefficient R~2 is 0.896.It is feasible to evaluate the permeability of concrete by resistivity,and a railway concrete impermeability evaluation standard based on the resistivity method is proposed.