Effect Of Coupling Of Seawater And Dry-wet Cycling On The Resistance Of Concrete To Chloride Penetration

In recent years,the durability of marine engineering concrete has received more and more attention,indoor accelerated simulation test research on related issues is also widely carried out.For the indoor accelerated test in the simulated marine environment,it is necessary to simulate not only the accelerated test of concrete under single or complex corrosive medium such as chloride salt or sulfate,but also the damage degree of other aggressive ions in seawater to concrete.In short,the following problems exist in the existing research:(1)Most of the indoor accelerated tests are simulated by using artificially prepared single or complex salt solutions,but the composition of ions in seawater is very complicated,the damage under salt solution is difficult to accurately simulate the actual ocean engineering situation;(2)Most scholars have studied the macroscopic performance changes of concrete structures under salt solution erosion,but only few scholars have studied on the microstructure changes of concrete materials themselvesIn this paper,artificial salt solution and Zhoushan seawater were used for indoor accelerated simulation test.Three accelerated simulation test conditions were designed,respectively are immersion test of concrete with chloride salt as corrosive liquid,dry and wet cycling test of concrete with chloride salt as corrosive liquid,dry and wet cycling test of concrete with seawater as corrosive liquid,the influence of immersion and dry wet cycling on the macro-microscopic properties of concrete was studied.The main research results are as follows:(1)The damage degree of concrete under immersion and dry-wet cycling conditions was characterized by compressive strength and different depth chloride ion concentration.The results show that the dry-wet cycling significantly accelerates the penetration speed and accumulation amount of chloride ions in concrete compared with the immersion conditions,and the penetration speed of chloride ion under the coupling of seawater and dry-wet cycling after 60 days of corrosion is lower than that under the coupling of chloride salt and dry-wet cycling.The incorporation of nano-modified mineral admixture can significantly reduce the chloride ion content in concrete and improve the chloride ion penetration resistance of concrete.(2)The microstructure evolution of concrete under immersion and dry-wet cycling was studied by means of MIP,SEM,XRD and TG-DTA.The results show that the dry-wet cycling can coarsen the pore structure of the concrete surface and increase the harmful pore content.In the dry-wet cycling test of concrete with chloride salt as corrosive liquid,the corrosion products are mainly based on Friedel salt.When concrete is subjected to seawater erosion,magnesium ions will penetrate into the concrete to cause corrosion,and the presence of SO42-will reduce the Friedel salt content for a certain period of time.(3)Through the parameters of strength,electric flux and pore structure of concrete 28d,the appropriate dosage and test mixture ratio of nano-modified mineral admixture were obtained.The simulation of three kinds of accelerated test conditions verified the concrete ratio of concrete.The anti-chloride ion permeability property provides an important basis for the application of nano-modified mineral admixture in marine engineering concrete,and also provides a technical approach for the composition design of marine engineering concrete.