Study On Structural Repair Materials In Marine Envir Onment

The mariner structures make the steel bars in the reinforced concrete structure rust,the concrete be corroded to crack,and its surface peel off after washing by seawater,harmful ion permeation and alternating wet and dry.These corrosions will seriously affect the service life of the marine structures.At present,many marine structures in China have undergone different degrees of corrosion,and although the service life has not reached the design expectations,they can no longer be used.Also,with the rapid development of China's coastal developed cities,there are still many cross-sea bridges,offshore work platforms and large-scale port projects under construction.Therefore,to explore the mechanism of corrosion damage of structures in the marine environment and find high-performance concrete repair materials that have seawater corrosion resistance are not only related to the service life and repair cost of offshore structures,but also related to sustainable development and environmental protection.Based on the task of the national key research and development plan project "Research on the recovery technology of key load-bearing structural materials in rail transit under complex environment",the test method for wet-dry cycle is used to explore the transmission mechanism of chloride ions in concrete.The main works as follows:(1)6mm long polypropylene fiber is selected,and the silica fume and microbeads are mixed to reduce the water-binder ratio to make high-performance concrete,which improves the mechanical properties of concrete,meets the requirements of construction performance,and also has good resistance to seawater corrosion according to the "Code for design of ordinary concrete" and "Technical specification for application of fiber reinforced concrete".(2)The effects of quartz sand and river sand on the mechanical properties and construction performance of concrete are compared.At the same time,the influence rules of polypropylene fibers with different volume(0%,0.5%,1%,2%)on mechanical properties,construction properties and internal microstructure of the concrete when cenosphere is added are analyzed.(3)The preliminary mix ratio and orthogonal mix ratio scheme are designed to analyze the effects of four factors,such as silica fume,microbeads,water-binder ratio and sand-cement ratio,on the compressive and flexural strength,construction performance and microstructure of concrete.The change law of mechanical properties of single-mixed microbeads and mixed microbeads-silica fume concrete is compared.(4)The test method for wet-dry cycle is used to prepare a solution of 5 times seawater concentration for concrete seawater corrosion test.The change law of basic properties of concrete is measured 50 times and 73 times.The corrosion mechanism of magnesium salt and sulfate in seawater on the concrete is analyzed from the microscopic point of view.(5)After the 73 times of wet-dry cycle,the content of chloride ion in different depth of the concrete is determined by silver nitrate colorimetry.The change law of chloride ion penetration resistance of concrete under different raw material ratios is initially explored,and the material plan with excellent resistance to chloride ion permeation is found.(6)Based on Fick's second law,the diffusion coefficient of chloride ions is calculated,and the diffusion model of chloride ion as a function of concrete depth is established.