Dissolution Of Stray Current On Slag/Cement-based Composite Materials

With the advancement of urbanization and the rapid development of transportation engineering,urban rail transportation,especially subway,has become one of the mainstream transportation in various cities.However,the subway structure is not completely insulated,and part of the electric current leaks,which is stray current.The subway engineering is in the complex corrosive environment of stray current and groundwater dissolution,which brings potential hidden dangers to the safety of its engineering structure.So,simulating the corrosive environment of subway project and studying the anti-dissolution performance of the main cement material under the stray current has important engineering value.As one of the commonly used mineral admixtures,the granulated blast furnace slag has been widely used in the field of building materials due to its excellent performance.In this paper,direct current is used to simulate the stray current in the subway project.And the influence of different slag powder content,different stray current intensity and different water-binder ratios on the corrosion resistance of cement-based composites under stray current is studied.XRD,TG/DTG,and other micro-testing methods have analyzed its mechanism.And the soft water dissolution process of cement-based materials under the stray current has been simulated and calculated by COMSOL Multiphysics,which is a finite element analysis software.The main research contents and conclusions are as follows:（1）The effects of slag powder content,stray current intensity and water-binder ratio on the mechanical properties,alkalinity of pore solution and Ca²⁺concentration of pore solution of slag powder cement-based composites after the coupling of stray current and soft water dissolution are studied.The results show that when the stray current voltage is 40V with the dissolution is 90 days,the compressive strength of cement-based composites is the highest with slag powder content is 40%and 50%,increasing by 40.71%and 58.10%.The p H value and Ca²⁺concentration of the pore solution gradually decrease.With the current increases,the compressive strength of the slag powder cement-based composite material first decreases and then increases.When the current is applied in the early stage of dissolution,the p H value of the pore solution decreases slowly,while the p H value of the pore solution in the later stage is significantly greater than that of no current.With the increase of the water-binder ratio,the compressive strength of the slag powder cement-based composite material gradually decreases,the p H value of the pore solution and the concentration of Ca²⁺gradually decrease.（2）The changes in the microstructure and composition of cement-based composite materials with slag powder content,stray current intensity and water-binder ratios after the coupling of stray current and soft water dissolution are studied.The test results show that the greater the amount of slag powder,the less Ca（OH）₂content in the cement-based composite material.And the formation of a gel phase with lower Ca/Si.Meanwhile,the material’s porosity becomes smaller,and the structure is more uniform and dense.With the increase of current,the content of Ca（OH）₂in the slag powder cement-based composite material decreases,and the phase boundary becomes blurred,but the hydration products of the material increase slightly,and the porosity decreases slightly.As the water-to-binder ratio increases,the content of Ca（OH）₂inside the material decreases,the phases that are eroded away increase,the microstructure becomes loose and porous,the overall pore structure becomes larger,and the porosity becomes larger.（3）The COMSOL software was used to simulate and calculate the corrosion characteristics of cement-based materials under stray current.The simulation results show that the time for the solid phase calcium and Ca²⁺of the slag powder cement-based composite material to dissolve completely decreases with the increase of the slag powder content.At the same dissolution age,the dissolution area and speed of solid phase calcium decrease with the increase of slag powder content.Under different electric field conditions,the dissolution time of solid phase calcium and Ca²⁺of the slag powder cement-based composites decreases with the increase of electric field.At the same dissolution age,the dissolution area and velocity of solid phase calcium increase with the increase of electric field.