Research On The Transmission Law Of SO₄^2- In Concrete Under High Water Pressure And Dry-Wet Cycling Mechanism

With the development of underground and seabed projects,such as energy,water conservancy,national defense,tunnel,and so on,the erosion environment of concrete structure is becoming worse and worse with the increase of depth.The environment often has the characteristics of high water pressure,which makes the extent and speed of damage in deep concrete structure much faster than those of shallow and surface concrete structures.Therefore,it is particularly important to study the internal transmission mechanism of erosive ions under high water pressure.Besides,drying and wetting cycles is one of the main reasons for accelerated deterioration of concrete in coastal areas and salt lake area.The transmission of SO₄^2-in concrete under dry and wet cycling mechanism is also worthy of attention and in-depth study.Based on these two aspects,with a metal mine auxiliary shaft concrete failure as an example,this paper studies the transmission of SO₄^2-under these two mechanisms.Through the experiment,it is found that the concrete test block will be in the three direction pressure state because of the effect of high water pressure,which makes the concrete more dense,thus affecting the transmission of the corrosion solution into the concrete,and the author has carried out the traditional high water pressure permeameter.The improved instrument is effective and eliminates the hoop effect under high water pressure.Under high water pressure,the propagation of SO₄^2-in concrete has been studied.The transmission law of SO₄^2-in concrete under three water pressure level of 1.2MPa,2.4MPa and 3.6MPa has been tested by the modified impermeable instrument.The distribution of SO₄^2-in concrete has been obtained by chemical titration.Combined with microscopic analysis,it is confirmed that there is obvious concentration lag phenomenon in the transmission of SO₄^2-in concrete under high water pressure.The transmission model of SO₄^2-in concrete under water pressure is established,and the simulation APP has been developed to estimate the distribution of SO₄^2-with depth in the prediction of underground concrete structure under water pressure.In the study of SO₄^2-transmission in the dry and wet cycle mechanism concrete,the dry-wet cycle test of 0.4,0.5 and 0.6 water cement test blocks has been carried out by using dry and wet cycle test machine with different circulating fluid,clean water and solution.The thickness of damage layer and cubic compressive strength at different times has been obtained.The concentration distribution of SO₄^2-under different water cement ratio and cycle number was obtained by chemical analysis.At the same time,combined with the microscopic examination results,it has been found that the cause of SO₄^2-acceleration to internal transmission under the mechanism of dry and wet cycle is three:dry and wet cycle mechanism itself will produce micro cracks in concrete;salt crystallization and corrosion of the object on the destruction of the pores;SO₄^2-and the hydration of concrete in the reaction.Then,based on Fick’s law and chemical reaction kinetics principle,a simplified SO₄^2-and Mg²⁺transport model under drying and wetting cycle mechanism has been established.With the study of high water pressure and the sampling analysis of the corrosion failure of the shaft wall concrete in a metal mine,the main reason for the accelerated failure of the mine is that the SO₄^2-/Mg²⁺accelerates into the concrete under high water pressure,which forms the overall corrosion.The actual engineering case further confirms the correctness of the conclusion of the study of sulfate ion transport in concrete under high water pressure.