Research On Sulfate Corrosion Law Of Shaft Wall Concrete Under High Water Pressure

With the implementation of the national strategy for the development of the western region,with the advancement of the national strategy for the development of deep underground spaces and deep-buried mineral resources,in the past 20 years,a large number of deep and large shafts have been constructed in the western region.The salinity of many and deep formation waters is generally high,and there are often formations rich in corrosive water.In recent years,the borehole wall has suffered more and more from groundwater corrosion disasters,causing significant losses.The service environment of the wellbore is complicated.At the same time,the borehole concrete is in a high water pressure environment.Mastering the corrosion law of the borehole concrete in a high water pressure environment is to prevent corrosion.The premise of it is of great significance in theory and practice.Aiming at the problem of sulfate corrosion of shaft wall concrete under the action of high water pressure,comprehensive research is carried out using indoor test block test,theoretical analysis and engineering measurement methods,and the main innovations are as follows:?1?In order to obtain the law of SO₄^2--concentration and corrosion transmission rate after corrosion of shaft wall concrete under the action of high-pressure sulfate-containing water,in order to reduce the detection error and minimize the impact of coarse aggregate in concrete on the test analysis,cement mortar is used The test block was subjected to a pressure corrosion test to determine the SO₄^2-content at different depths of the corrosion sample after a certain corrosion age.In order to accelerate the corrosion rate of concrete,10%sodium sulfate solution is used as the corrosion medium?using high-concentration corrosion solution is a common test method?,and different corrosion medium water pressures?0MPa,2.5MPa,5MPa?and different mortars are selected in the test Water-cement ratio?0.4,0.5,0.6?,determine the SO₄^2-content at different corrosion depths?5mm,15mm,25mm,35mm?.Studies have shown that the higher the pressure,the higher the content of corrosive ions at the same depth,the greater the water-cement ratio,the more significant the corrosion;the high water pressure causes the transmission rate and transmission depth of sulfate ions to be greatly improved,the water pressure is 5MPa and the water pressure is 0 At a depth of 5mm,the water-cement ratio increased by 6.03,6.21 and 6.60 times the SO₄^2-content of the corrosion specimens of 0.4,0.5 and 0.6;the head pressure changed the original transmission mode of SO₄^2-,SO₄^2-no longer separate The transmission is carried out by means of concentration difference diffusion,but by a pressure difference-driven seepage flow and concentration difference-driven diffusion coupling transmission.?2?Based on Fick's second law and Nernst-Planck equation,on the basis of previous research results,the influence of water pressure and water-cement ratio of the corrosive medium was considered,and the sulfate ion content was established The distribution model of time and depth changes,and compared with the measured data,the calculated value and the measured value are in good agreement when the water pressure is 0MPa and 2.5MPa,and the calculated value and the measured value have a certain error when the water pressure is 5MPa.The established analytical model can reflect the transmission characteristics of sulfate ions under the coupling action of concentration field and pressure field.The analysis results have laid a theoretical foundation for the study of the transmission law of sulfate ions under high water pressure.?3?In view of the softening and sludge phenomenon of the corrosion products on the inner edge of the shaft wall in the high water pressure environment,the indoor corrosion sample test method was used to study the corrosion law of concrete carbon-sulfur wollastonite-type sulfate under the action of high water pressure.In the test,10%sodium sulfate solution was used as the corrosion medium,and the water-cement ratio of the mortar was 0.5,the water pressure of different corrosion media?0MPa,2.5MPa,5MPa?,and the amount of different limestone powder?limestone powder/cementing material ratio was 0,15%and 30%?,using XRD,SEM,EDS and FT-IR and other micro-testing methods to analyze and analyze the composition and composition of the corrosion products after 120d corrosion,and obtained the corrosion age 0,30d,60d,90d,120d The change rule of the strength of the corrosion sample;research shows that the greater the amount of limestone powder,the greater the change in the strength of the test block,and the lower the final strength;when the corrosion is 120d under 5MPa water pressure,the amount is 0%,15%and30 The strength loss rate of%is 51.16%,57.92%and 59.38%respectively;the influence of water pressure on the corrosion of the test block is mainly reflected in the accelerated corrosion rate.The overall strength of the corrosion specimen and the corrosion age show a trend of increasing first and then decreasing.This is because the SO₄^2-reacts with the hydration product,and the pores in the test block are continuously filled,but as the corrosion progresses,the product fills the pores and generates huge internal stress,resulting in micro cracks in the test block.The cracks penetrated each other to crack the test block.In a pressureless state,the main corrosion product of mortar is gypsum;when the corrosion solution pressure is 2.5MPa,the corrosion product is gypsum,ettringite,or wollastonite;when the corrosion solution pressure is 5 MPa,the main corrosion product is calcium Alumite or wollastonite has different corrosion products under different corrosive media under water pressure.When the pressure of the corrosion solution is 5 MPa,the corrosion products on the surface and inside of the sample are not the same.The surface is mainly doped wollastonite,and the ettringite is mainly inside.?4?After about 10 years of service in the auxiliary shaft of a mine in Ordos City,Inner Mongolia,the inner surface of the wall of the bedrock section was corroded to varying degrees.The corrosion products in the corrosion area and the groundwater quality were sampled and analyzed.The main material composition of the corrosion products was Gypsum,ettringite and thaumasite,etc.,the sulfate ion content in the groundwater in the corrosion area of the well wall reaches 2328mg/L.According to the different corrosion products generated on the inner surface of the well wall,the formation mechanism of the corrosion products was analyzed.The concrete on the inner edge of the auxiliary well shaft was in a complex service environment with dry and wet cycles and annual temperature changes?-5?20??.The coupling effect of the seepage driven and the diffusion driven by the concentration difference is the main cause of the corrosion and damage of the concrete at the inner edge of the shaft wall.The corrosion products generated under the action of various factors-carbalite will cause the inner edge of the shaft wall to soften and sludge.Combined with the research on the corrosion law of concrete test under high water pressure,the preliminary analysis believes that the corrosion rate of the outer edge of the shaft wall under high water pressure may be faster and the corrosion may be more serious.Salt corrosion technology route.In this paper,we obtained the corrosion law of shaft wall concrete under the action of high water pressure.The research results provide theoretical support for the study of shaft wall corrosion in deep wells with high stress and high water pressure.The research results have important theoretical and practical significance for deepening the understanding of the corrosion mechanism and corrosion prevention in the service environment of the shaft wall.There are 78 pictures,21 tables,and 100 references in this paper.