Experimental Research On The Effects Of Different Dry-wet Ratios On The Corrosion Of Concrete Sulfate

Concrete materials have the advantages of low cost,convenient material selection and good durability,and are widely used in various building structures such as roads,bridges,dams and house construction.The durability of concrete varies greatly under different working conditions.It is found that the dry-wet cycle greatly accelerates the degradation rate of concrete.The concrete structure in the water level change areas such as coastal areas,northwest salt lakes and sewer pipes is often the most vulnerable.Sulfate erosion is an important factor leading to the durability failure of concrete structures.It is also one of the most influential and most complex erosion environments,and it has received more and more attention.However,the test methods used by various scholars are different,and the research results are often difficult to compare.The research on the sulfate erosion performance of concrete under different dry and wet cycles has become a hot topic at present.In this paper,7d is used as a cycle,and five dry-wet time ratios(10:1,5:1,3:1,1:1,1:3)are designed.The 5% Na2SO4 solution is used as the corrosion solution.The effects of different dry-wet ratios on the macroscopic properties of concrete compressive strength,tensile strength,dynamic elastic modulus,mass change and apparent damage were simulated under natural conditions.Finally,the microscopic damage mechanism and damage evolution of concrete structures under sulfate attack were revealed by SEM microscopic observation technology.The performance of concrete sulfate erosion under different dry-wet ratios was studied in depth from macroscopic and microscopic levels.The main conclusions are as follows:(1)The changes of compressive strength,tensile strength and dynamic elastic modulus of concrete under different dry-wet ratios are consistent,and both tend to rise first and then decrease.(2)The degree of erosion of concrete under different dry-wet ratios is significantly different.In the initial stage of dry-wet cycle,the higher the dry-wet ratio,the faster the concrete performance strengthening speed,and the later the dry-wet cycle,the higher the dry-wet ratio,the faster the concrete performance declines.Within a certain range,the higher the dry-wet ratio,the faster the concrete degradation rate.It is recommended to extend the drying time appropriately when developing the dry and wet cycle test method.(3)After 28 dry and wet cycles,D5W1 compressive strength,tensile strength and dynamic elastic modulus decreased by 21.5%,33.3%,and 6.7% compared with their peak values.(4)The dynamic elastic modulus has high precision and less dispersion,which better characterizes the deterioration of concrete.The variation law of dynamic elastic modulus of concrete under different dry-wet ratios is obviously different.It is recommended as the preferred evaluation index.(5)With the progress of dry-wet cycle test,the internal erosion products and micro-cracks of concrete increase gradually,and the microstructure of concrete under different dry-wet ratios is obviously different.The ratio of ettringite and gypsum crystals is more than 5:1.The concrete corrosion is more serious.