Study On The Durability Of Fly Ash Concrete Against Sulfate Attack In Complex Environment

In most regions of our country concrete structure often suffer from a variety of sulfate erosion environment coupling effect,lead to performance degradation of concrete damage,thus durability failure.In this paper,the study on the durability of fly ash concrete under natural sulfate erosion environment,freeze-thaw cycle-sulfate natural erosion environment,dry-wet cycle-sulfate erosion environment,freeze-thaw-dry-wet cycle coupling erosion environment was carried out through laboratory tests.The research content and main conclusions are as follows:(1)The variation rules of mass loss,elastic wave velocity and compressive strength of concrete under natural sulfate erosion,freeze-thaw cycle-sulfate natural erosion,dry-wet cycle-sulfate erosion,freeze-thaw-dry-wet cycle coupling erosion were studied.The test results show that the mass loss,shock elastic wave velocity and ultimate compressive strength of fly ash concrete increase first and then decrease with the increase of the erosion time or the number of dry and wet times.At the early stage of erosion,the concrete parameters have little attenuation range.However,the longer the erosion time is,the more significant the parameter attenuation is.(2)The effects of natural sulfate erosion,freeze-thaw cycle-sulfate natural erosion,dry-wet cycle-sulfate erosion,freeze-thaw-dry-wet cycle coupling erosion environment on the physical and mechanical properties of concrete were studied.The experimental results show that the degree of influence of erosion environment on mass loss,elastic wave velocity and ultimate compressive strength is from the largest to the least: freeze-thawing-dry-wet cycle coupling sulfate erosion environment > dry-wet cycle-sulfate erosion environment > freeze-thawing cycle-natural erosion environment > sulfate natural erosion environment.Among them,both freeze-thaw and dry-wet cycle can accelerate sulfate erosion,while dry-wet cycle has a greater impact on sulfate erosion of concrete,which is to promote sulfate crystallization and accelerate internal expansion and deterioration of concrete.(3)The relationship between the shock elastic wave velocity,compressive strength and dynamic modulus of concrete under different sulfate attack environments was studied.The results show that there is a quadratic function relationship between the compressive strength and the elastic wave velocity of concrete and between the moving mode and the erosion time under different erosion conditions.The results can provide theoretical basis for nondestructive testing and durability evaluation of concrete under sulfate attack.(4)This experiment used digital image processing technology to study the whole process of concrete surface change and damage after sulfate attack.The results show that,when the erosion begins,the compactness of concrete increases with the increase of erosion time,but with the increase of erosion time,the range value increases,the compactness decreases,and finally the concrete is destroyed.