Study On Performance Of Underground Fly Ash Concrete Under The Action Of Sulfate And Chloride

The environment of the underground concrete structure is different from that of the above-ground structure.There is load on the surrounding rock,and seepage water pressure in the underwater part.Also,sometimes chlorine salt and sulfate are in the groundwater.Under this multi-factor coupling,there are some problems in the underground concrete structures,such as leakage,falling off,arch cracking and so on,so it is necessary to improve the performance of the concrete.The most effective way is to improve the salt permeability of concrete.As a mineral admixture,fly ash can greatly improve the impermeability of concrete under sulfate and chloride corrosion.In this paper,the optimum design of concrete mix ratio was carried out.By means of concrete test and microscope analysis,the mechanical properties and microscope mechanism of fly ash concrete were studied under the action of"seepage-stress field",sulfate and chloride.The best amount of fly ash was searched.The transport mechanism and regularity of sulfate and chloride ions in fly ash concrete under unilateral corrosion were studied under optimum fly ash content.The most effective solution is to improve the salt-resistance of concrete.As a mineral admixture,fly ash has a great effect on the impermeability of concrete under the corrosion of sulfate and chloride.In this paper,the concrete mix ratio was optimized.By means of concrete experiment,the mechanical properties and microscope mechanism of fly ash concrete were studied under the action of"seepage-stress field",sulfate and chloride,and the optimal fly ash content was found.The mechanical properties and micro-mechanism of fly ash concrete were studied in the underground multi-factor environment under the optimum fly ash content,and the transmission mechanism and rule of the sulfate and chlorine salt in the underground fly ash concrete were analyzed.?1?The optimum range of fly ash content is determined.The content of fly ash is 0%,10%,30%,50%respectively,the head difference?0,0.5MPa?and the load?0,50kN?.The corrosion appearance and ultrasonic velocity of concrete are observed.The compressive strength results show that the optimum content of fly ash is 30%.?2?The mechanical properties and micro-mechanism of fly ash in underground concrete corrosion were studied.The orthogonal design was carried out by selecting the amount of fly ash?30%?,head difference?0,0.3,0.5MPa?,load?0,50,100kN?and corrosion time?30,60,90d?.The ultrasonic velocity and compressive strength of corroded concrete were measured,the fracture characteristics of corrosion section were summarized,the distribution of ion concentration was detected,and the micro-analysis was carried out by means of X-ray diffractometer and electron microscope scanner.The results show that the order of factors affecting the ultrasonic and compressive strength of corrosion was as follows:head difference>corrosion time>unidirectional axial load.The strength attenuation equation of fly ash concrete was established under the action of"seepage-stress field",SO₄^2-and Cl^-;the compressive strength and the ultrasonic velocity of the underground fly ash concrete were basically linear.In the early stage of one-side corrosion,the fly ash mainly played a filling role,but the surface of the fly ash was obviously hydrated under the underground multi-factor corrosion of the same age,and a plurality of products such as C-A?S?-H gel and gypsum were also gathered around.?3?The mixed solution of sodium sulfate?0,5%,10%?,sodium chloride?0,5%,10%?with different mass fraction was used to soak the 100mm×100mm×300mm blocks in one side corrosion mode.The ultrasonic velocity and axial compressive strength of the blocks were measured at different corrosion time.Chloride ion and sulfate ion concentration,and microscope analysis were also measured.The results were as follows:under pure sulfate one-sided corrosion,the strength of fly ash concrete increased rapidly and decreased slowly,while chloride inhibited sulfate corrosion of fly ash concrete,but the concentration of chloride continued to increase,which will accelerate sulfate corrosion.The diffusion coefficient of chloride ion and sulfate ion were obviously lower than that of underground multi-factor corrosion.