Research On Concrete Degradation Under Multi-factor Coupling Effect Dominated By Landfill Leachate In Severe Cold Region

The problem of erosion and deterioration of concrete structures in landfills by leachate has received widespread attention,particularly in extremely cold regions,and the related mechanisms have gradually been investigated.Research on the erosion and deterioration of concrete mainly focuses on acidic environments,salt erosion,microorganisms,and freeze-thaw cycles.However,the effects of landfill leachate and the coupling effects of leachate under specific conditions on the deterioration characteristics and mechanisms of concrete still need further exploration.This study aims to compare the degree of deterioration of concrete under different influencing factors and to find the deterioration mechanism of concrete under the coupling effects of various factors,based on the mechanical properties,surface morphology,and microstructure of concrete.The results of this study will provide theoretical guidance for the construction and protection of practical engineering cases by establishing protective measures.This study conducted four sets of single-factor experiments,including freeze-thaw cycles,salt solution,soil polluted by landfill leachate and landfill leachate erosion.Comparative experimental results showed that with the increase of freeze-thaw cycles,the strength of concrete continuously decreased.After 120 cycles of freeze-thaw,the compressive and flexural strength of concrete decreased by 19.04% and 32.12%,respectively.After being immersed in landfill leachate,sodium chloride solution,and sodium sulfate solution for erosion,the strength of concrete specimens showed a certain degree of growth in the early stage,reached a peak,and then slowly decreased.Throughout the process,the strength of concrete specimens eroded by leachate was always the smallest.After 120 days of erosion,the strength of concrete in soil polluted by salt solution and leachate both showed a slight increase,while the compressive and flexural strength of concrete in landfill leachate decreased by 6.40% and 7.83%,respectively.Combined with the microstructure characteristics,it was found that after 90 days of erosion by leachate,expansive materials such as ettringite and gypsum appeared inside the concrete specimens,microcracks increased,and the deterioration of concrete under erosion was obvious.The coupling tests were divided into three groups: salt and freeze-thaw cycles coupling test group YD,landfill leachate contaminated soil coupled with freeze-thaw cycles test group TD and landfill leachate coupled with freeze-thaw cycles test group(including test group DS and test group SD),where the first to be acted upon by freezethaw cycles was test group DS and the first to be eroded by waste leachate was test group SD.The results showed that the degradation effect of coupling test group DS on concrete was the greatest.After four cycles of erosion,the compressive and flexural strength of test group DS decreased by 27.93% and 37.98%,respectively.With the extension of erosion cycles,the quality loss rate of concrete in the coupling test increased to varying degrees,and the order was test group DS > test group SD > test group YD > test group TD.Combining the microscopic structural characteristics,it was found that in the third erosion cycle,a large number of cracks,calcium aluminate,gypsum,and other expansive substances appeared inside the concrete of test group DS,and the mechanical properties of the concrete also decreased significantly during the same period.This indicates that the fundamental reason for the deterioration of concrete under erosion is the degradation of local microscopic structures.Through the analysis of the erosion mechanism and key factors of concrete in cold regions landfill sites,it was found that freeze-thaw cycles only accelerate the erosion process,while the landfill leachate undergoes complex chemical reactions after entering the concrete.In order to prevent harmful substances from landfill leachate entering the concrete,an external coating is applied to block it and achieve the purpose of protecting the concrete.This study selected epoxy coal tar pitch anti-corrosion coating(ECTPC)and cement-based permeable crystalline waterproof coating(CCCWC)to protect the concrete.Experimental studies have shown that ECTPC is more effective than CCCWC in protecting the concrete.The results of the coated concrete corrosion test further verified this conclusion.The above research proves that the coupling effect has a much greater impact on the erosion of concrete than a single factor.In order to prevent the erosion of concrete caused by landfill leachate in cold regions landfill sites,it is necessary to not only reduce the damage of freeze-thaw cycles to the interior and surface of the concrete,but also to isolate the leachate from the concrete to ensure the integrity and strength of the concrete structure are not affected.This study provides a theoretical basis for the protection of concrete structures in cold regions landfill sites.In the future,more in-depth research should be conducted on the erosion mechanism and protection methods,in order to find more economical and reliable protection methods,improve the service life of concrete structures,and provide theoretical support for the stable operation of public facilities.