Macro Mechanical Characteristics And Micro-Mechanism Of Impermeable Layer Of Solidified Sludge Landfill Liner

Among the commonly used anti-seepage system materials in landfills,compacted clay is easy to crack,it is difficult to borrow soil.High-density polyethylene membrane is frequently torn and swelled,and bentonite waterproof blanket is often ion-exchanged with leachate,which leads to leakage.These problems seriously affect the service performance of anti-seepage system and pose a great threat to the long-term safe use of landfills and the ecological environment.In this study,taking solving the problem of landfill liner impermeable material as the starting point,combined with the issue of excessive production of industrial solid waste and the difficulty of sludge treatment and disposal in China at present,solidified sludge material was prepared and applied to landfill liner impermeable layer at standard temperature and pressure.Through response surface methodology（RSM）design and single factor control design,a series of experimental studies were carried out under chemical corrosion conditions.Including uniaxial compression creep test,direct shear test,uniaxial compressive strength test,permeability test,and other macroscopic mechanical tests,as well as ICP-OES,XRD,SEM-EDX,XRF,the change laws of macroscopic mechanics and microstructure of solidified sludge materials under chemical corrosion conditions are analyzed,and the corrosion mechanism of different chemical corrosion solutions on solidified sludge materials is revealed.These research results can be used for the recycling of sludge and industrial solid waste,the selection of landfill liner impermeable materials and the evaluation of long-term safe use of landfill impermeable materials.The main researches are as follows:（1）Twenty sets of Response surface methodology tests were designed to obtain the interaction relationship between solidified sludge raw materials.According to the optimal preparation ratio of solidified sludge materials obtained by response surface,fresh municipal sludge:FGD（flue gas desulfurization）gypsum:fly ash:GGBS（ground granulated blast furnace slag）was 1:0.6094:0.6228:0.5430.（2）A single factor control experiment was designed to screen five activator,and the optimal activator type and 0.2%Ca（OH）₂ were obtained,and its compressive strength,deformation performance and permeability characteristics were tested.（3）Eleven groups tests of solidified sludge materials corroded by leachate and acid-base solution were designed.The internal friction angleφand cohesion force C were 6.51-37.58°and 0.53-3.79 MPa.The compressive strength was 2.69-22.80 MPa.The hydraulic conductivity coefficient was 0.12-3.91×10^-8 cm/s.The mechanical strength index and hydraulic conductivity coefficient of corroded materials were provided.（4）Based on 11 groups of tests of mechanical properties,the corroded materials soaked for T=270 d were selected for microscopic tests.ICP-OES test identified that the leaching toxicity of inorganic elements was lower than the standard value.The phase composition obtained by XRD test mainly included ettringite,thaumasite,gypsum,calcite,mullite and so on.SEM-EDX was used to analyze the chemical corrosion mechanism on the surface of corroded materials.The types and contents of elements contained in corroded materials were explained by XRF test.It was found that the ratio of Ca O/SiO₂ ranged from 0.81 to 0.89,and Al₂O₃/SiO₂ ranged from 0.43 to 0.45,which indicated that alkali excitation process was the main source of mechanical properties of materials.