| With the increase of urban sewage treatment rate in China,the production of municipal sludge is also increasing,and how to―harmlessly and resourcefully‖treat municipal sludge has become the focus of attention in China and the world.In addition,combined with the problems and defects of traditional landfill cover materials such as easy cracking,bulging and poor impermeability,this study uses construction waste powder and industrial waste（slag powder,fly ash,desulfurization gypsum）as modifiers to modify municipal sludge,and uses the modified municipal sludge as landfill cover material.Considering that the landfill sealing materials are exposed to different climatic environments for a long time,mechanical tests,microscopic tests and rainfall model tests were conducted on the modified municipal sludge under the action of different environmental factors（natural conservation,wet and dry cycles,freeze-thaw cycles）.The mechanical properties,microscopic characteristics and seepage resistance of the modified sludge under the action of different environmental factors were analyzed to reveal the curing mechanism and microstructural changes of the modified sludge,which provided data reference for the feasibility and safety serviceability of the modified sludge as landfill cover material.The main research and findings of this paper are as follows:（1）A landfill cover material with construction waste powder and industrial wastes（slag powder,fly ash,desulfurization gypsum）as modifiers for curing municipal sludge was prepared.The moisture content,volume deformation,compressive strength,permeability coefficient and toxic leaching characteristics of the modified sludge were studied.The study showed that the industrial waste in combination with construction waste powder was effective in modifying the sludge.The mechanical properties of the modified sludge after 28 d of curing met the requirements of landfill sealing cover material,and the toxic leaching also met the requirements of national specifications.（2）The mechanical properties and microstructural characteristics of the modified sludge under the action of wet and dry cycles and freeze-thaw cycles were investigated.After 20 dry and wet cycles,the water content of the modified sludge specimens was41.36%-46.34%,the volume shrinkage was 0.56%-0.85%,the compressive strength was1.31-4.55 MPa,and the permeability coefficient was 9.510×10-8-5.677×10-7 cm/s;After 20freeze-thaw cycles,the volume shrinkage of modified sludge specimens was 1.80%-2.06%,the compressive strength was 6.00-10.83 MPa,and the permeability coefficient was8.870×10-8-4.135×10-7 cm/s.The study showed that the modified sludge basically met the requirements of landfill cover material after dry and wet cycles and freeze-thaw cycles,and the modified sludge had good durability against damage by dry and wet cycles and freeze-thaw cycles.（3）The microstructural evolution of modified sludge under the action of natural conservation,wet and dry cycles,and freeze-thaw cycles was investigated.The effects of conservation age,wet and dry cycles and freeze-thaw cycles on the hydration products,microscopic morphology and elemental composition of modified sludge were analyzed.The modification mechanism and microstructure change characteristics of municipal sludge by construction waste powder and industrial waste were revealed.（4）Rainfall model test of the modified sludge landfill cover was conducted.The impermeability of modified sludge under cyclic recharge of continuous moderate rainfall,heavy rainfall with evaporation,and very heavy rainfall with evaporation was investigated.The study showed that the landfill cover system constructed by pulverized clay（vegetation layer）-construction waste（drainage layer）-modified sludge（impermeable layer）has the performance of resisting strong precipitation impact,in which the 40 cm thick modified sludge as the impermeable layer plays a good water barrier effect. |
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