Experimental Study On The Mechanical Properties And Micromechanics Of Cement Modified Sludge Soil

Considering the fineness of cement as one of the important factors affecting the effect of sludge modification,this paper takes the foundation pit sludge of Yuefeng North Station as the research object and innovatively introduces ultra-fine Portland cement as the sludge curing material.The engineering mechanical properties and microstructure of the modified sludge of ultra-fine Portland cement under two different application methods were investigated by a series of indoor tests.One of the application methods is to use ultra-fine Portland cement directly alone,and the other application method is to use ultra-fine Portland cement to replace part of ordinary Portland cement to form a composite cement.The main contents and findings of this paper are as follows:（1）The basic physical properties of the test sludge were studied by indoor geotechnical tests,and the microscopic morphology and chemical composition of the sludge were analyzed.The test sludge was judged to be organic matter high liquid limit silt（MHO）,with loose microstructure and developed pore structure.The main mineral composition of the sludge is quartz,muscovite and kaolinite,and the chemical composition of the sludge is dominated by Si O₂,Al₂O₃ and Fe₂O₃.（2）The unconfined compressive strength q_u,stress-strain curve characteristics,failure mode,failure strainε_f,deformation modulus E₅₀,cohesion c_u and internal friction angleφ_u of ultra-fine Portland cement modified sludge and ordinary Portland cement modified sludge were compared and analyzed.It was found that the strength of ultra-fine Portland cement modified sludge is much stronger than ordinary Portland cement modified sludge,and the modification of sludge is more efficient and effective,while ultra-fine cement modified sludge also has early-strength property.In addition,compared with ordinary Portland cement modified sludge,ultra-fine Portland cement modified sludge has stronger deformation resistance,smaller failure strain and greater brittleness.All the specimens of ordinary Portland cement modified sludge showed brittle failure in the unconfined compressive strength test.（3）The total cement content was fixed at 20%,so that the ultra-fine Portland cement gradually replaced the ordinary Portland cement with a 5%gradient to form the composite cement.The unconfined compressive strength q_u,stress-strain curve characteristics,failure mode,failure strainε_f,deformation modulus E₅₀,cohesion c_u and internal friction angleφ_u of the composite cement modified sludge were investigated.It was found that in the composite cement modified sludge,the strength of the modified sludge increased linearly with the increase of ultra-fine Portland cement content,the failure strain decreased,the deformation modulus increased,and the brittleness increased.（4）The microscopic analysis revealed that the main chemical products of different cement modified sludge were calcium silicate hydrate（CSH）gel and ettringite（AFt）,both cement hydration products.The two chemical generators CSH gel and AFt intertwine with each other to wrap and cement the mineral aggregates in the sludge soil body,while filling the pores in the soil body.The formation of a dense and monolithic structure of the sludge body due to the hydration products of cement is the fundamental reason for the improvement of the macro-mechanical properties of the modified sludge.There are 85 figures,10 tables,and 111 references in this paper.