Study On The Engineering Characteristics Of High Moisture Content Waste Sludge Flow Solidified Soil

With the continuous improvement of China’s urbanization level,sewage production is increasing,sludge production is also increasing,and sludge harmless treatment has become a difficult point in major cities.In this thesis,high water content sludge is mixed with waste steel slag,and Portland cement is used as curing agent to develop sludge flow solidified soil for backfill of building fertilizer tank.Taking the dosage of cement and steel slag as variables,the working performance,mechanical properties,durability and permeability of sludge flow solidified soil under different dosage are studied.Based on the hydration reaction and microstructure of sludge flow solidified soil,the mechanism analysis was carried out.The main research contents and results are as follows:(1)The working characteristics of sludge flow solidified soil with different ratios were studied.With the increase of cement content and steel slag content,the fluidity of sludge flow solidified soil decreases,and the influence of steel slag on the fluidity of sludge flow solidified soil is much smaller than that of cement.The fluidity of sludge flow solidified soil is greatly reduced during 40 min～60 min,and the fluidity is 174 mm～227 mm.The fluidity of sludge flow solidified soil with cement content not more than 35%meets the requirements of flow pumping.The density of sludge flow solidified soil is between1300kg/m~3～1500kg/m~3,which is lower than the typical density range of1500kg/m~3～1700kg/m~3.(2)The unconfined compressive strength of sludge flow solidified soil with different ratios was studied.The unconfined compressive strength of sludge flow solidified soil is positively correlated with cement content and steel slag content.The increase of cement content on the strength of sludge flow solidified soil is much larger than that of steel slag content.The compressive strength of sludge flow solidified soil after 28 days of curing is28.25k Pa～640.03k Pa.The unconfined compressive strength of sludge flow solidified soil increases greatly when the cement content is 26%～30%.(3)The durability of sludge flow solidified soil was studied based on dry-wet cycle test.With the increase of the number of dry-wet cycles,the strength of the sludge flow solidified soil increases first and then decreases,and the strength reaches the maximum after the third dry-wet cycle.When the cement content exceeds 26%,the ability of sludge flow solidified soil to resist dry-wet cycle damage is more obvious.When the cement content is30%,the effect of resisting the destruction of dry-wet cycle is the best.(4)The permeability test of sludge flow solidified soil shows that:when the cement content is the same and the curing period of sludge flow solidified soil is short,the permeability coefficient of sludge flow solidified soil with large steel slag content is small.With the increase of curing period,the permeability coefficient of sludge flow solidified soil with large steel slag content is large.The size of the permeability coefficient changes during the curing period of 8d-15d.This is because there are fewer hydrates produced by the hydration reaction in the early stage of curing,and the steel slag content is high and the relative water content is low.With the increase of curing period,the hydration products gradually increase,and the relative porosity between the particles in the sludge flow solidified soil with large steel slag content is large and the permeability is high.The larger the cement content,the smaller the permeability coefficient of the sludge flow solidified soil,and the permeability coefficient gradually decreases with the increase of curing age.(5)The results of microstructure and mechanism analysis of sludge flow solidified soil show that C-S-H gel and AFt crystal are produced during the hydration reaction of cement and steel slag to fill the pores of sludge and steel slag,and the sludge particles and steel slag are bonded together to form a spatial network structure.The higher the cement content,the more perfect the spatial structure.For the sludge flow solidified soil that has experienced dry and wet cycles,its microstructure has the manifestation of disordered arrangement of hydration products,large voids and cracks.