Reuse Of Oyster Shell For Waste Residue Soil And Its Solidification

As the urbanization process in Shenzhen continues to advance,the infrastructure has produced a lot of residue soil.From 2017 to 2020,the total amount of waste residue soil in Shenzhen is expected to be about 400 million square meters.At present,most of the construction and demolition waste landfill has been filled,and waste residue soil is nowhere to be placed.Moreover,waste residue soil is buried in the landfill,which not only has potential safety hazards,but also causes waste of resources.Similarly,there is another waste resource in Shenzhen,which is the oyster shell.In China,oyster production will reach 5.15 million tons in 2022.Oyster shells,which account for 90%of oysters,are treated as garbage,which not only occupies places,but also causes contamination problems.In view of the current status of waste residue soil and discarded oyster shells,this paper proposes oyster shells for reuse of waste residue soil.The two types of waste are combined and reused to solve the problem of nowhere to waste,which is also in line with the concept of green development.This paper studies the basic properties of the collected waste residue soil and oyster shells.Based on these properties,it is proposed that oyster shells become a solidification material after activation by phosphoric acid or DAP(diammonium hydrogen phosphate)reaction.And the oyster shell solidified soil is prepared by physical-chemical reaction between activated oyster shell and soil.The unconfined compressive strength,water stability,splitting strength and p H value of the oyster shell solidified soil is determined by the test,and the influencing factors is analyzed,and the optimum utilization rate of the material is determined.Through experimental analysis,the oyster shell solidified soil doped with phosphoric acid or DAP can change the engineering properties such as compressive strength,splitting strength and p H value of the soil.As the amount of phosphoric acid or DAP increases,the strength of the oyster shell solidified soil increases,and the effect of DAP is better.The strength of the solidified soil increases as the amount of oyster shell increases and the size of the oyster shell decreases.The splitting strength of oyster shell solidified soil with DAP reaches0.2 MPa,which is equivalent to lime soil but lower than cement soil.The p H value of the oyster shell solidified soil with DAP is 7.7?7.8,which is more reasonable for the the environment.Considering the strength,p H and economic cost,the optimum utilization rate of the material of the oyster shell solidified soil is: 73.6% soil,18.4% oyster shell(particle size ?1 mm),8% DAP,its saturated water strength can reach 1.07 MPa,and the softening coefficient is 0.5.The oyster shell solidified soil changes the water disintegration characteristics of the original soil,and its strength satisfies the minimumstrength index of the road base layer.The solidification mechanism of oyster shell solidified soil under the excitation of phosphoric acid and DAP is discussed.The XRD result shows that the phosphoric acid reacted with the oyster shell in the solidified soil to form brushite;DAP is used to treat the oyster shell solidified soil,and the DAP reacted with the oyster shell to form hydroxyapatite(HAP).The microstructure of oyster shell solidified soil is observed by SEM and EDS test.The tests show that in the microstructure of the oyster shell solidified soil with phosphoric acid,the generated filamentous calcium phosphate crystals cover the soil particles,forming a spatial structure and improving soil integrity.In the microstructure of the oyster shell solidified soil with DAP,the surface of the soil is covered with a petal-like precipitation HAP,which aggregates the small particles and the generated crystal structures are interlaced and bonded between the particles.A stable network structure is formed in the pores or cracks to improve the strength of solidified soil.The reinforcement of artificially piled waste residue soil slope by oyster shell solidified soil was studied.In the laboratory test,the improvement of the shear strength and the scour resistance of the slope was improved.In the direct shear test,the inner friction angle and cohesion of the oyster shell solidified soil increased with the increase of DAP content,and the inner friction angle do not change much(30.1?37.8 °),which is mainly due to the improvement of cohesion(15.0?84.9 k Pa).In the slope scouring test,the oyster shell solidified soil with DAP can effectively reduce the sediment yield on the slope,reduce the soil erosion by rainfall,and improve the erosion resistance of the slope soil.