Study On The Applicability Of MSWI Bottom Ash In Roadbed

In recent years,due to the rapid development of Chinese industrialization and urbanization,the volume of municipal solid waste removal has also increased,and incineration is one of the main methods of waste disposal,which has led to a large amount of municipal solid waste incineration(refers as MSWI)bottom ash.The state encourages units and individuals to recycle and reuse these solid wastes.At the same time,the country ’s“13th Five-Year Plan” requires that Chinese infrastructure(including roads)require further construction and development,inevitably causing consumption of natural resources such as river sand and mountain stones;On the other hand,building a "sponge city" requires that the road can meet the integrated water permeability from the road surface to the roadbed,which is currently difficult to achieve with traditional roadbed filling.In order to solve the above problems,a series of studies are conducted on the applicability of MSWI slag in road subgrades.Based on the above research background,this thesis uses MSWI bottom ash as the test object,and discusses the applicability of the material in road subgrade from three aspects.First,the MSWI bottom ash is mainly studied from the aspect of environmental impact,and the environmental impact analysis includes the leaching toxicity,penetration characteristics,adsorption characteristics,and leaching characteristics of the MSWI slag.Second,the thesis conducts MSWI bottom ash from the aspect of physical and mechanical properties Research,and the physical and mechanical properties include the shear strength,load-bearing ratio,deformation characteristics and crushability of MSWI bottom ash.Finally,the feasibility of using MSWI slag to replace soil filling as a roadbed under traffic loads was simulated by abaqus,and the effects of different roadbed materials on the dynamic response of the road surface are discussed.The conclusions are summarized as follows:(1)The leaching toxicity of MSWI bottom ash is measured according to the toxicity characteristic leaching procedure(TCLP).It is found that the leaching concentration of MSWI bottom ash is lower than the identification standard for hazardous wastes.According to the specifications of garbage incineration slag aggregate(GBT 25032-2010),It has little effect on the environment and can be used as a roadbed filler.(2)There is a negative correlation between the permeability coefficient of MSWI slag sample,compaction degree and hydraulic gradient.The compaction degree is the main factor affecting the permeability coefficient of the slag sample.The permeability coefficient of99.4% compactness slag samples is much higher than that of traditional subgrade filling materials.Using MSWI bottom ash as roadbed material has very positive significance for the realization of fully permeable roads.(3)MSWI bottom ash has a significant adsorption effect on methylene blue.The unit adsorption of slag has a positive correlation with the initial concentration of methylene blue solution and adsorption time.The smaller the slag particle size is,the higher is the unit adsorption rate.The maximum unit adsorption rate of slag can reach 5.75 mg / g.The removal rate has a negative correlation with the initial concentration.When the initial concentration is low,the removal rate can reach more than 95%.Therefore,using MSWI slag as the roadbed material can play a role in "purifying" surface runoff.(4)First,the higher the liquid-solid ratio is,the lower is the slag leaching concentration and the higher is the leaching amount.Second,the leaching concentration is higher in the acidic environment with p H = 2.88 than in the neutral environment with p H = 7.Finally,the smaller the particle size of the slag particles is,the greater is the leaching concentration of some heavy metals but Cu,Ba,and Mn show opposite rules.(5)The higher the compaction degree of the MSWI slag sample is,the higher is the shear strength.On the other hand,under the same compaction degree,The bottom ash cohesion and internal friction angle are slightly higher in the wet side(right side of the optimal moisture content of the compaction curve)than in the dry side(left side of the optimal moisture content of the compaction curve).The bottom ash CBR value and compaction also show a positive correlation,and the maximum CBR value can reach 15.7%,which is nearly 4 times lager then the CBR value requirements of road subgrade design specification.Therefore,the MSWI bottom ash meets the strength requirements of road subgrade materials.(6)MSWI bottom ash has a negative correlation with the swell water expansion rate and compaction degree.The maximum value is 0.1%,which is far lower than the requirements of road subgrade design specification for industrial waste fillers.Second,the bottom ash has dilatancy,and the higher is the compaction,the smaller is the dilatancy and the greater the vertical stress is,and the larger is the dilatancy;On the other hand,the higher the compaction degree is,the greater is the slag compression modulus,and the highest can reach 30.864 MPa,which belongs to low-compressibility soil.Therefore,it can be proved that MSWI slag as a road subgrade material has outstanding resistance to deformation;The crushing rate of MSWI slag increased with the increase of vertical stress and compaction degree,but showed a negative correlation with the amount of dilatancy and peak expansion angle.(7)The elastic modulus is estimated through the compression modulus,and it is found that the elastic modulus of the slag is higher than the requirements for the elastic modulus of the roadbed filler in the design specifications of the asphalt pavement.Later,the finite element simulation software abaqus was used to simulate the two conditions of MSWI slag subgrade and traditional soil-filled Roadbed.It is found that when MSWI bottom ash is used as the Roadbed material,the settlement of road surface and roadbed is significantly smaller than the latter,and the lateral and longitudinal strains at the bottom of the surface layer and the top of the roadbed are also smaller than the latter.Therefore,it can be proved that MSWI slag can replace roadbed filling as Roadbed filler used,and it is beneficial to the stability of road structure.