Research On Application And Mechanism Of Cement-stabilized Contaminated Soil And Incineration Bottom Ash In Road Engineering

With the rapid development of economy and infrastructure in china,our national highway mileage is sharply increasing.It will consume a large amount of earth and stone material.While the distribution of earth and stone material resources of good quality is in disequilibrium.It seriously affecting the progress of construction.The stacking and landfill of cement-stabilized contaminated soil and incineration bottom ash will occupy a large amount of land resources.Therefore,the feasibility study on the utilization of cement-stabilized contaminated soil and incineration bottom ash in road engineering will not only reduce the consumption of natural earth and stone material resources,but also solve the problem of disposal of cement-stabilized contaminated soil and incineration bottom ash.This paper is based on this background to do a research on heavy metal contaminated soil and incineration bottom ash.On the one hand,the strength and toxicity leaching characteristics of heavy metal contaminated soil after solidification/stabilization of cement were studied,and the mechanism of action and its feasibility for using as subgrade materials were also discussed.On the other hand,the basic physical and chemical properties,mechanical and environmental characteristics of incineration bottom ash were studied to evaluate the possibility of replacing natural aggregate in engineering.The cemented aggregate containing bottom ash was evaluated through experimental analysis.Relying on the actual project,the guidance for design of cemented aggregate containing bottom ash roadbed is formulated.Finally,the cement-stabilized contaminated soil and cemented aggregate containing bottom ash are used in the numerical simulation of road engineering.The results are summarized as follows:(1)After the cement is mixed into the soil,various physical and chemical reactions are carried out with the curing age,and the strength and leaching characteristics of the soil are improved.When the concentration of heavy metal is low(1000 mg/kg),the incorporation of cement can effectively increase the strength of soil and reduce the concentration of heavy metals in leachate.However,the high concentration of metal(10000 mg/kg)can obviously inhibit the solidification and stabilization of cement.(2)When the concentration of lead ion is less than 10000 mg / kg and the cement content is not less than 7.5%,the unconfined compressive strength of cemented heavy metal contaminated soil is more than 1.0 MPa,which meets the repair standard of the Netherlands and France.In this test,only the lead ion concentration of 1000 mg / kg and the cement content of 10%,the leaching solution of lead ions is less than 5 mg / L,which can meet the TCLP test specified the maximum limit(U.S.EPA).Under the condition that the mechanics and environmental characteristics meet the relevant requirements,the re-utilization of heavy metal contaminated soil is feasible.(3)The crushing value of bottom ash with high water absorption and low density is between 30%~50%,more than limestone crushing index but similar to sea sand crushing index.The CBR value is greater than 25% and the bottom ash has good ability to withstand the crystallization pressure.When the pH value of the leachate is 2.88 and 6.92,the leaching of all kinds of heavy metals in the bottom ash is much lower than that of the hazardous waste.The utilization of the bottom ash resource has little effect on the environment.(4)The strength and rigidity of the cemented aggregate containing bottom ash increased with the growth of the curing age.The mixing of cracked bottom ash does not have much impact on the strength of the specimen,and it is beneficial to the development of later strength.The strength and rigidity of the cemented aggregate containing original bottom ash are significantly lower.When the cracked bottom ash content is no greater than 30% and the cement content is 4%,the representative value(7 days)of unconfined compressive strength is 4.15~6.00 MPa,which can meet the strength requirements of the subbase layer(? 2.5 MPa)and the base layer(? 3.5 MPa).The drilling core sample is well-formed and the surface of sample is smooth and crack-free.The cemented aggregate containing cracked bottom ash road base is feasible in construction projects.(5)When the vehicle load was applied to the center line of the pavement,the settlement of pavement reduced with the increase of distance away from the center line.The modulus of the roadbase is not the obvious factor for the pavement settlement,under the condition that the bearing capacity met the requirements.Increasing the thickness of roadbase containing bottom ash and roadbed could reduce the settlement at the center of the pavement remarkably and bring effect on the stresses distribution under the road surface.Although the performance of cemented aggregate containing bottom ash is not superior to that of traditional pavement base.It will not have obvious adverse effects on road performance.Because the mechanical property of the cemented heavy metal contaminated soil is better than general roadbed filler,so the road has a better inhibitory effect of settlement.