Experimental Study On Modification Of MSWI Bottom Ash By Mechanical Ball Milling And Limestone Powder

The municipal solid waste incineration bottom ash（MSWAIBA）is the solid waste produced after the incineration of MSW.The composition of the bottom ash is similar to that of ordinary Portland cement.It is mainly consisted of Ca O,Si O₂,Al₂O₃and other oxides,which have potential gelling properties.Mechanical ball milling is an environmentally friendly pretreatment method,changing the particle size of materials,increasing the specific surface area of particle,improving the activity of materials,which can finally improve the material properties of concrete.The filling effect and hydration effect of limestone powder can improve the particle size distribution and hydration performance of material.The purpose of this paper aims to use mechanical ball milling in conjunction with limestone powder to replace cement with bottom ash,which can preliminarily explore the microscopic effect of mechanical ball milling on bottom ash particles and the impact on the mechanical properties and microstructure of bottom ash cement concrete,which can also explore the impact of limestone powder on the hydration system and whether the leaching toxicity of the test sample after partial replacement of cement by the bottom ash meets the requirements.Finally we can get the optimal replacement amount of bottom ash.The specific research is as follows:（1）Through the study of the particle size,specific surface area and microstructure of the bottom ash under different ball milling times,it can be obtained that the particle size of the bottom ash after 30 minutes of ball milling can reach 41.5μm,which is close to the fineness of cement.The specific surface area of the bottom ash is as high as 6713 cm²/g.After 30 minutes of ball milling,the bottom ash particle distribution is more uniform,the particle surface is more regular,and it has more active ingredients such as Ca O,Al₂O₃,etc.The main chemical bond vibration peaks in the bottom ash are the strongest absorption peaks in their respective regions.（2）Through the uniform design experiment,we can explore the influence of different content of waste incineration bottom ash,limestone and different ball milling time on the mechanical strength of the bottom ash cement concrete test samples,and combine the results of the mechanical strength and the actual content of bottom ash.The optimum ratio of the test is as follows:the mass ratio of limestone/bottom ash is 30%,the mass ratio of bottom ash+limestone/cement is 40%,and the mechanical ball milling time is 30min.The content of bottom ash under this ratio is as high as 40%,but the microstructure of the concrete test samples has many compact hydration products（such as C-S-H,ettringite）,and the compressive strength reaches 40.94MPa.It not only meets the basic material strength,but also achieves the maximum resource utilization of bottom ash.（3）In the study of the influence of limestone powder on the hydration process,it was found that the mechanical strength of the samples without limestone powder was lower than that of the samples containing limestone powder.Although both groups of samples had hydration reaction,the surface structure of the sample containing limestone powder is denser,and more hydration products CaCO₃ and Aft are produced.This is the impact of the filling effect and hydration effect of limestone powder on cement-based materials.（4）Toxicity leaching test was carried out for the optimal ratio group,and the heavy metal concentrations（Cr,Cu,Ni,Pb and Zn）contained in the samples were tested,and the results shows that the leaching concentrations all meets the specification limits.It shows that bottom ash can be used as a cementitious material in the construction industry,and the amount of bottom ash that replaces cement is 40%.