Study On The Performance Of Cement Stabilized Bottom Ash Pellets/Macadam Mixture

In recent years,in order to alleviate the contradiction between the rapid growth of waste and the tension of landfill,waste incineration power plants are under construction all over the country.Bottom ash is the waste residue produced by high-temperature incineration of domestic waste,which can be resourcefully used in cement stabilized mixture base due to its certain engineering properties.However,the bottom ash has high water absorption rate and low strength,and a large amount of bottom ash will seriously affect the road performance of the base mixture,so the research group proposed to prepare high strength bottom ash pellets as coarse aggregates into cement stabilized macadam/bottom ash mixture to improve its road performance,but there are still problems such as insufficient dry shrinkage.In this paper,based on the previous research,on the one hand,the ratio of bottom ash pellets is optimized,silica fume is added as an auxiliary cementing material,and admixed activators are selected to enhance the compactness and strength of bottom ash pellets;on the other hand,appropriate amount of PVA fibers are added into the cement stabilized bottom ash pellets/macadam mixture,and the mechanical properties,water stability,dry shrinkage performance and economic benefits of the mixture are analyzed.Firstly,the particle size distribution,physical properties,mechanical properties,chemical properties and radioactivity of the bottom ash were analyzed.The results show that the particle size of the bottom ash increases gradually and the compactness and strength of the bottom ash improve in different degrees with the curing time,the physical and mechanical properties of bottom ash tend to stabilize after 90 days,and the bottom ash has no cementitious property and radioactivity.Therefore,it is recommended that the curing time of bottom ash is 90d before it is applied to the road base mixture.Secondly,with 0～2.36mm bottom ash as raw materials,cement,silica fume,fly ash as cementitious materials,through the strength test to determine the admixed activators of 3 groups bottom ash pellets,and the bottom ash pellets were prepared by pellet forming process,the optimized ratio of bottom ash pellets was proposed after 28d standard maintenance conditions through the comprehensive selection of physical and mechanical properties and material cost.Compared with the bottom ash pellets proposed in the previous study,the compactness and strength of the optimized bottom ash pellets were significantly improved.Then,the apparent relative density,water absorption,crushing value of bottom ash pellets at different curing ages were tested,and the changes of the microstructure,mineral composition,functional groups and pore characteristics of the bottom ash pellets with curing ages were analyzed.The results show that the hydration products such as ettringite and C-S-H gel gradually increase with the extension of the maintenance age,filling in the pores of the bottom ash pellets,making its compactness and strength gradually increase and water absorption decrease.The changes of physical and chemical properties of the bottom ash pellets tend to stabilize after 28 days,and the crushing value basically reaches the technical requirements of heavy,medium and light traffic base mixture of expressway and first-class highway.Therefore,it is recommended that the maintenance age of bottom ash pellets under standard maintenance conditions is 28d.Finally,bottom ash fine aggregates,bottom ash pellets and appropriate amount of PVA fiber were incorporated into the cement stabilized macadam mixture,and the effects of different amounts and lengths of fiber on the mechanical properties,water stability and drying shrinkage properties of the mixture were investigated,the optimal blending scheme of PVA fiber was proposed,and the economic effects was analyzed.The results show that the bottom ash used as coarse aggregates significantly reduce the performance of cement stabilized macadam/bottom ash mixture,while the incorporation of bottom ash pellets and PVA fibers significantly improve the strength,water stability and shrinkage resistance of the mixture.The performance of cement stabilized bottom ash pellets/macadam mixture with the best PVA fiber blending scheme is close to cement stabilized macadam,which can reach the technical requirements of heavy traffic base mixture of expressway and first-class highway.The results of this study are expected to provide a practical and effective way for the resource utilization of municipal solid waste incinerator bottom ash,which will not only greatly reduce the exploitation of natural aggregates,but also be beneficial to the protection of ecological environment,moreover,it can reduce the production cost of cement stabilized macadam and improve the economic benefit.