Study On Application Of Waste Incineration Bottom Ash In Cement Stabilized Macadam Mixture

In recent years,in order to alleviate the contradiction between the continuous growth of domestic waste and the increasingly tight capacity of landfill in China,waste incineration power plants are being actively built all over the country.Incineration can be used to dispose domestic waste,but some residues,such as fly ash and bottom ash,will be left behind.If all of them are disposed in landfill,it will not only occupy a large amount of land,but also cause a waste of resources.At present,it is an effective way for mixing waste incineration bottom ash into cement stabilized macadam base to realize resource utilization.However,the utilization rate of bottom ash is greatly limited because of its low strength and high water absorption rate.In this paper,on the basis of previous-research,bottom ash pellets with higher strength were prepared by using calcium dihydroxide and anhydrous sodium sulfate as activators through balling technology to use as coarse aggregate,and 25%of waste incineration bottom ashes with proper size were used as fine aggregates.Then,they were mixed together in cement stabilized macadam mixture,and the mechanical properties,shrinkage properties,environmental safety properties and comprehensive benefits of the mixture were discussed.First of all,from the appearance,particle diameter distribution,physical properties,mechanical properties and chemical composition of waste incineration bottom ash were analyzed.The results show that the sieving curve of waste incineration bottom ash has good continuity.Bottom ashes can work well when they are used as aggregates to mix mixture,but their strengths are low and it is not suitable to use them as coarse aggregates to bear the skeleton function of pavement base mixture.Secondly,a four-factor and three-level orthogonal test was designed.Waste incineration bottom ash was used as raw material,whose particle diameter is 50%in 0-1.18mm and 50%in 1.18-2.36mm,cement and fly ash were used as binders,and sodium calcium dihydroxide and anhydrous sulfate were used as activators.By using 7d compressive strength test,the optimum constituent proportion of bottom ash pellet was determined through the range analysis.The bottom ash pellets with particle diameter larger than 4.75mm were prepared by balling technique,and the technical properties of 28d bottom ash pellet were tested.The results show that the properties of the strength and water absorption of the bottom ash pellet are improved to some extent compared with that of waste incineration bottom ash,and they are also better than that of the bottom ash pellet prepared with quicklime and dihydrate gypsum as activators.Bottom ash pellet can meet the requirements of base course coarse aggregate of Grade Two and below highway.Then,the cement stabilized macadam and bottom ash mixtures were prepared by using different amount of 28d bottom ash pellets as coarse aggregates and 25%of 0-4.75mm waste incineration bottom ashes as fine aggregates.The compacting,mechanical and dry shrinkage properties of the mixtures were studied.The maximum content of bottom ash pellet in the mixture was put forward.The results show that the compressive and cracking strength of cement stabilized macadam and bottom ash mixture drop with the increase of bottom ash and bottom ash pellet contents,but the 7d unconfined compressive strength of cement stabilized macadam and bottom ash mixture with 30%of bottom ash pellet and 25%of bottom ash can meet the requirements of heavy,medium and light traffic pavements for Grade Two and below highway.The dry shrinkage indexes of the cement stabilized macadam and bottom ash mixture increase significantly with the addition of bottom ash aggregate.In contrast,the growth rates of various shrinkage indexes would decrease when bottom ash pellets are added.Finally,the environmental safety performance and comprehensive benefit of cement stabilized macadam and bottom ash mixture were analyzed.The results show that the leaching concentrations of heavy metals in the mixture are obviously lower than that in waste incineration bottom ash,which can meet the standards of Class V water quality identification,due to the consolidation of cement.Therefore,when used in road engineering,cement stabilized macadam and bottom ash mixture will do little harm to the surrounding environment.The scheme of using bottom ash pellets made by balling technology as coarse aggregates of cement stabilized macadam mixture can effectively improve the utilization rate of waste incineration bottom ash and avoid resource waste.The research results can not only reduce the landfill amount of bottom ash and save the land,but also help to reduce the exploitation of natural stone and promote the construction of resource-saving and environment-friendly society.