Experimental Study On Cement Stabilized Macadam And Bottom Ash Based On Cold-bonding Pelletization

In recent years,with the promotion of municipal solid waste incineration(MSWI),a lot of bottom ash is produced every year in China.If landfill is used,it will not only occupy the land resources but also generate a lot of landfill costs.At present,the resource utilization of bottom ash is still in the exploratory stage in China,and the research on using bottom ash in road base is also in-depth.However,due to the porosity and low bearing capacity of the bottom ash,the performance of the mixture will be affected if bottom ash is used as aggregate directly.In this study,based on the analysis of the technical properties of bottom ash,the cold-bonding pelletizing technique was used to prepare artificial coarse aggregates with a certain strength by using bottom ash as raw material.Then,they were mixed into cement stabilized macadam together with proper amount of bottom ashes as fine aggregates,and road properties,environmental safety characteristics and comprehensive benefits of the mixture were analyzedFirst of all,the chemical composition,particle size distribution,physical and mechanical properties of the bottom ash were analyzed by means of macro and micro detection techniques.The results show that the chemical property of the bottom ash is relatively stable and less reactive,which conforms to the basic conditions of road aggregate.However,the crushing value of bottom ash is greater than the technical requirement of the current specifications,so it is not suitable to be used as coarse aggregateSecondly,a four-factor,four-level orthogonal experiment was designed by using bottom ash in the range of 0-2.36 mm particle size,fly ash,cement,alkaline activator and water as raw materials.By adopting 7d unconfined compressive strength test and range analysis,and considering the cost factor,the optimum mix proportion of cold-bonding bottom ash pellet was determined.Then,the preparation process of the cold-bonding bottom ash pellet was explored from three aspects of the operation parameters of the pelletizer,the way of adding water and the curing mode,and the technical performance of cold-bonding bottom ash pellet was tested and analyzed at the age of 28d.The results show that the strength of the pellet is higher than that of bottom ash,and its crushing value has reached the technical requirement for the base aggregates of the second and lower grade highway.Then,the bottom ash pellet of the age of 28d was used as the coarse aggregate and the bottom ash was used as the fine aggregate to be mixed into the cement stabilized macadam mixture.Five groups of mixtures with different bottom ash pellet contents were designed.The mixture composition was determined by using heavy compaction test and 7d unconfined compressive strength test,and its mechanical and dry shrinkage properties were studied.The results show that with the addition of bottom ash and the increase of bottom ash pellet content,the 7d,28d unconfined compressive strength and 90d splitting strength of cement stabilized crushed stone and bottom ash gradually decrease.However,when the total mixing mass is 45%,the 7d unconfined compressive strength can meet the requirement of the current specification for the base mixture of the second and lower grade highway under heavy,medium and light traffic conditions.With the addition of bottom ash and the increase of pellet content,the shrinkage strain and shrinkage coefficient of cement stabilized crushed stone and bottom ash increase.The total amount of bottom ash and pellet should be controlled.Finally,the heavy metal leaching test was used to evaluate the environmental safety characteristics of cement stabilized crushed stone and bottom ash,and the economic and environmental benefits were analyzed.The results show the toxic leaching value of heavy metals in cement stabilized crushed stone and bottom ash with 45%of bottom ash and pellet content is far lower than that of bottom ash,which meets the class V surface water standard and has little impact on the environment.The addition of bottom ash and pellet can reduce the production cost of cement stabilized crushed stone,save the natural aggregate,and improve the economic and environmental benefit.The research results can not only improve the resource utilization rate of MSWI bottom ash in the road base,but also save land resources.They are beneficial to environment protection and play an important role in building a resource-saving and environment-friendly society.