Research And Application Of Circulating Fluidized Bed Ash Improved Soil As Subgrade Filling Material

Circulating fluidized bed ash(hereinafter referred to as CFB ash)is a by-product of circulating fluidized bed coal combustion.Since it contains anhydrite and f-CaO,it will cause obvious expansion,resulting in a large amount of accumulation and landfill,and the utilization rate of resources is low.Therefore,to promote the large-scale utilization of CFB ash and slag,it has theoretical value and practical application needs to study whether CFB ash slag modified soil can be used as roadbed filler.Since CFB bottom ash is an industrial solid waste,it is determined whether it meets the requirements of roadbed filler by studying its physical properties,chemical composition,and environmental performance.The results show that the CFB bottom ash contains active silica,alumina,and free calcium oxide,which constitute a SiO2-Al2O3-Ca(OH)2 pozzolanic reaction system,which is self-hardening in water,and the CFB bottom ash has good gradation,so self-hardening Higher than CFB fly ash;CFB ash leaching concentration of heavy metals is low,and radioactivity both meet the technical requirements for roadbed fillers.Therefore,CFB bottom ash has the potential to be used as a subgrade filling improvement material.Through laboratory tests such as standard compaction,bearing ratio,water absorption,water swelling rate,and penetration test,the composition design and performance influence of CFB ash-slag improved soil were discussed.mechanism.The results showed that the compaction properties,mechanics,water stability and permeability of the improved soil were significantly improved after the addition of CFB ash.When the content of CFB fly ash is 10 % and the content of CFB bottom ash is25 %,the CBR values of the improved soil are the highest,which are 25.7 % and123.9 %,respectively,which are 87.6 % and 804.4 % higher than those of the plain soil,and the water absorption,immersion expansion rate and permeability coefficient are all optimal.Through microscopic analysis,CFB fly ash has a large fineness,and with an appropriate dosage,it can fill the pores of soil particles to improve the strength,and the CFB bottom ash particle gradation is continuous.In the improved soil,it can build a skeleton and change the contact form to improve the strength;The internal structure of the improved soil is changed by hydration products,the thickness of the water film of the soil is reduced by ion exchange,the water absorption is reduced,the density is improved,and the water stability and permeability are improved.Based on the above mechanism,a model of CFB ash and slag improved soil was established.By studying the specific surface area,0.045 mm sieve and f-CaO mass fraction,the CFB fly ash of different power plants was studied.By studying the fineness,gradation and activity index,the CFB bottom ash of different power plants was studied.By studying the liquid plastic limit and bearing ratio,the different soil samples were compared.The results show that the CFB ash quality of different power plants fluctuates greatly,but the influence on the performance of soil improvement is consistent.The difference in liquid-plastic limit of different soil samples is small,but the bearing ratio of prime soil is quite different,and it has been significantly improved after CFB bottom ash improvement.Based on the above experimental results,this paper studies and optimizes the key construction technology based on the actual project,proposes the construction quality control and detection method,conducts the paving of the test section of the CFB ash and slag improved soil,and observes the road conditions of the test section.The results show that the CFB ash and slag improved soil test road meets the technical requirements and the road conditions are good,indicating that the CFB ash and slag improved soil has good social,economic,and practical value as a roadbed filler.