Preparation And Performance Study Of Biomass Ash Lightweight Soil

Under the vision of carbon neutrality in China,the energy utilization pattern has intensified.Biomass,as a renewable and clean energy,has been widely used and has become the fourth largest energy body in China.After the promulgation of the 13th five year plan,the installed capacity of biomass power plants in China has been increasing,and the combustion of biomass has been rising.A large amount of biomass ash produced by its combustion can not be effectively disposed of,which has brought new problems and challenges to the whole industry.In addition,in China's built highways,the persistent disease of vehicle jumping at the bridge head has become the main factor affecting the road service level.At present,the most used technical means is mainly to use light filler to reduce the uneven settlement of abutment structures and road structures,so as to improve the problem of vehicle jumping at the bridge head.As a kind of lightweight material,the self weight of biomass ash is about 2/3 of that of general soil.Therefore,this thesis takes it as the main raw material and uses cement,fly ash and other materials to study and prepare a lightweight,high strength,good fluidity and simple construction pouring material-biomass ash lightweight soil,which can not only effectively improve the problem of vehicle jumping at the bridge head,but also provide an effective way for the bulk utilization of biomass ash.In this thesis,the performance of raw materials is analyzed by indoor test,and then the influence law of various influencing factors on the consistency and strength of biomass ash lightweight soil is analyzed by orthogonal test,and the best mix proportion is determined.Secondly,a large number of laboratory tests were carried out to study the influence of binder content on the mechanical properties and durability of biomass ash lightweight soil,and analyze its applicability.Finally,ABAQUS finite element software is used to make a finite element comparative analysis between biomass ash as abutment backfill material and conventional filler,and its settlement deformation and stress distribution are analyzed.The main research contents and results are as follows:(1)Through the orthogonal test results and range analysis,the primary and secondary order of the influence of four factors a(percentage of cement in the total mixture),B(percentage of cement in the total mixture),C(percentage of water reducing agent in the cement)and D(water solid ratio)on the consistency is D>A>C>B,and the primary and secondary order of the influence on the strength is B>D>A>C.Factors a,B,C and D are positively correlated with consistency,and the consistency increases with the increase of its content.Factors A and B are positively correlated with the strength,the strength increases with the increase of its content,factor D is negatively correlated with the strength,the strength decreases with the increase of its content,and the strength increases first and then decreases for factor C.The wet density under the best mix proportion is only 1.42 g/cm~3,It is a relatively light material.(2)The unconfined compressive strength,shear strength and compressive resilience modulus of biomass ash lightweight soil increase with the increase of binder content,and the unit consolidation compression decreases with the increase of binder.Its unconfined compressive strength increases rapidly within 28 days,which is more than 80%of the strength of 120 days.The strength mechanism is analyzed by SEM.The strength mainly comes from cement hydration,fly ash filling and secondary hydration.The consolidation compression is small,about 50%of the unit consolidation compression of common abutment backfill materials,which can effectively reduce the settlement under load.Cohesion c is above 90kpa,internal friction angle?Above 30°,with high shear strength.The compressive resilience modulus is large,which is more than twice that of common abutment backfill materials.The 28d unconfined compressive strength and 28d compressive resilience modulus are preliminarily fitted,and the fitting equation is y=-300.4x~2+1656.7x-1799.6,R~2=0.962,with a high degree of fitting.(3)The dry shrinkage,water stability and freeze-thaw stability of biomass ash lightweight soil are improved by increasing the content of binder.The cumulative water loss rate and cumulative dry shrinkage value decrease with the increase of cement,and change rapidly to more than 70%of the total in the first 7 days,and the change law of dry shrinkage coefficient is not obvious.In the first three dry wet cycles,the strength of biomass ash lightweight soil increased slightly.After 15 dry wet cycles,the mass loss rate was 6.43%and the water stability coefficient was 71.91%.Under the first five freeze-thaw cycles,the freeze-thaw stability is high,all of which are more than 85%.After five freeze-thaw cycles,the deterioration of biomass ash light soil is intensified.After 15 cycles,the mass loss rate is 10.06%,and the water stability coefficient is only 48.12%.(4)Through finite element analysis,compared with biomass ash light soil and 6%cement soil,using biomass ash light soil for abutment back backfilling can greatly reduce the settlement deformation during the construction period under the action of self weight,reduce the horizontal thrust on the abutment back and improve the stability of the abutment.