Experimental Study On The Preparation Of Fluid Backfill Material By Solid Waste Cementitious Material Curing Shale Soil

The backfill quality of narrow or irregular space(such as underground cavity,pipeline,foundation pit,highway ’three backs’,etc.)in geotechnical engineering is an industry pain point for many years.In recent years,the backfilling technology of fluid solidified soil with the characteristics of self compaction and self hardening is considered to be an advanced and valuable measure.On the other hand,low-quality solid wastes such as rice husk ash,desulfurization ash and steel slag have long been difficult to be effectively utilized,occupying land and polluting the environment.The development and utilization of these low-quality solid wastes for fluid solidified soil can explore a feasible resource utilization technology path,which has obvious economic and environmental effects.In this paper,rice husk ash,desulfurization ash and steel slag are compounded in proportion,supplemented by appropriate activator,and the synergistic effect between solid wastes is used to prepare a new type of special low-carbon cementitious material,which is used to solidify shale soil and realize fluidization pouring construction.The main research contents and results are as follows:(1)The orthogonal test was carried out by selecting 10%～20%of rice husk ash,40%～60%of desulfurization ash,20%～50%of steel slag and 8%of activator.The hydration products and microstructure of solid waste based cementitious materials were analyzed by XRD and SEM.Both macro and micro levels reflect that the cementitious material composed of rice husk ash,desulfurization ash and steel slag has excellent cementitious properties,which is feasible to use it to solidify shale soil to prepare fluid backfill material.(2)Considering the obvious difference in the strength formation mechanism of cementitious materials in the two systems of geotechnical soil and standard sand,three groups of cementitious materials with excellent mechanical properties in orthogonal test were selected for solidified shale soil test.Based on the mechanical properties of solidified soil,the mass composition of solid waste cementitious materials was determined as rice husk ash:desulfurization ash:steel slag=1:6:3(8%activator).(3)The effects of the content of solid waste-based cementitious materials on the unconfined compressive strength,drying shrinkage,pore structure and heavy metal leaching performance of solidified soil were studied.The results show that the fluid solidified soil prepared by solid waste-based cementitious materials can meet the strength requirements of general backfill projects,and there is no environmental risk of heavy metal leaching during service.Compared with cement solidified soil,the hydration product of solid waste based cementitious material solidified soil is mainly ettringite crystal,and the solidified soil has lower drying shrinkage.(4)XRD and SEM-EDS were used to study the hydration mechanism of solidified soil with solid waste-based cementitious materials.The test shows that compared with the plain soil(shale soil)structure,the agglomeration degree of particles in the solidified soil is significantly improved.The hydration products fill the pores of the solidified soil and change the connection mode between soil particles.The microstructure and mineral composition reflect that the hydration process of solidified soil mainly includes hydration of solid waste cementitious materials,cation exchange between particles,pozzolanic reaction of active components in clay minerals,hardening reaction during curing,and filling effect of cementitious materials.(5)Using mechanical force to improve the performance of solid waste-based cementitious materials.The test results show that the particle size distribution curve,water consumption of standard consistency,setting time,hydration process,mortar strength and mortar shrinkage of solid waste base cementitious materials change to varying degrees under mechanical force.When it is used to prepare fluidized solidified soil,the initial flow expansion of solidified soil increases with the increase of grinding time,and the time-dependent loss accelerates.Mechanical excitation has no significant effect on the early strength of solidified soil,while the later strength increases first and then decreases.(6)Considering that the composition of solid waste based cementitious materials and the properties of soil are very different.Based on the constraints of flow expansion and strength,this paper explores and proposes a mix proportion design process for fluidized solidified soil,in order to quickly obtain a fluidized solidified soil mix that meets the performance requirements.