Experimental Investigation On Microstructure,Mesostructure And Mechanical Properties Of Cemented Paste Backfill

The backfilling method has high resource recovery rate and low depletion rate,which can effectively control ground pressure activities,especially in the mining of deposits with complex ore body occurrence conditions,the surface does not allow collapse and spontaneous combustion tendency.The cross-scale study of cemented paste backfill(CPB)is an inevitable way to deeply understand the nature of backfill.As an ideal way to protect the environment and eliminate hidden dangers in the mine,backfilling technology has been widely used in mine production practice.In this paper,by mixing different raw materials of CPB,CPB with different proportions were produced,and indoor micro,meso and macro tests were performed,respectively.Through digital image technique,the pore structure of CPB was quantified,and the relationship between the microstructure and mechanical properties of backfill was studied.The accurate physical PFC model of backfill was established based on SEM in the mesoscopic test,the mesoscopic structure of backfill was quantified,and the relationship between the mesoscopic structure and mechanical properties of backfill was studied.The macro test studies the mechanical properties of CPB by the uniaxial compressive strength(UCS),residual strength and elastic modulus.The main conclusions are as follows:(1)The microstructure of CPB had great influence on UCS of CPB.For example,during the development of CPB,porosity,porosity number and average pore area decrease first and then tended to be stable.The UCS of CPB changed with the change of these characteristic parameters in pore size.(2)The main hydration products of CPB were AFt,Ca(OH)2 and C-S-H.With the increased of curing time,the content of AFt and Ca(OH)2 decreased,while the content of C-S-H increased.The hydration products were closely related to the strength development of CPB.(3)Based on the powerful simulation software PFC2D for the meso-mechanical properties of geotechnical materials,a mesostructure PFC2D model of CPB was established based on SEM images.Through the numerical simulation test of CPB,mesoscopic information such as porosity,coordination number(Cn),contact force chain,which were difficult to obtain in the laboratory,were obtained.For example,the Cn of CPB decreased with the extension of curing time.(4)Cemented backfill material composed of whole tailings,cement and water.After 3-28 days curing,the strength of CPB increased rapidly.After curing for 28 d,the weibull average compressive strength of backfill was(1.06±0.15)MPa.As the T/C of backfill increased,the residual strength decreased gradually,and the correlation between them was negative.There was indeed a linear relationship between the strength and the elastic modulus of the backfill,but it was smaller than the coefficient value in the empirical formula.