Study On Fluidity Behaviour Of Cemented Paste Backfill Slurry Based On Water Film Thickness Theory

The fluidity behaviour of cemented paste backfill(CPB)slurry is a macro manifestation of multi-factor interaction.Due to the many influencing factors of slurry fluidity and the variety of composition components,most people establish a single response between a certain factor(such as water-cement ratio,solid concent,etc.)and flow parameters,so many common problems in the generation and evolution mechanism of fluidity have not been effectively solved.In addition,in practice,collapse degree or rheological parameters(yield stress and viscosity)are usually used to study the fluidity of filling slurry.However,the slump,as a macro parameter,cannot reflect the internal mechanism of the flow.Meanwhile,the determination of rheological parameters requires a rheometer,which is not available in field or many laboratories.Therefore,the concept of water film thickness is introduced in this paper to further study the fluidity behaviour of CPB slurry.Water film thickness(WFT)is a comprehensive index including water content,particle gradation,particle shape and specific surface area of solids.The theory of WFT has been widely used in the field of concrete,but has not been reported in the field of filling slurry.Therefore,it is very important to verify the applicability of the theory in CPB slurry.In addition,due to the increasingly fine particle size of tailings(development of dressing technology and national environmental protection requirements),it is necessary to carry out relevant studies on the influence of tailings fineness and ultra-fine tailings on the properties of CPB slurry or CPB.Based on the theory of WFT,the following aspects are studied in this paper:(1)Packing density and WFT were introduced to characterize the coupling effect of solid concent and binder dosage on the fluidity of CPB slurry.The CPB sulrry with different solid concent and binder dosage were prepared by artificial tailings(ST).The packing density of the solid mixture system with different binder dosage was measured by wet packing method,and then used to calculate WFT.The flow spread diameter of CPB slurry was measured by using a mini slump cone,and the slurry velocity was measured by using a mini V-funnel.In addition,WFT was associated with fluidity to evaluate the applicability of the theory of packing density and WFT in the CPB slurry.(2)In order to study the influence of tailings fineness on the fluidity,mechanical behavior and microstructure of CPB sulrry(CPB).Water film thickness(WFT)and packing density were introduced to characterize the effect of tailings fineness on the fluidity of the CPB slurry.The packing density and flow spread diameter of the CPB slurry with different tailings fineness(33.9-74.94%)were tested by wet packing method and slump test.At the same time,the influence of tailings fineness on ultrasonic pulse velocity(UPV)and uniaxial compressive strength(UCS)of hardened CPB was analyzed.Scanning electron microscopy(SEM)and mercury intrusion porosimetry(MIP)were used to study the microstructure characteristics of the CPB samples.(3)In order to solve the problem of poor flow performance of ultra-fine unclassified tailings CPB slurry,and to better understand the change law of CPB slurry(with water superplasticizer)flow performance,the mini slump test(0%,0.3%,0.4%,0.5%and 0.6%)and differential thermogravimetry(0%,0.3%and 0.6%)of CPB were carried out.On the basis of the experimental results obtained,it is expected to further understand the improvement effect of superplasticizer on the performance of ultra-fine unclassified tailings CPB,and quantify the dispersing effect of superplasticizer,so as to provide theoretical guidance for the design of ultrafine unclassified tailings CPB in the field and the application of efficient superplasticizer.