Experimental Study On The High Flowability And Super Early Strength Grouting Material And Its Slurry Diffusion Rule

Aiming at the problem that polymer grouting material is expensive to be used in grouting reinforcement of fine cracks in soft coal and rock mass in coal mine,and ordinary cement-based grouting material is difficult to be injected because of its large particle size,this paper develops high flowability and super early strength grouting material with ordinary Portland superfine cement as matrix material and nano-micro-particle material as reinforcement admixture.The rheological properties,injectability and super early strength of the grouting material are systematically studied.The grout diffusion law of the material is theoretically analyzed and numerically simulated.The field application of the material to the roof reinforcement of underground oxidation zone in coal mine is also studied.The main work and achievements of this paper are as follows:Composition design and rheological properties studies of the high flowability and super early strength grouting materials were carried out.The grouting performance indexes affecting the grouting effect of high flowability and super early strength grouting material are analyzed.Based on the measurement of particle size distribution of raw materials and the analysis of particle size distribution of Portland superfine cement and auxiliary particle reinforced materials,the components of high flowability andsuper early strength grouting materials were designed.The effects of glass beads,ultra-fine silica fume and nano-SiO₂ on the rheological properties of slurry,such as viscosity,fluidity,setting time and water consumption for standard consistency,were investigated through experiments,and the modification mechanism of high flow and ultra-early strength grouting material was revealed.The results show that:the slurry of high flowability and super early strength grouting material is a typical viscous time-varying power-law fluid.Glass beads can increase thixotropy,fluidity and setting time of slurry,reduce viscosity and water consumption of normal consisten of slurry;Ultrafine silica fume and nano-SiO₂ have little effect on thixotropy and fluidity of slurry,but they can reduce the setting time,increase the viscosity and water consumption of standard consistency.Glass beads have filling effect and ball effect,ultra-fine silica fume has filling effect,friction effect and pozzolanic activity,nano-SiO₂ has filling effect and crystallization nucleation effect,and the superposition effect of these effects can effectively control the rheological properties of high fluidity and ultra-early strength grouting materials.The hydration regularity and injectability of the high flowability and super early strength grouting material were studied.The hydration reaction process of the high flowability and super early strength grouting material was studied by low field nuclear magnetic resonance analyzer,and the variation rule of grout composition during the hydration process was revealed.A grout grouting monitoring platform based on low field nuclear magnetic resonance?NMR?was established,and the grouting performance of the high flowability and super early strength grouting material was compared with that of ordinary cement.The results show that:The dissolution period and latent period of high flowability and super early strength grouting material are 10³5min,shorter than that of ordinary 425 Portland cement.The duration of slurry viscosity stabilization period is basically equal to the sum of dissolution period and latent period.Grouting work should be carried out during slurry dissolution period and stabilization period.The grouting monitoring platform based on low field NMR imaging can apply grouting pressure of 0³0 MPa to the injected core,maintain stable confining pressure in the range of 0⁴0 MPa,and maintain stable grouting temperature in the range of 0⁸0?,thus realizing real-time,dynamic and accurate imaging monitoring simulation of grouting diffusion in underground coal mine grouting engineering.The grout of he high flowability and super early strength grouting material has better grouting performance than that of ordinary cement.The super early strength and hardening mechanism of the high flowability and super early strength grouting material were studied.By preparing standard samples with different additives and different ages,the effects of additives on compressive strength,peak strain,secant modulus and residual strength of hardened ultra-fine cement pastes with different ages were studied.The porosity and pore size distribution of hardened ultra-fine cement pastes with different admixture content and age were detected by low field nuclear magnetic resonance analyzer.The effect of additives and age on the microstructure of hardened superfinefine cement was tested by TG,DSC and scanning electron microscopy.The mechanism of super early strength of hardened superfine cement was revealed.The results show that:the strength of the high flowability and super early strength grouting material is determined by two main factors:porosity and pore size distribution,composition and composition and microstructure of hardened superfine Cement Paste.The strength of hardened superfine cement paste decreases gradually with the addition of glass beads,increases first and then decreases with the addition of ultra-fine silica fume,and increases by 37.8%with the addition of 8%.The addition of nano-SiO₂ can increase the strength of both 1d and 28d,and the maximum strength of 28d can be increased by 98.8%.The addition of nano-particle reinforcing admixture can adjust and optimize the porosity and pore size distribution of hardened cement paste and improve its strength.The pozzolanic activity,crystallization nucleation and filling effect of nano particle reinforced additives can promote the formation of three calcium gel structure of hydrated silicic acid,reduce the Ca?OH?₂plate crystal,and play a good reinforcement effect.Study on grouting diffusion law of the high flowability and super early strength grouting material considering fluid-solid coupling effect.On the basis of studying the rheological characteristics of high-flow super-early strength grouting material,considering the time-varying parameters of slurry such as viscosity and rheological model,the dynamic changes of porosity and permeability of grouted medium,and considering the fluid-solid coupling effect of slurry diffusion in porous medium,the high-flow super-early strength grouting material is studied and analyzed by COMSOL multi-physical field modeling software.The results show that the average diffusion radius of the fluid-solid coupling model is always smaller than that of the non-fluid-solid coupling model under the same grouting pressure.Under the same grouting pressure,the average porosity and permeability decrease with the grouting process,while the average porosity and permeability decrease with the increase of grouting pressure.With the recovery of the wind oxidation zone in 13116 working face of Gubei Coal Mine as the engineering background,the occurrence condition of coal seam and the bedrock wind oxidation zone characteristics were analyzed.On this basis,the time-varying rheological parameters of superfine cement slurry and the permeability characteristic parameters of roof strata in wind oxidation zone were measured;then a grout diffusion equation was established with the parameters obtained previously for the permeability characteristics of roof strata in the wind oxidation zone of Gubei Coal Mine.The grouting design was applied in actual engineering projects and its engineering effect has been proved to be satisfactory.The results indicate that superfine cement slurry whose water-cement ratio is 0.6 is a typical power-law slurry consistent with time-varying rheological parameters.It has better rheological properties during pumpable period and its rheological parameters can be controlled by highly dispersive nano-SiO₂ and polycarboxylate superplasticizer.For grouting in wind oxidized zone,comprehensive consideration must be given to effective permeability,porosity and time-varying rheological parameters c₀,k and n.To realize effective diffusion of grouting in coal and rock mass,grouting pressure and diffusion time must be reasonably designed rather than excessively increased.