Rheology Behavior And Pipe Flow Performance Of Wet-sprayed Shotcrete Under Initial Temperature Effect

The two most important research contents of wet-sprayed shotcrete supporting technique are ensuring the pipe flow performance of concrete slurry and the supporting mechanical property of shotcrete layer.Of which,propitious pipeline transportation is the foundation of concrete slurry being successfully ejected to the rock surface.Concrete slurry prepared in ground mixing station is easy to be influenced by low temperature and other factors when wet-sprayed shotcrete technique is utilized in cold area.This brings bad conditions like poor flow performance of slurry,high frequency of pipe blockage and unsteady jet velocity of shotcrete which makes concrete can not be even adhered to the rock surface.These will eventually lead to high rebound rate of concrete and easy cracking and shedding of wet spray layer.It indicates that the low initial temperature of slurry,which in this paper means the temperature of concrete slurry newly prepared in ground mixing station,makes the rheological and flow performance of wet-sprayed shotcrete can not meet the requiretments of mines.So,construction efficiency and mechanical properties of the concrete layer are badly influenced which greatly reduced the enthusiasm of employing wet shotcreting technology by cold area.Therefore,it is necessary to study the rheology behavior and pipe flow performance of wet-sprayed shotcrete under low temperature.This thesis mainly focused on the problems existing in the application of wet-sprayed shotcrete technique in alpine areas,so the initial temperature range of concrete slurry was below normal temperature(20?).Thus in this thesis,optimization of mix proportion for wet-sprayed shotcrete under low temperature was set as the breakthrough point,and then the related experimental research and theoretical analysis were carried out around the rheology behavior and pipe flow performance of slurry.Finally,the accurate prediction of pipe delivery resistance for wet-sprayed shotcrete was achieved and impact mechanism of initial temperature of slurry upon rheology behavior and pipe flow performance of wet-sprayed shotcrete in cold area was revealed.This thesis provided some theoretical basis and necessary conditions for popularization of wet-sprayed shotcrete in cold area.The work could be summarized as follows:(1)The optimum initial temperature of slurry and mix proportion of materials suitable for wet-sprayed shotcrete in cold area were determined.Firstly,the orthogonal rheolocgy experiments about mix proportion of wet-sprayed shotcrete under different initial temperatures of slurry were carried out.Secondly,the range method was utilized to select the optimum initial temperature(20?)of slurry and mix proportion of materials(cement content,sand ratio and water cement ratio were 460kg/m3.54%and 0.46 respectively).Then,another rheology experiment was carried out to verify the optimum parameters.Last,the Round Determinant Panel Test(RDP Test)was conducted to test the mechanical properties of the optimum parameters.All the above measures ensured the best rheology behavior of slurr\and the mechanical performance requirements of mine support.(2)A new rheological model and a calculation model of pipe resistance considering the initial temperature effect were built.Firstly,based upon the above orthogonal rheology experiments,a new rheological model and a new pipe resistance model were built.For engineering,the mix proportion of concrete,diameter of the wet spraying machine and current velocity of the slurry were known.Then,the slurry rheological parameters and pipe resistance could be easily obtained using the above two new models which made great progress compared with previous model research.(3)The influence law of initial temperature on pipe flow performance of slurry was revealed and the two new models were tested and verified.Firstly,a kind of semi-industrial loop test system was designed and built.Then by changing the initial temperature of slurry,pipe flow performance of wet-sprayed shotcrete under the selected mix proportion was analysed.Finally,the test results were utilized to verify the two new models.The results showed prediction accuracies of the new rheological model of concrete for yield stress and plastic viscosity were 85.39%and 85.86%respectively,and for pipe resistance,it was 83.83%which proved reliability of the models.In the initial temperature range of this thesis,the higher temperature could effectively reduce the on-way resistance in the precess of wet-sprayed shotcrete transport.(4)The accurate prediction of pipe delivery resistance under initial temperature for wet-sprayed shotcrete was achieved.Softwares FLUENT and EDEM were employed to simulate the flow velocity and pipe resistance of wet-sprayed shotcrete under different initial temperatures of slurry.The results showed that the coupling simulation results are highly consistent with the loop test results.It indicated that the newly built models and DEM-CFD simulation could accurately predict pipe flow performance of wet-sprayed shotcrete.(5)The influence mechanism of initial temperature on rheology behavior and pipe flow performance of wet-sprayed shotcrete was expounded.Firstly,SEM technique was utilized to analyse the influence mechanism of initial temperature on rheology behavior from the perspective of free water content.Then,a mathematical analysis method was used to establish a quality control equation of shotcrete,and for this reason,the influence mechanism of initial temperature on pipe flow performance of wet-sprayed shotcrete was revealed.(6)Some technical control measures for wet-sprayed shotcrete in cold area were proposed.Firstly,in view of problems occurred in the application of wet-sprayed shotcrete in a gold mine during cold period,technical regulations and optimization measures of wet-sprayed shotcrete for cold area were proposed.Then,various contrasts such as frequency of pipe blockage,rebound degree of sprayed concrete,compressive strength of concrete blocks and convergence deformation of the roadways before and after optimization were conducted in the underground roadway.The results showed that the research could commendably solve problems like poor bad pipe flow performance and bad supporting effect during wet-sprayed shotcrete technique being utilized in cold area.