Research On Mixing Quality And Discharging Efficiency Of Concrete Mixer Truck

As the transportation equipment of fresh mixed concrete,the unreasonable setting of process parameters and structural parameters of mixing truck will lead to segregation and bleeding of fresh mixed concrete,which will reduce the uniformity of concrete put into use,and ultimately affect the quality of engineering construction.Therefore,the uniformity of fresh mixed concrete is closely related to the quality of engineering construction,and it is very important to ensure the uniformity of concrete discharge.Compared with the experimental method,numerical simulation can better observe the flow behavior of concrete in the mixing cylinder,and easily obtain the movement information of concrete particles,so as to better study the movement behavior of concrete in the mixing cylinder.This paper mainly studies the influence of technological parameters and internal structural parameters of mixing drum on the homogenization of mixing drum through DEM numerical simulation,so as to improve the homogenization of mixing drum.The main research contents are as follows:(1)Fresh mixed concrete was prepared according to the national standard,and the flow performance of fresh mixed concrete was tested through slump test and L box test.The concrete numerical simulation model was established,and the concrete model was calibrated by slump and L-box test,so as to obtain the parameters needed for simulation.Based on the structural parameters of the mixing drum,a numerical model was established.(2)DEM was used to simulate the transportation process and discharging process of fresh concrete in the mixing cylinder,analyze the mixing condition,and evaluate the mixing quality and the characterization of discharging quality.The single factor test method was used to explore the influence of mixing speed on the homogenization of concrete under the condition of dry material mixing.It was found that when the speed varied from 10 rpm to 30 rpm,a larger mixing speed could advance the time when the homogenization of concrete reached stability.The effect of oblique Angle on the quality of fresh concrete mixing and discharging efficiency was analyzed.When the oblique Angle α varied from 13.4° to 17.4°,the results showed that the smaller oblique Angle could accelerate the discharging speed and improve the discharging evenness.(3)By changing the height,swing Angle and pitch of the mixing blade,a three-factor and three-level orthogonal test was established based on the simulation results obtained from the single-factor test to determine the best combination of blade structural parameters.The simulation results show that the installation of expanded wings accelerates the completion time of fresh mixed concrete discharge and improves the discharge efficiency.The installation of mixing plate improves the homogenization of discharge,and the homogenization of mixing plate in the front cone is more obvious than that in the back cone.According to the best technological parameters and structural parameters,the mixing tank was optimized,and compared with the basic simulation,the results showed that the homogenization of the optimized material was improved by 15%,and the number of the material was reduced by6.25%.(4)In the actual working condition,the concrete discharging uniformity of the mixing drum is analyzed,and the discharging uniformity of the mixing drum is explored under the two conditions of accelerating mixing and not accelerating mixing before unloading.Sampling,cleaning and screening,drying and weighing concrete at the three moments of 15%,50% and85% discharge of the mixing drum,taking 50% unit volume coarse aggregate quality as the standard.By changing the high speed mixing time in the simulation and comparing with the conclusion under the experimental conditions,it is proved that the discrete element method is feasible to simulate the discharge and mixing process of new mixed concrete in the mixer truck.