Study On The Layout Optimization Of Concrete Pump Truck Conveying Pipe And Its Elbow Wear

Concrete pump truck has become a preferred construction machine for concrete pouring in the construction occasions of low-rise or medium-rise buildings,and its fresh concrete pumping technology has always been the key technology for successful concrete pouring.In the process of pumping concrete,there are often some phenomena that are not conducive to pumping,including segregatio n,bleeding,and even pipeline blockage.Once these undesirable phenomena exist,they often cause concrete pumping failure.Therefore,there is an urgent need to conduct necessary research on the flow characteristics of concrete and pumping process in a conveying pipe,and it is also of great significance to predict the pumping pressure loss and pipe wall wear during construction.At present,there have been a large number of pumping experiments to study the flow behavior of fresh concrete in a conveying pipe.Although the pressure loss caused by pumping can be obtained,the detailed information of its flow behavior is not available,including the movement of coarse aggregate and the wear mechanism of pipe wall,etc.For this reason,the numerical simulat ion method has become an effective tool for studying the pumping of fresh concrete.In this paper,the method of combining computational fluid dynamics and discrete element method(CFD-DEM)will be used to establish a numerical model for the pumping of fresh concrete.In this paper,the layout of the concrete pump truck conveying pipe(including the conveying pipe in the pumping system and the conveying pipe in the boom system)is optimized with the goal of minimizing the pumping pressure loss.In addition,the pipe wall wear of a 90° elbow that is common in concrete pump truck is studied.The main research contents of this paper are as follows:(1)In order to establish a numerical model of fresh concrete pumping,this CFD-DEM coupling method was involved,and reasonable boundary conditions were set in the process of establishing the model.Without considering the boundary lubrication layer,the pressure loss of the tapered pipe and bend pipe was predicted,and compared with the empirical formula in the pumping construction technical regulations.The pressure loss of straight pipes was predicted with consideration of the boundary lubrication layer and verified with the pressure loss calculation formula value derived by Kaplan and the experimental value by Choi.In addition,by carrying out a small pumping test,the pressure loss per meter of the straight pipe section under different displacements was measured and compared with the simulated value of whether there is a boundary lubrication layer.(2)The layout of conveying pipes of the first part in concrete pump truck(that is,the conveying pipes of the fixed part in the pumping system)has been optimized.Through the pumping simulation,the relationship between the length,inclination angle,curvature radius and bending angle of different types of pipes and the pumping pressure loss is obtained,and the total pumping pressure loss of the first part pipes can be obtained by the accumulation of the pressure loss produced by each pipe.The layout of the first part pipes was optimized with its fixed spatial position as a constraint.(3)The spatial gesture of conveying pipes of the second part in concrete pump truck(that is,the conveying pipe in the boom system)has been optimized.First,the relationship between the pressure loss of the boom conveying pipe and inclination angles are obtained,and the pressure loss of the entire boom conveying pipe can be obtained by the accumulation of the pressure loss of each pipe.Finally,the space gesture is optimized based on the maximum turning angle of each boom section and pouring position.(4)Based on the CFD-DEM coupling method and Archard wear model,a pumping wear model of fresh concrete was established.First,the wear coefficient in the Archard equation is obtained through wear experiments.And then the influence of curvature radius of elbow,the content of coarse aggregate,the shape of coarse aggregate,and the size of coarse aggregate on the degree of wear of the pipe wall is analyzed.Finally,the gray correlation method was used to evaluate the influence of these factors on the maximum wear rate of the pipe wall,and the correlation degree of the factors was sorted.