| In recent years,with my country’s vigorous investment in various infrastructure construction projects,the output and consumption of cement concrete have become larger and larger,and the requirements for concrete performance have become more and more stringent.The study found that the overall uniformity of concrete after mixing directly affects its strength.In addition,the macro-uniform cement-paste is found under the microscope that a part of the cement particles are agglomerated together without being dispersed,which adversely affects the strength and engineering durability of concrete.Therefore,exploring methods to improve the macro-uniformity and micro-uniformity of cement-paste has very important practical significance for enhancing the strength of concrete and improving the quality of the project.The thesis studies a medium-high speed cement-paste mixing equipment,which aims to prepare ideal cement-paste with cement aggregates broken and cement particles uniformly dispersed,and then mixed with aggregates to prepare high-performance concrete.The Fluent software was used to simulate the two-phase flow field of cement and water-solid-liquid in the mixing equipment,and the factors affecting the macro-uniformity of the cement-paste were explored by adjusting the mixing parameters.At the same time,the discrete element method is used to simulate the microscopic cement aggregate crushing process using EDEM software to explore the factors that affect cement aggregate crushing and the micro-uniformity of cementpaste.The main work and conclusions are as follows:(1)Combining the current solid-liquid two-phase flow mixing research theories and results,using the existing medium and high-speed cement-paste mixing equipment as a prototype,the mixing equipment has been 3D modeling,area division,and area division through Solid Works software and ANSYS Workbench Fluent module.Grid division,boundary conditions and calculation condition settings,etc.Additionally,the flow field distribution of the cement and water solid-liquid two-phase flow can be simulated and calculated.(2)Using the controlled variable method,the Fluent software was used to calculate the factors such as different stirring speeds,different blade diameters,presence or absence of spoilers,different stirring arm lengths,different axial distances of pressure plate isolation discs and hole openings of the mixing equipment.Simulation and analysis of cement particle traces and solid holdup cloud diagrams.At the same time,axial and radial monitoring surfaces are set to monitor the change process of cement volume fraction during the mixing process,and comprehensively analyze the two-phase flow law of cement and water under different mixing parameters and the The influence of the macro-uniformity of cement-paste.The results found that: the stirring speed is 800 rpm,the diameter of the stirring blade is 15 mm,the spoiler is set on the upper part of the stirring equipment,the long arm type is selected for the length of the stirring arm,the axial distance of the pressure plate isolation disk is 15 mm and the opening of the pressure plate isolation disk hole is higher.Half-open,which is beneficial to the two-phase mixing of cement and water inside the mixing equipment,and is beneficial to the improvement of the macro-uniformity of the cement-paste.(3)Use EDEM software to simulate the crushing process of cement aggregates,complete the replacement and bonding of cement aggregates by writing API files and setting the bonding contact model,calculate the different rotation speeds and blade diameters of the mixing equipment,and introduce the crushing percentage parameter.The results showed that compared with the mixing speed of 500 rpm,the crushing effect of cement pellets was better at 700 rpm,and the smaller the diameter of the stirring blade was 20 mm,which was more conducive to the crushing of cement pellets and the improvement of the micro-uniformity of the cement-paste. |
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