Analysis Of The Motion State Of Microcapsules In The Process Of Cement Paste Mixing

Microcapsule based self-healing technology is an effective repair method for microcracking of concrete.It is of great significance in the improvement of durability of concrete and its service life.The achievement of the self-healing function induced by the microcapsules is due to that the microcapsules preserve the integrity during the mixing process of the cement-based material,and after hardening,rupture occur when the cracks expand.In this thesis,the CFD-DEM method is used to analyze the motion movement of microcapsules during the process of slurry agitation.In the process of slurry agitation,the existing experimental methods can not accurately obtain the motion state of the particles and fluid.In order to solve this problem,this study used a simulation and an experimental example to verify the suggested approach,and validated the subsequent computing results.This study analyzes the movement of microcapsules from three aspects.(1)The flow field changes of the slurry in the mixing tank are analyzed,including the velocity field,pressure field and turbulence intensity field.(2)Analyze the movement state of the microcapsules in the mixing tank.Including particle velocity field,coupling force,total force,compressive force,collision force.(3)The breakage rate of the microcapsules during the stirring process was estimated by judging the breakage value of the microcapsules.It was found that the coupling force,total force and average tangential collision force exerted on microcapsules during the slurry agitation process had no influence on the microcapsule rupture,whereas the pressure and average normal collision force may cause microcapsule breakage easily.The factors affecting the movement of the microcapsules in the mixing tank were analyzed,including the particle size and mass fraction of the particles and the stirring speed of the blades.It is found that as the particle size and stirring speed increase,the breaking rate of the microcapsules during the stirring process is increased.As the mass fraction increases,the particle breakage rate decreases first and then increases.It is recommended to stir the cementbased material containing microcapsules at a low-speed agitation with a mass fraction of 2% or 3% and a particle size of 600 ?m or less.This can effectively prevent the microcapsule from rupturing.In order to simulate the actual state of the microcapsules,the hollow microcapsules were modeled by the bonding model method,which provided a basis for further study on the rupture rate of the microcapsules.