Analysis Of RAP Mixing Uniformity Of Road Maintenance Vehicles And Evaluative Studies

During the mixing process,hot recycled asphalt mixture will produce uneven mixing phenomenon,which affects the quality of the pavement,and should be evaluated and tested.Relying on the hot recycled asphalt pavement maintenance vehicle project of Zhejiang Meitong Road Construction Machinery Co.,Ltd.,this thesis takes the mixing device as the research object,theoretically analyzes the force and stirring mechanism of asphalt mixture particles in the RAP mixing process,optimizes and improves the structure of the mixing device,puts forward accurate and rapid mixing uniformity evaluation indicators,and carries out the analysis and evaluation of the RAP mixing uniformity of the road maintenance vehicle based on EDEM discrete element and digital image technology,combined with simulation test and engineering measurement.The main conclusions reached are as follows:(1)The structural composition and mechanical characteristics of the hot-recycled asphalt mixture and the stress of the hot-recycled asphalt mixture were analyzed;According to the original structure of the mixing device,the structural improvement was carried out,the relevant parameter design of the three-blade spiral mixer knife and the arrangement of the six-blade mixing arm at the interval angle of 60° were completed,and through the force analysis of the improved mixture particles,it was concluded that the improved mixing device was conducive to improving the mixing uniformity of asphalt mixture.The mixing and recycling mechanism of hot-recycled asphalt mixture and the change trend of mixture uniformity during the mixing process were analyzed,and the diffusion and fusion model and mathematical equation of hot-recycled asphalt mixture were established,and the analysis results showed that the parameters such as the ratio of new and old asphalt mixture,the gradation of new asphalt aggregate,the stirring speed,and the mixing time affected the diffusion and fusion process of the mixture microscopically,and the mixing uniformity at the macroscopic level,and then affected the regeneration quality.(2)The basic principle of discrete element method is analyzed,and the HertzMindlin with JKR model is used in the simulation process.According to the main structural parameters and working parameters of LMT5180 maintenance vehicle,the geometric model of the mixing device was established by CATIA.According to the gradation of AC20 asphalt mixture,the particle model of hot recycled asphalt mixture was established by using the spherical particle stacking method.The parameter settings in EDEM and the solver settings for the entire model run process have been completed.(3)The uniformity evaluation index was established,and the uniformity of the mixture in each block area was evaluated by using the separation coefficient Qi of the asphalt mixture in each region,and the overall mass separation coefficient Qc was used to evaluate the mixing uniformity of the overall asphalt mixture.Based on EDEM discrete element software,the mixing uniformity of hot recycled asphalt mixture was simulated and analyzed,and the particle distribution map and correlation curve of the mixture under different parameters were obtained,and the results showed that the large particles in the hot recycled asphalt mixture had a greater influence on the mixing uniformity.The proportion of fine aggregate can be appropriately increased in the new aggregate gradation to improve the mixing uniformity;When the ratio of new and old materials of asphalt mixture is 1:1,the speed is 30 r/min,and the mixing time is 16 min,the Qcg value of the mixture in the mixing pot and after paving the mixing area and the Qcd value of the mixture in each area are smaller,and the mixing uniformity is better.Under different working conditions,the change law of hot recycled asphalt mixture in the mixing pot or after paving shows good consistency,and the mixing uniformity in the mixing pot can be evaluated with the help of the uniformity of the asphalt mixture after paving.(4)The considerations for evaluating the uniformity of RAP are analyzed,and the weighted binned four-sided static distance heterogeneity coefficient Cv relative to the ideal uniform distribution is proposed as the evaluation index of the uniformity of hotrecycled asphalt mixture,and the calculation equation and calculation procedure of the weighted binned quadrangular static distance variation coefficient are given.Based on digital image processing technology,the image of the hot recycled asphalt mixture obtained in the actual measurement was imaged,and the characteristic parameters of the particles in the image of the hot recycled asphalt mixture were extracted.According to the uniformity evaluation index Cv and the measured image of the project,the Cv value of the digital image of RAP pavement under different ratio of new and old materials,new aggregate gradation,different stirring speed and mixing time was obtained,and the results showed that the best working parameters were as follows: the ratio of new and old materials was 1:1.The stirring speed is 30r/min;The stirring time is 16 min.Compared with the simulation test results,the results obtained by the engineering measurement have high consistency,indicating that the uniformity evaluation index Qc of the hot-recycled asphalt mixture proposed in the simulation analysis and the uniformity evaluation index of asphalt mixture proposed in the engineering measurement Cv can fully and accurately reflect the mixing uniformity of the hot-recycled asphalt mixture.