Study On Agglomeration Rate Of Recycled Asphalt Mixture Based On Discrete Element Method

With the promotion of green,low-carbon and sustainable development by the country,the recycling and utilization of recycled asphalt mixture(RAP)has gradually become an important way for China to develop the green transportation industry.The significant influencing factor of road surface regeneration technology is the nature of RAP itself.Compared with native mineral materials,due to the uneven service life,traffic load,and maintenance history of old asphalt pavement,the quality and characteristics of RAP from different sources are complex.In addition,the milling method,degree of fragmentation,and precision of screening and grading are different pre-treatment methods,and there are a large number of agglomerated particles in RAP,Not only does it cause variations in the physical properties of RAP old aggregates and old asphalt properties,but the high agglomeration rate of RAP will also cause significant variations in the grading of old aggregates,which will have an impact on the road performance of recycled asphalt mixtures.Based on this,utilizes the applicability characteristics of discrete element method in asphalt mixtures,simulates and analyzes the production process of old materials through discrete element EDEM software,studies the agglomeration rate of RAP in different stages of milling,crushing,and screening,analyzes the degree of variation of RAP grading under different stages of agglomeration rate,and conducts simulation optimization tests for each stage,Obtaining suitable working parameters and methods for mechanical equipment,while ensuring that the structure of RAP old materials is not damaged,reduces RAP agglomeration rate and improves work efficiency.Finally,for the RAP old materials produced under the optimized working parameters in each stage,the agglomeration rate is verified through extraction and screening tests,and the particle size distribution in the old material agglomeration is analyzed.Combined with road performance tests,the specific performance of RAP old materials produced under common parameters and optimized parameters in high,low temperature,and water stability is compared,verifying that the simulated equipment optimization parameters have guidance.The relevant research content and conclusions are as follows:(1)By analyzing the theoretical basis,basic assumptions,and solution process of the discrete element method,the applicability characteristics of the discrete element method are studied.At the same time,the solving steps and applicability characteristics of the three-dimensional discrete element EDEM simulation software are studied.The research shows that the contact model in the discrete element EDEM software can describe the bonding state of asphalt mixtures and is suitable for simulation of asphalt mixtures.(2)Successively established discrete element models of old asphalt pavement,milling rotor,crusher,and vibrating screen,and simulated the processes of milling old asphalt pavement,crusher crushing and milling materials,and vibrating screen screening of old materials through EDEM software.By analyzing the characteristics of the simulation model,it was found that particle accumulation in each stage can affect the efficiency of equipment work,and fragmentation has a strong effect on the bond failure between RAP particles.Through numerical analysis and calculation,the agglomeration rate of old materials in each stage was obtained.The results showed that the agglomeration rate of milling materials in each stage of pretreatment was generally above80%,with a higher agglomeration rate.After crushing,the agglomeration rate significantly decreased,and after screening,the agglomeration rate of old materials was25%.(3)By using grading deviation degree,grading variation degree,and maximum grading deviation degree to evaluate the RAP grading variation degree of equipment at various stages under common parameters,research shows that the milling material has the highest degree of grading variation,and the RAP grading variation is the smallest after crushing and screening.Based on the premise that the structure of RAP itself is not damaged,the working parameters of the equipment in each pre-treatment stage were optimized through simulation optimization experiments.The research shows that the influence of various factors in the milling stage on the RAP agglomeration rate is as follows: milling depth,forward speed,milling speed.The appropriate milling machine parameters are: milling speed is 180r/min,milling depth is 40 mm,and forward speed is4m/min;After secondary crushing,the agglomeration rate of RAP significantly decreases and the crushing efficiency improves.However,through screening tests,it was found that the grading of the old material after secondary crushing will be refined,and the power of the hammer rotor should be reduced;The agglomeration rate and overall pass rate both perform well under a 20 ° screen inclination angle,which is beneficial for improving RAP screening efficiency.(4)Through extraction and screening experiments,verify whether the simulation is consistent with the agglomeration rate of old materials in the milling,crushing,and screening stages of actual production.The results show that the agglomeration rate of old materials in each stage is consistent with the simulation test results.By studying the particle size distribution in agglomerates,the results indicate that the formation of agglomerated particles in old materials is mostly dominated by aggregates with smaller particle sizes,with other particle size aggregates attached to them;The mass of agglomerated particles in RAP old materials with a size of 9.5mm and above exceeds50%,while the agglomerated rate in RAP old materials with a size of 4.75 mm is the lowest;In fine aggregates,the old RAP material with a thickness of 0.075 mm is also prone to agglomeration.By conducting road performance tests on RAP old materials produced with commonly used and optimized operating parameters of the equipment,the results showed that the quality of the old materials produced with optimized operating parameters improved,the agglomeration rate decreased,and to some extent,the hightemperature stability performance of the recycled asphalt mixture was influenced,the low-temperature crack resistance and water stability performance of the recycled mixture were improved.