Research On The Structure And Mixture Of Hot In-place Recycling Of Asphalt Pavement

Hot in-place recycling(HIR)of asphalt pavement is widely used in recent years as an environmental and efficient preventive maintenance technology.At present,the main concern of using HIR is the recycled asphalt mixture performance,and the structural mechanics characteristics of pavement has been less concerned.Therefore,this article starts research both on structural analysis and mixture design of HIR of asphalt pavement.First,relying on the project of HIR of asphalt pavement on Nanchang-Jiujiang Expressway,put analysis to the old road and its traffic condition;investigate the old road,and then analyze the main diseases of pavement and the relationship between diseases and route characteristics;take core-drilling on the pavement to give intuitive judgment on the horizon and the development status of pavement diseases;through testing the old pavement deflection,evaluate its structural stability;analyze the causes of its diseases and evaluate the technology applicability of HIR which is based on comprehensive traffic conditions,disease characteristics and structure characteristics.Second,cut the core-drilling from pavement in layers and test the compression rebound modulus of each layer;derive the relation of each layer by the linear elastic theory to determine their modulus combinations;regard the layer between surface course and earth subgrade as one layer,and inverse operation of this layer is done by BISAR with the index of old pavement deflection;three factors,old pavement deflection,lower middle layer modulus and recycling layer modulus,which influence studying the mechanics characteristics of recycling asphalt pavement,are used to set finite element model and analyze the influence on mechanics characteristics.Third,comparing the common design method of hot asphalt mixture and combining the performance of recycled asphalt mixture,define its major method and process of designing;mineral aggregate gradation and old asphalt performance in RAP are analyzed to design three distinguishable gradation;content of recycling agent is determined by practical experience,aiming on improving perfonnance of recycled asphalt;the best new asphalt content is estimated by formula,combining characteristics of HIR,and then fixed through Marshall stability test;test the high-temperature stability,water stability and compression rebound modulus of asphalt mixture which has two different mineral aggregate gradation.Fourth,analyze the key factors,content of recycling agent,mixing temperature,RAP fragmentation degrees and mixing time,which influence its performance through experiments and proportion variation of old and new asphalt in HIR construction;analysis method of recycled asphalt mixture gradation is set up and influence of new asphalt mixture gradation and content on recycled asphalt mixture gradation is studied.The result shows that the HIR technology is applicable with judgment of pavement diseases,combining with pavement structure and material characteristics;the inverse operation modulus of surface course and base course can reflect modulus of each layers;old pavement deflection influences the mechanics performance of each layer while mechanics performance of recycling layer is mainly influenced by its modulus;modulus of recycled asphalt mixture is lower than original one.when this recycled mixture is applied in recycling layer,the mechanics performance can fully meet its requirements,a higher level tensile stress set bad effect on the bottom of recycling layer;in HIR construction,content of recycling agent,mixing temperature and mixing time need controlling strictly,which can influence the performance of mixture;as the proportion of new and old asphalt fluctuates,in order to guarantee the stability of recycled mixture,recycled mixture gradation should be set near original RAP one under the circumstance that RAP gradation can be used as recycled mixture gradation.