Study On The Dry Process Crumb Rubber Modified Anti-Skid Layer Based On The Tire-Road Coupling

When an expressway enters a mountainous area,there is a large section of downhill.While driving on such type of road sections,the vehicle speed increases rapidly and the braking time and braking distance are relatively long due to acceleration effect of the vehicle gravity component in the advancing direction.However,when the vehicle is in a braking status for a long time,it can esaily lead to braking failure,following by serious transportation accidents like rollovers,rear-end collisions or even chain collisions.For certain vehicle,in the vehicle-tire-road coupling system,the strongest braking effect that the vehicle can achieve mainly depneds on the maximum braking force that the pavement surface provides for the tire.The pavement anti-skip design of the traditional advanced roads is generally based on micro-structure roughness and aggregate abrasion resistance without considering the braking effect that the friction between road deformation and the tire has on the tire.In fact,properly decreasing pavement stiffness can improve the elasticity of road surface materials,the attaching effect between the tire and the road surface for the purpose of increasing road surface braking force.Regarding all these problems,this paper adopts the method of adding crumb rubber particles and develops dry process CRM anti-skid pavement asphalt mixture.This kind of mixture,if used in highway long down hill,can realize the quick braking of vehicles on the long down hill highway,by improving the elasticity and ability to coordinate with deformation of pavement material,increasing the direct contact area between tire and pavement,and enhancing the adhering effect between the two.First,the paper proposed the rubber particle quality control index and density test method applicable to the dry process CRM and finished the skeleton interlocking dense gradation design used in the anti-skid pavement proportioning research.Second,the paper,by the method of coarse aggregate level-by-level tamping and fine aggregate level-by-level tapping and with the minimum voids in the coarse aggregate in the dry-rodded condition as evaluation basis,combined coarse aggregate void filling method(CAVF)so as to design skeleton interlocking dense grradation(SIDG)used in the dry process CRM anti-skid pavement asphalt mixture.The paper finished the single factor research on the dry process CRM anti-skid pavement compaction procedure,proposed the CRM anti-skid pavement asphalt mix design method,concluded the optimized compaction procedure of CRM anti-skid pavement by orthogonal test,put forward to the addition of crumb rubber for keeping CRM anti-skid pavement volume stability,obtained the height expansion ratio calculation method applicable for CRM anti-skid pavement by comparison and finally gained the optimized formula of dry process CRM anti-skid pavement.The details were as follows:1)by comparing the compaction times and compaction temperature of CRM anti-skid pavement asphalt mixture,internal and external addition method of crumb rubber,replacing the aggregate with same quality and same volume of crumb rubber,crumb rubber particle size,particle size of aggregate alternated with crumb rubber and compaction effects of different compacting machines on the anti-skid pavement,the paper proposed systematic mix proportion design method of dry process CRM anti-skid pavement asphalt mixture;2)by orthogonal test,the proposed compaction procedure of CRM anti-skid pavement was like this:crumb rubber content:not exceeding 5.5%of mineral material bulk volume;vibratory frequency:28.7Hz;vibratory duration:90s;vibratory temperature:180-175 ?;compaction temperature of Marshall Specimen:140? and 90 ?.Based on the above research,the compaction procedure of dry process CRM anti-skid pavement asphalt mixture was obtained:a.put the crumb rubber into aggregate and mix for 30s in dry status;b.add the asphalt into mineral material and mix for 90s;c.add the fiber into the mixture and mix for 90s;e.vibrate the mixture for 90s in 28Hz,170?;f.tamp the specimen with large Marshall compactor in 140?;3)compared the height expansion ratio of CRM anti-skid pavement Marshall Specimens and it was found that the expansion ratio grew faster and water damage risk increased accordingly when the rubber addition exceeded 8%;on this basis,the paper proposed 5.5%as the best content for keeping CRM anti-skid pavement compaction stability and gave the rational CRM anti-skid pavement expansion ratio calculation formula;4)by orthogonal test,the optimized formula of dry process CRM anti-skid pavement asphalt mixture was obtained as follows:grading:skeleton interlocking dense gradation(SIDG was recommended and SMA was acceptable);coarse rubber particle content(account for the volume of all the added rubber):50%;asphalt aggregate ratio increment percentage:0.3%;rubber swelling inhibitor content:0.5%;ozone oxidized duration:15min.Based on the above research,the paper systematically put forward to gradation design,compaction procedure,mix design and formula design method of CRM anti-skid pavement.All these can provide references for the research and development and preparation of similar type pavement material.This paper finished the research on the high and low temperature performance,water stability and dynamic performance of CRM anti-skid pavement,and according to current asphalt pavement structure design method in China,tested the uniaxial compressive modulus of elasticity of anti-skid pavement mixture and took the value as material characteristic of pavement three-dimensional modeling.The conclusions of the research are as follows:1)Proper amount of crumb rubber can significantly improve the high temperature performance of CRM anti-skid pavement.When the addition of crumb rubber increases to 3%from 0%,the mixture's high temperature performance is improved most significantly.However,when the addition of crumb rubber exceeds 5.5%,the mixture's high temperature performance begins to decrease;2)the appropriate increment of asphalt aggregate ratio can improve the low temperature performance and water stability of CRM anti-skid pavement.3)the small addition of crumb rubber can strengthen the elasticity recovery ability and anti-permanent deformation ability of CRM mixture;the increase of crumb rubber content can improve the mixture elasticity,strengthen recoverable deformation and shorten the elastic recovery time;4)the BPN of the CRM anti-skid pavement increases and the reduction of road surface friction coefficient slows with the increase of crumb rubber addition.The above research indicates that the CRM anti-skid pavement performance is good when the crumb rubber content doesn't exceed 5.5%;The small content of crumb rubber can significantly improve the high temperature performance of anti-skid pavement;while a large amount of crumb rubber can significantly improve the pavement elasticity.This paper establishes the three-dimensional model of longitudinal groove tires with tire and road surface contact area,road surface braking force and road surface dynamic coefficient as the main evaluation indexes and finishes the braking function analysis of CRM anti-skip pavement with different rubber content in ABAQUS\Standard and ABAQUS\Explicit analyses.1)first,drew the tire two-dimensionla cross section and then import in ABAQUS to divide gridding and inflate,on basis of which the method of symmetry model manufacturing was used to finish the three-dimensionl modeling of indenting tire;2)according to basic theory of pavement dynamics and refer to Specifications for Design of Highway Asphalt Pavement,took the actually measured value of uniaxial compressive modulus of elasticity of CRM anti-skid pavement and other material characteristic parameter as the pavement modeling parameters,built road three-dimensional model of CRM anti-skid pavement and finished the assembling of tire-CRM anti-skid pavement by the switch from displacement contact control to load contact control;3)did the friction contact analysis of tire-CRM anti-skid pavement under the conditon of different upper loads,different tire pressure and different longitudinal slip ratios.It was found that with the gradual increase of crumb rubber content,the grouding pressure distribution of tire on the CRM anti-skid pavement was more even;under the same external load,the pavement with a higher amount of crumb rubber had most significant braking effect;if the tire pressure was low,the tire rolling obstruction was mainly up to self characteristics;if the skid ratio was same,the CRM anti-skid pavement with 5.5%crumb rubber could provide largest braking coefficient;4)applying horizontal tension and reverse bening moment on the tire center could achieve the simulation of high-speed braking process of rolling tire on the down hill for 0.1s,and at the end of 0.1s,compared with the common pavement,the transient speed of vehicle on the CRM anti-skid pavement with 5.5%crumb rubber reduced 0.60%,and driving distance shortened 0.55%.By the above friction simulation analysis of tire-CRM anti-skid pavement,it can be concluded that CRM anti-skid pavement with better elasticity has obvious braking action,and can provide larger braking force and braking coefficient,thus effectively lower the tire braking speed and shorten braking distance.This paper did the application research of dry process CRM anti-skid pavement,built field project of dry process CRM anti-skid pavement and finished the mix design of field project according to the mix design method and compaction procedure obtained through previous laboratory research.It confirmed the completely dry process CRM anti-skid pavement construction procedure,and did the engine disengaged 0-type braking distance site test of same M3 coach on the trial road and adjacent SMA comparison pavement.The braking duration and braking distance of vehicles on the entity section were measured as 2.50s and 22.60m,0.17s and 0.93m less than that of vehicle on the adjacent comparison road respectively,and the mean fully developed deceleration(MFDD)and mean breaking deceleration increased 3.5%and 4.2%respectively.Therefore,the additon of crumb rubber increases the pavement elasticity,strengthens the adhering action of tire on the pavement,enhances the braking coefficient of pavement on the tire,and shortens the braking duration and distance.MFDD and mean deceleration of field project are 6.59 m/s2 and 6.14 m/s2 respectively.These values are close to the mean braking deceleration value of tire on the CRM anti-skid pavement with 5.5%crumb rubber content obtained in the explicit analysis of the tire-pavement friction transience which lead to the same conclusion,namely,the CRM anti-skid pavement with higher crumb rubber content can have obvious braking deceleration action on the vehicles,thus reducing vehicle's braking time,shortening braking distance and lowering the various serious traffic accidents occurrence probability caused by long braking time.By above research work,this paper,on the basis of previous test research,realizes the mutual demonstration of effectiveness and feasibility of braking action of CRM anti-skid pavement in the section of highway long down hill on the vehicles from the aspects of theoretical modeling and field project tests.