Study On Visco-Elastic-Plastic Parameters And Rutting Prediction Model For Asphalt Mixture

Rutting is one of the main distresses for asphalt pavement in Jiangsu Province.At present,most highways in Jiangsu Province have been used for over 10 years,with some of them over 15 years.The service times have been already exceeded the original design life,thus,a big question placed in front of the road managers is whether the high-temperature performance of the existing asphalt layers has been degraded,and whether the rutting growth will accelerate in the next few years.In order to answer this question,it is necessary to thoroughly investigate the change law of the high-temperature performance of asphalt mixture,and make a reasonable rutting prediction for the future.Firstly,a new laboratory test called multi-sequenced repeated load(MSRL)test was developed in this study and based on this test,two new evaluation indicators,compound average strain rate(CASR)and compound creep stiffness modulus(CCSM)were also proposed.Through carrying on the MSRL test under different loading order and various stress loops and repeated load(RL)test under two stress levels,the effects of loading order on CASR,the effects of stress loops on permanent strain rate and the change rule of permanent strain rate with stress level were investigated,respectively.Besides,the variability and potential between conventional and newly-proposed indicator on evaluation of high-temperature performance of different modified asphalt mixtures were compared.Based on the calculation results from finite element pavement model,the indenter size,stress range and test temperature used for each asphalt layer in multi-sequenced partial load(MSPL)test were determined.Secondly,based on the MSPL test,a method for calculation the dynamic modulus of asphalt mixture from creep curve was proposed.The conventional dynamic modulus test and MSPL test under different stress levels were carried out on various types of asphalt mixtures.According to the results of dynamic modulus test,the effects of loading frequency,stress level,maximum nominal particle size,asphalt type and PG grade on the dynamic modulus of the mixture were investigated,respectively.Furthermore,with the results of MSPL test,the effects of stress level,repeated loading cycles,stress loop,the type of asphalt mixture and the height of specimen on dynamic modulus were also analyzed,respectively.Finally,the difference of dynamic modulus measured by the two methods was compared.Thirdly,the indirect tensile test(IDT),the Hamburg wheel tracking test(HWTT)and the MSPL test were performed on the field cores from different highway sections,then the correlation analyses were explored between different evaluation indicators from different test as well as between these evaluation indicators and field rutting performances.Fourthly,the MSPL tests were again performed on the field cores from various highways sections.Based on the test results,the effects of the factors on permanent strain rate of asphalt mixture,such as the position of the cores,asphalt type,density of mixture,layer,equivalent cumulative axle loads(ESALs),and service time were analyzed,respectively.According to the analysis results,a fourstage change law of permanent strain rate of asphalt mixture was proposed,and the stage of development of permanent strain rate for each layer under different stress levels were determined,respectively.At the same time,the permanent deformation is analyzed for different layers.Finally,a mechanical-empirical rutting prediction model was established,including five empirical parameters(calibration coefficient,contribution proportion of permanent deformation,thickness of asphalt layer,coefficient of traffic distribution,ESALs)and one mechanical parameter(double-compounded average strain rate).Yanjiang highway was taken as an example for rutting prediction.The coefficients of temperature distribution and the axle load distribution were calculated,respectively.The ESALs for each service year were concluded.Then the change rules between temperature-compounded strain rate and service time for each layer under different axle loads were fitted,respectively.Subsequently,the double-compounded average strain rate was calculated for each service year according to the above fitting functions.Next,the development of the rutting growth from opening to traffic to the next five years was predicted.Finally,calibration coefficient was obtained by comparison with the rutting performance of Yanjiang highway.In addition,the calibration coefficient was also used to predict and verify the rutting increment from 2017 to 2018 for Zhenli and Xuji highways.To sum up,this research provides a new test method and two indicators for evaluation of hightemperature properties of asphalt mixture,and offers a new perspective to reveal the change rule of permanent strain rate for asphalt mixture,and established a more accurate rutting prediction model incorporating the axle load spectrum from actual pavement,which can provide more reasonable and accurate solutions for maintenance management of pavement rutting.