Research On Design Controlling Index For Semi-rigid Base Asphalt Pavement

Semi-rigid base asphalt pavement is the most important structural type of highway in China.The research object of this paper is the designing controlling index for Semi-rigid base asphalt pavement.The durability of semi-rigid base is verified on the basis of pavement structural mechanics analysis,so the pavement design for this type of structure only needs to control the development of asphalt layer performance.Based on the development analysis of asphalt pavement performance,two typical damage types of semi-rigid base asphalt pavement are determined.Then the prediction models of typical damage types are constructed respectively,which lays a foundation for establishing mechanical-empirical design method of semi-rigid base asphalt pavement mechanics.Firstly,taking the expressway in Jiangsu province as an example,the decay law of the performance and structural strength of semi-rigid base asphalt pavement under the action of traffic volume was analyzed,and the correlation between each performance index and the cumulative equivalent axial load times was analyzed by using the single factor analysis method,and it was determined that the transverse crack which accounts for a very high proportion of damage and the rut which increases with the road age were the typical damage types of semi-rigid base asphalt pavement,and the correlation between them and the cumulative equivalent axial load times was significant.Secondly,the pavement temperature field of Jiangsu province in different seasons was analyzed by finite element method.According to the temperature field,three characteristic climates(spring /autumn,summer and winter)by four typical structure of semi-rigid base asphalt pavement were selected to generate total 12 working conditions.The actual temperature of different layers in different characteristic climates was determined according to the temperature field established by ABAQUS.The Dynamic modulus of totally 8 asphalt concrete types were tested in labrotory under 5 temperatures and 6 frequcies.Then the master curves for these 8 asphalt concrete types were established to calculate the actual dynamic modulus of each pavement layer under different characteristic climates,which acting as important inputs for structural mechanical response calculation.ABAQUS software was used to simulate and calculate the dynamic response of semi-rigid base asphalt pavement under vertical moving load in the upper mentioned 12 working conditions.The influence factors of driving speed,temperature,axial material modulus and pavement structure were studied.The fatigue life of semi-rigid base is calculated according to the bending-tensile stress level of the base under dynamic load.By analyzing the fatigue life calculation results of semi-rigid base,the semi-rigid base would not suffer from fatigue destroy and could be considered as a permanent structure.Then,based on traffic load,climate conditions and material properties of Jiangsu semi-rigid base asphalt pavement,the localization calibration of rutting prediction model of MEPDG was performed,obtaining suitable calibration coefficients for jiangsu expressway semi-rigid base asphalt pavement rutting prediction model.Results show that after the calibration,the predicting relative error of MEPDG rut predicting model was decreased to 14.59%,superior to the new specification rutting prediction model with prediction relative error of 42.3%.And at last,another typical damaged transverse crack of semi-rigid base asphalt pavement is studied in depth.Through multivariate factor analysis of indexes such as road age,increasing speed of transverse crack per kilometer,and interval of transverse crack after opening to traffic 5,10 and 15 years,it is determined that the significant influencing factors for the occurrence and development of transverse crack are traffic volume,mixture type of each layer of pavement,thickness of modified asphalt layer,total pavement thickness and type of base.Through correlationt analysis between ransverse crack spacing and traffic volume,traffic level significantly influences the formation and increasing speed of transverse crack during the first 10 years or so.but the influence degree gradually weakened as the crack energy release.The compound fracture significantly related with transverse crack spacing can be used as evaluation index of pavement material crack resistance.The sum of thickness of all pavement layers,accumulative total equivalent axle load pavement thickness and compound fracture energy were determined finally to set up the prediction model of transverse crack spacing in different stages.