Study On Standard Of High Temperature Performance Of Asphalt Mixture In Gansu Province Based On The Full-scale ALF Test

The rutting prediction and standard and index of high temperature performance of asphalt mixture have beening focused point to the road sector. A rutting predictive model was established based on the ALF (Accelerated Load Facility) rutting test, the LWT (Load Wheel Test) rutting test, pavement mechanics analysis and the direct shear test. The indicators and specification of mixture high temperature performance in Gansu province were determined,which were releted with temperature, traffic volume, pavement conditions of structural mechanics, structural layer and so on. The research will have great significance of perfecting mixture rutting prediction and high temperature performance standards and achieving the integration controlling rutting of material and structure design.Firstly, this paper did investigation on asphalt pavement distress in arid and semiarid regions of Gansu and analyzed the unity between the distress of asphalt pavement and the use the environment to ensure the major types of distress of asphalt pavement in arid and semiarid regions. And then, this thesis proposed a new design specifications system. For arid and semiarid regions of Gansu, the main distress of the asphalt pavement were rutting, subsidence and low-temperature cracking. To control the above three distresses, the surface shear stress, the low temperature fracture stress and the compressive strain on top of sub-grade were proposed to added to the current specification (the flexure and the bottom layer tensile stress).The direct shear apparatus was used to test and analyze the anti-shear strength of mixtures. Many factors had influences on the anti-shear strength, such as asphalt type and grade, gradation type, nominal maximum aggregate size, temperature and so on. When the direct shear apparatus was utilized to test the anti-shear strength of mixtures, the reproducibility test of parallel was good in the same mixture. But the coefficient of variation of anti-shear strength was smaller in different mixtures. The direct shear strength could not effectively distinguish the performances of different mixtures. So, We proposed shear strength as a research-level indicator, but not a application-level indicator.The ALF accelerated pavement test was carried under different temperature and axle to three different pavement structures. The result showed that the anti-rutting performance of different pavements was great difference. The pavement thickness, temperature and axle load were important factors to the pavement rutting. Rutting occurred mainly in the middle and the top layer, and the lowest-layer was minimal. So we should control rutting hierarchically and improve the technical standards of the main rutting area. The calculation method of the rutting equivalent load factor was proposed and the value of which was determined by the rutting data from the ALF test.The shear stress, the vertical elastic deformation and the vertical stress of ALF test pavements were calculated. Through comparing the ratio of the sub-layer rutting of ALF test pavement with the ratio of mechanical index of the sub-layer, the anti-shear strength recommend as the mechanical index which determines the ratio of the sub-layer rutting.Considering these factors had obvious influence on rutting, the mixture performance parameters, shear stress of pavement structure, axle load number, pavement temperature, vehicle speed and pavement thickness were chosen as the basic parameters of the rutting predictive model. Based on the ALF rutting test, the indoor rutting test, pavement mechanics analysis and the direct shear test, two rutting prediction models were established, one was that characterizing the performance of mixture as anti-shear strength of mixture and the other characterizing the performance of mixture as the rutting depth RDo of LWT test at60min. According to the time hardening creep model, this paper used theoretical methods to implant vehicle speed into the rutting predictive model.The method and process of determining the pavement temperature, axle load number, vehicle speed, shear stress and anti-shear strength was proposed. The process of rutting incremental calculation was proposed reference to AASHTO2002. An example for calculating predictive rutting was given out, and the predictive accuracy was verified by comparing the predictive rutting and measured rutting of Linqing test road in Gansu province.The rutting controlling must took the sub-layer rutting into consideration. The traditional method was only to control the surface rutting. The tolerance rutting of sub-layer was multiplied by the partition coefficient of the sub-layer rutting with the surface tolerance rutting, and the partition coefficient of the sub-layer rutting was proposed determined by the ratio of sub-layer shear stress.For the problems in our present specifications of rutting test evaluation system, proposing the indicators of the mixture high temperature performance,which were releted with temperature, traffic volume, pavement conditions of structural mechanics, structural layer and so on. The indicators of the mixture high temperature performance were the mixture anti-shear strength, dynamic stability DS and RDo. At last the standards of the mixture anti-shear strength, DS and RDo in different typical structure and different layer in Gansu province were determined.