Structural Design Indexes And Parameters For Flexible Base Asphalt Pavement Based On Accelerated Pavement Testing

With the rapid growth of the traffic volume and the aggravation of heavy load andoverloading, the early stage damage of expressway asphalt pavement is serious which effectsoperation safety and decreases the pavement life greatly. Through investigation of asphaltpavement structure and service performance all over the world, according to the adaptabilityof pavement structure and material under heavy traffic, flexible base asphalt pavementstructure is considered as an effective technical mean. However, the structure of flexible baseasphalt pavement is different from semi-rigid asphalt pavement, and the damage type and itsmechanism of flexible asphalt pavement became increasingly complicated and diversifiedunder heavy-traffic conditions especially. Therefore, according to the heavy-traffic conditions,technical problems about the design theories and methods of flexible base asphalt pavementstructure which includes design parameters, design indexes and control standard were to besolved urgently.With full-scale accelerated pavement testing, through paving flexible base full-scalestraight test track which embedded asphalt strain gauge at the bottom of asphalt layer,structural simulation experiment was conducted to study the pavement service performances.Dynamic modulus parameters of typical asphalt mixtures were tested by laboratory testing,and dynamic compress resilient moduli of graded broken stone and subgrade soil were testedby repeated loading triaxial test; Structure layer modulus of test track were backcalculated byutilizing FWD deflection basin, and the conversion relation between backcalculated modulusand dynamic modulus was built; Based on the measured actual pavement response, materialparameters of flexible base asphalt pavement structure was determined. Combined with thestatic axle loads collected by the toll station of Beijing-Shanghai Expressway, and based onvehicle classification criteria, axle load spectrum of expressway heavy traffic in ShandongProvince were established, and design axle load used in pavement design under heavy trafficconditions was proposed. Correlation analysis between tensile strain at the bottom of asphaltlayer and pavement temperatures at different depths beneath the surface was conducted.Representative temperature used to fatigue analysis of asphalt layer was determined. Withmulti-parameter regression method, temperature prediction equation which is used to fatigueanalysis of asphalt layer was built, and its temperature distribution frequency was alsodetermined in Shandong Province.Based on the analysis of damage type and damage mechanism, tensile strain at the bottom of asphalt layer course was proposed to be the design index of flexible base asphaltpavement so as to control fatigue cracking initiated from the bottom. Shear stress at the top ofasphalt layer was proposed to be the checking index for asphalt mixture design, which is usedto prevent Top-Down cracking of asphalt layer. Through the continuous observation ofpavement response of full-scale test track, combined with the pavement damage condition ofaccelerated loading test track, in-situ fatigue limit of asphalt mixture was proposed. Withlaboratory trabecular fatigue test of remodeling specimens with field hot asphalt mixture andthe prediction with Weibull function, laboratory fatigue limit of asphalt mixture was obtainedand then the strain ratio between field and laboratory was determined. Based on the statisticalresults of laboratoty fatigue test with different types of asphalt mixture home and abroad, andtaking further analysis of tensile strain limit levels of six kinds of typical long-life asphaltpavement structures, in-situ fatigue limit of different kinds of typical mixture were proposedrespectively. Field correction for fatigue prediction equation of laboratory asphalt mixtureswas carried out by Miner law.According to the design axle load, pavement materials parameters and environmentalparameters based on APT response study, and combined with fatigue limit of asphalt mixturesand material shear strength in-situ, design frame of flexible base asphalt pavement was builtinitially to prevent pavement cracking, design processes and procedures for flexible baseasphalt pavement were put forward, reasonable structure layer thickness of granular baseasphalt pavement is proposed under heavy load.