Analysis And Evaluation Of Bond Condition Between Structural Layers For Asphalt Pavements

Based on the computational method of double round vertical uniformlydistributed load under layered elastic system, the semi-rigid base asphalt pavementwith the presumption of completely friction between every two layers during thedesign is one of the most popular pavement structures in China. However, roadsdesigned by this method often lead to several early damages, such as elapse, upheaval,top down cracking, etc., which will dramatically reduce the service life of thepavements, affect the ride performance, increase operational costs as well as bringother negative effects to the traffic and social development to some extent.In addition, different loading conditions during service life and unstableanalytical results should be attributed to the disadvantages described above as well.Theoretical calculation shows that, compared with completely contact state, thestress-strain relationship of the pavement structure changes a lot when the interfaceof pavement is under half contact. Currently, there is no widely accepted method andindex to analyze the contact condition between the layers of pavement, which alsoresults in lack of design index to estimate bonding condition of layers. So it isnecessary to analyze and emulate the bonding condition of pavement layers throughtheoretic and experimental methods simultaneously.In this study, reasons for the early drawbacks of the pavement as well as itsconnection to the bonding condition of pavement layers followed by the mechanicalanalysis and related tests of bonding condition of pavement layers were qualitativelyintroduced. The main contents and conclusions are as follows:(1) On the basis of previous theoretical and experimental studies, composition ofthe shear strength with its influencing factors were analyzed. The mechanical modeland the evaluation index applicable to the further analysis as well as the evaluationapproach of the bonding condition of pavement layers were developed.(2) By using related analytical software, stress-strain relationship of thepavement structure with the change of interlayer bonding condition was analyzed. Theresults show that: when the shear modulus exceeds10~6MN/m~3, the bonding conditionof layers can be considered as completely contact; when the value is between10~2MN/m~3and10~4MN/m~3, the stress-strain relationship of the pavement structurechanges significantly. Once the value is less than10~2MN/m~3, the change is much slower and the bonding condition of layers can think as completely smooth.(3) This study evaluated the interlayer shear strength through practicable tests,considering some factors affect the interlayer bonding condition. It was shown that anoptimum binder amount leading to maximum interlayer shear modulus could alwaysbe found. The average value of the direct shear test is approximately10~3MN/m~3,which locates within the unstable stage of the stress-strain curve.(4) Modification of the interlayer shear modulus and evaluation of interlayerbonding conditions were made by comparing with experimental results. Thepercentage of interlayer bonding condition of vertical displacement, bottom stress andmaximum shear stress are73%,42%and36%respectively.