| In enhancing the lifespan of pavement structures in China,the Research Institute of Highway(RIOH)developed a 2.038 km full-scale pavement test facility referred to as“RIOHTRACK full-scale test loop”,to generate full-scale test data needed to validate,update and optimize the current Chinese design method of pavement structures and materials.Although in-situ measurement of pavement responses under various loading and environmental conditions has particular advantages relating to its ability to accurately represent on-site conditions(effects of size,material,environment,and traffic loading)and to overcome the limitations of theoretical analysis.Nevertheless,there is the need for alternative tools capable of computing dynamic responses at any point or location in the pavement structure for further investigation of the mechanical and structural behavior of instrumented pavement structures.This trend toward mechanistic and empirical pavement design methods underscores the need to better understand the mechanical and structural behavior of asphalt pavements for the future design of more durable pavement structures.This research combined full-scale pavement testing of the RIOHTRACK full-scale test loop facility with numerical analysis for an in-depth study of the distribution of mechanical responses in four conventional semi-rigid base asphalt pavement structures with typical functional and structural requirements,specifically designed to withstand various semi-rigid pavement-related distresses.The rationality of the different structural thickness combinations of asphalt layers,the structural adequacy of each pavement in terms of the distribution of dynamic response along the pavement depth was assessed in accordance with the mechanical and functional requirement of each layer.Furthermore,the characteristics of critical responses and their relative locations in the pavements were defined and the range of beneficial responses to improve the performance of these pavement structures was determined.The optimal set of structural design parameters such as structural thickness and thickness combination of the asphalt concrete layers,semi-rigid layers,and cement-stabilized subgrade,as well as the design stiffness and stiffness combination of the cement-stabilized materials used for the base,subbase,and subgrade were identified based on the functional and structural requirements of each pavement layer when the actual materials used in the RIOHTRACK full-scale test loop facilities were applied.To this end,an overview of the RIOHTRACK full-scale test loop facility,the structural and functional information of the experimental pavement structure,field instrumentation program,and the state-of-the-art data acquisition system were described.Details of the material characteristics of asphalt concrete and stabilized cement layers of the experimental structures were presented along with the design properties as well as the technical requirements for their implementation.The test program and mechanical behavior of four conventional semi-rigid base asphalt pavement structures at the traffic load applied by the controlled-load truck were evaluated.The mechanical characterization and performance of the proposed asphalt concrete behavior were examined.Appropriate test protocols were implemented to identify the main mechanical characteristics of asphalt materials.Input parameters such as stress-,time-and temperature-dependent viscoelastic properties of the asphalt concrete layers were thus derived from the results of dynamic modulus and creep-recovery laboratory tests.The recursive-iterative algorithms for numerical integration and implementation of the Schapery nonlinear viscoelastic material model in the ABAQUS finite element code were derived.Then,the material model was used to analyze the behavior of different asphalt concrete mixtures subjected to creep recovery tests at different stress and temperature levels to successfully evaluate the robustness of the developed nonlinear material subroutine code UMAT.To accurately simulate the four conventional semi-rigid pavements in the RIOHTRACK full-scale test loop test facility,a full-scale nonlinear viscoelastic 3D finite element pavement model was developed.The model incorporated laboratory and fielddetermined mechanical and thermophysical properties of the pavement layer materials and implemented a realistic traffic loading that accounts for the influence and complex stress state of each wheel under the controlled-load truck when the pavement is exposed to environmental conditions.Hence,to capture the nonlinear temperature gradient in the pavement system,the user subroutines FILM and DFLUX were developed and integrated into the model.Likewise,the user subroutines DLOAD and UTRACLOAD were developed and incorporated into the model to include controlled-load truck axle load configurations,field measured tire footprints,non-uniform three-dimensional tirepavement contact pressure,and their spatial distributions.The measured field responses of the full-scale pavement test section in the RIOHTRACK full-scale test loop facility were used to successfully evaluate the accuracy of the thermal and combined thermal and dynamic load responses of the full-scale viscoelastic 3D finite element pavement model.An in-depth analysis of the spatial distribution of mechanistic parameters inside the four conventional semi-rigid asphalt pavement structures was done using the developed full-scale nonlinear viscoelastic 3D finite element pavement model.A parametric study was then performed to assess the sensitivity of influencing factors such as interface bonding condition,pavement temperature gradient,the combined effect of axle load and temperature gradient,truck speed,weight,and axle load,and the combined effect of wheel load on the mechanical response at critical locations as a function of pavement structure depth.The level of impact of each of the selected factors and the influence of their twoway interaction on the critical response of the pavement structure was investigated and a simple prediction model of the critical response based on selected influencing factors was proposed.The mechanical response of the conventional semi-rigid pavement structures with asphalt layer combination of 4+10+2 cm and 4+6+8 cm was compared with each other to evaluate the effectiveness of the applied structural and functional design parameters as well as the suitability of their structural combination and the materials constituting the different layers of each pavement structure.The performance of each conventional semi-rigid asphalt pavement in terms of the number of repetitions of traffic loads leading to structural cracking and structural deformation was assessed using the results of the finite element analysis and appropriate empirical transfer functions.The influence of structural design parameters including thickness combination of the asphalt concrete layers,semi-rigid layers,and cementstabilized subgrade,as well as design stiffness and stiffness combination of the cementstabilized materials used for the base,subbase,and subgrade on the structural performance of each semi-rigid asphalt pavement structure were extensively analyzed.Furthermore,a mathematical model was derived from the numerical simulation data according to a full factorial experimental design array.Then,desirability analysis was performed to simultaneously optimize the fatigue life of the asphalt concrete to prevent top-down fatigue cracking,fatigue life of the asphalt concrete to avoid middle-or bottom-up cracking,fatigue life of the semi-rigid layer to avoid flexural fatigue,and rutting life of the asphalt concrete layers to avoid permanent deformation.The results of this comprehensive study were presented,analyzed,and discussed.The key findings of this research study revealed the following:(1)The distribution of dynamic responses,the location and magnitude of the critical mechanical parameters,and the structural performance of the pavement depends significantly not only on the thickness and materials of the different layers but more importantly on their structural combination.(2)At the bottom of the asphalt concrete base layer of the four conventional semi-rigid asphalt pavement structures investigated,the compressive strains were significantly greater than the residual tensile strains when subjected to a full-scale loading truck.The critical tensile strains at the bottom of the asphalt concrete base layer were offset towards the location of the critical tensile strain at the bottom of the semi-rigid layer.The asphalt concrete surface and the intermediate layer and the semi-rigid subbase layer were found to be the unsuitable layers of the conventional semi-rigid asphalt pavement structures.(3)Asphalt layer thickness distribution combination of 4+10+2 of the semi-rigid pavement structures provided optimal performance division of the structural layers.(4)The nonlinear temperature gradient,although often neglected in mechanistic modeling,is a key parameter for the accurate prediction of stress and strain distribution in the pavement system.Factors such as high-temperature conditions,low-speed traffic,or overloading adversely affect mechanical parameters as well as service life of the pavement structure.Also,improving the contact conditions at the interface allows for the attainment of good structural performance.Overall,the research results of this thesis have significant theoretical significance and practical application values for the scientific design and analysis of improved performance pavement structures and the construction of more durable semi-rigid pavement structures. |
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