Performance-based evaluation of unbound aggregates affecting mechanistic response and performance of flexible pavements

Unbound Aggregates;Flexible Pavements;Performance-based Evaluation;Resilient Modulus;Shear Strength;Permanent Deformation;Rutting;Mechanistic-Empirical Pavement Design Guide (MEPDG)

Xiao, Yuanjie

关键词: Unbound Aggregates;    Flexible Pavements;    Performance-based Evaluation;    Resilient Modulus;    Shear Strength;    Permanent Deformation;    Rutting;    Mechanistic-Empirical Pavement Design Guide (MEPDG);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/50366/Yuanjie_Xiao.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Unbound aggregates are widely used in road construction to replace unsuitable soil, prepare pavement working platform or construct pavement foundation layers. Their primary function in flexible pavements is to distribute wheel loads and provide adequate protection of the subgrade. However, the empirical strength based quality evaluations and current “recipe-based” specifications have little direct consideration of the actual performance of materials used in unbound aggregate layers. Based on a comprehensive set of laboratory repeated load triaxial test results archived for a variety of unbound aggregate materials, research efforts in this dissertation are aimed at linking aggregate physical and mechanical properties to pavement response and performance, identifying correlations among resilient modulus (MR), plastic deformation and shear strength behavior under repeated loading, and developing viable models to predict engineering behavior and field performance. This thesis is organized into three sections. First, statistical and generic algorithm (GA) based models are developed to estimate MR and shear strength properties for performance prediction using aggregate properties. The MR sensitivities are assessed using both Monte Carlo type simulation and First-order Reliability Method (FORM) with the interactions between aggregate properties properly taken into account. Both gradation and aggregate shape properties are identified as influential factors affecting MR. The effects of unbound aggregate quality on mechanistic response and performance (MR, shear strength and rutting) and layer characteristics on pavement life expectancies are investigated. Secondly, aggregate gradation effects on strength and modulus characteristics of unbound aggregates are analyzed from laboratory test results to develop improved material specifications. The most significant correlations are found between a gravel-to-sand ratio (proposed based on ASTM D2487-11) and aggregate shear strength properties. A certain value of gravel-to-sand ratio is proposed to optimize aggregate gradations for improved unbound layer performances primarily influenced by shear strength. To further confirm the optimal range of the gravel-to-sand ratio and verify existing packing theory based analytical gradation framework, a validated image-aided DEM approach is also employed to realistically study optimum contact and packing arrangements of the aggregate skeleton from various gradations and morphological levels for better aggregate interlock. Guidelines are recommended for engineering the aggregate shape and gradation properties to achieve such desired improved engineering performances of unbound aggregate layers. Finally, this research described employs the shakedown concept to interpret laboratory single-stage repeated load triaxial permanent deformation test results performed at varying dynamic stress states and aggregate physical conditions. A stable permanent strain rate is highlighted to give a viable criterion for ranking the rutting potential of unbound aggregate layers under realistic field stress states and also relating to shear strength via the Mohr-Coulomb failure criteria. A unified approach to rutting prediction that is applicable to a much wider range of stress states and physical conditions is also developed based on shear strength properties and validated using actual rutting measurements from field full-scale accelerated pavement testing (APT) sections. The methodology and results in this dissertation provide insights that could potentially be used to develop performance based material characterization and design framework for unbound aggregates.