This Is AuburnElectronic Theses and Dissertations





Nakhaei, Mostafa

Type of Degree

PhD Dissertation


Civil and Environmental Engineering


The current study aimed to develop a mechanistic understanding of the behavior of flexible pavements with stabilized foundations through full-scale testing, instrumentation, and simulation. In pursuit of this objective, a full-scale pavement section was constructed at the National Center for Asphalt Technology (NCAT) Test Track in 2018 featuring stabilized foundation layers under the asphalt layers. For comparison, three additional full-scale pavement sections were included in this study. The behavior of all sections was observed over time under accelerated truck trafficking using embedded strain and stress sensors. In addition, surface performance was measured routinely with a falling weight deflectometer (FWD) and a condition survey van. The strain measurement at the bottom of asphalt concrete (AC) for the conventional pavement sections showed a familiar trend in which the tensile strain increased exponentially with temperature. However, the tensile strain response for the stabilized foundation section showed a fundamentally different behavior in which the horizontal tensile strain response decreased with the increase in temperature. Further investigation showed the strain response at the bottom of the AC layer switched to predominantly compression for the stabilized foundation section. The compressive strain response at the bottom of AC contradicts the well-established premise that the bottom of AC is in tension. Computational simulations of the stabilized section illustrated the same trend that the bottom of AC should be in compression in summer. However, the analysis predicted that the maximum tensile strain actually occurs near the middle of the AC layer and thus fatigue cracking could initiate at shallower depths leading to middle-up cracking. MASTIC program, originally developed in this research study, was used for backcalculation since other commercial software programs led to unrealistic results with high variance for the stabilized foundation section. It was found that a four-layer system with the original cross-section and fully bonded condition for the top interface along with a nearly slip conditions for other interfaces was the best-case scenario for having reasonable results and less variability. This study also proposed a new methodology based on Boussinesq elastic half-space equation to remove erroneous deflection basins and thus having less variability. In general, it is suggested that the stabilized foundation sections that behave mechanistically different than conventional flexible pavements be designed and evaluated differently using mechanistic concepts introduced in this study.