United States Department of Transportation
i
Characterization of Unbound Materials for Mechanistic-Empirical Pavement Design for NDOT Districts 2 and 3
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2022-07-01
[PDF-5.93 MB]
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Edition:Final Report 08/2020 to 07/2022
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Abstract:The resilient modulus is a critical engineering property used to characterize the unbound and subgrade materials in the AASHTO Mechanistic Empirical Pavement Design Guide (MEPDG) where a hierarchical approach is followed. Three levels of input are specified in the AASHTOWare® Pavement ME design software. This includes direct measurement from the laboratory testing offering the highest level of accuracy (i.e., Level 1), estimated values using correlations with materials properties (i.e., Level 2), and typical values offering the lowest level of accuracy (i.e., Level 3). The major objective of this study is to develop resilient modulus models for new design and rehabilitation projects for NDOT Districts 2 & 3 to be used in the MEPDG. Unbound and subgrade materials were sampled from Districts 2 & 3 and various testing were conducted to determine numerous properties and characteristics including; materials classification (AASHTO and USCS), R-value, moisture-density relations, unconfined compressive strength, and resilient modulus. The resilient modulus test was conducted according to AASHTO T 307 procedure. The stress dependent resilient modulus models were developed for the unbound and subgrade materials. In summary, the stress dependent behavior of the resilient modulus for base and borrow materials in NDOT Districts 2 & 3 were found to fit very well the theta model. Meanwhile, the stress dependent behavior of the resilient modulus for the subgrade materials fitted very well both the universal model and Uzan model. The MEPDG procedure was used to determine the design resilient modulus for the new design projects. On the other hand, for the rehabilitation projects, a new approach based on the simulation of FWD testing was developed in this research and implemented to determine the design resilient modulus. It was observed that the design resilient modulus of the subgrade layer is independent of the pavement structure while the design resilient modulus of the borrow and base layers are dependent on the pavement structure. Based on the analyses of the data generated from this research, two different resilient modulus models were developed; a) for new pavement design and b) for rehabilitation pavement design. The statistical analyses of the generated data indicated that the design resilient modulus of the subgrade layer for new and rehabilitation projects can be estimated based on the R-value or the unconfined compressive strength properties. However, the design resilient modulus of the borrow and base layers for new and rehabilitation projects can only be estimated based on the R-value. This leads to the conclusion that the unconfined compressive strength is not a good indicator of the strength properties of the borrow and base layers and a confined compressive strength must be measured.
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