Date of Award

Spring 2019

Project Type


Program or Major

Civil Engineering

Degree Name

Doctor of Philosophy

First Advisor

Eshan V Dave

Second Advisor

Jo E Sias

Third Advisor

Majid Ghayoomi


A variety of approaches are available to design the pavement structures. These approaches are generally divided into two main categories as empirical and mechanistic-empirical (M-E) methods. The most widely used empirical method is the AASHTO 1993 design approach which uses material specific coefficients (layer coefficients) to quantify the structural capacity provided by each pavement layer. These coefficients are experimentally developed values from the AASHO road test which was conducted in the early 1960s and are based on statistical regressions. Almost no fundamental or engineering mixture properties or explicit failure criterion were used in their original development. On the other hand, the M-E approaches use fundamental mixture properties such as complex modulus (E* and phase angle) to determine the pavement’s structural response. However, M-E approaches require extensive data for local calibration and as a results, many state agencies are still using the empirical approach.

One of the major modifications in the AASHTO 1993 design approach has been to update the layer coefficients (a-value) of the asphalt mixtures using different mechanistic and performance-based measures. The layer coefficients have significant influence in determining the layer thickness which translates into the structural contribution of the layers as well as the long term performance of the

pavement and consequently the construction and maintenance costs. Therefore, it is critical to determine reliable a-values that are most relevant to the regional conditions and locally used materials.

A set of 18 commonly used mixtures in New Hampshire were selected for performance testing and evaluation of structural contribution in terms of layer coefficients. In order to develop the layer coefficients, comprehensive research was performed on the performance and properties of the mixtures through different mechanistic-based laboratory testing methods. In addition, mixtures from all over the New England region were used to develop and validate three novel performance index parameters for rutting, fatigue and transverse cracking. The developed parameters were incorporated with the field distress data such as International Roughness Index (IRI) in order to develop mechanistically informed layer coefficients for New Hampshire flexible pavement design approach.