Probabilistic Performance-Related Specifications Methodology Based on Mechanistic-Empirical Pavement Design Guide

In current construction practice, as-built asphalt concrete acceptance is typically based on several key quality assurance-quality control parameters. These parameters have pay factors that are empirically established by judgment of the pavement community. The pay factor has been used to reward or penalize the contractor for construction quality. These properties are known to influence pavement performance, but the specific effect on performance and project life has been impossible to estimate. Because of this, there is an urgent need to tie deviations of the field production from the specified job mix to performance and pavement life. This research focused on the integration of AASHTO's Mechanistic Empirical Pavement Design Guide (NCHRP 1-37A and NCHRP 1-40D) with the Simple Performance Test (NCHRP 9-19) to develop a probabilistic quality specification for quality assurance of hot-mix asphalt (HMA) construction. This has been the major objective of NCHRP 9-22. The methodology is based on relating the HMA dynamic modulus, through a closed-form solution, to major pavement distress. A Monte Carlo simulation is run by using the project mix design to predict the as-designed distress and its associated variability. Then the remaining service life of the pavement is predicted from the as-designed distress. Similarly, Monte Carlo simulation is run for the as-built material to estimate the remaining service life. The difference between the as-built and the as-design distress provides the predicted difference in quality of construction from the mix design. The difference is used to calculate the pay factor for each distress. The total pay factor is the sum of the individual distress pay factors. Finally, the initial international roughness index, representing the ride quality pay factor, is added.