Comparison of Existing Flexible Pavements Damaged Index for PMED Rehabilitation Levels

Abstract: Asphalt pavements experience changes over their lifespan, including aging, traffic compaction, distress from loads, moisture damage, and environmental influences. These factors collectively influence the dynamic modulus (|E*|) of the Hot Mix Asphalt (HMA) layer and its overall performance. This paper aims to characterize the dynamic modulus master curves (|E*|) of the existing hot mix asphalt (HMA) layers using the AASHTOWare Pavement ME Design (PMED) methodology across various levels of rehabilitation. Specifically, it evaluates the three hierarchical PMED rehabilitation input levels for predicting damaged |E*| master curves—Level 1 uses Falling Weight Deflectometer (FWD) backcalculated HMA moduli, Level 2 incorporates field surface conditions such as alligator cracking, and Level 3 utilizes pavement condition ratings. The undamaged dynamic modulus curve is obtained using Witzack’s equation based on existing HMA volumetrics.
The paper examines fourteen sections of HMA overlays over existing HMA pavements from various locations across Michigan. Fatigue cracking in all sections was less than 10%, corresponding to “excellent” and “good” pavement ratings for rehabilitation Level 3. The results reveal that the PMED-predicted damaged |E*| master curves at Level 2 are consistently equivalent to the undamaged dynamic modulus master curves and are higher than the damaged modulus master curves at Levels 1 and 3. This is attributed to the low fatigue cracking, which resulted in a lower damage index for the existing pavements. For Level 3, the “fair” conditional rating leads to a higher damaged modulus master curve than those at Level 1 but lower than at Level 2.
A sensitivity analysis of the damage factors was also performed across varying combinations of FWD temperatures and backcalculated moduli. At Level 1, a decrease in damage index was observed with decreasing layer moduli for a given temperature. At Levels 2 and 3, the damage increased with rising alligator cracking and declining pavement condition ratings. The realistic range for damage factors across all rehabilitation levels was between 0.01 and 1.4. There is a need to refine the PMED methodology for damage estimation at Level 2 compared to a more conservative Level 1 approach to ensure reliable characterization of existing HMA layers for overlay design.