Design of Optimal Perpetual Pavement Structure

In this study, combinations of layer, stiffness, and thickness that produce an optimal perpetual pavement are determined for implementation on New Mexico State highways. Using a number of trial designs in the Mechanistic-Empirical Pavement Design Guide (MEPDG), pavement performances are determined and analyzed for a 50-year design life. The required thickness of a perpetual pavement varies from 10 to 15 in. (0.254 to 0.381 m) for moderate to high truck traffic roads. One example is a pavement that has a 3 in. (76.2 mm) surface layer containing a fine asphalt mix and a 7 in. (177.8 mm) intermediate layer that uses a coarse asphalt mix. This perpetual pavement carries up to 180 million equivalent single axle loads (ESALs) over its 50-year design life. Low bottom-up fatigue cracking (<12%) and little or no top-down cracking [<0.2 ft/mi (37.88 mm/km)] are observed at the end of 50 years. Rutting in the intermediate layer is also low [<0.05 in. (1.27 mm)] at the end of the 10-year maintenance cycle. Overall, fatigue cracking is not a major concern in the design of perpetual pavements for New Mexico’s conditions, rather rutting is more of a concern. For implementation of the perpetual pavements, a resurfacing plan is recommended to remove rutting [if>0.1 in. (2.54 mm)] in the top surface every 10 years. Additionally, perpetual pavements with and without rich-binder layers (RBLs) are examined in this study. Recommendations are made for using a perpetual pavement that does not include a RBL on the basis of life-cycle cost analysis. Another factor that is investigated in this study is debonding of hot mix asphalt (HMA) layers. Analysis shows that 88% of the perpetual pavements may fail by top-down cracking if debonding occurs between two HMA layers. Bottom-up cracking also increases significantly in a debonded environment.