Published in 2020
The Strategic Highway Research Program 2 (SHRP2) identified composite pavement as a “renewal solution” to support for implementation, and the Virginia Department of Transportation (VDOT) received funding to demonstrate its potential. In 2017, this funding was applied to support major rehabilitation of two westbound lanes of US 60 in Henrico County, Virginia, a project that essentially replaced 1.1 miles of deteriorated concrete pavement with a new composite system consisting of continuously reinforced concrete pavement (CRCP) overlaid with stone matrix asphalt (SMA).
This new composite pavement was designed in accordance with the 1993 AASHTO Guide for Design of Pavement Structures and was constructed in accordance with VDOT specifications and standards existing at the time. During construction, material properties were characterized to enable mechanistic-empirical (ME) analysis, and AASHTOWare Pavement ME Design software was then used to analyze the pavement again using the “asphalt concrete overlay over CRCP” option as suggested in the SHRP2 research. Because of the low truck traffic count on US 60, the predicted distresses for a 30-year design life were found to be very low compared to an analysis that uses the Pavement ME Design software default criteria. Through-the-thickness temperature changes were also monitored and it was found that the asphalt overlay provides an insulating effect for the underlying concrete, hence reducing the curling and thermal stresses in the concrete pavement.
SHRP2 researchers suggested that the thickness of the concrete portion of a composite pavement could usually be 1 to 3 in less than that of a plain (bare) concrete for comparable performance. Similar trends were observed for a higher truck traffic scenario in this study when a composite pavement (CRCP overlaid with SMA) was analyzed using the Pavement ME Design software.
VDOT maintains more than 500 lane-miles of CRCP that has been overlaid with asphalt at an average age of 26 years. These pavements, now considered “composite” pavements, are still in service, often after multiple asphalt mill and replace operations, with some as old as 52 years. The average life of these overlays is 10 to 15 years, with the combination of CRCP and SMA often providing 16 to 23 years per cycle.
The main distress mechanisms in a composite pavement are reflective cracking and rutting. The natural cracking and rut resistance of SMA therefore make it an ideal option for the asphalt component of a composite system. Such a design will protect the concrete base before any distresses have developed while also moderating thermal stresses (the insulating effect). The prospects for superior long-term service with low maintenance costs are excellent.
Last updated: November 9, 2023