Environmental and Economic Efficiency of Stone-Matrix Asphalt with Surface Micro-Milling

Abstract

The Georgia Department of Transportation (GDOT) has employed a combination of open-graded friction course (OGFC) and stone-matrix asphalt (SMA) layers on its Interstate highways for more than two decades. Given that the SMA layer was structurally intact, GDOT implemented micro-milling to solely remove the OGFC layer. Four conventional resurfacing cycles were considered to compare the environmental and economic impacts for a section of Interstate 95 using life-cycle assessment and life-cycle cost analysis, assuming 8-, 10-, 12-, and 14-year resurfacing intervals of asphalt concrete (AC) resurfacing. Within the pavement life cycle, the maintenance and rehabilitation (M&R), and the use stages were significantly influenced by the change of scenarios. The M&R stage revealed a twofold cost increase for the full-depth AC, as compared with SMA, over the pavement life, because of the latter’s relative improved structural performance and a delay in future rehabilitation. Furthermore, in the use stage, M&R affected the agency costs significantly, whereas the work-zone delay governed the user cost. The holistic evaluation of the SMA and micro-milling combination revealed positive outcomes in field performance, along with environmental and economic impacts. However, it is worth noting that the scenarios presented follow GDOT’s approach with a long-standing use of SMA and micro-milling. Given the extensive experience with the aforementioned combination, it was evident that the method provided significant benefits, especially in the long-term outlook, and may be applicable for locations that have conditions analogous to GDOT’s.