A Cost-comparison Methodology for Selecting Appropriate Hot-mix Asphalt Materials

About the report:

The Virginia Department of Transportation's (VDOT) Road and Bridge Specifications lists 9 dense-graded hot-mix asphalt (HMA) surface mixes (three aggregate gradations x three binder types) that could be used on Virginia's highways. VDOT's Special Provision for Stone Matrix Asphalt (SMA) provides 4 additional surface mix options (two gradations x two binder types), for a total of 13 mixes. Although the specifications offer recommendations regarding the types of facilities to program for each mix type, local conditions and experiences heavily influence the predominantly selected mix. Over the past 4 years or so, district pavement managers have routinely used only about 4 dense-graded mixes and 3 of the SMA surface mixes. As material prices continue to climb without budgets doing the same, local circumstances are more often going to contribute to the selection of the less expensive mixes, especially as long as these managers lack a defensible rationale for specifying a more expensive option. This study offers an economic analysis procedure to help field (i.e., district) pavement engineers select the most cost-effective mix for a given application. The procedure is based on the expected performance of each mix. The performance predictions were developed using the 2006 "windshield" condition rating for Virginia's interstate and state primary roads, which reflects the performance for at least 6 years of Virginia's contemporary dense-graded HMA mixes and for up to 11 years of SMA surface mixes. Through examples using typical project families, the study demonstrated that premium prices for SMA can generally be justified by better performance. In one illustration using actual condition and awarded price data, a life cycle cost analysis revealed that the use of SMA in lieu of dense-graded mixtures on interstates might save VDOT in excess of $7,500 per lane-mile in net present value costs. Extrapolated to the entire Virginia interstate system, the net present value costs associated with an SMA-only resurfacing program would be approximately $25 million less than the next best hot-mix alternative. A final step in this illustration suggests that VDOT can afford (within the FY 2008 spending plan) to pursue an interstate resurfacing program that makes extensive (if not exclusive) use of SMA.

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