General

A simple overview of thin overlay project costs is provided in figure 5 (Fick 2010). This figure represents project costs for thin overlays bid and constructed during 2008 and 2009, where the total cost in this case excludes the costs of pre-overlay repairs and the costs of the placement of the separation layer (including interlayer material costs and surface preparation).

In general, the costs during this time period for the eight thin whitetopping and four thin overlays of existing concrete projects are fairly stable, and represent projects constructed in Illinois, Iowa, Minnesota, and Oklahoma. The project costs reported in figure 5 are normalized to the project thickness, as raw costs per square yard generally increase with overlay thickness, as noted by Fick (2010). Also indicated in figure 5 is the average cost by reported project type; as of 2010, a thin whitetopping project was reported to cost an average of $3.28 per yd2 per overlay inch ($0.15 per m2 per overlay mm). Similarly, the average cost for a thin overlay of concrete was $2.64 per yd2 per overlay inch ($0.12 per m2 per overlay mm).

A study of thin overlay construction costs currently underway surveyed 33 overlay projects in 7 states (J. Gross, July 14, 2017, Personal Communication). Of these projects, 28 had an overlay thickness of 6 inches (152 mm) or less. A summary of the costs for these 28 projects is provided in figure 6. Fifteen of the reported projects are whitetopping, with the remainder being overlays of existing concrete, and the estimated costs are based on design overlay thickness rather than the as-built thickness as in Fick (2010). According to the reported cost data and assumed thicknesses, between 2010 and 2015, a thin whitetopping project cost an average of $4.32 per yd2 per overlay inch ($0.17 per m2 per overlay mm) whereas a thin overlay of concrete cost an average of

$3.70 per yd2 per overlay inch ($0.16 per m2 per overlay mm). Both average costs represent an increase over the pre-2010 values (see figure 6) of 32 and 40 percent, respectively.

Given the extent of the cost information available from 2008 forward, one can estimate the construction costs of a thin overlay to fall between $3.00 and $4.00 per yd2 per overlay inch ($0.13 and $0.16 per m2 per overlay mm).