Utility maintenance. Because concrete overlays typically aren't replaced for more than a decade, CDOT coordinates with appropriate agencies to schedule utility maintenance before thin whitetopping is placed. If emergency repairs must be made, the department advises local crews on how to remove and replace pavement sections — a more involved process than patching asphalt. “Crews are getting used to cutting out sections when full-depth repair is necessary,” says Goldbaum. In the Denver area, local agencies specify a flowable or flash fill material prior to replacing the concrete pavement to avoid settlement or material incompatibilities.

Local materials. A word of caution: know your aggregates. In areas where aggregates are highly expansive, thin whitetopping overlays may require pressure relief joints similar to those used on bridges. After several days of high temperatures, the concrete can expand too much. “It can blow up on you — just pop up at a random joint. We've seen it a couple of times,” says Goldbaum. Although there's no way to entirely predict or prevent the problem, it can be mitigated with a pressure relief joint.

Education. Working with thin white-topping requires a paradigm shift for maintenance crews who have placed and patched only asphalt. The American Concrete Pavement Association (ACPA) conducts classes for state agencies to help bridge the gap to concrete. Goldbaum also recommends the association's Concrete Pavement Restoration reference binder as a resource.

Goldbaum offers a list of parameters that can help determine if thin whitetopping is the right solution for a project:

• Evaluate the existing pavement — if there is not enough hot-mix asphalt base leftover after grinding, full-depth replacement may be needed.
• Evaluate the subgrade soil — is the subgrade stable, or does it require reconditioning before an overlay is added?
• Estimate future traffic loads —in areas with heavy truck traffic, a conventional whitetopping or full-depth replacement may last longer.
• Existing curb and gutter — whitetopping is easier in rural areas, or on highways with shoulders instead of curbs and gutters that require an overlay.
• Overhead clearance — pay attention to overpasses, light poles, power lines, or anything that could be an issue with vertical clearance for paving equipment (For CDOT, the minimum is 16 feet).
• Constructability issues — can you shut down the lane and reroute traffic without excessive impact to the traveling public?

• The ACPA provides an online Bonded Concrete Overlay on Asphalt Thickness Designer that calculates the amount of concrete needed, based on specific project parameters.