The art and science of pothole repair ranges from the band-aid, quick-fix solution to a complete road recycling process.
The classic quick-fix is called “throw-and-roll.”
The name says it all. Workers shovel some cold-mix asphalt into the pothole, then compact it by rolling over it with the wheels of the work truck.
The Federal Highway Administration’s pothole manual cites the throw-and-roll method as best used as a temporary repair under conditions when it is difficult to control the placement of material, such as winter-time.
In a recent column for Toronto’s The Globe and Mail, Andrew Clark has another name for the process: “Pothole fertilizer.”
“Potholes create jobs. Every year they appear. Every year we fill some in. The following year they reappear, often in the same place. That costs money. Each year, federal, provincial and municipal governments spend untold millions paying to have asphalt mixtures poured into our street indentations. This acts as a kind of fertilizer that allows the pothole to return the following season bigger, deeper and more resplendent."
For a more permanent solution than throw-and-roll, engineers and public works officials are turning to a process called full-depth reclamation or FDR.
FDR goes straight to the root of the problem: the underlying pavement base. Potholes form when moisture weakens the base and, combined with traffic and freeze-thaw cycles, it can no longer support the paved surface.
FDR rebuilds worn out asphalt pavements by recycling the existing roadway. The old asphalt and base are pulverized, mixed with cement and water, and compacted to produce a strong, durable base. The new base is surfaced with either asphalt or concrete.
The best part is that the road is recycled in place, saving energy and natural resources. The full-depth reclamation process uses the old asphalt and base material for the new road; therefore, there’s no need to haul in new material or haul out old material for disposal. Truck traffic and fuel use is reduced, and there is little or no waste.
According to a recent report by the Portland Cement Association, the practice is catching on.Ten percent of asphalt pavement maintenance projects are estimated to be full-depth reclamation.That figure is expected to grow to 15% by 2020.
Part of the reason is that the economic downturn has lead to increased a pent-up demand for pavement resurfacing. And the harsh winter that left our streets one big pothole only served heighten that demand.
Is it going to far to call FDR the new deal for roads and streets?