The City of Havre De Grace, MD, sits at the intersection of the Susquehanna River and the start of the Chesapeake Bay. This is one of the East Coast’s most naturally beautiful and sensitive locations, so it’s only fitting that a very green technology was used to reconstruct one of its roadways.
The City Public Works Director Larry Parks and the consulting engineer, Kercher Engineering of Newark, DE, had a major issue with one of the roadways within the city. Canvasback Road services a very large residential population as a feeder road and also serves as a short-cut to Maryland SR 40 and SR 155.
SR 155 has a direct exit onto I-95 North and South just west of the city. A very large number of school buses also used Canvasback Road to pick up and drop off school children in the city and other locations within Havre De Grace and Harford County.
Total reconstruction needed
The cross section of Canvasback Road was 4 inches of old asphalt, zero to 2 inches of aggregate and a subbase of clay and other unsuitable materials. The old oxidized asphalt was inundated with potholes, alligator or corrugated cracking, and longitudinal cracks.
In some areas, there were subbase issues with the underlying base pushing through the asphalt causing occasional “soft and yielding.” Storm water penetrated the cracked pavement making these already deteriorated pavements even more susceptible to continued damage. Canvasback Road needed to be totally reconstructed.
With total reconstruction, the city would need to mill and remove the existing asphalt pavement. The reclaimed asphalt pavement (RAP) would then go to an asphalt plant for crushing and be introduced back into a new hot mix asphalt (HMA) base or a HMA wearing layer.
One of the issues with the removal of the asphalt on Canvasback Road was the inconsistent depth of the asphalt. In some areas there were 4 inches of asphalt, in other areas, there was as little as 2 inches. The added unsuitable soils pushing up through the asphalt would cause these materials to not be accepted by asphalt plants because of contaminated RAP.
“If the roadway asphalt depth is varying, it’s hard to control the depth of cut on a mill machine and contaminated RAP is produced,” says Mike Polak, a partner with E. J. Breneman. “This type of material is likely not to be recycled back into a new HMA, as separating the aggregates and soils from the RAP is time consuming and difficult.”
After the asphalt pavement is removed, the underlying aggregate would be removed. On Canvasback Road, the aggregate was very limited. “What do we do with the unstable soils?” says Polak. “At what depth should they be removed? How should the remaining material be stabilized?”
With the issues of total reconstruction mounting and realizing that the excavated waste material would have to be placed into a landfill or disposed of environmentally, the city had to look for another option.
Kercher Engineering had the task of finding a solution to the reconstruction of Canvasback Road. Alan Kercher contacted E.J. Breneman L.P. and consulted with Polak.
Choosing the process
A survey was conducted on Canvasback Road that started with a walk through the project from SR 155 to Chapel Road. It became very clear that the roadway needed to be stabilized using full depth reclamation (FDR).
The FDR process rebuilds a worn out asphalt pavement by recycling the existing pavement. The old asphalt and base materials are pulverized, mixed with cement and water, and compacted to produce a strong, durable base for an asphalt surface.
“Unfortunately, on new development roads, subgrade issues are a problem,” says Polak. “Specifications and inspections are not adhered to, then after several years, the problems start to surface. Asphalt pavements start to crack or just totally fail; mud pushes up through the aggregate and the cost to repair is a heavy one. Canvasback Road had been one of these unfortunate roadways.”