We continue to be excited about the Pavement Preservation & Recycling Alliance (PPRA) Treatment Toolbox we introduced to you late last year. It is available as a free, online resource for your pavement preservation planning and another great tool in their Treatment Resource Center is some in-depth guidance on full depth reclamation (FDR) for pavements.
As you likely know, effective pavement preservation truly relies upon the right treatment for the right road at the right time and there are many tools in the toolbox that can be used, when the time is right. Some of those treatments, like crack seals, are appropriate at the first signs of distress. Others are most effective when some more minor distresses begin to show, but the surface is still largely solid. But at times, some pavements will be too distressed for those methods and more aggressive recycling and reclamation tools are a cost effective way to restore the pavement. FDR is a popular method to use at that point.
Full depth reclamation is a process whereby the surface layers of asphalt and some depth of subbase material is pulverized and homogenized, often with the addition of stabilizing agents like cement or lime, then graded and compacted back in place to form a much more stable base for surface finishing. The stabilized material is commonly topped with traditional asphalt but sometimes chip seals or microsurfacing is used, and even cold mix asphalt has been applied.
FDR is often less expensive than other reconstructive techniques and its application allows a design optimized to the in-situ materials for the best possible outcome. Because the cross section is homogenized at some depth (often 6-9 inches, but sometimes 12 inches and more), all surface distresses are removed and the overall condition of the road base can be improved considerably over what existed. However, it should be noted that features of the roadway, such as poor drainage, that contributed to the distresses should also be addressed concurrently or the same distresses will simply reappear in short order.
An often overlooked or underappreciated aspect of FDR is that, unlike traditional reconstruction, most or all of the material remains in place and is truly reused. As a result, virgin materials (aggregate, asphalt binder) are minimized in the process and the number of truck cycles to and from the project site to remove and replace those materials, reducing unnecessary exhaust emissions and the loading impacts to the roads.
Of course, there are many considerations for investigations, mix design, time of year, stabilization materials, weather, and so on and the PPRA resource center digs into all that. So, take a little time, browse the PPRA site, and consider whether your pavements can benefit from some preservation techniques this spring. The Delaware T2/LTAP Center’s Municipal Engineering Circuit Rider is intended to provide technical assistance and training to local agencies and so if you have pavement management questions or other transportation issues, contact Matt Carter at matheu@udel.edu or (302) 831-7236.
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