Talking Asphalt: Full Depth Reclamation – June 2012

Talking AsphaltThis month’s blog is about a pavement restoration technique that intrigues me (and I probably should admit that it is one I have never worked with). But I believe it is a technique that should be used more.

I’m talking about Full Depth Reclamation (FDR). The Asphalt Recycling and Reclaiming Association’s (ARRA) Basic Asphalt Recycling Manual defines FDR as “… the rehabilitation technique in which the full thickness of the asphalt pavement and a predetermined portion of the underlying materials (base, sub-base, and/or sub-grade) is uniformly pulverized and blended to provide an upgraded, homogenous material.” This reclaimed material becomes the base for a new pavement structure.

The manual describes FDR as appropriate for addressing pavements with these distresses:

• Cracking
• Poor ride quality
• Rutting and shoving
• Stripping, raveling, potholes and bleeding, and
• Lack of structural capacity.

I know of a lot of roads (and I’ll bet you do, too) that have some of those problems. Many of these roads have a thick layer of material in place that still has some value but is not working well in its present condition. FDR offers a means of regaining the use and value of this in-place material.

FDR is not just grinding up the existing material and capping it with a new wearing course. There is some information needed to optimize the reclamation. Samples of the in-place materials are needed; coring is the usual means of obtaining samples. The cores are examined for different pavement layers and types, surface treatments, interlayers or fabrics, specialty mixes, and pavement distresses such as stripping, poor quality aggregate and other pavement problems. Thicknesses of the layers are noted. The cores are then crushed and the asphalt binder and aggregate can be more closely analyzed. The granular base or sub-base can also be sampled and evaluated for information used in the thickness design of the overall new pavement.

Pavements with subgrade or drainage problems must have these deficiencies corrected before FDR is done. Weak or wet sub-grades require stabilization in order to ensure adequate compaction of the reclaimed mix and to provide support for traffic. The reclaimed material can be improved and/or stabilized with the addition of foamed asphalt or asphalt emulsion lime, Portland Cement and/or selected aggregates. In addition to materials deficiencies, FDR can be used to correct geometric concerns such as alignment, cross-section, and grade.

Reclaimers have fixed cutting widths, typically 6 to 12 feet. Modern equipment is maneuverable so most pavements can be treated, including those in urban areas. Typical production rates are in the 4,000 to 10,000 square yards per day range.

For more information, I suggest you obtain a copy of the “Basic Asphalt Recycling Manual” or contact ARRA. The manual has an overview chapter, one on mix design, one on construction information, and another on specifications and inspection. It is a great source of information on FDR.

Rather than just stacking another overlay or surface treatment on top of a distressed pavement, consider using FDR. It may be the long-term answer to your pavement problem.

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