According to the 2017 ASCE Infrastructure Report Card, our nation's roadway infrastructure is in poor condition. There is an ever-increasing backlog of rehabilitation needs with minimal resources. In fact, this underfunded system needs approximately $420 billion to repair roadways. As our nation's infrastructure continues to decline, agencies are tasked with maintaining and rehabilitating roads with shrinking budgets and costly construction. With that, engineers must explore cost-effective, sustainable techniques to maintain and rehabilitate pavement.
One such technique is full-depth reclamation (FDR). It is typically 25% to 50% less expensive than removal and replacement and could be an answer to help improve our nation's roadways. The FDR method involves using a road reclaimer to pulverize the existing base and asphalt, mixing the material with cement and water and compacting it in place with rollers. Asphalt or concrete is used as the surface material. The results are a stronger, more uniform and moisture-resistant pavement system.
FDR is known to increase the structural capacity and durability of the pavement structure, decrease the construction schedule, reduce impacts on the public due to construction, reduce the carbon footprint, and increase the life expectancy of the pavement. The materials used are reduced since the existing pavement remains in place unless some portion of material is removed to maintain a specific elevation. The stiffer base exhibits characteristics of a slab, and there is a reduction in deflections caused by traffic loading, thus extending the pavement life.
There are three types of FDR stabilization methods: mechanical, chemical, and bituminous. Mechanical stabilization is when the existing pavement and base are pulverized, mixed with granular aggregate, crushed concrete, or recycled asphalt pavement (RAP), and compacted. This method relies on particles of the granular aggregate and pulverized mixture to interlock. Chemical stabilization is the most common method. This is when the existing material is pulverized, and a chemical is added with water and compacted. The most common materials added are Portland cement, lime, and Class C of F fly ash. Bituminous stabilization is achieved when the pulverized asphalt and base are mixed with an emulsified asphalt or foamed asphalt.
Most roadway systems are good candidates for FDR. Roads that have excessive rutting, patching or alligator cracking in the wheel path, or show signs of base failure are all good reasons to consider FDR. However, there are some instances when FDR alone will not fix the issue, such as projects that have drainage problems (like saturated subgrade). FDR can still be done, but geotextile fabric should be incorporated into the design. All in all, agencies must perform extensive pavement condition surveys and try to determine the causes of distress before FDR is chosen. Other factors to consider are future traffic loads and the location of existing utilities. The FDR process and pulverizing equipment can exceed 18 inches in depth, so having a clear picture of where these utilities are prior to design is important.