Restoring Road Subbase with Full Depth Reclamation

Full depth reclamation (FDR) with cement is used to correct extensive subgrade problems in Cecil County, Maryland.

Roadways that develop widespread structural distresses such as settlement and alligator cracking indicate that the supportive roadway materials are insufficient for the vehicle loads seen by the road, particularly heavy trucks with stopping, starting, and turning movements. Milling and resurfacing no longer yields the expected service life. If the distress areas are limited, full depth patching is appropriate, but when the distress areas become substantial, it is more economical to rehabilitate the roadway with FDR. Moderate expectations for full depth reclamation are 15-25 years of extended life for the roadway (https://roadresource.org/).

Here, you see a roadway reclaimer pulverize the surface asphalt and subgrade materials (bank run gravel, aggregate, sand, clay mix) to generally no more than 1-3/4" size. Hydraulic cement is added at the rate of 45#/SY, based on roadway cores and the geotechnical engineer's recommendations. The wetted material is again mixed with the reclaimer for a homogenous mixture of aggregate, asphalt, and cement. A vibratory pad foot roller is used to initially compact the material, a motor grader is used to establish grade for the roadway (prior to surface treatment), and a smooth, vibratory roller seals the surface and completes the compaction. The target for recovered samples is an unconfined compressive strength of 150 pounds per square inch (psi). The surface can later be paved or receive other surface treatments, such as chip seal.

When distresses are extensive in a roadway section, the traditional route is to remove and reconstruct the roadway, resulting in a substantial use of virgin materials, damaging impacts on surrounding roadways from heavily loaded trucks, unnecessary fugitive emissions, and great expense. FDR minimizes use of virgin materials, substantially reduces emissions, lessens impacts on nearby roadways, and saves money, all while producing a substantial foundation for the roadway.

The Delaware T2/LTAP Center provides direct technical assistance, training, and technology transfer to Delaware local agencies relative to their transportation challenges.

https://sites.udel.edu/dct/t2-center/
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