Full Depth Reclamation (FDR) Techniques

Control Strip

• If required, a control strip should be placed at the beginning of the project to evaluate the equipment, construction methodology, workmanship and to verify that the construction process meets specification requirements

Pulverization

• Overlap longitudinal joints a minimum of 6 inches and transverse joints a minimum of 2 feet 
• Check depth of pulverization by removing the pulverized material on each on each side of the reclaimer and checking the depth. 
• Check gradation of reclaimed material. Reclaimers are not crushers; therefore, it is impractical to require more than 95% of processed material to pass a 2 inch sieve. An occasional oversized chunk should be acceptable
• Lightly roll and reshape reclaimed material prior to application of dry stabilizing agents and prior to mixing passes of the reclaimer

Application of Granular Materials and Dry Stabilizing Agents

• For mechanical stabilization apply granular materials prior to pulverization using a mechanical spreader, paver or by haul trucks and then spread to a uniform thickness with a motor grader
• If required, granular materials for bituminous and chemical stabilization can be placed prior to or after pulverization but before mixing passes
• Dry chemical stabilizing agents can be added prior to pulverization or after pulverization and prior to the mixing pass of the reclaimer. Applying after pulverization generally results in a more uniform application
• Dry chemical stabilizing agents should be applied with non-pressurized mechanical vane-feed, cyclone or screw type bulk spreaders/distributors
• Check application rates either volumetrically or by using a “canvas patch” test or similar procedure  

Application of Stabilizing Agents Applied as Slurry

• Chemical stabilizing agents applied as slurry can be spread ahead of mixing passes using a calibrated liquid distributor or added during the mixing pass of the reclaimer using the reclaimer’s on-board additive system. Application through the reclaimer generally results in a more uniform application 
• Verify application of slurry stabilizing agents using the consumption of stabilizing agent (and water) obtained from the computer that controls the slurry mixing unit.

Application of Bituminous Stabilizing Agents

• Apply bituminous stabilizing agents during the mixing pass of the reclaimer using the reclaimer’s on-board additive system. 
• Verify the application rate by evaluating the mass of recycled material against the volume of recycling agent used for a single tanker.
• For foamed asphalt stabilization, check the temperature of the asphalt before connecting a tanker to the reclaimer.
• For foamed asphalt stabilization, verify the expansion ratio and half-life using the test nozzle on the reclaimer.

Mixing Pass

Check depth of mixing by removing the pulverized material on each side of the reclaimer and checking the depth. Pulverizing fluffs up the material and should be accounted for when determining treatment depths. A tolerance of ± 1/2 inch (12.5 mm) is usually allowed. 

Overlap longitudinal joints a minimum of 6 inches and transverse joints a minimum of 2 feet 

Compaction

• Establish a rolling pattern to achieve the required percent compaction
• Compact the reclaimed material to the required percent compaction using any combination of segmented padfoot, vibratory padfoot, rubber-tired, vibratory single or double drum rollers 
• Compaction requirements for Pulverization, Mechanical and Bituminous stabilization are typically based on 95% of the maximum dry density determined in accordance with AASHTO T 180 or ASTM D1557, modified Proctor
• The total time for mixing, placing and compacting FDR mixtures with cementitious stabilizing agents should be less than 2 hours
• Compaction requirements for Cement stabilization are typically 95 to 98% of ASTM D588.
• FDR stabilization with hydrated lime or LKD, the mix is usually allowed to mellow prior to compaction
• For FDR stabilization with quicklime, the first and final mixing should not be performed on the same day. The mix is usually allowed to mellow for at least 12 hours prior to final mixing and compaction
• Compaction requirements for Lime/LKD stabilization are typically based on standard Proctor, 95% of the maximum dry density
• Check compaction with a nuclear gauge, sand cone or other approved method
• Check cross-slope after final rolling 

Curing

• Stabilized reclaimed materials need to be properly cured to achieve ultimate strength, prevent raveling and facilitate placement of the surface course
• Minimize vehicular traffic on stabilized materials for 30 to 60 minutes 
• Limit truck traffic until the recycled material has cured sufficiently to support the anticipated traffic without damaging the reclaimed mixture
• For chemical stabilizing agents either keep the surface moist or apply a curing membrane to allow proper hydration and strength gain of the materials, typically 2-7 days

Surface Course

• A surface course is required over FDR materials
• Prior to placing the subsequent course sweep the reclaimed mixture with a power broom. A fog or tack coat of emulsified asphalt may be required, depending on local practice.