FDR is the process of pulverizing the full thickness of the asphalt pavement and a predetermined portion of the underlying materials (base, subbase and/or subgrade) with a reclaimer. If no stabilizing agents are required, a single pass is often sufficient to uniformly pulverized and blend the materials. If a stabilizing agent is used (chemical or bituminous), it is typically added and mixed during a second (mixing) pass of the reclaimer. Prior to the mixing pass, the prepulverized material should be compacted and shaped. After mixing, the pulverized and mixed material is bladed and shaped, moisture conditioned for compaction, and compacted using a padfoot, smooth drum and/or pneumatic-tired compactors. The reclaimed materials are then trimmed to final grade and allowed to cure until sufficient strength is obtained to carry anticipated traffic.
Equipment used to perform FDR will vary from contractor to contractor, but no matter how configured, the equipment performs the same general steps. The minimum equipment required for the FDR process consists of:
For more complex FDR projects, including the application of a stabilizing agent and additive, additional construction equipment could include some or all of the following:
Pulverization is the FDR process in which the full thickness of the asphalt pavement and a predetermined portion of the underlying materials (base, subbase and/or subgrade) is uniformly pulverized and blended to provide an upgraded, homogeneous material. Often, this blend of material alone is sufficient to act as the base for a new surface course.
Mechanical Stabilization is achieved with the addition of granular materials, such as new aggregate, or recycled materials (reclaimed asphalt pavement (RAP) or crushed concrete) to the pulverized materials. Additional granular materials may be required to supplement the existing material gradation, increase the thickness of the layer to be processed and/or to meet performance requirements of the mix design. The gradation of the granular material will vary depending on the desired effect on the final reclaimed material.
Chemical Stabilization is achieved with the addition of cement (portland or hydraulic), lime (hydrated or quicklime), self-cementing class C fly ash, class F fly ash (when used in combination with other additives), cement kiln dust (CKD), lime kiln dust (LKD), calcium chloride, magnesium chloride or proprietary products to the pulverized materials.
Bituminous Stabilization is accomplished with the addition of emulsified asphalt or foamed (expanded) asphalt to the pulverized materials.
FDR + Single or Double Chip Seal: A surface course is required over FDR sections and where the reclaimed pavement structure is sufficient to carry the anticipated loads, chip seals are very economical.
FDR + Micro or Slurry Surfacing: Where the reclaimed pavement structure is sufficient to carry the anticipated loads micro or slurry surfacing are additional economical surfacing options.
FDR + HMA Overlay: To increase the structural capacity of the road, a hot mix overlay can be placed over the FDR section.
FDR + Cold Mix Overlay: For low volume road applications, a cold asphalt mix or CCPR asphalt mix can be placed over the FDR section. A seal coat may be required to prevent moisture infiltration.