During the Full Depth Reclamation process, when is calcium (or another stabilizer) supposed to be applied?
Full Depth Reclamation (FDR) is usually a 2-pass process which is used when you want to add a chemical or bituminous additive to the base. The first pass is done to make sure that the base material is pulverized to specified sizes to the design depth. Excess material is then removed as well as larger chunks that are greater than 3 inches across. The surface is then shaped and compacted. The stabilizer (calcium, cement, asphalt, or another product) is then added just prior to the second pass of the reclamation process, mixed throughout the remaining material, fine graded, and compacted. There is typically a cure time necessary prior to the placement of the surface material.
While adding the stabilizer prior to the first pass may seem efficient, doing so would allow it to mix through the entire layer of ground up material, and when the excess material is removed some of the stabilizer is removed as well. This will dilute the concentration of the stabilizer in the final base material, reducing its intended effect. Also, there is a limited time to do the fine grading with some stabilizers such as cement and asphalt so waiting until the second pass can be critical.
In many cases, the excess material is described as “waste” and is designated to be removed by the contractor and disposed of. This material is the property of the municipality and contracts should consider having the material hauled to a town storage site for use as needed by the town for base or shoulder back up material. Alternatively, the contractor can be asked to provide a better price to account for the value of this material.
The two-pass system is recommended in the Geotechnical Engineering Manual GEM-27 put out by the New York State DOT, and is identified in the Method of Payment section at the end as stated below.
6. METHOD OF PAYMENT Full Depth Reclamation process is divided into three pay items:
• Full Depth Rreclamation of asphalt pavement – Addresses the payment for work including cleaning the existing pavement free of all debris and material that may interfere with the reclamations’ milling process; milling; pulverizing and mixing the existing asphalt pavement; adding new aggregate and chemical or bituminous stabilizing agent(s) as required; then remixing; grading; compacting; and curing in conformity with the lines, grades, depths and typical sections as shown in the contract documents.
• Stabilizing Agent – Addresses the payment for the stabilizing agent (chemical or bituminous).
• Aggregate – Addresses the payment for adding aggregate.
It is recommended to work with an engineer who is familiar with the FDR process to ensure proper construction methods are specified and followed.
Design and Construction Guidelines for Full-Depth Reclamation of Asphalt Pavement