Road Recycling Methods

Purpose

Roads are rehabilitated to correct deficiencies such as rutting, cracking, oxidation, brittleness, irregular shrinkage, and aggregate stripped of asphalt.

Methods

The following methods of roadway rehabilitation recycle old pavement into new:

Cold, In-Place Recycling. The pavement is removed by cold planing to a depth of 3 to 4 inches. The material is pulverized, sized, and mixed with an additive. Virgin aggregate may be added to modify RAP characteristics. An asphalt emulsion or a recycling agent is added, then the material is placed and compacted. An additional layer is optional, such as a chip seal, or 1 to 3 inches of hot-mix asphalt.

A 3-piece "train" may be used, consisting of a cold planing machine, a screening/crushing/ mixing unit, and conventional laydown and rolling equipment. This "train" occupies only one lane, thus maximizing traffic flow. Caltrans has used cold in-place recycling in over 25 projects in California.

According to the Asphalt Recycling and Reclaiming Association, cost savings can range from 20 to 40 percent over conventional techniques. Because no heat is used, energy savings can be from 40 to 50 percent.

Hot Recycling. At a central plant, RAP is combined with hot new aggregate, and asphalt or a recycling agent to produce AC, using a batch or drum plant. The RAP is usually obtained from a cold planing machine, but could also be from a ripping/crushing operation.

Hot, In-Place Recycling. The pavement is softened by heating, and is scarified or hot milled to a depth of 3/4 to 1-1/2 inches and mixed. New hot mix material and/or a recycling agent is added in a single pass of the machine. A new wearing course may also be added with an additional pass after compaction.

Hot Mix--Remixing. The road is heated to 1-1/2 to 2 inches, and the existing AC is removed to that depth. It is then mixed with virgin mix and/or rejuvenating agents and laid as a single course.

Hot Mix--Repave. This method is the same as remixing, but it is overlaid with new hot mix.

Hot Mix--Heater Scarification. This method is appropriate for roadways that have a stable and structurally adequate base. The road is heated, scarifiers scrape and loosen the pavement, rejuvenating agent is applied, and the surface is leveled in preparation for the addition of a final, thin, wearing course.

Full-Depth Reclamation. All of the asphalt pavement section and a portion of the underlying materials are processed to produce a stabilized base course. The materials are crushed and additives are introduced; the materials are then shaped and compacted, and a surface or wearing course is applied.

source:calrecycle.ca.gov

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