Cold Recycling of asphalt pavement is a tried and tested method of recycling that can yield significant savings in labor and materials, greatly reduce a project’s negative impact on the environment, and provide a sustainable answer to the problem of asphalt concrete maintenance. There are two types of cold recycling in common use today. The first is Cold In-Place Recycling and the other is Cold Central-Plant Recycling.
The current method of Cold In-Place Recycling of bituminous pavement was tried in the United States as early as the mid-1980s. The most widely known application is for road replacement. This method involves a “train” of equipment that mills the existing asphalt concrete. Then the reclaimed asphalt is crushed to gradation and mixed with an engineered cold recycling emulsion. This mix is repaved as the new base layer, compacted to specified densities and readied for surface treatment.
The Cold Central-Plant Recycling process involves removing the distressed asphalt concrete and trucking it to a central plant which then crushes, screens and mixes in emulsion agents and other additives. For optimum results, a mix design is formulated based on the characteristics of the pavement being recycled. This mix design determines the formula for the emulsified recycling agent and any other additives that may be needed to bring the recycled mix up to the highest structural value possible. An advantage to Cold Central-Plant is that if there are subgrade issues the asphalt pavement can still be stripped off and saved on site. Then, failed areas of the base section can be repaired prior to recycling and placing the salvaged asphalt concrete.
Because of the train that is used in Cold In-Place Recycling, it is an excellent option for paved areas that are configured in a long, narrow strip, such as roads and runways. However, because the equipment is attached in a long line, it is not a good option for the large square paved areas found at such properties as malls, stadiums, arenas, university parking lots, and commercial centers. An adaption of the Cold Central-Plant method was developed so that the cost and environmental efficiencies realized with Cold In-Place Recycling in road applications could also benefit these other property types. This adapted method calls for a mobile central plant to be erected on the site of the project. This method was used to repave a portion of the Vintage Faire Mall in Modesto, CA in September 2008. The adaptation of this method has been referred to as Cold On-Site Recycling, to differentiate it from the central plant method that utilizes on off-site plant.
The temporary plant used in Cold On-Site Recycling method requires about a 15,000-square-foot pad. A portion to all of the existing, distressed asphalt concrete is milled and trucked to the on-site plant where it is crushed, screened, mixed with an emulsifying agent per a job-mix formula and re-laid as the new base pavement. A cap of hot-mix asphalt is then applied. All projects, however, must be reviewed and analyzed to determine whether or not the cold-mix asphalt is an appropriate substitute. Deciding factors include the strength and quality of the underlying base section on which the new pavement will be placed, drainage issues, traffic loading or other loading the pavement will receive, the composition of the existing asphalt section including whether Petromat has been used, and the “user-delay” sensitivity of the project.
Though a relatively new application, Cold On-Site Recycling combines methodology that has been tried and found wide acceptance for decades. Cold In-Place Recycling is recommended by many of the Departments of Transportation in the United States, and is standard operating procedure for road replacement in many other countries, including Canada. The Federal Aviation Administration has used Cold In-Place Recycling on runways, including recently Riverside Municipal Airport and Sacramento Executive Airport.