Recycling Technology: COLD RECYCLING
- Introduction
- A Brief Background Of Cold Recycling Of Asphalt Concrete
- The Process Of Cold On-Site Recycling Described
- Benefits Of On-Site Recycling
- The Process Documented – Vintage Faire Mall, Modesto, Ca
- Summary
Pave West and Pavement Recycling Systems, Inc. (Pavement Recycling) of Riverside, CA are cooperatively offering a process for recycling asphalt concrete on the job site. This process is called Cold On-Site Recycling and is an adaptation of the more familiar Cold In-place Recycling Method.
Pavement Recycling Systems is a Specialty Contracting firm with Engineering capability offering a full range of state-of-the art recycling solutions to reclaim, preserve and rehabilitate at any stage of the pavement’s life-curve. The only company of its kind in California, they offer proven alternatives that raise quality, cut costs, and preserve the environment.
There are two noticeable differences between cold recycling and traditional hot-mix asphalt. Cold recycling processes use a water-based emulsion that requires a “break” and cure (evaporation) to harden the pavement, while hot-mix asphalt requires high heat and high energy to soften the asphalt binder. Additionally, the placement techniques for cold recycling are different than the traditional techniques required for hot-mix asphalt. As such, Pavement Recycling, which manufactures ReNew™ cold recycled pavement, allows only certified installers to purchase this product. Pave West is one of only a few companies certified by Pavement Recycling experienced in Cold On-Site Recycling.
A BRIEF BACKGROUND
OF COLD RECYCLING OF ASPHALT CONCRETE
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 Recycling with ReNew Pavement™ 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.
THE PROCESS
OF COLD ON-SITE RECYCLING DESCRIBED
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. Consequently, Cold On-site Recycling 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.
The Cold On-Site Recycling method involves the installation of a temporary plant (a smaller version of the one used in the Cold Central-Plant Recycling), requiring about 15,000-square-foot pad, on the job site. 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 ReNew™ Pavement 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.
Experience has shown that the cost of Cold On-Site Recycling is less expensive than conventional paving methods.
- For starters, all or most of the needed material is in place, so the total cost of new asphalt is noticeably less. Often, the only necessary new material purchase is the hot-mix asphalt cap.
- Because material is being recycled onsite, many fewer truck hauls are required.
- There are no dump fees for the recycled asphalt concrete.
- Labor costs are significantly reduced because of the shorter duration of the project.
In August of 2008 Pave West and Pavement Recycling used Cold On-Site Recycling to repave Vintage Faire Mall in Modesto, CA. The estimated cost to pave this mall using traditional milling and surfacing was $1.8 million. The job cost using Cold On-Site Recycling was $1.2 million, for an actual cost savings of $600,000!
The Cold On-Site Recycling process removes only the top 2 to 4 inches of asphalt concrete. Traditional remove and replace methods take not only the asphalt layer, but the rock and potentially some of the soil layers and replaces them. Because this is not necessary, assuming the subgrade is in good condition, it is not necessary to take the time (and spend the money) to replace the rock and prepare the soil, resulting in much shorter downtimes. Another advantage to both Cold On-Site and Cold Central-Plant Recycling methods with ReNew Pavement™ 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.
AS DURABLE AS TRADITIONAL SURFACING METHODS
A concern often raised with recycling is the quality of the recycled product; Cold Recycled Asphalt has different properties than “virgin” hot mix. On a structural basis, CALTRANS assigns Cold Recycled Asphalt a “Gravel Equivalency Factor’ of 1.7, while for most Hot Mix Asphalts (“HMA”) the Gravel Factor is 2.0. In the field this often translates into a slightly thicker section when using ReNew™ pavement. For example, if the design calls for 4” AC section and the Owner wants to substitute ReNew™ for part of the section, then a typical substitution is 3” of cold recycled renew over-laid by 1.5’ of HMA. The resulting 4.5” section is structurally equivalent to 4” of HMA. But, because ReNew™ has a different internal structure, and the new section is a two-layer system, the pavement is more resistant to thermal and reflective cracking.
Energy Savings And Reduced Green House Gas Emissions
Because of the greatly reduced number of truck hauls and the use of recycled asphalt, the need for petroleum-based products is significantly reduced. Additionally, the green house gas emissions are noticeably lower. A study done by Dr. Arpad Horvath of the University of California, Berkeley for the Ministry of Transportation of Ontario found that green house gas emissions using Cold In-place Recycling were one half to one third of traditional rehabilitation techniques (mill 100mm and 130mm hot-mix asphalt).
Society has an increasingly heightened awareness of and the desire to mitigate the negative impacts of its actions on the planet. Pave West is leading the paving industry’s efforts towards sustainable and renewable pavement by seeking out effective recycling options. Cold recycling, when appropriate, exemplifies the strides the paving industry is making in contributing to the global effort to reduce green house gas emissions and the carbon footprint. Additionally, in the future, should there be cap and trade limitations placed on the paving industry, cold recycling should contribute to a company’s need to limit its green house emissions.
Along the same lines, the use of Cold On-Site Recycling will potentially contribute LEEDS credits for a major renovation project, should the owner/general contractor choose to pursue LEEDS certification. Specific areas of potential credits include MR 2.1 and 2.2 (Construction Waste Management: Divert from Disposal), MR 3.1 and 3.2 (Materials Reuse), MR 4.1 and 4.2 (Recycled Content) and MR 5.1 and 5.2 (Regional Materials: Extracted, Processed and Manufactured Regionally).
Sustainability: Preserving Virgin Materials and Reduction in Land Filling
Asphalt and aggregate are not a renewable resource, and as such the ability to reuse existing asphalt concrete is a benefit both from the point of sustainability and cost savings. Additionally, some of our best aggregates are found in place. ReNew™ Pavement is largely comprised of engineered aggregates and binder already in place. Recycling in-place material preserves currently owned assets for the owner.
THE PROCESS DOCUMENTED
–VINTAGE FAIRE MALL, MODESTO, CA
Size: 1.1 million square feet
Duration of Project: 8 days
Cost Savings: est. $600,000
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| Milling and Removal of Old Asphalt | Removal of Old Asphalt |
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| on-site plant | recycled asphalt |
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| application of cold asphalt | application of unrolled cold asphalt |
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| Reclaimer Repairing Poor Subgrade Section Prior to Recycle Overlay | CAPPING HOT AC OVER COLD BASE PAVE |
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| finished with 1-inch hot ac cap | |
Cold On-Site Recycling is an exciting adaptation of a tried and tested method of recycling that can yield significant savings in labor and materials, as well as greatly reducing a project’s negative impact on the environment. Pave West and Pavement Recycling are collaborating to offer this process for use when large areas need repaving, such as parking lots for malls, stadiums, arenas, universities, and commercial and industrial centers.