Overview

Far from being a new idea, much experience has demonstrated the value of using recycled materials as a supplement to natural aggregate in roads. Both in cost and performance, recycled aggregates have successfully proven themselves in many engineering applications by the Minnesota Department of Transportation (Mn/DOT) as well as county and city public works departments. Portland cement concrete pavements are commonly recycled and used in place of virgin aggregate as base material. Several Minnesota counties have also used recycled glass in road base, and more public works departments are expected to do so, too.

Recent advances have made using recycled materials in road base even easier. Mn/Dot's Technical memorandum No. 99-08-MRR-04 created the Class 7 specificationA concise statement of a set of requirements to be satisfied by a product, material, or process; indicating whenever appropriate the procedures to determine whether the requirements are satisfied. As far as practicable, it is desirable that the requirement be expressed numerically in terms of appropriate units together with their limits., which identifies recycled materials such as glass, concrete, and asphalt to be used in road construction projects.

As a result in 2002, Minnesota road crews are deploying cost-saving technology. Benefiting from a public-private partnership between local asphalt producer Bituminous Roadways and the Minnesota Office of Environmental Assistance, the crews have taken advantage of a 5% roofing shingle byproduct in hot-mix asphalt. This recycled aggregate reuses the cuttings from shingles composed of paper or fiberglass mat. Once added, the resulting high performance asphalt is suitable for a variety of residential paving and reconstruction applications. Currently, Mn/Dot's specification limits use to 5% shingle byproduct from the manufacturing process only; used roofing (tear-off) shingles are not yet allowed.

For more information on demonstration sites showcasing the use of recycled materials in road paving and reconstruction projects, see Success Stories.

Performance

From an engineering standpoint, the properties of recycled aggregates are similar to those of natural aggregates. The various materials in recycled aggregate have been proven to be as safe and easy to handle, while also providing effective compaction.

Demonstrating no appreciable environmental impact, recycled aggregates have also tested safe for potential harmful contaminants. While many different applications have been demonstrated in Minnesota and other states, the use of 10% glass blend for road base is the most common and well-proven to date.

Any recycled aggregate that meets the Mn/Dot specification is considered environmentally safe. If you are interested in obtaining specific test results, research findings, and case studies, see Resources and Web Sites.

In practice, recycled aggregate yields performance gains. Supplementing road base with recycled glass can improve permeability and gradation. The use of shingle byproduct improves the performance of hot-mix asphalt by increasing the pavement's resistance to wear and moisture, while reducing susceptibility to such problems as deformation, rutting, thermal fatigue, and cracking.

Availability

Recycled aggregate may be used as an alternative or supplement to natural aggregate. The State of Minnesota uses around 300,000 tons of recycled concrete per year, a significant portion of it in road bases. The use of recycled asphalt pavement is also well established.

As a relatively new source of aggregate substitute, reclaimed glass may not be consistently available. For this reason, planning well in advance of any application is recommended. For instance, county recycling programs may want to stockpile glass for two to three years for use in a particular road project; alternatively, consider using the material in smaller construction projects. As a general rule of thumb, a county that generates an average of 200 tons of recycled glass per year would yield roughly half a mile of road after blending the glass as a 10% mix in road aggregate per Mn/Dot specifications.

Other promising recycled aggregates have been tested for various road construction applications. These include roofing shingle byproducts, taconite tailings, coal fly ash, and scrap tires. The availability of these aggregate materials will vary as their applications continue to expand. For information on the availability of roofing shingle byproducts, see public and private resources in Resources and Web Sites.

Cost

In many instances, recycled aggregate competes favorably with natural aggregate. For example, recycled concrete is often cheaper than virgin aggregate. Under current estimates, the potential savings for using up to 5% shingle byproduct in hot-mix asphalt is 50 cents to $1 per ton.

Specifications

Mn/Dot's specification 3138 (refer to Appendix D) establishes a new grade of aggregate known as Class 7. This class of aggregate can be made from 100% recycled materials or blended with a combination of virgin and recycled aggregates. If recycled materials are used, up to 10% of the aggregate can be made from reclaimed glass. To assure recycled aggregates are used in road base, project managers may require it in construction project bids. The following is a sample specification:

"The (3138) Class 7 aggregate base shall be produced from up to 100% recycled material. The final Class 7 aggregate base material shall meet gradation requirements of Class 6. The composition of the Class 7 aggregate base may be made up from any combination of salvaged bituminous, crushed concrete or reclaimed glass, subject to the restrictions in 3138."

Some project managers may wish to go a step further and require the use of recycled glass. If so, the following wording could also be added to the specification:

"The Contractor shall use aggregate base constructed with material meeting Mn/Dot specification 3138 for Class 7 utilizing reclaimed glass. The use of glass shall be subject to availability as determined by the Engineer."

Vendors

It is common practice to use recycled asphalt, concrete, or Portland cement concrete in the road base. To locate sources of these recycled aggregates for a project, simply look in the Yellow Pages under "Sand and Gravel," or ask your aggregate supplier about recycled aggregate.

Since use of recycled glass to make aggregate is less common, it is important to facilitate communication between your county solid waste office or a local recycler that collects reclaimed glass and the aggregate producers that may blend the material. Below is a list of aggregate dealers known to have supplied recycled glass aggregate compliant with Mn/Dot specifications.

Carl Bolander & Sons, Inc.
St. Paul, MN
651/224-6299
fax: 651/223-8197

Central Specialties, Inc.
Alexandria, MN
320/762-7289
fax: 320/762-7290

Tri-City Paving, Inc.
Little Falls, MN
320/632-5435
fax: 320/632-5436

Tire Shreds as Lightweight Fill
Every year, Minnesotans discard between four and five million tires, or roughly one tire per person each year! Tires need not sit in dumps. Many can be retread, some are burned for fuel, and still others can be transformed into valuable construction materials. One application that has proven particularly successful is the use of tires as lightweight fill in roads. Several counties as well as Mn/Dot have used it in a variety of road projects. In one such case, Pine City used nearly one million tires to fill an area at a road intersection.

In a pioneering application, the Minneapolis Convention Center was among the first projects in the nation to use tire chips as lightweight fill. Approximately 72,000 shredded scrap tires were used as fill material over the center's parking garage foundation, saving the city over $110,000. For more information about using tires in civil engineering applications, contact the following Minnesota suppliers and Resources and Web Sites.

First State Tire Recycling
Contact: Monte Niemi
East Bethel, MN
763/434-6172
fax: 763/434-3072

Monitor Tire Disposal
Contact: Mike Overmann
or Art Binsfeld
St. Martin, MN
320/548-3496
fax: 320/548-3515

Tire Depot
Contact: Jon Engelstad
Moorhead, MN
218/233-7417
fax: 218/233-7698

Resources

Success Stories

Sources

"Glass Recycling in Minnesota: Alternative Markets"
Deborah Carter McCoy and Dan Krivit
Resource Recycling
September 1999

Ramsey County Demonstrations of Recycled
Glass as an Aggregate Supplement
Dan Krivit and Associates
January 1999

Waste Product Utilization at Mn/Dot
Gerald J. Rohrbach, Director of Mn/Dot
Materials and Road Research
Presented to the Legislative Task Force on
Aggregate
April 28, 1999