Frequently Asked Questions about TDA (TIRE-DERIVED AGGREGATE)
Where does TDA come from?
Our recycling facility (First State Tire Recycling) collects discarded used tires from across Minnesota. These end-of-life tires are used as feedstock in the manufacturing of TDA. This feedstock flows through our slow-speed, high-tolerance shredding machines (sharp cutters are necessary to produce clean cuts without leaving significant amounts of exposed wire). A single pass through the machine produces a product called rough shreds. Running the material through two shredders can produce the ASTM 6270 type B, TDA-sized tire shreds.
How is TDA used?
You might be surprised by the number of places TDA is being used today. Some examples include road repair/construction; stabilizing embankments; backfilling bridge abutments; preventing frost in driveways and parking lots; stabilizing parks/recreational trails; septic system drain fields and underground stormwater systems; rain gardens; landfills and gas collection; and backfilling retaining walls. See applications.
Why use TDA?
The idea for utilizing shredded tires in construction applications spurred from the legislated prohibition of land-filling used tires, and as a means to find a positive re-use for the hundreds of millions of tires that are discarded each year. Monte Niemi, our founder and president, proposed the idea in the early 1980s. Following several successful road building projects in northern Minnesota, engineering firms found that TDA could perform as well as other lightweight aggregates, and better than conventional materials in several different applications.
TDA is currently used not just as a means to recycle tires, but because it has many advantageous engineering properties compared to conventional and lightweight aggregates and fill material.
What does the American Society for Testing and Materials (ASTM) say about TDA?
The American Society for Testing and Materials (ASTM) has outlined the Standard Practice for Use of Scrap Tires in Civil Engineering Applications (ASTM D6270-20). Type B TDA is defined as “pieces of scrap tires that have a basic geometrical shape and are generally between 3 and 12 inches in size and are intended for use in civil engineering applications.” The full Standard can be accessed here.
Does TDA meet regulatory requirements?
The U.S. Environmental Protection Agency calls the use of shredded, recycled tires “viable” and “useful”, recognizing they are a cost-effective option in civil engineering projects.
What are the environmental impacts?
Typically in the United States, nearly one tire per person is discarded every year (over 5 million in Minnesota alone). The need for recycling tires in secondary markets is essential, as unattended tire piles can hold water and harbor disease-carrying mosquitoes or rodents, and tire fires are dangerous and toxic. Using TDA preserves natural aggregate resources as it can be used as a substitute for sand, rock, gravel, etc., and reduces carbon emissions by lowering trucking volumes. In addition, TDA can be utilized in projects seeking LEED and GREEN ROADS certification. See more about our commitment to sustainability.
Does TDA leach unwanted pollutants?
Research conducted over the last 30 years by the Environmental Protection Agency, universities and other firms and organizations concludes that TDA has negligible effect on water quality, and leach metals fall below detection limits just a few feet from a TDA fill.
EPA-funded research concludes: “The preponderance of evidence shows that TDA (used below the water table) does not cause metals with primary drinking water standards to be exceeded. Moreover, the data shows that TDA is unlikely to increase level of metals with primary drinking water standards above naturally occurring background levels.” EPA Data.
Shredded tires don’t break down when not exposed to the sun. The metals iron, zinc and manganese can leach from TDA, but not at levels to have real negative environmental impacts to plant, aquatic or human life.
What is the cost of TDA?
In the United States, TDA is typically less expensive (sometimes up to 40%!) than its counterpart for a given civil engineering design. We will work with you to make sure you are getting a cost-effective solution!
How do I design a project with TDA?
We work hard to educate people about benefits, design, and construction practices using TDA. We offer over 30 years of empirical experience for free, and share historic design and construction practices.
We’ve conducted hundreds of short (usually 1-hour) TDA Continuing Education training sessions for civil engineering firms, contracting companies, governmental and zoning departments. (You can even obtain CEU credits for attending!)
How do I work with TDA?
Construction equipment needed for TDA is similar to typical aggregate, such as stone or gravel. Special machinery isn’t necessary! It is important, however, to keep in mind the compressibility of TDA in reaching final grade elevations and TDA compaction. The general rule is that 100 cubic yards TDA loose volume equals 50 cubic yards volume after compaction and compression.. So, if you need to fill a 500-cubic-yard area, you would need 1000 cube yards of TDA. 1 compacted cubic yard = 2 loose volume cubic yards. See Installation.
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