Controlling dust and environmental impacts
With 69,000 miles of aggregate road in Minnesota, controlling dust produced by traffic is a major concern. Besides increased expense for road maintenance and decreased visibility for drivers, one of the potential effects of dust, or particulate matter, is air pollution.
Dust is one of the six primary pollutants monitored by the U.S. Environmental Protection Agency (EPA). It is harmful to human respiratory health and coats crops and homes. But are the negative environmental impacts of dust greater than the effects of pouring dust control chemicals onto aggregate roads?
Many dust control products are currently available: chlorides (calcium, sodium, and magnesium), soybean soapstock, and bentonite are some of the options. Most research focuses on these products'; performance issues, but minimal research exists about environmental issues. Internet research, however, provided some further information about the latest products in the industry. (Ed. note: Minnesota T2 does not endorse particular products.)
Web search results
"Calcium chloride absorbs water vapor from the air and liquid water from the road bed…keeping the moisture in the road," according to usroads.com. But compared with lignosulfanate and magnesium chloride, calcium chloride does not perform as well in the areas of reducing dust, reducing the loss of road aggregate, and in lowering maintenance costs of unpaved roads. (Colorado State University study: www.buysalt.com/magchloride/dustgard/studyeffectiveness.htm)
Magnesium chloride is a naturally occurring element that is extracted from saltwater solutions, such as those found in sea water. Lignosulfunate is derived from trees during the acid bisulfite pulping of wood—the non-toxic material left over after the pulping process removes the cellulosic material from the wood. It is sold both as powder and liquid. (www.wtl.com/products.htm)
A more natural product available at half the cost of calcium chloride is beet extract. One product, Molex, is a concentrated liquid extract of beet molasses produced by Savannah Foods of Fremont, Ohio. Molex is very hygroscopic (attaches to and holds water), has a high level of potassium chloride (which can replace calcium chloride), has a near neutral, non-corrosive pH level, and doesn't freeze. (www.usroads.com/journals/rmej/9806/ rm980603.htm)
Soybean soapstock-related products also have fewer environmental consequences. Three Minnesota grain farmers who wanted to promote the use of this naturally occurring, agricultural byproduct formed Environmental Dust Control (EDC), Inc. in 1996. EDC has applied its Dustlock solution, a byproduct of soybean and vegetable oil refining, on private and public roads and in spaces throughout Minnesota and South Dakota. EDC claims its product is "biodegradable, environmentally friendly, and affordable." (www.auri.org/clients/ EDCinc.htm)
According to Technology News, an Iowa State University Transportation Center publication, a benefit of bentonite, a natural clay, is its environmental friendliness. Iowans are increasingly concerned about possible environmental damage associated with chemical dust-control materials such as calcium chloride. Iowa State's professor Ken Bergeson says that bentonite is a naturally occurring mineral containing no salt and poses no danger to the environment, and it does not contribute to vehicle rusting, as calcium chloride does. (www.usroads.com/journals/rmej/9803/rm980303.htm)
From control to stabilization
Traffic, weather, and gravel type all effect dust control product choice. "The industry is also moving away from 'dust control' and moving toward 'stabilization' of aggregate roads," explains Tom Broadbent, former CTAP van instructor, now working for Envirotech Services. Stabilized roads produce less dust, reducing maintenance costs by 75 percent and gravel loss by 50 percent. Oil resin is an example of a substance that controls dust and stabilizes roads, he says.
National evaluation
Organizations such as the Environmental Technology Evaluation Center (EvTEC), part of the Civil Engineering Research Foundation (CERF), are also encouraging development of environmentally sound dust control products in cooperation with the EPA. According to the EPA web site, "The intent of the EvTEC program is to verify the performance of new, commercially ready environmental technologies and transfer this information to important customer groups such as state permitting agencies and consulting engineering organizations." (www.epa.gov/etv/06 /fsht-06.pdf)
This is not a government program but a market-driven, private sector effort. Once companies or entrepreneurs submit their applications, a technical evaluation panel consisting of regulatory officials, industry reps, researchers, public interests, and others determine the product's environmental characteristics, safety aspects, functionality, and cost. The reports will be distributed to federal, state, and local officials and will be available through CERF's web site. (www.cerf.org/evtec/about.htm)
EvTEC recently coordinated a national evaluation of dust suppressants and base stabilization products with the Highway Innovative Technology Evaluation Center (HITEC) and the Minnesota Local Road Research Board (LRRB). This project assessed both performance and potential environmental impacts of the use of various dust suppression and roadway stabilization products. Minnesota counties will participate in the testing phase as field evaluation sites. Products that will be tested include calcium chloride, lignosulfonate, organic polymers, and polymer emulsion. The results are tentatively scheduled for publication in early 2002. (www.cerf.org/evtec/eval/dustagnt.htm and Aggregate Roads Research Bulletin 2000 M & RR 04)
—Hilary Davis
What's new in dust control?
New materials are always being tested for use as dust suppressants. Often the materials result from recycling efforts and from attempts to take advantage of natural materials that may be safer for the environment.
Do you smell french fries?
Last year, the Iowa Waste Reduction Center (IWRC) at the University of Northern Iowa (UNI) conducted a study overseen by the Department of Natural Resources (DNR). The preliminary report discusses applying used vegetable oil as a dust suppressant.
Used vegetable oil was found to be as effective a dust suppressant as the soy oil tested, but the used vegetable oil proved to be more cost-effective during initial application. The food service venues using vegetable oil must usually pay for its disposal, so currently there is a cost for collecting the used vegetable oil.
Unfortunately, early in the study the vegetable oil contributed to the formation of ruts, which may result in higher road maintenance costs later on. Also, the fried food odor lingered through the summer months.
Old roads and roofs
Recycled asphalt from roads or roofing material can also be used as a dust suppressant. Using millings from asphalt roads as a dust suppressant may help county agencies save on disposal or storage costs for the used material. However, millings can contribute to the formation of road ruts, resulting in higher maintenance costs.
If asphalt shingles are cleaned properly, they can be ground up and mixed with water to form an effective dust suppressant. At least two Iowa agencies, however, have had problems with nails remaining in the ground-up shingles, which have punctured travelers' tires.
In our own backyard
Bentonite, a natural clay material, has some advantages over other inorganic dust suppressants. Bentonite can be used for long-term treatment (two to three years), is effective, and in the long term can be less expensive than chemical road treatments. Bentonite does not pose any threat of metal corrosion or environmental damage.
The decision to use bentonite depends on the type of aggregate being used. Bentonite's negative charge allows the material to adhere to limestone aggregate, but these same electrochemical properties prevent bentonite from adhering to other negatively charged (igneous rock) aggregate.
For more information
For information about the IWRC study, contact Tim Trumbull, Iowa Waste Reduction Center environmental specialist, 319-273-8905, tim.trumbull @uni.edu.
(Reprinted with permission from Iowa State University's Technology News, May-June 2001.)