Jan. 14, 2013 04:05

Dust Control

There was a time, long ago, when dust control wasn’t needed. Correction—it was always needed, but it wasn’t always required. People built roads and graded sites with little thought to controlling the dust being kicked up. If they did think about it, they sprayed water, or used something else that was less earth-friendly.

Then came the 1970s and a growing awareness of the environment, and the health issues connected to breathing in particulate matter, and of drinking polluted water. Suddenly, you couldn’t use just any old thing to keep the dirt down.

A new industry sprang up around creating safe, reliable products that would help keep the dust down and not blowin’ in the wind. Of course, water was still used— and still is used — for dust control. However, water isn’t the plentiful commodity it once was. Last summer’s extreme drought saw water restrictions in many parts of the country. And, as with any commodity, with scarcity comes increased cost.

But dust still has to be controlled. When water is not available or is simply too expensive, contractors involved in construction must look to tackifiers, either natural or chemical, for help. Straw and other mulches, as well as anionic asphalt emulsions, acrylic polymer emulsions, resin-water emulsions, wood derivatives, soybean oil and calcium and magnesium chlorides can also be used. All of these have their strengths; they also have their drawbacks.

Perhaps no state was as hard hit by the drought in the summer of 2012 as Texas. Yet Darren Hazlett, deputy director, construction division of the Texas Department of Transportation, said that water is still the cheapest thing a contractor can use for dust control, unless there is such an extreme shortage that he can’t get it at all.

In cases where a contractor doing a road project comes back to the Texas DOT saying there’s no water and he needs it to work, the department has the authority to postpone the project until water is more available. But a contractor who’s not working for the government probably won’t have that luxury.

Rapid City, South Dakota, was no stranger to drought this summer, either. It’s the home of Z&S Dust Control, a company that provides services to the state highway department, the National Forest Service, the Bureau of Land Management and many county and city governments. “Many of these smaller towns have a lot of gravel roads,” says owner Alan Sarver. Z&S also does quite a bit of work in the oil fields, which have a tremendous amount of traffic—trucks constantly going back and forth. That kicks up a lot of particulate matter.

Z&S mainly uses magnesium chloride for control. “We feel it’s more hygroscopic—pulls more moisture from the air—and does a better job than anything else we’ve found,” says Sarver. “Especially in these drought-time scenarios, we need all the breaks we can get.”

Over the years, Sarver’s tried just about every dust control product available, including polymers, coherents, pine derivatives and soybean oils, but still feels that “nothing works any better than what we’re doing.”

The drought was pretty severe in South Dakota, and is not letting up yet. They’re eight or nine inches down from normal rainfall; that’s almost 50 percent. It makes water pretty much a non-starter for dust control.

“No one can afford to mess with water,” said Sarver. “It’s too time-consuming and expensive. Some of our competitors might try adding surfactant to it, but in the long run it’s probably way more expensive to do that.” Since water evaporates, it has to be applied over and over again. “And there are more and more restrictions on using water just for dust control.”

However, the drought has caused extremely low humidity, and with a hygroscopic product, that’s a problem. Says Sarver, “When you have humidity levels into single digits as we’ve had, there’s just no moisture in the air to pull out. Until we get more humidity, the magnesium chloride is still there, but it can’t do what it’s supposed to do.”

With less moisture to pull from the air, magnesium chloride has less staying power, and vehicles erode it from road surfaces faster. So, instead of applying magnesium chloride once a year to a site, Z&S has found itself having to go back two or three times to maintain the same quality of dust control.

Magnesium chloride isn’t good for every application, either. “There is research that suggests that magnesium chloride can cause problems with roadside vegetation,” said Marty Koether, a managing member of EarthCare Consultants, LLC, a Tucson, Arizona, dust control, soil stabilization and erosion control consulting firm.

That concern is due to the fact that it’s essentially a salt, and as we know, salt is the sworn enemy of plant life. “But in a mining area or on a temporary road where there really isn’t any vegetation, then you don’t have to be concerned about it.”

“There are a number of aspects to be considered when doing dust control during a drought,” said Bob Vitale, owner and CEO of Midwest Industrial Supply, Inc., in Canton, Ohio. His company makes a number of different products for controlling dust, like polymer emulsions such as Soil-Sement and EnviroKleen.

According to Vitale, many of the common or generic methods used to control dust, such as magnesium or calcium, require moisture. They are not effective under drought conditions. Water-based asphalt emulsions are not going to be as effective either, because lack of moisture combined with high heat makes them brittle and oxidized. They’ll be less effective than polymer emulsions. These products bind soil particles together and work effectively once all the moisture is evaporated out of the system.

Water-based products, such as the chlorides, are also not quite up to the challenge of controlling dust in high-traffic situations—drought or no drought, according to Vitale. And chlorides can be caustic, causing rust and corrosion. However, they remain popular because they are inexpensive. They’re not patented, so you’re not paying for brand-name advertising.

Koether finds that polymeric binder products work well in Arizona’s dry, arid climate. He used them successfully on a 60-mile road shoulder project for Maricopa County, Arizona (where he got the nickname “The Dust Doctor”).

“We had to do a dust control project at a steel yard,” said Koether.

“From constant forklift activity, it had developed this extremely fine powdered dust—we called it ‘moondust.’ EnviroKleen worked where none of the waterborne products would even penetrate or hold it down.”

After water, oil is the original dust control product. “Up through the 1960s, the main dust control substance was old crankcase oil from engines, machines and transformers,” said Vitale. “Everybody just used waste products and sprayed them around. But because of human health and environmental regulations, many of those things have been outlawed.” In fact, says Vitale, environmental legislation, which really began in earnest in the 1970s, is what spawned today’s dust control industry. New requirements called for new products to replace crankcase oil, which Vitale and others rushed to create.

Because of this, there are many environmentally safe, biodegradable dust control products on the market, some of them oils, many of them derived from natural sources. RoadKill is one of these; it’s made from pure soybean oil that’s been cleaned and had fats extracted from it. Dave Streitelmeier, founder and owner of Dustkill, LLC in Columbus, Indiana, has been its exclusive distributor since 1993. “It’s my main product during a drought, chiefly because it’s applied as a ‘straight oil,’ meaning that you don’t have to blend it with water—in fact, it won’t blend with water. That’s one of the reasons why it works so well in drought conditions.” Streitelmeier claims that once the product is down, it will actually repel water.

Lignin sulfate or ‘tree sap’ is another natural dust control solution, a wood byproduct derived from pulp paper production. It’s also inexpensive, but quality varies widely and it has some limitations. Lignin can contain debris that clogs sprayer nozzles. It’s also sticky, and can cling to clothing and vehicles. And it needs an additional product to seal it to surfaces.

There may be another drawback as well. “The makers of lignin sulfate will tell you it’s a natural product, because it comes from trees,” says Koether. “But if you look at the processing—how the glue is separated from the pulp—you would see that it’s a virtual chemical soup.”

Koether says that his company has “missed a lot of opportunities,” because it won’t use lignin. “Some air quality departments won’t allow it, because they don’t feel that it’s right for the environment, either.”

Our extreme drought this summer didn’t exactly turn our country into Iraq. But something that is used successfully in the extremely low humidity of the Iraqi desert is another environmentally safe acrylic polymer product called Envirotac II, affectionately nicknamed “Rhino Snot.” It’s made by Environmental Products & Applications, Inc., in La Quinta, California.

It works similarly to other copolymer products, such as Soil- Sement. The Marine Corps used it for roads and helipads in Iraq, finding it able to stand up to the beating sand whirlwinds created by helicopter blades. One of its drawbacks, however, is that it must be mixed with water. It’s also extremely sticky and almost impossible to remove from clothing.

Another eco-friendly product, GelTrak, is made by Ecologel Solutions, LLC, in Ocala, Florida.

According to company president Rick Irwin, it was developed by a chemist in Australia in the early 1990s. “There was a severe drought right after the country had outlawed the use of petroleumbased products (for dust control).”

The chemist had developed other dust control products for the mining industry, so they came to him after pulling their lakes almost completely dry. Irwin says the product is essentially composed of food-grade materials, made from nontoxic polysaccharide adhesives and some hygroscopic components, including a small amount of chloride. Besides pulling moisture from the air, the company claims it also helps retain subsurface moisture. It combines this with a coagulant quality, merging fine dust volumes into larger particles.

However, since GelTrak is hygroscopic, periodic rewatering of surfaces is necessary. Each application remains effective for up to three months, depending on rainfall and traffic. Results are cumulative with each application.

There’s no single answer to the question of what dust control product or technique works best during a drought. That’s a determination you’ll have to make, depending on the job, the circumstances, and your own personal preferences. Happily, there are many different methods to choose from, and more being developed every day.

In the meantime, water shortages continue in many places, and probably will for some time to come. Just as environmental awareness sparked the development of alternatives to petroleum-based dust control methods, the need to conserve water may spur even more research and development into new methods of keeping the dust down during the dry times.

Also in Soil Erosion News

In many ways, we are fortunate that, in our chosen profession, we are able to help people when certain disasters occur: the tornadoes in Missouri, Oklahoma, Louisiana and Georgia, the flooding in Louisiana, the snows in the northeastern part of the country, the rain in California, and the snow in Colorado....

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