Road maintenance techniques and products have made great strides.

By David Engle

It might not rank with finding the vaccine for polio, but the dust-abatement industry is now turning the corner on an ancient nemesis: hovering clouds of sometimes blinding, sometimes choking road dust. Years of research and experimentation by laboratories, highway departments, and manufacturers are paying off with improved second- and third-generation products and better road maintenance techniques.

The concern wasn't that earlier methods were ineffective - just that none was completely satisfactory at dampening dust cost-effectively without frequent labor, thousands of gallons of water, reapplications of the quickly degrading (and often expensive) suppressant goo, or risk of harm to the environment. For this article, we've spoken with persistent experimenters, vendors, and product users who say that indeed recent dust-control innovations are ushering the task of road maintenance into a dramatically more effective phase.

A half-dozen or more users reported getting amazingly strong roads and 90%-plus dust abatement, sometimes enabling them to postpone indefinitely the need for paving. And these are not just easy, routine jobs at optimal sites. Especially good results are now coming from a range of tough climates and conditions where repeated efforts with earlier-generation products had been disappointing. We heard from users facing dusty droughts and desert heat; loamy and clay soils with poor absorption; a granite logging road; long-unpaved, unrocked powdery roads in central California's agricultural belt, which required daily watering; a gravel bed servicing a sooty steel mill in Indiana; and a landfill in the Pacific Northwest. Space limitations prevent reporting all of these accounts in depth, but the following few comments illustrate the general trend:

• Rod Ault, owner of a road-service business in Estes Park, CO, uses a product called Caliber DC 2000 on high-elevation roads in Colorado during drought. He reports, "It works fabulously," adding, "Oh, boy, it will stabilize a class-six road base of crushed and screened blue granite!" And it "sticks much better" than the various combinations of lignins, chlorides, and emulsions he previously used.
• A dust-control contractor in late summer 2003 began road-testing a product called Earthbind, attempting to stabilize extremely sandy and rain-drenched coastal roads in South Carolina. Very preliminary results are the most dramatic that he and others have ever seen. "There are some really exciting things happening in [South] Carolina [with Earthbind]," says Timothy Owings of Seaco Inc., and county road departments are eagerly awaiting results of his long-term tests. "We want to be downright excited, but at this point we are just cautiously optimistic until time bears out early promise."
• At a landfill transfer station, Brian Wilkins, operation manager with Waste Management in Arlington, OR, struggled in futility with dust. He resigned himself to paying for a full-time water wagon until he started applying Earthbind in early 2003. "This stuff works well" on gravel road sections being pounded by heavy trucks, he reports. "It sets up hard. It's pretty amazing." But after only three months of use, it might be too early to reach a final verdict.
• Even the United States Army Corps of Engineers - extensive testers of dust abatement dating back three generations - is encouraged by product tests currently wrapping up in Missouri. As Research Contractor Dick L. Gebhart, Ph.D., notes, "A number of products performed very well - beyond our expectations under military traffic conditions." A second, longer-term test phase will yield a final report in midyear (see sidebar).

What's making it all happen is a growing knowledge base of best practices, combined with products that mix old standbys, such as lignins and chlorides, with heavy-duty hardening and binding agents. Stickiness is really the key; not only does dust adhere better, but more importantly - for a surprisingly long time and despite punishing weather and traffic - so does the gravel. It's not unlike the effect of pouring caramel over peanuts to form a solid, crunchy candy bar. After decades of chemical trial and error, several manufacturers have finally discovered some very good "caramel." This particular analogy is more literal than you might think; one of the more powerful gravel-road binders turns out to be food derivatives. The critical element here is finally the right combination of lignins, chlorides, and other materials for the right applications. As Ault puts it, any one of the old stock suppressants "by itself doesn't last that long. But put them all together, and they make one hell of a road."

Satisfying a Roadbed's Basic Needs
With gravel roads, dust abatement usually isn't the primary issue; instead it's all about road cohesion or deep roadbed stabilization. Loose gravel under pounding traffic grinds into powder and rises in dust, but gravel that's been sufficiently sticky-coated will be preserved. A late 1990s study by Colorado State University (CSU) revealed the rather astounding conclusion that unpaved limestone roads in that state were losing approximately 2.5 tons of rock material per mile per average daily traffic (ADT). "In other words," explains Road Superintendent Bob Henry of Johnson County, KS, "200 average cars per day will add up to 500 tons of fine limestone dust" being released into the air per year. Henry used the CSU study to cost-justify a budget for the revamping of his county's road maintenance.

As a half-dozen gravel road experts told us, binding gravel together or adding deep "caramel coating" below the surface costs more initially but pays back in savings on constant rerocking and regrading. Rocky roads become safer to drive at higher speeds and induce less wear on vehicle tires and undercarriages, and the quality of life in the neighborhoods is vastly improved. Then, too, some of the emergent new-generation products have a cumulative effect; the "caramel" builds up year after year so that even maintenance costs can decline slightly over time. As the EPA's 1999 booklet on gravel roads (available at www.epa.gov) points out encouragingly, "The cost of dust control can more than pay for itself with the benefits of reduced material loss and reduced need for blade maintenance" if the traffic is relatively high. We even found one public works department - Platte County, MO's - offering dust abatement as a thriving little sideline business to farmers and landowners. County crews treat 25,000 ft. of private roads and lots, spraying basic no-frills calcium chloride, preferred for its low price and relatively high effectiveness. Platte County Director of Public Works Dale Thomas reports that the arrangement "works out very well."

Product Proliferation and Innovation
The quest for dust control has been collaborative but also intensely competitive. Sold by scores of manufacturers through the decades, hundreds of products have hit the market. It's hard to inventory them all, let alone discover which ones work and which don't. An array of questions and technical issues make the selection process perplexing. It's likely that no single solution exists because each soil or gravel composition differs, as do climates and ADTs. Some products, such as moisture-absorbing chlorides, turn out to be inappropriate in dry desert climes yet work well and are the most affordable in other areas.

New products come, and older ones fade away. Some manufacturers fiddle with their formulas perennially, altering ratios or contents and experimenting with new "tackifying" or stickiness additives, such as exotic polymers, petroleum, or synthetic petroleums. Are the newer versions really effective? Have former shortcomings been fixed? In many cases, the only evidence to substantiate claims is the manufacturers' own testing or perhaps testimonials from collaborative distributors - whose local conditions and climates might not accurately represent the results to be expected from a new application. Naturally, short- and long-term product cost is an ever-present factor, as is the difficulty level of applying it. Products are not only patented, but their precise ingredients are also fiercely guarded company secrets; selecting the right one becomes even trickier.

Still other products work adequately in terms of effectiveness but, as Ault puts it, singling out his experience with one particular polymer-and-concrete soil treatment he tried and abandoned, are "terribly expensive or are a terrible pain in the butt to apply and work in to soil." Other products work initially but collapse when the rainy season sets in; Owings, for example, had been using an organic soil-binding liquid developed from the wood pulp industry but found that it easily degraded under pockets of water. And the results of using products that earned rave reviews from multiple customers in our survey were not always replicated by others we talked to - although several added disclaimers to the effect of "maybe it's too early to tell," or "maybe this product will work with a different concentration."

With the profusion of options, it's obviously prohibitive for anyone to test all good candidates methodically. Currently the testing leader is probably the US Army Corps of Engineers and its contractors, who are testing seven products. Other assorted research is underway. The Federal Highway Administration is now midway through a two-year experiment with the Caliber DC 2000, matching it against several competitors at testing stations in Freeport, TX, and Sells, AZ, according to application expert Klif Rader of Desert Mountain Inc. in Kirtland, NM. Tests by various state and county highway departments are also in progress, and as they're completed, the findings will likely percolate among major marketers.

A critical test element is simply time; what's needed to demonstrate good performance isn't a trial lasting a few months but one that lasts a year or two, under all types of conditions. Unfortunately market pressures make it difficult for manufacturers to stick to long-term testing programs and not adjust their products if rivals seem to be gaining ground. Every local road department must become, in a sense, its own ongoing experimental lab, and several of those we talked to have followed this approach as a matter of course. The regional grapevine, as well as advice from well-established product distributors, should also be a helpful resource.

Methodology Matters
Nor is it as simple as finding "the right product and ingredients" for a given soil and climate. Application procedures are critical too, meaning the volume of liquid sprayed per square yard, concentration strength, and even the hour-by-hour weather conditions present before, during, and after the spraying. If applied too thickly, a product won't penetrate; if applied too thinly, it won't adhere. Both the density of solids contained (25%? 40%?) and the application rate (e.g., 0.25, 0.30, or 0.50 gal./yd.2) can translate into success, costly wastefulness, failure, and more difficult maintenance down the line. Often top coats for antidust coverage are best applied in two or even three applications like coats of paint. Also, notes Rader, "If you put it all on at once, it won't penetrate and you get some runoff. You have to put some of it on to help it penetrate and then do a second shot that kind of tops it off."

To help achieve optimum results and protect the environment, specially designed application spray-bar systems are available with nozzles positioned within a foot or so from the roadway. Spray volume can be precision guided by computerized controls, such as by the widely used palm-size DICKEY-john Corporation computer. It connects the spray bars with the tank truck's odometer. Notes Rader, "If you speed up, an air valve opens wider, so it keeps a consistent spray. We can know within one-tenth of a gallon what we're spraying."

Timing is also critical. Most treatments are scheduled for the narrow window between the April showers and summer's dryness. Tales of ill-timed roadbed treatments damaged by moisture or washed away entirely are not at all uncommon. If crews are careful and pay attention to the Weather Channel, they should have no problem, says Rader, especially if they're using a nonchloride product or a product with a binding agent in the right application.

With these caveats in mind, the following sections cite some encouraging reports from customers in the field who literally are seeing the end of the trail for their dusty country roads.

Arlington, OR: Taming a Trucking Alley
Brian Wilkins of Waste Management Inc. faced some of the toughest conditions and the most frustrating and seemingly insoluble dust problems. Wilkins's bane is a gravel road connecting a rural train stop with the Columbia Ridge Landfill, where his hefty loaded trucks haul garbage in a 5.5-mi. round trip. Streams of vehicles pulverize the gravel into powder. "It's incredibly dusty," says Wilkins, and suppression requires a full-time water wagon. "We were hauling 20 to 25 loads of water - 10,000 gallons a load, or about 250,000 gallons of water a day," he recalls.

Moreover, beginning in mid-2003, he was sensing some impending regulatory heat from the Oregon Department of Quality. Its issuance of a new rule called Title 5 mandates stringent control of fugitive dust; only a small percentage of a facility's own air pollution can legally drift over its property line. Even before the rule came along, though, Wilkins had sought in vain to find a successful dust-abatement agent, if only to save water. He had tried and failed with so many products that, when manufacturer Don Blackmon told him about another one, Wilkins recalls, "I laughed at him."

Those days appear to be over. Earthbind has stabilized and controlled the dust. "On the main road, it's great stuff," Wilkins says. "It has saved us a lot of time and money. I would recommend it to anybody" - except in areas where trucks turn tight circles, which are still impervious to any remedy.

Wilkins offers this application tip: "Just make sure you have a pretty smooth surface and that the gravel is brushed off. We hit the road with it every other day. Just start off really heavy, then progressively step it down."

Columbia, SC: "Doing Everything They Say It'll Do"
Nature recently solved South Carolina's five-year drought and ensuing dust with a monsoonlike rainy summer in 2003, says Timothy Owings of Seaco Inc., a service company that applies antidust and antierosion measures on several county roads. Soils here range from high-clay content in the interior to pure sandy beach roads along the coast. So, instead of dust, Owings has been coping with erosion and flooding. "Ditches in [the Columbia] area have fish in them from flooded swamps adjacent," he relates.

But this drenching has also provided him with a good natural test of the durability of roads he had been treating experimentally with Earthbind. In Bamburg County, Owings has done 4- to 6-in. road-base stabilization to prepare for paving; conversely in nearby Newberry County, he's using the product to coat sandy roads as a solid, dust-free alternative to paving. Early results are "extremely impressive," he says, although it still is too soon and roads are too soggy to give a definitive verdict. In the very sandy and erosion-prone road-base project, Earthbind penetrated well "and has withstood blading, rolling, and compacting to produce very nicely crowned roads" with drainage running effectively into chronically soggy ditches. He's waiting to see if the sand base fully solidifies before he'll recommend paving. Motor-grader operators have told him that the treatment "really sets up hard," even on a road that inadvertently hasn't been prepared. Owings says one operator reported that on one application on crushed gravel, "the road set up so hard it was throwing sparks off of the blade."

Getting the concentration right becomes trickier because crews might work with highly porous sandy beds the first day, damp ones the second day, and soils of humus or clay the third day. "We're learning a lot," he observes about this process. The early findings indicate that if Earthbind penetrates, "it is doing everything they [Enviroad, the manufacturer,] say it'll do. The material really seems to be locking up the soils wherever we've applied it." One sandy roadbed hardened surprisingly quickly, so a heavy downpour the next night didn't destroy compaction - although a late-afternoon top spray was washed away entirely.

Estes Park, CO: "The Best Thing I've Ever Done"
In his road maintenance service for assorted high-elevation tracks of dirt, granite, and sandier native materials, Ron Ault's primary concern is road durability. Ault hadn't faced serious dust problems until a drought hit the Rockies three years ago. Now his maintenance strategy must balance both issues. Over the years he's used straight lignins, magnesium chlorides, and a blend of magnesium chloride and lignins. The latter, being water soluble, "has a hard time staying in material," he reports. "It gets leeched out really quickly."

Ault's prize goes to Caliber DC 2000, composed of 80% magnesium chloride and 20% of an engineered corn-based product, Caliber, from Glacial Technologies. For the past two years he's treated about 20 mi. of road with it, shaping and compacting it easily. "It makes a fantastic road surface," he reports. It binds fine materials, generates a hard surface, and almost completely eliminates dust. Homeowners' driveways abutting the roads stay cleaner because they don't track the fine particles. "It also stays in native material a lot better, a lot longer," Ault says, although it is considerably more expensive than straight chlorides.

The Caliber hardens into a very durable crust, "sort of like when you make rock candy," he explains. This surface withstands drastic and severe climate changes and accumulates with each reapplication. Caliber DC 2000 is distributed by Envirotech Services Inc. of Greeley, CO. "It's the best thing I've ever done," says Ault.

Initial application consists of a simple top-dressing with 0.25 gal./yd.2 once a year on most roads or twice a year on heavily traveled ones. First wet the road, then spray the mixture. "Roll the daylights out of it, and you're good to go," Ault says. For annual maintenance, moistening allows the road to be rebladed and reshaped.

Johnson County, KS: Getting a GRIP on Dust
For Bob Henry, a county road superintendent in Johnson County, KS, it wasn't a wonder-working formula that reduced his road dust but a more systematic application program. Johnson County suffered through a drought last summer and has witnessed a major influx of suburbanites. "They love the country atmosphere," Henry observes, and in soaking up that atmosphere they're bringing a faster-moving and higher volume of traffic. ADT is now climbing to 500, 600, and 700 cars a day - a lot for extremely dust-prone limestone beds of 1-in. chips down to small fines. "It is all going up in dust," he says, "and if you didn't have some sort of treatment on there, you wouldn't be able to see."

For cost reasons, calcium chloride and magnesium chloride are his staples, but he's also experimented with other suppressants, including MC 30, a cutback asphalt; an emulsion asphalt called Pep; and a soybean residual product "that was not really successful," he remarks.

In 1999, Henry began looking into abatement measures that also might reduce the need for maintenance and help preserve his fast-disappearing and dissipating limestone. A Colorado seminar on road maintenance expounded for him the principles of an annual nine-pass maintenance program. It consists of scraping back the surface rock; adding magnesium chloride or calcium chloride; and laying the surface back down, spraying it, and rolling it repeatedly. The result is a low-maintenance, low-dust gravel road.
Henry decided to modify the Colorado program to combat his own much tougher problems, and he emerged with what he dubbed a gravel road improvement program, or a GRIP. Because these procedures are illustrative of application methods with many products, it's useful to summarize them all:

• First he decided to maintain roads in mile-long segments rather than by adding loads of rock and regrading haphazardly and sporadically. "Whenever we rocked a road, we decided we were going to go ahead and rock the whole mile," adding, for example, 3 or 4 in., or 2,000 tons, of gravel to high-ADT roads (those accommodating an average of 300–1,000 trips per day). This routine would enable him to tackle road maintenance more systematically and keep better track of results.
• Next came saturation of the new rock with water to reach the optimum point for absorbing calcium chloride (a bargain back then at only $0.27/gal.).
• After that, Henry's crew shot the wet road at a concentration of 0.5 gal./yd.2 of calcium chloride at 34–35% solids.
• The next step was blending the mile with a Bomag asphalt recycler. "That mixes all the material up really good along with the product," he says.
• After blending came smoothing the surface with a steel roller and shaping the cross-slope with a motor grader "while adding water to ensure that it is compacted really tight," Henry says. "We like to have about a one-half-inch-per-foot cross-slope fall to the outside to establish our crown," he explains. "The enemy of a gravel road is traffic count, and by shaping roads and putting the cross-slope in and by giving them a good, hard surface, people are going to drive on each side of the road like they're supposed to." If you can "persuade" drivers to stay to the right instead of in the middle - as they tend to do on poorly shaped roads - you effectively cut the traffic count in half. This balances the wear and reduces the fine pulverizing effect that becomes dust.
• After the rolled surface cured for about a week, "We came back and shot two-tenths of a gallon on the top to heel the top down," Henry says. And the GRIP was finished for the season.

After a mile of rocky road is fortified, the annual surface maintenance consists of blading for superficial reshaping when wet. This maintains the contour, fills some holes, and retouches the crown. Henry recommends doing this once a year or, for heavily traveled roads, twice. "That's about 80% less work than was required before" in his fortnightly maintenance regimen on this high-ADT, untreated road, he says.

Annual blading degrades the dust control by about 10%, he estimates. "But you can rewet the top and reshoot it with two-tenths of a gallon on top of that at the end, if need be."
The only mild complaint he hears is that rain or high humidity makes the road appear sloppier because chlorides draw moisture like a salt shaker. Otherwise, he reports, "the public really likes it."

What's the Answer? Do Your Homework
It's certainly advisable to stay tuned for future research reports. You'll want to select an experienced service firm, distributor, or consultant with extensive local experience and a track record of successes in conditions comparable to yours. Check, too, with the manufacturers' research data: What has been done, where, and for how long? Even if testing isn't completely independent and objective, the research might refer to actual field tests you can see and evaluate. Talk with crew foremen who have seen the before-and-after results over time.

Another potentially good resource is a free publication from the Army Corps of Engineers, Dust Control Guidance and Technology Selection Key, which has helpfully systematized the selection process. It lists product types, application rates, durability, control efficiencies, soil types, and climates. As Gebhart explains, it enables a user to determine what will be the most effective product for a particular road surface, moisture range, or traffic load. Get it from the Army Environmental Center Web site (http://aec.army.mil).

To conclude on a positive note, all of our sources told us that - although environmental impact from runoff is a concern and is something to be aware of - few, if any, applications have ever produced significantly negative results. Obviously applicators should follow best practices to minimize the chance for any mishaps. For example, on steeply sloped road with adjacent vegetation and landscaping, operators should know how to create a small berm as a fluid retainer. "Chlorides might kill a little grass at the edge of a road, but it's grass that you would have to mow anyway," one road superintendent points out. Henry states that Kansas residents "are aware of the environmental impact, and they're concerned about the runoff issues, but for people there, eliminating dust is like a blessing."

La Mesa, CA - based David Engle is a frequent contributor to Forester Communications publications, specializing in construction topics.

EC - January/February 2004