Real World Dust Control
By Dave Poole
Applications of the latest technology in dust control are successfully used in various forms of chemical dust suppression for roads, intermodal yards, haul roads, quarries – where ever traffic on aggregate surfaces produce dust. The choice of what chemical suppressant to use involves careful consideration and weighing of product advantages and drawbacks. Likewise, the unique operating situation that any organization faces is a broad array of internal and external considerations. Any of these influences can dictate what route to choose in controlling dust. The following are not test or lab conditions where cost is no object. These are commercial, paid dust control programs that represent what companies actually do in the real world.
| Grindings are an inexpensive way to stone any traffic surface and make use of a recycled material. They cost 1/3 to ½ as much as virgin stone. The drawbacks are a lack of availability, away from urban centers and some variability in asphalt content.If an asphalt surface being ground up is fairly new, it will have a high asphalt oil content and may compact into a homogenous surface with the passage of traffic and a little summer heat. More likely, the road source being ground will be old and weathered so that grindings spread from it do not coalesce. Grindings will then become a source of dust, but no more so that if virgin stone of the same size had been placed. |
Holnam, Inc.
Holnam Inc. purchased the Northwest Cement Co. about 10 years ago. The plant at Mason City, Iowa has a long history under Northwest and began operations in the early 1900’s. The fact that they have operated so long in one location defines a key external consideration in that the city has grown right up to the edge of their property. It also defines a key internal consideration in the length of their haul road. Over the year, close in limestone deposits with the proper chemical properties for cement production have been exhausted. The company presently goes 3.1 miles to a crusher facility on the edge of their quarry. A recently completed mining plan indicates adequate reserves for 20 years into the new century, using the current basic haul road set up.
Honam enjoys a well-built road, from ballast rock up through to the road surface consisting of –1/2” crushed limestone and fines. Calcium chloride was used as a dust suppressant through the mid 90’s. It was inexpensive at the time and was effective under the punishment of the three primary 120-ton capacity cab/trailer rock haulers that supply the plant. In addition to these units, numerous semi-trailer dump trucks haul out overburden soil, sand and rock for building projects in the area.
The rusting effects of heavy calcium chloride application began to take a toll on haul equipment and scrapers used to retrieve stock piled clay, after about a decade of regular use. The cost of the material also began to rise, a trend that has accelerated recently, with the exit from the market of a large calcium chloride producer. Environmental considerations did not play a direct roll, but continuous application of chlorides will eventually contaminate ground water. Honam’s quarry supervisor began to look at other options.
One way to eliminate haul trucks and their dust is a conveyor system; an idea discarded when a study calculated the capital investment.Paving might be considered a reasonable solution for a cement company, but the huge up-front cost ruled it out and the experience that paving does not end intensive maintenance also weighed in. Just as steel plants, intermodal and trucking companies have found paving will not end dust unless every square inch of the facility can be paved. There is something called “track-out” of fines and dust from unpaved areas, transported by all vehicle tires. A rock facility has the further complication of spillage.Regular vacuum sweeping will be required to maintain dust free conditions and any paved surface will need replacement at some point.
Another facility had worked with an asphalt emulsion and had some success with it. At this time, the Department of Natural Resources had complaints from nearby residents of excessive dust and began requiring an asphalt based dust suppression chemical as part of a court order.
When Midwest Industrial Supply, Inc. began talking with the quarry operators at Holnam, they were able to offer an asphalt emulsion with a very important difference over ordinary asphalt emulsions. They add a plastic polymer component to their asphalt: a proprietary plastic emulsion called Soil-Sement®. This polymer adds load carrying capacity to the roadbed, makes the asphalt component firmer in all weather (even in extreme heat), and delays the brittleness that comes with the aging of most asphalt emulsions. With assurances that the Road Pro Plus® brand of asphalt emulsion stayed firm after set up, a contract was negotiated and the first year of service began with the dust season of 1998.
Midwest has just ended the year 2000 dust season; three continuous seasons of using the asphalt/polymer dust suppression agent on the Mason City Holnam property. Costs have held in the $2 per square yard range, per season. This amount covers all application and material costs for a seven month long season.
The start up of treatment was not totally trouble-free, as both Midwest and Holnam had learning curves to climb. Adjustments and fine-tuning over the first year have lead to an all weather haul road that requires no watering and little maintenance from Holnam. There has been some carry over of dust control chemical from year to year, allowing Holnam to extend treatment further into the quarry for the same cost. Start up for a new season begins when the spring thaw has abated and weather conditions have dried and stabilized – usually early April. Holnam will grade over the road and add some – 1/2” road mix aggregate to low spots from the spring thaw. This is the only grading the road will see until next year’s spring start up. Because the first of the season applications are heavy, a Saturday is set for the very first application, the only day of production lost to road maintenance.
Holnam could run on recently applied material without affecting the efficiency of the application, but chooses not to. The decision has a lot to do with the new 150-ton cab/trailer units that were delivered in 1999. Maintenance applications from here on are done after the day shift wraps up.Frequent, light applications are made in the areas prone to heavy wear: curves and public road crossings where stops and starts are made. The season will wrap up in early November, when rain and lengthening time needed to dry an application will dictate closing out the season.
Other Quarry Roads
Not all haul roads have this same built-in stability. When a road is not as well built, and reconstruction is not an option, Soil-Sement® polymer can add load carrying ability. Frequent application lends itself to amending the road surface from the top down, by adding fines and sealing them over the course of a dust control season.
Road maintenance philosophy in this case becomes a continual build up of the road surface. They spread – 1/2” recycled ground asphalt, “grindings” (see side bar previous page), in a thin layer over the surface. This is then sprayed with dust suppressant. When traffic comes on the road the next day, the grindings get pushed into the road surface and bound with it.The net effect of one such cycle of treatment is to build up the road ¼ to 3/8”. Repeated 6 to 8 times over the dust control season, an inch or more of road surface is built up. This process has continued with Road Pro Plus®. The surface has become noticeably harder over this first season and much less inclined to pull up during hot periods over July and August.
By adjusting the ratio of polymer to asphalt, they can further increase hardness and aim to reduce and eliminate the ground wave effect. This will result in greater fuel economy, a big factor in operating expense. A small incremental increase here acts like compound interest, multiplying into large savings when looked at over a years’ time and applied to the total number of haul trucks.
Road Pro Plus® can aid haul road operations in polar operating environments. The main difference is in how the suppressant is applied. One quarry has seen better results in frequent, light applications. Other roads apply fewer applications that are much heavier, and this has produced good results, with the addition of rock fines or grindings.
Summary
These examples do more in fugitive dust suppression than the typical quarry operator. While their expense is quite significant, a great deal of money spent on dust control comes back to them in several very important operating advantages.Off-highway hauler tires and fuel are ordinarily the two highest operating expenses. An improved, stabilized roadway will offer a significant return on investment as these costs are reduced substantially. Increased speed means increased efficiency in haul truck utilization and overall efficiency. Reduced unit repair costs and decreased downtime for unit repair are further dividends. The unproductive labor expense and maintenance of a watering unit is eliminated for the haul road. Visibility and improved safety are a further bonus. Corrosion of parts and equipment is not a side effect of asphalt emulsion dust control. Watch for more on haul road cost analysis in future articles – a case can be made that dust control does not cost; it literally pays!
L&W
For more information, contact David Poole, Midwest Industrial Supply, Inc., P.O. Box 8431, Canton, OH 44711.Fax: (815)485-0588, www.midwestind.com, davep@midwestind.com.
Land and Water - March/April 2001
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