Dust Palliative Selection and Application Guide
Peter Bolander and Alan Yamada
The purpose of this publication is to help practitioners understand and correctly choose and apply the dust palliative that is appropriate for their particular site, traffic conditions, and climate. In addition, this publication describes the expected performance, limitations, and potential environmental impacts of various palliatives.
This guide examines most of the commonly available dust palliatives currently available and does not endorse any particular product. Since new products will become available and existing products will most likely change following publication of this report, it is recommended that this guide be used as a starting point for determining which palliative would be most appropriate for a given situation.
DUST ABATEMENT BASICS
Dust from unpaved roads is not only a nuisance but creates a safety hazard by reducing the driver’s visibility. Dust also affects the health of road users and increases wear-and-tear on vehicles. Dust is always considered an intruder at campsites and picnic areas. In some areas there are regulations that limit the amount of particulate allowed in the atmosphere.
Fine particles, including dust, act to help hold the surface of unpaved roads together. With a loss of fine particles from the roadway, there is an increase in roadway surface raveling and maintenance costs. These fines are smaller than what the eye can see and pass through the 75 µm (No. 200) sieve.
How can dust emissions from the roadway be reduced or eliminated? Since the fines act as a binder that holds the surface of the unpaved road together, removing them is not a good option. Sealing the surface with an asphalt or concrete pavement or Bituminous Surface Treatment eliminates the dust problem; however, the low traffic on most Forest Service roads does not justify the cost of sealing the road with asphalt, concrete, or a surface treatment. Another alternative is to apply a dust suppressant product. These products are not a permanent solution and will require further applications as the effectiveness of the product decreases with time. Dust suppressants are one of many possible methods to control dust (Foley 1996; UMA 1987; Washington Dept. of Ecology 1996).
Dust suppressants work by either agglomerating the fine particles, adhering/binding the surface particles together, or increasing the density of the road surface material. They reduce the ability of the surface particles to be lifted and suspended by either vehicle tires or wind.
To properly select the appropriate palliative one must understand the primary factors that generate dust. They include the following:
- Vehicle speed
- Number of wheels per vehicle
- Number of vehicles
- Vehicle weight
- Particle size distribution (gradation) of the surface material
- Restraint of the surface fines (compaction, cohesiveness/bonding, durability)
- Surface moisture (humidity, amount of precipitation, amount of evaporation).
An excellent description of these factors that generate dust and how to analyze total long-term costs can be found in Foley et al. (1996) and UMA Engineering (1987).
Selection of the proper dust abatement program must include an understanding of not only the above factors, but the total long-term cost and environmental impacts of that program. Long-term costs include road improvement, road preparation, application of the suppressant in conjunction with the number of times the palliative needs to be applied, and expected change in maintenance practices. Environmental considerations typically include impacts to the water quality, aquatic habitat, and plant community.
Besides controlling dust, a good dust abatement program may include reduced maintenance bladings and decreased aggregate loss (UMA 1987; Addo and Sanders 1995; Lund 1973).
DUST PALLIATIVE BASICS
There are a wide variety of dust suppressants available on the market today and there will continue to be more in the future. They can be divided into seven basic categories: water, water absorbing products, petroleum based products, organic nonpetroleum based products, electrochemical products, polymer products, and clay additive products. The categories are listed in order based on an estimate of past usage/ popularity.
Typical suppressants in each category are:
- Water Absorbing Products (deliquescent/ hydroscopic)
- calcium chloride brine and flakes
- magnesium chloride brine
- sodium chloride (salt)
- Organic Petroleum Products
- asphalt emulsions
- cutback asphalt (liquid asphalt)
- dust oils
- modified asphalt emulsions
- Organic Nonpetroleum Products
- animal fats
- molasses/sugar beet
- tall oil emulsions
- vegetable oils
- Electrochemical Products
- ionic products
- sulfonated oils
- Synthetic Polymer Products
- polyvinyl acetate
- vinyl acrylic
- Clay Additives
Table 1 gives an overview of these seven categories, listing their attributes, limitations, typical application rates, and common names based on Foley et al. (1996), UMA Engineering (1987), TTAO (1986), Bolander (1997), and Scholen (1992). Table 2 lists manufacturers and some distributors of the various dust palliatives.
SUPPRESSANT SELECTION TIPS
To determine the most cost-effective dust palliative, it is recommended that the flow diagram by UMA Engineering (1987) and Washington State Department of Ecology (1996) in figure 1 be followed. Important benefiting factors (Langdon 1980) of dust palliatives that should be considered when evaluating and selecting the proper dust palliative include:
- Cohering the dust particles to themselves or to larger particles
- Resisting wear by traffic
- Remaining on the road
- Resisting aging
Based on the above characteristics, the product selection chart shown in table 3 should aid in selecting the most suitable dust palliative (Foley et al. 1996; UMA 1987; Bolander 1997; Bolander 1999; Scholen 1992; Langdon et al. 1980; Han 1992). When using the information in table 3, first perform a soils analysis to classify the surface material. Some palliatives require a clay component (plasticity index) or specific amount of fines to properly bind and/or agglomorate. Table 1 provides additional information about dust suppressant limitations, application methods, and environmental impact, which helps further in selecting the best dust palliative. The flow diagram in figure 1 leads the practitioner to figure 2, which is a guide for determining the overall cost of the dust abatement program including the yearly and possibly the multi-year cost of a dust abatement application. Figure 3 is a guide for summarizing the expected benefits of the selected dust control plan.
If a petroleum dust palliative is being considered, further suppressant selection information can be found in Langdon (1980) and Langdon, Hicks, and Williamson (1980).
Table 1—Road dust suppressants.
Table 2—Suppressant manufacturers.
Figure 1—Guidelines for cost-effective selection and use of dust palliatives.
Table 3—Product selection chart.
Figure 2—Cost record for dust control programs.
Figure 3—Benefits of dust control programs.
SUPPRESSANT APPLICATION TIPS
Once a suitable product is selected, the next step is to determine the appropriate application rate and frequency. Table 1 lists broad ranges of application rates for various products and can be used as a guideline. Manufacturer’s literature, past experience, and field or laboratory test plots over a square meter (1 square yard) can also be used to help determine the appropriate application rate.
Generally, higher application rates or increased frequency is required when the following conditions are present:
- High traffic volumes with high speeds and a larger percentage of truck traffic
- Low humidity conditions, especially when using calcium chloride
- Low fines content in road surface, typically when there is less than 10 percent passing through the 75 µm (No. 200) sieve
- Poorly bladed surface and/or loose wearing surface.
General Application Tips
The performance of any dust suppressant is related to many application factors. Application method, rate, frequency, and product concentration are a few of these factors. A stable, tight surface that readily sheds surface water is another. If properly applied and constructed, a longer life and higher level of service can be expected from the dust abatement efforts (Foley et al. 1996; UMA 1987; Washington Dept. of Ecology 1996; Giummarra, Foley, and Cropley 1997). Since dust suppression and road maintenance efforts are usually combined, it is prudent to include the following practices in the maintenance and rehabilitation of road surfaces prior to applying a dust palliative:
- Repair unstable surfacing and/or subgrade areas
- Adequately drain (crown and crossfall) the road surface
- Remove boney (poorly graded) surface material
- Grade sufficient depth of roadway to remove ruts, potholes, and erosion gullies
- Compact the roadway (depending on treatment and sequence of operations)
Maximum benefits can also be achieved by adequate penetration of the liquid dust suppressant. This penetration should be on the order of 10 to 20 millimeters (3/8 to 3/4 inches). Proper penetration mitigates loss of the palliative resulting from surface wear. Adequate penetration also resists leaching, imparts cohesion, and resists aging (Langdon 1980).
Application tips that apply to all liquid dust suppressant products include:
- Apply suppressants, especially salts, immediately following the wet season.
- If possible, apply after rain so materials are moister (aids mixing) and more workable. If applied just before a rain, the material may wash away.
- Adhere to manufacturers’ recommendations on minimum application rate, compaction and curing time prior to allowing traffic.
- If the surface material is dry, dampen, except when using cut-back asphalt products.
- If a hard crust is present, break up and loosen the surface.
- Use a pressure distributor to uniformly distribute the dust suppressant.
- Ensure that the necessary “residual” of the product is obtained. The residual is the amount of product that remains after the evaporation of water from the concentrate, as well as that used to dilute the product prior to application. The residual (sometimes called solids or binder) is the portion of the product that is responsible for the binding and/or agglomeration of the particles.
Water Application Tips
Regular, light watering is more effective than less frequent, heavy watering.
Chloride Application Tips
Light compaction is recommended after a chloride brine application.
Petroleum Application Tips
Soil type and density greatly affect the rate and amount of penetration. In all instances, it is desirable to attain a 12 to 25 millimeter (1/2 to 1 inch) penetration. Most products (with the exception of SS- and CSS-1) will penetrate and coat most soils if they have been loosened by scarification. For surfaces which have not been scarified, only those products with low viscosities will penetrate.
Organic Nonpetroleum Application Tips
Remove loose material prior to application unless the road surface will be mixed and/or compacted after the spray application. When applying vegetable oils, the top 25 to 50 millimeter (1 to 2 inches) of the surface should be loose to improve penetration.
Electrochemical Application Tips
Typically these products are mixed into the road surface.
Polymer Application Tips
Light compaction is recommended after a polymer application, unless the polymer is mixed into the road surface.
Clay Additive Application Tips
Ensure that the clay and the associated water used for compaction is uniformly distributed throughout the surface material. This method requires a minimum of 8 passes with a motor-grader or use of a cross-shaft rotary mixer.
All dust suppressants have a limited lifespan and require regular applications to satisfactorily control dust on a long-term basis. Subsequent applications should be made if and when dust levels exceed acceptable levels. These subsequent applications may be lighter than the initial application.
Any suppressant ingredient may migrate due to carelessness in application, run-off, leaching, dust particle migration, or adhesion to vehicles. Carefully review the product literature, Material Safety Data Sheet, and manufacturer’s instructions before purchase and use. Observe all safety precautions and follow manufacturer’s directions when handling, mixing, and applying dust suppressants. Application of all dust suppressants must comply with federal, state, and local laws and regulations. These vary by locality and need to be checked prior to implementing the dust abatement program.
The primary environmental concern with dust palliatives is how they impact the groundwater quality, freshwater aquatic environment, and plant community. Take all necessary precautions to keep dust palliative material out of water drainages and roadway ditches leading to streams.
The impact of dust palliatives on groundwater quality is based on how the suppressant migrates to the local groundwater table in conjunction with the chemicals used in the suppressant. Chemical analysis of the suppressant will assist in determining if harmful constituents are present. Knowing the depth to groundwater and the permeability of the native soil will assist in determining how and if the chemicals will leach to the groundwater table. A direct way to evaluate the contamination of harmful constituents to the groundwater is to conduct water quality sampling of the surrounding area before and after dust palliative application.
The impact of dust palliatives on the freshwater aquatic environment is measured by both the toxicity to fish and the availability of oxygen. Each state sets its own standards and they may vary by watershed and the type and age of the fish population. The test to determine toxicity is the LC50 test and the test to determine available oxygen is the BOD (Biochemical Oxygen Demand) test. The LC50 test measures the lethal concentration (LC) of product, expressed in parts per million (ppm), that will produce a 50 percent mortality rate in the test group in 96 hours. The larger the concentration, the less toxic the material. Typically, less than 100 ppm is considered toxic, 1,000 ppm is considered practically nontoxic, and greater than 10,000 ppm is considered nontoxic. The BOD test measures the oxygen used by microbes as it digests (feeds on) the product in water. Typically, the products that are derived from organic nonpetroleum suppressants are the most likely to have high BOD results.
There are no standard tests for measuring how dust palliatives impact the plant community; however, some tests have been performed that simply observe the impact on plant life.
Addo and Sanders (1995) summarize a number of environmental impact studies on the use of various chlorides on water quality, plants, and animals. Heffner (1997) updates the work by Schwendeman (1981) concerning the environmental impacts of some of the most common dust palliatives used by the Forest Service. Based on their efforts, the following is recommended when using these palliatives once or twice a year at their typical application rates:
Lignosulfonate - Determine prior to application if significant migration (water drainage) might occur from the treated area into local streams, ponds, and lakes. Ensure that migration will not impact the oxygen needs of the aquatic community.
Calcium and Magnesium Chlorides - Restrict the use of chlorides within 8 meters (25 feet) of a body of water. In areas of shallow groundwater, determine if significant migration of the chloride would reach the groundwater table. Restrict the use of chlorides if low salt tolerant vegetation is within 8 meters (25 feet) of the treated area. Typical low-tolerant vegetation includes various varieties of alder, hemlock, larch, maple, ornamentals, and pine.
Evaluations of other dust palliatives have not been made. If there is concern regarding the impact of a dust palliative on the environment, then, as a minimum, the LC50 and BOD tests should be performed. Results can be used to estimate the potential impact of the dust palliative in question on the local aquatic and plant communities.
PAST FIELD OR LABORATORY STUDY REFERENCES
Gifford Pinchot National Forest Study (1988)
“Dust Abatement Review and Recommendation,” by Marjorie Apodaca and Don Huffmon (internal report).
Lolo National Forest Study (1992)
“Dust Abatement Product Comparisons in the Northern Region,” by Steve Monlux, Engineering Field Notes, Volume 26, May–June, 1993.
Fremont National Forest Study (1991)
“Asphotac, A Demonstration of a Dust Palliative,” by Joe Acosta, Jim Bassel, and John Crumrine (internal report).
Larimer County, Colorado Study (1995)
“Effectiveness and Environmental Impact of Road Dust Suppressants,” by Jonathan Addo and Thomas Sanders, Department of Civil Engineering, Colorado State University, Report No. 95-28A, March 1995.
Forest Service Region Six Laboratory Study (1999)
“Laboratory Testing of Nontraditional Additives for Dust Abatement and Stabilization of Roads and Trails,” by Peter Bolander, Transportation Research Board, Proceedings of the 7th International Conference on Low Volume Roads, TRR No. 1652, Volume 2, May 1999.
US Army Corps of Engineers Waterways Experiment Station (WES-1993)
“Evaluation of Methods for Controlling Dust,” by Richard Grau, Technical Report No. GL-93-25, September 1993.
US Army Corps of Engineers Construction Engineering Research Laboratory (1997) “Effectiveness of Dust Control Agents Applied to Tank Trails and Helicopter Landing Zones,” by Dick Gebhart and Thomas Hale, Technical Report 97/69, April 1997.
ONGOING FIELD OR LABORATORY STUDIES
Council for Scientific and Industrial Research (CSIR), South Africa
“Holistic Approach to Research into Dust and Dust Control on Unsealed Roads,” by David Jones, Transportation Research Board, Proceedings of the 7th International Conference on Low Volume Roads, TRR No. 1652, Volume 2, May 1999.
Environmental Technology Evaluation Center (EvTEC), Highway Innovative Technology Evaluation Center, Civil Engineering Research Foundation, Washington, D.C.
“Dust Control/Road Stabilization Agents” (ongoing study).
Addo, J., and T. Sanders. 1995. Effectiveness and Environmental Impact of Road Dust Suppressants,
Mountain-Plains Consortium, Colorado State University, MPC Report No. 92-28A.
Bolander, P. 1999. “Laboratory Testing of Nontraditional Additives for Dust Abatement and Stabilization of Roads and Trails,” Transportation Research Board, Proceedings from the Seventh International Conference on Low-Volume Roads, Transportation Research Record No. 1652, Volume 2, Washington D.C.
Bolander, P. 1997. “Chemical Additives for Dust Control-–What We Have Used and What We Have Learned.” In Variable tire pressure, flowable fill, dust control, and base and slope stabilization, Transportation Research Board, Transportation Research Record No. 1589, Washington D.C.
Foley G., S. Cropley, and G. Giummarra. 1996. Road Dust Control Techniques—Evaluation of Chemical Dust Suppressants’ Performance, ARRB Transport Research Ltd., Special Report 54, Victoria, Australia.
Giummarra, G., G. Foley, and S. Cropley. 1997. “Dust Control—Australian Experiences with Various Chemical Additives,” In Variable tire pressure, flowable fill, dust control, and base and slope stabilization, Transportation Research Board, Transportation Research Record No. 1589, Washington D.C.
Han, C. 1992. Dust Control on Unpaved Roads, Minnesota Local Roads Research Board (LRRB), Report No. MN/RC-92/07.
Heffner, K. 1997. Water Quality Effects of Three Dust-Abatement Compounds, USDA Forest Service Engineering Field Notes, Volume 29.
Langdon, B. 1992. An Evaluation of Dust Abatement Materials Used in Region 6, Transportation Research Institute, Civil Engineering Department, Oregon State University, Research Report 80-3.
Langdon, B., G. Hicks, and R. Williamson. 1980. A Guide for Selecting and Using Dust Palliatives, Transportation Research Institute, Civil Engineering Department, Oregon State University, Research Report 80-13.
Lund, J. 1973. Surfacing Loss Study, unpublished, USDA Forest Service, Portland, Oregon.
Scholen, D.E. 1992. Non-Standard Stabilizers, Federal Highway Administration, FHWA-FLP-92-011, Washington D.C.
Schwendeman, T. 1981. Dust Control Study—Part 2—Dust Palliative Evaluation, USDA Forest Service, Gallatin National Forest.
Transportation Technical Assistance Office of the University of Missouri-Rolla. 1986. Operating Tips - Road Dust Suppressants, Northwest Technology Transfer Center, Olympia, Washington.
UMA Engineering Ltd. 1987. Guidelines for Cost Effective Use and Application of Dust Palliatives, Roads and Transportation Association of Canada, Ottawa, Canada.
Washington Department of Ecology. 1996. Techniques for Dust Prevention and Suppression, Washington Department of Ecology Fact Sheet, Publication No. 96-433.
About the Authors…
Pete graduated from Michigan State University with a degree in civil engineering. He has a master’s degree in soil mechanics and foundation engineering from Oregon State University. Pete began his career with the Forest Service as a geotechnical engineer on the Willamette NF. After 10 years on the Willamette, Pete moved to the Pacific Northwest Regional Office (Region 6) in Portland, OR as the Regional Pavement Engineer.
Alan graduated from the University of Hawaii with a Bachelor of Science in Civil Engineering and is a licensed Professional Engineer in the State of Oregon. He served as a Zone Engineer in Region 2 and on the construction team for the Coldwater Visitor Center and the Johnston Ridge Observatory within the Mount St. Helens National Volcanic Monument in Region 6. Alan joined the Center in December 1996 and serves as a project leader supporting the Engineering Program.
Bolander, Peter, ed. 1999. Dust palliative selection and application guide. Project Report. 9977- 1207-SDTDC. San Dimas, CA: U.S. Department of Agriculture, Forest Service, San Dimas Technology and Development Center. 20 p.
This publication helps practitioners understand and correctly choose and apply the dust palliative that is appropriate for their particular site, traffic conditions, and climate. Describes the expected performance, limitations, and potential environmental impacts of various palliatives. It is recommended that this guide be used as a starting point for determining which palliative would be most appropriate for a given situation.
Keywords: dust abatement, palliatives, suppressants
Additional single copies of this document may be ordered from:
USDA Forest Service
San Dimas Technology and Development Center
ATTN: Richard Martinez
444 E. Bonita Avenue
San Dimas, CA 91773
Phone: (909) 599-1267 x201
Fax: (909) 592-2309
FSNotes: Richard Martinez/WO/USDAFS
For additional technical information, contact Peter Bolander at the following address:
USDA Forest Service
Pacific Northwest Region
333 SW 1st Avenue
P.O. Box 3623
Portland, OR 97204
Phone: (503) 808-2500
Fax: (503) 808-2511