Recommendations for Vehicle Dust Control at McMurdo Station, Antarctica
By Peter M. Seman; Rosa T. Affleck
A network of unsurfaced roads runs throughout McMurdo Station—road segments between densely spaced buildings and storage areas and to the ice shelf transition—that receive constant vehicle and pedestrian traffic. Primarily, vehicle traffic on the unsurfaced roads of Ross Island creates airborne dust, leading to several problems. Dust poses both safety and health hazards, and leads to the loss of material from the roadway itself. In addition, dust generation is influenced by the unique environment and dry climatic conditions. The purpose of this report is to 1) identify standard vehicle-generated dust control measures that are potentially applicable in cold climates, 2) discuss the unique conditions at McMurdo Station that may influence the performance of these measures, and 3) recommend the most promising measures to test and evaluate.
Table of Contents Page
List of Figures and Tables Page
This report was prepared by Peter Seman and Rosa Affleck, Force Projection and Sustainment Branch (Dr. Edel Cortez, Chief) from the Cold Regions Research and Engineering Laboratory (CRREL), U.S. Army Engineer Research and Development Center (ERDC), Hanover, NH.
Editing was provided by our technical staff, Mark Hardenberg. Technical reviews are provided by George Blaisdell, National Science Foundation, Office of Polar Programs, Antarctic Infrastructure and Logistics; and Margaret Knuth, Force Projection and Sustainment Branch, CRREL.
Funding was provided by the National Science Foundation, Office of Polar Programs, Division of Antarctic Infrastructure and Logistics, and the Office of Polar Environment, Health and Safety.
The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official U.S. Government position unless so designated by other authorized documents.
This project was prepared under the general supervision of Dr. Jennifer Mercer, Manager, Engineering for Polar Operations, Logistics and Research (EPOLAR), Dr. Edel Cortez, Chief, Force Projection and Sustainment Branch; Dr. Justin B. Berman, Division Chief; Dr. Lance D. Hansen, Deputy Director; and Dr. Robert E. Davis, Director, CRREL.
COL Kevin J. Wilson was the Commander of ERDC, and Dr. Jeffery P. Holland was the Director.
Unit Conversion Factors Table
A network of unsurfaced roads runs throughout McMurdo Station—road segments between densely spaced buildings and storage areas and to the ice shelf transition—that receive constant vehicle and pedestrian traffic. Primarily, vehicle traffic on the unsurfaced roads of Ross Island creates airborne dust, leading to several problems. Dust poses both safety and health hazards, and leads to the loss of material from the roadway itself. In addition, dust generation is influenced by the unique environment and dry climatic conditions. The main objective is to identify what techniques, materials, and methods of application are best suited for controlling dust generated by vehicles in the challenging conditions present at McMurdo Station.
2 GOAL AND OBJECTIVE
The purpose of this report is to 1) identify standard vehicle-generated dust control measures that are potentially applicable in cold climates, 2) discuss the unique conditions at McMurdo Station that may influence the performance of these measures, and 3) recommend the most promising measures to test and evaluate.
McMurdo Station sits on an outcrop of barren volcanic rock on the southern tip of Ross Island. A network of gravel roads runs throughout the station between densely spaced buildings and storage areas where there is constant vehicle and pedestrian traffic (Fig. 1). Extending outside of “town” is the heavily traveled road to Scott Base that runs approximately 2 miles from station center to the transition with the Ross Ice Shelf. This major route receives heavy traffic throughout the Austral summer season. The road that stretches 0.25 mile to the ice pier also receives intense, round-the-clock traffic in February when ships off-load cargo. Several other roads around McMurdo receive significant use, including those in the Fortress Rocks area that are subject to heavy and tracked equipment working to harvest and process rock material.
Figure 1. General overview of dense road network in and around McMurdo Station. Fortress Rocks at upper right and road to Scott Base exiting at lower right.
Factors that generate dust on unsurfaced roads include loose surface materials, strong winds, vehicle traffic, and an arid environment—all conditions that prevail at McMurdo. The amount of dust from vehicle traffic is determined primarily by traffic volume, while vehicle speed, weight, and number of axles also play roles. Additional contributors include the amount of fines present in the surface material, and the abrasion resistance of the aggregate (Addo et al. 2004). Dust is created by the rolling wheels removing fine particles from the roadbed, pulverizing surface aggregates, and ejecting the dust into the air by tire shear forces and turbulent vehicle wakes (Gebhart et al. 1999). Additionally, tracked vehicles have an even greater effect, as all of these mechanisms are amplified by the significant shear force component that grinds the gravel materials.
Current practice for dust control at McMurdo is to apply water to the roads with a tanker truck (Reed 2011). A simple, unmetered gravity feed distributes the water from a spreader bar at the back of the truck. Freshwater processed by the reverse osmosis system is used, but sea water is also available and used when freshwater is in short supply. The water tends to evaporate very quickly, which necessitates several applications over the course of a day to allow the water to soak into the road surface. Windy conditions can cause even higher evaporation rates and make the process extremely difficult. Because of its short effectiveness, the use of water is a labor intensive solution. Similar problems at a surface coal mining operation in southwest Wyoming with comparable conditions were reported by Ross (1977). Roads surfaced with scoria mineral aggregate, the same that exists at McMurdo, carried very heavy coal trucks and ash haulers. In the very low humidity environment, continuously applied water could not control the dust and 30 to 40 mph winds caused water to evaporate within minutes.
The Antarctic Treaty’s Protocol on Environmental Protection (Antarctic Treaty Secretariat 1991) provides strict guidelines on importing materials to the continent and the effects of activities on the natural resources. Any chemical dust palliative and the associated activities to apply it will need to undergo an environmental impact assessment to make sure that its effects on things like flora, fauna, and water quality are acceptable. However, palliatives have been used at McMurdo before. Previously, a small area was tested with a polymer emulsion dust palliative product during the 2006−2007 Austral summer. The reported performance was mixed. Details on its application and performance are discussed in the Rejected Alternatives section.
4 LOCAL CONDITIONS
The physical and climatic conditions combined with the practices and equipment in the McMurdo Station area must be considered to select appropriate measures for dust control.
Temperature and moisture conditions of both the air and the soil play important roles in the performance of dust control measures. During the Austral summer field season, the average maximum daily air temperature varies from about 15°F in October, climbs to 40−50°F in December and January, then falls back to approximately 20°F by the end of February.
Typical average minimums start at −30°F, climb to 15−20°F, and then drop to 5°F over the same months. Like most polar regions, the Ross Island area has an arid climate. Snowfall only yields an average annual total of 6.84 in. of water equivalent at McMurdo station (DMJM Design 2003). Relative humidity ranges from 50 to 80%, typically remaining near 70% (NRCS 2011). Although the relative humidity may be high, the absolute amount of moisture held in the cold air is considerably less than in temperate climates.
Soil temperature at 0.75 in. below the surface varies from about 5°F in October, 40−50°F in December and January, and then falls to approximately 15°F in March. Reflecting the arid nature of the overall climate, the gravimetric soil moisture content at 0.75 in. in the area is very low. In the summer field season, it varies from about 1% during cold periods to 3% when warm (NRCS 2011; Seybold et al. 2009; Affleck et. al 2010).
The material used for road construction at McMurdo is volcanic rock harvested from pyroclastic deposits on the local hill slopes. It is classified by size via screening through a metal grate. The fraction of loose rock that passes a 2-in. screen is locally known as “fines,” and contains a range of sizes from 2 in. to dust. Among other uses, fines are used for road, foot- path, and pad surfaces (Raytheon Polar Services 2005).
Two different types of fines are harvested for use: red felsitic scoria and grey vesicular basalt. Fines produced from the two source rocks are known locally as “red fines,” and “grey fines” respectively. The red fines are extremely porous and the grey fines are less porous. The red material is far less resistant to abrasion than the grey. Minerals in both the red and grey fines produce alkaline salts in a matter of days upon chemical weathering. The effects of these salts on chemical palliative performance are not known. Greys will also produce clay from weathering; however, the process takes many, many years to make a significant amount (Raytheon Polar Services 2005). The harvesting process to gather the construction material unfortunately provides unweathered material. No clay is present then to aid in the absorption of water to help bind the aggregate and create a dense packed road surface to control dust.
The red felsitic scoria is highly friable (crushable), owing to its highly porous structure, collapsing easily under stress. The grey vesicular basalt is much less friable because of the relatively lower fraction of pores in the rock mass. Observation has shown that much of the red material is easily crushed by the passage of both tracked and wheeled vehicles (Raytheon Polar Services 2005). The grey surface aggregate and the red fines left from sanding and crushing action under traffic combine to produce a material that classifies as poorly graded sand with silt and gravel [SP-SM]. Because of these properties, for town construction and maintenance, the grey material is typically used for surface pads while the red is used heavily for sanding to provide traction (Reed 2011). There are approximately 5% fines passing the number 200 sieve (0.074 mm) and they are non-plastic (Affleck et al. 2010). The combination of a lack of plastic fines and poor gradation make it difficult to achieve the high density and cohesion in the road surface that is necessary to reduce dust generation.
5 GENERAL APPROACH TO DUST CONTROL
Three major types of dust control methods exist: 1) careful construction and maintenance practices, 2) mechanical stabilization, and 3) chemical palliatives. Gebhart et al. (1999) suggest that these should be considered in this order to address the problem. Chemical palliatives can be used as an adjunct to the first two methods if they do not produce suitable results.
Good construction and maintenance practices important for controlling dust include proper road crowning, well graded materials with sufficient fines, and adequate drainage (Gebhart et al. 1999). Roads are generally well maintained in the McMurdo area, given the very challenging climatic conditions, mix of traffic types, and traffic intensity. The very porous nature of the aggregate provides excellent drainage, though some drainage issues do exist in locations because of ditch and culvert placement and maintenance. But owing to the limitations of aggregate availability, there is no opportunity to address the issue of the lack of fines (in the true sense of the word, as used in the construction industry, meaning silt or clay particle sizes).
The second approach is to use mechanical stabilization by mixing different materials to obtain a good combination of desirable properties for the road surface. “A substrate that will considerably reduce dust generation is composed of well-graded gravel−sand mixtures with sufficient amounts of clayey [cohesive] fines to promote surface bonding and wear resistance” (Gebhart et al. 1999). Mechanical stabilization can produce a surface that can reduce dust over many years with proper maintenance. Again, owing to the limitations of the aggregate and mineral types available, as well as Antarctic Treaty requirements, this approach is not possible at McMurdo.
McMurdo must then rely on the final, and least desirable, method of using chemical palliatives as the sole means for controlling dust. Chemical palliatives typically have a limited period of effectiveness, so regular reapplications are necessary, which imposes ongoing labor and material costs beyond standard maintenance practices. Tracked vehicle traffic may reduce chemical dust control product performance by as much as 50 to 75% (Gebhart et al. 1999). In addition, constraints at the Station lead to some general observations about materials and applications that will affect selection. A careful consideration of all these factors is important in making the best selection.
Many methods using chemical palliatives require mixing with the aggregate to work effectively. Constant traffic makes closure of roads at McMurdo impractical for any significant length of time. Regular resurfacing of the roads, which might present an opportunity to incorporate dust palliative application, is not done (Reed 2011). Topical application of palliatives will be important for practical use at the Station.
There are some advantages to the coarse nature of the road surface aggregates present. Coarse grained soils generally require lower application rates because the particles have less surface area to bind together. They are also more permeable, so topical applications can penetrate the surface deeper and there is less ponding and runoff of the liquid palliatives (Rushing and Tingle 2006). On roads with high load bearing capacity, there are some reports that a topical application of palliative can provide good control (Rushing et al. 2005).
6 REJECTED ALTERNATIVES
Many different classes of chemical palliatives exist, each with their own mechanisms to help control dust on unsurfaced roadways. Some act as binders to capture fine particles, while others draw moisture from the air to keep the roadway from drying out and becoming dusty. Some common dust palliatives are poorly suited for McMurdo Station because of physical and climate conditions, operational considerations, equipment and logistics constraints, or environmental sensitivity. These include the following, with their drawbacks noted that make them impractical or unlikely to be effective.
Traditional asphalt products are effective for dust control but are no longer used because of significant environmental issues. They contain diesel fuel, used motor oil, and kerosene that threaten water quality and wildlife. Asphalt emulsions are one of the few remaining asphalt products in use. They are not widely used because they require specialized equipment for application and must be delivered in a heated tanker to the worksite (Skorseth and Selim 2000).
Polyacrylamides are water-soluble polymers that control dust by absorbing moisture from the air to keep the soil moist (Rushing and Tingle 2006). These would not be effective in the extremely arid Antarctic environment. Also, polyacrylamides undergo large volume expansions when wet and so are not recommended for use on roads. They must also be mixed into soil, causing significant operational disruption.
6.3 Natural clays
High plasticity natural clays can be mixed into the surface aggregate in the right proportions to help bind the surface together tightly to control dust. It has a relatively high initial cost, but creates the equivalent of a low grade pavement for a more permanent solution (Bennett 1994). Importing large volumes of natural clays to McMurdo to amend the soil would not be practical for logistical and cost reasons. The need to mix the clay with the existing road surface would be very disruptive to traffic during placement. Most importantly, importation would not be permissible under Antarctic Treaty rules on foreign natural materials.
6.4 Chloride salts
Salt is the simplest and most common method used for controlling road dust. Like polyacrylamides, chloride salts are hygroscopic and work by drawing moisture from the air to keep the road surface damp; they are not binders. The outflow of the reverse osmosis plant could provide a potential source of liquid brine; however sodium chloride is the prevalent salt in seawater and not very effective (compared to calcium or magnesium chloride). Chlorides have other drawbacks including corrosive effects, being susceptible to leaching away, possible harm to water quality, and potential surface crystallization leading to more dust. They work best with well-graded gravel containing adequate cohesive fines (Skorseth and Selim 2000). For these reasons, the deliberate use of seawater is also discouraged and the current practice of using excess potable water when it is available should be maintained for the time being.
6.5 Lignin derivatives (lignosulfonates, tall oils)
Another very common method is using byproducts of the pulp making process that are derived from the lignins that bind the cellulose together in wood (Bennett 1994). Similarly, they provide cohesion to bind soil grains together but a sufficient amount of clayey fines in the road material is necessary for successful use (Bennett 1994; Addo et al. 2004). Mineralogy can also affect success. Based on their own research, an Australian lignosulfonate producer stated “Investigation of the suitability of pavement materials for this type of binder [tall oil pitch] allows identification of its limitations, such as the geological formation. A typical example of this limitation is Scoria. The high porosity and moisture retention properties of Scoria have not permitted [the] Soilbond [product] to bind this material effectively (Fat 2005).” However they do have some positive aspects, like topical application, possible use without allowing a set time, and stability of emulsions to freezing (Bennett 1994).
6.6 Biocatylitic proteins
Biocatylitic proteins produce an organic reaction to bind soil grains, increasing soil density and strength. With higher density, the particles agglomerate; this increases interparticle forces and leads to higher internal cohesion of the soil (Bennett 1994). Placement of the palliative requires spraying with water, mixing, compaction, and close control of soil moisture content. It is reworkable and considered acceptable for environmentally sensitive areas (Bennett 1994). Results have been mixed, with Bennett (1994) reporting excellent performance after 1 year; however, others (Gilles et al. 1999) found it marginally effective and short lived. Minimum recommended daytime temperature during application is 50°F, but when necessary it can be applied colder (Bennett 1994). Because organic reactions proceed very slowly at low temperatures, this product would not be suited to the climate at McMurdo. Soil mixing and compaction would pose unacceptable operational disruptions. Further disadvantages also include being a water-based material and the reported mixed performance results.
Polysaccharides are suspensions of sugars and starches in water that are designed to encapsulate and bind soil grains into a network (Rushing and Tingle 2006). Surfactants are added to the solutions to aid in dispersion and penetration into the soil surface (Rushing et al. 2005). Polysaccharides are biodegradable and can be reworked after application (Rushing et al. 2007). They are generally shipped in a concentrated form and diluted for use, but they may settle from solution during storage. Drawbacks include limited period of effectiveness, lower strength bonding than polymer emulsions, and susceptibility to leaching from the soil (Rushing and Tingle 2006). Being water soluble, they are susceptible to freezing during transport or storage and will leach from the soil. Also, the limited effective lifespan and lower binding strength would provide even less benefit than other water-based products with similar freezing issues. However, some promising lab test results were seen on a soil with the same USCS classification [SP-SM] as McMurdo (Rushing et al. 2007). At higher application rates, polysaccharides performed well in a simulation of a trafficked helipad subjected to high velocity air bursts. But, the authors acknowledged that “the air impingement test does not simulate the effect of wheeled vehicles on dust-treated soils.”
6.8 Powdered polymer
Powdered polymers are water soluble and undergo a chemical reaction while curing. They create a water resistant film that binds the soil grains together. They have poor penetration into the road surface when applied topically and exhibit lower strengths than polymer emulsions—discussed below (Rushing and Tingle 2006). Slow curing reactions at low temperature and poor topical performance are both very undesirable. One advantage is that they have an unlimited shelf life (Rushing and Tingle 2006).
6.9 Polymer emulsions
Polymer emulsions are the most popular and widely marketed of the chemical palliatives specifically formulated for dust control. They are generally vinyl acetate or acrylic based copolymers and surfactants in a water emulsion. The water evaporates after application and the polymer binds with the soil grains to form a matrix that incorporates fine dust particles (Rushing et al. 2007). Polymer emulsions have been used in a wide range of environments over many years. Two references to their performance on silty sand soils provide promising results. Application to a low volume road in California provided excellent performance over 6000 passes and 12 months (Watson 1996). Testing on helipads in California on an non-plastic SP-SM soil concluded they would perform well but high doses were required, mostly to avoid the generation of foreign object debris (FOD) (Rushing et al. 2006). However, polymer emulsions suffer the same draw-backs as other water emulsions: they cannot be exposed to extreme cold (frozen) or heat, are sensitive to ultraviolet light, have a limited shelf life, and can be susceptible to bacterial contamination (Rushing and Tingle 2006). These materials require curing before opening a road to traffic. Curing, slowed considerably by cold weather, occurs with evaporation, so temperatures must remain above freezing during application. Typically, this method involves soil mixing; however, some have suggested that it may be possible to use several light topical applications with some success (Rushing and Tingle 2006).
A polymer emulsion product, Envirotac II® (Environmental Products & Applications 2011), was field tested during the 2006−2007 Austral summer at McMurdo Station. The test plan (National Science Foundation 2006) included applications of varying dosages to three roadway sections and one helipad. The strongest concentration of product was a dilution of 1:4 with fresh water. The application method involved loosening the surface (not clear to what degree), spraying the product, compacting, and allowing it to cure for a period of time depending on the temperature. Distribution by gravity from a tanker truck or pumping with a fire hose was specified. It is not clear how closely the actual field test mirrored the test plan, as a limited amount of information about the test results is available. The material was reportedly hard to apply (Blaisdell 2011). The testing was not tracked or documented so the resulting performance is unclear.
The manufacturer of another leading brand of polymer emulsions indicated that this type of product would not be a good candidate in such an environment and suggested synthetic fluids (discussed later) as a better alternative.
6.10 Soybean oil
Acidulated soybean oil soapstock is a byproduct of the soybean oil refining process. It has the characteristics of light petroleum oil, is non-toxic and biodegradable, and will penetrate a gravel surface to provide a light bonding of the aggregate. However, it must be applied warm (greater than 75°F) and requires heated storage in cold weather (TransSafety 1998). There are few commercial products available based on soybean oil and little information in the literature discussing its use or effectiveness.
Glycerol is a water soluble fluid that provides dust control by encapsulating soil particles and inducing high surface tension at the granular level (Rushing et al. 2007). It is a byproduct of biofuel production and is colorless, odorless, and viscous with a minimum freezing point temperature of about −36°F (Wikipedia 2011). It is approved by the FDA for use in pharmaceuticals, human and animal food, and is used as a sugar substitute. It has some promise for being environmentally safe. In fact, it is a component in some emulsified hydrocarbon resin palliatives, discussed in the Recommend Methods section. To be applied to soil, it must be diluted with water to reduce the viscosity for spraying (Rushing et al. 2007). Under the same trafficked helipad test conditions described in the Polysaccharides section, performance was good at high application rates (Rushing et al.
2007). There are few references in the literature to testing or full-scale use of glycerol as a dust suppressant. With its low freezing point, low toxicity, and promising performance on a soil type similar to that at McMurdo, glycerol deserves further exploration. However, it is not a good choice at this time to include as a final candidate without further experimentation. It might be useful to include a very limited test when performing trials with the recommended palliatives.
1Promising, but cannot recommend at this time.
7 RECOMMENDED METHODS
From the survey of available alternatives, there is a final pair of dust palliatives that are the best candidates for McMurdo that merit full testing: synthetic fluids and emulsified hydrocarbon resins. Table 1, comparing the two, follows the detailed discussion of each method.
7.1 Synthetic fluids1
Synthetic fluids do not contain water and are applied as received without dilution, unlike many other dust control products. They consist of isoalkanes that do not dry or cure with time, but form a reworkable binder that adheres to the dust particles in the soil (Rushing and Tingle 2006). Synthetic fluids are applied topically and penetrate deeply into the soil (Rushing et al. 2007).
Manufacturers of synthetic fluids highlight the following properties of these products (Soilworks 2011; Midwest Industries 2011). Roads can be opened to traffic immediately after treatment and benefit from the compactive effort of traffic. The material is suitable for tracked vehicles and heavy loads. Synthetic fluids can be applied in wet and freezing conditions, down to 5°F, and stored at temperatures down to −50°F. They do not freeze and have an unlimited shelf life. They are non-tracking and will not stick to vehicles, which is important given the problems posed by carrying contaminants onto the snow roads. The material can applied with any equipment that can spray water. Equipment is cleaned with soap and water, or even just water in some cases. They are non-corrosive, non-toxic, biodegradable, environmentally sound, and do not leach away with moisture.
The nature of a synthetic fluid forming a reworkable binder in the soil is promising for use with a weak Scoria aggregate. As the particles are crushed and new fines are formed, the existing chemical may adhere to the newly generated dust before it becomes airborne. If this is true, it would be one of the few products that could provide ongoing control without frequent reapplication.
Synthetic fluids are expensive compared to other palliatives, but maintain effectiveness over extended periods (Rushing and Tingle 2006). There are some competing mechanisms that may prove to lengthen or shorten the longevity of a treatment. The material is biodegradable but the low temperatures and limited biological activity at McMurdo could mean the product remains effective longer. On the other hand, the need to continually capture new dust from crushed aggregate, unlike typical soils, will decrease the period of effectiveness. Deep penetration of the fluid into a porous material may also have beneficial effects. A porous aggregate would likely require a high initial application, but the fluid that soaks into the grains might be at the fracture location when crushing occurs. So it is possible that absorbed fluid might not be considered wasted chemical in the process.
Retreatment requires a lower dosage than the initial application because the material has a cumulative effect. Suggested retreatment amounts range from 50% (Rushing and Tingle 2006) to 30% (Soilworks 2011) to 10% (Midwest Industries 2011) of the original application rate. Longevity of a treatment suggested by manufacturers is 9 to 16 months of continuous traffic (Soilworks 2011; Midwest Industries 2011). Because effectiveness lasts from year to year, the seasonal nature of traffic on the road surfaces at McMurdo would extend this period over several summer seasons. However, as noted previously, the crushable aggregate producing new fines that need to be bound will tend to decrease longevity. The addition of new fines to the roadway for providing traction in snow and ice will also proportionately reduce the lifespan of the material, as there will be additional fines to control once the snow and ice melts away. Loss of treated surface material to plowing may also reduce the period of effectiveness.
7.2 Emulsified hydrocarbon resins1
Despite being an emulsion, these palliatives deserve special consideration because they have other desirable properties that may make them perform well at McMurdo. They are low molecular weight hydrocarbons suspended in water that provide dust control by mechanisms similar to polymer emulsions; however, they do not form a strong bond. Once the water evaporates, the material remains soft and exhibits properties similar to a wax (Rushing et al. 2007).
The major reason this class should be looked at closely is that it was the only one found in the literature that had any success on a scoria aggregate or soil. Ross (1977) detailed use of the product at a surface coal mine operation in southwest Wyoming with conditions similar to many that exist at the Station. Two miles of roads were surfaced with 12 to 18 in. of scoria waste material from the mining operations. It carried constant, heavy traffic of 120-ton coal trucks and 85-ton ash haulers. Continuous application of water could not control dust. In extremely low humidity and 30 to 40 mph winds, the water would evaporate in minutes. They found that the palliative material successfully controlled dust and that treated roads required less winter maintenance than untreated roads. It was applied during scarifying maintenance operations carried out to control rutting, and then the road was opened immediately to traffic for compaction. The product was reapplied every 4 to 6 weeks.
For one product, a version of the emulsion, freeze-stabilized with glycol, may be available, making this much more attractive than other classes of water-based palliatives. It can be applied when the air temperature is near freezing. Despite being an emulsion, the claim is that it can be stored for long periods of time and remixed if it stratifies. Emulsified hydrocarbon resins can be applied topically by water trucks, hand sprayers, and other standard water distribution equipment. They are environmentally safe, non-toxic, non-hazardous, non-water soluble when cured, and may be biodegradable. They are cleaned up with water, though light citrus solvent may be necessary to clean remaining residues.
Like synthetic fluids, the effects of treatments are cumulative and because the material remains soft it can be reworked. Again, these properties are desirable for a scoria soil with continuous generation of new fines to control. However, reapplication on undisturbed areas of treated soil may tend to repel the penetration of new product and require scarification to take place (Rushing and Tingle 2006).
1Recommended, with reservations
Table 1. Comparison between two recommended dust palliatives for roads at McMurdo Station.
8 TRIALS AND FURTHER STUDY
The combination of the physical and chemical properties of the soil and the chemistry of the additive are main factors to successfully controlling dust (Addo et al. 2004). And the relative performance of products within the same palliative class can range from little or no difference to significant (Rushing and Tingle 2006). This makes testing specific products on actual soil from or at McMurdo Station important to gauge potential effectiveness. Application rates will likely be difficult to determine from manufacturer guidance because of the very porous nature of the soil particles. Before any field or lab trials can begin there needs to be a discussion of the environmental acceptability of each palliative group and specific products.
The advantages and disadvantages of field testing vs. laboratory testing include the following.
- Observe performance under actual field conditions.
- Gain experience with field specific issues—application, effects of shipment and storage, etc.
- If testing is successful, could develop guidance for standard use.
- Uncontrolled testing conditions—temperature, traffic, moisture conditions, curing time.
- Single or few trials—product types, application rate, curing times.
- Objective field measurement methods for dust can be challenging and probably more so for McMurdo, but ultimately the subjective result determines if the community is pleased with performance or not.
- Controlled conditions—temperature, moisture content, traffic, curing time.
- Practical to vary dosages, test the effect of reapplication.
- Replicates and controlled conditions make meaningful, objective comparisons possible.
- Can develop a sound, targeted field test plan based on lab results.
- Applying a mix of traffic types not practical.
- May need to get a significant amount of fines from McMurdo, depending on size of test setup, number of palliatives, varying application rates, replicates, etc.
- Bench scale testing and setup, especially trafficking, may not scale or transfer well to actual field conditions.
- Don’t gain field experience, for example: application processes with local equipment, effects of shipment, and cleanup.
For the laboratory, a small scale apparatus for wheeled traffic testing is envisioned. A similar device was built and used to study the behavior of roadway base course materials (Gonzalez 1992). The dust generated inside a chamber could be measured by several methods. A simple approach would be to measure the accumulation of dust that settles onto a flat adhesive plate. Collecting dust on filter paper attached to an air pump might be another simple method. Others have used optical sensors of personal dust monitors to measure dust in laboratory tests (Rushing et al. 2007).
A detailed analysis is also needed to determine the relative costs of each treatment, not just the cost of the product itself. Palliatives can vary in unit cost of material but other factors play an important role as well, such as application frequency, differences in necessary labor or equipment, etc. Accounting for differences in these factors can lead to a much better judgment of the comparative cost between products.
Trade-offs between field testing and laboratory testing are quite significant, based on this preliminary assessment, with varying degree of complexities and outcomes. Once testing is complete, guidance can be generated based on the results of the trials. These can be incorporated in the standard practices for the maintenance operations of the road system at McMurdo Station.
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APPENDIX A: PRODUCT SAFETY AND ENVIRONMENTAL DATA FOR EXAMPLE PRODUCTS IN THE RECOMMENDED PALLIATIVE GROUPS
Information provided below does not constitute endorsement of any such product by the author, U.S. army, or federal government, but instead are examples of products available
EnviroKleen® EPA Environmental Technology Verification Statement
EnviroKleen® EPA Environmental Technology Verification Report/Laboratory Analysis Report
EnviroKleen® Material Safety Data Sheet
Durasoil Certificate of Analysis/Laboratory Analysis Report
Durasoil Material Safety Data Sheet
EMULSIFIED HYDROCARBON RESINS
COHEREX® Product Data Sheet
Coherex Material Safety Data Sheet
Report Documentation Page