DUST CONTROL COVERS MANY FACETS
What is the most important factor in dust control - engineering, maintenance, or dust control products? And, which dust control product should you use for your specific project? Those questions have been asked by most mines. They were also asked by the US Army, which also has a big interest in dust control. Excessive dust can inhibit helicopter operations, weapons targeting, mechanized movements, and combat operations. It also increases vehicle maintenance costs.
Consequently, dust control has been a major concern for the Army Corps of Engineers since World War Two. One of the most important findings was that equipment, dust control products, and manpower costs could be reduced by 30% with smart use. The most important factor is not dust control products, but road design and maintenance. Dust control products are a secondary consideration. They should only be used when road maintenance methods have failed.
The most important factor is construction and maintenance of the roads. Properly crowned roads, well graded materials composed of sufficient fines for strength and durability, and adequate drainage are better for reducing airborne dust. The choice of materials depends on potential frost conditions. The final road material must resist abrasion (which causes dust), have a high density, and few voids. If there are voids where water can collect, frost will cause the water to freeze, thus causing an expansion of the void and damage to the road. This can be avoided by layering the road material and making sure that there is good drainage. However, the drainage must not allow the fines to drain away too fast.
Good maintenance is also critical as the rain eventually washes away fines and road traffic displaces road materials. Contrary to common sense, road maintenance is the most critical for the first few years of the road. If properly maintained over time, the requirement for maintenance will actually decline. Most maintenance will be grading to reduce potholes and ruts. Occasionally aggregate will need to be added and the road re-compacted.
The next most important factor in dust control is mechanical stabilization. That means mixing materials with the local dirt to make a dirt road surface that can handle the traffic and loads. Only after looking at the road construction, maintenance, and stabilization issues, should dust control products be looked at. Since dust control agents have a limited lifespan, have to be regularly re-applied, and can become expensive over time, the Army suggests looking at other solutions like blacktopping that might be cheaper over the long run.
The Army looked at the following dust control products and made these recommendations:
Water attracting chemicals (salts, and chlorides). These provide the best combination of cost, durability, ease of application, and dust control in semi-arid, semi-humid, and humid climates. They will not provide adequate dust control in the second season and reduced amounts will probably have to be re-applied.
These agents are corrosive and the cost of water and washing equipment should be considered. Organic, non-bituminous chemicals (Lignosulfonates, pine tar, vegetable oil, molasses). These are best in arid and semi-arid climates, but not on igneous rock, crushed gravel, or low fine materials. These products tend to stop working after rains because they leach out of the soil and may be visibly unappealing or sticky. They also need reapplication in the second season.
Petroleum based binders. These are the most effective, but have environmental issues. Asphalt emulsions are very good under a wide range of climates and soils, but are more expensive. Like organic binders, they can be sticky and unappealing.
Electrochemical stabilizers. These products neutralize soils that attract water and allow bonds to form between particles. Electrochemical stabilizers need to be worked into the road surface and require specific heavy equipment. They work over a wide range of soils and climates and are especially effective on clay and sandy road materials.
Polymers (polyvinyl acrylics and acetates). They bind to the soil and create a semi rigid road surface. They are most effective over lightly trafficked surfaces or helicopter pads. Microbiological binders. Some enzymes are absorbed by clay particles, which help their compaction and reduce dust. These are highly specific products and may not help in many conditions.
However, don't forget other methods for dust control: Windbreaks. Windbreaks are barriers designed to slow the speed and redirect the flow of wind. Effective windbreaks do not stop the wind but break its forward movement, to slow it down. Windbreak materials may include picket and board fences (with gaps between pickets), berms, snow fences, and rows or hedges of plants. Windbreaks are most useful when designed for specific wind directions.
The effective zone of protection created by a windbreak is approximately 25 times its height, although maximum-protection wind reduction occurs in a range of 5 to 8 times the height of the screen. Therefore, a 10-foot windbreak provides maximum protection to 75 feet and some reduction of wind (about 10 percent) up to 250 feet.
Reduce exposed ground. Covered ground doesn't blow away and create dust. Each dirt parking area, footpath, shortcut, or eroding bluff can produce dust. Every new trail makes the problem worse. Maintaining the native vegetation, replanting barren areas, and just driving only on designated roads or trails can all be dust control measures. Living plants not only cover the ground, but their roots hold soil together as well.
Reducing speed. Fast moving vehicles stir up dust. Studies show that dust goes up with vehicle speed. Reducing speed from 40 miles per hour (mph) to 20 mph reduces airborne dust by 65%. Drainage channels across roads and speed bumps can reduce speeds.