Dust Suppression on Unpaved Roads

Air Pollution Control Program fact sheet
Division of Environmental Quality Director: Ed Galbraith

Many Missouri industries use unpaved roads. These roads are used for transport in construction, mining and logging operations. Dust created by traffic on these roads is a common problem. Missouri air pollution control regulations prohibit dust from private roads in commercial operations from going off the property. Therefore, many businesses with private unpaved roads must use some method of dust control to comply with this regulation. While unregulated, local governments with unpaved roads to maintain may also be interested in dust control treatments to reduce the concerns of residents.

Fine particles in dust contribute to holding a road surface together. Therefore, dust suppression treatments may result in lower maintenance and helps prevent complaints about off-site air quality problems caused by operations on unpaved roads.

The most common and least expensive method of road dust control is to water the surface using a water tanker truck with a spray bar whenever dust problems occur. This method may pose some challenges:

Several chemical treatments are also available that improve on the ability of water as a dust control agent (also called a palliative). Salts have been used for many years to control dust, and they have the side benefit of stabilizing the road surface resulting in reduced loss of gravel from the road surface and lower maintenance requirements. The two most common salts are calcium chloride and magnesium chloride. Some studies show that magnesium chloride is more cost effective than calcium chloride. Calcium chloride comes in flakes or pellets and is mixed with water to be applied by a water truck. Magnesium chloride usually comes in brine form so mixing is not required. Articles used for this technical bulletin cite application rates for calcium chloride from 0.2 to 1 gallon per square yard of road surface; and for magnesium chloride from 0.25 to 0.5 gallon per square yard.

These salts have the disadvantage of being harmful to many plants and some animal life. Treatments must be carefully applied in order to avoid contaminating the environment.

Both salts work by absorbing moisture from the air, which wets the small particles in the gravel and keeps them out of the air. Heavy rains may leach the salt from the road resulting in loss of dust control when the road dries. Certain salt-treated surfaces may become slick during heavy rains. Salt is also corrosive to steel, but this is not a problem with normal application rates. During dry spells, magnesium chloride retains dust control better than calcium chloride because of a higher affinity for moisture.

Another treatment is an organic derivative of pulp and paper processing, lignosulfonate, also called lignin. The method of application is different from brines. It is mechanically incorporated into the gravel using the same equipment used for maintaining the road. The chemical binds the small gravel particles together and the result is less dust. It too can leach during heavy rain, but not as much as the salt treatments. Lignin-treated surfaces become slippery when wet and brittle when dry and potholes may form. The treatment retains its effectiveness during dry spells.

Lignin treatment may be more expensive than the brines because it has to be incorporated into the road material. The treatment life varies for all these chemicals according to traffic and precipitation.

Other dust suppressants include polymers, vegetable oil and petroleum products. Polymers bind the small gravel particles like lignin, but do not leach. Surfaces treated with polymers may be difficult to maintain, and polymers are usually more expensive than competitive treatments. In Missouri where agriculture is a major industry, soybean oil is readily available. However, the oil oxidizes quickly and the road surface becomes brittle, which can cause potholes.

There are proprietary petroleum resin products on the market that are non-toxic, not water-soluble and have the benefit of stabilizing the road for reduced maintenance cost. These products are sprayed on the road surface much like the process of chip and seal on an asphalt road. The dust control/stabilizer treatments do not contain asphalt and are not harmful to the environment, according to the manufacturers.

Cutback asphalt is another option. It is asphalt that has been mixed with diesel oil to make the asphalt spread easier. This material is commonly known as road oil. This treatment may cost more than chemicals, but it may also last longer. Another form of asphalt is emulsified with water. For information on asphalt application, contact a paving contractor. There are some restrictions on the use of cutback asphalt in the St. Louis metropolitan area.

Dust suppression treatments are not permanent. The chemicals have to be periodically reapplied, although for the salts, subsequent treatments usually require less than the initial treatment. Calcium and magnesium chloride may need to be reapplied once or twice a season, depending on the traffic and the amount of rainfall.

To select the optimum treatment, a soil analysis should be conducted to classify the road material. Some treatments are better suited to certain types of road material (i.e. clay content or amount of fines). Before undertaking a chemical dust suppression treatment, the road surface must be in proper shape, with particular attention paid to crowning the road for good drainage. In the case of lignin, this would be done when the chemical is applied.

The department’s Water Protection Program does not require a permit for application of road dust suppression chemicals if the following conditions are met:

Common sense application of these chemicals will help ensure that there are no complaints. Improper surface preparation, incorrect application and indifference to environmental concerns will cause public complaints that will result in close scrutiny of future dust suppression activity. If a stream or lake is located near the site, call the Water Protection Program to find out if applying chemicals should be avoided or if any other conditions may apply.