Introduction
Dust control on construction and demolition sites is essential to prevent particulate from becoming airborne, minimizing its impact on workers, the public and the environment—and to comply with air quality regulations. The most common approach involves employing water trucks to spray water directly onto dusty surfaces as needed during site activities. However, this poses significant challenges during the winter months when water trucks and the ground are at risk of freezing.
Alternative Solutions for Cold Weather
When water spraying is not feasible due to freezing temperatures, a solution of water and magnesium chloride hexahydrate, often referred to as Mag flake or Mag brine, is commonly employed to control dust. Most of us are familiar with magnesium chloride as a pretreatment applied to roads as part of an anti-icing strategy prior to a winter storm. It works by lowering the freezing point of water, which prevents ice from forming a strong bond with the road surface. For dust control, it is added to the water in the water trucks to prevent them from freezing as well as preventing ice on the ground.
Considerations for Solution Concentration and Application
Mag brine is commercially available in concentrations up to 33%, which amounts to over 2.5 tons of magnesium chloride in a standard 2,000-gallon water truck. While such high concentrations may be suitable for seasonal treatment of roads, this may be overly strong for frequent use in dust control on construction sites. Therefore, it is crucial to adjust the solution’s concentration according to the specific requirements, i.e., the freezing point. The main objective is to achieve a solution concentration that remains liquid at the target operating temperature.
To prepare an effective cold-weather solution in a 2,000-gallon water truck, start by characterizing the pending weather conditions to determine the required concentration. Adding 1,500 pounds of magnesium chloride hexahydrate to a 2,000-gallon water truck should result in a 9% solution which is suitable for temperatures around 25°F. For significantly colder environments, a higher concentration will be needed. As a reference:
- A 30% magnesium chloride brine solution will prevent freezing at temperatures around -18°F to -28°F (-28°C to -33°C)
- A 20% magnesium chloride brine solution will prevent freezing at temperatures around -10°F to -20°F (-23.3°C to -28.9°C)
- A 15% magnesium chloride brine solution will prevent freezing at temperatures around 13°F to 17°F (-10.6°C to -8.3°C)
Application Tips
- Safety: Magnesium chloride is highly corrosive, so always wear appropriate protective gear during handling and application and verify that all parts of the water truck—including the tank, hoses, and spray bar—are compatible with the brine solution. After application, flush the equipment with clean water to reduce the risk of corrosion.
- Proper Mixing: Ensure that the magnesium chloride flakes or pellets are thoroughly mixed into the water using the truck’s agitator or circulation system until fully dissolved.
- Application Method: The brine solution should be applied evenly using a pressurized spray bar. The ideal application rate typically ranges from 0.2 to 0.5 gallons per square yard, depending on soil type and site activities.
- Post-Application Care: Do not add additional clean water to the surface after applying the magnesium chloride solution, as the presence of moisture is essential for the dust binding action to work effectively.