The City uses three types of chemical deicers for its snow and ice response: rock salt (sodium chloride), liquid calcium chloride (a 32-percent solution of calcium chloride), and salt brine. All deicers work by lowering the freezing point of water. Factors affecting the deicing capability of chemicals include the concentration of the chemical relative to water, temperatures (especially pavement temperatures), time, weather, road type, topography (specifically when material or man-made objects shade the road surface), and traffic patterns.
Rock salt is an effective deicing chemical until temperatures drop to about 20 degrees. Rates for salt application vary. At a temperature range of 25 to 30 degrees, application rates of 100 to 200 pounds per lane mile can provide adequate control. At temperatures of 20 degrees, a rate of 300-400 pounds of salt might be required for adequate control.
Liquid calcium will melt snow and ice at lower temperatures than rock salt. Typically, liquid calcium is mixed with rock salt at a ratio of 6 to 12 gallons of liquid to 1 ton of salt, although rates up to 15 gallons can be used. Used in combination with salt, the mixture gives a quicker response than salt alone, will work at temperatures as low as five degrees, and reduce “bounce.” Wetting the salt material with liquid calcium chloride reduces salt “bounce” and keeps more of the salt on the drive area of the pavement.
Salt brine, a 23-percent solution of salt water, will also provide benefits as a pre-wetting agent. This liquid solution is used at higher temperatures than liquid calcium. Salt brine will be used when temperatures are expected to be above 25 degrees during the event. Salt brine can be mixed at rates of 6 to 12 gallons per ton of salt.
Anti-icing is a treatment strategy that aims to prevent ice from bonding to pavement surfaces. It involves applying ice control chemicals before, or at the onset, of a snow and ice event. Liquid materials can be applied at rates of 25 to 50 gallons per lane mile up to 72 hours in advance of a storm. The liquid material dries, leaving behind an anti-icing coating that will prevent moisture from bonding to the pavement.
Depending on expected precipitation and temperatures, either brine or liquid calcium is used.