Brine has been used in many European countries for many years as both a prewetting agent for dry materials and as an anti-icing agent for the proactive treatment of snow and ice. For prewetting there are two methods commonly used to wet the dry chemical freeze-point depressant before it is placed on the roadway.
- Brine can be sprayed over the load while in the vehicle just prior to use. This requires an overhead sprayer device capable of delivering a strong stream of liquid uniformly over the load.
- Brine can be sprayed onto the dry materials just as it leaves the truck or just prior to contact with the pavement by direct application at the spinner or auger.
For anti-icing, the key is to place the brine on the roadway surface prior to a precipitation event. This action helps prevent the snow and ice from bonding to the pavement. The city of Oskaloosa was an early advocate of anti-icing as a way to keep snow and ice from bonding to the road surface. The city has also used it with great success on city sidewalks. The following article, written in 1995, explains how the city began using brine in their operations. Click on the link below to view the article.
Now, over seven years after this article was written, the use of salt brine for prewetting and anti-icing is no longer experimental or unusual. In the winter 2002-2003, the Iowa Department of Transportation (DOT) used more than seven million gallons of brine. All of the Iowa DOT's snowplow trucks are equipped with units that prewet dry materials at the spinner. Anti-icing equipment is available to anti-ice the entire commercial and industrial network (more than 9,000 lane-miles) when conditions make it an effective strategy. Many cities and counties, including many of the major metro areas are now active users of salt brine.
Traditional practices depended on rock salt or mixtures of rock salt and abrasives to remove snow and ice from the roadways. The materials were delivered from the bed of the truck to a spinner where it could be widely dispersed onto the pavement. The idea was to concentrate much of the chemical over the middle of the roadway when the chemicals began the melting process the melting liquid would move away from the crown of the roadway to the lower levels of the roadway and help break the snow and ice bond with the pavement. A study conducted by the Michigan DOT measured the amount of chemicals left on the roadway after a typical spinner application of materials and found that nearly 30 percent of the materials left the roadway after application and landed on shoulders or in ditches due to bouncing. With a typical Iowa DOT application of 300 pounds per lane-mile of a 50/50 mix of salt and abrasives, that would mean that once the truck passes only 210 pounds of the mix remains on the roadway.
Further studies conducted in Switzerland and Germany also measured the amount of dry chemicals that remained on the roadway after vehicle movement and found that after five vehicles had passed, only 30 percent of the dry materials remained on the roadway. After 100 vehicles had passed, only 20 percent of the dry chemicals remained to do the job. When the materials were prewet and after five vehicles had passed, 93 percent of the materials remained on the road; and after 100 vehicles, 80 percent remained on the roadway surface. If a dry 50/50 mix is being used to remove snow and ice, it is obvious that a roadway with large volumes of traffic will quickly lose most of the materials onto the shoulder or ditch where it is of little help to melt snow and ice.