Slurry for more sustainable road salt use
At the 2017 Road Salt Symposium, Marty Wolske and Steve Lueken presented information on how agencies can reduce both their road salt budgets and salt’s negative effects.
Referring to a Marquette University study, Wolske, a manager at Highway Equipment Company of Cedar Rapids, Iowa, said road salt reduces crashes by 88%, injuries by 85%, and crash costs by 85%. However, citing a Minnesota Pollution Control Agency report, he said annual damage to infrastructure, vehicles, vegetation, human health, and the environment due to road salt in Minnesota is from $280 million to $1.17 billion. He said the same report showed that reducing annual road salt use by 10% in the Twin Cities metro area would reduce the combined costs of infrastructure damage and material use by between $36 million and $124 million.
Then Wolske showed that a 70–30 mixture of rock salt and salt brine can actually reduce salt use by much more than 10%: “Using a 150-pound rate example, 45 pounds of dry salt will be replaced with 45 pounds of brine. That amount of brine contains 11 pounds of dissolved salt, which means you’re using 116 total pounds of salt, thus reducing your overall salt use by 23%.”
In addition to reducing both material cost and damage to infrastructure, vehicles, vegetation, and human health, Wolske said slurry sticks to the road better, thus reducing waste due to bounce and starting the melting process sooner. He said Waukesha County, Wisconsin, has reduced its salt use by more than 23% when using the 70–30 mix.
Lueken, shop supervisor in MnDOT’s District 6 West (Owatonna), showed how his workers outfit trucks to dispense salt slurry. He said about 75% of his trucks are set up for slurry. However, unlike equipment that mixes rock salt and liquid at the spinner disk, his slurry is mixed in the sander. The trucks are equipped with saddle tanks, pumps, and flow meters. In tandem-axle trucks, his shop also has installed 800-gallon tanks in the boxes; with the saddle tanks, those trucks carry about 1,000 gallons of brine.
Lueken showed photos and videos of an auger with modified nozzles that direct the brine more precisely onto the roadway, thus avoiding overspray onto the truck. Lueken also showed how reinforced plastic tubing and spray bars are used to shoot slurry directly at centerlines and wheel tracks to melt hard-packed snow and ice.
—Richard L. Kronick, LTAP freelancer