As we are expecting snow this weekend, likely heavy Saturday night, there is the challenge of snow removal. Most of us know the general concept. Snowplows and roadsalt of some sort. Sometimes it’s the treatment of the roads first, then plowing. Sometimes plowing then treatment, sometimes a combination.
I just moved back to the region after being gone for awhile. Last I knew, the roads were treated with roadsalt. Sometimes sand mixed in with the salt. There are several types or combinations of materials and chemicals used to treat roads. Here is what I found out:
In parts of the state, especially the hilly areas in southwestern Wisconsin, sand is applied to the roadways and critical locations like hills, curves and intersections, but it is not always an adequate substitute for salt. Sand helps provide traction, but it does not melt snow or ice. Also it is easily blown off of roadways and can blow or flow into nearby bodies of water contributing to sedimentation and carrying other pollutants absorbed from the roadways. Excess sand can be expensive to clean up and corrosion from sand-salt mixtures can damage vehicles as abrasive particles hit and rust metal or crack windshields.
In fact, salt and abrasives do different things and can oppose each other. A common belief is that salt will anchor the sand, and/or sand will anchor the salt to the road. In reality, if they remain dry, wind and traffic will quickly move both of them off the pavement.
Salting is cost effective down to a pavement temperature of only about 15-20 degrees. It takes about 13 times more salt to melt ice when the pavement temperature is 0°F than when it is 30°F.
Cutting Back on Salt
Some agencies have gotten creative in seeking to make the salt stick even better by adding sugarcane molasses, cheese or dregs from beer-making to the brine. West Des Moines uses beet molasses. It’s sugary and sticky.
Polk County Wisconsin has sprayed its roads since 2008 with cheese brine — a liquid mixture used in the process of making cheese that it gets from a local dairy. The county found it reduced the amount of salt needed on the roads and the county’s costs, said Moe Norby, the county’s highway commissioner.
Some salt may become brine, dissolved by moisture in the sand or from melting ice on the pavement. In theory, a small amount of moisture will help embed the sand in the surface of the snow and then refreeze to create a sandpaper effect. But this rarely occurs. If there is melting, it is not likely that the abrasive will float and stay on the surface. More likely it settles, or gets pounded into the melting snow mixture. When that happens, it is no longer “anchored” to the surface and provides little value for traffic safety. Sand is most effective when it is too cold for de-icing chemicals to work and in low volume traffic where it stays on the road surface.
The most popular alternatives to common salt are other chloride salts. Calcium chloride and magnesium chloride melt snow and ice more quickly at lower temperatures, but they are way more expensive than sodium chloride.
A big effort is on and has been to identify environmentally safe options for road treatment. Urea, a fertilizer, can melt snow but adds nutrients to surface water and depletes oxygen depletion in receiving waters. Calcium magnesium acetate can also reduce available oxygen. Recent research on CMA and a few other liquid de-icers indicate they are more toxic to fish than salt brine. Several municipalities around the state are trying beet juice mixed with salt to reduce the amount of chloride being used. This organic alternative has its own downsides. It’s not cheap and it makes a mess. You ever get beet juice stains on your clothes? It’s like a red-wine stain.
For the winter of 2016-17, 63 of the 72 counties in Wisconsin used a technique called anti-icing, which can save time and money by reducing the effort and materials needed to remove snow and ice.
Anti-icing prevents the formation of frost and the bonding of snow and ice to the pavement.
Anti-icing agents, which are primarily liquids, are applied before or early in a snow storm.
Other removal techniques include pre-wetting and de-icing.
Pre-wetting is the addition of calcium chloride, magnesium chloride, salt brine or other liquid agents to salt and sand. This helps the mixture stick to the road instead of blowing off to the shoulder, which reduces the amount of material needed. It also helps the salt start working more quickly. Several studies have shown that with pre-wetting up to 30% more salt stays on the roadway. (Currently only a 3 counties do not pre-wet their salt.)
De-icing uses chemical or mechanical means to break the bond that has formed between ice and the pavement.