LIQUID, rock salt, or another solid chemical?
That is the question that vexes snow and ice control administrators in states and municipalities across the United States.
Sixty years ago, the only choice was between salt and sand. After the first spreaders were built, New Hampshire became the first state to adopt an official policy of using salt, and a total of 5,000 tons of salt was applied on US roads in the 1941-42 winter. By 1955, the total was one million, with salt usage doubling every five years until 1970. After reaching a peak of nearly 12 million tons in 1978, salt usage leveled off for about 15 years.
With options now available, decisions have to be made. Do you maintain the status quo and continue to spread salt or another solid chemical, either because you're sold on it or your budget won't allow you to retrofit your equipment? Or do you retrofit, realizing that the initial cost most likely will be recouped due to a more efficient material and method of spreading it?
It's a big business involving some critical financial decisions. The 33 snow-belt states spend 16.2% of their road maintenance budgets on snow and ice removal. In an average year, $1.5 billion is spent on snow and ice control in the US.
John Stenz, vice-president of manufacturing for Force America, says liquid usage will go “through the roof” in the next five years.
“We're not to the point where more people are using liquid than salt,” he says. “It's gaining momentum. But the reality is that there are so many trucks out there that spread salt. With every little city, county, municipality, it's going to take a lot of years and a lot of education to get to the point where liquid is more prevalent than salt.
“The challenge is educating the public that liquid is a way of saving tax dollars, a way of being more effective. A lot of municipalities just aren't ready for that challenge yet. Status quo is good. They don't want to rock the boat. But as budgets tighten up and there's backlash onto the tax dollar, we're starting to see surpluses turning into deficits, and saving money on material usage is going to become very attractive.”
Some ready, some not
Joe Chimenti, project manager of the Southeastern Pennsylvania Transportation Authority's non-revenue fleet, says it uses only salt.
“The initial outlay for storage tanks, the infrastructure, and tanks for trucks poses a problem for us,” he says. “After a storm, we usually keep a couple of trucks with tailgate spreaders, and use them for normal construction work. That's where we think it's cost effective.”
On the other hand, there's the state of Ohio, which by the end of the year will have spent between $3 million and $4 million to convert to liquid. In Wisconsin, it is estimated that at least 80% of the state's 72 counties are now using a preventive salt brine-chemical liquid anti-icer. The Nevada Department of Transportation and the Colorado DOT have modified and successfully used asphalt distributor trucks, liquid fertilizer spreaders, and spreaders used to spray for weed control. The California DOT built a customized spray bar that is capable of applying 25 gallons of solution per lane at 3 mph, and after just one year decided to build two additional liquid spreaders.
Stenz says most state DOTs are using or will be using liquid, and market trends always have shown that smaller municipalities follow the state DOTs.
Stenz believes liquids are a more attractive option whether they're used as an anti-icer (applied directly to the road surface a certain time before a storm hits) or a de-icer (applied after there is accumulation of snow or ice).
He says the key is control of the material, being able to spread it where you want it, when you want it, and how you want it.
“With salt, the big issue has been how to keep that salt on the road long enough to have it make a difference,” he says. “You drop a grain of salt, it's going to bounce. Studies have shown that 70% can end up in the ditches if it's not put on correctly.”
That's because dry solid chemicals generally rebound up to two feet from a dry pavement when dispensed from a conventional spreader spinner.
“You're applying a lot of material, but it's only really effective if it's on the road,” Stenz says. “And it's only really effective if it's on the road when it's needed on the road.
“It's been proven that liquid stays longer in the location you place it. You can more closely meter exactly what you want on the road. A lot of people over the years have determined that if a little salt's good, then a lot's better. They just pour it on, knowing that if there's not a lot of snow on the road yet, just the wind action created by cars passing by will push the salt off.”
Cleanup not an issue
He says if liquid is spread on a roadway or bridge, it will stay there, and at the end of the event, it dissipates and is not a cleanup issue.
“Studies have shown cleanup can be one-third of the cost,” he says. “If you're just sending a truck out to take care of frost on bridges in the spring and early parts of the year when the ground temperature is still up and the air temperature is down, your truck is going out to maintain a road but maybe it's going to drive 10 miles and then treat a 1/4-mile long bridge. When you put dry material on, you're still going to have cleanup issues and have to send the truck out later to sweep.
“With liquid, you can do it as the storm approaches because liquid will go down into the pores of the road into the cracks and crevices of concrete and blacktop, and it will remain there. So when the snow or frost comes, the liquid will be re-activated and will keep the bridge from icing. If you put salt on, you pretty much have to put it on shortly before or right after the ice shows up.”
Then there are the issues of safety and the environment. According to a study published in the New England Journal of Medicine, each 10 micrograms of airborne particulate per cubic meter of air increase death rates and respiratory illnesses. One study showed that a winter road sanding resulted in air particulate loading as high as 89%.
Because salt is an effective deicer at warmer temperatures but has limitations at colder temperatures, along with environmental concerns and its corrosive nature, some companies/municipalities have blended materials with salt: calcium chloride, magnesium chloride, and sand. The same problem, though, remained: when the materials fell to the surface, there was no effective synergy unless they were actually touching each other.
Alternatives? Completely homogenous products like Ice Slicer (produced in Utah) or Mineral Melt (produced in Canada). According to Better Roads magazine, Ice Slicer is popular in the western states and is one of the primary deicers used by the Colorado DOT, while Mineral Melt is popular in Canada and the Midwest, particularly in Minnesota.
Those materials require no retrofit of existing equipment or purchase of additional equipment, and also are spread in 30% smaller quantities. Better Roads says that while they are between 1½ and 2½ times as expensive as regular salt, they are less expensive in the long run. The de-icer component of the total cost associated with de-icing is estimated to be less than 30%, dwarfed by the capital cost of the truck, pre-wetting systems, storage, labor, overtime, fuel, maintenance, and insurance.
Salt brine least expensive
Stenz says the least expensive and most effective option is salt brine, a solution of water saturated with salt that costs about 4-6 cents per gallon — compared to magnesium chloride or calcium chloride, which cost 80 cents to $1.25 a gallon, or up to $4 for other chemicals.
Salt brine freezes at -5°F and is most effective at 18-20°F. Magnesium chloride and calcium chloride have a freezing point of between -20° and -60°F, but Stenz says most snowstorms occur between 15° and 30°F.
“You don't get snow at 0°F — it's just not a common event,” he says. “Most snowstorms come in, and you have a lot of moisture in the air. The front comes through at temperatures right around freezing or just below it. In that range, salt brine is very effective, and it's a fraction of the cost.”
The availability also can remain constant because salt is usually in supply on property, as opposed to having to wait on delivery of more chemicals when a state's supply has been depleted.
The negatives of salt brine: If it is applied when the temperature is too cold, it can freeze in the lines, and become gummy or icy when it hits the road; and proper dilution/saturation is necessary. More is not better. It is more forgiving on higher dilution.
It can either be purchased — in some parts of the country from mining or oil companies, where it is a byproduct — or made on site in a salt-brine production unit.
Dual-containment system
Varitech Industries, a division of Force America that has seen its revenue grow from $300,000 to $3 million in the past three years, manufactures the SB600, a dual-containment system that is capable of producing 3,600 gallons of salt brine per hour. The solution is 100% saturated immediately on contact, then diluted down to the correct level by adding fresh water into a salt overflow tube before it enters the 600-gallon storage tank. The unit can be enclosed in an 8'×12' shelter that is insulated, with optional heaters and a top that lifts up pneumatically for adding salt.
Self-contained storage tanks of 10,000 to 12,000 gallons are available, with double walls and transfer pumps.
Trucks are retrofitted for tanks either on the side or the rear to hold the liquid. As they drive down the road, the liquid is directly applied, using a spray bar on the back of the truck that allows up to three lanes to be covered at a time, or a spinner made up of either multiple rotating disks or a single disk. Either spreader can be mounted on the chassis; or a slip-in unit that can be placed in the bed of a dump truck; or on a trailer or tow-behind unit.
Electronic and hydraulic equipment apply the material precisely from tanks ranging from 100 gallons to 1,800 gallons. A basic system would be available from a truck-equipment dealer for around $1,000, while the most sophisticated system could cost as much as $15,000.
Stenz acknowledges that many customers are scared off by the initial investment needed to retrofit equipment and buy storage tanks, but says it can be recovered very quickly.
A 1996 study done by the Washington State DOT showed that on a 23-mile section of road, liquid anti-icer cost $1,409, compared to $4,089 for the traditional method using some combination of salt and sand. Savings: $2,680.
The costs for the anti-icer application included $1,046 for 1,000 gallons of liquid calcium magnesium acetate, $68 for labor, and $295 for equipment. The costs for the traditional method included $1,564 for 60 yards of sand mixed 10:1 granular chemical, $540 for labor, $707 for equipment, $363 for labor to run the sweeper truck, $543 for sweeper equipment, $334 for labor to run the buffer vehicle for the sweeper, and $38 for buffer equipment.
Dale Keep, the maintenance methods specialist for WSDOT, concluded that there was a “remarkable savings with the use of pre-treatments over traditional methods,” and that pre-treatments were “equally effective in providing a comparable level of service to the traveling public.” He also stated that there would be fewer tort claims from broken windshields, that there would be environmental benefits, improved public relations, and comparable accident rates.
“Our research indicated that this approach will not succeed without an extensive training program for field personnel, including how de-icers work, why they work, and what to expect under various conditions,” he wrote. “Some resistance should be expected from field personnel to testing pre-treatment methods. It may take a significant amount of time and patience to convince people who have spent many years successfully controlling snow and ice by plowing, sanding, and salting that there are other effective ways of doing business. Fortunately, the positive results of this project have done much to change the attitudes of the participants, many of whom are now strong advocates of the program.”
Says Stenz, noting the $2,680 savings: “With that one application, you could pay off the equipment on a truck.”
He believes perception is the only other factor working against liquids.
“The driving public is used to seeing a truck spreading salt,” he says. “Some of the resistance is this scenario: You're driving down the road and it's getting ready to snow, and you see a truck driving down the road spraying what you think could be water. You think, ‘What is that idiot doing? Why is he putting water on the road right before it snows?’ It's just a matter of education.”