By Matt Kennedy
The anti-icing of asphalt roads is an interesting topic to review as climate change and global warming were among the main agenda items addressed during the most recent G20 summit.
Phrases such as “polar vortex” have become common household terms over the past few years, forcing the northern climates (and some southern states) to deal with the lowest temperatures and wind chill factors they have experienced in some time.
Many technologies have been forced to adapt to these changes, including roadway deicing services throughout North America.
SALT AND BRINE
The usage of salt and brine solutions are far from new, they have been used on our roadways for some time now. Salt traditionally has been used during the winter months to melt ice and snow from roadways, while providing more traction for vehicles.
Brine, on the other hand, is a salt solution derived from gas and oil wells, or via any salt solution mixture, and has traditionally been used as a dust palliative on gravel roads, and more recently transitioning to roadway ice prevention practices.
The most commonly used products for ice and snow prevention/melting on roadways are (see chart below):
The most common products used are the sodium chlorides, mainly due to their availability and being least expensive. They have been used as an ice control chemical since the early 1900s; though they have been subject to toxicity scrutiny. Both calcium and magnesium chlorides are better known to be less biologically impactful than sodium, and therefore preferable, although research suggests these claims are only through literature discussions as opposed to raw data. Anti-corrosive additives can also be added to these products to further enhance their uses, and having lesser effects on vehicles.
New products are introduced every year with catchy names that often promise magic or wizardry, with proprietary mixtures of the same chemical deicers that have been used for years. Chemical deicers are typically chloride salts of sodium, calcium, potassium or magnesium (all shown in table above/below).
There are also non-chloride chemicals including calcium magnesium acetate, potassium acetate and urea. Some new products on the market are blended with liquid byproducts from the food or beverage industry such as beer waste and beet juice or general agricultural byproducts such as corn carbohydrates or molasses.
These byproducts enhance the eutectic point (the lowest melting point of ice to water) and increase friction coefficients to prevent slickness of roadways sometimes experienced with straight chloride brines. By comparison, MgCl2 solutions run around 22% concentration by weight, with a typical eutectic point around -6°F (-21°C), while liquid calcium chlorides contain 30-32% CaCl2 with a eutectic point of -60°F (-51°C). A blend of MgCl2 at 27% and 6% corn carbohydrates will enhance the eutectic point to -85°F (-65°C). Coupled with other enhanced benefits, this and many other relatively newer chemical compositions are often and readily useable as new-age anti-icing practices.
Other innovations such as anti-ice pavements have also been tested around the world, with what seems to be mixed results on the various test sections preformed since the late 1980s. The idea is to add chemical deicers to the hot mix itself at the time of production, which is designed to slow the icing effect on roadways when winter hits.
The deicers are encapsulated calcium chloride pellets, which have been tested at 5-7% addition by weight to the hot mix, as part of the mix design, and are designed to keep the calcium chloride inactive until the pavement surface wears under the action of traffic. The pellets are uniform throughout the mix, so as to be active throughout the entire depth of the overlay. At these addition rates, a dramatic increase in production costs of the finished mix was seen, while slickness of the pavement was also noted.
Several North American test sections have been done using this technology, spanning from Colorado, New York, Pennsylvania, Minnesota and ten in Ontario. The Office of Materials, Research and Standards from the Minnesota DOT states the test section they performed had the manufacturer claiming maintenance vehicles and man hours associated with snow and ice control will be reduced, while maintaining adequate safety levels through the use of an anti-ice pavement construction.
After laydown and throughout the observation period, significant deicing observations were not noted, with an inadequate performance of the overlay itself taking place, forcing the state to mill and replace a few sections of the trial. No further trials have taken place. The other DOTs reported similar results from their trial sections, with no known programs currently taking place. A few agencies did say with a very mild snowfall, they did see some melting benefits, however they experienced overall mix and compaction issues as well.
Solar-powered radiant heating devices have been trialed on bridge decks for ice melting, with success. Pave Guard Technologies, a Missouri firm, designed the solar power systems. They were installed on two bridges on Route 10 near Excelsior Springs, a town near Kansas City. Pave Guard’s systems use solar panels to heat an antifreeze solution. The solution circulates in pipes underneath the pavement, keeping ice from forming and making roads safer in wintry conditions. Noticeable, safer results have been noted by the MODOT. This technology has promise for bridge deck ice prevention.
On a similar note, from ideology conceived in the mid-1990s, “Asphalt” magazine previously reported four possible techniques for solar power implementation in asphalt roadways through research done at the University of Rhode Island. One of which is to install pipes filled with water below the surface of the roadway. The water heated in the piping could be used to warm buildings or to move turbines in power plants. Interestingly though, the heated water could also be stored, and returned to the roadway to potentially prevent or thaw icing. Theoretical in nature, this could be examined in the future. This method will be expensive on a large-scale project.
By talking with industry professionals, I learned that much of the advancements in the chloride markets are centered on the equipment and advanced monitoring.
“The major recent advancements have been seen in the technology used to monitor roadways in preparation of a storm, as well as with the follow-up. Equipment is now available and used that documents a road’s condition, documents wind or gusty areas within a given section of roadway, grade change, speed limit changes, sheltered areas and generates chloride spray rates for each section of roadway,” said Cecil Loder of Innovative Surface Solutions, a chloride supplier in the northeast U.S. and across Canada.
“This data can be programmed into spray equipment computers, generating exact spray application rates necessary for a given section of roadway. Aside from this major benefit, the equipment also has the benefit of documentation should there be an accident, which will quickly produce information applicable to the prior preventative maintenance activities performed by the maintenance contractor. This is a major advancement for all stakeholders, ensuring the necessary measures are being taken to maintain roadways to protect civilians, while protecting the contractor from liability should an issue arise,” added Loder.
Kennedy is Sales and Marketing Manager at McAsphalt Industries Limited.