The art—and science—of deicing with liquids
BY DR. SCOTT KOEFOD, PRINCIPAL SCIENTIST, CARGILL DEICING TECHNOLOGY
I suspect the general population greatly underestimates the difficulty of winter road maintenance and the skill required by frontline plow drivers. Returning roads quickly to a safe condition following a snowstorm may be likened to operating on a patient—a patient who is constantly moving and whose diagnosis is changing from minute to minute!
Among the most challenging aspects of winter road maintenance is that it is often a wildly moving target. We have an ever-growing range of tools, chemicals, and techniques to deal with icy roads, but the optimum application of these tools will vary depending on frequently changing conditions of weather, forecast, traffic, pavement type, and level of service demand—just to name a few.
Thus, while our industry has made great advances in winter road maintenance over the past 20 years, the inherent complexity of the task will always require a great deal of “art”—that intuitive understanding of how to deal with ever-changing conditions that only comes from real-world experience.
However, art is only made better by a deeper understanding of the tools available (the “paints” and “brushes” of the trade), and this is where the science of deicing can assist the art. Under the controlled conditions of the laboratory, we can learn things about how our deicing tools work that are difficult to learn under the very uncontrolled conditions in the field.
The most important deicing chemical tool that has been developed in recent years is probably the liquid deicer. The appropriate use of liquids has been shown over many years of experience to permit dramatic reduction in the amount of road salt needed. But using liquids is considerably more complex than using road salt alone—hence the need for both art (field experience) and science (knowing what different liquids and blends will actually do under different conditions).
Liquids provide two main values: fast ice melting and precision application. When applied as antiicers, liquids permit much more efficient application of a small amount of chemical (just enough to prevent snow bonding at the pavement surface) than can be accomplished with rock salt. And long years of field experience have shown that anti-icing under the right conditions can result in a cost savings of 75 percent compared to deicing a road that has become ice bonded.
Furthermore, liquids even improve the application efficiency of rock salt. A general rule of thumb is that rock salt wetted with a liquid will adhere to the road better than dry salt, permitting about 30 percent lower salt application rates.
The other fundamental value that liquids provide is accelerated ice-melting speed. The value of this should not be underestimated. The ice-melting performance of any chemical is constrained by two things: ice-melting capacity (how much total ice can be melted per pound of chemical) and ice-melting speed. As the temperature drops, rock salt melts less ice and melts more slowly. Any melting capacity that has not had enough time to occur before the salt is plowed or knocked off the road is wasted.
There is nothing that can be done to change ice-melting capacity at a given temperature, but liquids enable us to increase ice-melting speed. In Direct Liquid Application deicing, brines can provide enormously faster ice melting than rock salt. They do this at the price of reduced ice-melting capacity, which in turn requires a higher application rate than rock salt and care to not overapply liquid at colder temperatures; still, it can be a valuable trade-off under some conditions. And even when applying rock salt, pre-wetting the salt with liquid accelerates the rock salt’s ice melting by facilitating its conversion to a brine. Ultimately, it is always in the brine form that a deicer does most of its work—whether it is applied originally as a solid or not.
The use of liquids can be further optimized to specific conditions via application rates, application type, and the use of different brine blends. This brief article does not permit a more in-depth discussion, but there are many training resources on the use of liquids in winter road maintenance—a great place to start is the Clear Roads website.
- Cargill Salt works to protect lives and enhance commerce by providing sustainable road safety solutions, including deicing products, liquid and specialty pavement anti-icer products, and brine makers. Visit the Cargill Salt website to learn more.
- Please feel free to forward questions to Scott Koefeld.