Surface temperatures are key to deicing strategies

By Dale Keep

Truly understanding how deicers work and how surface temperature affects their melting capacities and rates is one of the most important things you can do to save money while still delivering quality customer service.

Understanding the melting process is central to the intelligent use of chemicals. The manager’s task is knowing how to correctly determine the amount of chemical to use and when to apply it to best achieve the established goals. Success depends on understanding the relationship between pavement surface temperatures and deicer performance, while also taking into account recent and expected weather conditions, time of day and customer expectations, to determine the correct amount of chemical to apply and when.

Surface temperature, and the time it takes deicers to form a solution and melt ice at that temperature, is often overlooked in the planning process. The colder it is, the more chemical and time it takes. Ignoring this fact leads to repeat applications, overapplication, higher overall costs and a waste of materials.

Melting capacity
All chemicals, when applied as a solid, melt ice by first forming a brine solution with water available from the ice or snow present. This process takes time and depends on the pavement surface temperature, the amount of water available and, to some extent, traffic action to assist in mixing the solution. Very simply, the colder it is, the more chemical it takes to get the job done.

The table below shows how temperature affects the ability of salt to melt ice (melting capacity) in terms of the weight of the water created.

As temperatures fall, salt (and all chemicals) are less effective at melting ice or have a smaller melting capacity. For example, more salt is needed at 20° than at 30° because of the reduction in melting capacity (46.3 vs. 8.6). The capacity is reduced by a factor of 5.4 with all other conditions being equal. In other words, if one pound of salt applied at 30° F achieved the results desired, at 20° F it would take 5.4 pounds. Note that all deicers share this same trait, but not all deicers are equal in melting capacity. The data here applies to salt only.

Melting rate
Melting rate is a measurement of how fast melting occurs at different temperatures. Like melting capacity, it is influenced by temperature. The table below shows a comparison of melting effectiveness and the effect of temperature on the rate of melting.

Application rates
Based on the melting rate information, it appears that a heavier application would increase the amount of ice melted in the near term; realistically, however, the extra amount of chemical and cost is wasted because it is ultimately not needed to melt the ice. Applicators too often expect nearly instant melting, and when the pavement does not turn black in the rearview mirror, the immediate thought is to apply more chemical. This unrealistic expectation often results in overapplication and a waste of resources. The lag time between application and complete melting is another reason for proactive action. Early application gives the chemical much more time to act. Good pavement surface temperature information, weather forecasts and an understanding of how deicers work provide the necessary information to determine the application rate that best fits the need.   

Other considerations
Retention. The lag time between application and melting can be a problem, particularly when the chemical is applied at low temperatures or on dry pavement. Dry salt is susceptible to displacement by wind and traffic action before it can begin to penetrate the ice. Pre-wetting with brine during application speeds up the liquefying process and can minimize this problem. 

Training. Good training on how deicers work and how their application affects the ice or snow based on current conditions, including surface temperature, is essential. When used correctly, surface temperature is key to determining the correct application rate and time expectations between the application and the final results. Training must address how to determine correct application rates based on the deicer being used, current surface temperature and conditions, expected weather, time of day and overall goals. Good training in this area not only pays for itself quickly, it also consists of more than saying “Put out X amount per square yard and re-apply as necessary.”

Customer communication and level of service. The customer should be advised of how melting rates change as temperatures change, and how at colder temperatures application rates must go up to deliver the expected results. They should also understand that, most times, patience will eliminate the need for repeat applications. Open discussions with customers on deicer use provides for better customer service while preventing overapplications (which can impact the environment and landscaping) and saving you time and money.

Dale Keep owns Ice & Snow Technologies, a training and consulting company based in Walla Walla, WA.