Chloride Cocktail

Jan. 1, 2006

Liquid use in winter operations has always been a hot topic. Despite seminars, articles and proven programs, many local agencies have yet to try liquids in prewetting applications or in anti-icing operations. Contrast this with the fact that the Iowa Department of Transportation (DOT) used over 11 million gal of liquids this past season. Agencies that have followed Iowa’s lead have found liquids to be one of the best tools in snow and ice operations when used correctly and under specific conditions.

Liquid use in winter operations has always been a hot topic. Despite seminars, articles and proven programs, many local agencies have yet to try liquids in prewetting applications or in anti-icing operations. Contrast this with the fact that the Iowa Department of Transportation (DOT) used over 11 million gal of liquids this past season. Agencies that have followed Iowa’s lead have found liquids to be one of the best tools in snow and ice operations when used correctly and under specific conditions.

The blending of liquids seems to be the next step in enhancing an operation that is already using liquids as part of their operation and may prove to be the answer for an agency just starting out. Blending itself is not all that new. Neither is liquid use. It has just taken time to get agencies to buy into its effectiveness. Blending is something that many agencies and vendors have tried to some extent but with limited success and not precisely.

The theory is this: If salt brine is good, enhancing it must be better, correct? But how do you go about mixing those chemicals? What amounts do you use? What chemicals should you use? Will they stay mixed? How will they react? Will they do a better job? All these questions and more play into blending liquids. Two agencies have taken an active approach in the blending process, and their efforts are having an effect on the industry.

The McHenry County Division of Transportation (MCDOT) in Woodstock, Ill., was perhaps the first agency to seriously look at blending winter deicing chemicals and how it could be accomplished. The desire to blend different chemicals did not stem from a goal to change the industry but the need to fix an inherent problem faced by many agencies using more than one product. Many of them use different products for different conditions. In the case of the MCDOT, they were using salt brine for prewetting and anti-icing when pavement temperatures where above 15°F. When pavement temperatures dropped, they switched to liquid calcium chloride. When pavement temperatures rose, they switched back to brine. The cycle continued throughout the season.

The problem with a system like this is that operators must manually switch from one storage tank to another and must ensure that the tanks on the truck are substantially empty. One also must consider the residual chemical in the hose leading from the storage tank to the pump and then to the truck. Calcium chloride and salt brine are best suited in a mixture of 90% brine and 10% calcium. Greater amounts of calcium can create an interesting blend that does not flow well and resembles gelatin or mayonnaise. This is exactly what occurred in McHenry County. Combine this with the desire to enhance the brine, to give it a kick, and the division set out to cure the problem.

Sketchy prototype

The first concept of a brine-enhancing mixing system was drawn on a sheet of paper in a break room. The idea was to come up with one mixture so operators did not have to switch products. The MCDOT also had been testing alternative chemicals in its operations. These in-house tests pitted agricultural byproducts and mixtures purchased from vendors against salt brine and calcium chloride. The division also tested treated salt and compared it with the division’s current practices. The division chose Geo-melt (De-ice 55) to incorporate into its operation, mainly due to the good residual effect noticed when applied to the roadways. Another factor was that the substance could be mixed in any amount to any other product.

In every field there are experts, and snow and ice is no different. One of the experts in liquids resides in Illinois. Harvey Williams is a former Illinois DOT (IDOT) research and development employee. He was largely responsible for getting liquid use started in the Midwest. Williams has since retired from IDOT and now does research and development for Dultimeier Corp.

Williams and DeVries sat down and drew up the first plans. The system needed to be designed to mix products but also to dispense any one product in case mixtures proved to be ineffective. Recirculation needed to be considered to keep the chemicals from separating.

Additionally, the MCDOT was looking for any other improvements to enhance its operation, and filling trucks was one area that needed to be improved.

After many redesigns, the first manifolds were constructed, and a system was built in an existing structure. New lines were run to each storage tank, and a salt brine maker was added to the facility. A new 10,000-gal storage tank also was added to hold the blended product. The system worked by pulling products from the tanks, running them through a filter, through flow meters and through a static mixer before pushing it to the tank.

Deicer spreading

Gathering advice from many different sources, including Dr. Wilfred Nixon of the University of Iowa, led the Iowa DOT to choose the composition of 85% brine, 10% De-ice 55 and 5% calcium chloride. The calcium percentage was kept low because of fears that too much may cause problems in storage. The new mixture was dubbed “Supermix.”

Supermix was first tried in late December 2004. It was used in only two trucks initially and was applied directly to the salt in the auger at a rate of 10 gal per ton. Positive results soon had the mix in every truck prewetting at the same 10-gal-per-ton rate. In the anti-icing units the mixture was applied to the pavement at a rate of 40 gal per lane-mile. Initial results had the operators excited about its performance. It seemed to work well in all temperatures and had a dark color that was easy to see. It seemed to last, which resulted in less re-treatment. Not one operator claimed to experience re-freeze, which the division had seen using straight calcium. The residual effect, especially in anti-icing, seemed to be excellent. The product seemed to work well in all conditions.

In anti-icing operations, Supermix was not applied below 15° pavement temperatures despite the possibility that it may work at lower temperatures. While in prewetting applications, it seemed to work well at pavement temperatures down to 2°F. It was determined that antifoam was needed during loading. The 100-gal tanks were now being loaded in 45 seconds compared to 4 to 5 minutes. At these increased volumes, foaming was taking place. Another unforeseen benefit was the overall reduction in calcium chloride use.

While switching between products, the MCDOT annually used about 23,000 gal of calcium per season. That number was reduced to 2,704 gal the first year of using Supermix at 5% calcium.

After the initial success, word got out quickly about the system and the mix, and in West Des Moines, Bret Hodne, superintendent for the city, and his staff started development of a similar system with the intention of making it automated. Hodne’s vision was to develop the system so it would make different blends at the stroke of a keyboard. One of Hodne’s goals was to load Supermix directly into tankers and have the mixture blended to the day’s conditions.

Innovation on a theme

They have gone a step further now and are incorporating the system to work with the maintenance decision support system (MDSS) of their weather service. Hodne also sought advice and worked hand in hand with Williams to develop the West Des Moines system.

The second year of using the system and Supermix had similar positive results. Both agencies received good results in the residual effect of the product applied to the pavement. In an anti-icing application, the product was still evident after a week even on higher-volume roads. The darker color shows up well on pavement, and the product does not blow away like the white dust that forms with straight brine.

A very mild winter in West Des Moines did not allow for a great deal of testing of different blends. A commonly asked question is how low does Supermix work and what about different blends? Samples of Supermix were sent to an independent lab in Utah for testing. Hodne also sent different mixtures of the same products to compare how different percentages would affect the freezing points. The results are still coming in, but they are surprising. The lowest temperatures were in the mix being used and mixes with slight changes. One thing to keep in mind is that the eutectic temperature (the point at which a product can no longer melt ice) is not a working temperature. The synergy of this product just seems to work. Further testing will be done, and other products may be tried, including magnesium chlorides and corn salts.

About The Author: DeVries is maintenance superintendent for the MCDOT. He can be reached at [email protected]. Hodne is superintendent of public works for the city of West Des Moines, Iowa. He can be reached at [email protected].

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