Anti-Icers: Driving Toward Clearer Roads
These chemicals will change the way you think about snow removal.
Traditionally, much of your snow-removal work involves clearing snow and ice from roads and parking lots after a snow event. While that’s a large part of a winter-management plan, there’s something else to consider, something that could make an easier job of your normal snow and ice removal: anti-icers. By integrating them into your overall snow-removal strategy, you can get the jump on the next snow event by approaching it proactively.
Anti-icing has been defined as “the snow and ice control practice of preventing the formation or development of bonded snow and ice by timely applications of a chemical freezing-point depressant.” Essentially, the idea behind anti-icers involves timing: putting chemicals on the road surface prior to snowfall. Generally, the chemicals you will use in an anti-icing program are liquid chemicals, although in certain circumstances, you may also use solid chemicals that have been pre-wet at the spinner.
For more information on anti-icers, see the Federal Highway Administration’s (FHWA) Manual of Practice for an Effective Anti-Icing Program: A Guide for Highway Winter Maintenance Personnel, available electronically at: http://www.fhwa.dot.gov/reports/mopeap/eapcov.htm.
Taking a proactive approach
Experience suggests that anti-icing is an extremely effective technique for providing high levels of service during winter storms and for providing that level of service with reduced costs and reduced quantities of chemicals as compared with more traditional methods. If you need some specific confirmation of the effectiveness of anti-icing, an NCHRP (National Cooperative Highway Research Project) study (number 20-7/117) has been published with a detailed cost-benefit study for anti-icing. A specific case study is also available, based on the maintenance of U.S. Highway 12 in Idaho. On this stretch of road, several years of usage of anti-icing has produced an 83 percent reduction in accidents, a reduction of 83 percent in abrasives used and a 62 percent reduction in labor hours. It’s hard to argue with those numbers!
To read the full NCHRP report, go to the online publication at: http://www.sicop.net/NCHRP20-7(117).pdf. The Idaho case study is available online at:http://www.sicop.net/US-12%20Anti%20Icing%20 Success.pdf.
So, what do you do if you want to implement anti-icing in your area of responsibility? You need to implement four areas of change.
- Special equipment. Your equipment must include chemical storage and chemical delivery systems. You may also decide to mix the anti-icing liquids yourself, in which case you’ll need a production facility. Chemical storage requires a sufficient number of large storage tanks (capable of holding thousands of gallons of liquids), along with pumps to deliver the liquid onto the trucks. Your trucks will need tanks and spray equipment.
- New operational methods. The way you operate your snow and ice control business will have to change if you are going to use anti-icing. Specifically, because anti-icing is proactive, you need to be proactive as well, working before a storm begins and putting chemicals down on the road surface to prevent formation of a bond between the snow and ice and the pavement. The key factor in making this change is getting good forecasts for the road surface condition, rather than for just the “weather.” The temperature of the road surface can be, and often is, a couple of degrees different from the air temperature, and that difference is more than enough to make life very awkward indeed for you.
- New management techniques. You also have to train your crews in this new way of doing business. They may be skeptical about putting chemicals on the road before it snows. They may not feel comfortable using fewer abrasives than they have historically. If they aren’t trained appropriately, the switch to anti-icing will not be a success. The FHWA Manual (see above) has lots of useful ideas on how best to do this training.
- Selecting anti-icers. How do you go about selecting the best chemical for your needs, if you are making the switch to anti-icing? The first step toward choosing a chemical is considering the various factors that determine how well a given chemical will meet your needs. However, three key ones are worthy of special attention.
- First, you have to figure whether a given chemical will function effectively in your climate. This is a function of the temperatures that you normally see in wintertime.
- Second, you might be concerned about how corrosive the chemical is. If you have infrastructure that is particularly vulnerable to corrosion, or that you wish to take special pains to protect (a new bridge, for example), then the corrosion factor is an important one.
- A third factor is the environmental impact of the chemicals you will use. All the chemicals eventually end up off the road. Depending on your year-round climate (do you get a lot of rain that will dilute and flush away chemicals, or are you fairly arid?) and the sensitivity of your environment (do you live in a fishing paradise?), this too can be a critical factor. We’ll review each of these factors below.
While these factors are some of the most important ones, you should also consider others, such as the completeness of documentation, the consistency of the product from batch to batch, the stability of the product and what it takes to handle the product safely and effectively. Whatever chemical you decide to use, you need complete documentation and a quality assurance program in place. You need to be certain that what you put on the road will do the job you expect it to do, each and every time you use it. You also need to be sure that the product you choose will not change substantially from batch to batch. Simple checks on viscosity and specific gravity can serve as indicators of any problems, but again, this is one of those things you just have to know. Also, some of the new products on the market have significant agricultural components in them (perhaps derived from corn, or other crops). These things can change over time (for example, they might start growing mold), so be aware of whether this is a concern for your choice of product. And if you get a particularly thick or heavy product, it may “stick” very well to the road but it could be difficult (to be generous) to pump it through your delivery system. Also, the tanks you store it in may require some form of reinforcement to hold it safely.
There are a number of factors considered in detail for selecting an anti-icer in the “Guide for Selecting Anti-Icing Chemicals” which is available on the Web at: http://www.anti-ice-guide.com/.
There are a number of sources that will provide information on the equipment you will need. The Iowa Department of Transportation (DOT) provides its anti-icing equipment guide on the Web at http://www.dot.state.ia.us/maintenance/manuals/equip/index.htm. In addition, there are specifications for various anti-icing pieces of equipment used by Idaho DOT at http://www.sicop.net/documents.htm.
The classic way of getting information about the road temperature is through an RWIS (Road Weather Information Station) system. However, these systems can be very expensive (between $25,000 and $75,000 per site), so unless you have one already, your best bet may be to obtain data from somebody else’s system. Many state transportation departments have extensive RWIS systems in place, and provide temperature information on the Web. In addition to just using the Web data, you might also be able to access your state DOT pavement temperature forecasts if you ask for them. (The worst that could happen is that they say no, right?) However you get the information, knowing your pavement temperature and whether it is increasing or decreasing will be critical to your success.
As an example, you can view the temperature across Iowa’s road network at: http://www.weatherview.dot.state.ia.us/.
Temperature is likely to be your first concern. Often, but not always, producers will talk about a eutectic temperature (see diagram, above). The way any deicing or anti-icing chemical works is by forming an “alloy” with water to depress the freezing point. The diagram shows this, in what is termed a phase diagram (or sometimes a eutectic curve). The lowest temperature the water-chemical mixture can go to before it freezes is termed the eutectic temperature or the eutectic point. However, operationally it’s not very helpful. For example, the eutectic point for a salt (sodium chloride) water mix is about –6º F. But if you apply salt at that temperature, it will do you no good at all. While it might (eventually) melt some ice, it won’t melt much. Typically, salt should not be used below about 15º F at best, and in general, 20º F would be a better cut off point.
Temperature performance has to be considered as more than just one number off a graph, and I’d suggest you compare chemicals as follows. First, find out what concentration of mixture the supplier recommends you use (for a salt brine this would be close to the eutectic mixture, as this is the most potent possible mixture). Then find out at what temperatures the mixture will start to freeze (that’s the “freezing line” in the diagram), as well as the freezing point for a mixture that is diluted to half strength and then for another mixture diluted to quarter strength. For salt brine, those temperatures would be 18º F and 26º F respectively. You should choose a chemical that has a quarter-point temperature (the freezing point of the quarter-strength liquid) that is below a typical mid-storm temperature for your region. Also, the chemical should have a half-point temperature (the freezing point of the half strength liquid) that is below about 90 percent of your storms. And if the supplier can’t give you that information (preferably measured by an independent agency), then you should no longer consider the product for your needs.
In terms of corrosion, tests are a little more difficult. A group of states (and one Canadian province) has formed a loose organization called the Pacific Northwest Snowfighters, and have developed a specification for corrosion resistance. If corrosion is a concern for you, then any product you consider should have been tested according to the PNS protocol.
Further details on corrosion are available at the PNS Web site: http://www.wsdot.wa.gov/fossc/maint/pns/.
Measurement of environmental impact of deicers is less well developed. If environmental concerns loom large for you, then you need information on the BOD and COD (Biological Oxygen Demand and Chemical Oxygen Demand) for the products you are considering. You might also consider some sort of toxicity testing and, if stream water quality is a major concern, you probably need to have a measure of the nitrogen content done too (the Kjeldahl Method would be the applicable standard here). Again, manufacturers with good products can help you with these matters.
The basic liquid chemicals at present would be liquid brines of sodium chloride, calcium chloride and magnesium chloride. Added to these would be two acetate-based deicers: calcium magnesium acetate and potassium acetate. Other new chemicals are in development but haven’t made it to the market to any great degree—yet! Often, suppliers will add things to these basic brines to change certain performance factors. They may add an element to reduce corrosion (called a corrosion inhibitor) or to mitigate environmental effects or even to improve temperature performance. Sometimes what they add is developed as a by-product of some other process (agricultural by-products are becoming more and more common in the anti-icing market these days). However, whatever they add, you need to be sure that the final product will do what you want it to do—and that means you should request appropriate test data from the suppliers.
Finally, you’ll notice I’ve said nothing in all of this about price. That’s quite deliberate. Obviously, price is important (and perhaps even critical) in making your choice. However, paying less to get a product that won’t do what you need it to is a false economy. First, find the products that can do what you need them to; then, rank them according to price (and availability, delivery, service and other factors).
Anti-icing is an extremely effective approach for winter maintenance. We now have substantial experience with it in North America, and it’s well worth taking a look to see if it can help you in your winter maintenance. Good luck, and keep warm!
Wilfrid Nixon is professor of engineering for the University of Iowa (Iowa City, Iowa).
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