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Materials


Rock salt is the Iowa Department of Transportationís primary deicing material to combat winter storms. Each year, the department uses approximately 200,000 tons of rock salt to keep Iowa highways clear of snow and ice. Typically, the rock salt used in Iowa comes from underground mines in Kansas or Louisiana. The salt is purchased each season through a competitive bidding process for delivery directly to 113 delivery points managed by the Iowa DOT. Kansas salt is shipped to Iowa delivery points using rail and trucking. The Louisiana salt is brought to Iowa via barges on the Mississippi River and then trucked to the delivery point.

The Iowa DOT also has an active testing program for new deicing materials or additives. The goal of that testing program is to find an alternate deicing product or additive that works as well or better than rock salt with minimal impact to the budget, environment and infrastructure.

Brine information

This brine information is not an endorsement of any particular brand or product, but simply an account of the Iowa DOT's experiences as it moved from not using salt brine to using more than 12 million gallons in a time span of 10 years.

Brine is defined as any liquid saturated or nearly full of chloride. This could mean that any dry chemical, freeze-point depressant containing chlorides, such as magnesium chloride, sodium chloride, potassium chloride or calcium chloride when mixed with a liquid would be considered a brine. For the purposes of this discussion, the information provided will concentrate on a brine made from the mixture of sodium chloride (rock salt) and water. This is the brine most often used in Iowa for prewetting and anti-icing operations.

Brine has been used in many European countries for many years as both a prewetting agent for dry materials and as an anti-icing agent for the proactive treatment of snow and ice. For prewetting there are two methods commonly used to wet the dry chemical freeze-point depressant before it is placed on the roadway.
  1. Brine can be sprayed over the load while in the vehicle just prior to use. This requires an overhead sprayer device capable of delivering a strong stream of liquid uniformly over the load.
  2. Brine can be sprayed onto the dry materials just as it leaves the truck or just prior to contact with the pavement by direct application at the spinner or auger.
For anti-icing, the key is to place the brine on the roadway surface prior to a precipitation event. This action helps prevent the snow and ice from bonding to the pavement. The city of Oskaloosa was an early advocate of anti-icing as a way to keep snow and ice from bonding to the road surface. The city has also used it with great success on city sidewalks. The following article, written in 1995, explains how the city began using brine in their operations. Click on the link below to view the article.

Saltwater solution aids in controlling ice buildup on city streets.


Now, over seven years after this article was written, the use of salt brine for prewetting and anti-icing is no longer experimental or unusual. In the winter 2002-2003, the Iowa Department of Transportation (DOT) used more than seven million gallons of brine. All of the Iowa DOT's snowplow trucks are equipped with units that prewet dry materials at the spinner. Anti-icing equipment is available to anti-ice the entire commercial and industrial network (more than 9,000 lane-miles) when conditions make it an effective strategy. Many cities and counties, including many of the major metro areas are now active users of salt brine.

Traditional practices depended on rock salt or mixtures of rock salt and abrasives to remove snow and ice from the roadways. The materials were delivered from the bed of the truck to a spinner where it could be widely dispersed onto the pavement. The idea was to concentrate much of the chemical over the middle of the roadway when the chemicals began the melting process the melting liquid would move away from the crown of the roadway to the lower levels of the roadway and help break the snow and ice bond with the pavement. A study conducted by the Michigan DOT measured the amount of chemicals left on the roadway after a typical spinner application of materials and found that nearly 30 percent of the materials left the roadway after application and landed on shoulders or in ditches due to bouncing. With a typical Iowa DOT application of 300 pounds per lane-mile of a 50/50 mix of salt and abrasives, that would mean that once the truck passes only 210 pounds of the mix remains on the roadway.

Further studies conducted in Switzerland and Germany also measured the amount of dry chemicals that remained on the roadway after vehicle movement and found that after five vehicles had passed, only 30 percent of the dry materials remained on the roadway. After 100 vehicles had passed, only 20 percent of the dry chemicals remained to do the job. When the materials were prewet and after five vehicles had passed, 93 percent of the materials remained on the road; and after 100 vehicles, 80 percent remained on the roadway surface. If a dry 50/50 mix is being used to remove snow and ice, it is obvious that a roadway with large volumes of traffic will quickly lose most of the materials onto the shoulder or ditch where it is of little help to melt snow and ice.

  • Rock salt can be spread more uniformly and less is wasted on shoulders and ditches reducing the impact to the environment.
  • Materials adhere to the surface because the salt and brine mixture has a thicker consistency. The slurry-like mixture tends to "plop" onto the roadway and better stay where it lands.
  • Melting begins faster because a liquid has been introduced to the salt. (Salt must find moisture before it can begin to work.)
  • Spreading speeds can be increased because more material stays on the roadway.
  • Because brine begins working and diluting as it hits the surface, it will dry much more rapidly, returning the roadway to normal winter driving conditions much sooner.
  • Residual salt may remain on the road that will immediately begin working with the next storm.
  • When dry materials are prewet with brine, application rate can actually be cut back 20 percent to 30 percent because more of the material remains on the roadway. The additional brine adds some quick melting action.
  • Can be used as a deicer on very thin layers of frost or black ice, but with caution. Salt brine is not recommended for snowpack unless it is treated regularly and frequently with a sufficient quantity of salt brine and/or salt brine and rock salt. Brine alone will rapidly dilute and if an insufficient concentration is maintained, may refreeze before it can burrow through the snow or ice pack

  • Application prior to a storm can help prevent snow and ice from bonding to the pavement.
  • Helps keep roadway wet longer into a storm or in the case of a very light precipitation event, possibly throughout the storm.
  • Makes cleanup quicker and returns roads to normal driving conditions more rapidly.
  • Reduces labor hours.
  • Reduces wear on ice blades and underbody plows.

Annual cost to produce 100,000 gallons of salt brine

Assume 2,500 gallons per hour

Labor @ $22 per hour$860
Building*$886
Water$750
Salt$795
Electricity$750
Storage tanks*$60
Brine maker*$650
Total annual cost$4,751
Cost per gallon$0.00475
*Annual depreciation for life of equipment.

The following are cost savings that might be expected when using brine as a prewetting agent.

Assumptions

Salt$45 per ton
50/50 salt/sand mix$26 per ton
Brine$0.09 per gallon
Prewet at 15 gallons per ton of dry material

50/50 salt/sand mix applied at 300 pounds per lane-mile on a 40-lane-mile route

Without prewetting
6 tons of material at $26/ton $156
With prewetting assuming application rate is reduced by 25 percent (225 pounds per lane-mile)
4.5 tons of dry material at $26 per ton$117.00
68 gallons of brine at $0.05 per gallon$6.12
Total costs$88.90
Total savings
$32.88

Straight salt applied at 200 pounds per lane-mile on a 40-lane-mile route

Without prewetting
4 tons of material used at $45 per ton $180

With prewetting assuming application rate is reduced by 25 percent (150 pounds per lane-mile)
3 tons of dry material at $45 per ton$135.00
45 gallons of brine at $0.09 per gallon$4.05
Total costs$139.05
Total savings
$40.95

It does not take long to recognize that for larger operations the savings can be significant over a period of time. If you choose to prewet and not reduce the application rates, service levels will improve because more material remains on the roadway to melt snow and ice and less would be found (and wasted) in the ditches or shoulders.

Making brine is a fairly simple process requiring only two ingredients — water and salt. Of course, a container to mix the materials properly and storage tanks are also required. To achieve the ideal concentration of 23.3 percent a hydrometer or salimeter is needed to measure the quantity of salt, by weight, in the brine concentration. Hydrometers can be purchased with readouts in specific gravity, percent solution or salt concentration.

Hydrometer used to measure salt solution

Hydrometer to measure salt solution

If the concentration of salt is too high or too low the temperature when the concentration freezes, the concentration will be much higher than at the ideal 23.3 percent concentration. It is very similar to adding anti-freeze to a vehicle. Water freezes at 32 degrees fahrenheit and straight anti-freeze freezes at 2 degrees fahrenheit, but when they are mixed at 30 percent water and 70 percent anti-freeze, the freezing temperature of the two ingredients mixed together becomes minus 84 degrees fahrenheit. As the percent of anti-freeze is increased or decreased from the ideal percentage of 30/70, the freezing temperature continues to climb. The following phase diagrams help explain how the freezing point (eutectic temperature) of common deicing chemicals will change when mixed at different concentrations.

Phase diagram of different brines

Phase Diagram of different brines

The hydrometer is actually the device that measures the specific gravity of a solution in water, but for this purpose it basically measures the percent concentration of salt in the brine solution. The following is a specific gravity chart for brine and a conversion to the percentage of solution and a salimeter reading using a readout on a scale of 0 percent to 100 percent solution.
  Percent of Salt Hydrometer
Specific Gravity
Hydrometer (Salimeter)
using 0 percent to 100 percent
  1 0
1 1.007 4
2 1.014  7
3 1.021  11
4 1.028  15
5 1.036  19
6 1.043  22
7 1.051  26
8 1.059  30
9 1.067  33
10 1.074  37
11 1.082  41
12 1.089  44
13 1.097  48
14 1.104  52
15 1.112  56
16 1.119  59
17 1.127  63
18 1.135  67
19 1.143  70
20 1.152  74
21 1.159  78
22 1.168  81
23
1.176*
85*
24 1.184  89
25 1.193  93
26 1.201  96
27   100
*Ideal solution level

The container you use can be as simple as a bucket. For this discussion, several options will be presented — everything from a simple homemade unit using locally available parts and purchased models of various designs and capacities. The city of Oskaloosa and Iowa DOT have used the homemade version for their initial use of prewetting and anti-icing. As confidence and satisfaction grew in the techniques and use increased, the Iowa DOT progressed to more sophisticated purchased units with greater capacities. There are differences in the homemade and purchased models beyond price, but both are capable of producing brine at 23.3 percent.

Simple diagram of the brine making process in a purchased unit

The Iowa DOT's first locations to use salt brine constructed their own brine makers. All of the parts required to build a brine maker are readily available at any farm implement store. The bill for construction should be relatively small, especially when considered in comparison to the material savings that can be gained from the use of brine. Typical cost for a homemade brine making system using galvanized stock tanks is approximately $600 — excluding the cost of plastic storage tanks.

Iowa DOT homemade brine maker





Plans for a homemade brine maker


In 1995, the Iowa DOT purchased its first commercially produced brine makers when 32 units were purchased from VariTech Industries for use in garages with responsibility for interstate highway maintenance. The brine makers were able to produce 600 gallons of brine in 40 minutes. Since then, the department has purchased additional brine makers that have the ability to provide larger volumes faster than the original brine makers. Brine making speed and volumes are dependent primarily on the water supply. If you only have 1-inch water lines, brine making will be a much slower process than when a 2-inch supply line is available. The following are pictures of a number of brine makers that have been successfully used by the Iowa DOT, including the most current model (and specifications).

The original Varitech brine maker
The original Varitech brine maker

Inside a Varitech brine maker
Inside a Varitech brine maker

Sprayer Specialties brine maker
Sprayer Specialties brine maker

Sprayer Specialties brine maker
A mobile brine maker was constructed to travel to shops with low-volume salt brine needs and/or for use at rural facilities with wells that would not support the volume of water needed to produce brine. Now most facilities have their own salt brine production units. If not, the brine is normally produced at a fixed location and delivered via a tanker truck to outlying shops.

Sprayer Specialties brine maker
Brine facility with outside storage. Though Iowa's winter low temperatures occasionally fall below salt brine's freeze point (minus 6 degrees fahrenheit) for short periods of times, brine produced at the correct concentration has never frozen. In one instance a tank did freeze, but laboratory tests showed that the brine concentration was well below 23 percent.

Sprayer Specialties brine maker
A new model of VariTech brine maker. The tank on this brine maker was molded rather than welded plastic as the original units, but its design is very similar.

Sprayer Specialties brine maker

Sprayer Specialties brine maker
VariTech VCSB 1400-SS brine maker. This is the current model of brine maker purchased by the Iowa DOT. The tanks are constructed of stainless steel. Production capacity is 5,000 gallons per hour.

Sprayer Specialties brine maker
The mixing tank can be easily lifted off using an front-end loader to dump out impurities and clean the tank.


If you are considering adding a brine-making production plant to your facility, there are a few other lessons learned in the Iowa DOT's experience that you may want to be aware of or consider.

Water

  • Water supply line size can limit production capabilities. A minimum of a 2-inch supply line is recommended if substantial quantities of brine will be produced.
  • Consider a separate water meter for the brine maker to avoid paying sewer charges on the water used to make brine.
  • Facilities with well water must carefully consider if the additional load required to make substantial quantities of brine can be "borne" by the natural water supply.

Salt

  • Despite what you may think, very fine salt does not work well in brine makers. A standard gradation salt with as few impurities as possible is best.
  • If salt is too fine, the water can not circulate freely through the salt and you may end up with a lump of salt that will not appropriately go into solution.
  • If impurities are allowed to build up in the mixing tank, it is more difficult to get a consistent, fully concentrated salt solution and production may suffer.

Facilities

When selecting a brine-production facility, consider the corrosive nature of the salt and minimize those effects wherever possible.
  • Consider a separate building or section off a portion of a building so corrosiveness can be controlled or contained. Separate heating and ventilation systems are recommended.
  • Electrical connections and equipment are especially subject to corrosion. Investigate weatherproof switches, fans, etc., and consider mounting as much equipment as possible outside the building.
  • Use moisture-resistant lighting and encase all interior wiring in well-sealed plastic conduit for protection.
  • A standard overhead door will have a shortened life span due to the corrosive atmosphere. Consider the additional replacement expense down the road or investigate upgrades that may better withstand the corrosion.

Storage

  • Consider the need and/or local or state requirements for secondary containment.
  • Make sure tanks used outdoors contain a UV inhibitor.
  • A gallon of salt brine is more than 2 pounds heavier than a gallon of water. Make sure the tanks you purchase are designed to handle the additional weight.

There are many ways to deliver the brine to the roadway. Again, the units can range from very small, inexpensive homemade units to large sophisticated pieces of equipment. Though there are many variations, the following photos demonstrate some of the prewetting and anti-icing equipment that has been successfully used by the Iowa DOT.

Homemade 80 gallon unit
Homemade 80-gallon unit. Made from scavenged PVC pipe plus end caps.

Swenson 140 gallon tailgate mounted prewet unit
Swenson 140-gallon tailgate mounted prewet unit.

Monroe tailgate
Monroe tailgate mounted prewet unit with 180-gallon capacity.

Iowa DOT dump truck with integrated tailgate
Integrated tailgate - Iowa DOT dump trucks are now purchased with an integrated tailgate. The tailgate is constructed of stainless steel and has a capacity to hold 225 gallons of brine. The tailgate operates identical to a traditional tailgate, swinging open to allow easy unloading.

Integrated tailgate
The integrated tailgate also includes a dual auger feature. The first auger breaks up any clumps in the material before they reach the feed auger, providing better reliability and less clogging.

The Iowa DOT has used a variety of equipment, dependent on the particular needs of a location. Slip-in units, trailers, tankers, and hybrid combination units are all in use.

The hybrid combination units have more liquid capacity than a traditional prewet unit, yet less capacity than a stand-alone anti-icer, and still has the capacity for a quantity of dry material. The combo unit has both a prewet pump and an anti-icing spraybar.

A number of combo units are now in use or being field tested. The combination units provide maximum flexibility for treatment options.
  • Use liquids for traditional prewetting of dry material (10-15 gallons per ton)
  • Traditional anti-icing of roadways or bridges (40-50 gallons per lane-mile)
  • Any combination of the two (e.g., on light snowpack, you could apply dry materials along with 40 gallons per lane-mile of brine to get quick melting action and maximize the chemical concentration available for melting).
Homemade 1800-gallon slip-in unit
Homemade 1800-gallon slip-in unit

Homemade 1800-gallon slip-in unit
Homemade 1800-gallon slip-in unit

Pickup with homemade 250-gallon anti-icing unit used for treatment of bridge frost.
Homemade 250-gallon anti-icing unit. This unit is used to treat bridge frost.


Plans for slip-in unit
Pressurized system

First Anti-icer used in the FHWA TE-28 project.
First anti-icer used in FHWA. TE-28 project in 1993 (no longer in service).

Homemade 1800 gallon mounted on trailer.
Homemade 1800-gallon unit mounted on trailer.

Homemade 2700 gallon mounted on trailer.
Homemade 2700-gallon unit mounted on trailer.

Homemade 3600 gallon tailer mounted unit.
Homemade 3600-gallon trailer mounted unit (four 900-gallon tanks mounted on a lowboy trailer used in the summer to haul equipment, but was sitting idle throughout the winter months).

Anti-icing trailer with 1850 gallons capacity
Current anti-icing trailer with capacity of 1850 gallons.

5000 gallon tanker trailer used for anti-icing the Interstate.
5000-gallon tanker trailer used for anti-icing the interstate.

Homemade combo unit
Homemade combo unit with 900-gallon liquid capacity and 6-ton dry material capacity can apply dry, prewet or anti-icing/frost treatment.

Homemade combo unit
Another combo unit that uses 600-gallon stainless steel modular tanks in the truck bed. With this particular unit, the truck can be loaded with two tanks to carry 1200 gallons of liquid along with approximately 5 tons of dry material or a third tank can be set into the truck bed and the truck then becomes strictly an anti-icing unit with 1800-gallon capacity.

A wide variety of different types of nozzles and spray bars have been used in the Iowa DOT's history with anti-icing. Some of the first units used were simple gravity fed units, where the size and number of holes drilled in the piping regulated the application rate. The current units are controlled by a Raven ground speed controller for precise, consistent application rates.

Fan nozzles were first used, some with the capability to spray multiple lanes. Most current units are designed to anti-ice a single lane and possibly a shoulder, and the units are equipped with streamer nozzles to minimize the impact to traffic. All have been successfully used in different environments.

Gravity fed spray bar
Simple homemade gravity fed unit.

Fan spray nozzles
Fan spray nozzles in action. Nozzles mounted at the sides of the spray bar can be turned off or on to get wider lane coverage. Though fan nozzles can effectively and evenly cover a lot of pavement, there is some drift and misting. Fan nozzles are no longer recommended for new systems.

Anti-icing combination
Anti-icing combination of multiple liquids at the same time—can combine liquid CaCl with liquid NaCl

Anit-icing and prewet spinner on a combo unit
Anti-icing and prewet to spinner on a combo unit.

Fan and streamer combination
Fan and streamer combination.

Clip on streamer nozzles
Clip on streamer nozzles.

Rubber sheeting to control drift
Rubber sheeting to control drift.

Inexpensive rubber tubing attached to spray bar
Inexpensive and easily replaced rubber tubing was attached to the spray bar to bring the brine very close to the road surface. This is currently in field testing and has promise for a simple, inexpensive delivery system.

Brine has shown to be an effective new tool in the battle against snow and ice and should be carefully considered for use when preparing for winter storms. The percentage of salt in the brine solution is one of the keys to success with the use of brine. Too much salt and the freezing point goes up, too little and the freezing point also goes up.

The Iowa DOT used more than 7 million gallons of salt brine in the state last year for snow and ice control. The Iowa DOT has equipped the entire fleet of nearly 879 snowplows with the ability to prewet all dry materials used in winter operations and last year had sufficient anti-icing equipment for coverage of the commercial and industrial network (more than 10,000 lane-miles) plus the Interstate Highway System in the state.

The department continues to work with manufacturers and staff to continually improve the methods we use to deliver deicing chemicals on the roadway. Liquids may well be the most efficient method available today to deliver quality service at lower costs with minimal impact to the environment.


Printable version of brine information

Other links

The following links contain information on how the Iowa DOT got started in the mid-1990s using liquid applicators and anti-icing equipment.

Liquid Applicators to Combat Snow and Ice in Iowa DOT
Anti-icing equipment, recommendations and modifications