Road Salt Brine Concentration: A Field Guide to Measuring Salt Brine for DOT Road Deicing

Road Salt Brine Concentration: A Field Guide to Measuring Salt Brine for DOT Road Deicing

When winter weather arrives, transportation departments and road maintenance crews have a simple objective: keep roads safe while using the minimum amount of deicing material necessary to do the job.

That sounds straightforward. In practice, effective winter road maintenance depends on getting several variables right at the same time: pavement temperature, precipitation, traffic, timing, application rate, chemical selection and, when liquid deicing brine is used, the concentration of the solution being applied.

For sodium chloride road salt brine, concentration is especially important.

A solution that is too weak may not provide the expected freezing-point depression or melting performance. A solution that is too concentrated is not necessarily better. In fact, sodium chloride brine has a well-defined optimum concentration, and exceeding that concentration can actually raise its freezing point and create operational problems.

For road departments, municipal public works crews, airports, private snow-removal contractors and other winter maintenance operations, a portable refractometer provides a fast way to verify that salt brine is being produced and applied at the intended concentration.

The BOSS Professional Brine Salinity Refractometer from National Industrial Supply is specifically designed for applications including salt deicing and brine testing. It measures salinity from 0-28% by weight, with an additional 0-280 ppt/PSU scale, and is designed for professional field use. (NISupply)

Why Salt Brine Concentration Matters

The most common road salt is sodium chloride, or NaCl. It is inexpensive, widely available and remains one of the most important chemicals used for winter road maintenance.

But sodium chloride does not simply “melt ice.” It must dissolve in water and form a brine. The resulting salt solution lowers the freezing point of water, helping prevent ice from forming and helping weaken the bond between existing ice and pavement.

The concentration of that solution matters because the freezing point of sodium chloride brine changes dramatically as the amount of dissolved salt changes.

For standard sodium chloride road brine, approximately 23.3% NaCl by weight is commonly identified as the eutectic or near-eutectic concentration. At this concentration, the solution reaches its lowest freezing point, approximately -6°F (-21°C). (MDPI)

This is one reason 23.3% has become such an important number in winter road maintenance.

The American Association of State Highway and Transportation Officials specification for sodium chloride used in roadway deicing identifies 23.3% NaCl by weight as the specified brine concentration, while recognizing that agencies may adjust the concentration based on expected roadway temperatures and performance requirements. (Scribd)

That gives a new winter-maintenance employee an important principle to remember:

The goal is not to make the strongest possible salt solution. The goal is to make the correct solution.

More Salt Does Not Always Mean Better Deicing

One of the easiest mistakes for someone new to brine production is assuming that a higher salt concentration must produce better deicing performance.

It does not.

The sodium chloride-water system has a characteristic freezing-point curve. As salt concentration increases, the freezing point initially falls. At approximately 23.3% NaCl, the freezing point reaches its minimum.

Beyond that point, the freezing point rises again.

A technical review of sodium chloride brine concentrations illustrates the effect. A 23.3% solution has a freezing point around -21°C (-6°F), while concentrations above the eutectic point can begin to crystallize salt rather than simply providing additional freezing-point depression. (TRL)

That means a brine-making operation should not simply add more salt whenever possible.

The objective should be concentration control.

For many standard sodium chloride anti-icing and brine applications, approximately 23.3% is the target. The exact operating specification should always follow the agency’s approved winter maintenance procedures, chemical specifications and pavement-temperature requirements.

What Happens When Brine Is Too Weak?

Under-concentrated brine creates several problems.

If a road department intends to produce 23.3% sodium chloride brine but actually produces a solution significantly below that concentration, the material may not perform as expected under cold conditions.

The problem can become worse after the brine reaches the roadway.

Snow, ice, precipitation and moisture can dilute the chemical. If the resulting solution becomes too weak, it can lose its ability to prevent freezing and can contribute to refreezing.

Iowa DOT specifically warns that salt brine used on snowpack can rapidly dilute and may refreeze if sufficient concentration is not maintained. (Department of Transportation)

That is why concentration testing is not merely a laboratory exercise. It is a quality-control procedure.

The 23.3% Brine Target

The FHWA’s Manual of Practice for an Effective Anti-Icing Program provides a practical methodology for preparing sodium chloride brine.

For a known-volume mixing system, FHWA recommends determining the amount of salt required for the desired concentration, filling the tank partially with water, adding the salt while agitating, then adding water to the final working volume. After mixing, the brine should be tested to determine the actual concentration. FHWA recommends a concentration as close to 23.3% as possible for anti-icing, with the guidance stating that it should not exceed 25%. (Federal Highway Administration)

This is where a field refractometer becomes extremely useful.

Instead of assuming that the calculated amount of salt and water produced the intended solution, the operator can take a sample and measure the actual brine.

That distinction matters.

A calculation tells you what you intended to produce.

A concentration measurement tells you what you actually produced.

How a Refractometer Fits Into the Brine-Making Process

A refractometer measures how light behaves as it passes through a liquid. The optical measurement can be correlated with the concentration of dissolved material in the solution.

For salt brine, a salinity refractometer provides a rapid field measurement without requiring a laboratory balance, chemical titration or a hydrometer.

The BOSS Professional Brine Salinity Refractometer has a 0-28% salinity concentration range and a 0-280 parts-per-thousand (ppt)/PSU scale. Its stated salinity concentration accuracy is ±0.20%, and it incorporates automatic temperature compensation over 50-86°F (10-30°C). (NISupply)

For a transportation department making 23.3% sodium chloride brine, that range is particularly useful because the desired concentration falls comfortably within the instrument’s measurement range.

A practical field procedure

A new operator can incorporate the refractometer into a basic quality-control routine:

1. Prepare the brine according to the department’s established recipe or brine-maker settings.
2. Allow the solution to mix thoroughly.
3. Obtain a representative sample from the tank or designated sampling point.
4. Calibrate the refractometer with distilled water according to the manufacturer’s instructions.
5. Place several drops of the brine sample onto the prism using the supplied pipette.
6. Close the prism cover and allow the sample to spread across the measurement surface.
7. Look through the optical system and read the salinity scale.
8. Compare the measured concentration with the department’s target.
9. If necessary, adjust the brine with additional water or salt and remix.
10. Test again before releasing the material for operational use.

The BOSS refractometer is supplied with a pipette, calibration screwdriver, hard carrying case and user guide. The manufacturer specifically instructs users to place the sample on the prism with the pipette rather than immersing the instrument in the brine. (NISupply)

Why This Is Better Than Guessing

Brine production is often based on calculations involving salt weight, water volume, tank volume and the characteristics of the salt being used.

Those calculations are useful.

They are not infallible.

Road salt is not necessarily laboratory-grade sodium chloride. Commercial deicing salt can contain impurities, moisture and other materials. AASHTO’s M 143 specification recognizes sodium chloride mined from natural deposits as well as salt produced from brine and establishes chemical requirements for roadway deicing applications. The specification identifies a minimum sodium chloride content of 95% for the sodium chloride material. (Scribd)

This means two batches made from the same nominal weight of “road salt” can behave differently if the material characteristics differ.

Moisture can also affect the calculation.

So can changes in water quality, salt purity, mixing efficiency and equipment operation.

A refractometer provides an independent measurement of the finished solution.

That is particularly valuable when a brine-making system is operating continuously.

Continuous Brine Production Requires Ongoing Testing

FHWA describes a second brine-production method in which water passes through dry salt and the resulting brine is collected in a holding tank and then transferred to storage.

This type of system can produce highly concentrated brine, potentially approaching saturation. FHWA recommends diluting the resulting solution to the desired 23-25% range and emphasizes frequent monitoring when brine is produced continuously during a storm. (Federal Highway Administration)

That is an ideal environment for a portable refractometer.

Rather than treating concentration as a one-time setup measurement, a department can establish a testing schedule such as:

• At startup
• After a new batch of salt is introduced
• After changes to water flow
• After changes to brine-maker settings
• At regular intervals during continuous production
• When a tank is transferred or replenished
• When field crews report unusual performance
• After equipment maintenance or calibration

The exact testing frequency should be established by the agency’s operating procedures.

Real-World Example: Iowa DOT and Large-Scale Road Salt Use

The need for effective concentration control becomes clearer when looking at actual highway operations.

The Federal Highway Administration has documented winter maintenance operations involving state transportation departments, including Iowa DOT. Iowa uses rock salt as its primary winter deicing material and has historically used approximately 200,000 tons of rock salt annually to keep state highways clear during winter storms. (FHWA Operations)

At that scale, small improvements in material efficiency can become significant.

The objective isn’t simply to put more chemical on the road. Transportation agencies have to balance safety, material costs, labor, equipment time, corrosion and environmental impacts.

Liquid brine is one tool that can help.

Iowa DOT describes several advantages of pre-storm brine application, including helping prevent snow and ice from bonding to pavement, reducing labor requirements and reducing wear on snowplow equipment. The agency also emphasizes the need to maintain the proper brine concentration. (Department of Transportation)

This is a good example of why concentration testing belongs in the operational process rather than being treated as an afterthought.

MnDOT: Pre-Wetting Can Reduce Salt Loss

Minnesota provides another useful example.

MnDOT uses salt brine for anti-icing, deicing and pre-wetting operations. The agency explains that pre-wetting helps salt adhere to the pavement and reduces bounce and scatter. It also starts the melting process sooner because moisture is immediately available to dissolve the salt. (Minnesota Department of Transportation)

MnDOT’s maintenance guidance has also documented applications where pre-wetting and slurry techniques reduced the amount of granular salt required.

In one MnDOT research project, a 70% granular/30% liquid application system was evaluated, with a test setup using substantially less dry salt than a conventional application. The project was intended to reduce material use, salt scatter and the number of truck passes required. (Minnesota Department of Transportation)

The lesson for a new operator is straightforward:

The effectiveness of winter chemicals depends on how they are prepared and applied, not simply how much material is loaded onto the truck.

Pre-Wetting, Anti-Icing and Deicing Are Not the Same Thing

Winter maintenance terminology can be confusing to someone new to the industry.

Anti-icing

Anti-icing generally means applying a liquid chemical before snow or ice bonds to the pavement.

The goal is to prevent or weaken the bond between the precipitation and roadway.

Pre-wetting

Pre-wetting means applying a liquid, often salt brine or another deicing chemical, to granular material as it is being applied.

The liquid helps the material stick to the road and can initiate the dissolving process more quickly.

Deicing

Deicing is generally reactive. The roadway already has snow or ice, and chemicals are applied to weaken the bond and assist mechanical removal.

The distinction matters because the required application strategy can change with pavement temperature, storm timing, precipitation type and roadway conditions.

MnDOT notes that deicing should not be viewed as an attempt to chemically melt every bit of snow and ice on the roadway. The chemical treatment is intended to loosen the bond so mechanical removal can be more effective. (Minnesota Department of Transportation)

What About Calcium Chloride and Magnesium Chloride?

Sodium chloride is not the only chemical used in winter road maintenance.

Calcium chloride (CaCl₂) and magnesium chloride (MgCl₂) are commonly used either independently or as components of blended deicing systems.

These chemicals can provide advantages at temperatures where straight sodium chloride becomes less effective.

For example, MnDOT notes that below approximately 15°F, agencies may add calcium chloride or magnesium chloride to salt because straight sodium chloride becomes significantly less effective. (Minnesota Department of Transportation)

A Nevada DOT research report similarly discusses the use of calcium chloride and magnesium chloride in colder conditions and describes studies evaluating mixtures of sodium chloride with calcium chloride. (Nevada Department of Transportation)

However, this creates an important limitation when selecting a refractometer.

A basic sodium chloride salinity refractometer should not be treated as a chemical analyzer capable of identifying every individual compound in a blended deicer.

The BOSS Professional Brine Salinity Refractometer measures total salinity. It does not distinguish sodium chloride from potassium chloride or other salts. (NISupply)

That makes it particularly appropriate for monitoring straightforward salt brine operations where the target is expressed as overall salinity or sodium chloride concentration.

For proprietary blends containing multiple chloride compounds, operators should use the manufacturer’s recommended measurement method and calibration scale.

The Importance of Using the Right Road Salt

Road salt used for highway maintenance may be mined rock salt or produced through other processes.

AASHTO M 143 specifically covers sodium chloride used for pretreatment and deicing of road surfaces and includes both mined rock salt and salt produced from naturally occurring or hydraulically produced brine. The specification calls for a minimum sodium chloride content of 95% for the sodium chloride material. (Scribd)

Commercial products from major road-salt suppliers can therefore be appropriate starting materials for making brine when they meet the purchasing agency’s specifications.

But the operator should not assume that a particular brand automatically guarantees a finished brine concentration.

The finished solution still needs to be tested.

This is especially true when changing suppliers, receiving a new salt shipment or changing from one grade or source of road salt to another.

Why a Portable Refractometer Belongs in the Winter Maintenance Toolbox

A brine concentration measurement takes only a small sample.

The BOSS Professional Brine Salinity Refractometer does not require batteries or an external power supply. It uses ambient light, has an aluminum construction and is supplied with a hard carrying case. The instrument also has a five-year warranty. (NISupply)

For a winter maintenance operation, that means the instrument can be kept with the brine-making equipment, in a maintenance shop or with the crew responsible for chemical quality control.

It is small enough to be practical for field use while providing a quantitative measurement instead of relying solely on assumptions based on tank volume or mixing time.

A Simple New-Employee Checklist

If you are new to winter road maintenance, remember these basic rules when working with salt brine:

1. Know the chemical.
Determine whether you are working with sodium chloride, calcium chloride, magnesium chloride or a blended product.

2. Know the target concentration.
For standard sodium chloride road brine, approximately 23.3% by weight is a common target and is identified in AASHTO guidance.

3. Do not assume stronger is better.
Sodium chloride has an optimum concentration for minimum freezing point. Increasing concentration beyond that point does not continue lowering the freezing point.

4. Mix thoroughly.
A sample taken before the tank is properly mixed may not represent the solution that will ultimately be applied.

5. Measure the finished brine.
Use a refractometer or the measurement method specified by your agency.

6. Record the result.
Concentration readings can become part of the operation’s quality-control record.

7. Watch pavement temperature.
Chemical performance depends heavily on pavement temperature and weather conditions.

8. Remember dilution.
Rain, snow and melting ice can dilute brine after application.

9. Do not confuse salinity with chemical identity.
A total-salinity measurement does not tell you exactly how much NaCl, MgCl₂ or CaCl₂ is present in a complex blend.

10. Follow your agency’s specifications.
State DOTs, counties, municipalities and contractors may have specific requirements that supersede general industry guidance.

BOSS Professional Brine Salinity Refractometer

For crews making or applying sodium chloride road brine, the BOSS Professional Brine Salinity Refractometer provides a practical way to verify concentration in the field.

Its 0-28% salinity range encompasses the standard 23.3% sodium chloride brine target. The instrument also provides a 0-280 ppt/PSU scale and a 0-100% water-in-salt-saturation scale. Its stated accuracy is ±0.20% for salinity concentration and ±2 ppt/PSU. Automatic temperature compensation is provided over 50-86°F (10-30°C), and the manufacturer recommends calibration with distilled water. (NISupply)

For winter maintenance operations, the biggest benefit is simple:

You can test the brine you actually made rather than assuming the mixture is correct.

That can help a road department maintain more consistent deicing performance, reduce the risk of applying under-concentrated or improperly mixed brine, and provide operators with a straightforward quality-control measurement.

Proper brine concentration is only one part of an effective winter maintenance program. Pavement temperature, weather conditions, traffic, application rate, chemical selection, timing and mechanical snow removal all matter.

But concentration is one variable that can be measured quickly.

And when you’re responsible for keeping roads safe during a winter storm, having an objective measurement is far better than guessing.

Shop the BOSS Professional Brine Salinity Refractometer

The BOSS Professional Brine Salinity Refractometer is available from National Industrial Supply for measuring salt brine concentration for road deicing, anti-icing, pre-wetting and related applications.

Professional Brine Salinity Refractometer 0-28% / 0-280 ppt/PSU

National Industrial Supply
30777 Rancho California #891420
Temecula, CA 92589
Phone: (310) 748-6858
Email: nisupply@gmail.com
Website: www.nisupply.com