As temperatures drop, sodium chloride loses its deicing power. Depending on conditions, adding more salt to a roadway may be ineffective and wasteful.
To help maintenance managers make the most of their stockpiles and keep roads clear, a Clear Roads research project investigated how salt behaves at different temperatures and concentrations.
The project resulted in informational materials that clearly explain a salt phase diagram and how it applies to keeping winter roads clear. The diagram, commonly used by scientists and engineers, shows the effects of temperatures and concentrations on salt brine solutions but doesn’t explain how it applies to practical purposes such as road maintenance.
A one-page fact sheet illustrates the impact of brine concentration on anti-icing operations, showing how temperature and salt concentration influence ice formation. This resource includes the solubility curve below which salt crystallizes and precipitates from the liquid.
According to the fact sheet, peak performance is obtained above 15°F. However, at temperatures below 20°F, most agencies will consider blending other products or brine additives to expand the effectiveness of the brine solution and provide an additional margin of error for actual weather variations.
A series of images from lab tests and a short video explain salt phase diagram concepts and how they apply to winter road operations. The video and images show that as solutions freeze, liquid brine is trapped inside the ice. This implies that a frozen brine solution may not be as strong as ice from water alone and may be active when temperatures rise.
Learn more:
- Understanding the Chemistry of Road Salt: Watch the videos or download the fact sheet, final report, and the two-page brief at clearroads.org.