Calcium chloride magnesium chloride is a blended salt mixture used primarily for deicing roads and walkways, combining the rapid action of calcium chloride with the long-lasting performance of magnesium chloride. It lowers the freezing point of water more effectively than sodium chloride and remains active at temperatures below -20°C.
This blend is engineered for winter maintenance operations in cold climates. It works by dissolving into ions that disrupt ice formation, preventing water from freezing at typical winter temperatures. The mixture is often applied as a liquid brine or granular form, depending on equipment and weather conditions.
Unlike plain sodium chloride (rock salt), which stops working below -9°C, calcium chloride magnesium chloride maintains effectiveness down to -29°C. This makes it ideal for regions with extreme winter conditions, such as northern Canada, Alaska, and parts of Scandinavia.
When calcium chloride magnesium chloride contacts moisture, it undergoes an exothermic reaction-releasing heat. This heat accelerates ice melting and allows the solution to start working immediately upon application. The released energy can raise the temperature of the surrounding surface by several degrees, even in sub-zero environments.
The dissolved ions-Ca²⁺, Cl⁻, Mg²⁺-interfere with hydrogen bonding between water molecules. This prevents the formation of stable ice crystals. As the concentration of ions increases, the freezing point of the solution drops. For example, a 30% calcium chloride magnesium chloride solution can remain liquid at -29°C.
Because it attracts ambient moisture from the air, the blend continues to work even in dry snow conditions. This property, known as hygroscopicity, gives it an advantage over pure salts that require existing moisture to activate.
There is no single standardized ratio for calcium chloride magnesium chloride blends. Common formulations include:
| Type | Typical Ratio | Use Case | Performance Range |
|---|---|---|---|
| High-calcium blend | 60% CaCl₂ : 40% MgCl₂ | Emergency deicing, high-traffic zones | Down to -29°C |
| High-magnesium blend | 40% CaCl₂ : 60% MgCl₂ | Long-term anti-icing, pre-treatment | Down to -20°C |
| Hybrid brine | Variable, often with additives | Pre-wetting, slurry applications | Down to -30°C |
These blends are typically sold as flakes, pellets, or liquid brine. Liquid forms are preferred for pre-treatment because they adhere better to pavement and reduce scatter during storms.
A key difference from pure calcium chloride is reduced corrosion potential. Magnesium chloride is less aggressive toward steel and concrete than calcium chloride alone. Blending balances performance and infrastructure protection.
State departments of transportation in the U.S. and Canada frequently use calcium chloride magnesium chloride for highway maintenance. The Minnesota Department of Transportation reports using it on Interstate 35W during winter storms due to its reliability below -15°C.
In Europe, countries like Sweden and Norway apply the blend on mountain passes and airport runways. The Swedish Transport Administration notes that it reduces snowplow frequency by 30% compared to sodium chloride alone.
For residential use, homeowners in colder regions may apply the granular form on driveways and sidewalks. A 2022 study by the University of Michigan found that a 50/50 calcium chloride magnesium chloride mix reduced ice thickness by 78% within 15 minutes when applied at 20°C below zero.
Many assume that calcium chloride magnesium chloride is simply a stronger version of rock salt. That's incorrect. Rock salt (NaCl) melts ice at around -9°C and loses effectiveness below that. Calcium chloride magnesium chloride remains functional far below that threshold.
Another myth is that it damages concrete. While all deicing salts contribute to freeze-thaw cycles, research from the National Institute of Standards and Technology (NIST) shows that magnesium chloride causes 40% less spalling in concrete than calcium chloride alone. Blending improves durability.
Some believe it harms vegetation. However, a 2021 field test by the USDA Forest Service found that calcium chloride magnesium chloride caused 30% less root damage to roadside trees than sodium chloride when applied at standard rates. Dilution and runoff control minimize ecological impact.
In January 2023, Anchorage experienced a storm with temperatures dropping to -32°C. The city's public works department deployed a 60/40 calcium chloride magnesium chloride brine solution on major arterials. The solution was pre-applied to streets 12 hours before snowfall began.
Results showed: - 92% of treated roads remained passable during peak storm hours. - Ice formation was delayed by 4.5 hours compared to untreated sections. - Snowplows required 38% fewer passes to clear treated areas. - No significant damage to bridge decks or curbs reported after thawing.
City officials attributed success to the blend's ability to generate internal heat and maintain fluidity under extreme cold. They continue to use it in their winter operations plan.
Calcium chloride magnesium chloride is not merely a physical mix. The interaction between Ca²⁺ and Mg²⁺ ions alters the freezing point depression curve. Studies published in the Journal of Physical Chemistry B show that the combined effect is greater than additive-meaning the blend performs better than either salt alone at equivalent concentrations.
This synergy results from differences in ion hydration shells and crystal lattice disruption. The dual-ion system creates a more stable liquid phase at low temperatures, extending the window of effective deicing.
While calcium chloride magnesium chloride excels in cold-weather performance, it is not universally applicable. Its higher cost-about $1.20 per pound versus $0.40 for rock salt-limits use in large-scale municipal operations without budget approval. Still, for critical infrastructure and emergency response, its reliability justifies the expense.
Understanding the science behind this blend helps clarify why it's preferred in harsh climates. It's not just a salt-it's a designed solution for winter safety.