Buzz
For those living in areas with harsh winters, the danger of slippery, icy driveways is all too familiar. Under the right conditions, pavement can become as slick as an ice rink, making every step a risky venture with the potential for falls and painful injuries, like a bruised rib or elbow—or worse.
The typical remedy for this winter hazard is sodium chloride, or rock salt, which quickly breaks up ice and provides traction. It's a quick fix, but unfortunately, using salt or other de-icers on concrete driveways can lead to unexpected problems.
Salt and de-icers don't actually melt ice but instead work by lowering the freezing point of water, which normally freezes at 32°F. Depending on the chemical used, the freezing point can drop to 20°F or even as low as -25°F. (If you've used a de-icer without success, it’s likely because the temperature was simply too cold, falling below the chemical's effective freezing point.)
As temperatures shift, water undergoes a freeze/thaw cycle. For example, it might thaw at 22°F, freeze again at 18°F, and thaw once more at 22°F. Water seeps into concrete due to its porous nature. When it freezes (or refreezes), it expands, leading to damage of concrete driveways. (Asphalt driveways, on the other hand, are much less prone to salt damage, thanks to their mix of stones, sand, and petroleum, which is designed to endure these freeze/thaw cycles.)
Rock salt is often the worst culprit, as it only lowers the freezing point by a small margin—to about 25°F. It’s also hygroscopic, meaning it draws in roughly 10 percent more water than would otherwise seep into the concrete.
What should you use instead? Other ice melters that lower the freezing point more effectively help prevent water from cycling through the freeze/thaw process as frequently. Calcium chloride, for example, lowers the freezing point to -25°F, meaning the water in concrete or asphalt stays liquid rather than freezing and expanding. Just be careful not to overuse it, as runoff can damage lawns by killing grass and flowers.
Alternative melters, such as magnesium chloride (with a freezing point of 0°F) or calcium magnesium acetate (with a freezing point of 20°F), are more environmentally-friendly and safer for pets, though they have a higher freezing point than calcium chloride. Which product you choose should depend on the type of driveway and other specific conditions. Remember, though, that rock salt—especially on newer driveways—can be a real threat to concrete.
