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Winter brings the inevitable struggle of icy roads, vehicles covered in salt, and slippery surfaces. To keep ourselves safe, we often turn to de-icing chemicals or salts to melt that stubborn ice. But there’s a hidden cost: those same chemicals that help us walk and drive can also silently degrade our concrete sidewalks, driveways, and structures. In fact, Edmonton Council has even tested out the best alternative.
Source: City of Edmonton chooses road salt over calcium chloride for winter roads
Understanding the Science of Concrete Damage
- Freeze-Thaw Cycles: The Basics de-icing chemicals work by lowering the freezing point of water, which helps melt ice. However, when a de-icer laden, slushy mixture refreezes, the water within the concrete’s tiny pores expands. This repeated freezing and expansion stresses the concrete’s structure, leading to cracks, scaling (flaking of the surface), and spalling (deeper surface damage).
- The Chemistry of Destruction: Chloride-based de-icers, like sodium chloride (rock salt), calcium chloride, and magnesium chloride, are particularly harmful. They react with compounds within the concrete, including calcium hydroxide, a key component of cement paste. These reactions can produce expansive products, like calcium oxychloride, that exert intense pressure from within the concrete matrix, causing internal damage and weakening its structure [1].
- Steel Under Attack: Corrosion of Reinforcement Many concrete structures, like driveways or bridge decks, use steel reinforcement (rebar) to provide additional strength. Chlorides from de-icing chemicals accelerate the corrosion of this steel. Rust occupies more volume than the original steel, putting further pressure on the concrete, which can lead to cracking and potentially even structural failure.
Choosing Your De-icing Chemicals Wisely
Unfortunately, not all de-icing chemicals are equal when it comes to damaging concrete.
- Worst Offenders: Magnesium chloride and calcium chloride are highly effective at melting ice but significantly increase the risk of concrete deterioration.
- Bad, but Less So: Sodium chloride (rock salt) is common and affordable but contributes to damage over time. Both are sold in your local big box stores.
- Safer Options: Potassium chloride and calcium magnesium acetate (CMA) are generally less damaging, but CMA can be more expensive.
Protecting Your Concrete: Prevention and Mitigation
- Be Proactive: Minimize de-icing chemical use by shoveling snow promptly before it turns into compacted ice with traffic use.
- Choose Wisely: Opt for safer alternatives when possible and apply de-icers in moderation, following the instructions.
- Seal the Deal: Apply a quality concrete sealer to help create a barrier against moisture and de-icing chemicals. Reapply sealers as needed.
- Maintenance Matters: Repair cracks and surface damage on your concrete promptly to prevent de-icers from causing more extensive issues.
Alternatives to Traditional De-icers
- Sand: Provides traction without melting ice. It can be messy, but it is cheap and safe for concrete.
- Kitty Litter: Offers similar traction benefits as sand and can even absorb some moisture.
- Rock Chips: Similar to sand, rock chips can be used for an aggressive approach to large icy areas where foot traffic is abundant.
The Bottom Line
De-icing chemicals can be essential for winter safety. However, being aware of how they can degrade concrete helps us make informed decisions. By understanding the risks, choosing fewer damaging products, maintaining our concrete, and exploring alternatives, we can protect our sidewalks, driveways, and structures for the long term.
Sources [1] Sutter, L., Hooton, R.D., Toutanji, H.A. and Bayless, J., “Deleterious chemical reactions of concrete with deicing chemicals” Cement and Concrete Composites (2006).
