Concrete Exposure to De-Icing Chemicals31 Oct 2021, Posted by Concrete Facts in
If you live in an area with snow, you’re likely familiar with the idea of “salting” the roads, sidewalks, and your driveway throughout the winter. This salt is actually a product specifically crafted to melt ice that can be dangerous when it forms on these surfaces and is crucial for many people to make it safely through the winter. However, these chemicals can have a negative impact on the concrete beneath the ice. You don’t want to begin work over again every spring, finding concrete form rentals and laying new pavement year over year. So how do you protect your concrete while still melting ice?
Any chemical used to remove ice is a de-icing chemical, and while the most common is salt, others do exist. Some sidewalks are de-iced using CMA or Sodium Acetate, while airplanes are de-iced with a mix made from primarily propylene glycol or ethylene glycol, environmentally friendly chemicals used in anti-freezers. All de-icers work by simply changing the melting temperature of the water that has formed ice. By adjusting this freezing point, the ice can melt even in subfreezing conditions.
Rock salt is the most popular chemical to de-ice roads and pavements because it is easy to spread over large areas and is generally the most cost-effective. The lowest working temperature for this solution is about 15 degrees Fahrenheit.
Concrete and Rock Salt
Chemicals on their own are not dangerous, but they can have reactions that cause problems. In this case, the calcium hydroxide present in the concrete reacts with the calcium oxychloride (CAOXY) in salt. When the ice from snow starts to melt onto concrete, it soaks into the concrete, where it could refreeze if temperatures drop again. The water then expands, causing tiny cracks or more serious issues in the concrete.
This response is known as scaling, and it can cause blemishes, pockmarks, and flaking of the concrete in small amounts. Over time, it can cause the concrete to lose its integrity entirely.
How to Prevent Scaling
The first thing to do when working on cold weather concreting to prevent scaling is to ensure your concrete has been properly specified. Any concrete that could be exposed to winter conditions should be at least 4000 psi, have a maximum water to cementitious ratio of .45, and have 5-7% air entertainment. It also needs to be placed, finished, and cured properly. If possible, avoid the use of de-icers for the first year after placement, and then use appropriate sealers.
De-icer should never be used on concrete that hasn’t reached sufficient strength so that it can provide resistance to damage from freezing and thawing.
While many de-icers are listed as “Safe” on the bag, the back of the back usually lists conditions for its use and exactly what chemicals are present. This can give you an indication of how safe something is for use on concrete.
Sodium chloride or calcium chloride are usually considered acceptable for use on high-quality, dense concrete. However, there are much higher rates of deterioration with de-icers that contain magnesium chloride, potassium chloride, calcium magnesium acetate, urea, ammonium sulfate, and nitrogen salts. It is never safe to use anything containing ammonium sulfate or aluminum nitrate, as they are more aggressive and will quickly destroy concrete surfaces.
If you choose to use a sealer, silane- or siloxane-based penetrating sealers provide the highest level of resistance to the damage effects from de-icers, freezing, and thawing. Water repellant sealers that are specifically made for use on concrete can also be effective.
Are There Alternative De-Icers?
Despite the impact on concrete, rock salt is still the most common and safe de-icer on the market when used properly. Some experts recommend using regular table salt that is 100% sodium chloride. However, this should only be done on concrete that has been set for a long period of time.
Some construction companies have floated more creative ideas for natural ice melters, including pickle brine and beet juice. These are likely not scalable options for large city areas but may work for a personal driveway. You can also simply remove snow and ice by shoveling it from private property.
De-icing keeps roads safe and is highly recommended, even on concrete, as long as it is done safely.