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Deicing Salts and Concrete

When snow and ice start to accumulate on your driveway and walks, typically for most homeowners, providing safe walking surfaces is the primary concern. Perhaps the next concern would be to have the ability to operate your vehicles so that they are not sliding around on the driveway, or getting stuck at the bottom of the driveway.

Snow removal can easily be accomplished in various ways: mechanically with a snowplow (plow should have a rubberized edge to reduce the risk of damaging the pavement) or a snow blower; or, manually with a snow shovel. Even a broom can be used if the snow is not too deep or too wet.

Deicing salts can react with concrete and may cause spalling overtime

If ice forms on the pavements creating a slippery surface, homeowners typically want the ice removed. Ice can create more of a safety issue than the snow. There are a couple of ways to deal with the ice, including materials that increase traction like sand, and deicing chemicals that melt the ice.

Sand will not melt the ice, but does provide some degree of traction over the surface of the ice. It is not damaging to outdoor pavements and plants, and it is not corrosive. It may get tracked into the house though. I used sand one year, and it did take some extra effort to keep it from getting tracked indoors. To help with this situation, try using a thick fibrous (like coir) doormat for wiping your shoes before coming inside.

Chemical deicers are a big favorite for many homeowners, for ease of use in melting the ice. Ice on steps, black ice, and ice on walks used by older folks can be big safety concerns. But before you use any deicing salts, you should know the pros and cons of these products, so that your can make a decision based on your own situation.

The pros of deicing salts include that they work fairly quickly (some quicker than others) in melting the ice to reduce safety hazards, are readily available, easy to use, for the most part inexpensive, and are effective in temperatures well below zero.

Even though deicing salts may have those attributes, you may be concerned as to whether they are harmful to your concrete pavement. To some degree they are. Some contributing factors to potential damage can be how often you use them and the amount you use.

The chemicals used most often in deicing salts are sodium chloride (rock salt – effective to about 20°F), calcium chloride (effective to -20° F), magnesium chloride (effective to 5° F), and potassium chloride (effective to about 15° to 20°F). These chemicals actually lower the freezing point of water thereby making the ice melt, well below the freezing point of water. Lowering the freezing point leads to increasing the number of freeze/thaw cycles the concrete goes through.

Exposure to increased freeze/thaw cycles is where surface damage like spalling and flaking can occur to concrete that is poor in quality. The first line of defense against damage to concrete is a high quality concrete. High quality concrete will contain an air entrained admixture, which enables it to withstand freeze/thaw cycles. The air entrained admixture creates billions of microscopic bubbles, or voids that hold the water that permeates the concrete’s surface (hardened concrete is porous). As the water expands when it freezes, it creates pressure just under the concrete’s surface. The voids provide area for the water to expand, and reduces the pressure place on the concrete. A good quality concrete involves more than including air entrainment to the mix. The correct ratios of materials, proper handling while it is being placed, and proper curing are all important for concrete to be very durable.

Beside the increase in freeze/thaw cycles brought on by these chemicals, the chlorides in deicing salts can damage concrete over time by chemically reacting with the cement paste (the ‘glue’ that structurally holds concrete together). This reaction can cause the cement paste to loosen from the aggregate in the concrete which can contribute to crumbling or cracking. Use the deicing salts in moderation; when the brine, produced by the deicer melting the ice, has gotten beneath the ice and separated it from the pavement, the ice can then be removed with a snow shovel. This can help reduce the amount of deicing salts used.

Another quality any pavement should have is proper drainage. In regard to the use of deicing salts, good drainage helps to move the salt-water solution off the pavement, reducing the amount of time the pavement is exposed to deicing chemicals.

To help reduce the amount of salt-water solution that permeates the concrete surface, the use of silicon-based (silanes and siloxanes) penetrating concrete sealers can be used. These form a breathable resin layer that repels water and chlorides, but allows moisture vapor to escape from the concrete. Repelling water can reduce the amount of the concrete’s exposure to freeze/thaw cycles.

Deicing salts can be corrosive to metals, also. Many concrete slabs and driveways are reinforced with uncoated steel rebars or wire mesh. Studies have shown that over time the deicing salts permeate down to the reinforcing and begin to corrode it. This can cause cracking as the concrete pulls away. Some deicers come with a corrosion inhibitor, but would only be beneficial if the inhibitor travels through the concrete to the depth of the reinforcing. In properly placed concrete, the reinforcing should have at least 2” of concrete cover which helps protect against corrosion.

Rock salt does not harm concrete, but it is corrosive to metals and can be more harmful to plants than the other deicing salts.

Be careful when dispensing the deicers around nearby aluminum railings and metal landscape lighting fixtures which can be susceptible to corrosion, as well.

On another note, ammonium-based chemicals (ammonium nitrate and ammonium sulfate) aggressively damage concrete and should never be used. Also, do not use deicing salts on new concrete for the first year; even though it has hardened, the hydration process is still going on and the concrete is more vulnerable to the deicing salts. You could use sand to help with traction.

Some Good Practices

The best practice would be to minimize the use of deicers, without causing a safety concern. Use sand to help improve traction. Remove as much snow as possible before applying deicing salts, and once the ice loosens from the pavement, remove the ice with a snow shovel. Never use a metal tool, like a pick axe to break up the ice – it will very likely cause much surface damage to your concrete.

Read all of the manufacturer’s recommendations for the use of deicing salts.

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