In today’s blog we have decided to provide some information on a common problem that has become much more prevalent in the Treasure Valley these last few years. This problem is damage from salts and ice melts being used on driveways and sidewalks. We out like the types of damage and causes below. In many cases where concrete damage, often called spalling, occurs there are few if any options to “repair” the concrete. Hopefully this article will educate, explain, and help you avoid this type of damage.
What Is Salt Damage?
Salt damage is most commonly due to exposure to de-icing salts. However, any chemical containing chlorides, including sodium chloride, potassium chloride, calcium chloride etc. found in “safe de-icing chemicals,” fertilizers, ocean water, etc. present a danger to the concrete. All are mildly acidic, and attack the bonds that hold concrete together.
What Can Deteriorate Concrete Floors?
While the exact mechanism of salt damage is not known, a number of known, related factors instigated by exposure to salt contribute to the deterioration of concrete.
- First, salt, a mild acid, lowers the pH in the concrete. The acidic reaction attacks the concrete paste and aggregate, increasing the pore size and allowing additional water and chemicals into the concrete which can exacerbate the freeze/thaw cycle damage.
- Secondly, salt is hygroscopic, meaning that salt attracts and retains water. When salts are applied to concrete, they attract additional water (up to 10% more) into the pore structure of the concrete. This process leaves less room for expansion in the pore structure which, in turn, creates more pressure inside the concrete when it freezes, causing the surface to chip, flake, and pop (typically called “spalling”).
- Third, salt accelerates the carbonation process. Carbonation is a process that slowly reduces the pH levels in concrete through contact with Carbon Dioxide (air) and contributes to the corrosion of reinforcing steel. Most salts are neutral to mildly acidic (pH of 4.5 – 7), and absorption of the salts (brine) by the concrete will accelerate the pH reduction of the concrete.
- Fourth, salts are the primary source of chlorides introduced into concrete. Chlorides are also a major player in the corrosion of reinforcement, as they pierce the thin, protective iron oxide layer surrounding the reinforcement and initiate a corrosive reaction in the steel.
What Is A Concrete Sulfate Attack?
Sulfates are, quite simply, a salt of sulfuric acid. They are found in all natural waters, and are a major dissolved component of rain. Concrete is exposed to sulfates in two ways, externally sourced and internally sourced. Most commonly, sulfate attack occurs where concrete is exposed to high sulfate content in the soil, in areas of run-off, and in wastewater. Secondly, Portland cement contains a small percentage of gypsum (calcium sulfate dihydrate). The sulfate in the Portland cement is an internal source, and is activated when the internal temperature of the curing concrete reaches 160 degrees Fahrenheit, a condition which can and should be avoided.
Sulfates react in the alkaline environment of the concrete paste and create highly expansive crystals called Ettringites. Ettringite is calcium aluminum sulfate. Aluminum is also frequently found as a component of Portland cement in trace amounts. The formation of these expansive crystals creates a great deal of pressure inside the concrete and cause the concrete to crack and spall.
In addition, sulfates are acidic, break down the alkaline environment in the concrete and deteriorate the concrete paste through acidic attack. This acidic reaction causes the concrete to weaken and crumble.
How To Fix and Repair Salt Damaged Concrete?
Professional concrete repair is necessary for both commercial and residential applications. Salt can destroy concrete surfaces, especially when it is applied to melt ice or snow on the surface. There are methods that homeowners can use to repair salt damaged areas on their own property, but they should always consider hiring a professional contractor for larger repairs.
Salt damage happens several ways on concrete surfaces. The most common cause is when salt is used to melt snow or ice on the surface of concrete, usually on sidewalks or driveways. Salt is also used to kill grass underneath concrete slabs so that it won’t grow through the surface of the concrete.
If homeowners are tired of cleaning up stains from salt damage, then they may choose to have salt damaged concrete repaired. Salt can also cause surface fractures or pitting. Surface repairs are often made by using a cement-based product meant to patch holes and cover cracks in concrete, which can be applied at home with the right preparation.
If only a small area of salt damage has happened, then homeowners have several options that they can try to repair the problem themselves. If the damage is a thin layer of salt that can be cleaned off with a broom or a pressure washer then this method will usually work.
If the salt has penetrated deeper into the concrete, however, homeowners may have better luck using one of several concrete resurfacing products from their local home improvement store. However, often times it is much easier to call a true professional like Silverline Systems to take care of this issue for you in a professional manner.
How To Stop Salt Damage To Concrete?
The best way to stop salt damage to concrete is to seal up the concrete so that salt can’t affect the concrete. Getting an epoxy or an epoxy alternative to garage flooring can help preserve your concrete floors for years to come. Contact Silverline Systems for more information on how to keep your concrete floors in great shape and lasting for years to come.