How Salt Damages Concrete
- Salt damage is most commonly due to exposure to de-icing salts. However, any chemicalcontaining chlorides, including sodium chloride, potassium chloride, or calcium chloride,found in “safe de-icing chemicals,” fertilizers, ocean water, marine air, etc., presents adanger to the concrete. All are mildly acidic and attack the bonds that hold concretetogether.While the exact mechanism of salt damage is not known, a number of well understood,related factors instigated by exposure to salt contribute to the deterioration of concrete.* Salt is a mild acid and lowers the pH in the concrete. The acidic reaction attacksthe concrete paste and aggregate, weakening the structure and strength of theconcrete. It also increases the pore size, allowing additional water and chemicalsinto the concrete, which can exacerbate freeze/thaw cycle damage.* Salt is hygroscopic, meaning that salt attracts and retains water. When salts areapplied to concrete, they attract up to 10% more water into the pore structure ofthe concrete. This process leaves less room for expansion in the pore structurewhich, in turn, creates more pressure inside the concrete when it freezes, causingthe surface to chip, flake, and pop (typically called “spalling”).* Salt accelerates carbonation, a process that slowly reduces the pH levels inconcrete through contact with Carbon Dioxide (air) and contributes to thecorrosion 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 pHreduction of the concrete.* Salts are the primary source of chlorides introduced into concrete. Chlorides are amajor player in the corrosion of reinforcement, as they pierce the thin, protectiveiron oxide layer surrounding the reinforcement and initiate a corrosive reaction inthe steel.
Sulfate Attack:Sulfates are, quite simply, a salt of sulfuric acid. They are found in all natural waters, andare a major dissolved component of rain. Concrete is exposed to sulfates in two ways,externally sourced and internally sourced. Most commonly, sulfate attack occurs whereconcrete 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 (calciumsulfate dihydrate). The sulfate in the portland cement is an internal source, and isactivated when the internal temperature of the curing concrete reaches 160 degreesfahrenheit, a condition which can and should be avoided.Sulfates react in the alkaline environment of the concrete paste and create highlyexpansive crystals called Ettringites. Ettringite is calcium aluminum sulfate. Aluminum isalso frequently found as a component of portland cement in trace amounts. The formationof these expansive crystals creates a great deal of pressure inside the concrete and causesthe concrete to crack and spall.In addition, sulfates are acidic, break down the alkaline environment in the concrete anddeteriorate the concrete paste through acidic attack. This acidic reaction causes theconcrete to weaken and crumble.
Reactive Silicates:Reactive silicates have been demonstrated to nearly completely inhibit water penetrationand chloride ion infiltration, significantly reduce carbonation due to their high pH, andprovide excellent protection from acidic attacks, including salts and sulfates. Theseproducts are highly effective at preventing freeze/thaw damage, and do not have anynegative impact on air-entrained concrete.A unique characteristic of reactive sodium silicates is that, as they penetrate the porestructure, they raise the pH of the concrete and can force residual salts and otherimpurities to the surface of the concrete. Concrete is a highly alkaline substance that isstable at a pH between 10 and 13. Raising and maintaining the pH in concrete has theeffect of arresting the damage occurring in the concrete, which gives sodium silicates adistinct advantage over other products. While a sodium silicate won’t repair large voidscaused by either poor placement or acidic deterioration, and won’t stop corrosion that isalready in the propagation phase, it will have an extremely positive effect on soundconcrete, even if deterioration has been initiated.CreteDefender P2 is this type of formulation… A reactive sodium silicate permanentconcrete sealer that can extend the useful life of your concrete, prevent freeze thawdamage, and protect against salt damage, sulfate attack and chloride penetration… Call oremail us to find out how CreteDefender P2 can make your business dollar go farther andkeep your assets looking sharp longer!