During the winter months, roads and bridges ice over and pose a threat to drivers, especially if black ice is present. Salt is commonly used to melt snow and ice; however, its use on concrete surfaces and bridges is not recommended. Deicing salts can cause salt scaling and calcium oxychloride formation.
Salt Scaling
Deicing salt can damage concrete surfaces. Any area that is exposed to deicing chemicals, such as sodium chloride, calcium chloride, and magnesium chloride, are susceptible to scaling.
To prevent salt scaling, it is important to measure air entrainment during production. Low water-cementitious material ratios below 0.45, curing compound or extended wet curing, and good finishing practices are proven to improve concrete surface strength and resistance to salt scaling.
Calcium Oxychloride
Calcium oxychloride formation causes concrete joint deterioration in colder regions and is caused when chlorides from deicing salts chemically react with calcium hydroxide and water, resulting in expansion, cracking, and deterioration. The formation of calcium oxychloride increases with salt concentration as the temperature drops below 40 degrees Fahrenheit.
To lower the melting temperature of ice below that of sodium chloride, many salt suppliers use impure salts and add calcium chloride or magnesium chloride. The best way to reduce joint deterioration is to avoid deicing salts that contain calcium chloride or magnesium chloride if temperatures are not significantly below zero. Good drainage, joint sealant maintenance, use of concrete sealers, low w/cm, and SCM’s help keep salts out of concrete.
Concrete bridges and surfaces in cold temperatures can be resilient to damage from freeze/thaw cycles, salt scaling, and calcium oxychloride formation with proper materials, construction, and maintenance practices.
The Precast/Prestressed Concrete Institute provides valuable industry resources for engineers and construction professionals. Refer to the ASPIRE – The Concrete Bridge Magazine publication to learn more.
