Question:

What's the effect of deicers and salts on concrete? How can I make concrete more resistant to salt and deicer damage?

Answer:

Deicing salts used for ice and snowmelt on concrete contribute to surface scaling and spalling. The scaling and spalling in these cases is almost always physical deterioration.

Deicing salts induce mortar flake, scaling and surface spalling of non-air-entrained concrete during frost conditions, and are thought to be the first cause of this surface deterioration. By contrast, air-entrained concrete is designed to resist freeze-thaw attack and attack from some deicers. Entrained air consists of microscopic bubbles intentionally incorporated in concrete cement paste during mixing. Entrained air bubbles in the cement paste fraction of concrete are caused by the addition of an admixture for concrete which causes air to form into microscopic bubbles in the concrete cement paste during mixing. (Dig into Phil Smith's excellent article about air-entrainment in this issue.)

Internal freezing pressures in the concrete become destructive and, if there are no microscopic voids or bubbles to relieve the freezing pressure, mortar flake, scaling or surface spalling will take place.

Air-entrainment is successful in resisting mortar flake, scaling and surface spalling of exterior concrete. Air-entrainment is suggested for all exterior concrete. History has shown that tight (hard) troweling of exterior concrete critically reduces its air-entrainment protection. Therefore, do not tightly trowel exterior concrete. Concrete prepared for air-entrainment should also be sloped for drainage if it is used in the exterior, thus preventing water ponding. The slope can be as gentle as 1/10 of an inch per running foot.

Concrete placed in the spring and summer usually has enough naturally induced drying time to free itself of its early water-saturated condition. Concrete placed in the fall does not have the same advantage. However, concrete placed in the fall needs special planning for drying and protection during curing in the fall season. Thick curing membranes may remain in place overly long and the new water saturated concrete may not dry sufficiently. Concrete placed in the fall should be allowed at least a month of drying once the moist curing period is finished before exposing it to freezing conditions.

The physical mechanism of deicing salt deterioration normally requires the presence of water. Therefore, a recommended way to minimize the damaging effects of deicing salts is to reduce the amount of water entering the concrete pore structure through the use of an effective water repellent. Advancements in water repellent technology now encourage the use of water based, odorless, penetrating silane, siloxane or blended products. (See article in Spring, 2002 L&M Concrete News) L&M offers very effective protection of exterior concrete with its AQUAPEL and AQUAPEL PLUS products. AQUAPEL products are designed to deny additional water access to the interior of the concrete and therefore provide long-term protection of exterior concrete in severe weather areas of the United States. (See map in the Q&A Article, Spring 2002 issue of Concrete News.*) AQUAPEL products penetrate the concrete and become a permanent part of the near surface wear zone, providing long-term protection.

In summary, to prepare concrete for the greatest resistance against deicer and salt damage:

  • Always avoid hard troweling of exterior air-entrained concrete mixes.
  • Cure for the proper period of time.
  • Then, uncover the concrete surface and allow it to dry.
  • Finally, treat your exterior concrete surfaces with L&M AQUAPEL or AQUAPEL PLUS for maximum wintertime protection!