Unintended ice-melting consequences

February 1, 2013

slaton patterson FAILURES
Deborah Slaton & David S. Patterson, AIA
For many parts of the country, this time of year means dealing with ice and snow. A range of materials can be used to help remove these hazards with varying degrees of effectiveness. Some products can adversely affect stone paving, concrete and embedded steel reinforcement, adjacent building features, and landscape plantings, or be harmful to animals. Therefore, care is needed in selecting a solution.

Many ice-melting materials contain chloride salts, which have the unintended effect of corroding steel (including embedded reinforcement, leading to concrete spalling), and can cause scaling in lower-quality concrete. The presence of chlorides in ice-melters can also lead to cracking, spalling, and deterioration in stone paving and façade claddings against which snow, ice, and de-icers accumulate.

Sodium chloride (rock salt) is commonly used by highway departments; it is effective in melting ice, but is corrosive and damaging to paving and vegetation. Anhydrous calcium chloride is an effective de-icer because it generates heat, so less is usually required. Calcium chloride melts ice rapidly and is effective at cold temperatures, but can attract moisture and result in slippery surfaces. Ice-melters containing chloride salts are also harmful to vegetation, typically resulting in damage to grass and plantings adjacent to paving exposed to these products. Potassium and magnesium chlorides are generally less harmful to vegetation or paving than sodium or calcium chlorides. In any case, if chlorides are used, the risk of potential damage can be limited by using the minimum de-icer needed to melt snow and ice.

Alternatives to chlorides for melting ice and snow include calcium magnesium acetate (CMA), which is generally safe for concrete paving and vegetation, but not as effective at melting ice and may leave slush on surfaces (although it can help prevent re-icing). Urea, which is used by many airports, is not as effective as chlorides as a de-icer and is more expensive, but does not corrode metals, damage paving, or harm vegetation.

There are also several products described as ‘pet/plant/environment-friendly,’ including an amide/glycol mixture. However, some of these products consist of sodium chloride with a small proportion of other ingredients, such as CMA. Other, more traditional alternatives to chloride-containing ice-melters include sand, cinders, and cat litter. All these products need to be swept up to avoid being tracked indoors.

Since many products contain a mixture of ice-melting components, the product label should be consulted. Varying widely in cost, de-icers are also effective at different temperatures, which should be considered if the material is to be used in extremely cold conditions.

Of course, an effective (though tiring) alternative to de-icers is shoveling—a practice to which the authors must now return…

Left: These stone stairs and adjacent brick walls have undergone several repair campaigns, but continue to be damaged by chloride-containing ice-melters. Right: The underside of the concrete support structure reveals evidence of the damage caused by ice-melters, including corrosion of steel reinforcement and spalling of concrete. Photos courtesy Justin Spivey, WJE[1]
Left: These stone stairs and adjacent brick walls have undergone several repair campaigns, but continue to be damaged by chloride-containing ice-melters. Right: The underside of the concrete support structure reveals evidence of the damage caused by ice-melters, including corrosion of steel reinforcement and spalling of concrete.
Photos courtesy Justin Spivey, WJE

 

Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at dslaton@wje.com[2].

David S. Patterson, AIA, is an architect and senior principal with the Princeton, New Jersey, office of WJE, specializing in investigation and repair of the building envelope. He can be contacted at dpatterson@wje.com[3].

Endnotes:
  1. [Image]: http://www.constructionspecifier.com/wp-content/uploads/2013/02/failures_Pic1.jpg
  2. dslaton@wje.com: mailto:dslaton@wje.com
  3. dpatterson@wje.com: mailto:dpatterson@wje.com

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