Q.: We put in a sidewalk in August or September in front of a business establishment in Alaska. Two months later it was being salted continually and heavily to prevent even the chance of ice and snow buildup on the surface. This spring the top 1/8 inch has scaled. The concrete contained 6 percent air. I've been looking at ACI 210R-55, Erosion of Concrete in Hydraulic Structures, in the section on "Erosion by Chemical Attack." This doesn't make the salt clearly responsible for the trouble. Are there some other documents that do?
A.: The problem seems to be too early and too frequent an application of deicers, which can damage even air-entrained concrete if the concrete is not old enough to have been both fully cured and then been dried. It is usually recommended that salts not be applied during the first winter.
In ACI 201.2R-77, Section 1.3, there is a good discussion of the effect of ice removal agents on concrete pavements subject to freezing and thawing. The action is physical, not chemical.
In ACI 302.1R-80, Chapter 9, the recommendation is made: "The owner should be cautioned not to apply deicing salts until curing has been completed, the concrete (adequately air-entrained) has dried out, and has preferably been through one winter. Under most circumstances a concrete which has been given this preparation, and which contains an adequate air content in accordance with [ACI 302 recommendations], will withstand deicer application without damage.
"Not all concrete to be exposed to deicers contains enough air--either because of bad practices, or because of job difficulties that caused an air content lower than specified. Such concrete can be made more resistant to attack of deicing agents by the application of two coats of boiled linseed oil." ACI 302 then gives instructions for applying the linseed oil.
