Even if there was no freezing, hardened concrete with little or no entrained air that is exposed to freeze/ thaw cycles has a high potential for scaling. And there are many conditions that could reduce the entrained content in one particular floor area. First, the engineer who wrote the specifications could have called for a concrete without air, thinking that the floor would be under roof and enclosed. The contractor could have overworked a wet concrete trying to create a smooth surface. Or he may have prematurely finished that floor section. In addition, there could have been a problem with the fresh concrete supplied by the producer. For example, the mix could have been too old, over-agitated, or the air entrainment admixture improperly dosed during batching.
Degrees of scaling
A good place to start is to review the “Guide for Making a Condition Survey of Concrete in Service” prepared by ACI Committee 201. This gives examples you can use to categorize the problem. There are typically four degrees of scaling:
Light — When there’s a loss of surface mortar without coarse aggregate exposure.
Medium — When the loss of surface mortar is 5 to 10 mm deep and there is exposure of coarse aggregate’s upper surface.
Severe — When the loss of surface mortar is 5 to 10 mm deep and there is some loss of mortar surrounding aggregate particles 10 to 20 mm in depth.
Very severe — when there is loss of coarse aggregate particles as well as mortar, generally to a depth greater than 20 mm.
Since the concrete is structurally sound, it’s acceptable to repair the scaled surface area if it is rated as either light or medium.
Begin by throughly removing any loose material to create a relatively smooth surface. Contact the repair material manufacturer for guidance. Most manufacturers suggest surface preparation should include repairing shallow delaminations, surface, scaling, and aggregate popouts. This may require grinding the resulting rough surface. The committee recommends trying to achieve a concrete surface profile in the range of 3 to 5 as described in the International Concrete Repairs Institute’s Document 03732.
This is often the best range for applying most liquid-applied membranes and most thin coatings. Most liquid-applied products are not intended to level off or hide imperfections, although trowel-grade materials can sometimes be used for this purpose. Remember that the temperature of the repair material should be as close to the floor slab as possible.
Create a test panel using both the repair material and the floor treatment before submitting a work proposal for the project.
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