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Will salt break down concrete?

Q: We had a concrete ramp laid for a client 16 months ago. There has been no problem to date but the last few weeks they have been putting table salt on the concrete steps. This has broken up the surface. I have not seen this before. The unaffected concrete is rock hard to the areas where the salt has been. My question is will table salt in reasonable accumulation break down the surface on the edges and top of the concrete?

A: As far as I know, concrete is not attacked by salt. Rather the deterioration you are seeing is a result of a physical phenomenon. When salt is put on concrete to melt snow and ice, the salt dissolves the snow and makes a salt water slush and the liquid can be absorbed by the concrete. If the temperature then drops and the water freezes, the growing ice crystals expand and break up the concrete surface. A similar mechanism can occur in warm weather. When concrete is repeatedly wetted by salt water with alternate periods of evaporation, salt crystals are left behind in the concrete pores and surface. These crystals can then re-hydrate when exposed to moisture causing them to re-hydrate and grow in size thereby exerting forces that can break up the concrete. A good quality concrete mix with the appropriate amount of cement can create a strong concrete surface and minimize salt attack. You can also treat concrete with a clear coating specifically design for this purpose to minimize or eliminate water absorption thereby minimizing deterioration of the concrete by this mechanism.

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