What makes a surface vulnerable to it
Water inside concrete expands when it freezes, and a mix built with air entrainment gives that expanding water microscopic pockets to move into instead of pushing straight out at the surface. That is not an upgrade, it is what keeps a driveway from scaling apart a few winters in, in a climate that runs a real freeze thaw cycle every year the way this part of Virginia does.
A surface loses that protection two ways: a mix that was not built with enough entrained air for the job to begin with, or a finish that overworked the top of the slab and pushed the air back out of it right where the freezing and thawing happens first.
Scaling versus spalling
Scaling is shallow and it spreads evenly, a thin layer lost across a broad area rather than one spot, and in its early stages it is mostly a texture and durability problem more than a structural one. Spalling goes deeper and tends to stay local, larger fragments breaking away, sometimes down to the aggregate or the reinforcing steel, and it can come from causes beyond freeze thaw alone, including rebar that has started to rust and push the surface off from underneath as it expands. Left alone for enough winters, scaling can work its way toward spalling, but they start out as two different problems with two different causes.
- A rough, pitted texture where a smooth trowel or broom finish used to be
- Loose, sand like grains at the surface that were not there the first year or two
- Wear that follows the whole slab or a whole exposed area evenly, not one spot
- Worse along edges and any low spot that holds water or ice longer than the rest
What helps a slab that is only lightly scaled
A sealer can slow further loss on a surface that is only lightly scaled, but it will not put back what has already flaked away, since it is a coating, not a rebuilding product. A surface that has gone past light texture loss into a genuinely rough, pitted, sand shedding condition is closer to a resurfacer job. Fresh de-icing salt on a slab through its first winter makes all of this worse before the concrete has finished curing, which is its own topic worth asking about when a slab is new.