Exposure class
A classification of the environment concrete will live in — freezing, sulfates, water contact, or chloride corrosion risk — that drives durability requirements for the mix.
What does exposure class mean?
Exposure classes let a specifier describe conditions rather than dictate ingredients, with severity tiers within each category ranging from negligible to severe. The assigned class then triggers requirements for the mix that are separate from and additional to the specified strength. Concrete on the same project can fall into different classes depending on where it is placed.
In practice
An exterior stair and an interior slab in the same building carry different exposure classes, which is why they are different mixes.