Concrete Discoloration (Blue-Grey) 2

[Jerehmy]

Friend of coworkers slab is discolored below grade and was curioud as to why. Is this discoloration caused by slag in the mix?

https://files.engineering.com/getfi...ile=CF1DE1AC-ECAB-4499-BC12-332FCFFD38E0.jpeg

 

[JAE]

Is it just residue on the surface? Was this surface previously in contact with the subgrade and is that subgrade that color?

Otherwise, when you chip away at that blue-gray surface do you find more blue-gray beneath?

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[Ron]

Yes.... likely slag cement mixed with portland cement. Commonly done.

Gives a blue-gray color that will change to gray upon long term exposure to air. Not a concern unless there are other issues.

You can see in the photo that the upper part of the section has already oxidized and at a point below where the section was in contact with the ground, the change has not yet occurred.