Call me boring but...
A focus of our work is concerned with Architectural concrete repair to fair faced concrete. For me this image is fascinating. Not just because I've never seen grout loss quite so honestly displayed before but also because this image clearly illustrates cause and effect.
The base of the column (steel shuttering) had a tiny band of hydration staining (dark line) and some very minor honeycombing (voids around larger aggregates). On the floor, in almost a mirror image was the grout that was lost, lying in place. Call me boring but THIS is my Friday night out.
Plenty of repair posts and advice to come.