1. How long has it been like that?
2. Did it happen suddenly or grow over time?
It started to be yellow after some few weeks on the dry but new concrete surface below. We do not know if it's caused by the marble as it's shipped or if it's water and other chemical components from the concrete in combination with long dry time. The problem is bigger inside the building than outside.
3. Is the entire floor area like that?
No. Big parts are.
4. What is the substrate wood or concrete?
Concrete. Cure time of concrete was a lot longer than normal to be sure it was dry enough.
5. Has the floor ever been flooded?
It was cleaned with some water once. Then covered with wooden plates for months for protection.
6. Do you live in the city or the country?
Picture of building:
All the white is this type marble...
The marble order was about 10 million dollars. The floor is huge...
The building cost more than 7.5 billion dollar
Suggestion: Yellow may be pyrite oxidation (rust)
Suggestion to solve problem:
From: Adam Forsythe
Creative Covering Solutions