We've seen spots like that where Armorall has gotten on driveways.....basically the concrete has been "sealed" to a degree.
try to use 24% hydrogen chloride it usually remove top of concrete surface( brings original concrete color)..very strong chemical
WHAT?
Okay -
1 - You need to add a signature....name, COMPANY name, location, phone & website
2 - WHY would you even THINK about removing the top of the concrete surface?
Are you real?
I agree with Celeste. Possibly an Armorall stain . These type of stain really pop when the cement is wet.
Just wish we knew how to take it out. I would give one desire a shot.