My wife pointed out the ‘stripes’ were too close together so I ran my hand across them and they are actually ripples in the concrete. The sun was setting and highlighted it, making it look like stripes.
The place was built in 1982.
Any of you concrete gurus know what’s going on here?
Too uniform and close together for it to have been caused by you. It was already there, I tell people all the time we won’t know what we have until we get the dirt off. Dirt and organics are wonderful camouflage.