Help me identify this invasive weed that is growing through my tarmac

[ProDave]

Yes, first dose (daily for a week until it started to turn brown) appeared to work.  Then a month later a few shoots appeared again, only in 1 of the three places, so daily does of Gallup XL for another week until they turned brown.  Finally 1 month later just 2 shoots which got the daily treatment for a week again.

 

I expect that is the last I will see of it this year as it's turned cold but fully expect to have the sprayer on standby ready to pounce in the spring and just keep at it.