Ive never tried it on concrete before... I am a Mason by trade and would recommend using muriatic acid to clean up your concrete floor. It will make the concrete look new again and take any stains out. But be careful, its vary powerful stuff and will cause you to go blind if you get it in your eyes. I would recommend diluting the acid so it works just enough to remove the stains. This will also make it a little safer to work with. And when using you want to make sure the area is well ventilated, you wear goggles, long sleeves and pants, gloves, shoes you dont care about, and a mask. Just pour into a bucket and get your dilution right, and use a stiff broom to apply. You will no if its working, if the area you applied the solution to starts to bubble. And thats it! quick and easy, and I think youll be happy with the results.