The Coke works because it has a very high phosphate content. Remember when we had to stop using phosphate based soaps and detergents? They worked well, but had to be removed from the environment. Never mind that 2/3 of Florida and 1/2 of western Canada is phosphate rock. Anyway, always be careful using soaps, (simple green, joy, tide, etc.) early in the cleaning cycle. The soaps will lift the oils and then cause them to seep deeper into the concrete. This only compounds the staining. Absorb as much as possible with
oil dry, cat litter, dirt, portland cement, etc. Then start the soap application. But put more absorbant on very soon after. This will wick the
oil to the top rather than gravity pulling the stain deeper. Some soaps emulsify (make water soluble) the
oil. But ALL soaps break the surface tension of the water droplet and allow it to pass thru smaller pore spaces. This is why it will go deeper into the concrete.
RP