Did you power wash or pressure wash? Pressure washers are not always that effective in removing stuff from concrete. Power washers are better because they use extremely hot water.
Assuming you used a pressure washer, your best bet is to rent a floor maintainer and purchase a couple of green or black scrub pads to go with it. Working in sections, mix up a strong degreaser solution and pour it out on the floor. Let it soak for 5 to 10 minutes, then run the scrubber over it. Rinse and move to the next section. It is one of the more effective ways of cleaning concrete.