Whats the most effecient method of removing paint from a concrete porch floor ?

I'm trying to remove six layers of oil based paint from a concrete porch floor. Already tried power washing with limited results. Next I tried a gell based oil paint remover and that method has not been very effective as well. Already used one third of a gallon for a 3 x 4 area. At nearly $ 30.00 a gallon it will end up being a very expensive project. Before going any furthur, does anyone have any suggestions that will yield more effective results ?