Well be careful if you to use a pressure washer. Too much pressure too close to the brick or concrete will blast away the finer material that was encouraged by brick makers or cement finishers to come to the top. After I did that to one of the sidewalks leading up to a house I used to have, then I had even more head aches with maintaining the appearance of it. Might be why I just don't care anymore about such.
However a slurry of powdered laundry detergent as someone else mentioned along with just time will let the stuff in WD40 disappear. It was clean WD40? Or was there chain gunk mixed in?