This is not my area of expertise; however, I was able to locate this item:
http://www.essortment.com/articles/remove-molds-concrete_3612.htm
Kevin Bristol, President of Advance Mold Remediation states, "concrete needs to be scrubbed down" in a process "called wire brushing, where you apply a chemical biocide to the actual concrete and you scrub it until the mold is gone". In some cases you can remove and clean up the mold on your own. If the area is larger than 10 or 12 feet you should call a mold removal specialist. If you, "do try to do it on your own you need to have the right equipment and chemicals. You should also wear a respirator, not just a paper face mask and make sure the area is properly ventilated so that the odor will dissipate" states Bristol. When mold is embedded in concrete, using a biocide is the only cleaner that will work permanently and usually this kind of chemical is not available to the general public. If the area is small and you would like to try to clean it yourself, use a wire brush and scrub it with ammonia. You can use a solution of bleach and water, but never mix bleach and ammonia together as this will let off poisonous fumes that can be very harmful.
*~ Good luck ~*