Ask This Old House (Published August 2013 Issue) - From Q&A Section: How to get driveway mold under control?
To remove mold or mildew from concrete, clay brick, cinder blocks or pavers you will need SealGreen Mold and Mildew Remover. This product is totally environmentally safe.and simple to apply.
For a video of this process visit SealGreen Mold and Mildew Remover Video
Mix the product according to directions, apply with a garden pump sprayer soaking the surface to over saturation. Allow to rest for 10 minutes before pressure washing. For better results you can apply the cleaner a day before washing and let it sit overnight. The next day apply some more cleaner to wet the surface and pressure wash.