Asphalt is an organic compound because of the ingredient Bitumen –an
oil product.
The coarse surface of asphalt makes a good hold for damp and dirt –which
includes nutrients- and therefore gives the algae spores' good hold.
Affective growth of algae will recur as long as there are spores left
on the asphalt surface. Sterilizing and disinfection are necessary to
stop the affect reoccur.