Concrete contains cement, whose content of resin gives it organic qualities.
Therefore the moss spores are supplied with the nutrients it needs to
The concrete surface becomes damp and therefore binds dirt which also gives nutrients to the moss. When the moss has gained a foothold, it grows fast and gains a secure hold in the concrete pores.
Spores and residues of growth on the surface pores enable the affection to recur constantly. The only way to prohibit and counteract affection is to sterilize and disinfect spores and moss.
The surface gets disinfected and makes it impossible for new moss to grow on it.