The rear entrance pathway at the southern side of the external 'common area' pools a thin vale of rain water (near the access door) causing unsightly green mould that will eventually undermine the structural integrity of the concrete slab. 

Application of a waterproof membrane sealant that slightly slopes away from the doorway should rectify this problem, particularly as it is a very low traffic pathway, so that a waterproof membrane would not be warn away from foot traffic. 
A waterproof membrane would likely only need to be applied over the concrete surface area up to about 50cm before the edge of the vertical brickwork in the immediate below photo on RHS.  The maximum thickness would likely be 12mm immediately outside the door, tapering down to about 3mm, so that rainwater ran-off and didn't puddle.

A tradesman expert in waterproofing such concrete pathways needs to be engaged

Bunnings sells Crommelin 15L Water Based Paving Sealer for $180.50.  One tub should suffice. However, an expert tradesman may prefer a different waterproof sealant