This is a monoblocked patio and driveway with a blonde circle kit and retaining wall that finds its self being discoloured by algae and traffic.
The picture shows the start of the cleaning process but just as important is what happens after the area is cleaned.
In most cases kiln dried sand is applied to all gaps between the bricks, this is sand dried in a Kiln which extracts the moisture allowing it to smoothly fall into the gaps of the bricks, the idea is that you stop any movement in the mono block by filling the gaps between them. This process also inhibits weed growth and stops the buildup of organic matter between joins, adding to the longevity of the cleaning.
We always re-sand after our jobs and I recommend if you are doing it yourself that after every pressure wash the driveway is re-sanded.