Before we go through the ways of minimizing the appearance of efflorescence, you need to understand about primary and secondary sources.
Primary
As the concrete cures, some of the water mix reacts with the cement to produce Calcium Hydroxide, as the paving dries the water evaporates leaving the water-soluble Calcium Hydroxide behind, creating the white marks you can see on the paving.
Secondary
Concrete products such as paving can have a relatively quick turn around time from the factory this comparatively brief time leaves the paving curing while on site. When the paving is used and laid into the ground it leaves them exposed to external factors like rain and water from the earth. These "secondary" sources will dissolve and transport Calcium Hydroxide to the surface from the curing paving.
Ways to minimize efflorescence
The ways contractors can minimize the effects of secondary sources of effloresce are threefold. Use as little cement in the bedding mix, this minimizes the amount of additional Calcium Hydroxide that can be drawn through to the surface of the paving. Use as dry a cement mix as possible, reducing the amount of water will lower the amount of Calcium Hydroxide dissolved and brought to the surface. Using a bond bridge like a slurry primer can reduce the amount of water pulled through from the mortar bed.
Using an efflorescence remover if all else fails
Using a product that removes Calcium Hydroxide from your paving can help with large deposits while also reducing the amount left in the paving we recommend the following product. EASY Care - Efflorescence Remover Plus - 1 Litre