This buildup is nothing more than efflorescence, an annoying and ugly yet ultimately harmless affliction that plagues concrete and brick materials. The phenomenon itself is due to water leaking to the surface of the concrete or brick material, carrying salts that are otherwise locked beneath the surface. The water travels through various pathways within the concrete, bringing along salts that it deposits on the surface before evaporating. After the water evaporates, it leaves behind the salts, which harden into the white gunk that you are currently faced with.
There are three necessary conditions for efflorescence to occur: there must be salts and other chemical additives within the actual material, there must be water leakage into the concrete to bring out the salts, and there must be pathways for the water/salt mixture to travel to the surface. These three conditions are almost impossible to prevent entirely, as you cannot know, for instance, if there are any salts and/or chemical additives within your concrete.
And while efflorescence is harmless, being more of an aesthetic matter rather than posing any structural danger, it is an indicator of an even bigger issue: water leakage within your concrete, a problem that can lead to other, more serious issues such as mold, mildew, and general deterioration of the material.
In order to remove efflorescene use the Hydro-Etch 1000, a powerful, acid-based cleaner, specifically formulated to clean, brighten and etch concrete in addition to removing efflorescence and excess concrete residue.