Alternative Method of Cleaning Aggregate Concrete Entryway?
The driveway and entry way are a fine 1/4 in aggregate finish and are 18 years old and in very nice shape.
Except for one area along the entryway where some white buildup or discoloration is taken root. It seems to be concentrated in an area that contains two planters and we are pretty certain whatever it is has to do with run off from the planters. The driveway and entryway were sealed with some kind of glossy sealer a few years ago but it has worn off to a point it pretty much doesn't exist visibly.
We have tried Pressure washing with 3,000 Psi, Muratec Acid 100% with scrub brush, CLR with scrub brush, Kleen Warrior (Citrus Cleaner/Degreaser) with scrubbing. Nothing has even touched it and we may have even made it a little worse. 
We thought of sandblasting or even more severe Grinding. Any Ideas?
it may be a paint residue…try some mineral spirits and a stiff brush…
your cleaning methods are the most sensible and correct, what i suggest is to scrap some of this materials and see if you can get it analyzed somewhere(University, some county office, etc.) It very well may be something simple or maybe even worse.
References :
it may be a paint residue…try some mineral spirits and a stiff brush…
References :