The Process:  The concrete arrives at site containing your chosen aggregate or pebble belnd. The concrete is placed and then sprayed with a surface retarder which slows the curing process down.  When the concrete is sufficiently hard, the thin film of concrete on top is "washed off" to reveal or "expose" the aggreagate or pebble. At a later date the surface will then be acid washed and possibly sealed, depending on preference and budget.