What is revibration, and is it harmful?
Vibration done some time after the concrete has been placed and consolidated is known as revibration. When properly done, revibration can be beneficial. It is most effective when the running vibrator will just barely sink from its own weight and energy, which may in some circumstances be several hours after casting. Revibrated concrete may be considerably stronger and more free of bugholes than ordinary concrete, but care must be taken, especially with architectural concrete, not to allow the vibrator to penetrate into a layer of hardened concrete below.