Vibrating Concrete

Mechanical vibrators are used to compact freshly placed concrete in forms and around the reinforcement to expel the entrapped air and form a dense concrete mass.

Commonly, an internal vibrator, such as a poker vibrator, is plunged swiftly through the entire thickness of the freshly placed concrete and partially into the underlying layer of concrete existing in a plastic state. 

Vibrations are provided every 2 to 3 feet along the concrete surface for durations spanning 5 seconds to 2 minutes, depending on the concrete's consistency.

The poker is gradually pulled to ensure that the space it had occupied in the concrete seals naturally. 

Unlike internal vibrators that work directly on the concrete, external vibrators are firmly attached to the formwork via an elastic support, allowing simultaneous vibration of both the form and concrete.

It is used for precast or thin in situ sections and may require positional adjustments during concrete pouring.

Alternatively, a vibrating table can be used to provide uniform vibrations to precast concrete units by clamping the formwork to the vibrator.