Mechanical vibrators are instrumental in compacting newly poured concrete within formwork and around reinforcements. This process is essential to eliminate trapped air pockets and establish a dense concrete mass. One widely used method is vibrating by internal vibrators, often referred to as a poker vibrator or immersion vibrator. It is rapidly inserted through the full depth of the freshly laid concrete and slightly extends into the layer below it (which remains in a plastic state). Consistent vibrations are applied across the concrete surface at intervals of every 2 to 3 feet for a period of 5 seconds to 2 minutes, depending on the consistency of the concrete mix. As the vibrator is slowly withdrawn, the hole left behind is naturally sealed, preventing the formation of voids.
Another method employs external vibrators that are attached to the formwork to vibrate the formwork and the concrete simultaneously. This is used for precast elements or thinner sections of concrete. In contrast to internal vibrators that directly vibrate the concrete, external vibrators do additional work by vibrating the formworks, making them less efficient than the internal vibrators. Occasionally, external vibrators have to be shifted from place to place depending on the placement of the concrete. For precast concrete units, a vibrating table is used, wherein the formwork is fixed directly onto the platform to achieve a uniform vibration throughout the unit.
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.
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