When concrete is poured into formwork, it can contain many air bubbles that must be eliminated to provide a solid and durable surface. These air pockets can deteriorate the concrete over time, causing it to crack and break down.
Eliminating these air bubbles requires the use of a concrete vibrator. These machines are designed to vigorously shake the freshly poured concrete, dissolving and eliminating these air pockets.
Internal concrete vibrators (also known as needle or immersion internal vibrators) rely on eccentric components inside the poker head to generate vibrations within concrete. These types of vibrators are more efficient than external concrete vibrators, which rely on the power source to drive an eccentric shaft.
They can be used on formwork, rebar and concrete to eliminate air bubbles from the mix. They are also a valuable tool in concrete repair, where they can help to re-consolidate previously poured slabs and walls before they’re removed.
The insertion level and removal speed of the vibrator are crucial to the effectiveness of concrete vibrators. Under-vibration and hit-and-miss insertion can result in uneven compaction, whereas a regular pattern of insertions and removals ensures a smooth and consistent end product.
When pouring new concrete in formwork, the vibrator should be inserted quickly all the way to the bottom of the form, and left there for 5 -15 seconds before it’s slowly withdrawn. This will disperse entrapped air and prevent cold joints from forming between the previous layer of concrete and the next.
For more comprehensive compaction, consider using a single internal vibrator in conjunction with surface or immersion vibrators. These devices are suitable for concrete that is 6 inches deep or less and can be used on a wide range of projects.
If you’re working on a project with a large number of formwork, a multi-head vibrator can save money and provide more complete concrete vibration than a single internal or surface vibrator. However, it’s important to note that the vibrators’ vibration frequency must be limited to 11,000 vpm to avoid damage to the concrete mix.
The rebar vibrator helps to remove air from concrete by creating small, but sufficient forces that separate the rebar from the concrete. These forces, when combined with a strong sonic hammer blow, will improve the overall density and strength of the entire mass of concrete.
Rebar vibrators are most effective on wall and column foundations because the rebar is usually in a position to be consolidated by vibration alone. Nevertheless, the vibrators can be used to compact the surface of the concrete on columns, which will reduce or prevent cold joints from forming.