What is Concrete Vibration and Why is it Important?

What is Concrete Vibration and Why is it Important? . Concrete vibration is a process essential to the construction industry that ensures the strength, durability, and longevity of concrete structures. This technique involves applying vibratory energy to freshly poured concrete to remove trapped air bubbles and excess water, creating a dense and cohesive material.

Without vibration, the quality of concrete is compromised, leading to structural issues and a shorter lifespan of the structure. But what exactly does the process entail, and why is it indispensable? Let’s dive in.

What is Concrete Vibration?

The process of vibrating concrete is a vital part of any concrete pour which cannot be overlooked. Cement Concrete and Aggregates Australia, also known as CCAA, describes concrete vibration and compaction as the process which expels entrapped air from freshly placed concrete and packs the aggregate particles together so as to increase the density of concrete.

Why is it Important?

Vibrating concrete is critical because by removing air pockets & packing the aggregate particles together, it increases the density and strength of the concrete. Tightly packed particles will result in a stronger, more durable concrete structure. Concrete which has not been vibrated is full of small air pockets (sometimes known as honeycombing) which results in a poor finish and weak structure.

How is Concrete Vibration Achieved?

As a vital part of a successful concrete pour, concrete vibrating techniques have been widely used to ensure the correct compaction of concrete structures all over the globe.

Due to concrete being used in so many varying structures and applications, concrete vibrating tools come in different forms and variations. Below is the three key categories of vibrators used across the globe by concrete contractors and builders.

Immersion Vibrators

Commonly referred to as “poker” or “needle” vibrators due to its tubular shape, immersion vibrators rotate with an eccentric weight which causes the vibrations to ripple from the casing and throughout the concrete to which it is immersed to.

The vibration’s radius produced depends on the diameter of the casing, the tool being used, and the setting of its frequency and amplitude. In the current market, immersion vibrations come in different action radiuses and are powered either by fuel, electricity or compressed air motors.

When it comes to the actual process of concrete vibration, the Compaction of Concrete Guide published by CCAA recommends 15 to 20 seconds stationary insertion of the immersion vibrator until air bubbles cease to surface.

The vibrator is said to penetrate through the top layer and up to 150 millimetres into the previous layer to consistently meld both layers together when laying vertical or deep concrete pours.

Immersion vibrators are available in shaft lengths of up to 12m for very deep column applications.

Read More : What Is Self-Compacting Concrete?

Surface Vibrators

Ideal for compacting concrete slabs, roads, and industrial floors, surface vibrators offer a different approach in concrete vibration compared to immersion vibrators. This type of concrete vibrator applies an external downward force onto the concrete, making it easier to work on larger areas of flat concrete pours. However, it only reaches a limited depth and the degree of compaction is not as consistent across the width of the beam. Thus, immersion vibrators are used to complement surface vibrators, especially for slabs of more than 200 millimetres to even ensure that the particles are thoroughly and equally compacted. Depending on the desired use and the size of the concrete surface, a wide variety of surface vibrators are available in the current market, which includes: single or double vibrating beam screeds, vibrating roller screeds, and pan-type vibrators, which are mainly used on specialised road paving equipment.

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Form Vibrators

For concrete structures with high-density reinforcement, form vibrators, also known as external vibrators, are clamped to specially designed formwork. Through consistently vibrating the formwork, concrete compaction is achieved once there are no more air bubbles visibly released to the surface of the concrete pour.

External vibrators are popular in precast yards and are ideally used for concrete floors, beams, and one-sided blind walls.

Methods of Concrete Vibration

Manual Vibration Techniques

Manual techniques involve handheld tools or methods, such as tapping the formwork. Although simple, these methods are less efficient and often used for small-scale projects.

Automated Vibration Techniques

Automated methods use advanced vibratory equipment, ensuring uniformity and faster compaction, especially in large-scale constructions.

Read More : What is No-Fines Concrete?

Benefits of Concrete Vibration

vibration offers numerous advantages, transforming ordinary concrete into a high-performance material.

Improved Structural Integrity

Proper vibration enhances the interlocking of aggregates, resulting in a strong and durable structure capable of withstanding external pressures and environmental conditions.

Enhanced Surface Finish

Vibration eliminates surface voids, leading to smoother finishes that are both visually appealing and functional.

Reduced Permeability

Densely compacted concrete is less permeable, reducing the risk of water seepage and corrosion of reinforcement bars.

Consequences of Poor Concrete Vibration

Failing to vibrate concrete properly leads to significant issues that compromise the structure’s functionality and lifespan.

Formation of Honeycombs

Honeycombs are cavities caused by trapped air. They weaken the concrete and can lead to structural failures.

Weakness in Structural Integrity

Unvibrated concrete lacks cohesion, resulting in poor load-bearing capacity and vulnerability to external forces.

Common Mistakes to Avoid in Concrete Vibration

Over-Vibration

Excessive vibration can cause segregation, where aggregates settle unevenly, weakening the structure.

Under-Vibration

Insufficient vibration fails to eliminate air pockets, resulting in honeycombs and voids.

Concrete Vibrating Tips

● Do not over vibrate the concrete as it lets the mixture break and separate. Also, do not under vibrate the concrete because air might still be trapped in the lower layers of the cement pour, which leads to a weak concrete structure that easily breaks with minimum pressure.

● The most common technique with an internal vibrator is to withdraw the vibrator slowly, at a rate of around 25mm inch per second. If bubbles are still emerging as the concrete vibrator is withdrawn, more vibration is necessary.

● To prevent cold joints from occurring to concrete layers as these are poured over with a new layer of cement mixture, make sure to penetrate the pour thoroughly with a vibrator and mixing in the previously poured layer with then newly placed one.

● For maximum efficiency, use only vertical movements when vibrating to have an even mixture of aggregate and concrete. Horizontal motion can lead to uneven distribution and increases the possibility of the vibrator tangling in the rebar or reinforcing steel.

● Avoid using the vibrator as a concrete placement tool because it will not produce a consistent surface and it might even provide more problems in structural strength and form.

● Use the appropriate type of concrete vibrator depending on the structure being built or the size of the working area. Consider using a compact lightweight concrete vibrator for smaller jobs for manageability and efficiency.

● Consider having a back-up concrete vibrator on hand to have a second replacement tool instantly if the first one encounters any problems while on the job.

FAQs About Concrete Vibration

1. What is the purpose of vibration?
Concrete vibration removes trapped air and excess water, ensuring dense and durable concrete.

2. What happens if concrete is not vibrated?
Unvibrated concrete may have voids and honeycombs, leading to weak structural integrity.

3. How long should concrete be vibrated?
Concrete should be vibrated until air bubbles stop surfacing, typically a few seconds per insertion point.