22/05/2022
CONCRETE VIBRATION
- WHAT IS IT AND HOW IS IT DONE?
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. 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 vi*****rs used across the globe by concrete contractors and builders.
IMMERSION VI*****RS
Commonly referred to as “poker” or “needle” vi*****rs due to its tubular shape, immersion vi*****rs 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 vi****or until air bubbles cease to surface.
The vi****or is said to pe*****te 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 vi*****rs are available in shaft lengths of up to 12m for very deep column.
SURFACE VI*****RS
Ideal for compacting concrete slabs, roads, and industrial floors, surface vi*****rs offer a different approach in concrete vibration compared to immersion vi*****rs. This type of concrete vi****or 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 vi*****rs are used to complement surface vi*****rs, 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 vi*****rs are available in the current market, which includes: single or double vibrating beam screeds, vibrating roller screeds, and pan-type vi*****rs, which are mainly used on specialised road paving equipment.
FORM VI****OR.
For concrete structures with high-density reinforcement, form vi*****rs, also known as external vi*****rs, 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 vi*****rs are popular in precast yards and are ideally used for concrete floors, beams, and one-sided blind walls.
Click here for more information on electric external vi*****rs.
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 vi****or is to withdraw the vi****or slowly, at a rate of around 25mm inch per second. If bubbles are still emerging as the concrete vi****or 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 pe*****te the pour thoroughly with a vi****or 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 vi****or tangling in the rebar or reinforcing steel.
● Avoid using the vi****or 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 vi****or depending on the structure being built or the size of the working area. Consider using a compact lightweight concrete vi****or for smaller jobs for manageability and efficiency.
● Consider having a back-up concrete vi****or on hand to have a second replacement tool instantly if the first one encounters any problems while on the job.
