A concrete vibrator is a heavy tool commonly used at construction sites which involve a lot of concrete pouring. These machines ensure that the concrete pour is free of air bubbles that may potentially weaken the structure. This process is essential to concrete pouring, as it guarantees that the concrete remains strong long after it has hardened.
Concrete is a simple mixture of four basic components: water, cement, sand and rock. But a lot of problems can occur at every stage of the concrete production process: the concrete might be incorrectly mixed, too much water added to the mixture, or the poured concrete improperly cured. A simple mistake can quickly snowball into bigger problems like cold joints and honeycombing. These can drastically affect the overall quality of the pour, leading to a poor and uneven concrete finish or worse, structural failure.
Immediately after a pouring, the concrete can contain as much as 20% trapped air. This percentage varies with the mix type and its slump, the amount of reinforcing steel, form size and shape, and placement method. A properly consolidated pour is essential in ensuring optimal concrete strength. Without concrete vibration, the trapped air leave behind a void that drastically weakens the concrete. The vibration process can improve the concrete’s compressive strength by 3% – 5% for each percent of air bubbles eliminated. While it is impossible to remove all trapped air, the vibration process eliminates most of it.
If you’re new to the construction business or looking to honing anew your skills, here are a few tips and pointers about proper and effective concrete vibration. I hope you’ll find these handy and informative.
Even if you properly vibrated the pour, it won’t make a difference if the concrete wasn’t handled and poured correctly. Make sure you have a backup plan for incidents and mistakes that may occur at every stage of the process, and to have spare concrete vibrators and other tools and machinery.
Do not pour without planning beforehand. Design a scheme for pouring to ensure the concrete settles well and to keep mistakes from occurring. Check if the concrete mixture is correct and properly mixed. Use a superplasticizer or water reducer if it’s too runny.
When pouring the concrete, take into account the presence of reinforcing bars. Rebar tends to interfere with the pour, sifting out sand and rock from the mortar and creating air pockets.
Do not use a concrete vibrator on self-compacting/self-consolidating concrete
UP AND DOWN
When using a concrete vibrator, only do so in a vertical motion. Moving the concrete vibrator side to side can create uneven aggregate and concrete mixtures. Apart from visible flow lines and possible discoloration, you are also more likely to entangle the concrete vibrator in the rebar. Remember: up and down.
Do not move or dip the concrete vibrator into the pour too fast. Let it down slowly, and use the weight of the concrete vibrator to allow for natural sinking into the bottom of the pour. Let it sit there for 10-15 seconds, then pull it out an inch per second. You’ll know you’re doing it right if you see large bubbles coming out of the concrete pour surface and a layer of mortar.
TYPE OF CONCRETE VIBRATOR
Not all concrete vibrators are built the same, and it’s important to gauge your work-site needs so you’d know what kind of concrete vibrator to use. First element you need to consider is the size of the concrete vibrator. A rule of thumb: the more concrete you’re working with, the larger the vibrator.
For precast work, you can use external concrete vibrators that is mounted on the exterior of the form-work. Ideal for larger pours, the external vibrators are spaced 6 inches apart.
When the slab is not less than 6 inches deep, you can use large concrete vibrators that are placed manually on the surface of the pour. One advantage of using a jumper vibrator is they provide a smooth surface, improving the appearance of the slab.
But the most common vibrators used at work-sites are internal concrete vibrators. Used by a single operator, the user just dips the concrete vibrator down into the concrete pour, then withdrawing it slowly.
Depending on the strength of the vibrator used, different amounts of poured concrete are worked and affected by the vibration. One way to calculate this is to measure the size of the action radius of the vibrator. When working on a pour, make sure these action radiuses overlap one another to ensure maximum coverage. It is always better to have more overlap than not enough.
OVER-VIBRATION AND UNDER-VIBRATION
The operator should strive to avoid under-vibrating and over-vibrating the concrete pour, although it’s typically better to over-vibrate than to under-vibrate. Under-vibration can cause many problems, such as honeycombing, bug holes, cold joints and not enough trapped air removed.
As you’ve seen, one small mistake can snowball into a colossal concrete disaster. Always keep in mind to be cautious and to keep your focus during every step of the concrete process. While concrete vibration is just one part of the pouring process, it is also one of the most important ones, and screwing up this part won’t only lead to costly delays, it can also cause death and injury if the structure fails. Never compromise quality for speed, as the future welfare of the occupants depend on the quality of work done today.