Concrete Vibration Tips
Concrete can be poured easily but when it comes to vibration, it’s all about quality. A good quality process will ensure that your concrete is finished properly and that it will have the required strength once it reaches its 28 day life. Here are some do’s and don’ts about concrete vibration.
Concrete Vibration Best Practices
- Before starting a job, be sure to have a spare vibrator ready as a backup plan.
- Do not over vibrate concrete. Over-vibration of concrete will lead to honeycombing instead of reducing it. It will also cause the concrete to lose air, sometimes as much as one half of the air content.
- If you are pouring a low slump concrete be sure not to under vibrate it, as honeycomb will also be a problem.
- Concrete with higher slump will require little vibration.
- When pouring self-consolidating concrete, the vibration shall be discarded.
- Be sure to penetrate previous lift or layers of concrete already placed to reduce cold joints. The vibrator shall penetrate at least 6 inches into the previous layer
- The vibrator shall be penetrated vertically to maximize its effects
- Do not over-bend the vibrator, it will fail
- A common mal practice is to use the vibrator as a concrete placement tool. If you do this, you could be creating an inconsistent surface and the concrete mix will be affected in certain areas.
- Concrete vibrator shall be hold at least 10 seconds into the concrete mix
- Vibrator shall be pulled up at an average rate of 3 inches per second
- Remember to use hand spading or puddling.
- Every time the vibrator is inserted, it radius of action shall overlap from the previous one. Remember that every concrete vibrator has its own field of action. It is estimated that the field of action is four times the vibrator tip diameter
- Vibration shall be stopped when air no longer escapes concrete
- The vibrator shall not be turned on outside of the concrete.
- Stop vibration concrete when the concrete surface takes on a sheen
- Do not force the vibrator into the concrete; it might get caught in the reinforcing steel.
- Not all concrete vibrators work for all jobs
Concrete Vibration Benefits
A good vibrated concrete will offer some benefits such as:
- Have a higher compressive strength.
- A properly vibrated concrete will increase the bonding capacity between concrete and rebar.
- Provide a better sealed concrete surface reducing its permeability.
- Reduce cold joints, honeycombing and segregation
- When the builder knows how to vibrate concrete, it can order drier mixtures that require less cement
- Offers greater durability
- Bonding strength between layers of concrete will increase
- Horizontally spread layers of 20” thick, will provide with best results in concrete
Now that you know the basics of concrete vibration, we also need to discuss a common issue that takes place in construction projects. Sometimes, the vibration starts late, even when the concrete has already started its chemical reaction. Once the concrete reaches its initial set, concrete could be vibrated as it will interrupt the chemical process that forms calcium hydroxide. By interrupting this process, and if concrete is plastic enough so the vibrator can sink by its own weight, you can eliminate joints that could occur if the revibration is not done. Revibration is permitted but it is a controversial action to do.