We have discussed different beneficial effects of re-vibration of concrete. We have learned that the concrete becomes improved by the rearrangement of aggregate, expelling air and water thus improving bond strength of concrete and better bond strength producing less development length. As steel is saved, strength is increased and concrete becomes watertight as well, the re-vibration, no doubt, produces better concrete with some extra and wise effort, not changing economy.
Now question is-----if concrete is hardened and vibration is done forcibly, is it produce strong and durable concrete? Now, we, in this post, will learn about the high time to be re-vibrated fresh concrete or partially set concrete.
|Leaving vibrator head to sink |
into concrete to its own weight
Normally, the time is measured from application of initial vibration of concrete, applied previously.
In the previous post, in defining, beneficial effect, we have used a phrase “repeating of vibration for a long period”. Now we will learn how long the period is. The answer is re-vibration/ or repeating effort of vibration should be between one hour just initial vibration has applied to fresh concrete.
The plastic shrinkage cracks and other drawbacks of not sufficiently compacted concrete like void space below coarse aggregate and reinforcing bar can be closed to form compacted concrete, only when repetition of vibration head immersion results a soft concrete.
It is wise to apply vibration at maximum as possible from initial vibration time but condition is concrete should be plastic and no effort is required by vibrator operator to sink the vibrator head i.e. the head immersed into concrete to its own weight. So proper timing is important to re-vibrate a concrete mass otherwise it doesn’t result well. In the next post we will discussed about what is happened when hardened concrete is disturbed. This point is very important in concrete technology as with the best ingredient we cannot produce a best concrete without a best techniques. Please stay with us.