Vibration: It's a Small Margin

Figure 1 Description: A probe is inserted at a distance away from the vibration source and the transfer of force at a rate is analyzed. The concrete is then subject to destructive testing to measure consolidation versus material separation.

As the vibration research information comes in supporting frequency limitations for the new ACI Consolidation Guide, we find a uniform theme. No matter what the concrete’s slump value, the margin of frequency between adequate consolidation and material separation from over-vibration by higher frequency is only a range 1,500 vpm range.

When frequency targets were met before the use of water reducing agents for pumping concrete, they were tested with a product that had no frequency controls. Now that testing is done in many of the concrete application categories, we begin to understand how vibration should be applied to different mixtures. Researchers have technologies to properly analyze what vibration does to the concrete. The verdict is predictable---as workability gets greater vibration should be decreased.?

10,000 vpm was recorded as a maximum value to consolidate 4-inch structural concrete in 1970. It then was treated as a minimum value. As the frequency increased in vibrator design, the design of pumpable mixtures called for less vibration. For many carbon saving reasons this is no longer acceptable. It is a small margin between sustainable practices and wasteful carbon generation ---about 1500 vpm.?? ???