Vibratory rollers have two additional variables that the operator must control during the compaction process. The first is the frequency of the vibration. Most vibratory rollers have a range of vibratory frequencies available.
With very few exceptions, the maximum possible frequency setting available should be chosen. This permits the roller to maximize the amount of compactive effort applied to the mix by minimizing the spacing between impacts.
Frequency is measured in terms of vibrations per minute (vpm). At the same roller speed, a vibratory roller operated at a frequency of 2,400 vpm will provide more impacts per foot than will the same roller operated at a frequency of 2,000 vpm.
More impacts per foot provides more compactive effort for each pass of the roller. Frequency of vibration, in conjunction with roller speed, plays a very significant role in the ability of the vibratory roller to efficiently obtain density in the HMA material.
The amplitude setting (impact height) on a vibratory roller depends on the thickness of the layer being compacted. For the vast majority of mixes placed, the roller should be operated at the lowest amplitude setting. Only when the lift thickness is greater than about 3 in. should the use of a higher amplitude setting be considered.Vibratory Roller
