Within the last couple of years, a number of high frequency vibratory rollers have hit the road building market. The trend is growing so rapidly that frequency has become the one specification in which potential buyers seem most interested. Why?
The reason for their increased interest is quite logical. Higher frequency rollers offer the promise of performance at a faster travel speed. When contractors bid a job, they are expected to get the project done to a certain quality specification and within a particular time frame. If the contractor does not meet the quality and time requirements, he or she may incur a monetary penalty. Conversely, if the job is done well and ahead of schedule, he or she may be rewarded with bonus dollars - not to mention achieving decreased labor, equipment and maintenance expense. Thus, any piece of equipment that can offer the potential of more profit is understandably of great interest to the contractor.
It is reasonable to conclude that since higher vibration frequency results in faster travel speed, productivity and performance should increase as well - but that's not exactly accurate. There are some major pieces missing from this formula. Frequency is an important factor in calculating compaction performance, but it is only one factor. Although frequency capabilities influence roller productivity and performance, it does not necessarily translate into better compaction results.
Selecting the right roller for a particular operation does not need to be confusing, nor does it need to involve a certified mathematician to calculate countless performance values. It simply requires understanding some of the basic specifications found on most manufacturers' product sheets, such as frequency, amplitude and centrifugal force, and having a general idea of how these all relate to each other. Additionally, there is another rarely published specification known as "output horsepower." Derived from all three of the previously mentioned values, output horsepower can be easily calculated using information provided on any complete product sheet and provides an absolute measurement value to compare one roller's performance to another.
For more on the story, read the April issue of ROADS & BRIDGES magazine.
