Proof of performance
Many of these systems provide proof of performance, which is becoming more important as specs become tighter.
"From a quality control standpoint, there is a lot of information you can go back and review," says Sjoblad. "From a contractor's standpoint, if he can get documentation that tells him how he's done, then get someone to verify it, he's confident he can move on with the job. There are less testing costs and fewer people on the jobsite. Plus, you have documentation that tells you how uniform your jobsite is."
BOMAG's BOP (BOMAG Operating Panel) displays the stiffness, or EVIB, value of the material (as a bar scale or numerical display on screen), rolling speed, machine amplitude and temperature (for asphalt). You then have the ability to produce a printout, or strip tape. "For example, after you've made a pass, you can print out the data and quickly provide it to the quality control technician for justification and confirmation," says Dennison.
A step beyond BOP is the BOMAG BCM 05. This tablet PC shows the operator the work pattern in real time. "It won't replace any job responsibilities," Dennison states. "It's an additional tool that gives the operator and quality control personnel data earlier in the construction process, so they can identify soft spots or areas with low load-bearing capacity.
"By knowing where those are," he adds, "you can determine if you need to excavate the area, stabilize the area, improve the soil somehow, etc. The key is that you're getting information before you lay the asphalt and build the building."
Onboard compaction monitoring systems for asphalt are similar to those for soil in that rebound and response of the drum are measured, then data is fed back to the roller and/or operator. But unlike soil, temperature plays a critical role with asphalt, so the systems also include a temperature gauge.
Once asphalt reaches a certain temperature - about 140° to 150° F - it doesn't move much. If you continue to roll over it, you can over-compact it and start to shatter the aggregate, which creates more air voids.
"Sometimes operators stay on the material longer than necessary and give it another pass or two, just to be sure," says Dennison. "Experience may tell them they need a certain number of passes. But onboard compaction monitoring systems may indicate they've achieved a target stiffness in fewer passes. If you're saving passes, you're saving time, fuel and wear and tear on the roller, which are all positive things."
Compactor manufacturers are also addressing some of the challenges with asphalt by introducing drum technology that focuses on some of the obstacles.
For example, BOMAG offers drums with vectoring features that allow the drum to vibrate vertically, horizontally and at different positions in between. "The ?intelligence' in these rollers is the ability of the roller to make decisions for itself," says Dennison. "The roller can decrease the amount of force put into the material."
In addition, Wirtgen America has incorporated oscillation technology into some of its Hamm compactors. Oscillation technology adapts amplitude value automatically; ensures the roller stays in constant contact with the asphalt for faster compaction; and widens the temperature range by nearly 20%, so the roller can continue to work.
"The objective behind vibratory compaction is to rearrange the particles to draw them in and make them tighter to each other with as little air in between as possible," notes Bruce Monical, Wirtgen America. "There are a couple of ways to do that."
One is to pound the asphalt from the top down and drive impact forces at the surface downward. In this case, the force is greater at the surface than it is inside the material.
Oscillation, on the other hand, uses a side to side motion that sends a vibration wave into the asphalt. "It essentially shakes the material into place and allows the material to compact from the bottom up," Monical explains. Because it uses a "rocking" motion, the roller drums never leave the mat.