Technology designed to help you achieve your soil and asphalt compaction objectives has made tremendous headway in recent years, and is continuing to evolve at a relatively rapid pace. Its ultimate goal is to quantify density on the run - i.e., identify density in real time under the roller.
While the technology isn't quite there yet, there are several options currently available that can help you quickly and effectively reach target densities.
Monitoring soil stiffness
Soil compaction has essentially led the way with onboard compaction monitoring. As early as the 1980s, Europeans were using these systems to help determine the effectiveness of the compaction process. Similar systems began appearing in the U.S. earlier this decade.
At the heart of onboard compaction monitors is an accelerometer that measures the response or rebound of the drum in respect to the frame.
This measurement allows a stiffness value to be displayed and correlated to density. (It's important to note that stiffness is not the same as density.)
For example, loose, lightly compacted soil or asphalt will have a smaller response or rebound. "As you make successive passes, you typically will get a higher degree of rebound and a higher reading," notes Dave Dennison, BOMAG Americas.
This information can be used by an intelligent compaction roller - a roller equipped with a documentation and feedback system - to automatically adjust parameters such as vibration direction. The roller operator can also use the stiffness data to determine at what point to conduct traditional sonic and nuclear density tests and spot core tests.
"Currently this new technology needs to be used in conjunction with existing density tests," says Dennison. "We're not at a point where it can replace those tests. It's another quality control tool contractors can use to reduce the cost of the job by, in one way, reducing the number of core samples that may need to be taken."
"These systems provide operators with instant feedback and information they wouldn't otherwise have," adds Jon Sjoblad, Caterpillar. "The technology allows operators to be more proactive, and it provides information needed to make the correct choices to most efficiently build a good base."
Mapping a clearer picture
GPS mapping systems are also becoming more accepted on compactors. They can help "paint the picture" by showing an operator's work pattern in real time, plus can improve night-time operations where darkness may obscure the rolling pattern.
"GPS is another quality control tool," says Dennison. "It shows areas you've covered, and how many times you've covered them. Plus, it shows you areas you may have missed so you can get higher quality, more consistent compaction that should result in more consistent density."
Take Caterpillar's AccuGrade Compaction GPS Mapping and Measurement System, which ties in with the family of AccuGrade earthmoving technologies and grade control systems, including the analysis software suite AccuGrade Office. It allows you to track jobs and monitor productivity to ensure quality, as well as find hidden efficiencies on the job.
"These systems can improve quality through process control," Sjoblad explains. "Previous to these systems, operators would rely more on their senses, then wait for verification. There's downtime in this scenario. Also, only localized spots are tested, so you never really know if the whole job is compacted uniformly. There can be areas where there is poor compaction. But with this technology, you can see visual indications of compaction over every square foot.
"Uniformity is important," he continues. "If you have localized areas that fail, you have to go back and fix them. And remediation is a lot more expensive if it is done after pavement is laid, compared to fixing problems while the ground is open. An onboard compaction monitoring system can pick up hidden clay balls that a tester might miss. It boils down to if you can see it with the compaction monitoring system, you can fix it."