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By Rodney Garrett
Contributing Editor
Reprinted with permission, ASPHALT TODAY, February 2007

Introducing new roller technology to the asphalt paving industry is ongoing, and with good reason. Much of the technology is centered on achieving an improved pavement quality and is often combined with lower application costs. Naturally, forward-thinking contractors are willing to try any cutting-edge applications technology that potentially can be more profitable for them. Wider margins that result from lower paving production costs enable the contractor to realize greater profits and be in position to submit more competitive bids.

A contractor known for evaluating new technologies by trying them out on its construction projects is Rea Contracting Ltd., Charlotte, N.C. Rea Contracting is a wholly owned subsidiary of the Lane Construction Corp. and has 70 years of experience as a leading highway, paving and bridge contractor. Today, it is one of the biggest contractors of its kind in North Carolina.

Hiring a new manager
Rea Contracting is using a high-tech BOMAG vibratory roller on the biggest highway construction project now under way in North Carolina. Actually, there are two contracts associated with the construction project. Contract C200893 is held by Rea Contracting at a value of $99.5 million. Contract C200970 is held by R.E. Goodson Construction Co. Inc. for $76.3 million. Both contracts involve the relocation of a section of U.S. 74 to build I-74, which is considered a Strategic Highway Corridor by the North Carolina Board of Transportation. I-74 is a partially completed interstate that, when completed, will link Iowa to South Carolina.

When this project is finished, the new highway section will be 20.23 miles long with four travel lanes (2+2) divided by a variable median 46 to 70 ft wide. Each travel lane will be 12 ft wide with paved inside shoulders 4 ft wide and paved outside shoulders 12 ft wide. Rea’s contract is for constructing 11.3 miles of the highway and a cloverleaf. Highway construction stipulations call for bringing the highway alignment to the specified grade, building a drainage system, paving the travel lanes and shoulders and installing guardrails and other safety structures.

Rea Contracting started its section of the project at the beginning of December 2004, and by the end of 2006, 40% of the work has been completed. It is projected that the job will be completed at or before the end of 2008.

The high-tech roller being used on this project is a BOMAG BW190AD-4 AM (Asphalt Manager) tandem-drum vibratory roller. Central to an AM roller is the Variomatic system that takes the guess work out of achieving the wanted degree of compaction with preciseness and efficiency. Generally, the AM roller is positioned as the breakdown (lead) roller in a paving compaction train.

Here is how the Variomatic system functions on the roller: In the breakdown position and at the start of the compaction process, all of the roller’s vibratory drum energy is directed into the freshly laid “soft” asphalt. As compaction progresses throughout several passes by the roller, the vibratory drum energy increasingly is reflected back to the drums. The rate of the energy reflection correlates directly to the degree of material stiffness. As the material stiffness increases, less and less energy is needed to reach the desired material density. Essentially, a changing response to the increased material stiffness is created that is read by accelerometers installed in the roller’s front drum. A microprocessor installed in the operator’s cab in turn receives this reading from the accelerometers, computes the input data and redirects or vectors the front drum’s vibratory energy. The result of this precise density monitoring and generated energy placement control ensures no over or under-compaction of the material.

Achieving precise compaction densities with the least number of passes is very difficult for even an experienced operator to achieve using a conventional roller.