Building smooth roads in Mississippi

Case Studies
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Dunn Roadbuilders, Laurel, Miss., owns and maintains a substantial fleet of roadbuilding equipment. Unlike other similar companies, Dunn has its own asphalt plants and QC/QA labs to ensure a quality end result.

A few years back, Ken Welborn, local sales representative for Stribling Equipment, pulled up with a new Sakai double-drum roller in tow. Operations Manager Randy Adams and QC/QA Materials & Plants Manager Rick Croy were skeptical but impressed after taking a look.

The Dunn roller fleet now includes eight Sakai rollers. Adams said the company owns four SW900s, which are the larger 84-in. machine, and four 67-in. SW800s.

“When we’re doing mainline paving of state and interstate highways, two of the 900s turn the trick,” Adams said. “With 4,000-vpm high frequency, we’ve had great success with a pair of Sakais in tandem to make breakdown density on some pretty tricky Superpave mixes.”

Croy keeps a keen eye on the mixes he designs and how they act in the field.

“The paying public rarely applauds a great paving job. But they sure let you know when they don’t like it,” he said. The state of Mississippi pays bonuses for a smooth ride and imposes stiff penalties for failure to meet density. These problems can also give a company a bad reputation.

Using the Sakai rollers, Dunn saw excellent results and has maintained its strong reputation.

Mississippi mixes come in three different sizes and the choice of mix is dependent on traffic volume, size of road and other factors. These contemporary Superpave mixes can be difficult to compact, and the mix turns tender shortly after laydown. “So we have to get on it and off it quickly, gaining density fast,” Adams said.

The Sakai rollers were created for this type of job. Asphalt Compaction 101 dictates that vibratory compaction is best achieved at impact spacings between 10 and 12 per ft. This impact spacing is key to gaining the highest density in
the shortest time.

Rolling too fast causes the impact spacing to stretch, increasing the number of passes required to achieve density. This affects smoothness and the bottom line. Rolling too slowly, on the other hand, achieves density at the expense of productivity.

Since the frequency and speed of the roller determine impact spacing, a high-frequency roller will permit higher rolling speeds at the same target impact spacing. These speeds allow the rollers to beat difficult tender zones while gaining necessary compaction. In addition, the standard counter-rotating eccentrics direct the centrifugal force downward as opposed to interacting the mat at an angle.

“Other key considerations challenging contractors working with Superpave are distance from the plant to the site, ambient temperature and wind, all of which affect laydown temperature and thus the window of opportunity to compact the mix properly ahead of the tender zone,” Croy said. “ Sakai rollers help us meet those challenges every day.”

The latest Sakai double-drum asphalt rollers can be seen this coming week at ConExpo ’08 in Las Vegas.

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