Get compaction right at night

Compacting a new road surface for optimum smoothness, rideability and density can be challenging enough during the day given the number of variables that affect them. Coupled with a veil of darkness at night, the goal can become even more difficult.

But contractors such as Highways Inc. are up to the task. Like a growing number of construction firms nationwide, the Tennessee-based company is experiencing an increased demand to take on night roadbuilding projects, due in part to the driving public's aversion to bottlenecks and detours during periods of high traffic volume typically found during the day.

Mark Odom, vice president of Highways Inc., took on his first night roadbuilding project roughly eight years ago. He currently handles about six of these jobs a year, and anticipates the number of night job bid requests to continue to rise. He certainly isn't shying away from accepting them.

Carefully monitor temperature
According to Odom, one of the biggest challenges of nighttime operations is maintaining sufficient heat in the asphalt mix to ensure proper compaction. "Cooler temperatures are more conducive to workers," he notes. "But when combined with the wind and rush of air created by excessive highway truck traffic, they cool down the polymers."

"Monitoring the temperature drop in asphalt material is very important to the success of the compaction process," states Bruce Monical, marketing manager, Hamm Compaction Division. "That rapid fall in temperature has to be handled differently at night than during the day."

The level of temperature drop between day- and nighttime operations varies depending on the region of the country in which a job is located.

For example, a compaction crew in Phoenix, AZ, will need to handle asphalt much differently at night, when temperatures may reach only 50° F, than during the day, when the ambient temperature is 110° F. "That asphalt is going through a much more rapid cooling off process, which means you have a shorter period of time for compaction," Monical points out.

Compare that scenario to crews working in central Illinois, where the temperature may be 92° F during the day, but only drop to 80° F at night. "That temperature differential may not affect the compaction process as much," he says.

In extreme cases, a dramatic temperature drop may require that more rollers be brought onto the jobsite. Operators may also have to run their rollers at higher speeds.

"Higher frequency machines can allow the operator to operate the machine at faster travel speeds, while maintaining the optimum impact spacing, which is important for density and smoothness," explains Wayne Tomlinson, training specialist, Volvo Road Institute. "If the mix cools beyond a certain point, you can't compact it anymore. You can break the rock in the mix because it can't take the energy that the drum is trying to put into it. If that happens, you're making paths for water to get in. You can also damage the machine."

The use of Superpave mixes has helped to minimize some of the challenges of nighttime operation. Because they can be successfully compacted at lower temperatures, these mixes provide crews with a longer window of opportunity to achieve optimum results.

"Polymer modified asphalt is a great invention," says Odom. "When compacted properly and at the right times, they give you a tremendous riding surface as far as smoothness and degree of compaction."

Manage logistics
Odom also emphasizes the importance of logistics in achieving proper compaction - a task that can become even more complex at night.

Odom's crews work every night, except Saturdays and holidays. "Traffic is just too great on those days," he says. "On days where you have a lot of traveling public and/or truck freight, you don't want to be trying to travel on an Interstate that is bogged down or clogged with excessive traffic."