Over the course of the past few years, the New Hampshire Department of Transportation (NHDOT) has honed its Pavement Management System to save money while also achieving environmental benefits.
In 2006, the NHDOT began researching the benefits of micro surfacing, a treatment that had never been used before in New Hampshire. Seven years later, after completing at least one micro surfacing project each year and achieving much success, the NHDOT has added micro surfacing to its Pavement Management System and has three micro surfacing projects scheduled for 2013.
Eric Thibodeau, NHDOT pavement management chief, first heard about the use of micro surfacing in surrounding states including Maine and Massachusetts. During his research he came across contractor Sealcoating Inc., located in Braintree, MA.
“They came in and did a presentation on the process, and we decided to do a test section,” Thibodeau says. “The test section was completed in 2006 and was 1.3 miles long.”
Initially, the maintenance district personnel had a positive response to the test section until it came time to plow the treated pavement.
“In the winter of 2006, we lost the painted centerlines and edge lines for that 1.3 miles because the roadway was in poor condition exhibiting extensive wheel path rutting and cracking prior to the micro surfacing,” Thibodeau says. “The cutting edge of the plows rode the high points on the road so that it shaved the micro down taking off the pavement markings.”
After experiencing these challenges with the surface during plowing, potential solutions were discussed internally to address some of the issues. Another test section was completed in 2007 on a one-mile-long section of Interstate that was in better condition compared to the first test section.
“We recognized the need to use the treatment on better conditioned roads,” Thibodeau says. “We also recessed or inlaid the pavement markings so the paint isn’t on top of the riding surface. It is recessed about 40 mils to allow the plows to ride up over it without losing the pavement markings.”
The 2007 Interstate test section showed that the surface held up well to heavy traffic, was easy to put down, and that it must be applied in good weather. “Our micro surfacing season is June through August,” Thibodeau says. “We do not allow micro to be placed before Memorial Day or after Labor Day because the temperature won’t support that kind of asphalt emulsion based operation.”
After successfully testing the micro surfacing application, NHDOT added the treatment to its Pavement Management System as a potential preservation treatment in 2008. Currently, NHDOT specifies a Type II gradation applied at a rate of 32 pounds/square yard.
As NHDOT continues to refine and improve its Pavement Management System, preservation applications are gaining momentum as a cost effective way of maintaining new construction or rehabilitated pavements.
“The standard practice used to involve performing rehabilitations on a 12 to 15 year cycle to restore pavements to new condition,” Thibodeau says. “The newer strategy is now to apply thin lift preservation type treatments like micro surfacing every 5 to 7 years to ‘keep good roads good’ and prevent the need the more costly rehabilitation.”
There are several aspects of a project that is considered before micro surfacing is selected as the pavement preservation method including traffic volume, climate and pavement condition.
“We look at traffic volume because some of our other pavement preservation treatments, like chip seals, are applicable to lower-to-medium volume roadways due to concerns for loose stones and flushing,” Thibodeau says. “Micro surfacing comes to mind with a higher traffic road.”