Climate also plays a determining role for the choice of where to use micro surfacing. “In this state we have everything from seacoast to mountains,” Thibodeau says. “We get more snow in the mountain areas so we have more plowing activity and snow removal in those locales. Micro surfacing is not considered for that type of environment knowing it will be plowed more aggressively than in the southern part of the state.”
Sealcoating Inc. completes micro surfacing
Dan Patenaude, of Sealcoating Inc., has spent the past 10 years partnering with dozens of agencies up and down the east coast helping them optimize their pavement management programs and assisting in developing and completing many micro surfacing projects.
Sealcoating Inc. completed three micro surfacing highway segments for the NHDOT this past season including NH 25 Tamworth-Ossipee, NH 9 Chesterfield and NH 12 Troy-Swanzey.
On the NH 12 Troy-Swanzey project, Sealcoating Inc. completed prep work including some isolated mill-and-fill spot repairs of areas too distressed to be suitable for micro surfacing.
Crews also cracksealed all existing cracks to prevent water from penetrating the surface. The existing thermoplastic and other built up pavement markings were removed so that the new micro surfacing would adhere directly to the existing asphalt.
Once the prep work was completed, crews readied themselves to complete the actual micro surfacing application.
“After the selection of suitable pavement candidates for micro surfacing the next step in the process is to develop a mix design based on suitable local aggregates,” Patenaude says. “The aggregates must be high quality and meet very specific gradation and durability requirements. They must also be compatible with the asphalt emulsion to be used on the job.”
Aside from the aggregates, additional components of the micro surfacing material mix include a polymer-modified asphalt emulsion, a mineral filler such as Portland cement, water to enhance mix consistency and workability, and a field additive to adjust the set time of the material as temperatures and other environmental conditions change throughout the project.
“Once a mix design is developed and the prep work of the existing asphalt surface is complete, crews and equipment are mobilized to a staging area near the project where the aggregate has been stockpiled,” Patenaude says. “There, the micro surfacing paver is calibrated for the local aggregate and other mixture ingredients to verify compliance with the mix design, and then the equipment and materials are moved out onto the roads where paving is to be done.”
The contractor used a continuous feed paver as well as support trucks to shuttle the aggregate, emulsion and water from the staging area out to the paver on the road. The asphalt emulsion was supplied by Ergon with the majority of the micro surfacing equipment manufactured by Bergkamp.
“The goal is to have enough of those feeder trucks available so that the paver can pave non-stop minimizing the transverse paving joints,” Patenaude says. “After traffic control patterns are established the tack coat is applied and projects include a two-course application of the micro surfacing materials.”
According to Patenaude, NHDOT typically specifies a total of 32 pounds per square yard with the first lift of material applied at about 16 pounds per square yard and the second coarse applied at about the same rate.
“We prefer to do the ‘scratch course’ [first lift] and the wearing course on successive days to ensure that the majority of the water in the bottom course material is evaporated and cured out before covering it with the second layer,” Patenaude says. “Both layers are usually cured adequately to put traffic on them within about 45 minutes of paving — depending upon the temperature and humidity at the time.
“After paving, temporary pavement markings are applied, and about a week later when the micro surfacing is near fully cured the permanent pavement markings are applied.”