Micro Surfacing for Maintenance

Minnesota DOT redefines its paving role with truck-mounted micro surfacing machines

Like many agencies across the country, the Minnesota Department of Transportation (MnDOT) has addressed its road maintenance needs in a number of ways over the years. As the organization’s reliance on pavement preservation has grown, it has come to practice a variety of methods in order to keep its network of roads in good condition.

“For the Minnesota Department of Transportation, and across the country, local governmental paving crews are slowly becoming a thing of the past,” says Paul Nolan, Project Supervisor, MnDOT Materials and Road Research.

He explains that similar to many agencies, the end of MnDOT’s fiscal year is June 30. As a northern-climate state, the weather always plays a role in funds availability at the end of the fiscal year. The amount of overtime paid for snow and ice removal, as well as funds spent on roadway anti-icing chemicals and salt, all significantly affect the available funds for road maintenance and paving as spring and summer arrive, and the fiscal year is drawing to a close.

“To have these fiscal constraints hanging over the head of a paving crew makes any work prior to the new funding stream on July 1 very tough to predict. And to have the expense of all the necessary paving equipment just sitting for the first part of an already short construction season doesn’t make a whole lot of sense, either,” he says.

On the other hand, MnDOT decided several years ago that the argument for retaining specific equipment to preserve and maintain pavement does make a great deal of sense. In particular, the agency has become a strong proponent of micro surfacing.

Redefining the Process

According to Nolan, for certain projects, the MnDOT highway maintenance management decided to move away from traditional paving with asphalt, and instead chose to purchase a micro surfacing machine.

The versatility of micro surfacing as a preventative maintenance strategy appealed to MnDOT, as the treatment preserves pavement, sealing cracks and locking out moisture. The method is beneficial for safety improvements, such as adding surface friction, rut removal, and wedge paving on sunken bituminous shoulders along a concrete mainline. Nolan says it also is an inexpensive application to fill in the pavement until more permanent solutions can be made.

“Micro surfacing requires less equipment than traditional paving – no rollers, mills, or lowboys needed,” Nolan says. “We don’t have to worry about the installation of new utilities. No need to worry about traffic loops.”

“Rock and mineral filler can be bought and stockpiled throughout the year. Having the dry material on hand requires only the emulsion to be purchased at or near the time of the project. This process has allowed the crews to be out working in late April, May, and June,” he says, adding, “We’re very fortunate to have quality rock sources readily available that react well with the emulsion.”

Incremental Progression

MnDOT’s first micro surfacing paver was a VSS Minimac Micro-paver. Nolan describes the machine as a Zamboni-sized paver used to fill in one wheel rut at a time. He says it proved to be helpful in filling in deteriorated and raveling cold-joints between lanes. “This unit served MnDOT well, but we are retiring it because truck-mounted micro surfacing units can do most everything that the smaller Minimac can do, plus much more,” he says.

The agency purchased its first truck-mounted micro surfacing paver, a Bergkamp M310, in 2012. The machine was shared between the MnDOT Metro (Minneapolis) District and the St. Cloud District 3. In September 2018, MnDOT took possession of a new Bergkamp M310E truck-mounted micro surfacing machine, which stays in the Metro District; the older Bergkamp machine will remain in the St. Cloud District.

The M310E truck-mounted slurry seal and micro surfacing paver receive power from a Tier 4 truck engine that fulfills stringent emissions regulations. Designed with customer feedback playing an important role, Bergkamp developed the M310E with the same proven design, efficiency, and productivity as its original M310 paver, but with PTO-driven hydraulic pumps that allow the elimination of the side engine. This feature, along with the Tier 4 truck engine technology, allows customers to reduce their emissions reporting and equipment maintenance needs.

The M310E utilizes direct-drive hydraulics that is controlled by Bergkamp’s advanced EMCAD (Electronic Mix Control And Diagnostic) System, which is designed to manage power inputs and electronically control material outputs to maintain the desired mix design. Standard on the older M310 and M310E, EMCAD displays current and average material ratios, total material used and material application rates, eliminating manual calculations and simplifying calibration. In addition, it electronically self-diagnoses and displays easy-to-read indication lights and diagnostics, reducing troubleshooting and repair time. Even less-experienced operators can quickly make adjustments during production without compromising the accuracy of the mix. EMCAD can produce on-demand and end-of-day reports to track production for individual sections of the job, or the entire job, via an onboard printer. Ultimately, the system allows the operator to control the production with simple adjustments, while the driver progresses at an optimized rate of speed – ensuring faster project completion.

MnDOT utilizes a two-fold approach with its use of micro surfacing for pavement preservation. For major roadways, the agency bids the work out to contractors. For smaller areas such as ramps, frontage roads, and intersections, MnDOT uses its own M310 and M310E micro surfacing equipment.

“The work that our machines perform are small projects, like exit and entrance ramps, hard-to-get-at locations, and intersections,” says Nolan. “MnDOT still contracts out several hundred lane miles of micro surfacing each year by contract. Our truck-mounted machines are not set up to do continuous paving for larger projects, and it would not be practical to try and get the contractors in to do the small-footprint projects that we now handle.”

Small Projects – Big Benefits

The benefits of handling its own micro surfacing for small projects, using the Bergkamp truck-mounted pavers, have proven themselves to MnDOT over the past six years. Nolan ticks these benefits off in rapid progression:

• MnDOT has the ability to stockpile dry materials when surplus funds are available.
• Fewer employees are needed to run the crew.
• Micro surfacing work offers a safer environment – no hot products, no hot off-gassing.
• Micro surfacing is ideal for smaller areas that need attention – ramps, frontage roads, intersections.
• No need to worry about traffic loops.
• Micro surfacing improves friction, fills in rutting and small potholes, and works well for cold-joint repair.
• The treatment has a lifecycle of 5 – 7 years.
• Truck-mounted pavers have the ability to drive to the Jobsite.
• Micro surfacing sets up fast; the area can open back up to traffic within a couple of hours.
• Micro surfacing can be applied at night, versus other treatments, which must be applied during daytime hours.

Nolan notes that MnDOT’s micro surfacing paving crews have been using a CSS-1hLM emulsion. It is a slower-setting emulsion that allows them a little more time to work with the product. Because of the small-job nature of most projects, this slower setting time provides some flexibility to the crews. Alternatively, MnDOT’s contracted micro surfacing work specifies rapid-set emulsions – both CQS -1hP and CQS-1p. Most of the contract work comprises long straightaways, covering greater distance and with much less handwork, so a faster-setting emulsion is ideal.

“MnDOT’s Bergkamp micro surfacing pavers provide a great benefit for the people in the metro-Minneapolis area,” says Nolan. “They are allowing us to proactively maintain and even improve our streets and roadways. And we are able to work within our fiscal budget constraints. This is a win-win for our districts.”