North Central Asphalt User Producer Group Conference Summary

The agenda and linked presentations for the North Central User Producer Group Conference are available at this link.

 

Key Highlights:

A national update was presented by Matt Corrigan with the FHWA. Matt discussed the Fast Act funding increase over the next 5 years. Click here to view the MAPA fact sheet for the Fast Act. 

 

Mark Blow with the Asphalt Institute presented on the implementation of the Multiple-Stress Creep Recovery (MSCR) test. Most states either partially or fully implemented MSCR. Minnesota is fully implementing MSCR in 2016. More information is available here from MnDOT.

MSCR Implementation

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Superpave 5 concept is to lower air voids in the field to improve durability. The design air void level is 5% and the mix is field compacted to 5%. Test sections were placed for superpave 5 in Indiana. The conclusions were that mixtures can be designed at 5% air voids without lowering effective binder content. These mixtures can have equivalent mechanical properties as traditional superpave designed mixtures and the mix can be compacted to 95% density without additional compaction effort.

Recommendations for superpave 5 include:

  • 50 gyrations for medium to high traffic levels and 30 gyrations for low traffic levels
  • Perform low-temperature mixture testing
  • Place additional field projects and monitor performance

 

An overview from the National Center for Asphalt Technology (NCAT) of thin lift asphalt surfaces for pavement preservation was presented by Mike Heitzman. Definition of Thinlays from NAPA: Thinlays successfully extend the life of structurally sound pavements. Thinlays can be as thin as 5⁄8 inch and of greater thickness as surface conditions necessitate.

Some of the benefits of thin lift surfaces are:

  • Improve smoothness
  • Extend pavement performance
  • Lower material cost
  • Reduce noise
  • Improve friction (limited)
  • Cost per square yard, per year of service
  • Projected performance life
  • Material and equipment availability
  • Market competition

Pavement preservation in general should be used when the pavement is in good structural condition, the smoothness is good to fair, there is low visible distress and safety considerations are good to moderate.

Some construction considerations for thin lifts include:

  • Limit moisture in stock piles with fine aggregates
  • Use of at least two bins for each primary stockpile is recommended
  • Uniform and correct application rate of tack is critical
  • Continuous and uniform paving operation to avoid temperature segregation
  • Window of compaction time is limited. Use multi-cool during construction http://www.asphaltisbest.com/2014/04/multicool-app-available-now/
  • Vibratory compaction may not be needed for thin lifts
  • Use nuclear density gauges to set up rolling pattern. Cores are difficult to take and are usually not an accurate measurement for thing lift density.

MAPA with cooperation with MnDOT will be soon releasing a specification for Thinlay.

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