Tag Archives: NRRA

Research Pays Off Webinar Series: Determining Pavement Design Criteria for Recycled Aggregate Base and Large Stone Subbase

The National Road Research Alliance (NRRA) is hosting “Research Pays Off: Determining Pavement Design Criteria for Recycled Aggregate Base and Large Stone Subbase” on April 20 at 10 a.m. CST, presented by Bora Cetin, Ph.D., Michigan State University and Raul Velasquez, Ph.D., P.E., Minnesota Department of Transportation.

The NRRA’s monthly seminar highlights research topics that will make an impact on the work done here in the state of Minnesota and around the country.

Project Summary

Although recycled pavement materials have been used in roadway base layers for many years, a specific design method does not exist that describes how to build roadways with these materials. Many state Departments of Transportation (DOTs) assume recycled base materials behave similar to base layers built with conventional virgin aggregates (VA). There is a similar lack of an existing design methodology for pavement systems built with a large stone subbase (LSSB).

The proposed project has three main goals. The first goal of the project is to determine the field and laboratory performance of materials and test sections built with recycled aggregate bases (RAB) including recycled concrete aggregate (RCA), recycled asphalt pavement (RAP), and mixtures of these materials with VA. In addition, similar analyses will be conducted for the test sections built with 18 inches thick LSSB with different compaction methods (1-lift and 2-lift), and those 9 inches thick LSSB built with geogrids and geotextiles. To accomplish this goal, the research team will evaluate both the geomechanical and environmental properties of these pavement systems. It should be noted that the LSSB sections have only one type of aggregate base and the multiple recycled aggregate base sections do not have LSSB indicating that experiments for each different design methods are separate. The second goal of the project is to develop a method to estimate the stiffness and permeability of RAB and LSSB designs. This goal will be achieved by establishing correlations between common laboratory test data and both laboratory and field modulus and permeability values. The third goal is to prepare a pavement design and construction specification for roadways built with RAB and LSSB designs. This goal will be accomplished via a summary of the results of all tasks, taking into account the performance, cost benefits, and life cycle costs of these systems. The outcome of this research will optimize the use of recycled materials and LSSB designs, while maintaining pavement quality, resulting in cost savings and conservation of natural resources.

Visit the MnROAD website for webinar connection information.

Research Pays Off Webinar Series: FRC Jointless Roundabouts in Minnesota

The National Road Research Alliance (NRRA) is hosting “Research Pays Off: FRC Jointless Roundabouts in Minnesota” on March 16 at 10 a.m. CST, presented by Principal Investigator Peter Taylor, Ph.D., P.E., Iowa State and Technical Liaison Maria Masten, P.E., MnDOT.

The NRRA’s monthly seminar highlights research topics that will make an impact on the work done here in the state of Minnesota and around the country.

Project Summary

The use of roundabouts to improve safety and traffic flow in rural areas is growing rapidly in the U.S. Proper design details and construction methods are important to the long term performance of these facilities. Joint layout in roundabouts constructed with concrete pavement are especially challenging. To reduce the need for sophisticated joint layouts, some roundabouts are now be constructed without joints, utilizing structural fiber-reinforced concrete to bridge cracking that might occur. Fiber-reinforced concrete is also being used in thin concrete overlays to increase longevity and enhance joint load transfer capacity.

In 2018, Minnesota’s first jointless fiber-reinforced concrete (FRC) pavement roundabout was constructed near the city of Sleepy Eye. It is of interest to the NRRA Rigid Team members to understand the design, construction, and near-term performance of this roundabout. Also constructed in 2018 were two fiber-reinforced concrete whitetopping (bonded concrete overlay on asphalt) projects in southern Minnesota. These projects were unique in that early construction vehicle loading was applied to each project to encourage the deployment of transverse contraction joints. The NRRA Rigid Team members are interested in documenting the innovative steps performed during the early loading process.

The objectives of this study are twofold:

  1. Write a construction report and carryout a 3-year performance monitoring regime for the jointless FRC roundabout project
  2. Write a construction report for the two FRC whitetopping projects subjected to early loading.

Visit the MnROAD website for webinar connection information.

MnROAD Breaks New Ground

In June, MnROAD, the only cold-weather accelerated pavement testing facility of its kind in North America, begins construction on its third phase of research since 1994, the first time MnDOT has rebuilt in partnership with other states.

Dozens of new experiments are planned along MnROAD’s test tracks in rural Albertville: the high-volume original Interstate-94 westbound (built in 1973), the mainline I-94 westbound (originally opened in 1994) and an adjacent low-volume road closed track.

Six states and numerous  industry partners recently formed the National Road Research Alliance (NRRA) to co-sponsor  the reconstruction.

NRRA-prioritized research will support state and local needs, including effective use of fiber-reinforced concrete, asphalt overlays of concrete pavements, cold central plant recycling and concrete partial depth repairs to name a few.

MnROAD has two 3.5 mile test segments on Interstate 94 and one closed 2.5-mile low-volume road.
MnROAD has two 3.5 mile test segments on Interstate 94 and one closed 2.5-mile low-volume road.

“The advantage of having these test  sections at MnROAD is we can take  bigger risks and push the envelope in terms of mix designs and layer thicknesses for both asphalt and concrete  layers that could not be done on a public roadway,” MnDOT Research Operations Engineer,   Dave Van Deusen said.

Forensic analysis of failed cells
Many old test cells will be dug up.  Before any reconstruction starts, however, each test section that is being reconstructed will receive a final forensic study. This allows researchers a look at each layer to see the distress that has occurred over the years—and make the final analysis of why it failed. There are always a lot of theories on the causes of what actually failed, but until the forensic is performed, there isn’t proof on what happened. These findings will help build longer-lasting pavements in the future.

The bid letting date for this year’s construction is April 28, but plans were made available for contractors on March 31. This should give the projects more exposure and generate more interest. Construction begins June 5 and continues until November 2017.

Focus Areas

  • HMA overlay and rehab of concrete and methods of enhancing compaction – States are looking for longer lasting HMA overlays of concrete. New mix designs were developed to promote long-term performance, including how reflective cracking effects can be minimized through design or other joint treatment.
  • Cold central plant recycling – Other states have used reclaimed asphalt pavement stockpiles into plant mix base course mixes (layers below the wear surface) to effectively recycle these materials in a controlled mix design. How can these layers best be used and what type of surface mix or chip seal can be placed on top?
  • Fiber reinforced concrete pavements – Nationally, states want to get a better understanding of the beneficial use of fibers in concrete pavement layers. Is it worth the cost? How can it be best used in both thin city streets and higher volume roadways? Can it be used in new construction and in concrete overlays? The research will provide the answers.
  • Long-term effects of diamond grinding – Each state has aggregates that have been used in concrete pavements that are considered reactive aggregates. Questions arise as to whether diamond grinding might accelerate deterioration in these pavements. What types of topical sealers can be used to treat the surface after the diamond grinding will also be tested.
  • Early opening strength to traffic – What effect does heavy traffic loading have on the long-term performance of full-depth concrete pavement, as well as fast–setting repairs? Test sections will be loaded by a pickup truck in one lane early enough to produce shallow ruts in the surface. In the other lane, a loaded 18-wheeler will travel over the new concrete immediately after it sets, and then sequentially every six hours up to 30 hours. The long-term effects of these early loadings will then be evaluated.
  • Optimizing the mix components for contractors – What effect do low-cementitious content mixes have on long-term performance and constructability of concrete pavements?  Two low cementitious content mixes will be studied to give agencies a better understanding of cost savings. Can these savings be achieved without significantly affecting long-term performance?
  • Compacted concrete pavement for local streets – Compacted concrete pavement is a form of roller compacted concrete that has a standard concrete pavement surface texture. The RCC industry has been successful in Michigan and Kansas constructing CCP pavement on local streets.  This research will determine if the texture that is accomplished is durable in harsh freeze-thaw climates.
  • Recycled aggregates in aggregate base and larger sub-base materials – States continue to look for effective ways to recycle materials into unbound bases. This research will add to MnROAD’s understanding of recycled bases and what seasonal strength values can be used for advanced mechanistic designs–and how they are affected by size/gradation.
  • Maintaining poor pavements– Road owners continually have less funding to maintain their roadway systems. What practices should be used for stabilizing both hot mix asphalt and Portland cement concrete roadways when longer-term repairs cannot be done due to funding levels?
  • Partial depth repair of concrete pavements – Agencies continually seek improved materials and methods for the repair of concrete pavements. In this study, up to 15 innovative concrete pavement repair materials will be evaluated on the concrete panels of the westbound I-94 bypass parallel to the MnROAD mainline.
  • Thin overlays-Experimenting with very thin overlays could provide a real benefit for a lot the roads currently out there. The premise is that with thin overlays, the ride can be smoother and the life of older roads can be extended.

“We don’t often get to reconstruct random roads these days, and when we do, we have much better specifications for low temperature cracking. By the same token, we have to maintain all those older roads built before we had performance grade binders,” said Dave Van Deusen, Materials and Road Research Lab principal engineer. “We will be doing this makeover on an original section of MnROAD built back in the 90’s.”

In one experiment, there is a head-to-head comparison of thin overlays on two sections of road. One section has a thick base and subbase under the asphalt. The other has a heavy asphalt top with very little base.

Van Deusen says if they can get an extra five years of life out of road using thin overlays, he would be pleased. Often, he admits, he is surprised by how long these “short-term” fixes actually last.

Stay up-to-date on construction by signing up for email alerts at mndot.gov/mnroad.  

Partner States Get First Look at Minnesota Road Experiment

Walking along a half-mile segment of Co. Rd. 8 near Milaca last month, materials engineers from around the country got a first look at a shared test site for pavement preservation.

Nearly 60 one-tenth mile sections of Co. Rd. 8 and nearby Hwy 169 were recently treated with various combinations of fog seals, chip seals, crack seals, scrub seals and microsurfacing and a number of thin overlays. Data will be collected from these experimental test roads for three years and compared with the results of a similar experiment in Alabama, where the same test sections were also built on a low- and high-volume roadway, to see which techniques are the most effective for preserving road life.

“Evaluating pavement performance in both northern and southern climates will provide cost-effective solutions that can be implemented nationwide,” said Ben Worel, MnROAD operations engineer.

Photo of Barry Paye, Wisconsin DOT chief materials engineer; and Tim Clyne, MnDOT Metro District materials engineer.

From left, Barry Paye, Wisconsin DOT chief materials engineer, and Tim Clyne, MnDOT Metro District materials engineer, participate in a discussion about future road research needs. Photo by Shannon Fiecke

Nineteen states, which are co-funding the study through MnDOT’s road research facility (MnROAD), were in town Oct. 26-27 for a joint meeting with the National Center for Asphalt Technology in Auburn, Ala. In addition to touring test sections built this summer near Milaca and at MnROAD’s permanent test track in Albertville, the group reviewed preliminary research results and discussed ideas for new experiments.

MnROAD began two joint research efforts with NCAT last year to advance pavement engineering issues that affect both warm and cold climates. In addition to determining the life-extending benefits of different pavement preservation techniques, the partnership has also built test cells to evaluate which asphalt cracking prediction tests best predict future pavement performance. This second study will help state DOTs improve the quality of asphalt mixes, so roads hold up better through harsh winters, leading to less thermal cracking and fewer potholes.

Click here to learn more about the MnROAD-NCAT partnership.