Evaluating Cracking Resistance Test Methods for Asphalt Pavements

A new method of testing low-temperature cracking in asphalt pavement shows promise for design, quality control and quality assurance. Test results produced by the new method, which is faster and less expensive than the previous method, match well with results from the older method. 

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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.

Urban Rapid Transit Reduces Traffic on Nearby Roads

Light rail transit and bus rapid transit in the Twin Cities provide urban residents with fast, safe and reliable transportation. These transitways have the potential to attract more riders and further reduce automobile traffic, relieving the growth of congestion on nearby roads as people decide to be transitway passengers rather than motorists. 

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Strategies for Recruiting and Retaining Minnesota’s Transportation Workforce

Across the transportation industry, public and private employers are experiencing workforce shortages and an uncertain future. As older employees retire and younger workers fill their roles, organizations must naturally adjust to accommodate their changing workforce. In the transportation industry, shifting demographics have also brought new attitudes regarding technical jobs. The result is that fewer engineers and other highly skilled professionals are entering the field, and keeping those who do is becoming increasingly difficult. To address this changing landscape, transportation agencies of all sizes must be prepared to meet the challenges ahead or risk falling behind.

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Evaluating the Impact of J-Band on Pavement Service Life and Crack Resistance

Potholes and other pavement failures in asphalt typically occur at the seams between lanes, where the mixture loses density during compaction because the edges are not confined like they would be with cement concrete forms. Researchers found that spraying J-Band, a void-reducing asphalt membrane (VRAM), in a band along longitudinal joints before asphalt layers are applied increased bond strength, lowered permeability and air void levels, and improved crack resistance.

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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.

Researchers Develop Analytics Tool to Predict Gaps in Metro Transit Bus Driver Schedules

This article was originally published in Catalyst, February 2021.

Solving real-world problems sometimes requires a very boots-on-the-ground approach. When Metro Transit began experiencing a bus driver shortage, researchers from the University of Minnesota (U of M) decided to do some first-hand observations of bus dispatcher life in order to develop a tool that could make scheduling easier.

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Freight Industry Ends Tumultuous Year With Cautious Optimism for 2021

This article was originally published in Catalyst, February 2021.

Among the attendees at the Center for Transportation Studies Freight and Logistics Symposium in December, 44 percent expected to add staff to their organization in 2021, according to a live poll conducted by keynote speaker Joe Mahon. Another 39 percent of respondents expected staffing to remain steady.

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