Clyne, Timothy R.

MnROAD, located near Albertville, Minnesota (40 miles northwest of Minneapolis-St. Paul) is one of the most sophisticated, independently operated pavement test facilities of its type in the world. MnROAD has collected data since 1993 on three unique road segments located parallel to Interstate 94. MnROAD data is collected in a number of different methods and processes, which impacts how we store the data (both calculated and raw values). The purpose of this document is to describe what data has been collected, where it is stored for research use, and how to access the data.

The sound absorption test measures the sound absorptiveness of a pavement surface. The sound analyzed is not generated by the interaction of the rolling tire with pavement surface but by noise source above the impedance tube. During the test, the impedance tube is placed on the pavement surface and a set of sensitive microphones are attached to the pre-installed housing at the lower end of the tube. These microphones are also connected to an analyzer. The noise source sends the incident sound energy (white noise) to the surface and the incident and reflected waves are captured by the two microphones. Software analyzes the reflected waves and converts the data to the 3rd octave sound absorption coefficient at 315, 400, 500, 750, 1000, 1250 and 1650 Hertz. Thus, the sound absorption coefficients at each frequency are between one and zero, where a value of one would mean that all of the sound is being absorbed by the pavement surface.

Warm mix asphalt (WMA) is a general term describing the use of any additive or technology that allows for lower asphalt plant mixing temperatures. Developed in Europe, WMA was brought to the United States in 2004 and has since gained widespread use around the country. Environmental benefits experienced with WMA include reduced emissions, fumes, and odors. With a cooler work environment enabled by WMA technology, reduced production temperatures add up to energy savings. The Minnesota Department of Transportation (MnDOT) saw the promise in this technology, especially the anticipated benefit of reduced low temperature and reflective cracking because of the reduced binder aging at the plant.

Bituminous test cell 4, on the Mainline at MnROAD was constructed in October 2008 as a partnership between Mn/DOT and Road Science LLC. Cores were taken by Road Science staff soon after construction and then filled the holes with an open graded Hot Mix Asphalt (HMA). In the spring of 2010 significant heaving was noticed in the pavement surrounding the core hole areas. It was decided that a small scale forensic be conducted to determine what caused the heaving in these areas in conjunction of repairing the pavements.

Pavement surface characteristics include ride quality, frictional resistance, hydroplaning potential, texture, sound absorption properties, and overall pavement performance. Growing interest in pavement surface characteristics and concerns about safety, traffic noise and performance has resulted in focused pavement research. Research shows that porous pavements absorb more traffic noise than normal pavements. There is an optimal porosity for durability and sound attenuation characteristics. In general, pavements with smaller aggregates and more open surface textures provide more noise reduction than a typical dense-graded Hot Mix Asphalt (HMA) mixture. How they perform over time depends on their ability to maintain porosity.

Transportation and its supporting infrastructure have significant economic, social, and environmental impacts. Using more sustainable methods to design, construct, and preserve roads will better protect the environment and meet our ongoing needs. Mn/DOT and our partners in government, industry, and academia have been researching and implementing ways to make our roads greener, while maintaining or improving roadway quality.

The objective of this study is to demonstrate the use of fine and coarse taconite aggregate materials in hot mix asphalt, Portland cement concrete, and other pavement applications for both its constructability and field performance over time. This would help create a greater comfort level for the use of taconite aggregate and help promote its use in the state and around the nation. The specific goal of Task F is to perform laboratory tests on taconite aggregates and on pavements made out of taconite aggregates to establish how these materials will be used in the most appropriate manner for long-lasting roadways. Mn/DOT has the laboratory equipment and expertise to do this required material testing.

A field review was done to investigate three roadways that incorporated a strong stone base or Scandinavian design built in central Minnesota (Mn/DOT District-3). These were initially built though a partnership with Mn/DOT and Finland where Gary Niemi (now retired D-3 engineer) visited Finland and brought back these designs to Minnesota in the late 1990’s. The whole idea of a large stone base design is to gain the strength or support for your roadway through the unbound base materials and have a relatively thin asphalt layer that can be milled and recycled at a lower cost while still preserving the underlying base materials. The top asphalt layer is not designed to carry the traffic loadings.

Transportation and its supporting infrastructure have significant economic, social, and environmental impacts. Using more sustainable methods to design, construct, and preserve roads will better protect the environment and meet our ongoing needs. Mn/DOT and our partners in government, industry, and academia have been researching and implementing ways to make our roads greener, while maintaining or improving roadway quality. MnROAD is conducting research on several “green” pavement technologies that reduce environmental impacts, reuse roadway materials, or use recycled materials in pavement applications:

Low temperature cracking occurs when cold weather temperatures cause the upper part of a pavement section to contract, while the pavement’s bottom section is held in place by its granular base and prevented from contracting. To relieve stress, cracks are formed at semi-regular intervals, thus degrading the pavement and reducing riding comfort. Low temperature cracking is the main cause of pavement roughness and reduced service life in northern climates.