Roads and Bridges Online Magazine, January 2016 Issue, reported on the newest pavement texture in an article by Ashley Kizzire, Contributing Author, titled “Best of Both Worlds: New pavement surface technique renews I-394 in Minneapolis”. Historically, pavement engineers have strived to balance safety and driver comfort when designing long-lasting concrete pavements. In recent years, tire/pavement noise has become a hot-button issue for motorists and residents living near high-volume roadways. In the past this was a dilemma since many of the more aggressive concrete surfaces that provided the best traction and safe driving also brought the unintended consequence of increased tire/pavement noise. But now, departments of transportation can have both with a new Next Generation Concrete Surface (NGCS). The I-394 rehab project in Minneapolis, Minnesota, USA demonstrates this.
For years, the Minnesota Department of Transportation (MnDOT) fielded public concerns over the din created by car traveling across I-394. Now, with a new NGCS in place, residents of the Bryn Mawr neighborhood near downtown Minneapolis will experience a long-lasting, significant reduction in tire/pavement noise. Motorists driving along this busy metropolitan section will enjoy a quieter ride, but the new pavement surface is designed with safety in mind.
A NOISY HISTORY: The circa 1988 section of I-394—from Highway 100 in Golden Valley to I-94 in Minneapolis—was originally constructed with a transversely tined concrete surface. A transverse tined surface is constructed perpendicular to the direction the tires travel along the surface, which provides significant friction and reduces the chance of hydroplaning. But, due to its noisiness, transverse tining has been discontinued today by most transportation authorities in the U.S.
Residents complained to the Minnesota State Legislature about the noise related to I-394, thus mandating that the surface be overlaid with asphalt to lessen the noise. In 1996, MnDOT applied the first of two asphalt overlays to I-394, even though the structural condition of the original concrete was still of high quality. Noise was reduced, but only temporarily, as the harsh Minnesota winters descended with their customary force. Over time, the different rates of expansion caused I-394’s asphalt overlay to crack, exposing the concrete joints underneath, forming large potholes.
Matt Zeller, Executive Director-Concrete Paving Association of Minnesota said, “At that time, MnDOT considered removing the asphalt overlay and diamond grinding the concrete to mitigate the noise. But, unfamiliar with diamond-grinding, residents chose to stick with the perpetual mill-and-overlay solution for noise mitigation, even if that surface would not last as long as a concrete surface.”
REPAIR SOLUTIONS: In 2014, MnDOT once again needed to rehab I-394, but this time, the repair solutions came in the form of two concrete pavement strategies gaining national momentum:
1. The “buried treasure” preservation concept—a procedure used to recover an otherwise structurally sound concrete pavement overlaid due to functional deficiencies such as excessive noise or poor ride. To implement, the crews removed the aging asphalt overlay, exposing the concrete roadway underneath, then installed the new NGCS low-noise surface finish atop the older concrete. The underlying 27-year-old was in need of some limited repair, so the buried treasure concept provided an ideal solution, allowing MnDOT to address the root cause of the deterioration rather than simply cover it up.
2. NGCS—Represents the quietest non-porous concrete surface developed to date and is the first new concrete pavement texture introduced in the last 30 years. A hybrid texture, the NGCS resembles a combination of diamond grinding and longitudinal grooving. The NGCS’ diamond saw-cut surface provides a consistent profile that is absent positive or upward texture, resulting in a uniform landprofile design with a predominantly negative texture. Testing has shown that these textures can be used for both new construction and rehabilitation of existing surfaces. The result is a dramatic decrease in noise.
Recognizing the need for quieter pavements, a vast partnership between the International Grooving & Grinding Association (IGGA), American Concrete Pavement Association (ACPA), Portland Cement Association (PCA), and Purdue University developed the NGCS, between 2006 and 2008, at Purdue’s Herrick Laboratories in West Lafayette, Indiana. Research was conducted using its Tire Pavement Test Apparatus (TPTA), which can test nearly any pavement texture. Test findings indicated the resulting fin profile was the most important factor—producing a low-noise, diamond-ground surface required creating uniform and consistent land profiles. The research findings led to the NGCS solution for pavements. Following the research phase, proof of concept occurred at the MnRoads Low-Volume Road Facility.
SCOPE: MnDOT took steps to complete the project as quickly as possible. Work began in June 2015 and was completed by November 2015.
NOISE TESTING: A research team from the MnDOT Office of Materials and Road Research conducted On-Board Sound Intensity (OBSI) measurements both before and after construction, and found a significant improvement in noise levels as a result of the NGCS. Tests were performed in accordance with American Association of State Highway Officials (AASHTO) specification TP 76-11, “Measurement of Tire/Pavement Noise Using the OBSI Method,” with a pair of vertically oriented microphones affixed to the vehicle and positioned near the pavement/tire contact patch. For this vital artery in Minneapolis, structural integrity is maintained, and with the NGCS solution in place, I-394 is expected to live another 20 to 30 years in peace and quiet.
For all of the details of the project and to read the entire article, please go to: http://www.roadsbridges.com/sites/rb/files/40_X_I-394_Minn_0116RB.pdf.
For more information about this topic, please go to the “concrete” section of Roads & Bridges Magazine: http://www.roadsbridges.com/concrete.
Home page cover photo: Compromised asphalt overlay was removed,
allowing crews to address the underlying deficiences in the concrete on I-394—
in some areas performing a full-depth excision and repair.