Best of both worlds

By: Ashley Kizzire; Contributing Author

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 alike. 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. Times have changed. With a new Next Generation Concrete Surface (NGCS), the I-394 rehab project in Minneapolis demonstrates departments of transportation now can have both.

For years, the Minnesota Department of Transportation (MnDOT) fielded public concerns over the din created by cars 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 also will enjoy a quieter ride. But the new pavement surface is designed with safety in mind. The first new concrete pavement surface developed in the last 30 years, the NGCS solution combines a quiet ride with a safer pavement.

A noisy history

The circa 1988 section of I-394—from Highway 100 to I-94 in Golden Valley and 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. This orientation provides significant friction and reduces the chance of hydroplaning, but transverse tining is noisy. A standard practice at the time of I-394’s construction, transverse tining has been discontinued today by most transportation authorities in the U.S.

Complaints from residents related to I-394’s noise eventually reached the Minnesota State Legislature, which in turn passed legislation 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, while 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, performance issues arose in the pavement. During freeze-thaw cycles, asphalt and concrete expand and contract at different rates. Over time, the different rates of expansion caused I-394’s asphalt overlay to crack, exposing the concrete joints underneath. The overlay began to delaminate in these areas and large potholes formed. 

Eight years after the first overlay, the deteriorating surface was replaced in 2004 with another bituminous overlay.

“At that time, MnDOT did consider removing the asphalt overlay and diamond grinding the concrete to mitigate the noise,” said Matt Zeller, executive director of the Concrete Paving Association of Minnesota. “MnDOT discussed the options with the surrounding neighborhoods, but due to their unfamiliarity with the diamond-ground concrete surface, 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. Repair solutions came in the form of two concrete pavement strategies gaining national momentum: the “buried treasure” preservation concept and NGCS. 

The buried treasure preservation concept is a procedure used to recover an otherwise structurally sound concrete pavement that was overlaid due to functional deficiencies such as excessive noise or poor ride. To implement the buried treasure concept, crews remove the aging asphalt overlay placed atop the concrete roadway followed by the installation of a low-noise surface finish on the newly exposed concrete. Because the underlying concrete on I-394 was now 27 years old and in need of some limited repair, the buried treasure concept provided an ideal solution, allowing MnDOT to address the root cause of the deterioration rather than simply cover it up.

The NGCS was conceived by the industry while working with Purdue University between 2006 and 2008 and fully developed at MnDOT’s MnROAD pavement test track. It 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 texture is most easily constructed in a two-pass operation using diamond-tipped saw blades mounted on conventional diamond-grinding and grooving equipment. The NGCS’ diamond saw-cut surface provides a consistent profile that is absent positive or upward texture, resulting in a uniform land-profile 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. A high-traffic freeway with a transversely tined surface can experience a 50% decrease in tire/pavement noise by applying the NGCS, according to the International Grooving & Grinding Association (IGGA). This represents a considerable benefit for areas with a greater need for quieter roads, such as urban or residential areas.  

Recognizing the need for quieter pavements, a vast partnership that included the IGGA, American Concrete Pavement Association (ACPA), Portland Cement Association (PCA) and Purdue University developed the NGCS at Purdue’s Herrick Laboratories in West Lafayette, Ind., where research was conducted using its Tire Pavement Test Apparatus (TPTA), which can test nearly any pavement texture. 

Test findings indicated the geometric configuration of the blades and spacers used to construct diamond-ground textures was not the controlling factor in noise generation; rather, 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 of work

The $13 million I-394 rehab included removing the existing asphalt overlay, assessing and repairing the exposed concrete, and constructing the new NGCS diamond-ground surface.

First, crews milled off the existing asphalt overlay. Deteriorated areas of concrete were removed and repaired where needed, with work including both full- and partial-depth repairs. Once concrete repairs were complete, the surface was retextured using the NGCS and all repaired areas had joints resealed.

Work began in June 2015 and was completed by November 2015. MnDOT took steps to complete the project as quickly as possible. Asphalt milling took place during night non-peak hours. When concrete repair work began, MnDOT closed westbound lanes for two weeks, using reversible HOV lanes to accommodate westbound traffic while crews worked around the clock. The process was repeated during a second two-week period to repair eastbound lanes. The weekday lane closures allowed for a more rapid completion than weekend-only closures. All of the NGCS grinding was performed during night non-peak hours to minimize the impact to the traveling public.

Like any major rehab project in a big city, safety and logistics were top priorities on I-394. Concrete barriers separated the crews from traffic to keep workers as safe as possible. In addition, managing the logistics of crews and equipment on a busy metropolitan interstate is critical. Crews and equipment must be safely moved on and off the jobsite, while old material is hauled off for recycling—all while creating minimal disruption to the traveling public.

In addition to I-394, the project included constructing a new deck for the Lyndale Avenue Bridge over Dunwoody Boulevard; Wayzata Boulevard improvements; enhanced bike and pedestrian lanes; and guardrail maintenance.