Demonstration of a new method of paving concrete roads attracted people from a variety of construction industries to northern Minnesota where the Minnesota Department of Transportation, the Concrete Paving Association of Minnesota (CPAM), and the International Grooving and Grinding Association (IGGA) provided a tour of the Next Generation Concrete Surface (NGCS).
The live demonstration of the innovative project was the first large-scale urban use of this method that was constructed on Interstate 35 northbound and southbound from Boundary Avenue to Cody Street near Duluth, Minn. The repaired sections are equal to 3.7 miles of a four-lane freeway. Both segments are located within an ongoing concrete pavement rehabilitation project.
Participants took a tour of the project site followed by a field demonstration of the On Board Sound Intensity testing apparatus that measures sound on that stretch of the high-traffic thoroughfare.
Partnership created product
A partnership between the International Grooving and Grinding Association, American Concrete Pavement Association (ACPA), Portland Cement Association, and Purdue University developed the NGCS surface. Purdue University, which performed extensive testing, then created a surface with a texture that produced the lowest tire-pavement noise levels in the study. The surface was then constructed in the field using actual diamond grinding equipment to confirm the laboratory study.
NGCS is a hybrid texture constructed on concrete surfaces that resembles a combination of diamond grinding and longitudinal grooving. It contains diamond saw-cut surfaces that will provide a consistent profile without the positive or upward texture; it’s a uniform land profile design with basically all negative texture. The surface is more consistent and predictable than most traditional surfaces. The texture can be constructed by means of either a single- or two-pass operation using diamond-tipped saw blades mounted on conventional diamond grinding and grooving equipment. These textures can be used for both new construction and rehabilitation of existing surfaces.
Following the Purdue research, Mn/DOT conducted extensive field tests and evaluation at the MnROAD pavement research facility in Albertville.
Noise reduction testing
“The NGCS has undergone three full years of research at our MnROAD facility, and each stage has delivered a noticeable improvement in quietness, friction and durability. It has been tested in low-volume traffic and high-volume traffic where a total of four cells at MnROAD have an innovative grinding configuration,” said Bernard Izevbekhai, research operations engineer, Minnesota Department of Transportation.
“Research shows that by performing this innovative grind on a pavement that was formerly transversely tined, there is a 6-dB reduction when measured using the On Board Sound Intensity method. In the decibel scale, 6 dB is equivalent to approximately a 75-percent reduction in the tire-pavement sound source,” said Izevbekhai. “To understand the difference in the sound level with NGCS, a high-traffic freeway with 240 vehicles will now sound comparable to only 120 vehicles of traffic, a substantial reduction in sound.”
The extensive testing of NGCS confirmed it met the needed characteristics. “Many things had to be addressed and one of them was quietness,” said Izevbekhai. With these results, the partnership knew it had developed the quietest concrete surface around.
Concern about noise
For the segment of I-35 from 21st Avenue East to 26th Avenue East, Mn/DOT was particularly interested in the added benefit of tire-pavement noise reduction. “At the newest portion of I-35, where it ends, are several hotels, and they were voicing concerns about the noise. Mn/DOT was currently repairing the road and decided to try this grinding technique. NGCS was chosen because we were looking for a grinding pattern that was quieter,” said Pat Huston, resident engineer, Mn/DOT District 1, which covers northeastern Minnesota.
“The response to the quieter ride has been overwhelming,” said John Roberts, executive director of the International Grooving and Grinding Association. “Residents have called asking how the roads became so quiet and it has even made the front page in the local newspapers.”
The demonstration attracted contractors, suppliers, agencies and a top representative from the Federal Highway Administration. “I think everybody really liked what they saw,” said Matt Zeller, executive director, Concrete Paving Association of Minnesota.
At the event, representatives of Mn/DOT explained the construction process and their purpose in using the NGCS on this section of roadway. Pat Huston explained that Mn/DOT considered three primary reasons in selecting NGCS for this particular project: to supply enhanced friction/skid resistance, to enhance the pavement ride, and to reduce noise.
Many saw-blade and equipment manufacturers attended because they were interested in learning how to better construct the NGCS while minimizing costs. “Everyone at the demonstration was excited to hear about the results and see the actual surface constructed on the highway,” said Zeller.
Zeller said several large-scale projects must be built before competition will determine and set a baseline cost. Currently, costs are running 25 percent higher than conventional grinding. But, Zeller said, “In exchange [for the cost], residents and business owners living next to the roadway are experiencing a better quality of life.”
The event also included a demonstration of the On Board Sound Intensity apparatus, a system used to measure noise created by the tire meeting the pavement using a set of sophisticated microphones mounted on the rear wheel near the tire-pavement interface. Tire-pavement noise is a dominant traffic noise source on any highway. Passenger cars actually generate 70 to 90 percent of their total noise through the tire-pavement interaction.
Construction on the Duluth I-35 project will end in 2011, and the remainder ramp work will end in 2012. “We look forward to seeing the NGCS implemented throughout the country,” said Roberts. “The initial reaction has been so favorable that we believe as the word spreads about this technique, demand for it will quickly rise. Municipalities are always looking for new ways to improve the quality of life for their residents, and this one provides a quieter community.”
NGCS’s impact on the industry will be a road treatment that drivers, the surrounding community, and departments of transportation will notice and appreciate because of the safety, quietness and better ride. n
Kari Moosman is an editorial manager writing about architecture, engineering and construction at Constructive Communications, Woodridge, Illinois.