Attendees of the recent 2008 Michigan Concrete Paving Association's 38th Annual Workshop were told that quieter concrete surfaces have been developed and are being tested by two states. John Roberts, of the International Grooving and Grinding Association (IGGA), said that other states are being sought out to test this Next Generation Concrete Surface (NGCS) category of concrete pavements.
"The first state was Minnesota. They have a section of Interstate 94 that is used for testing. We created a standard diamond ground texture on top. That ended up being 102 decibels," Roberts said. The NGCS test section was 99 decibels.
"The NGCS was far more uniform. We found out that uniformity means a lot. We did this on a low-volume section first. There were a couple of challenges that we had to overcome. Basically, the NGCS is a combination of a groove and a grind. The question was, can we do this in one pass, or is this a two-pass operation? Because costs, of course, are going to be a big issue," Roberts said.
"Once the sections were cut, the Minnesota Department of Transportation ran their truck around to see how it would hold up under load and that is still ongoing at this time. We're also looking at how it handles in snow and ice. The most recent report I received is that it performs as well if not better than the adjacent sections of pavement.
"We tried a couple of different configurations. Basically, we did wheel paths." Roberts said that a small diamond grinder was used. The blade stack was replaced with a new stack in a matter of minutes. A standard diamond grinding blade spacer was used. Different diameter blades were creating different troughs in the diamond-ground section.
Roberts said that there was a lot of room on the surface for water displacement. He said that in addition to the pavement producing less noise, it also provided good friction. It was tested for single pass and two-pass operations.
"Once we were reasonably confident that we were doing OK on the low-volume section, we went onto the interstate. We did a full lane width for approximately 2,000 feet," Roberts said. There was a host of other testing that took place as well, including pre- and post-grinding, smoothness, aggregates, the impact of hardness on the operation, the impact of hardness on the friction characteristics of the pavement, etc.
It was discovered that the work could be done in a single pass. "That's good. That means that we can keep the price lower than if we have to go through twice," Roberts said.
Roberts said that a test was also performed on a section of toll road in Illinois. "They had just built a brand-new section of concrete coming out of Chicago, and they granted us a 1-mile section where we could try a couple of different NGCS textures," Roberts said.
In a single and double-pass operation, the decibel level was, again, below 100. "We compared all of the data, and we found that NGCS is rather consistent. Of course, there will be variations, depending on the wind, air temperature, humidity, and heat; the decibel numbers will vary somewhat. The bottom line is that the majority of the tests fell under the 100-decibel mark, and that puts the concrete pavement sections in the same realm as the quietest asphalt pavement treatments that you can find," Roberts said.