Here's why some concrete pavements are loud while others are quiet
Bothered by Road Noise?
Phoenix has a variety of pavement surfaces. Many are aging asphalt rubber friction course (ARFC), which started out quiet many years ago but has become deteriorated and noisy. Phoenix also has some concrete pavements. But when it comes to road noise, it’s not a simple matter of comparing all asphalt to all concrete.
What explains the difference between one concrete pavement and another? You may have noticed that the Coalition for Responsible Roads (CRR) talks a lot about diamond-ground concrete. It’s not just the “concrete” part that’s important, or even just the “diamond” part. “Grinding” refers to a very specific mechanical action performed using specialized equipment, and if a roadway surface isn’t diamond-ground concrete, then it’s not the most durable, long-lived and quiet concrete paving surface available. A second—and noisier—concrete surface you may find yourself driving on is milled concrete.
What is milling?
Carbide milling (also referred to as cold planing, rotomilling and profiling) is a demolition and removal technique, not a concrete surface restoration technique. The carbide milling process is similar to a jackhammer or a chisel, in that it chips away at the surface of the concrete with a milling head—a cylindrical drum equipped with carbide-tipped-teeth—which may or may not be impregnated with diamonds. Any type of milling tooth, even a diamond-impregnated one, breaks away the top layer of concrete from the pavement surface, leaving a roughened pavement and possible fractured aggregates and joint faces. Despite recent advancements incorporating greater numbers of machined teeth and a smoother drum, the carbide milling process falls short of the diamond-grinding process and is not a substitute for diamond grinding when performing surface restoration and improvement on concrete pavement.
What is diamond grinding?
Diamond grinding uses closely spaced diamond saw blades that gently abrade away the top surface of the concrete. On average, the diamond cutting media will contact the pavement nearly 27,000,000 times per square yard. This accounts for the gentle removal action. The level surface is achieved by running the blade assembly at a predetermined height across the pavement. Diamond grinding results in a surface that is smooth, safe, quiet and pleasing to ride on.
DOTs confirm the difference:
According to a Caltrans report, “Unless an agency is willing to accept badly spalled joints, the cold planer (rotomill) is NOT considered a satisfactory substitute for diamond grinding.”
Washington DOT notes in a report that “use of a roto-milling machine impacts the surface and results in the ‘popping’ out of aggregate rather than cutting it. The roto-milling process causes significant damage to the joint.”
In addition to causing pavement degradation, immediate results associated with carbide milling are much less pleasing than those associated with diamond grinding. Carbide milled surfaces are considerably rougher than diamond ground surfaces, and they are noisier as well. Diamond grinding improves road noise by providing a longitudinal texture, which is quieter than transverse textures. Additionally, the longitudinal texture enhances surface macro-texture and skid resistance in polished pavements.
Which Pavements are Which in Maricopa County?
Take a drive on diamond-ground concrete and see for yourself!
In 2020, diamond grinding was performed on two Phoenix area freeways: the Loop 202 (Santan Freeway) and the Loop 101 (Price Freeway). Other concrete surfaces you may notice in the area’s highway system—notably on US 60, I-17 and I-10—are milled surfaces, not diamond-ground ones. So the next time you’re on SR202 or SR101 (on the sections indicated on the map below), take the time to notice the diamond-ground concrete underneath your tires. Then, we encourage you to be part of the decision-making process for your community and advocate for safe, sustainable, smooth, quiet AND affordable pavements!
The Concrete Pavement Restoration Guide, TB020P, American Concrete Pavement Association, Skokie, IL, 1998.
Diamond Grinding and Concrete Pavement Restoration, TB008P, American Concrete Pavement Association, Skokie, IL, 2000.
Roa, S., Yu, H. T., and Darter, M. I., “The Longevity and Performance of Diamond-Ground Concrete Pavements,” RD118P, Portland Cement Association, 1999.
Caltrans report number FHWA-CA-TL-78-15, Evaluation of Cold Planers for Grinding PCC Pavements,” Final Report, September 1978.