Concrete pavements can be designed and constructed to be as quiet as any other conventional pavement type in use today. This report provides an overview of how this can be done—and done consistently.
Quieter concrete pavements are built around the world using typical concrete pavement textures, including diamond grinding, drags, longitudinal tining, and even transverse tining. They can be durable and cost-effective to build. Also, the data indicate that quieter concrete pavements do not sacrifice safety. In fact, there is not a direct relationship between friction and noise; quieter surfaces vary in friction just as louder surfaces do.
One reason why not all concrete pavements are quiet is the lack of a collective understanding about what makes them quiet. To address this need, the National Concrete Pavement Technology Center at Iowa State University has amassed the largest existing database of concrete pavement surface characteristics, including measurements of noise, texture, and friction. Nearly 1,600 test sections from North America and Europe have been evaluated.
From this, the Concrete Pavement Surface Characteristics Program (CPSCP) has come to understand the fundamental surface properties that increase noise and has developed better practices to avoid them. As part of the evaluation, CPSCP has catalogued both the best and worst of virtually every nominal concrete pavement texture in use today. With so many measurements, distributions have emerged showing what noise characteristics are possible for each nominal texture type. The variability within these distributions is due to differences in design, construction, age, climate, traffic, and many other factors.
The graph below illustrates the range of tire-pavement noise levels that have been measured to date. The pavements are broken down by nominal texture type and shown as normalized distributions of the noise levels evaluated using OBSI. The pavements measured under the CPSCP tend to be earlier in life since one of the program goals is to link the measurements to construction factors that are generally only available for earlier sections.
Based on the work conducted to date, an A-weighted tire-pavement noise level of between 101–102 dB, measured using OBSI at 60 mph, appears to be a reasonable target threshold for new concrete pavements. With this in mind, and referring to the graph on page 21, the following can be concluded:
- Most conventionally diamond-ground surfaces that were measured met the target threshold.
- About a third of the drag textures measured also met the target threshold.
- About a quarter of the longitudinally tined surfaces measured met the target threshold.
- A small but important fraction of transversely tined surfaces that were measured met the target threshold. For those that met the target, the nominal tine spacings were at or below 1/2 inch.
These data suggest that virtually all conventional nominal textures have the potential to be constructed as quieter concrete surfaces, though some are more likely to be quiet than others.
While selecting the nominal texture might be a logical first step toward achieving a quieter pavement, this was not the sole intent of this study. Instead, the goal was to develop better practices to help owner-agencies and contractors achieve the quietest surface possible within any given nominal texture. This requires the combined experience of both concrete paving contractors and paving equipment manufacturers.
Summary of better practices
To build a quieter concrete pavement, one must:
The first item has been addressed in large part under the CPSCP and through the results of numerous other studies. The key relationships can serve as a reference for those seeking to better understand the link from the design and construction to the most relevant as-built properties affecting tire-pavement noise.
Better practices to improve surface properties, and thus tire pavement noise, are really about establishing increased control over texture and other surface properties. It’s important to recognize the impact of subtle operational characteristics on the texture as constructed.
Predictable tire-pavement noise levels depend less on how the texture is imparted than on recognition and management of the sources of variability. Fresh concrete is inherently variable in both stiffness and plasticity. Concrete changes from batch-to-batch, and it changes within a batch. Wind and sun play a major role, as does the timing of the concrete mixing, transport, placement, texturing, and curing.
Click the next few pages for a sidebar summarizing practices to help reduce noise. Many of these also improve smoothness, durability, and reduce costs.
Controlling concrete pavement surface texture
The methods and practices used today to impart and control surface textures are often ineffective in meeting a nominal texture pattern, much less doing it consistently. Even if tining, dragging, and diamond grinding are all done with the best equipment, other variables will ultimately affect the final texture. Some of these variables are listed in the sidebar on the next page, Concrete Pavement Surface Properties that Affect Tire- Pavement Noise.
The photos in the slideshow show how variability in the as-constructed texture can lead to very different tire-pavement noise levels (shown as OBSI measured at 60 mph with the SRTT). These photographs were taken on a CPSCP test site on U.S. Highway 30 in Iowa. In each figure, the texture’s appearance differs between the louder and quieter areas. One or more of the texture characteristics can be observed in the louder sections.
The RoboTex 3-dimensional texture profiler provides texture scans. These depict the subtle curvature of the lands between tine grooves in the louder section, while the tine grooves are much less aggressive in the quieter sections. Note, too, that the texture depth in all cases was very similar; the differences in geometry of the lands was the major contributor to noise, largely due to the land (tine) spacing, which was more than 1 inch in many cases. This as-constructed variability in texture is another example of the impetus for better practices. As better practices are followed, the probability of constructing the nominal texture should increase.
For today, the concrete pavement industry can promote better practices. For tomorrow, the solution will likely be automation of the texturing operation. Over the years, slipform concrete paving operations have become more automated. To meet the demands for predictable low-noise surfaces, automation will eventually allow the paver, texture cart, and grinding operators to monitor the texture being produced and make adjustments on the fly. Ultimately, this approach may be the best way to achieve a specified target texture on concrete pavements. For now, we can make significant improvements by adopting better practices. CC/TCP
About the Authors:
Robert Otto Rasmussen is vice president and chief engineer and Richard C. Soheney is a project manager with The Transtec Group Inc., Austin, Tex.
Gary J. Fick is president of Trinity Construction Management Services, Inc., Edmond, Okla.
E. Thomas Cackler is the director of the National Concrete Pavement Technology Center, Iowa State University, Ames, Iowa.
This article is based on the best paper presented at the International Conference on Concrete Pavements, July 2012.
Click the next few pages for sidebars titled Concrete Pavement Surface Properties that Affect Tire- Pavement Noise and Summary of Better Practices to Reduce Tire-Pavement Noise.