The American Concrete Pavement Association’s (ACPA) surface characteristics research and testing program recently achieved a critical milestone in the form of two sections of concrete pavement that are documented as the quietest surface textures ever constructed in the U.S.
Diamond Surfaces Inc., an ACPA and International Grooving & Grinding Association member, diamond-ground three textures on section 37 at the Minnesota DOT’s (Mn/DOT) Mn/Road Road Research to field validate the ACPA’s diamond grinding research efforts at Purdue University.
This program represents an important milestone in ACPA’s tire/pavement noise and surface characteristics testing program, which began in earnest in 2005. The program goals are to develop quieter highways and roadways that still provide safe and durable surfaces for motorists. The program involves research, field experiments and advocacy efforts.
Purdue proofed
Purdue University’s Herrick Laboratory developed the textures and provided the laboratory evaluation of the concept. Dr. Robert Bernhard is the principal investigator on the ACPA research project. The new Purdue-developed textures tested at 99 dBA, approximately 3 dBA quieter than a conventional diamond grinding technique constructed at the same time at Mn/Road.
The Purdue proof-testing research indicated that blade width and spacing are not the controlling factors in noise generation, as was previously believed. The research indicated that the resulting profile or smoothness of the fins was the critical aspect. The picture on page 19 shows the resulting surface produced by conventional diamond grinding. As evident, the fins protrude upward and are very irregular in shape. This shape leads to additional noise at the tire/pavement contact area.
The picture below depicts the newly developed texture that provides a very smooth riding surface and low-noise generation characteristics. Equally important, the new surface can be controlled better, thereby allowing greater consistency. With conventional diamond grinding, the resulting fin shape is affected by the blade geometry, concrete and aggregate quality and the vibration of the equipment.
The purpose of the Mn/Road test sections was to validate the concept that fin profile controlled the noise generation characteristics and to validate the efficacy of the Tire Pavement Test Apparatus (TPTA) used by Purdue to conduct ACPA’s research. Since TPTA research is conducted in a laboratory setting, it was not known whether similar results could be obtained in the field on real concrete pavements using actual diamond grinding equipment. Both questions were answered by the Mn/Road field test sections.
Knowing that the TPTA surface texture was field-proven allows continued laboratory development of textures with confidence they can be field-implemented.
Mn/DOT, being the lead state in a Federal Highway Administration (FHWA)-pooled fund effort on concrete surface characteristics, provided a section of their Low Volume Road Test Area for the grinding experiment. They also provided personnel, equipment and testing support in this joint venture between the pooled fund study and ACPA. Bernard Izevbekhai of Mn/DOT coordinated the pooled fund effort and assisted in the development and conduct of the experiment.
Terry Kraemer, president of Diamond Surface, developed the custom-built grinding head which was used on Purdue’s TPTA to evaluate a range of concrete pavement textures. This testing has been a centerpin of ACPA’s tire pavement and surface characteristics testing program.
In addition to Kraemer, a number of other people and organizations were involved in the project, including Purdue University, the FHWA, Mn/DOT, Mn/Road and the Concrete Paving Association of Minnesota.
The next phase of this experiment will be to construct the Purdue-developed texture on an in-service highway so additional construction and performance measurements can be obtained.
ACPA, the National Concrete Pavement Technology Center (CP Tech Center) and the FHWA, along with support from key agencies and ACPA chapter states throughout the U.S. and Canada, worked together to evaluate pavement surface characteristics on a far-reaching field research project.
The defined goal of the testing was to understand the relationship between noise and pavement texturing, as well as diamond grinding to impart texture. The research also was aimed at evaluating the noise/texture/time relationship, as well as developing construction techniques that are repeatable and cost-effective.
The first phase of the research has been completed and the final report will be published soon. Additional testing will be carried on by the CP Tech Center to monitor some sections through time, as well as to determine what contractors can do during construction to reduce the variability of texturing (GFV1).
Position change
No article about surface characteristics would be complete without acknowledging the major policy change effected in September 2005 by the FHWA. The agency, encouraged by ACPA, changed its long-standing position on the use of transverse-tined texture.
The FHWA’s original position was adopted in 1979 and stood until the change. ACPA pushed for a full spectrum of concrete pavement textures to be allowed. The new policy allows states to use a variety of textures, including the types used in Europe, as long as the states demonstrate that they meet safety requirements.
As a next step, ACPA will compile and validate more data from the testing. Then, the two new diamond-grinding textures will be tested on roadways under traffic. If they perform as expected, there could soon be another valuable technology available to contractors and agencies wanting to strike a balance between surface characteristics and the other positive features of concrete pavements.
As for the balance of the ACPA’s tire/pavement noise and surface characteristics research, the program will continue with further analysis and documentation, which the association will report as they become available.
