Annotated Literature Review for NCHRP Report 640 (2009)

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47 1.10 Kuennen, T. “Open – Graded Mixes: Better the second time around”. American City & County, August 1996 1.10.1 General With asphalt modifiers providing stability and noise suppression, open-graded mixes are receiving the applause they deserve after an initial mixed response. This article describes how open graded friction course (OGFC) (also known as “popcorn” or porous asphalt) is getting a second look by the asphalt pavement industry. According to Kuennen, the uses of the newest polymer modifiers lead to a more durable asphalt binder. 1.10.2 Benefits According to the American City & County magazine article, the benefits from the use of OGFC are fast drainage of water from the surface as well as the virtual elimination of tire spray and hydroplaning. Researchers in the United States and Europe have stated that OGFC provides instant reduction in annoying tire/pavement noise by as much as 5 dB(A), although the effect diminishes with time. The researchers were also quick to say all the benefits come with a high cost, about 35 percent more per ton than conventional asphalt pavements. 1.10.3 Materials and Mix Design OGFC is a HMA that incorporates a uniform aggregate size with a minimum amount of fines. Air void contents range from as low as 12 percent to as high as 15 percent, while in Europe it is even higher (17 to 22 percent). The stone-on-stone structure can hold up better to heavy traffic, especially trucks. The texture created by the use of larger aggregates without fines provides better traction. 1.10.4 Construction Practices According to American City & County magazine article, OGFCs are constructed as a conventional asphalt mix. The major difference is the materials and structural design practices. 1.10.5 Maintenance Practices No specifics of maintenance practices were described in this article. 1.10.6 Rehabilitation Practices No specifics of rehabilitation practices were described in this article. 1.10.7 Performance In addition to high drainage ability combined with minimized spray, hydroplaning, reduced glare at night and improved skid resistance; OGFC helps to attenuate highway noise. This capability has been studied extensively in Europe where the environmental impact of highway in high- density urban area has undergone close scrutiny for years. 1.10.8 Structural Design No specifics on inclusion within structural design were given. 1.10.9 Limitations