Annotated Literature Review for NCHRP Report 640 (2009)

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244 1.61.8 Structural Design No information on structural design is provided in this paper 1.61.9 Limitations No information on limitation on use of PFC is provided in this paper 1.62 Brousseaud, Y. and F. Anfosso-Lédée. “Silvia Project Report: Review of Existing Low Noise Pavement Solutions in France.” SILVIA-LCPC-011-01- WP4-310505. Sustainable Road Surfaces for Traffic Noise Control. European Commission. May 2005. 1.62.1 General This report provides an overview of low noise pavement solutions in France. The report was written for the SILVIA (Sustainable Road Surfaces for Traffic Noise Control) project which is funded by the European Commission. Mostly single layer porous asphalt is utilized in France; however, double-layer porous asphalt is sometimes used. Typically, porous asphalt will have a 6mm or 10mm maximum aggregate size gradation and be placed on the roadway 30 to 40mm in thickness. 1.62.2 Materials and Mix Design In France, porous asphalt is divided into one of two classes. Class 1 porous asphalt is designed at 20 to 25 percent air voids while Class 2 is designed at 25 to 30 percent air voids. Typical porous asphalt has a 10mm maximum aggregate size gradation with a gap in the grading between 2 and 6mm. The material passing the 0.075mm sieve is generally about 3 to 4 percent of the aggregate fraction. In most applications, a polymer-modified binder is used. Typical asphalt binder contents range from 4.6 to 5.0 percent. Acrylic, glass or cellulose fibers are added to reduce draindown potential. Mix designs are conducted with a Gyratory Shear Compactor. A total of 25 gyrations are used. 1.62.3 Benefits The primary benefit of porous asphalt discussed in this paper was the reduction of tire/pavement noise. Porous asphalt in France has typical noise levels of approximately 71 to 73 dB(A) when measured by the Statistical By-Pass method. For comparison, typical dense-graded HMA has a noise level of approximately 76 dB(A). Skid resistance was briefly mentioned as a benefit. The authors indicated that speed has nearly no effect on the braking force coefficient.

245 1.62.4 Construction Practices The authors suggest that prior to placement of a porous asphalt layer, a water drainage study should be conducted on the existing layer. The water drainage study should entail evaluating the permeability and the grade and cross slope of the existing layer. Existing layers that are permeable or areas that will hold water should be avoided. Because the porous layer and underlying layer are only in contact through the coarse aggregate of the porous asphalt, a good quality tack coat is needed. The authors recommended a tack coat with 400g/m2 of residual binder. 1.62.5 Maintenance Practices The primary problem with general maintenance is clogging of the porous asphalt void structure. The authors state that roadways with low traffic volumes (especially heavy trucks) can clog at an early age. With respect to winter maintenance, the authors state that experience is the only true method of developing a winter maintenance program. Porous asphalt presents unique winter conditions because frost emerges at a higher ambient temperature as the surface temperature of porous asphalt is 1.5 to 2.0˚C lower than typical pavements. Also, typical de-icing practices are not as effective as porous asphalt as on typical dense-graded pavement surfaces. 1.62.6 Rehabilitation Practices The authors mentioned, but did not elaborate, on three rehabilitation techniques: replacement with a new porous asphalt, overlaying (with or without seal coat), and recycling in-place or in a plant. 1.62.7 Performance Permeability was mentioned as a performance measure for porous asphalt. Table 119 presents typical results from a permeability related test. No specifics are provided for the permeability related test; however, it appears similar to other devices used in Europe that simply determine the time required for a certain volume of water to infiltrate into a layer (expressed as cm/sec). Results of this test are reported as percolation speed. An interesting observation of Table 119 is that as the maximum aggregate size of the gradation increases (10mm compared to 6mm) the permeability increases (percolation speed increases). Table 119: Typical Percolation Speed of Porous Asphalt in France Class 1 Class 2 Type of Porous Asphalt 0/6mm 0/10mm 0/6mm 0/10mm Percolation speed (cm/sec) (NF P 98-254-3) 0.6 0.8 0.9 1.2 1.62.8 Structural Design The only information provided on structural design is that a typical thickness of porous asphalt is 30 to 40mm.