Annotated Literature Review for NCHRP Report 640 (2009)

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154 Technology, University of Arkansas, and Worcester Polytechnic Institute. The device is simply sealed to the pavement surface and water is introduced into a vertical standpipe. A cock-valve is located at the bottom of the device that when opened, water flows from the standpipe into the pavement. The test is run until 400 ml of water flows into the pavement. 1.34.8 Structural Design Not addressed 1.34.9 Limitations Not addressed 1.35 Bendtsen, H., C. B. Nielsen, J.Raaberg, and R.A. Macdonald. “Clogging of Porous Bituminous Surfacings – an Investigation in Copenhagen.” Danish Road Institute Report 120. Road Directorate, Danish Road Institute. Denmark. June 2002. 1.35.1 General This paper outlines the research of porous pavement clogging and noise reduction undertaken by the Danish government in 1998. The use of porous pavement in Denmark had been halted in the early 1970’s because of unsuccessful trials. In the early 1990’s two trials using porous asphalt as a surface layer led to its resurgence. The driving force behind the 1998 research project was the implementation of a new plan called Transport 2005. In this plan the Danish government set goals for reducing traffic noise to 65 dB by the year 2010. The research conducted by Bendtsen et al consisted of the construction of four porous asphalt test sections. Section 1 was comprised of a 45 mm thick base layer (16 mm maximum aggregate size) with a 25 mm thick top layer (8 mm maximum aggregate size). Section 2 was comprised of a 35 mm thick base layer (16 mm maximum aggregate size) with a 20 mm thick top layer (5 mm maximum aggregate size). Section 3 was comprised of a 65 mm thick base layer (22 mm maximum aggregate size) with a 25 mm thick top layer (5 mm maximum aggregate size). Section 4 was a 30 mm single layer control section of dense mix (8 mm maximum chipping size). All mixes were constructed with a SBS (Styrene-Butadiene-Styrene) modified asphalt. The research presented in this paper outlines the experimental approach taken by Bendtsen at al. Four test sites were constructed to conduct permeability testing using the Becker’s Tube method, noise measurements following ISO 11819-1 (1997) applying the Statistical Pass-By Method, and forensic analysis tests (Plane and Thin Section tests) on cores. More specifically permeability tests using Becker’s tube were conducted at the opening of the road and before/after each semi-annual flushing operation. Bendtsen et al

155 proposed classification for the degree of clogging as related to permeability testing as shown in Table 85. Table 85: Classification of Degree of Clogging Degree of Clogging of Porous Asphalt Outflow Time (s) Permeability Class New porous asphalt 30 High Partly clogged porous asphalt (can be flushed clean) 50 Medium Clogged porous asphalt (cannot be flushed clean) 75 Low Bendtsen et al further state, “With regards to noise reduction, permeability is also an important property since the pumping of air from vehicle wheels is the cause of some of the noise emanating from moving vehicles. If the voids in the surfacing are clogged, air from tyre-pumping cannot be absorbed and dissipated by the surfacing.” Thus noise measurements were also taken in this research. Test section 1 showed no decrease in noise, although that section did have the coarsest aggregate. Section 2 showed a 1.4 dB reduction in noise and Section 3 showed a 2.2 dB decrease in noise between 1999 and 2000. The forensic analysis tests, Plane and Thin Section tests, were conducted on cores taken immediately after construction in 1999. These cores showed no signs of stripping and all aggregates appeared well coated. Some sections did show the presence of dirt in some of the voids. After the 2000 permeability tests Bendtsen et al decided to take cores from the low permeability areas and. Cores were also taken from areas with good permeability as a check. From the cores with low permeability, it was observed that clogging occurred in the top 20 to 25 mm of the layer. From the cores with high permeability, clogging was still observed in the top 10 to 15 mm. Results of the research undertaken by Bendtsen et al yielded evidence that the porous pavement does reduce noise levels, permeability in the upper few centimeters of the porous pavement will be reduced over time because of the clogging of voids of asphalt, and the loss of permeability in the porous asphalt can lead to a lessened noise reduction effect as compared with new surfacing. 1.35.2 Benefits of Permeable Asphalt Mixtures Bendtsen et al mentioned that the main reason for using porous asphalt is its ability to drain water from the surface. This ability reduces aquaplaning (hydroplaning) and reduces splash and spray. 1.35.3 Materials and Design Bendtsen et al did not discuss materials and design.