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224 Punith et al mentions that skid resistance testing was carried out according to the ASTM 303 test method using the pendulum type skid resistance tester. As the test specimens used in this study were of 100 mm diameter and as the values of coefficient of surface friction of test specimens of different types of porous asphalt mixtures were only for comparative purposes, the slider assembly of aluminum backing plate with a bonded rubber strip of 31.8 by 25.4 by 6.35 mm was used to obtain a contact path length of 75 to 78 mm. The test specimens were tested for coefficient of friction values by applying sufficient quantity of water on the top surface area of the test specimens. The average value of coefficient of friction for the porous asphalt specimens was found to be 0.75, and no significant difference was found between the friction values of the different mixes (25 and 50 blow, and different types of asphalt binders) 1.56.8 Structural Design No information is provided on structural design. 1.56.9 Limitations No information is provided on limitations of use. 1.57 Tan, S.A., T.F. Fwa and K.C. Chai. âDrainage Considerations for Porous Asphalt Surface Course Design.â Transportation Research Record 1868, TRB. National Research Council. Washington, D.C. 2004. pp. 142-149. 1.57.1 General This paper discusses the development of drainage design charts used to determine the required thickness of a porous asphalt surface course for a given rainfall intensity. Tan et al theorized that the drainage performance of porous asphalt was a function of not only the drainage characteristics of the material, but also geometric design of the roadway. They further theorized that an under designed porous asphalt would not be able to keep the pavement surface dry under wet conditions. A 3D finite element program (SEEP3D) was utilized to construct and analyze models with varying rainfall intensities, surface course thicknesses, width of pavement, longitudinal slope, and cross slope. These models were validated with laboratory seepage tests. The analysis of these models showed that the drainage performance was enhanced with increased cross slope, regardless of the longitudinal slope. Similarly the effect of the longitudinal slope decreased as the cross slope and ratio of porous asphalt thickness to pavement width increased. 1.57.2 Benefits of Permeable Asphalt Mixtures Tan et al did not discuss any benefits of permeable asphalt mixtures. 1.57.3 Materials and Design Tan et al did not discuss materials and design.
