Annotated Literature Review for NCHRP Report 640 (2009)

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162 1.38.6 Rehabilitation Practices No specifics on rehabilitation practices were given. 1.38.7 Performance No specifics on performance measures were given. 1.38.8 Structural Design No specifics on inclusion within structural design were given. 1.38.9 Limitations No. specific limitations were given. 1.39 Iwata, H., T. Watanabe, and T. Saito. “Study on the Performance of Porous Asphalt Pavement on Winter Road Surface Conditions.” XIth International Winter Road Conference. World Road Association (PIARC). Sapporo, Japan. 2002. 1.39.1 General This paper presents results of research conducted by the Japan Highway Public Corporation on porous asphalt. Japan has plans to construct 11,520 km (7,200 miles) of expressway, approximately 6,850 km (4,300 miles) of which have already been constructed. Half of these expressways will pass through snowy or cold regions with a 10 year average maximum snow fall of 30 cm or more. In Japan, snow and ice control generally takes the form of a special water mixed solution for removal of snow. This poses a potential problem when porous asphalt pavements are used because the snow and ice control solution can drain into the porous asphalt layer. The authors list the current status on the use of porous asphalt in Japan as follows: 1. Approximately 33 percent of the in-service expressways currently include porous asphalt as the wearing layer. 2. Air void contents within porous asphalt layers are approximately 20 percent. 3. There is approximately an 80 percent reduction in wet weather accidents when comparing porous asphalt to dense-graded layers. 4. Japan uses a permeability requirement for porous asphalt layers. The test criterion is that 400 ml of water must penetrate into the porous layer within 10 seconds. 5. Japan has experienced an average reduction of 3 dB when using porous asphalt as compared to dense-graded HMA layers. The authors also provided the following technical problems associated with porous asphalt: 1. Methods for snow and ice control need to be established. 2. Methods for restoring permeability need to be established. 3. The durability of porous asphalt needs to be improved in regions where tire chains are used. 4. Methods for rehabilitation of porous asphalt need to be established.

163 5. Methods for ensuring an impermeable layer below the porous asphalt layer are needed. 6. Ways to reduce costs for porous asphalt are needed. The authors conducted a number of experiments to evaluate the performance of porous asphalt in winter conditions. The first experiment entailed comparing the temperature in porous asphalt and dense-graded HMA layers during cold weather. During the daytime, the road surface temperature of dense-grade layers was higher than nearby porous asphalt layers by about 2ºC at the largest difference. At nighttime, the road surface temperature was higher on porous asphalt layers by about 0.5ºC at the largest difference. During snowfalls, the authors indicate that the temperature of porous asphalt was lower than that of dense-graded layers by an average of 0.2ºC. Another experiment conducted by the authors entailed many visual examinations of pavement surfaces during dry, wet, slush, snow, and ice road conditions. Tables 88 and 89 present the results of the author’s examinations of pavement sections listed as either rutted or non-rutted. The upper right part of each of these tables represents the number of cases where the visual surface condition of porous asphalt was considered to be worse than nearby dense-graded surface layers. Alternatively, the lower left portion of each table signifies where the porous asphalt layers were considered in better condition than nearby dense-graded layers. The highlighted cells going diagonally across the tables are instances where the pavement surfaces of porous asphalt and dense-graded layers were considered similar. Table 88: Road Surface Conditions during a Snowfall (Rutted Sections) Porous Asphalt Pavement Rutted Sections dry wet slush snow ice total dry 33 33 wet 1 297 23 321 slush 14 96 2 112 snow 10 2 88 100 ice 10 3 3 23 39 Dense- Graded Pavement total 34 331 124 93 23 605

164 Table 89: Road Surface Conditions during a Snowfall (Non-Rutted Sections) Porous Asphalt Pavement Non-Rutted Sections dry wet slush snow ice total dry 34 34 wet 2 247 29 4 282 slush 13 114 8 3 138 snow 1 11 109 2 123 ice 4 5 1 18 28 Dense- Graded Pavement total 36 265 159 122 23 605 Based upon Tables 88 and 89, the authors indicated that two cases needed to be highlighted. The first scenario is when the dense-graded HMA surface was wet. In this situation, the snow falling onto the dense-graded surface is being melted while on the porous asphalt it is becoming slush or the snow was collecting on the porous asphalt surface. Therefore, conditions on the porous asphalt layer were worse than the comparing dense-graded surfaces. Based upon the data, these conditions only occurred less than 6 percent of the time during snowfall events. The second condition noted by the authors was when the dense-graded surfaces were covered with ice and the surface of the porous asphalt layer was either wet, slush or snow. In these instances the freezing of the road surface is difficult to occur on porous asphalt surfaces because any melted snow does not stay on the pavement surface. For the dense-graded surfaces, the melted snow stays on the road surface and can freeze if the temperature and salinity conditions are right. In another experiment, the authors monitored the salinity concentration on the pavement surface using three different spreading methods: solution, solid and wet salt. Data presented by the authors indicated that the rate of decrease in salinity concentration was less for porous asphalt than for dense-graded HMA. This observation was independent of the manner of spreading the winter maintenance materials. The authors indicate that the small decrease in salinity concentration offered by the porous asphalt allows the amount of anti-icing chemicals for freezing prevention to be reduced. When anti-icing chemical solution is spread, the porous asphalt maintained a higher salinity concentration than the dense-graded layers. When solid or wet salt are used for anti-icing, the salinity concentration of the dense-graded layer stayed higher. The authors also conducted skid testing using the Japan Highway Public Corporation’s locked wheel skid tester at 50 km/hr. Results from this testing indicated that except for when the porous asphalt was covered with compacted snow, the porous asphalt had higher skid resistance coefficients than dense-graded surfaces. When compacted snow was encountered, the friction coefficients were similar for the two surfaces. This indicated that the porous asphalt maintained equal or higher friction coefficients. The final experiment conducted by the authors was to evaluate wet weather accident data for roadways in which a dense-graded layer was replaced by porous asphalt. In these