Annotated Literature Review for NCHRP Report 640 (2009)

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172 continuous stretches of OGFC are more desirable than alternate applications of dense- graded HMA and OGFC. The timing of preventative winter maintenance is very important. Salting is only beneficial on dry pavements when the temperature is less than -10˚C. Referencing work from Austria, Kandhal indicates that a combination of 70 percent dry salt and 30 percent salt water solution applied at a rate of 10 to 20 g/m2 has been effective for OGFC. The use of brine at the appropriate time has also been found effective in Holland and reduces the amount of dry salt needed to only 15 percent more than that required for dense-graded HMA. 1.40.6 Rehabilitation Practices Kandhal states that it is generally recommended to mill off the existing OGFC and replacing with a new OGFC or other type HMA. 1.40.7 Performance No specific performance measures were given. 1.40.8 Structural Design In the U.S., OGFC layers are generally placed at a thickness of 20mm; however, Oregon has used 50mm for many years. In Europe, thicknesses also range from 20 to 50mm. Assignment of a structural coefficient for OGFC layers vary throughout the U.S. California assigns a structural coefficient similar to permeable base layers. Oregon assigns the same structural number for both OGFC and dense-graded layers. Some states do not assign a structural number to OGFC. 1.40.9 Limitations Kandhal provides a number of situations where OGFC should not be used. OGFC should likely not be used on projects that include long haul distances. Long haul distances increase the potential for draindown and/or cooling of the mix. Oregon restricts haul distance for OGFC to 56km (35 miles). OGFC should not be used in inlays. OGFCs should be free draining at the pavement edge; therefore, they should not be used as an inlay. Handwork is difficult with OGFC mixes. Therefore, projects that include a lot of handwork should probably not include OGFC. Kandhal noted that OGFC should not be used in snow zones where extensive snow plowing is required. OGFC may ravel and shove in some critical pavement locations such as intersections, locations with heavy turning movements, ramp terminals, curbed sections and other adverse geometric locations. The final limitation noted by Kandhal has to do with underlying layers. OGFC should not be placed on a permeable layer. Water can infiltrate a permeable underlying layer causing moisture damage. 1.41 Larsen, L.E. and H. Bendtsen. “Noise Reduction with Porous Asphalt – Costs and Perceived Effect.” Ninth International Conference on Asphalt Pavements. International Society of Asphalt Pavements. Copenhagen, Denmark. 2002.

173 1.41.1 General This paper presents a cost comparison between various options of noise abatement including noise barriers, building insulation and porous asphalt. The authors state that approximately 20 percent of all homes in Denmark are exposed to noise levels exceeding 55 dB. Six percent are exposed to more than 65 dB. Within Denmark, a noise level of 65 dB requires noise abatement. Larsen and Bendtsen indicate that noise reducing pavements are the most realistic means for noise abatement. Noise barriers are not feasible along many urban roadways. Insulation of building facades reduces noise within the structure but does nothing for persons outdoors. For roads with traveling speeds greater than 70 km/hr, a single layer of porous asphalt having an 8 mm maximum aggregate size has been used to reduce noise levels by an average of 3dB compared to typical dense-graded wearing layers. At speeds lower than 70 km/hr, there has been a problem with the void structure of the porous asphalt clogging, whereby, much of the noise reduction is lost. Another alternative porous asphalt technique for slower speed roadways that was currently being evaluated in Denmark was the placement of two-layer porous asphalt. The two layer porous asphalt system being investigated included a 25 mm top layer comprised of an 8 mm maximum aggregate size porous asphalt overlying 45 mm of 16 mm maximum aggregate size porous asphalt. The authors indicated that the pores within the top layer could be kept open by high pressure cleaning twice a year. The objective of this study was to compare the cost of two layer porous asphalt to noise barriers and sound insulation as noise abatement techniques. The authors created three scenarios representing city streets, ring roads and freeways. The unit of measure that was used to define noise levels within the study was the Danish Noise Exposure Factor (NEF). The NEF is an expression for accumulated noise annoyance within housing areas. As NEF is reduced, noise annoyance is also reduced. For each of the three scenarios, the authors estimated costs for reducing the NEF. Assumptions used for the three scenarios included: City Streets • Two lane roadway with an annual daily traffic of 12,000 vehicles including 10 percent trucks. • Vehicle speed of 50 km/hr • Closed rows of apartment buildings that are 6 stories tall with shops on the bottom floor. On a 1000 m section of roadway, 655 apartments line the road. • With no noise abatement, the first floor level of noise would be 68 dB and the noise level on the fifth floor would be 65 dB.

174 Ring Road • Four lane roadway with an annual daily traffic of 30,000 vehicles including 10 percent trucks. • Three-story apartments on each side of the road. On a 1000 m section of roadway, 399 apartments line the road. • Vehicle speed of 70 km/hr. • With no noise abatement, the noise levels would be approximately 73 to 74 dB. Freeways • Three lanes in each direction with an annual daily traffic of 60,000 including 10 percent trucks. • Row houses on each side of the freeway. Half of houses are single story and half are two-story. • Vehicle speed is 110 km/hr. • Noise levels are 77 dB on facades of houses within the first row. Table 93 presents the results of the cost analyses comparing two layer porous asphalt, noise barriers and building insulation. Table 93: Costs (net present value) and Effect of the Three Noise Abatement Techniques City Street Ring Road Freeway 30 year cost Euro 296,000 Euro 360,000 Euro 477,000 dB reduction 4 5 6 NEF reduction 85.7 153.2 179.4 Cost/dB/dwelling Euro 111 Euro 180 Euro 183 Two-Layer Porous Asphalt Cost/NEF Euro 3,454 Euro 2,350 Euro 2,659 30 year cost --- Euro 1,335,000 Euro 1,590,000 dB reduction --- 0-12 (avg 3.9) 0-13 (avg 6.2) NEF reduction --- 75.5 195.3 Cost/dB/dwelling --- Euro 858 Euro 590 Noise Barrier Cost/NEF --- Euro 17,658 Euro 8,141 30 year cost Euro 2,685,000 Euro 1,607,000 Euro 2,890,000 dB reduction 9 9 9 NEF reduction 99.0 170.0 123.7 Cost/dB/dwelling Euro 449 Euro 448 Euro 738 Building Insulation Cost/NEF Euro 27,121 Euro 9,453 Euro 23,363 Based upon the data presented in Table 93, the authors stated that two-layer porous asphalt is an effective means of noise abatement both in terms of reductions in decibels and reductions in NEF. 1.41.2 Benefits of Permeable Asphalt Mixtures The authors state that the reduction in tire-pavement noise levels is a benefit of using porous asphalt.