Annotated Literature Review for NCHRP Report 640 (2009)

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150 only if surface repairs are conducted prior to the placement of class F mix. They indicate that surface repairs can include localized inlays, travel lane inlays, a dense HMAC lift below the Class F mix, or other forms of reflective crack control. Ruts of moderate to high severity should be leveled prior to the Class F mix overlay to prevent water from sitting in the deeper sections of Class F mix. 1.33.9 Limitations Moore et al mention three conditions under which open-graded mix is not recommended for use: 1) Low volume roads with ADT of less than 1,000. They mention that for this level of traffic the technical benefits are not as noticeable due to the low volume of traffic and lack of heavy loads. Moore et al mention that in eastern Oregon, emulsified asphalt concrete (EAC) is used extensively for the low volume highways because of lower cost of EAC and that maintenance patching will be the primary means of sustaining these low volume highways over a longer period of time. Maintenance has reported that patching over Class F mix is difficult (problems with getting the patch to “stick”). The patches also tend to dam the drainage path and reduce splash and spray benefits. 2) Curbed areas or areas requiring handwork. Class F mix is not recommended for use in areas with curbs or where a significant amount of handwork or feathering is required. The mix’s aggregate size and aggregate gradation makes handwork difficult around utility appurtenances and at driveways. Also, curbs block the drainage of the Class F mix. 3) Heavily plowed areas where steel plow blades are used. As a result of snowplow damage Class F mix is no longer recommended in areas where plowing is frequent. The snowplows can cause raveling and gouging resulting in a higher rate of surface deterioration. The determination of frequency of plowing is on an individual project basis, but generally involves elevation, any existing plow damage, and existing chain-up areas or snow zones. 1.34 Abe, T. and Y. Kishi. “Development of Low-Noise Pavement Function Recovery Machine.” Proceedings of the Ninth International Conference on Asphalt Pavements. Copenhagen, Denmark. August 2002. 1.34.1 General This paper presented the results of a research study designed to develop a method and associated equipment for returning the functionality (in terms of permeability) of permeable friction courses. The authors describe laboratory and field studies to evaluate methods of cleaning the void structure of permeable friction courses. Comparisons were made between water jets and the use of water jets along with cavitation. Cavitation occurs when a high speed water jet is injected into static water resulting in development of cavitation bubbles. When collapsing, the cavitation bubbles create a high pressure that dislodges debris. 1.34.2 Benefits of Porous Asphalt Mixtures Though not specifically studied, the authors indicate that permeable friction courses are low-noise pavements.

151 1.34.3 Materials and Design No specifics on materials and mix design were given. 1.34.4 Construction Practices No specifics on construction practices were given. 1.34.5 Maintenance Practices Research documented within this paper was conducted to evaluate two methods of de- clogging (removing debris) permeable friction courses. The two methods included a water jet and a water ejection system creating cavitation in water held within the pavement structure. The initial research was conducted in the laboratory to compare the ability of the two methods to create impulsive pressure. The first experiment entailed ejecting water by both methods onto a pressure sensitive film to compare the methods. Results of this testing indicated that the water jet accompanied by the cavitation bubbles had a significantly higher impulsive pressure. The area affected by the water jet accompanied by the cavitation bubbles was much larger than the water jet alone. [The areas were not quantified; however, pictures comparing the two indicated more than 20 times more area affected by the water jet accompanied by the cavitation bubbles.] The second laboratory evaluation entailed a plaster stripping test. Within this test, a 15 mm steel bar was coated with plaster. Both methods of water ejection were then held 30 mm from the steel bar. Results of the testing showed that the water jet in air stripped the plaster from the steel bar a distance of 20 mm. Twenty-six percent of the circumference of the bar was also stripped. For the water jet in water (cavitation), the distance of the steel bar stripped of plaster was 38 mm and 78 percent of the circumference of the bar was stripped. [Pictures of the bar illustrating the effects of both water ejection methods showed a marked difference in the amount of plaster stripped.] The authors stated that the results of these laboratory tests showed that the water jets within water creating cavitation was potentially a better method of cleaning porous pavements; therefore, additional testing was conducted in the field using this method. Based upon the results of the laboratory testing, the authors developed a small “function- recovery” test for porous pavements. The device allowed the authors to clean the porous pavement using both methods described above. A porous pavement was artificially clogged using the following method: 1. Mix fine sand, silt and plaster in a dry condition at a weight ratio of 35:35:10. 2. The material was spread onto the porous pavement and leveled. 3. Vibration was applied to cause the materials to settle within the pavement void structure. 4. More material was added and leveled using a rake. 5. Steps 2 and 3 were repeated. 6. Water was sprayed onto the pavement and the material allowed to cure. In order to compare the two methods in the field, a falling head field permeability test was used on the clogged pavement and again after cleaning. Table 83 presents data when comparing the two methods on the artificially clogged permeable friction course. Results indicate that both methods removed the clogging materials from the pavement structure;

152 however, on average, the water jet with cavitation method did improve draining characteristics more. Table 83: Results of Permeability Testing after Functional Recovery Type No. Data Points Avg. Time before cleaning Avg. Time after cleaning Water Jet 6 Impermeable 5.14 (seconds/400 ml) Water Jet w/ Cavitation 6 Impermeable 4.65 (seconds/400 ml) Following the laboratory and field experiments, the authors concluded that the best function recovery method was utilizing the water jet and cavitation method. This concept was then used to design a truck-mounted Function-Recovery machine. The new machine is truck-mounted (Figure 14) and is comprised of a specially designed high-pressure water ejection system with a high vacuum suction system (Figure 15). After developing the new equipment, the authors conducted some field trials to evaluate the effectiveness of the new equipment to remove clogging materials within permeable friction courses. This was again accomplished using the falling head field permeability test. Results are illustrated within Table 84. Figure 14: Truck-Mounted Function-Recovery Machine

153 Figure 15: High-Pressure Ejection and Vacuum Systems See rehabilitation practices below. This paper discusses a water jet cavitation process for rehabilitation of porous pavements. Nothing was discussed about when to use. Measurements were made comparing water jets in air and in water (cavitation) to determine which the better method was. Rehabilitation Practices Table 84: Results of Permeability Testing after Use of Truck-Mounted Function Recovery Machine Seconds/400 ml Measuring Point 1 2 3 4 5 6 7 8 Avg Before cleaning Imp Imp 400 125 243 Imp Imp 133 --- Sh. After cleaning 45 144 37 84 110 149 121 88 97 Before cleaning 8 8 7 14 10 7 14 14 10 BWP After cleaning 8 8 6 9 8 5 10 9 8 Before cleaning 38 Imp 72 2 32 65 73 178 175 OWP After cleaning 34 24 26 20 16 21 20 30 24 Sh. – Road Shoulder BWP – Between wheel paths OWP – outside wheel paths Imp – 400 ml of water did not flow into pavement during test. The authors concluded that the new water jet with cavitation equipment is an effective method of general maintenance for permeable friction courses. The self-contained, truck- mounted equipment was successful at improving the drainage capacity of permeable friction courses. 1.34.6 Rehabilitation Practices Not addressed 1.34.7 Performance As stated previously, a falling head permeability test was used as an indicator of performance. The test method and equipment is outlined within the Pavement Test Method Manual (1998) of the Japan Road Association. The device is somewhat similar to field permeability devices developed within the U.S. at the National Center for Asphalt