Annotated Literature Review for NCHRP Report 640 (2009)

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139 1.31.4 Construction Practices No specifics on construction practices were given. 1.31.5 Maintenance Practices This article briefly describes a truck mounted equipment that utilizes high pressure water and a suction system used to clean open-graded porous asphalt pavements. The system uses multiple high speed rotating water nozzles to apply a high water volume at a high pressure to dislodge debris within the pavement. A double suction bar is then used to remove the water and debris from the pavement surface. All processes are computer controlled which allows the operator to control water pressure and volume. The article states that New Zealand has been using this process for approximately 6 months with “substantial success.” 1.31.6 Rehabilitation Practices No specific rehabilitation practices were given. 1.31.7 Performance No specific performance measures were given; however, the article did state that cleaning was needed on open-graded porous asphalt pavements at an age ranging between 6 and 8 years. 1.31.8 Structural Design No specifics on inclusion within structural design were given. 1.31.9 Limitations No limitations on use were given. 1.32 Momm, L. and E. M. Filho. “Study of the Aggregate for the Pervious Asphalt Concrete.” 2nd International Symposium on Maintenance and Rehabilitations of Pavements and Technological Control. Auburn, Alabama. July 29-August 1, 2001. 1.32.1 General This paper presents the results of a laboratory study conducted to evaluate the effect of aggregate gradation on durability, permeability and rutting. The effect of gradation was evaluated as both maximum aggregate size and various aggregate sizes that were gapped to create the desired gradation (e.g., the breakpoint sieve was altered). 1.32.2 Benefits of Permeable Asphalt Mixtures No specific benefits were given. 1.32.3 Materials and Mix Design Contents of this paper do not specifically deal with materials or mix design; rather the paper provides research results that show the influence of aggregate gradation characteristics on laboratory performance. Therefore, the results presented in the paper are discussed within this section.

140 Aggregates used within this project were granite. No physical properties of the granite were provided other than it was crushed. A viscosity graded AC-20 that had been modified with 4 percent of a SBS polymer was used as the asphalt binder. Three maximum aggregate size (MAS) gradations were evaluated during the study: 9.5, 12.5 and 19mm. Evaluation of the effect of gradation on durability, permeability and rutting entailed three separate experiments. In the first experiment, a total of six gradations were fabricated: 9.5mm MAS with gap beginning with the 2mm sieve, 12.5mm MAS with gaps beginning at the 2 and 4mm sieves and 19mm MAS having gaps beginning at 2, 4 and 6mm. Each of the gradations had 3 to 5 percent passing the 0.075mm sieve. The six gradations were combined with asphalt binder at contents ranging from 3.6 to 5.2 percent. The paper does not provide information on how samples were compacted in the laboratory; however, the paper does mention Marshall samples. Two tests were conducted on the samples, a Cantabro Abrasion test and a test to determine the volume of interconnected voids. The test to determine the interconnected voids content was described as a test that measures the volume of water that penetrates into a test specimen. Results from this first experiment indicated that the percentage of interconnected voids within the samples was considered by the authors as low. Typical ranges were approximately 5 percent interconnected voids and lower. There was a trend toward higher percentages of interconnected voids for larger maximum aggregate size gradations and lower asphalt contents. Cantabro Abrasion results were also deemed low by the authors. All results were below 14 percent. There was a trend toward higher loss values as the maximum aggregate size increased and asphalt binder contents decreased. Using the information obtained from the first experiment, the authors fabricated three additional gradations for a second experiment. For these three gradations, the aggregates were essentially single size from the maximum aggregate size to 7.7 percent passing to create an open-grading. Each of the three gradations was combined with asphalt binder to yield binder contents of 3.6, 4.0 and 4.4 percent. Each mix was again evaluated for the percentage of interconnecting voids and Cantabro Abrasion; however, these mixes were also subjected to rut testing in the LCPC wheel tracking device and permeability testing. Cantabro loss values for these mixes were higher than from the first experiment. Results ranged from 10 percent to 29 percent loss. Similar to the first experiment, Cantabro loss values tend to increase for larger maximum aggregate size gradations and lower asphalt binder contents. The percentage of interconnected voids was higher for these open gradations of the second experiment. Results ranged from about 20 percent interconnected voids to 12 percent. Again, larger maximum aggregate size gradations and lower asphalt binder contents generally resulted in more interconnected voids. Accordingly, permeability values were much higher for larger maximum aggregate size gradations [the influence of asphalt binder content was not presented]. Results of the rutting tests from the LCPC wheel tracking device were similar for all three maximum aggregate size gradations. All three were shown to be resistant to rutting.