Annotated Literature Review for NCHRP Report 640 (2009)

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156 1.35.4 Construction Practices Bendtsen et al did not discuss construction practices. 1.35.5 Maintenance Practices Bendtsen et al did not discuss maintenance practices. 1.35.6 Rehabilitation Practices Bendtsen et al did not discuss rehabilitation practices. 1.35.7 Performance Bendtsen et al did not discuss performance of permeable asphalt mixes. 1.35.8 Structural Design Bendtsen et al did not discuss structural design. 1.35.9 Limitations Bendtsen et al did not discuss limitations. 1.36 Faghri, M. and M. H. Sadd. “Performance Improvement of Open Graded Asphalt Mixes.” Report on URI_TC Project No. 536144. October 2002. 1.36.1 General The objective of this study was to evaluate the effect of additives, fiber and polymer on strength and permeability properties of open-graded asphalt mixes. Faghri and Sadd designed mixes with the Marshal method – using different gradations, cellulose fiber and SBS polymer. They conducted tests to determine air voids, permeability and indirect tensile strength tests. A subset of samples was tested for permeability and strength at a range of temperatures. Faghri and Sadd mention that the air voids differ significantly when incorporating the different gradations, and that the addition of fiber resulted in decrease in voids in two of the three mixes. Permeability was also reduced with the addition of fibers. The addition of polymer enhanced permeability as well as strength significantly. Faghri and Sadd indicate that for the one mix tested for permeability and indirect tensile strength at different temperatures, an increase in permeability and a decrease in strength were noted with an increase in temperature. Faghri and Sadd conclude that using a polymer modifier only (as opposed to using fiber or a combination of fiber and polymer) is the best option for optimizing strength and permeability properties.[No durability testing was conducted.] 1.36.2 Benefits of Permeable Asphalt Mixtures In their introduction Faghri and Sadd indicate that open-graded mixes provide significantly better drainage compared to other mixes, and that the porous structure of the open-graded mixes allow both horizontal (surface) and vertical (through) drainage. They

157 mention that such enhanced and rapid removal of water lead to a dry pavement surface during moderate rainstorms and, hence, lead to increased safety of the drivers. 1.37.3 Materials and Design Faghri and Sadd provide information on different mixes used in this study. In the first phase of this study, to establish base line permeability values, four different gradations were used. However no results were provided for these mixes. For the mixes in which results were provided, three different gradations (Table 86) were used, referred to as the Arizona, Georgia and SMA mixes. The asphalt contents were determined using the Marshall method. A cellulose fiber and a SBS polymer were used. Table 86: Study Gradations Mix Property Arizona Georgia SMA Gradation Sieve Size (mm) 19 12.5 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075 Percent Passing 100 93 85 34 16 7 5 3 2 2 Percent Passing 100 90 75 24 20 20 14 14 14 9 Percent Passing 100 93 65 18 8 8 8 8 8 3 Asphalt Content (PG 64-22) 5.50 5.84 5.80 Note: Fiber – Technocel 1004 fiber; polymer – CITGO SBS polymer; four different mixes were prepared for each gradation – PG 64-22, PG 64-22 with fiber, PG 64-22 with SBS polymer and PG 64-22 with fiber and polymer Faghri and Sadd provide descriptions of tests conducted on the samples. The information is summarized in Table 87. Table 87: Tests Conducted on Samples Test Method Bulk specific gravity Test on paraffin coated specimens, ASTM D 1188-96 Theoretical maximum density ASTM D2041-95 Voids in total mix ASTM D3202-94 Permeability Falling head permeameter Strength Indirect tensile strength test, ASTM D4123-82

158 In discussing the results of volumetric property tests, Faghri and Sadd indicate that in general the air voids were the lowest in the SMA mixes and the highest in the Georgia mixes. The addition of fiber (alone or with polymer) resulted in lowering of voids in Arizona and SMA mixes, but not in Georgia mixes. The authors then present the results of permeability tests conducted at different temperatures. They indicate that the SMA mix had very low permeability, while the Georgia mix had the highest permeability. The permeabilities for both Arizona and Georgia mixes were the highest for the polymer only mixes, and lowest for those containing fiber only. Tests were run at 25oC, 35oC, 45oC and 55oC with samples from the Georgia mix. The author point out that the permeability increased with an increase in temperature. In discussion of results obtained from indirect tensile strength tests, Faghri and Sadd indicate that the strengths for all three mixes increased significantly with the addition of polymer (compared to the base mix containing neither fiber nor polymer). The addition of fiber increased the strength by only a small amount. Samples of the Georgia mix were tested for indirect tensile strength test at 25oC, 35oC, 45oC and 55oC. The authors indicate that the strength decreased significantly with an increase in temperature. Faghri and Sadd then provide discussion on correlations between permeability and air voids and permeability and strength of the mixes. One correlation between air voids and permeability, they compare their results with those obtained from a study reported by the National Center for Asphalt Technology (NCAT) in 2000. They point out that the trend line obtained from this study is significantly different from the one obtained from the NCAT study and that the range of air voids considered in this study is greater than that considered in the NCAT study. However, in the common range, they point out that the curves are reasonably close to each other. In discussing the plots of permeability versus strength, the authors contend that there is a significant enhancement in strength and permeability with the addition of polymer, whereas relatively low enhancement in strength and a significant decrease in permeability are achieved with the addition of fiber only. 1.36.4 Construction Practices No information has been provided on construction practices. 1.36.5 Maintenance Practices No information has been provided on maintenance practices. 1.36.6 Rehabilitation Practices No information has been provided on rehabilitation practices 1.36.7 Performance No information has been provided on performance.