Annotated Literature Review for NCHRP Report 640 (2009)

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83 Overall Backstrom concluded that, “…porous pavements are more resistant to freezing than an impermeable pavement due to higher water content in the soil, which increased the latent heat in the ground. Cooling of the porous pavement is governed by variations in ambient air temperature, and freezing of the soil below the subgrade is related to the freezing index. Thawing of the porous pavement is a quick process, which was explained by the meltwater infiltration. The thawing process in a comparable impermeable pavement is slower. The frost penetration depth is decreased, and the frost period is shorter in a porous pavement compared with an impermeable pavement. Consequently, there is a lower risk for frost heave damage on porous pavement rods than on conventional roads.” 1.19.2 Benefits of Permeable Asphalt Mixtures Backstrom states that porous asphalt provides benefits such as, “…storm-water flow attenuation, aquifer recharge, and storm-water pollution control.” 1.19.3 Materials and Design Backstrom did not discuss materials and design. 1.19.4 Construction Practices Backstrom did not discuss construction practices. 1.19.5 Maintenance Practices Backstrom did not discuss maintenance practices. 1.19.6 Rehabilitation Practices Backstrom did not discuss rehabilitation practices. 1.19.7 Performance Backstrom did not discuss performance of permeable asphalt mixes. 1.19.8 Structural Design Backstrom did not discuss structural design. 1.19.9 Limitations Backstrom did not discuss limitations. 1.20 Cooley, L. Allen, Jr., E. R. Brown, and D. E. Watson. “Evaluation of OGFC Mixtures Containing Cellulose Fibers.” Transportation Research Record No: 1723. Transportation Research Board. National Research Council. Washington, D.C. 2000. 1.20.1 General In this paper Cooley et al provide a description of a field and a laboratory study carried out to compare the performance of OGFC mixes with different types of fibers. The primary objective was to evaluate the use of cellulose fibers as stabilizers in OGFC mixes. To achieve this objective, the researchers looked at field sections containing OGFC mixes with cellulose and mineral fibers and tested materials and mixes prepared in the laboratory.

84 Cooley et al mention that fibers are used for reducing draindown in OGFC mixes, which results from the open gradation. This study was prompted by some concern that cellulose fibers would absorb water and lead to moisture damage in mixes. Cooley et al selected several field sites containing OGFC with a variety of asphalt binders and fibers, on an interstate in Atlanta, Georgia, and evaluated distresses in these sections. They also prepared OGFC mixes in the laboratory with different types of fibers and conducted tests to determine absorption characteristics of OGFC mixes with fibers and mechanical properties of the mixes. Based on both field and laboratory studies, Cooley et al concludes that OGFC mixes with cellulose fibers would perform as well as OGFC mixes with mineral fiber. 1.20.2 Benefits of Permeable Asphalt Mixtures In discussing the need for fibers in OGFC mixes in their introduction, Cooley et al mention the following benefits of OGFC: 1) Improved surface frictional resistance; 2) Minimized hydroplaning potential; 3) Reduced splash and spray; 4) Improved night visibility; and 5) Lower pavement noise levels. 1.20.3 Materials and Design Cooley et al provides result of both a field survey as well as laboratory testing of several OGFC mixes. The materials and design of the laboratory mixes are summarized in Table 45. Table 46 provides a description of test results from the laboratory mixes. (The materials of the in-place mixes and the results of survey conducted on the in-place mixes are provided in the “Performance” section of this review). Four different mixes were designed, corresponding to four different fibers. The mix design samples were compacted with 25 blows per face with a Marshall hammer at varying asphalt contents. Optimum asphalt content was selected as the one producing the lowest voids in mineral aggregate (VMA). Table 45: Materials and Mix Design for Laboratory Mixes Material Number - Type Aggregate One – Granite; One percent lime by total aggregate mass was used. Gradation One - Georgia DOT, 12.5 mm OGFC mix Asphalt Binder One - PG 76-22 modified with styrene butadiene styrene (SBS) polymer. Fiber Four – three cellulose (loose fiber, a 66/34 pelletized fiber (66 percent cellulose fiber and 34 percent asphalt), and an 80/20 pelletized fiber) and one mineral (slag wool)

85 Table 46: Tests and Results Property Test Results Absorption This test was conducted by allowing compacted OGFC mixtures to soak in a 60oC water bath for 72 hours. After soaking, the specimens were allowed to dry at room temperature. Mass measurements were obtained at 1, 2, 4, 21, 24, 48, and 72 hours to determine mass loss. Three replicates of each mixture were tested. The amount of water in a sample was determined by subtracting the mass of a sample prior to any conditioning from the mass of the same sample after conditioning and drying at room temperature for the various times. The percent water at any time was then calculated as the amount of water in the sample at that time divided by the original mass of that sample and expressing as a percentage. All four mixtures had approximately the same rate of water loss. Moisture sensitivity GDT-66, “Method of Test for Evaluating the Moisture Susceptibility of Bituminous Mixtures by Diametral Tensile Splitting.” (similar to modified Lottman procedure). The four mixtures were evaluated after 1, 3, and 6 freeze-thaw cycles. Four mixes performed similarly. Moisture sensitivity GDOT-56, “Test Method for Heat Stable Anti-Strip Additive.” Loose OGFC mixture was placed into boiling water for ten minutes. A visual inspection was then performed to determine the approximate percentage of aggregate particles in which the asphalt binder was totally or partially removed. No visual stripping in any of the four mixtures. Rutting/ Moisture sensitivity GDT-115, “Method of Test for Determining Rutting Susceptibility Using the Loaded Wheel Tester,” while submerged in water at 60oC. This testing was conducted for only the loose cellulose and mineral fiber mixtures at optimum asphalt content. Prior to testing, samples were conditioned in a 60oC water bath overnight. Loose cellulose mixture had a lower rut depth than did the mineral fiber mix. 1.20.4 Construction Practices No information on construction practices of porous asphalt mixtures has been provided 1.20.5 Maintenance Practices No information on maintenance practices of porous asphalt mixtures has been provided. 1.20.6 Rehabilitation Practices No information on rehabilitation of porous asphalt mixtures has been provided. 1.20.7 Performance Cooley et al indicates that performances of six sections with different OGFC mixes were evaluated. These sections, types of mixes and the distress surveyed are shown in Table 47. The results of visual survey are shown in Table 48.

86 Table 47: In-Place Mixes Property Types/Method Section/Route Six experimental OGFC pavement sections located on Interstate 75 south of Atlanta, Georgia; constructed in 1992 Types of mixes Coarse OGFC, Coarse OGFC with 16% crumb rubber, Coarse OGFC with mineral fibers, Coarse OGFC with cellulose fibers Coarse OGFC with styrene-butadiene (SB) polymer, Coarse OGFC with SB and cellulose fibers Survey Surface texture, rutting, cracking, and raveling. Permeability Testing Conducted on Cores Three 150 mm cores from each section were tested in the laboratory to determine permeability with a falling head permeameter. Cooley et al concluded that the field as well as the laboratory data shows that OGFC mixes containing cellulose fiber performed as well as mixes with mineral fiber. Table 48: Results of Visual Survey Property Results Surface texture All six showed some coarse aggregate pop-out. The Coarse OGFC with 16% crumb rubber section had the most coarse aggregate pop-out while the Coarse OGFC with cellulose fibers, Coarse OGFC with mineral fibers, and Coarse OGFC with styrene-butadiene (SB) polymer sections appeared to have the lowest amount. All sections showed fat spots, ranging in diameter from approximately 8 cm (3 in) to 20 cm (8 in), but insignificant in extent. The Coarse OGFC and Coarse OGFC with SB and cellulose fibers section had the most fat spots. Rutting Rut depth measurements were made in each experimental section with a stringline. The amount of rutting in all sections was insignificant. Cracking All six sections exhibited reflective cracking from underlying Portland cement concrete pavement. Percentage of reflective cracks was determined by counting the number of transverse reflective cracks visible at the pavement surface. Reflective longitudinal cracks were observed on all sections, except the one with Coarse OGFC with mineral fibers. Longitudinal reflective cracking was very low severity in the Coarse OGFC with cellulose fibers and Coarse OGFC with styrene-butadiene (SB) polymer sections. For the Coarse OGFC and Coarse OGFC with 16% crumb rubber sections some of the longitudinal cracks had opened. Only the Coarse OGFC with 16% crumb rubber section showed any other type of cracking, besides reflective, with secondary cracks near the reflective cracking. Raveling Raveling was minimal except for the Coarse OGFC with 16% crumb rubber section, which showed some medium severity raveling along cracks. Permeabil -ity Statistically, no significant differences were found between permeability values of the cores from the six sections. The Coarse OGFC with cellulose fibers and Coarse OGFC with SB and cellulose fibers sections showed the highest mean permeability values and the Coarse OGFC with styrene-butadiene (SB) polymer showed the least. 1.20.8 Structural Design No information on structural design of porous asphalt mixtures has been provided. 1.20.9 Limitations No information on limitations of porous asphalt mixtures has been provided.