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60 Tolman and Gorkum then proceeded to describe the results of modeling using data from load controlled cyclic tensile tests carried out on cores from pavements of different ages in Netherlands. They mention several adoptions for modeling: 1) Assumption of failure of binder film between two aggregates; 2) Assumption of a continuum with randomly distributed defects; 3) Fracture model with a zone of growing defects; and 4) Flow model with elongation and contraction forces. Through a series of equations and plots Tolman and Gorkum illustrate their approach in modeling the data from the pavement cores. They used 3 parameters from the tests, for each specimen: 1) The slope of the deformation versus time at the inflection point of the strain versus time curve; 2) The time until failure; and 3) The strain at 90 percent of the failure time. They mention that the time to failure and failure strain are functions of the load, the total binder film and the basic material parameters, which are the initial quality, the damage growth coefficient, the damage growth exponent, and the ratio of the surface energy and the fracture zone width for fracture failure or the lateral contraction coefficient for the flow failure. Tolman and Gorkum then exhibits a series of equations on how the material parameters can be derived as functions of the time until failure from known material properties and tested properties. In a table, the authors show that the reference stress, fracture energy per fracture zone width and the contraction coefficient are correlated to the minimum creep rate parameters and the expected condition of the specimens. They contend that the references stress of the fracture mode is of the order of the fracture strength, while the reference stress of the flow model is of the order of the mortar stiffness in thin films. Tolman and Gorkum conclude that the obtained and derived parameters from the cyclic tensile tests are meaningful, relevant, consistent and discriminating between the different types of specimens. 1.13.8 Structural Design No information has been provided on structural design. 1.13.9 Limitations No information has been provided on limitations. 1.14 Kandhal, P.S. and R.B. Mallick. âOpen Graded Asphalt Friction Course: State of Practice.â Transportation Research Circular E-C005. Transportation Research Board. Washington, D.C. 1998. 1.14.1 General This report provides the results of a survey of states conducted to evaluate current practices on the design and construction of OGFCs. A questionnaire was sent to all 50 state highway agencies and responses were received from 43 states. At the time of the survey, 45 percent of the responding agencies were utilizing OGFC. Similarly, 45 percent had indicated that they had discontinued use. Ten percent of the agencies indicated that OGFC had not been used.
61 1.14.2 Benefits of Permeable Asphalt Mixtures The authors mentioned improved frictional resistance, especially in wet weather, as a benefit of OGFC. 1.14.3 Materials and Design The survey included several questions about materials and mix design procedures for OGFCs. Figure 6 shows that 76 percent of the responding states indicated that they have formal mix design procedures for OGFC, 19 percent of the states reported that they used recipe specifications, and 5 percent of the states used a combination of a mix design procedure and recipe method. Forty-two percent of the states specified a range of allowable asphalt binder contents, whereas 58 percent did not. The different aggregate gradation ranges reported by the states are shown in Table 36. Figure 7 shows that 26 percent of the states followed the FHWA procedure to establish mixing temperature to prevent draindown of asphalt binder, 37 percent of the states used other draindown tests, whereas 37 percent of the states did not use any test, but used temperatures from viscosity-temperature charts for specific binders. Table 37 shows the different grades of asphalt binders used by the different agencies. Forty eight percent of the responding states used polymer modified binders, while 52 percent did not. However, these percentages are based on total number of states surveyed, including those which do not use OGFC at present. Forty six percent of the states used some type of additive, such as cellulose fiber, hydrated lime, or some form of anti-strip agents, whereas 54 percent of the states did not use any additive other than a modifier for binders. Nineteen percent of the states using additives used fiber, 13 percent used silicone, 13 percent used crumb rubber, 31 percent used liquid anti- strip agent and 44 percent used hydrated lime. These percentages total more than 100 percent because some states used more than one type additive.
62 76 19 5 0 10 20 30 40 50 60 70 80 90 Mix Design Recipe Mix Design and Recipe Method of Development of Job Mix Formula Pe rc en ta ge o f S ta te s Figure 6: Methods of Developing Job Mix Formulas for OGFCs 26 37 37 0 5 10 15 20 25 30 35 40 45 50 FHWA Test Draindown Standard Temperature/Viscosity Chart Method of Determination of Mix Temperature Pe rc en ta ge o f S ta te s Figure 7: Methods for Determining Mixing Temperatures
63 Table 36: Gradation of OGFC Mixes in Different States Percent Passing Sieve (mm) State 25 19 12.5 9.5 6.3 4.75 2.36 2 1.18 0.6 0.3 0.15 0.075 100 90-100 30-50 5-7 3-6 AL 100 90-100 40-70 5-30 4-12 3-6 CA 78-89 28-37 7-18 100 90-100 35-57 12-33 3-15 2-8 CO 100 90-100 40-60 20-47 4-18 2-9 FL 100 85-100 10-40 4-12 2-5 GA 100 85-100 55-75 15-25 5-10 2-4 HI 100 30-50 5-15 2-5 ID 100 95-100 30-80 35-46 8-15 2-5 IL 100 90-100 30-50 10-18 2-5 KY 100 90-100 25-50 5-15 2-5 100 90-100 30-50 10-30 5-20 2-6 LA 90-100 20-50 5-15 2-6 MD 100 90-100 20-40 5-15 0-5 MI 100 90-100 30-50 8-15 2-5 100 90-100 35-55 5-18 0-3 NV 95-100 40-65 12-22 0-4 NJ 100 80-100 30-50 5-15 2-5 NM 100 90-100 25-55 0-12 0-4 100 75-100 25-50 5-15 1-3 NC 100 85-100 55-75 15-25 5-10 2-4 OH 100 85-96 28-45 9-17 2-5 99-100 90-98 25-40 2-12 1-5 OR 99-100 85-96 55-71 15-30 5-15 1-6 PA 100 30-50 5-15 0-5 RI 90-100 20-50 5-15 2-5 SC 100 98-100 40-70 2-20 0-2 TX 100 95-100 50-80 0-8 0-4 UT 100 92-100 36-44 14-20 2-4 VT 100 95-100 30-50 5-15 2-5 100 97-100 25-45 10-25 2-7 WY 100 97-100 20-40 10-20 2-7
64 Table 37: Asphalt Binders used for OGFCs State Asphalt Binder AL PG 76-22 CA AR 2000, 4000, 8000 CO AC 20R FL AC 30 GA PG 76-22 HI AR 80 ID -- IL AC 10 KY PG 64-22 LA PG 70-22 MD AC 20 MI --- NV AC 20P, AC 30 NJ AC 20 NM --- NC AC 20P OH AC 20 OR PBA 5, PBA 6 PA AC 20 RI AC 20 SC PG 64-22 TX AC 20, AC 10 UT PG 64-34 VT AC 20 WY AC 20, AC 10 To draw meaningful conclusions on materials and mix designs from the survey, the states were classified by the authors according to Strategic Highway Research Program (SHRP) climatic zone criteria into four groups: Wet-Freeze, Wet-No Freeze, Dry-Freeze, and Dry-No Freeze. Table 38 shows specific problems reported by some state agencies in these four climatic zones. In the Wet-Freeze zone the main problem seemed to be raveling of the OGFC and stripping of underlying layers. Problems not related to mix performance included difficulty in removal of snow and clogging up of voids by ice control materials such as sand and reduced permeability. In the Dry-Freeze zone, the main problem seemed to be removal of snow and closing up of voids by sand, although one state reported stripping in underlying layers. In the Wet-No Freeze zone, the problems included raveling of OGFC, stripping of underlying layers, and closing up of voids. In the Dry-No Freeze zone, the only reported problem was raveling of OGFC due to absorptive aggregate. To study the differences in mix design of OGFC between states having good experience and states having bad experience with OGFC, three mix design items were listed by the authors for each state, as shown in Table 39. In the Wet-Freeze zone, most of the states which had good experience, and did use OGFC at the time of the survey used polymer modified binders, whereas those which had bad experience, and had stopped using OGFC did not use polymers. The percent passing the 2.36 mm sieve ranged from 5 and 15 percent for most of the states. Also, there was little difference in the use of other additives between states having good and bad experience.
65 In the Wet-No Freeze zone, most of the states with good experience used polymers, and half of them used some other type additive such as rubber or fiber. However, most of the states with bad experience did not use polymer or any other additive type. The percentage passing the 2.36 mm sieve of the one state with bad experience which the gradation requirements were available was finer than for most of the states with good experience. In the Dry-Freeze zone, all of the states which had good experience used hydrated lime, whereas three out of four states which had bad experience did not. The percentage passing 2.36 mm sieve seemed to be higher for states in this zone (about 10-30). Again, the most prominent difference seemed to be in the use of polymer modified binders: all of the states with good experience used polymer, whereas three out of four states which had bad experience did not use polymer. For the Dry-No Freeze zone, all of the states with good experience used polymers and most of them use other additives. The only state with bad experience did not use polymer, but used silicone as an additive. There was no distinct difference between the percentage passing the 2.36 mm sieve used by the states with good and the state with bad experience with OGFC. The survey on the use of OGFC revealed that the primary mix performance problems were raveling of OGFC and stripping of underlying layers. The authors indicated that raveling of OGFC is likely a problem with the loss of bond (cohesion) between the aggregate particles. The stripping of the underlying layers could be attributed to inadequate drainage of water through the OGFC. Therefore, the authors surmised that two of the most important features of OGFC mix are air voids and bonding of aggregates and asphalt binder. The drainage capacity of an OGFC is a direct function of the air voids. Experience of states using polymer modified binders indicated that proper use of polymer and/or other additives can allow the use of higher air voids (for drainage, and hence prevent stripping in the underlying layer), higher asphalt binder content (for durability, and hence prevent raveling) by controlling draindown, as well as to provide improved adhesion and greater resistance to aging of binder.
66 Table 38: Problems with OGFC Zone: Wet-Freeze State Problem IA Removal of ice very difficult.1 MD Raveling in OGFC ME Removal of ice very difficult1. MN Deicing sand clogged voids1; stripping of OGFC RI Durability problem; widespread debonding; OGFC scraped by snow plows. VA Stripping in underlying layers; needed heavy fog coat after several years to prevent raveling. Zone: Wet-No Freeze State Problem AK Filling up of voids, leading to moisture retention; prolonged freezing, and snow and ice removal problems. LA Extensive raveling. TN Stripping in underlying layers; aggregate loss in OGFC by raveling; snow and ice removal problem due to re-freezing of melted snow and ice1. Zone: Dry-Freeze State Problem CO Moisture damage to underlying layers. ID Sanding caused filling up of voids1. KS During winter snow and ice storm, voids became filled with water and froze; developed icy surface; took substantially higher amount of salt to melt ice1. SD Sand and salt plugged up the voids1. Zone: Dry-No Freeze State Problem HI Raveling because of absorptive aggregate. Note: 1: Problems not related to mix performance
67 Table 39: Mix Design Practices of States with Good and Bad Experiences Zone: Wet-Freeze Good Experience Bad Experience State Polymer Other Additive % Passing 2.36 mm Sieve State Polymer Other Additive % Passing 2.36 mm Sieve IL Yes No --- IA No No --- KY Yes No 5-15 MD Yes Antistrip 5-15 NJ Yes No 5-15 ME No No --- OH Yes No 9-17 MN No No --- PA No Antistrip 5-15 RI No Silicone, Antistrip 5-15 VT No Antistrip 5-15 WV No No --- Zone: Wet-No Freeze Good Experience Bad Experience State Polymer Other Additive % Passing 2.36 mm Sieve State Polymer Other Additive % Passing 2.36 mm Sieve AL Yes No 5-7 AK No No -- FL No Crumb Rubber 4-12 LA No No >5-20 GA Yes Hydrated Lime 5-10 TN No No -- NC Yes Fiber 5-15 OK Yes No --- SC No Hydrated lime 2-20 Zone: Dry-Freeze Good Experience Bad Experience State Polymer Other Additive % Passing 2.36 mm Sieve State Polymer Other Additive % Passing 2.36 mm Sieve NV Yes Hydrated lime --- CO Yes No 12-33 OR Yes Hydrated lime --- ID No Antistrip --- UT Yes Hydrated lime 14-20 KS No No --- WY Yes Hydrated lime 10-25 SD No No --- Zone: Dry-No Freeze Good Experience Bad Experience State Polymer Other Additive % Passing 2.36 mm Sieve State Polymer Other Additive Percent Passing 2.36 mm Sieve CA Yes No 7-18 HI No Silicone 5-15 NM Yes Hydrated Lime 0-12 TX Yes Fiber, Crumb Rubber 0-4
68 1.14.4 Construction Practices Most of the states specified the use of some kind of tack coat before construction of OGFC layers. As shown in Figure 8, 88 percent of the states surveyed used emulsion, where as only 8 percent used asphalt binder as tack coat material. Eight percent of the states surveyed did not use a tack coat. The percentages total more than 100 because some states allow the use of both emulsion and asphalt binder as tack coat material. Figure 9 shows that equal percentages of states specified 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5 liter sq. m application rates, respectively, whereas eight percent of the states specified an application rate of less than 0.1 liter per sq. m. Nine of the states specified a minimum air temperature to construct OGFC of 10ºC, 45 percent specified 15ºC, 32 percent specified 21ºC, and 14 percent do not have any specification. Twelve percent of the states specified minimum surface temperature of 9ºC, 35 percent specified 15ºC, 6 percent specified 21ºC, and 47 percent do not specified any minimum surface temperature. Five percent of the states specified in-place void content criteria for compaction of OGFC, 80 percent of the states specified roller weight and/or roller passes, whereas 15 percent do not have any specific compaction criteria. Eighty six percent of the states placed OGFC on new asphalt overlay in the same year, 5 percent placed after one year of traffic, whereas 9 percent of the states did not have any specific time period. 88 8 8 0 10 20 30 40 50 60 70 80 90 100 Emulsion Asphalt Cement None Type of Tack Coat Material Used Pe rc en ta ge o f S ta te s Figure 8: Tack Coat Materials Used for OGFC
69 8 23 23 23 23 0 5 10 15 20 25 <0.1 0.1-0.2 0.2-0.3 0.3-0.4 0.4-0.5 Application Rate, liter per sq. meter Pe rc en ta ge o f S ta te s Figure 9: Tack Coat Application Rates 1.14.5 Maintenance Practices No information on maintenance practices of porous asphalt mixtures was given. 1.14.6 Rehabilitation Practices No information on rehabilitation of porous asphalt mixtures was given. 1.14.7 Performance Reported average service life of OGFC by the different states is presented in Figure 10. Seventeen percent of the states reported an average service life of less than 6 years, 10 percent reported 6-8 years, 30 percent reported 8-10 years, 33 percent reported 10-12 years, whereas ten percent reported more than 12 years. Since 43 percent of states reported an average service life of more than 10 years, it indicates that OGFCs can be designed and constructed successfully.
