Transportation Research Record 1778 ■ 91Paper No. 01-0422

Oregon has been using open-graded hot mix on its roadway system sincethe late 1970s. Because of the performance of these early jobs (and thecontinued good performance of these mixes), open-graded hot mix hasbeen the preferred choice for a surface course on Oregon highways. Thefollowing are described with respect to the use of these mixes in Oregon:historical perspective; design, including mix and structural design; con-struction, including quality control/quality assurance considerations;and maintenance and rehabilitation practices with porous pavements.The continued success of the use of these materials from both a perfor-mance and a public acceptance standpoint indicates they will be thepavement of choice in Oregon for the foreseeable future.

Oregon began using open-graded hot-mix asphalt concrete mix-tures on the roadway system in the late 1970s. Because of the per-formance of these early jobs (and the continued good performanceof these mixes), open-graded hot mix has been the preferred choicefor a surface course on Oregon highways. Currently, about 3000centerline km of the Oregon highways are paved with open-gradedasphalt concrete.

Open-graded asphalt concrete is characterized by use of a largepercentage of coarse aggregate in the mix without a significant por-tion of fines, as commonly found in dense-graded mixes. In Oregon,the asphalt concrete mixtures have been represented by Classes Bto F since the early 1980s (1). Classes E and F are open graded,whereas Classes B, C, and D are dense graded. The Class E mix hasa nominal maximum size of 19 mm (0.75 in.) and generally is usedfor nonstructural thin overlays [25 mm (1 in.)] to improve skid andhydroplaning resistance. The Class F mix has a nominal maximumsize of 25 mm (1 in.) and generally is used for thin overlays [50 mm(2 in.)] and for wearing courses for new pavement construction orstructural overlays on all highways [up to 100 mm (4 in.)]. Table 1presents the broadband limits for three types of mix aggregate gradation most commonly used in Oregon, which are pertinent tothis paper (2).

The Class F mix is now being recommended for use on manyOregon roadways, including interstate highways. To assess the per-formance of the Class F mix, this paper presents an evaluation ofprojects constructed with the Class F mix. A comparison is also madewith pavements having dense-graded asphalt concrete (B or C mix)that were constructed at similar times and locations and have expe-rienced similar traffic applications. In addition, conditions underwhich open-graded mixes should not be used are identified.

The purpose of this paper is to provide an overview of the use ofporous pavements in Oregon. Details on performance, design, con-struction, and maintenance are provided. A detailed look at modelingperformance of the porous pavement in Oregon is also provided.

HISTORICAL PERSPECTIVE

Projects Constructed

The Oregon Department of Transportation (ODOT) constructed itsfirst Class F mix pavement in 1979. ODOT began using Class F mixregularly in 1984. To date (2000), over 300 projects (totaling over3000 centerline km) have been constructed with Class F mix on thestate highway system. Figure 1 presents the number of projects andcenterline kilometers completed by region and year through 1998,and Figure 2 is a representation of ODOT regions. A total of about216 centerline km were constructed in the 1999 paving season andabout 185 centerline km (13 projects) are planned for the year 2000.

Regions 1, 2, and 3 are located west of the Cascade Mountain rangeto the Pacific Ocean from the Washington to California state lines.Regions 4 and 5 are located east of the Cascade Mountains, withRegion 4 in central Oregon and Region 5 in easternmost Oregon.In 1989, extensive use of Class F mix began and has graduallyincreased as Oregon gains more experience with its use. Regions 2and 3 have the most Class F mix projects because these areas bestfit the guidelines for use and because of the greater number of proj-ects in these regions. Most of the projects completed in Region 4 (43percent) have been on U.S. Highway 97. This route is the majornorth-south highway for central Oregon. This area does not haveheavy rainfall, but Class F mix was used on the highway because ofits improved resistance to rutting. The dense-graded mixes on thisroute have suffered from extensive early rutting and moisture sen-sitivity problems. The use of Class F mix appears to have overcomemost of these problems.

Reasons for Use

The primary reasons for using open-graded mixes in Oregon aresafety through improved high-speed frictional properties and reducedsplash and spray, user comfort during winter driving, and quieterroads. In addition, the performance of the open-graded mixes hasbeen nearly equal to the dense-graded mixes historically used as thewearing surface (3).

Pavement Frictional Properties

One of the expectations of using the Class F mix as a wearing coursewas to provide a rougher surface texture and thereby increase the

Design, Construction, and MaintenanceGuidelines for Porous Asphalt Pavements

Lucinda M. Moore, R. G. Hicks, and David F. Rogge

L. M. Moore, Operations Support Section, Oregon Department of Transportation,Salem, OR 97310. R. G. Hicks and D. F. Rogge, Department of Civil, Construc-tion, and Environmental Engineering, Oregon State University, Corvallis, OR 97331. Current affiliation: R. G. Hicks, Law-Crandall, 791 Hillgrove Court,Chico, CA 95926.

frictional property, especially during wet weather. The frictionalproperty is measured at a traveling speed of 64 km/h (40 mph) andexpressed as a friction number (AASHTO T-242).

The friction numbers for the pavement management sections usedto model the performance were analyzed by standard statistics. Theresults are presented in Table 2 for a test speed of 64 km/h. The most

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TABLE 1 Aggregate Gradations for Typical Asphalt Concrete Mixtures Used inOregon (1, 2)

050

100150200250300350400450500

1979

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

Year

Kilo

met

ers

Kilo

met

ers

(a)

0

200

400

600

800

1000

1200

1400

1 2 3 4 5

Region

(b)

FIGURE 1 Historical use of F mixes in Oregon(1979–1998): (a) number of kilometers constructed byyear; (b) number of kilometers constructed by region.

current friction numbers (1997–1998) were used in the calculations.Not all the sections had associated friction numbers. The resultingaverage friction numbers of 50.5 for the Class F mix and 53.7 for theClass B mix are very close, given the number of tests upon whichthey are based. The data indicate that, under dry conditions, bothmix types provide acceptable frictional properties.

In addition to the standard friction tests, the speed gradients weredetermined for several projects. The speed gradients were deter-mined as the slope of the friction number versus speed curve from64 km/h (40 mph) to 88 km/h (55 mph). The tests were performedin a conventional manner on dry pavement and then repeated on thesame sections during heavy rainfall. The results are presented inTable 3 and plotted in Figure 3 (4) and they indicate that the Class Fmix has a slightly improved speed gradient in dry conditions and amuch improved gradient during rainy conditions when free water ispresent on the pavement.

Splash and Spray

Another advantage of using the open-graded mix as a surface coursein Oregon (where it rains frequently) is that the hydroplaning poten-tial and water splash and spray during wet weather are minimized(5, 6). This feature is obvious when one is driving on the selectedprojects during wet weather. Although there are no objective dataavailable related to splash and spray, the observed amount of watersplash and spray for the Class F mix projects is much less than forthe Class B/C mix projects (see Figure 4). Oregon has receivednumerous comments from motorists noting improved visibilitywhen they travel on Class F mix pavements during rainy weather.For Oregon’s unique climate, with nearly 6 months of rainy weather,this advantage may greatly reduce the number of vehicle accidents.

Noise Characteristics

Experience has indicated that Class F mix surfaced pavementsappear to have a different road noise frequency and are considered to

FIG

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Ore

gon

DO

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gion

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be quieter than Class B mix pavements. Studies also indicate that theopen-graded friction course surface provides reduced tire-pavementnoise (5–9). To verify this characteristic, a field investigation wasconducted to determine the noise level on both mixes (4).

Two types of noise measurements were taken. The first was road-side noise and the second was interior vehicle noise. Noise measure-ment testing for roadside noise can often be a difficult task becausevarious geometric configurations can cause severe changes in theacoustic characteristics from site to site. To remove any geometricvariables, test sites were chosen where fairly new pavement typesexisted and overlays of Class F mix were planned in the nearfuture. Tests were then performed before and after overlay at identicallocations.

For all sites in this study, the noise measurements were taken50 ft (15.24 m) from the centerline of the closest directional travellanes. Measurements were done with a Brüle and Kjær 2221 soundlevel meter to determine the A-weighted equivalent sound pressurelevel and a Rion SA-271⁄3 octave band analyzer for the noise spec-trum. All equipment was calibrated with a 1000-Hz calibrator at93.8 dB(A) before measurements (4).

The interior noise measurements were taken inside a 1993 DodgeCaravan. The microphone was placed in the middle seat of the vehi-cle at approximate ear height. Tests were done at 100 km/h. Carewas taken that no heavy trucks were traveling alongside the van dur-ing measurements. Noise levels for both an A-weighted decibellevel and a one-third octave frequency spectrum were taken for thisformat as well.

The results of the noise analysis confirm the data found in a liter-ature search, which indicate that porous pavements reduce the noisein the higher-frequency zones. This conclusion is supported mostlyfrom the roadside measurements and not from those taken in the inte-rior of the vehicle. A possible explanation for this is that the higherfrequencies are dampened by the vehicle shell. As high-frequencynoises have a shorter wavelength, they are more apt to be reflectedoff the vehicle’s thin shell and hide some of the data and make Class Fmix pavements appear a little more noisy inside than outside.

Current Guidelines for Use

Class F mix is considered for use on all projects where its benefitscan be best realized. Some benefits of Class F mix include anincrease in sight distance due to a reduction of splash and spray dur-ing wet weather, reduced potential for hydroplaning, and increasedrut resistance. Class F mix also appears to be more resistant to rut-ting and stripping than typical dense-graded mixes. The currentguidelines for usage define areas where Class F mix should not beplaced instead of areas where it should be placed. The three mainareas where Class F mix is not recommended are as follows:

94 Paper No. 01-0422 Transportation Research Record 1778

• Low-volume roads with average daily traffic of fewer than1,000 vehicles. Class F mix is not placed on low-volume highwaysbecause some of the technical benefits are not as noticeable due tothe low volume of traffic and lack of heavy loads. Also, in easternOregon, emulsified asphalt concrete is used extensively for the low-volume highways because of its lower cost. Also, maintenancepatching is the primary means of sustaining these low-volume high-ways over a longer period of time. Maintenance crews have reportedthat patching over Class F mix is difficult (problems with getting thepatch to stick). The patches also tend to dam the drainage path andreduce the splash and spray benefits.

• Curbed areas or areas requiring handwork. Class F mix is notrecommended for use in areas with curbs or where a significantamount of handwork or feathering is required. The mix’s aggregatesize and aggregate gradation makes handwork difficult around util-ity appurtenances and at driveways. Also, curbs block drainage ofthe Class F mix.

• Heavily plowed areas where steel plow blades are used. As aresult of snowplow damage, Class F mix is no longer recommendedin areas where plowing is frequent. The snowplows can cause rav-eling and gouging, resulting in a higher rate of surface deterioration.The determination of frequency of plowing is on an individualproject basis but generally involves the elevation, any existing plowdamage, and existing chain-up areas or snow zones.

DESIGN OF POROUS PAVEMENTS

Mix Design

Early mix designs were carried out following the Hveem mix designprocedure. The mix design procedures used for the B/C mix weremodified slightly for Class F mixes to allow higher air voids to beused. The index of retained strength for the Class F mix projects wasslightly lower than those of the B/C mix projects. This was believedto occur because of difficulties in testing open-graded mixes in anunconfined state and not because of increased stripping potential;stripping has not been a problem in these mixes. The stability val-ues of the early Class F mix projects were also lower than those ofthe Class B/C mix projects. This is also reflected in the mix designrequirements and criteria in Table 4. For the projects selected, thestability values (after first and second compaction) generally met orwere close to the design requirements. The low stability values havenot been related to rutting in the field.

In 1992, ODOT changed the mix design procedure and used the cri-teria presented in Table 4 (10). A draindown test and its criteria wereimplemented in 1992. Also, the method of bulk gravity determinationof compacted specimens was changed from immersion in water to ageometric method (AASHTO T-269). A modified asphalt (gradePBA-6) has been specified in some projects to reduce draindownduring transportation and laydown.

As of 1999, ODOT was evaluating open-graded mixes for airvoids, draindown, and voids filled with asphalt. The draindown pro-cedure used is described in the ODOT Contractor HMAC MixDesign Guidelines (11). Moisture susceptibility was evaluated withAASHTO T-283 but using the project aggregate in a dense gradation.The design criteria and the historical criteria are presented in Table 4.

Structural Design

ODOT completes the structural design of open-graded mixes byusing the same methods as for dense-graded mixes. ODOT uses the1993 AASHTO Guide for Design of Pavement Structures (12) and

TABLE 2 Summary of Friction Test Results at 64 km/h(1997/1998 Data)

TABLE 3 Friction Test Results (4)

other deflection-based procedures for selecting the recommendedstructural design.

The open-graded asphalt pavements are given the same structuralcredit as the dense-graded asphalt pavements based on past experi-ence and performance. Deflections taken on Class F mix pavementsafter placement have indicated the estimated deflection reduction

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was comparable to that expected from typical dense-graded overlaysof similar thickness. No studies have been completed on the topic,but past experience has not indicated any reason to alter currentmethods used in design.

The current minimum recommended thickness for a Class F mixis 50 mm. In the past, 37.5-mm overlays were placed, but to mini-

FIGURE 3 Frictional testing results (4) (PCC � portland cement concrete). FIGURE 4 Interstate 5 near Salem (August 1996): Class B mix

(left) and Class F mix (right).

TABLE 4 Mix Design Requirements and Criteria

mize laydown and compaction problems the lift thickness has beenincreased to 50 mm. To date, the maximum thickness of Class F mixthat has been placed is 100 mm (in two 50-mm lifts).

Another part of the design process is consideration of the exist-ing pavement condition. When an extensively cracked pavementis being overlaid, either Class F mix should not be used or surfacepreparation should be completed. On projects where the wearingsurface is to be Class F mix, potential surface repairs includelocalized inlays, travel lane inlays, a dense lift below the Class Fmix, or other forms of reflective crack control. To prevent waterfrom sitting in the deeper sections of Class F mix, ruts of moder-ate to high severity should be leveled before the Class F mix over-lay is placed.

Most of the preceding design considerations have come fromexperience on Class F mix projects. With continued experiencewith Class F mix, the design procedures will be further refined andperformance should also improve.

CONSTRUCTION CONSIDERATIONS

Manufacture and Placement

Class F mix is produced with standard batch or drum plants andplaced with conventional paving equipment with some minor adjust-ments to construction practices. The primary construction issues dur-ing transportation and placement are draindown of the binder andcooling of the mixture. Excessive draindown results in fat spots inthe finished surface, which may appear during rolling or within afew weeks of paving. This problem has been addressed throughproper selection of mixing and compacting temperatures, the use ofmodified binders (PBA-6), and the use of fibers. Mixture depositedin windrows from “belly-dump” trucks and transferred to the pavervia a pick-up machine is the most common method of deliveringClass F mix. End dump trucks have been successfully used to deliverClass F mix, but experience has been that the use of end dump trucksdepositing directly into the paver is most likely to result in fat spotson the finished surface. To date, a material transfer vehicle has notbeen used on a Class F mix project. Cooling of the mixture willresult in “chunks” that, if not removed or broken up before they aredeposited into the paver, can result in tears in the mat, differentialcompaction, and poor ride. The chunks can be minimized by increas-ing the temperature, tarping loads, and using trucks with insulatedbeds to deliver the mixture.

The recommended mixing temperature for the Class F mix isbased on an asphalt viscosity of 700 to 900 centistokes. For theseprojects, the maximum mix temperature was 129°C (265°F) at theplant. Minimum allowable temperature during laydown was 96°C(205°F). This is comparable to 163°C (325°F) and 116°C (240°F)for dense-graded mixes. The lower temperatures for the Class F mixhelp promote thick film coatings during hauling and laydown. Useof PBA-6 binders modified with polymers and ground tire rubberhave also minimized the draindown.

Class F mixes are evaluated in the field. Experienced personnel willadjust asphalt content and mixing temperature during production andlaydown to optimize film coatings for durability and temperature forworkability needed to achieve a smooth ride.

Compaction

Compaction is done with conventional equipment. However, for theClass F mix, a minimum relative density is not specified. The speci-fications call for a minimum of four coverages with a minimum 7 Mg

Moore et al. Paper No. 01-0422 97

(8 ton) gross static steel-wheeled roller before mix cooling below80°C. Additional passes may be necessary to eliminate roller marks.To avoid fracture of aggregate, vibratory compaction is not allowed.

Special Construction Considerations

As discussed previously, Class F mixes are not recommended for allprojects. Some situations in which the Class F mix is not used includethe following:

• Long hauls. Jobs far from the asphalt concrete plant are not rec-ommended for Class F mix because of problems with excessive drain-down of the asphalt binder, cooling of the mix, or both. Although suc-cess has been obtained with one-way haul distances of up to 112 km(70 mi), the current policy is to stay below 56 km (35 mi). Weatherconditions and asphalt grade may also influence the recommendedhaul distance.

• Inlays. The mixes must be allowed to drain. Drainage is accom-plished by daylighting the mix on the shoulder through a series ofoutlet trenches. If adequate drainage outlets are provided, Class Fmixes may be used for inlays. Although ODOT has used this optionon occasion, it is not recommended for standard practice.

• Handwork. The Class F mix, because of its coarse texture, is dif-ficult to rake and is not easily placed where an abundance of hand-work is necessary. Therefore, it is usually not specified for tapers, roadapproaches, or in city streets where there are inlets and manholes towork around.

• Night paving. Projects in high traffic areas require night paving.In these cases, the mix must be heated to higher temperatures to getthe necessary temperature for compaction. When F mix has beenplaced at night, fibers have been used to minimize draindown relatedto the higher temperatures. This practice has proven successful.

Quality Control–Quality Assurance Considerations

In early work, Oregon controlled aggregate gradation, asphalt con-tent, moisture, and compaction to ensure a quality product. The payadjustment factors used for dense-graded mixes were also used foropen-graded mixes. A study was initiated in 1995 to develop qual-ity control procedures (and pay factors) for open-graded mixesspecifically (13). The results of this study indicated the following:

• Problems noted on Class F mix projects included fat spots, rav-eling, and rutting. Some of the older projects are beginning to fatiguecrack. The results of the study indicated that the fat spots and ruttinggenerally occurred where there was excess asphalt and excess fines.

• The research indicated that the important factors to controlinclude aggregate gradation, asphalt content, and mix moisture. Rec-ommendations to pay adjustment schedules provided more weightfor asphalt content and P200.

• The new specifications have been implemented on a trial basisand are currently under evaluation.

MAINTENANCE AND REHABILITATION

Several maintenance issues have arisen with the use of Class F mix.The three main issues are snowplow damage, deicing, and patching.The problem encountered with plowing concerns the type of plowused. In areas where steel plow blades (without the rubber cover) areused, damage to the Class F mix is greater because the plow bladecan break and remove the large surface rock. This damage then

results in greater future raveling because of the loss of surfaceintegrity.

Maintenance has brought up the issue of the use of deicing chem-icals on Class F mix. Maintenance crews report that the Class F mixrequires more deicing chemicals because of the higher amount ofvoids in the mix and that the chemicals enter the pavement structureand thus higher concentrations are needed to keep the surface fromicing.

The issue of patching includes both blade/screed and inlay patch-ing. Although successful inlay patches have been done with Class Fmix, the type of asphalt mix the maintenance forces have availablefor use is typically a dense-graded commercial mix. Inlay patchingwith dense-graded hot mix may block the drainage path in the Class Fmix, causing problems such as black ice and patch deterioration (dueto water infiltration). However, no real evidence exists to prove thatsmall inlays cause these problems. The greatest concern about bladepatching is getting the 15- to 40-mm-thick patch to adhere to theexisting Class F mix pavement as well as they traditionally do fordense-graded mixes. Maintenance crews report that these thinpatches on the Class F mix last about half as long as patches ondense-graded mixes, although research undertaken to address thisconcern neither confirms nor refutes this (14). Even if Class F mixwere readily available, blade patches with this mix are not feasiblebecause of the inability to “feather” the edge.

Maintenance Treatments

The primary maintenance treatments currently used for open-gradedmixes include the following:

• Fog seals. These are applied periodically to minimize raveling.• Patching. This is the normal technique used to repair isolated

distress areas. Normally a Class C mix is used. As long as the patchedareas are small, the benefits of the open-graded mixes are not lost.

• Chip and sand seals. These treatments are normally used tocover gouges caused by snowplows. The gouges do not generallycause structural damage but they do create aesthetic problems.

Rehabilitation

The types of rehabilitation techniques used include the following:

• Overlays. Using either an open- or a dense-graded mix.• Mill and fill. This consists of milling off the open-graded mix

and replacing it with another. Care must be taken to ensure that thenew material is able to drain completely.

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The issue of rehabilitation of the Class F mix pavement is stillunder consideration. Only a small number of the Class F mix proj-ects have been or are scheduled to be rehabilitated. Issues that needto be dealt with are inlay repairs before overlaying, changing thewearing surface mix type, and drainage issues with a middle layerof open-graded asphalt. In areas where they have had problems withthe Class F mix, maintenance forces often do not want Class F mixagain. A plan on how to rehabilitate the Class F mix pavement needsto be established. European experience indicates a preference formill and inlay with recycling and millings (7 ). This approach elim-inates the previously mentioned challenges associated with overlaysand porous pavements.

Future Maintenance and Rehabilitation

A fall 1997 survey of ODOT maintenance personnel investigatedClass F mix maintenance practices (14). Table 5 summarizes tech-niques used and perceived success. Twenty-five maintenance super-visors responded to the survey. Blade patching with dense-graded hotmix was the most widely used technique and the most successful,with a mean success rating of 8.0 of a possible 10.0. Mill and inlayand screed patch with dense-graded hot mix were also widely usedand reasonably successful. Only three respondents had milled andinlayed with Class F mix and their experiences varied widely, with aminimum success rating of 3 and a maximum success rating of 10. Itshould be noted that Class F mix is not readily available to mainte-nance personnel in small quantities and that traditional maintenancetechniques have used dense-graded mixes.

CONCLUSIONS

This paper has provided an overview on the use of open-graded mixesin the state of Oregon. Specifically, it provides information on the his-torical development and use, design and construction considerations,and information on maintenance and rehabilitation practices. Specificconclusions resulting from this effort are as follows:

• Performance. The performance of the open-graded F mix hasbeen shown to be equivalent to conventional dense-graded mixes.

• Benefits. Benefits of Class F mix include reduction in splash andspray over dense-graded mixes, better rut resistance, less suscepti-bility to stripping, and reduced tire-pavement noise. The driving pub-lic recognizes these benefits, which is why the use of Class F mix willbe continued.

• Design. The mix and structural designs continue to be refinedas more experience with Class F mix is gained. Improvements in the

TABLE 5 Class F Mix Maintenance Techniques Survey Findings (14)

design processes should improve the overall performance of theClass F mix.

• Construction. Class F mix is constructed with conventionalpaving equipment and only minor adjustments to constructionpractices.

• Maintenance and rehabilitation. Major maintenance concernshave included patching, snow removal, and use of deicing chemi-cals on Class F mix. ODOT has not yet developed a plan to rehabil-itate the existing Class F mixes because only a few of the projectshave been rehabilitated.

REFERENCES

1. Standard Specifications for Highway Construction. Oregon State HighwayDivision, Oregon Department of Transportation, Salem, 1984.

2. Supplemental Standard Specifications for Highway Construction. OregonDepartment of Transportation, Salem, 1998.

3. Scott, K., J. Gower, and R. G. Hicks. Performance of Porous Asphalt Pave-ments in Oregon. Internal Report. Oregon Department of Transportation,Salem, 2000.

4. Younger, K., R. G. Hicks, and J. Gower. Evaluation of Porous Pavementsfor Road Surfaces. FHWA-OR-RD-95-13. FHWA, U.S. Department ofTransportation, Dec. 1994.

5. Huddleston, I. J., H. Zhou, and R. G. Hicks. Evaluation of Open-GradedAsphalt Concrete Mixtures Used in Oregon. In Transportation Research

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Record 1427, TRB, National Research Council, Washington, D.C.,1993, pp. 5–12.

6. Smith, H. A. NCHRP Synthesis of Highway Practice 180: PerformanceCharacteristics of Open-Graded Friction Courses. TRB, NationalResearch Council, Washington, D.C., 1992.

7. Lefebrve, G. Porous Asphalt. PIARC Technical Committee on FlexibleRoads, Permanent International Association of Road Congresses, Paris,France, 1993.

8. The Design and Use of Porous Asphalt Mixes. Manual 17. SouthAfrica Bitumen & Tar Association, Pinelands, Republic of SouthAfrica, Nov. 1995.

9. Kandhal, P. S., and R. B. Mallick. Open-Graded Friction Course: Stateof the Practice. Transportation Research Circular E-C005. TRB,National Research Council, Washington, D.C., 1998.

10. Dominick, D., and A. J. George. Asphalt Concrete Mix Design Guidelines.Oregon Department of Transportation, Salem, March 1995.

11. ODOT Contractor HMAC Mix Design Guidelines. Oregon Departmentof Transportation, Salem, March 1999.

12. AASHTO Guide for Design of Pavement Structures. AASHTO, Wash-ington, D.C., 1993.

13. Hicks, R. G., K. D. Dunn, J. Gray, L. Ilg, and J. Gower. Establishment ofQC/QA Procedures for Open-Graded Mixes. SPR Project 5268. OregonDepartment of Transportation, Salem, June 1996.

14. Rogge, D., and E. A. Hunt. Development of Maintenance Practices forOregon F-Mixes. Interim Report to Oregon Department of Transportation,Salem, June 1999.

Publication of this paper sponsored by Committee on Flexible Pavement Design.