Construction and Maintenance Practices for Permeable Friction Courses (2009)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Guidelines on the Use of Permeable Friction Courses

C O N T E N T S G-1 Introduction G-2 Objective G-2 Report Organization G-3 Standard Practice for Materials, Design and Construction of Permeable Friction Courses G-20 Standard Method of Test for Determining the Abrasion Loss of Permeable Friction Course (PFC) Asphalt Specimens by the Cantabro Procedure G-26 Standard Practice for Maintenance and Rehabilitation of Permeable Friction Courses (PFC)

G-1 Within the United States, the term open-graded friction (OGFC) has been used to describe hot-mix asphalt (HMA) having an open aggregate grading that is used as a wearing layer to improve friction properties. These mixes evolved through experimentation with plant mix seal coats. The ini- tial interest in these mix types resulted from problems associ- ated with the construction and performance of chip seals. Primarily, loose aggregates that either were not adequately seated during construction or dislodged by traffic were break- ing windshields. Additionally, there was a time constraint problem with setting the chip seal aggregates during a sudden rainstorm. During the 1930s Oregon began experimenting with the plant mix seal coats to improve frictional properties. During the 1940s, California also began using the plant mix seal coats as drainage interlayers and as an alternative to chip seals and slurry seals on pavement surfaces. During the late 1940s, a number of the western states began to use these mixes to improve frictional properties. An additional benefit from using these plant mix seal coats as a wearing layer was that hydroplaning and splash/spray was reduced. Even though plant mix seals provided excellent frictional properties and reduced potential for hydroplaning and splash/ spray, their use did not become widespread until the 1970s. The primary problems encountered with these mixes were related to durability and draindown. Because the plant mix seals had an almost uniform aggregate gradation with little fine aggregate, there was very little aggregate surface area. The term draindown is used to describe when the asphalt drains from the aggregates during storage and transportation.Asphalt binder that has drained from the aggregate structure results in pavement areas that have too little asphalt binder and areas that are very rich in asphalt binder. Areas without a sufficient amount of asphalt binder were prone to raveling, while areas rich in asphalt binder could become slick and did not provide the desired frictional properties. In the 1970s, the Federal Highway Administration (FHWA) initiated a program to improve the frictional resistance of the nation’s roadways. The plant mix seal coats were one of the tools an agency could use to improve frictional resistance and, thus, gained popularity. According to the 1978 NCHRP Syn- thesis Number 49, these plant mix seals became known as OGFCs. In 1980, the FHWA published a mix design proce- dure for these mix types. The procedure entailed an aggregate gradation requirement, a surface capacity of coarse aggregate, determination of fine aggregate content, determination of optimum mixing temperature, and resistance of the designed mixture to water. OGFC mixtures designed in accordance to the FHWA procedure were successful at performing their intended function: removing water from the pavement sur- face and improving frictional resistance. However, a number of states noted that the OGFC pavements were susceptible to sudden and catastrophic failures. The failures observed during the 1970s and 1980s were caused by mix design, material specification, and construc- tion problems. These problems primarily involved mix tem- perature during construction. Gradations associated with the OGFCs of the 1970s and 1980s were much coarser than typically used dense-graded mixes (Marshall and Hveem designed mixes).Additionally, very few states were using mod- ified asphalt binders. Because of the open nature of the aggre- gate gradings and neat asphalt binders, there were problems of draindown during transportation to the project site. To combat the draindown problems, most owners would allow contractors to reduce the mixture’s temperature during pro- duction. The draindown and mixture temperature problems led to catastrophic raveling and delamination, respectively. These problems were of such magnitude that a number of states put a moratorium on the use of OGFC mixtures during the 1980s. A survey of state highway agencies conducted in 1998 indi- cated that 19 states (38 percent) were currently using OGFCs. Over 70 percent of the states using OGFCs reported service lives of 8 years or more. The vast majority of the states report- ing good performance indicated the use of coarser gradations than the FHWA mix design procedure required and the use of stiffer, modified binders. Introduction

G-2 The question must be asked,“If OGFCs did not perform in the 1970s and 1980s, why did states continue to evolve these mixes such that performance improved?” The answer is sim- ple, safety. OGFCs most likely provide the safest wearing sur- face for our nation’s roadways. OGFCs have been shown to have excellent frictional resistance, reduce splash and spray, reduce the potential for hydroplaning, improve night visibil- ity, and improve visibility of pavement markings. Additional benefits of using OGFCs include reduced tire-pavement noise, smooth pavements, thereby increased fuel economy, and use of relatively thin layers. The property of OGFC that leads to the safety benefits men- tioned above is the relatively high permeability of OGFC com- pared to dense-graded HMAs. Because of the very coarse gradation and lack of fines, OGFCs have very high air void con- tents in the range of 15 percent to 22 percent. These high air void contents result in water infiltrating into the OGFC layer. Without water on the pavement surface, the frictional proper- ties of the pavement improve, splash and spray is reduced, and the potential for hydroplaning is greatly reduced. OGFCs that are designed to have at least 18 percent air voids are called permeable friction courses (PFCs). PFCs are a special type of OGFC that are specifically designed to have high air void contents, typically 18 to 22 percent, for removing water from the pavement surface. Other types of OGFCs also are used within the United States. In some states, friction courses having an open grading are used; however, these friction courses are not designed to be as permeable as PFCs. The purpose of these fric- tion courses is to provide a safe riding surface by improving fric- tional properties and/or to reduce tire/pavement noise. In 1992, the Georgia Department of Transportation (GDOT) built some test sections on Interstate 75 south of Atlanta, Georgia that were specifically designed to be coarser and have higher air void content than GDOT’s current version of OGFC. After these field experiments, the GDOT developed specifica- tion for what they termed as porous European Mixes (PEM). These PEM mixes are considered the first generation of PFCs used in the United States. A 1998 survey on the use of OGFC in the United States indicated that most DOTs reporting good performance with OGFCs had adopted coarser gradation than those specified in the FHWA procedure and were utilizing modified asphalt binders. After the 1998 survey was published, the National Center for Asphalt Technology (NCAT) undertook a research proj- ect to develop a mix design procedure for what they termed new-generation OGFCs. These new-generation OGFCs are considered PFCs because they are designed to have air void contents above 18 percent. Following the NCAT study, a number of DOTs developed specifications for PFCs. The sur- vey conducted as part of NCHRP 9-41 indicated that nine DOTs are currently utilizing PFCs. Seven of these DOTs are located in the southeast, ranging from Texas to North Car- olina. Other DOTs currently utilizing PFCs include Califor- nia, Oregon, and New Jersey. The use of PFCs in Europe has a longer history than in the United States, dating back to the 1970s. Within Europe, PFCs are called porous asphalt. Many of the European countries utilize PFCs including Switzerland, Spain, the Netherlands, Austria, France, Denmark, and the United Kingdom. In addi- tion to Europe, PFCs also are used in Australia, New Zealand, and Japan. Objective The objective of this project was to recommend design, construction, maintenance, and rehabilitation guidelines that will maximize the advantages and minimize the disadvan- tages associated with the use of PFC. In the context of this project, PFC was generally, but not exclusively, defined as a highly permeable mix containing polymer-modified asphalt binders or asphalt rubber and fibers, alone or in combination. Report Organization The draft final report for NCHRP Project 9-41 is divided into three volumes. Volume I of this report includes the cur- rent state-of-art for PFCs. This volume provides a synthesis two draft AASHTO Practices. The first practice was developed for the design and construction of PFCs, while the second practice was developed for the maintenance and rehabilita- tion of PFC layers. Also within this volume is a draft AASHTO test method for determining the abrasion loss of PFC samples using the Cantabro Abrasion Loss test. The final volume of the draft final report presents the annotated literature review.

G-3 Standard Practice for Materials, Design and Construction of Permeable Friction Courses AASHTO Format

D R A F T ________________________________________________________________________ Standard Practice for Materials, Design and Construction of Permeable Friction Courses (PFC) AASHTO Designation: PP XXX-YY ________________________________________________________________________ 1. SCOPE 1.1 This standard covers the materials requirements, mix design and construction of permeable friction course (PFC) asphalt mixtures. 1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. ________________________________________________________________________ 2. REFERENCED DOCUMENTS 2.1 AASHTO Standard: M 156, Requirements for Mixing Plants for Hot-Mixed, Hot-Laid Bituminous Paving Mixtures M 231, Weighing Devices Used in the Testing of Materials M 320, Performance-Graded Asphalt Binder R 30, Mixture Conditioning of Hot-Mix Asphalt (HMA) T 19, Bulk Density (‘Unit Weight”) and Voids in Aggregates T 96, Standard Method of Test for Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine T 104, Soundness of Aggregate by Use of Sodium Sulfate or Magnesium Sulfate T 209, Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures T 283, Resistance of Compacted Asphalt Mixtures to Moisture-Induced Damage T 305, Determination of Draindown Characteristics in Uncompacted Asphalt Mixtures T 312, Preparing and Determining the Density of Hot-Mix Asphalt (HMA) Specimens by Means of the Superpave Gyratory Compactor TP XXX, Determining the Abrasion Loss of Permeable Friction Course (PFC) Asphalt Specimens by the Cantabro Procedure 2.2 ASTM Standards: D 2995, Practice for Estimating Application Rate of Bituminous Distributors G-4

D 3549, Standard Test Method for Thickness or Height of Compacted Bituminous Mixture Specifications D 4791 Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregate ________________________________________________________________________ 3. TERMINOLOGY 3.1 Definitions: 3.1.1 permeable friction course (PFC)—a special type of porous hot mix asphalt mixture with air voids of at least 18% used for reducing hydroplaning and potential for skidding, where the function of the mixture is to provide a free-draining layer that permits surface water to migrate laterally through the mixture to the edge of the pavement. 3.1.2 asphalt binder—an asphalt-based cement that is produced from petroleum residue either with or without the addition of non-particulate organic modifiers. 3.1.3 abrasion loss—the loss of particles under the effect of abrasion. 3.1.4 air voids—the total volume of the small pockets of air between the coated aggregate particles throughout a compacted paving mixture, expressed as a percent of the total volume of the compacted specimen. 3.1.5 breakpoint sieve – the finest sieve to have at least 10 percent of the aggregate fraction retained. 3.1.6 draindown – separation of asphalt binder from the coarse aggregate structure, generally during storage or transportation. 3.1.7 stabilizing additive—materials used to minimize draindown of asphalt during transport and placement of PFC. 3.1.8 voids in coarse aggregate – the volume of voids between the coarse aggregate particles, where this volume includes filler, fine aggregate, air voids, asphalt binder, and stabilizing additives, if used. 3.1.9 stabilizing additive – polymer, crumb rubber, and/or fibers, used to minimize the draindown. ________________________________________________________________________ 4. SUMMARY OF PRACTICE 4.1 Aggregates, asphalt binder, stabilizing additives are selected that meet specification values. Selected aggregates are blended to meets specified gradation bands and compacted with a trial asphalt binder content in order to evaluate the trial mixes and select the design gradation. Once the trial gradation is selected, the asphalt binder G-5

content is altered and the optimum aspha lt binder content selected. The designed mixture is then evaluated for resistance to moisture susceptibility . 4.2 Permeable friction courses are constructed as wearing layers over a clean stable pavement structure. Permeable friction courses are produced in a manner similar to typical dense-graded hot mix asphalt (HMA). In some instances, special equipment is needed to introduce stabilizing additives. Transportation and placement of PFC is similar to other conventional HMA mixtures. Compaction of PFC is conducted to set the aggregates. ________________________________________________________________________ 5. SIGNIFICANCE AND USE 5.1 The procedure described in this practice is used to select materials, design and construct permeable friction courses that will provide good performance in terms of permeability and durability when subjected to high volumes of traffic. ________________________________________________________________________ 6. MATERIALS SELECTION AND MIX DESIGN 6.1 The first step in the design process is to select suitable materials. Materials needing selection include coarse aggregates, fine aggregates, asphalt binder and stabilizing additives. 6.1.1 Coarse Aggregates— Table 1 presents the coarse aggregate requirements for permeable friction courses. Table 1: Coarse Aggregate Quality Requirements of PFC Test Method Spec. Minimum Spec. Maximum Los Angeles Abrasion, % Loss AASHTO T96 - 30 Flat or Elongated, % ASTM D4791 2 to 1 - 50 Soundness (5 Cycles), % AASHTO T104 Sodium Sulfate - 10 Magnesium Sulfate - 15 Uncompacted Voids AASHTO TP-56 45 - M ethod A A Aggregates with L.A. Abrasion loss values up to 50 have been successfully used to produce OGFC mixtures. However, when the L.A. Abrasion exceeds approximately 30, excessive breakdown may occur in the laboratory compaction process or during in-place compaction. G-6

Table 2: Fine Aggregate Quality Requirements for OGFC Test Method Spec. Minimum Spec. Maximum Soundness (5Cycles), % AASHTO T104 Sodium Sulfate - 10 Magnesium Sulfate - 15 Uncompacted Voids AASHTO T304, Method A 45 - Sand Equivalency AASHTO T176 50 - 6.1.3 Asphalt Binders —Asphalt binders should be a Superpave performance grade (PG) meeting the requirements of AASHTO M320. Relatively high asphalt binder contents are required for permeable friction courses. Because of the open grading of the aggregate, a stiff asphalt binder is needed to ensure a durable mixture. For high- volume roadways or pavements with slow to standing traffic, the asphalt binder high- temperature grade should be increased by two grades over the standard asphalt binder. Adjustments should be an increase of one high-temperature grade for all other roadways. 6.1.4 Stabilizing Additives—Stabilizing additives are needed within permeable friction courses to prevent the draining of asphalt binder from the coarse aggregate skeleton during transportation and placement. Stabilizing additives such as cellulose fiber, mineral fiber, crumb rubber and poly mers have been used with success to minimize draindown potential. 6.2 Design Gradation—In order to provide the high level of permeability desirable with permeable friction courses, an aggregate gradation having a very open gradation is needed. Table 3 presents the specified gradation ranges. Table 3: PFC Gradation Specification Bands Sieve Size in. PFC ½ in. PFC ¾ in. PFC Grading Requirements % Passing 1 in. (25 mm) 100 ¾ in. (19 mm) 100 85-100 ½ in. (12.5 mm) 100 80-100 55-70 in. (9.5 mm) 85-100 35-60 --- No. 4 (4.75 mm) 20-30 10-25 10-25 No. 8 (2.36 mm) 5-15 5-10 5-10 No. 200 (0.075 mm) 0-4 0-4 0-4 6.1.2 Fine aggregates— Table 2 presents the fine aggregate requirements for permeable friction courses. G-7

6.2.1 Selection of Trial Gradations —The initial trail gradations must be selected to be within the master specification range shown in Table 3. To design a permeable friction course mix, it is recommended that at least three trial gradations be initially evaluated. It is suggested that the trial gradations fall along the coarse and fine limits of the gradation range along with one falling in the middle. These trial gradations are obtained by adjusting the amount of fine and coarse aggregates in each blend. 6.2.2 Determination of VCA in the Coarse Aggregate Fraction—For best performance, the PFC mixture must have a coarse aggregate skeleton with stone-on-stone contact. The coarse aggregate fraction is that portion of the total aggregate retained on the breakpoint sieve. The breakpoint sieve is defined as the finest (smallest) sieve to retain 10 percent of the aggregate gradation. The voids in coarse aggregate for the coarse aggregate fraction (VCA DRC ) are determined using AASHTO T19. When the dry-rodded density of the coarse aggregate fraction has been determined, the VCA DRC for the fraction can be calculated using the following equation: 100 w ca s w ca DRC G G VCA Equation 1 where, VCADRC = voids in coarse aggregate in dry-rodded condition s = unit weight of the coarse aggregate fraction in the dry-rodded condition (kg/m 3 ), w = unit weight of water (998 kg/m 3 ), and G ca = bulk specific gravity of the coarse aggregate The results from this test are compared to the VCA in the compacted PFC mixture (VC A mi x ). When the VC A mi x is equal to or less than the VCA DRC, stone-on-stone contact exists. 6.2.3 Selection of Trial Asphalt Content — The minimum desired asphalt binder content for permeable friction course mixtures is presented in Table 4. These minimum asphalt binder contents are provided to ensure sufficient volume of asphalt binder exists in the PFC mix. It is recommended that the mixture be designed at some amount over the minimum to allow for adjustments during plant production without falling below the minimum requirement. As a starting point for trial asphalt binder contents of PFCs, for aggregates with combined bulk specific gravities less than or equal to 2.75, an asphalt binder content between 6 and 6.5 percent should be selected. If the combined bulk specific gravity of the coarse aggregate exceeds 2.75, the trial asphalt binder content can be reduced slightly. G-8

Table 4: Minimum Asphalt Content Requirements for Aggregates with Varying Bulk Specific Gravities - Permeable Friction Courses Combined Aggregate Bulk Specific Gravity Minimum Asphalt Content Based on Mass, % 2.40 6.8 2.45 6.7 2.50 6.6 2.55 6.5 2.60 6.3 2.65 6.2 2.70 6.1 2.75 6.0 2.80 5.9 2.85 5.8 2.90 5.7 2.95 5.6 3.00 5.5 6.2.4 Sample Preparation—As with the design of any hot mix asphalt, the aggregates to be used in the mixture should be dried to a constant mass and separated by dry-sieving into individual size fractions. The following size fractions are recommended: 19.0 to 12.5 mm 12.5 to 9.5 mm 9.5 to 4.75 mm 4.75 to 2.36 mm Passing 2.36 mm (if 2.36 mm sieve is breakpoint sieve) 2.36 to 1.18 (if 1.18 mm is breakpoint sieve) After separating the aggregates into individual size fractions, they should be recombined to the proper percentages based upon the gradation blend being used. The mixing and compaction temperatures are determined in accordance with AASHTO T245, section 3.3.1. Mixing temperature will be the temperature needed to produce an asphalt binder viscosity of 170+ 20 cSt. Compaction temperature will be the temperature required to provide an asphalt binder viscosity of 280+ 30 cSt. However, while these temperatures work for neat asphalt binders, the selected temperatures may need to be changed for modified asphalt binders. The asphalt binder supplier’s guidelines for mixing and compaction temperatures should be used. When preparing PFC in the laboratory, a mechanical mi xing apparatus should be utilized. Aggregate batches and asphalt binder are heated to a temperature not exceeding 50°F (28°C) more than the temperature established for mixing G-9

temperature. The heated aggregate batch is placed into the mechanical mixing container. Asphalt binder and any stabilizing additive are placed into the container at the required masses. Mix the aggregate, asphalt binder, and stabilizing additives rapidly until thoroughly coated. Mixing times for PFC should be slightly longer than for conventional mixtures to ensure that the stabilizing additives are thoroughly dispersed within the mixture. After mixing, the PFC mixture should be short-term aged in accordance with AASHTO R30. 6.2.5 Number of Samples per Trial Blend— A total of eighteen samples are initially required: three samples for determining air voids and three uncompacted samples for determining theoretical maximum density at each binder content. Each sample is mixed with the trial asphalt binder content and three of the four samples for each trial gradation are compacted. The remaining sample of each trial gradation is used to determine the theoretical maximum density according to AASHTO T209. 6.2.6 Sample Compaction—Specimens should be compacted at the established compaction temperature after aging. Laboratory samples of PFC are compacted using 50 revolutions of the Superpave gyratory compactor in accordance with AASHTO T312. More than 50 revolutions should not be used; OFGC is relatively easy to compact in the laboratory and exceeding this compactive effort can cause excessive aggregate breakdown. 6.2.7 After the samples have been compacted, extruded and allowed to cool, they are tested to determine their bulk specific gravity, G mb using dimensional analysis. Dimensional analysis entails calculating the volume of the sample by obtaining four height measurements with a calibrated caliper, with each measurement being 90 degrees apart. The area of the specimen is then multiplied by the average height to obtain the sample volume. The G mb is determined through dividing the dry mass of the sample by the sample volume determined in accordance with D 3549. Uncompacted samples are used to determine the theoretical maximum density, G mm (AASHTO T209). Using Gmb, Gmm and Gca, percent air voids (VTM), and VCAmix are calculated. The VTM and VCA are calculated as shown below. mm mb G G VTM 1 100 Equation 2 ca ca mb mi x G P G VCA 100 Equation 3 where: Pca = percent of coarse aggregate in the mixture Gmb = combined bulk specific gravity of the total aggregate Gca = bulk specific gravity of the coarse aggregate G-10

Once the VTM and VCA mi x are determined, each trial blend mixture is compared to the PFC mixture requirements. Table 5 presents the requirements for OGFC designs. Of the three trial blends, the trial blend with the highest air void content that meets the 18 percent minimum and exhibits stone-on-stone contact is considered the design gradation. Table 5: PFC Mixture Specification for SGC Compacted Designs Property Requirement Asphalt Binder, % Table 4 Air Voids, % 18 to 22 Cantabro Loss % 15 min. VCA mi x % Less than VCA DRC Tensile Strength Ratio 0.70 min. Draindown at Production Temperature, % 0.30 max 6.3 Selection of Optimum Asphalt Binder Content—Once the design gradation has been selected, it is necessary to evaluate various asphalt binder contents in order to select an optimum binder content. Additional samples are prepared using the design gradation and at least three asphalt binder contents. The number of samples needed for this procedure is eighteen. This provides for three compacted (for G mb and Cantabro Abrasion Loss) and three uncompacted samples (one for determination of theoretical maximum density and two for draindown testing) at each of the three asphalt binder contents. Optimum asphalt binder content is selected as the binder content that meets all of the requirements of Table 5. 6.3.1 Cantabro Abrasion Loss— The Cantabro Abrasion test is used as a durability indicator during the design of OGFC mixtures. In this test, three OGFC specimens compacted with 50 gyrations of the Superpave gyratory compactor are used to evaluate the durability of an OGFC mixture at a given asphalt binder content. The test is conducted in accordance with the TP XXX. 6.3.2 Draindown Sensitivity— The draindown sensitivity of the selected mixture is determined in accordance with AASHTO T305 except that a 2.36-mm wire mesh basket should be used. Draindown testing is conducted at a temperature of 27°F (15 ˚ C) higher than the anticipated production temperature. 6.3.3 Permeability (optional)— An optional test is to conduct laboratory permeability tests. Laboratory permeability values greater than 528 ft/day (100 m/day) are recommended. 6.4 Evaluation of Moisture Susceptibility—Moisture susceptibility of the selected mixture is determined using the modified Lottman method in accordance with AASHTO T283 with one freeze-thaw cycle. The AASHTO T283 method should be modified as follows: (a) PFC specimens should be compacted with 50 gyrations of the Superpave gyratory compactor at the optimum asphalt binder content; (b) no specific air void content level is required; (c) apply a G-11

vacuum of 26 inches of Hg for 10 minutes to saturate the compacted specimens; however, no saturation level is required; (d) keep the specimens submerged in water during the freeze-thaw cycle. 6.5 Reports 6.5.1 The report should include the following information: 6.5.2 Identification of the project and the project number. 6.5.3 Aggregate source, asphalt source and grade, type and amount of stabilizing additive, and materials quality characteristics. 6.5.4 Results of the grading optimization or selected grading from experience. 6.5.5 Selected optimum grading and optimum asphalt content. 6.5.6 Volumetric properties, abrasion loss on unaged specimens, and draindown for each trial blend and at the optimum asphalt binder content. 6.5.7 Moisture susceptibility recommendations, and 6.5.8 Recommended job-mix formula for the permeable friction course. ________________________________________________________________________ 7. CONSTRUCTION OF PFC LAYERS 7.1 Production of PFC Mixture 7.1.1 Aggregates – To obtain the coarse aggregate-on-coarse aggregate contact inherent in PFCs, the mixture must contain a high percentage of coarse aggregate. Thus the gradation of the coarse aggregates can have a tremendous effect on the quality of the mixture produced. Therefore, it is imperative that the aggregates be carefully handled and stockpiled. Each coarse aggregate stockpile may need to be fed through more than one cold feeder since a high percentage of material is being fed. Using more than one feeder will also minimize variability in the gradation of coarse aggregate stockpiles. 7.1.2 Liquid Asphalt - The handling and storage of liquid asphalt binder for PFC production is similar to that for any HMA mixture. When modified asphalt binders are used, typically the storage temperatures may increase slightly from those of neat asphalt binders. However, contractors should follow the manufacturer’s recommendations for circulation and storage of modified asphalts. Metering and introduction of the asphalt binder into the mixture may be done by any of the standard methods using a temperature compensating system. It is very important however that the asphalt binder be metered accurately. 7.1.3 Stabilizing Additives - Due to the high asphalt binder contents in the PFC, a stabilizing additive of some type may be used to hold the binder on the coarse aggregate during hauling and placement. Two types of stabilizing methods have been used. One method is the use of fibers such as cellulose or mineral G-12

fibers. The second stabilizing method is to modify the asphalt binder in some manner. This may be done by modifying the asphalt binder at the refinery or by adding an asphalt binder modifier to the PFC mixture during production. Some projects have utilized both a fiber and a modified asphalt binder. 7.1.3.1 Fibers - Both cellulose and mineral fibers have been used. Typical dosage rates are 0.3% for cellulose and 0.4% for mineral fiber by total mixture mass. Fibers can generally be purchased in two forms, loose fibers and pellets. Fibers in a dry, loose state come packaged in plastic bags or in bulk. Both fiber types have been added into batch or drum mix plants with good success. For batch plant production, loose fibers are sometimes delivered to the plant site in bags. The bags are usually made from a material which melts easily at mixing temperatures. The bags can therefore be added to the pugmill during each dry mix cycle. When the bags melt only the fiber remains. Addition of the bags of fibers is done by workers on the pugmill platform. At the appropriate time in every dry mix cycle, the workers add the correct number of bags to the pugmill. The bags of fiber can be elevated to the pugmill platform by the use of a conveyor belt. While this method of manual introduction works satisfactorily, it is labor intensive. Another method for addition of fibers into a batch plant is by blowing them into the plant using a machine typically designed and supplied by the fiber manufacturer. The dry, loose fiber is placed in the hopper of the machine where it is fluffed by large paddles. The fluffed fiber next enters the auger system which conditions the material to a known density. The fiber is then metered by the machine and blown into the pugmill or weigh hopper at the appropriate time. These machines can meter in the proper amount of fiber by mass or blow in a known volume. This fiber blowing method can also be used in a drum mix plant. The same machine is used and the fibers are simply blown into the drum. When using this method in a drum mix plant, the fiber line may be placed in the drum beside the asphalt binder line and merged into a mixing head. This allows the fibers to be captured by the asphalt binder before being exposed to the high-velocity gases in the drum. If the fiber does get into the gas stream in large quantities, it will enter the dust control system of the plant. The pelletized form of fibers can be used in both drum mix and batch plants. The pellets are shipped to the plant in bulk form and when needed are placed in a hopper. From the hopper they can be metered and conveyed to the drum or pugmill via a calibrated conveyor belt. Addition of the pellets occurs at the RAP collar of the drum mix plant or they are added directly into the pugmill of a batch plant. Here the pellets are mixed with the aggregate where the heat from the aggregates causes the asphalt binder in the pellets to become fluid allowing the fiber to mix with the aggregate. G-13

The pelletized fibers do contain a given amount of asphalt binder that must be accounted for in the overall asphalt content of the mixture. Check with the fiber manufacturer to determine the asphalt contents of the pellets. It is again imperative that the fiber addition, whether it be bulk or pelletized, be calibrated to ensure that the mixture continually receives the correct amount of fiber. If the fiber content is not accurately controlled at the proper level, fat spots will almost certainly result on the surface of the finished pavement. For assistance with the fiber storage, handling, and introduction into the mixture, the fiber manufacturer should be consulted. 7.1.3.2 Asphalt Cement Modifiers - Another method of providing stabilization to PFC is with the use of asphalt binder modifiers. The asphalt binder in PFC can be modified at the refinery, or, in some cases, the modifier is added at the hot mix plant. For the first method, the hot mix producer takes delivery of the modified asphalt binder and meters it into the mixture in a traditional manner. Special storage techniques and/or temperatures may be required. With the second method, the contractor must ensure that the proper amount of modifier is added and thoroughly mixed with the asphalt binder. When an asphalt binder modifier is added at the hot mix plant, two different methods are utilized. The modifier is either blended into the asphalt binder before it is injected into the mixture or it is added directly to the dry aggregates during production. Addition of the modifier to the asphalt binder is accomplished by in-line blending or by blending the two in an auxiliary storage tank. If the modifier is added to the aggregates rather than the asphalt binder, it can be added directly into the pugmill or, in a drum mix plant, it can be delivered to the drum via the RAP delivery system. Use of the RAP belt weigh bridge is not recommended because of poor accuracy and a special metering device may be necessary if the RAP feeder cannot be calibrated. 7.2 Mixture Production - Production of PFC is similar to production of standard HMA from the standpoint that care should be taken to ensure a quality mixture is produced. Production of PFC is discussed in this section with special emphasis on production areas where PFC quality may be significantly affected. Facilities utilized to produce PFC should meet the requirements of M156. 7.2.1 Plant Calibration - It is important that all the feed systems of the plant be carefully calibrated prior to production of PFC. The aggregate cold feeds can make a large difference in the finished mixture even in a batch plant where hot bins exist. Calibration of the aggregate cold feed bins should therefore be performed with care. The stabilizing additive delivery system should be calibrated and continually monitored during production. Whether fibers, an asphalt binder modifier, or both are being utilized, variations in the amount of additive can have a G-14

detrimental impact on the finished pavement. Stabilizing additive manufacturers will usually assist the hot mix producer in setting up, calibrating, and monitoring the stabilizing additive delivery system. 7.2.2 Plant Production Temperature - Production temperatures of PFC mixtures vary somewhat according to aggregate moisture contents, weather conditions, grade of asphalt binder and type of stabilizing additive used. However, experience indicates that normal HMA production temperatures or slightly higher are adequate. Typically, a temperature of 293-310 F (145-155 C) can be used when a polymer is not included. Temperatures higher than this may be needed on some occasions, such as when a polymer modifier is added, but should be used with caution as rapid oxidation begins to occur at higher temperatures. The PFC mixture should never be heated above 350 F (176 C) since this may excessively damage the asphalt binder and may increase plant emissions. As the mixture temperature is increased, the chance of the mortar draining from the coarse aggregate also increases. The temperature should be chosen to ensure a uniform mixture that allows enough time for transporting, placing, and compaction of the mixture. 7.2.3 Mixing Time - When adding fibers to the PFC mixture, experience has shown that the mixing time should be increased slightly over that of conventional HMA. This additional time allows for the fiber to be sufficiently distributed in the mixture. In a batch plant this requires that both the dry and wet mix cycles be increased from 5 to 15 seconds each. In a parallel flow drum mix plant, the asphalt binder injection line may be relocated, usually extended, if necessary to provide improved mixing. When blowing fibers into a drum mix plant, it is imperative that the fiber line be placed in the drum beside the asphalt binder line and merged into a mixing head.The proper mixing times can be estimated by visual inspection of the mixture. If clumps of fibers or pellets still exist intact in the mixture at the discharge chute, or if aggregate particles are not sufficiently coated, mixing times should be increased or other changes made. For other plants such as double barrels and plants with coater boxes, the effective mixing time can be adjusted in a number of ways including reduction in production rate, slope reduction of the drum, etc. 7.2.4 Mixture Storage - The PFC mixture should not be stored at elevated temperatures for longer than 2 hours. This could facilitate draindown. 7.3 Placement and Compaction Procedures 7.3.1 Weather Limitations - In order to achieve proper placement and compaction, PFC should not be placed in cold or inclement weather. It is recommended that a minimum pavement temperature of 50 F (10 C) be achieved prior to placement. However, the ability to place PFC will also depend on wind conditions, humidity, the lift thickness being placed and the temperature of the existing pavement. G-15

7.3.2 Mixture Transportation - Haul times for PFC should be as short as possible. It is important that the temperature of the PFC mixture not be raised arbitrarily high in order to facilitate a longer haul time. Most agencies limit haul distance to 50 miles or haul times to 1 hour. Due to high asphalt binder contents, PFC may adhere to truck beds somewhat more than conventional HMA mixtures. This is particularly true when asphalt binder modifiers are employed in the mixture. It is therefore prudent to use a release agent and clean the truck beds frequently. Most agencies have approved lists of release agents. However, if not carefully utilized, these agents may cause problems. If the agent is allowed to pool in the bottom of the truck it may cause cold spots. The bed of the truck should be coated and the excess agent removed before loading. This can be accomplished by raising the truck bed after the agent has been sprayed into the truck. Any excess agent will then be discharged. Use of fuel oils in any form should be strictly prohibited. All transport vehicles should be tarped with the tarps tightly drawn and tied over the truck bed. 7.4 Pavement Surface Preparation - When placing PFC, preparation of the surface to be covered will depend on the type of surface; this preparation is generally the same as for conventional HMA. PFC is normally applied in any of several situations: over an old HMA pavement, over an old Portland cement concrete pavement or over a new HMA binder course. If an old pavement surface is to be covered by PFC then proper repair should first be performed. Areas containing large permanent deformations should be milled or filled using a leveling course. If the condition of the in-place mix is sufficiently bad it may have to be removed to some predetermined depth. Lightly and randomly cracked surfaces should have wide cracks cleaned and sealed. If the entire surface is randomly cracked a full-width treatment is needed to make the surface impermeable. Any distressed areas should be properly repaired. A tack coat should be applied after repairs and prior to placement of the PFC. For old and new surfaces, a tack coat should be used. Types of materials and their application rates need to vary from that of conventional HMA construction. Freshly compacted dense-graded HMA may be as much as 8 percent air voids and permeable to water. A uniform tack coat should be applied prior to placement of the PFC. Tack coats should be applied using a distributor truck that has been calibrated in accordance with D2995. 7.5 Paver Operation 7.5.1 Charging the Paver - The PFC mixture is normally delivered to the paver in the traditional manner of backing in trucks. A material transfer vehicle (MTV) can also be used for PFC 7.5.2 Paver Calibration - Prior to placement of the PFC, the paver should be correctly calibrated. This is no different than when placing conventional HMA and involves the flow gates, the slat conveyors, and the augers. The G-16

flow gates should be set to allow the slat conveyors to deliver the proper amount of mixture to the augers so that the augers turn 85-90 percent of the time. 7.5.3 Paving Speed - When placing PFC, the paving speed is for the most part dictated by the ability of the rolling operation to compact the mixture. It is critical that the plant production, mixture delivery, placement, and compaction be coordinated so that the paver does not have to continually stop and start. Paver stops and starts should be held to an absolute minimum because they will likely have a significant negative impact on the ride. In addition to continuous paver movement, the PFC mixture delivery and paver speed should be calibrated so that the augers can be kept turning 85-90 percent of the time. This helps ensure the slowest possible speed for the augers. Running the augers very fast for short periods of time should be avoided. The high auger speed may have a tendency to shear the mortar from the coarse aggregate thus causing fat spots in the pavement. Generally, the paver wings should not be lifted except when the material is to be discarded. 7.5.4 Lift Thickness - The majority of PFC pavements have been placed ¾ to 1¼ inches thick. It is imperative that the construction inspector not try to balance yield by adjusting the thickness of the PFC lift. This can cause unsatisfactory pavements to be built. A tolerance of + ¼ inch in the lift thickness is allowable. 7.5.5 Placement and Finishing - Immediately behind the paver, PFC mixtures are known to be harsh and very sticky. For this reason a minimum of raking and hand working should be performed. When needed, hand placement of the material can be accomplished with care. 7.6 Rolling – Compaction of PFC is conducted to seat the aggregates. Rolldown of PFC mixtures is slightly more than one-half that for conventional HMA mixtures. While conventional HMA mixtures roll down approximately 20-25 percent of the lift thickness, PFC will normally roll down 10-15 percent of the lift thickness. Therefore, to match longitudinal joints, the hot side should be 10-15 percent of the lift thickness or higher. Static, steel-wheel rollers should be used to compact PFC mixes. Rubber-tire pneumatic rollers should not be used as they tend to pick up material. Vibratory steel-wheel rollers should only be used for transverse joints. 7.7 Quality Control/Quality Assurance 7.7.1 Aggregates - As with conventional HMA, the producer should periodically monitor the aggregate stockpiles being used for the production of the PFC mixture. Stockpile gradations can change as additional material is added to the stockpile during mixture production. Even if the stockpiles do not receive additional aggregates during mixture production, their gradations may change G-17

due to stockpiling and/or load out procedures. Therefore the monitoring program must be frequent enough to warn the producer that a change has taken place before a significant amount of the aggregate has been used in PFC mixtures. In batch plant operations, hot bin analyses should also be performed. This testing serves as a further check of aggregate gradations. In both batch and drum mix plants the cold feed gradations should be monitored. Variations or deviations of aggregate gradation from the specified job-mix - formula are often more critical to the performance of PFC mixtures than they are for HMA. Therefore, close control of gradation must be accomplished for these mixtures. 7.7.2 Asphalt Binder - The asphalt binder used in the PFC should be tested as it is for any conventional HMA project. Some modified asphalt binders may require special testing techniques. 7.7.3 Trial Sections - Prior to full-scale production and placement, a trial section of the mixture should be produced and placed by the contractor. This trial section should be at the actual construction site and should be at least two paver widths wide. The trial section should consist of between 220 and 550 tons (200 and 500 Mg) of mixture. The length of the trial section will depend upon the capacity of the plant and other variables in the mixture production and placement. However, the trial section needs to be of sufficient size to allow the plant components to operate to the point of producing consistent mixture. The trial section is a good opportunity to determine any proportioning problems with the final job-mix-formula (JMF). The trial section should be constructed in advance of the production paving so as to allow for testing and adjustment in the JMF and to allow for a second trial section if major adjustments need to be made. 7.7.4 Mixture Sampling - Most agencies have established their own requirements for where and how mixture sampling must be done. PFC should be sampled according to these recognized procedures. Experience has shown that quartering of PFC can be difficult due to its tendency to stick to the tools thus potentially causing a low asphalt content to be measured. Frequency of sampling and testing is usually established by the owner. As a minimum, at least two test series per day (gradations, asphalt contents, volumetrics and draindown) should be performed. More frequent testing is advisable in order to maintain good quality control. Many agencies divide the mixture into lots and sublots and require two or three test series per lot. In addition, the time at which samples are taken should be obtained randomly so as not to bias the results. 7.7.5 Mixture Tests -Certain test data on the mixture must be collected to allow the producer of PFC to control the mixture as well as to allow the owner the ability to accept or reject the mixture. These tests are generally similar to those performed on conventional HMA. G-18

7.7.5.1 Laboratory Compacted Specimens - Laboratory compacted specimens should be examined for compliance with volumetric properties established for the mixture. These tests consist of compacting specimens using 50 gyrations of the Superpave Gyratory Compactor (SGC). The bulk specific gravity of the specimens can be determined by dimensional measurements, while the maximum theoretical specific gravity is determined by AASHTO T209. Air voids may then be determined. The resulting air voids should be within the specified range shown in Table 5. 7.7.5.2 Asphalt Content and Gradation - The stabilizing additives used in PFC can sometimes hinder the extraction process and some experimentation may be necessary to determine the optimum method of extracting the mixture. Most agencies allow one or more of any of the methods discussed in AASHTO T164. Note that while Method B is very reliable, it is generally not suited for field work due to the length of time needed for the test. The asphalt content by ignition method (T308) has also been shown to work well for determining the asphalt binder content of PFC. After removing the asphalt binder the aggregate should be graded according to AASHTO T27. The resulting gradation and asphalt content should meet the JMF established for the mixture within the tolerance limits specified. Typical tolerance limits for gradations are shown in Table 6. Table 6: Gradation Tolerances for Extracted PFC Samples. Sieve Size Percent Passing Tolerance 19.0-mm (¾ Inch) + 4.0 12.5-mm (½ Inch) + 4.0 9.5-mm ( Inch) + 4.0 4.75-mm (No. 4) + 3.0 2.36-mm (No. 8) + 3.0 0.60-mm (No. 30) + 3.0 0.30-mm (No. 50) + 3.0 0.075-mm (No.200) + 2.0 Asphalt Content (%) + 0.3 7.7.5.3 Draindown Test - Since the PFC mixture must have some stabilizing additive to prevent draindown of the mortar from the coarse aggregate, mixture samples should also routinely be checked for compliance with draindown requirements in accordance with T305. G-19

G-20 Standard Method of Test for Determining the Abrasion Loss of Permeable Friction Course (PFC) Asphalt Specimens by the Cantabro Procedure AASHTO Format

D R A F T ________________________________________________________________________ Standard Method of Test for Determining the Abrasion Loss of Permeable Friction Course (PFC) Asphalt Specimens by the Cantabro Procedure AASHTO Designation: T XXX-YY _______________________________________________________________________ 1. SCOPE 1.1 This standard covers a test method for determining the percent abrasion loss of permeable friction course (PFC) asphalt specimens using the Los Angeles abrasion machine. 1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. ________________________________________________________________________ 2. REFERENCED DOCUMENTS 2.1 AASHTO Standards: M 231, Weighing Devices Used in the Testing of Materials R 30, Mixture Conditioning of Hot-Mix Asphalt (HMA) T 96, Standard Method of Test for Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine T 209, Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures T 312, Preparing and Determining the Density of Hot-Mix Asphalt (HMA) Specimens by Means of the Superpave Gyratory Compactor 2.2 ASTM Standards: E 1, Specification for ASTM Thermometers D 3549, Standard Test Method for Thickness or Height of Compacted Bituminous Mixture Specifications D 7064, Standard Practice for Open-Graded Friction Course (OGFC) Mix Design 2.3 European Standards: EN 12697 - 17, Bituminous mixtures. Test methods for hot-mix asphalt. Particle loss of porous asphalt specimen G-21

________________________________________________________________________ 3. TERMINOLOGY 3.1 Definitions: 3.1.1 permeable friction course (PFC)— a special type of porous hot-mix asphalt mixture with air voids of at least 18% used for reducing hydroplaning and potential for skidding, where the function of the mixture is to provide a free-draining layer that permits surface water to migrate laterally through the mixture to the edge of the pavement. 3.1.2 asphalt binder— an asphalt-based cement that is produced from petroleum residue either with or without the addition of non-particulate organic modifiers. 3.1.3 abrasion loss— the loss of particles under the effect of abrasion. 3.1.4 air voids— the total volume of the small pockets of air between the coated aggregate particles throughout a compacted paving mixture, expressed as a percent of the total volume of the compacted specimen. 3.1.5 stabilizing additive— materials used to minimize draindown of asphalt during transport and placement of PFC. ________________________________________________________________________ 4. SUMMARY OF TEST METHOD 4.1 A single specimen of compacted PFC is placed within the drum of a Los Angeles abrasion machine without the charge of steel spheres. The specimen is subjected to a total of 300 revolutions within the Los Angeles abrasion drum. At the conclusion of the test, the percent material loss is determined based upon the original mass of the specimen. _______________________________________________________________________ 5. SIGNIFICANCE AND USE 5.1 The procedure described in this test standard is used to indirectly assess the cohesion, bonding, and effects of traffic abrasion and, when used with other tests, to determine the optimum asphalt binder content during PFC mixture design that will provide good performance in terms of permeability and durability when subjected to high volumes of traffic. The procedure can be used for either laboratory or field specimens. ________________________________________________________________________ 6. APPARATUS 6.1 Los Angeles Abrasion Machine— as specified in AASHTO T 96. 6.2 Thermometers— armored, glass, or dial-type with metal stems as set out in ASTM E 1. To measure the temperatures of the aggregates, binder, and PFC mixture, metal thermometers with a scale up to 200 ºC (392 ºF) and an accuracy of ±3 ºC (±5 ºF) or G-22

better shall be used. To measure the test temperature, a thermometer with a scale from 0 ºC to 40 ºC (32 ºF to 104 ºF) and an accuracy of ±0.5 ºC (±1 ºF) shall be used. 6.3 Balances— meeting the requirements as set out in AASHTO M 231 having suitable capacity and accuracy of 0.1% of the mass to be weighed. 6.4 Oven —meeting the requirements of M 231 with closed ventilation system, or chamber thermostatically controlled to maintain test temperature at ±1 ºC (±2 ºF) in the vicinity of the samples. The oven shall be capable of maintaining the temperature required in accordance with AASHTO R 30. 6.5 Chamber— or enclosed room large enough to hold the Los Angeles machine with temperature controls adjustable to a maximum margin of error of ±2 ºC (±4 ºF). This temperature being measured in the air close to the Los Angeles machine. 6.6 General materials —trays, pots, spatulas, heat-resistant gloves, grease pencils, curved scoops, filter paper rings, etc. ________________________________________________________________________ 7. HAZ ARDS 7.1 Use standard safety precautions and protective clothing when handling hot materials and preparing test specimens. ________________________________________________________________________ 8. SAMPLES AND TEST SPECIMENS 8.1 Specimens may be either laboratory-molded PFC mixtures. 8.2 A total of three (3) specimens are required per mixture being tested. 8.3 Preparation of Laboratory-Molded Specimens 8.3.1 Prepare replicate mixtures (Note1) at the appropriate aggregate gradation and asphalt binder content. NOTE 1: Three replicate specimens are required, but five specimens may be prepared if so desired. Generally, 4500 to 4700 g of aggregate is sufficient for each compacted specimen with a height of 110 mm to 120 mm for aggregates with combined bulk specific gravities of 2.55 to 2.70, respectively. 8.3.2 Condition the specimens according to R30 and compact the specimens to 50 gyrations in accordance with T312. Record the specimen height to the nearest 0.1 mm after each revolution. 8.3.3 Density and Voids— Once the specimens have been compacted, cooled to ambient temperature, and removed from the molds, determine their relative density and voids content using bulk specific gravity (see NOTE-2) and AASHTO T 209. G-23

NOTE 2: The bulk density of a cylindrical-shaped specimen of PFC shall be calculated from the compacted specimen’s dry mass (in grams) and volume (in cubic centimeters). In order to obtain the specimen volume, determine the height of the specimen in accordance with ASTM E3549 using calibrated calipers and the diameter of the specimen as the average of four equally spaced measurements using the same calipers. Calculate the area of the sample using the average diameter determined as described above. Calculate the volume of the specimen by multiplying the sample area and the average height. Calculate the bulk density by dividing the dry mass of the specimen by the calculated volume of the specimen. Convert the bulk density to bulk specific gravity by dividing by 0.99707 g/cm 3 , the density of water at 25ºC (77ºF). ________________________________________________________________________ 9. PROCEDURE 9.1 The test temperature is 25ºC (77ºF) and should be maintained during the test with a maximum margin of error of ±2 ºC (±4 ºF). 9.2 The mass of the compacted specimen shall be determined to within ± 0.1 g and the value recorded as W 1. Before testing, specimens must be kept at the test temperature for at least 4 hours. 9.3 After the specimens have been kept at the test temperature for the required period of time, one specimen is placed inside the Los Angles abrasion machine drum and, without the charge of steel spheres, the drum is turned at 300 revolutions at a velocity of 188 to 207 radians per second (30 to 33 revolutions per second) per T96. 9.4 When the test is completed, the specimen is removed from the drum, slightly cleaned with a cloth eliminating particles that are clearly loose, and weighed again to within ± 0.1 g and this value recorded as W 2. 9.5 The test is repeated in the same way for each of the specimens prepared. ________________________________________________________________________ 10. INTERPRETATION OF RESULTS 10.1 For each sample, the particle loss (percent) is determined using the following equation: PL = [( W 1 – W 2) / W 1] x 100 where: PL = Cantabro abrasion percent loss, W 1 = initial weight of the specimen, and W 2 = final weight of the specimen 10.2 Calculate the mean particle loss of all specimens tested. Round the result to the nearest 1%. 10.3 The values obtained from the test and, if required, the density and voids of specimens, are reported together with the test temperature. G-24

NOTE 3: The Cantabro abrasion test method was originally developed in Spain in 1986 and entitled Cantabrian Test of Abrasion Loss . The original Spanish test was based on a 50 blow Marshall compaction effort. If the user is unfamiliar with the Cantabro test, the results should be evaluated with considerable engineering judgment until some experience related to actual performance has been developed. ASTM D 7064 and European Standard EN 12697-17 were used to assist in the development of this test procedure. ________________________________________________________________________ 11. REPORT 11.1 Report the following information, if applicable: 11.1.1 Project name; 11.1.2 Date(s) of preparation and testing; 11.1.3 Specimen identification; 11.1.4 Percent binder in each specimen, nearest 0.1 percent; 11.1.5 Mass of each specimen, W 1, nearest 0.1 g; 11.1.6 Mass of each specimen , W 2, nearest 0.1 g; 11.1.7 Test temperature; 11.1.8 Maximum specific gravity ( G mm ) of each specimen by T 209, nearest 0.001; 11.1.9 Bulk specific gravity ( G mb ) of each specimen, nearest 0.001; 11.1.10 The particle loss for each specimen tested and the mean value for all specimens, nearest 1%. 11.1.11 Density and voids of each specimen, if required. ________________________________________________________________________ 12. PRECISION AND BIAS 12.1 The research required to determine the precision of this standard has not been performed. There is no information that can be presented on the bias of the procedure because no material having an accepted reference value is available. ________________________________________________________________________ 13. KEYWORDS 13.1 permeable friction courses, gyratory, Cantabro Abrasion G-25

G-26 Standard Practice for Maintenance and Rehabilitation of Permeable Friction Courses (PFC) AASHTO Format

D R A F T ________________________________________________________________________ Standard Practice for Maintenance and Rehabilitation of Permeable Friction Courses (PFC) AASHTO Designation: PP XXX-YY ________________________________________________________________________ 1. SCOPE 1.1 This standard covers activities related to the maintenance and rehabilitation of permeable friction course (PFC) asphalt mixtures. 1.2 This standard may involve hazardous materials, operations and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use . ________________________________________________________________________ 2. REFERENCED DOCUMENTS 2.1 AASHTO Standard ________________________________________________________________________ 3. TERMINOLOGY 3.1 Definitions 3.1.1 Permeable Friction Courses (PFC) – special type of porous hot-mix asphalt mixture with air voids of at least 18 percent used for reducing hydroplaning and potential for skidding, where the function of the mixture is to provide a free-draining layer that permits surface water to migrate laterally through the mixture to the edge of the pavement. ________________________________________________________________________ 4. SUMMARY OF PRACTICE 4.1 Maintenance of PFC mixtures is different than conventional dense-graded hot- mix asphalt. Maintenance can be generally grouped into one of two categories: general maintenance and winter maintenance. General G-27

maintenance involves activities such as cleaning of clogged PFC, preventative surface treatments, and corrective surface treatments. Winter maintenance involves those activities required to maintain a safe driving surface during winter events. 4.2 Rehabilitation of PFC layers involves those activities required to correct major surface distresses. ________________________________________________________________________ 5. SIGNIFICANCE AND USE 5.1 The information in this practice is used to make decisions on methods for maintaining or rehabilitating PFC pavements. ________________________________________________________________________ 6. MAINTENANCE 6.1 Maintenance activities can be broadly grouped into one of three categories: cleaning clogged PFC, preventative surface maintenance and corrective surface maintenance. 6.1.1 Over time, PFCs may gradually become choked and lose the ability to drain water due to dirt and debris entering the void structure. Therefore, cleaning may be necessary. Three methods have been utilized for cleaning PFC layers: a) cleaning with a fire hose, b) cleaning with a high water pressure cleaner, and c) cleaning with a specially manufactured cleaning vehicle. Research has indicated that cleaning PFC layers can be difficult if the cleaning activities are initiated after the layer has become clogged. Best results have been encountered when cleaning activities are initiated prior to the layer becoming clogged. 6.1.2 Fog seals have been used as a preventative surface maintenance treatment. Fog seals do reduce the permeability of PFC layers. Additionally, fog seals will reduce the frictional properties of the surface until the fog seal is worn away by traffic. Experience suggests this will take approximately one month. Fog seals do not affect the macrotexture of PFC layers; therefore, the reduced potential for hydroplaning is maintained. 6.1.3 Corrective surface maintenance activities are those conducted to repair minor surface distresses in PFC layers. Corrective surface maintenance can also be considered minor rehabilitation. 6.1.3.1 Occasionally, PFC layers will require the repair of delaminated areas and potholes. When distressed areas are large enough to justify, milling and overlaying with PFC has been recommended. If the distressed area is G-28

relatively small, a dense-graded hot-mix asphalt can be utilized for such patch repairs. It is desirable to maintain the drainage characteristics of the PFC layer when undertaking patch repairs. When the patch area is small and the flow of water around the patch is ensured, dense-graded hot-mix asphalt can be used. Rotation of the patch to a 45-degree angle to provide a diamond shape is recommended because it will facilitate the flow of water along the patch material and will also diminish wheel impact on the patch joint. When patching with PFC material, only a light tack coat should be applied to vertical faces . 6.1.3.2 PFC layers can develop transverse and longitudinal cracks while in service. Narrow cracks are generally not visible because of the open texture of the PFC surface. When cracks appear, they should be sealed. There is no problem in sealing the transverse cracks because the crack sealer will not impede the flow of water within the PFC. Sealing longitudinal cracks in PFC is problematic because the crack sealer could impede the transverse flow of water within the layer. One potential solution is to mill off the PFC in a narrow strip over the longitudinal crack and place an inlay with PFC material. If the longitudinal crack is also present in the underlying course, it must be sealed properly. Only a light tack coat should be applied to the vertical faces of the existing pavement. The other option is to rehabilitate the layer if the severity of the crack becomes too high. 6.2 Wi nter Maintenance 6.2.1 The literature and experience suggest several constants that are related to the winter maintenance of PFCs, including: a) PFC layers behave differently than dense-graded layers during winter events; b) PFC layers have a pavement temperature cooler than typical dense-graded layers at ambient temperatures just above and below freezing; c) PFC layers reach freezing temperature prior to dense-graded layers and stay at freezing temperatures longer than dense- graded layers; and d) PFC layers required more winter maintenance chemicals than typical dense-graded layers during winter events. Beyond these constants, the literature and experience suggest that each agency appears to have different winter maintenance strategies. Experience suggests that each agency should utilize special, locally adjusted strategies for winter maintenance. ________________________________________________________________________ 7. REHABILITATION OF PERMEABLE FRICTION COURSE 7.1 Rehabilitation of PFC layers can be categorized as minor or major rehabilitation activities. Minor rehabilitation involves correcting small, localized areas. Minor rehabilitation activities are identical to the corrective surface maintenance activities described in Section 6.1.3.1. Major G-29

rehabilitation is conducted when the entire layer is in need of replacement or refurbishment. 7.1.1 The most common method of rehabilitating PFC layers is to mill the entire old PFC layer and replace with another PFC layer or other type hot-mix asphalt layer. Some agencies have milled a PFC layer and placed a PFC inlay; however, this would only occur if the shoulders are also a PFC. One agency has expressed concerns about placing PFC on milled surfaces. The concern is that the grooves left by the milling operation may hold water due to the permeable nature of a PFC. This agency is investigating micro-milling as an alternative to milling. 7.1.2 PFC layers should not be overlaid with dense-grade hot-mix asphalt. 7.1.3 There is some evidence in Europe that hot in-place recycling can be utilized to rehabilitate a PFC layer. G-30