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Performance-Based Mix Design for Porous Friction Courses (2018)

Chapter: Chapter 4 - Methodology

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Suggested Citation:"Chapter 4 - Methodology." National Academies of Sciences, Engineering, and Medicine. 2018. Performance-Based Mix Design for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/25173.
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Suggested Citation:"Chapter 4 - Methodology." National Academies of Sciences, Engineering, and Medicine. 2018. Performance-Based Mix Design for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/25173.
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Suggested Citation:"Chapter 4 - Methodology." National Academies of Sciences, Engineering, and Medicine. 2018. Performance-Based Mix Design for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/25173.
×
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Suggested Citation:"Chapter 4 - Methodology." National Academies of Sciences, Engineering, and Medicine. 2018. Performance-Based Mix Design for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/25173.
×
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Suggested Citation:"Chapter 4 - Methodology." National Academies of Sciences, Engineering, and Medicine. 2018. Performance-Based Mix Design for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/25173.
×
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Suggested Citation:"Chapter 4 - Methodology." National Academies of Sciences, Engineering, and Medicine. 2018. Performance-Based Mix Design for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/25173.
×
Page 45
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Suggested Citation:"Chapter 4 - Methodology." National Academies of Sciences, Engineering, and Medicine. 2018. Performance-Based Mix Design for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/25173.
×
Page 46
Page 47
Suggested Citation:"Chapter 4 - Methodology." National Academies of Sciences, Engineering, and Medicine. 2018. Performance-Based Mix Design for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/25173.
×
Page 47
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Suggested Citation:"Chapter 4 - Methodology." National Academies of Sciences, Engineering, and Medicine. 2018. Performance-Based Mix Design for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/25173.
×
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Suggested Citation:"Chapter 4 - Methodology." National Academies of Sciences, Engineering, and Medicine. 2018. Performance-Based Mix Design for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/25173.
×
Page 49

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40 Introduction In order to have a well performing design, the PFC mixture must have a high enough air void content to achieve the permeability required for water to drain through and away from the pavement surface. Along with performance tests to evaluate durability and cracking concerns, testing was conducted to determine volumetric properties and permeability of the mixtures. The methods and processes followed for this testing are discussed in the following sections. Volumetric Analysis The volumetric properties were calculated based on data collected at the NCAT laboratory. The specific gravities of the aggregates were determined according to AASHTO T 84 and T 85. The PFC specimens were fabricated on a Superpave Gyratory Compactor with a compaction effort of 50 gyrations, which is recommended in both ASTM D7064 and AASHTO PP 77. All speci- mens were fabricated in this manner, even though some performance specimens require certain specimen heights. Fabricating all the specimens to a single design gyration allowed all of the specimens to have the same level of compaction effort and consequently close to the same design air void content. The specimen air voids were determined from their bulk specific gravity (Gmb) measured according to ASTM D6752, Bulk Specific Gravity and Density of Compacted Bituminous Mixtures Using Automatic Vacuum Sealing Method (Equation 1), and the theoretical maximum specific gravity (Gmm) of the mix. Equation 1 , G W W W W W CF mb b bs w b = + − − where W = the mass of the specimen in air (g) Wb = the mass of the bag in air (g) Wbs,w = the mass of the sealed bag and the specimen in water (g) CF = bag correction factor ASTM D6752 was used because of the accuracy it provides for specimen density. The voids in mineral aggregate (VMA) and voids in coarse aggregate (VCA) were calculated for each mix to determine if these factors showed any variation between the good and poor mixes. The equations used for calculating VMA, VCADRC, and VCAMIX are shown below. 100 Equation 2VMA G P G mb s sb = − ∗ C H A P T E R 4 Methodology

Methodology 41 100 Equation 3VCA G G DRC ca w s ca w = γ − γ γ ∗ 100 Equation 4VCA G P G MIX mb ca ca = − ∗    where VMA = voids in mineral aggregate VCADRC = voids in coarse aggregate in dry-rodded condition VCAMIX = voids in coarse aggregate of the compacted mixture Gsb = combined bulk specific gravity of the total aggregate Ps = percent of aggregate in the mixture γs = unit weight of the coarse aggregate fraction in the dry-rodded condition (kg/m3) γw = unit weight of water (998 kg/m3) Gca = bulk specific gravity of the coarse aggregate Pca = percent of coarse aggregate in the mixture Gmb = bulk specific gravity of the compacted mixture Gca = bulk specific gravity of the coarse aggregate The film thickness of each design was also calculated using surface area factors to determine if film thickness should be a design consideration. A minimum film thickness of 24.0 microns was originally targeted; however, after some trials, it was determined that this was an unrealistic threshold based on specimen performance. Cantabro Testing Cantabro testing is used to determine the durability of a mix in relation to the asphalt binder content and grade. It is primarily used for evaluating PFC mixes but has more recently been used to evaluate other asphalt mixes. The test method AASHTO TP 108-14, Standard Method of Test for Determining the Abrasion Loss of Asphalt Mixture Specimens, was followed for this testing. According to ASTM D7064, an acceptable amount of loss for unaged specimens is 20%, while 30% is allowed for aged specimens. All design specimens for this testing were unaged. Design specimens are individually placed in the L.A. abrasion machine, without the steel charges and tested for 300 revolutions at a rate of 30 to 33 rpm. The loose material is then discarded and the final specimen weight is recorded. The percent loss is then calculated for each specimen accord- ing to Equation 5. 100 Equation 5= − ∗CL A B A where CL = Cantabro loss, % A = Initial weight of test specimen B = Final weight of test specimen Draindown Draindown occurs when asphalt binder drains from the aggregate particles in the PFC mixture and settles in the bottom of the silo, transfer vehicles, and construction equipment. Draindown is due to several factors, the greatest of these being the absence of a stabilizing agent to hold the

42 Performance-Based Mix Design of Porous Friction Courses thick binder film in place. Cellulose or mineral fibers are the most common stabilizing agents and are very effective in preventing draindown. The degree of stiffness of the binder and the gra- dation of the mix can also contribute to draindown. Typically, mixing temperatures at the plant are 35°F–50°F greater than the recommended compaction temperature so that the mixture will coat completely and will not lose too much heat prior to reaching the job site. A softer asphalt binder and a coarse gradation typically have a greater draindown potential. The draindown test- ing was conducted according to AASHTO T 305, Draindown Characteristics in Uncompacted Asphalt Mixtures, using a 2.36 mm mesh sieve for the draindown baskets. Samples using the PG 76-22 with SBS and the PG 76-22 with 12% GTR were tested at 320° and 347°F. The samples using PG 82-22 (HiMA) were tested at 340°F and 367°F. According to the specification, the lower test temperature should be equivalent to the production temperature and the higher test tem- perature should be 15°C (27°F) above the production temperature, to account for the anticipated fluctuation in production temperature. The samples were conditioned in the basket over a pie plate for 1 hour. The maximum recommended amount of draindown allowed is 0.3%. The drain- down is recorded as the percent of material that is on the pie plate after the 1-hour conditioning. Wet Track Abrasion Test The Wet Track Abrasion Test was originally designed for determining the wearing potential of slurry treatments under wet conditions while modeling abrasive traffic. The setup (Figure 30) was modified to test the PFC mix. The weighted rubber hose abrades the submerged speci- men and potentially causes aggregate particles to lose their cohesive bond. Slab specimens were fabricated using a kneading compactor (Figure 31) at the NCAT laboratory, and 10-inch cores were removed from the slabs for testing. The slab’s target height was fixed at 1.0 inch to emulate in-place PFC pavements. Hamburg Wheel-Tracking Test The Hamburg Wheel-Tracking Test (HWTT) determines the susceptibility of asphalt mix- tures to stripping and rutting. All specimens were fabricated and tested according to AASHTO T 324, Hamburg Wheel-Track Testing of Compacted Hot Mix Asphalt (HMA). Six specimens were fabricated for each design so that statistical analysis could be performed on all of the mixtures. The machine used can only test four specimens at a time, so the extra sets of specimens were tested separately. Figure 30. Wet track abrasion tester.

Methodology 43 The specimens were subjected to a load of 158 ± 1 lb produced by a solid steel wheel and extra weights. The specimens were submerged and conditioned in a 50°C water bath for 30 minutes prior to testing. The water bath maintained the 50°C temperature for the duration of the testing (20,000 passes). All data output of the linear variable differential transformer (LVDT) attached to each arm was recorded by a computer and analyzed to determine the stripping inflection point (SIP) and moisture susceptibility of the mix. The SIP of the mix was determined by incorporating tangents to the secondary and tertiary sections of the graph. The SIP is the number of loaded wheel passes where the tangents intersect. An example of calculating the SIP can be found in Figure 32. There is currently no nationally accepted criterion for the maximum allowable rutting depth with the Hamburg device. Many states specify their own criteria based on the performance grade of the virgin binder in the mixture. The most widely accepted criteria are from the Texas Depart- ment of Transportation (TxDOT). TxDOT specifications differentiate results based on the binder grade used, but there is no difference allowed for different asphalt modifier types within the same Figure 31. Kneading compactor for 20 ë 20 inch slabs (Tran, 2012). Figure 32. Example Hamburg SIP determination (Pavement Tools Consortium, 2011).

44 Performance-Based Mix Design of Porous Friction Courses performance grade. All of the mix designs with the exception of the Part 2 mix with PG 82-22 were produced with a PG 76-22. The TxDOT criterion for a dense-graded mix with PG 76-xx is ≤ 12.5 mm of rutting at 20,000 passes (TxDOT, 2006). TxDOT specifications for PFC mixes only has HWTT criteria for fine-graded PFC mixes (PFC-F). Texas PFC-F mixes are required to rut no more than 12.5 mm after a minimum of 10,000 wheel passes. All but the New Jersey mix tested in this study were classified as coarse- graded PFC mixes (PFC-C), so it was decided to use the same criteria as for dense-graded mixes. Analyzing Hamburg data can be onerous when comparing different mix designs, due to the wide variability in results. The most concise way to report the data is to report the passes to failure and give a pass-fail status to the mix based on binder grade. A combined graphical depiction of the rut depth data for all the mix designs is also an effective method for comparing a mixture’s performance. In addition, a rutting resistance index (RRI) as defined in Equation 6 by Wen et al. (2016) can also be determined to analyze HWTT test results when some of the mixes exceed the rut depth limit of 12.5 mm before reaching the 20,000 passes. The higher the RRI value, the higher the mix- ture rutting resistance. Based on Equation 6, a minimum rut depth of 12.5 mm at 10,000 passes and 20,000 passes is equivalent to a minimum RRI of 5,000 in. and 10,000 in., respectively. RRI N 1 RD Equation 6( )= × − where RRI = rutting resistance index (in.) N = number of passes at completion of test; and RD = rut depth at completion of test (in.) Tensile Strength Ratio The tensile strength ratio (TSR) test was conducted on each mix design and performed accord- ing to AASHTO T 283, Resistance of Compacted Bituminous Mixture to Moisture-Induced Dam- age, with slight modifications to accommodate PFC mixes. The modifications are recommended in the ASTM D7064 test procedure. The specimens were compacted to the design gyration level and height instead of the target height in the procedure of 95 mm. While this differs from the specification, the height of the specimens is included in the final calculations so this change is accounted for in the final results. The weight of the design specimens was altered slightly for these specimens to target a height of 110 to 115 mm in order to ensure that the specimens fit inside the breaking head. The specimens were saturated at 26 in Hg (660.4 mm Hg) below atmospheric pressure for 10 minutes, and then the saturated specimens were frozen in plastic concrete cylinder molds. The specimens were kept submerged under water while freezing to keep the interior voids filled with water. The rest of the test procedure was followed according to the specification. The specimens were tested for indirect tensile strength (ITS) on a Marshall Stability press at a rate of 2 in. per minute. The ITS of the mixes was determined by using the peak load recorded on the device and the specimen dimensions. The ratio of the conditioned and unconditioned ITS must be at least 80%, according to ASTM D7064. Shear Strength The cohesive strength of a PFC sample should provide an indication of the mixture resistance to raveling. For this evaluation, standard 6-in. (150-mm) diameter gyratory samples 4.5 in. (115 mm) high were prepared at the JMF optimum AC and compacted for 50 gyrations. Air

Methodology 45 void properties of the compacted specimens were determined prior to shearing in order to determine if a relationship between cohesive strength and air voids exists. A device developed to determine bond strength of tack coats at the interface of pavement layers (Figure 33) was used to measure the force needed to shear a compacted PFC sample. This apparatus was used to shear across the PFC specimens with no interface in an attempt to measure PFC mixture cohesion in the laboratory. The force needed to shear the sample provides an indication of the cohesive strength of the mixture. The device was placed in a Marshall Stability test apparatus so that both load and deformation could be measured. A vertical shear load is applied at a loading rate of 2 in./min (50.8 mm/min) and the test is conducted at 77°F (25°C). The defor- mation was then used in conjunction with the load to calculate the area to peak. The shear stress is determined by dividing the peak load by the cross-sectional area. The area to peak is the calcu- lated area under the load-displacement curve from the initial loading to the point of peak load. Permeability The permeability of the specimens was tested according to FM 5-565, Florida Method of Test for Measurement of Water Permeability of Compacted Asphalt Paving Mixtures. The falling head perme- ability apparatus for 6-in. specimens along with the large diameter (6.985cm) graduated cylinder were used for this testing to determining the coefficient of permeability (k). Minimum permeability requirements vary by agency, with Mississippi requiring as low as 30 m/day (Putnam, 2012). The majority of the states surveyed by NCAT responded that they had no permeability requirements. Research conducted by NCAT in 1999 recommended a minimum permeability of 100 meter/day (Kandhal and Mallick, 1999). While permeability testing is optional according to ASTM D7064, it also recommends a rate of 100 meter/day. If the main purpose of the PFC is to reduce noise, the recommended minimum permeability requirement is 60 meter/day (Alvarez et al., 2006). The European standard requires a permeability range of 8.6 to 346 meter/day (Ongel et al., 2007). The specimens were submerged in a container and allowed to soak a minimum of 1 hour prior to testing in order to condition the specimens. A minimum of three specimens was tested for each Figure 33. Bond strength test device.

46 Performance-Based Mix Design of Porous Friction Courses mix design. In order to provide accurate results, three consecutive runs had to be within 4.0% of each other. The formula for calculating the permeability of each specimen can be seen in Equation 7. ln Equation 7 1 2 = ∗ ∗ ∗    ∗k a L A t h h tc where k = coefficient of permeability a = area of the testing pipe L = length of the specimen A = testing area of the specimen t = testing duration h1 = initial height of water h2 = final height of water tc = temperature correction for the water Cracking As cracking was one of the primary distresses observed in PFC mixtures, the Texas OT and the Illinois Flexibility Index Test (I-FIT) were performed on each mix and the subsequent altered designs. The OT was used to determine the fatigue or reflective cracking potential of the mixes while the I-FIT is used at intermediate temperatures to determine the fracture resistance of the mix. The Texas specification, Tex-248-F, Test Procedure for Overlay Test, was used for the overlay testing, and the Illinois Test Procedure 405, Determining the Fracture Potential of Asphalt Mixtures Using the Illinois Flexibility Index Test (I-FIT), was used for the I-FIT testing. The OT test has no AASHTO or ASTM specification; however, it is widely used and requested for reflective cracking testing. The I-FIT is relatively new to the industry but is making significant advancements and has a provisional AASHTO standard, AASHTO TP 124-16, Determining the Fracture Potential of Asphalt Mixtures Using Semicircular Bend Geometry (SCB) at Intermediate Temperature. The I-FIT is also classified as a SCB test. There are currently two intermediate temperature SCB tests that are being explored as viable options for determining mixture crack- ing potential. For this study, the I-FIT method was chosen over the Louisiana Transportation Research Center (LTRC) method due to a large coefficient of variance (COV) observed when testing SCB specimens according to the LTRC method. Texas Overlay Test The OT was performed on an IPC Global Asphalt Mixture Performance Tester (AMPT) accord- ing to Tex-248-F. The notes regarding PFC mixes were followed with the exception of measuring the density of the trimmed specimens. In Note 8, the procedure recommends not measuring the density of the trimmed PFC specimens; however, based on past research, it is known that specimens of dense-graded mixes typically lose 0.5% to 1.0% air voids. It was therefore decided to check the specimens after trimming using the CoreLok method to determine the amount of air void loss in the specimens. The amount of air void loss was different for each mix design, but the average loss for the PFC mixes tested for Part 1 was 2.1%. Prior to determining the bulk specific gravity of the specimens, they were vacuum dried to be sure all moisture was removed. The cut specimens were glued to two metal plates with a gap of 4.2 mm between the plates and tested at a constant temperature of 25°C ± 0.5°C. The 4.2 mm gap is a modification to the original Tex-248-F specification. The updated specification (February 2014) changed the gap from 2.0 to 4.2 mm (Figure 34). The specimens were tested using the controlled displacement mode at a rate of 0.1 Hz. The testing is designed to terminate when the specimens reach 93% reduction of the maximum load or at 1,200 cycles. In some cases, the 93% reduction did not

Methodology 47 take place prior to the 1,200 cycles, and the test was allowed to run for 2,000 cycles to deter- mine the failure point. Some specimens still did not fail prior to 2,000 cycles, and the data were extrapolated to predict the cycles at which the specimen would have reached the 93% reduction. One test specimen was cut from each gyratory compacted specimen. The specimen was trimmed to dimensions of 150 mm long by 76 mm wide by 38 mm high. A model of the Texas Overlay Tester with a specimen glued to the plates can be seen in Figure 34. This is the original concept of the overlay tester, and it has since been modified so that the test can be conducted in the AMPT with a conversion kit provided by the manufacturer. In the AMPT, the top plate remains fixed while the bottom plate applies the load to the specimen. An LVDT attached to the back of the conversion kit measures the cyclic saw-tooth load. The test uses a constant maximum opening displacement (MOD) of 0.025 in (0.635 mm) when applying the load to the bottom plate. I-FIT The I-FIT was designed to determine the fracture resistance of asphalt mixes at intermedi- ate temperatures (77°F). The relevant parameters, including fracture energy (Gf) and flexibility index (FI), are used to predict the fracture resistance. The Gf is the energy required to create a crack in the surface of the mix (IDOT, 2016), whereas the FI provides a way to categorize and identify brittle and stiff mixtures. With increasing amounts of reclaimed asphalt (RAP) and recycled asphalt shingles (RAS) being incorporated into mixes, it is becoming necessary to develop an efficient method of determining a mixture’s resistance to cracking. The PFC mixtures tested for this research had no RAP or RAS added to the mixes with the exception of the Virginia design with traprock, which only had 5% RAP. FI was primarily meant for use in comparing and ranking mix designs with similar design parameters. It is the intention of this study to use the FI to rank the PFC mixes from the least to most brittle and see if this coincides with the mix performance in the field. The Gf is part of the calculation for determining the FI but alone can indicate the mixture’s potential for damage resistance. The relationship between the Gf of the mix and the capacity of the mix to withstand stress is proportional. Illinois Test Procedure 405 notes that this testing is only applicable to mixes with an NMAS of 19.0 mm or less. The test specimens are trimmed from design specimens at a width of 50.0 mm with a tolerance of ±1.0 mm. The specimens are then cut in half so that the final specimen is a semicircular specimen with a thickness of 50 mm. A representation of the trimmed I-FIT specimen can be seen in Figure 35. While Figure 35 shows a notch tolerance of ±0.05 mm, the updated specification now specifies a tolerance of ±0.1 mm. This is difficult to achieve due to the amount of vibration that occurs in the saw blade when trimming the specimens. A smaller blade width (1.2 mm) Figure 34. Model of Texas Overlay Tester (Zhou et al., 2007).

48 Performance-Based Mix Design of Porous Friction Courses accounts for the vibration and allows the notch width to be within specification. The speci- mens are conditioned in an environmental chamber for 2 ± 0.5 hours at 25°C ± 0.5°C prior to testing. The specimens are placed under a seating load of 0.1 kN prior to beginning the test. After the seating load is obtained, the test applies a load at rate of 50 mm/min, which is maintained until the specimen fractures and the recorded load falls below the initial seating load of 0.1 kN. The load line displacement (LLD) and corresponding load data must be recorded for the entire duration of the test in order to accurately analyze the FI of the mix. The load and LLD results are used to calculate the post-peak slope (m), strength, critical displacement (u1), Gf , and FI. The calculation of the FI begins by determining the work of fracture (Wf), which is the area under the load versus LLD curve. A depiction of the load versus LLD curve can be seen in Figure 36. The Wf is used to calculate the Gf according to Equation 8 and 9. Equation 8G W Area f f lig = Figure 35. I-FIT Test specimen illustration (IDOT, 2016). Figure 36. Example of load versus LLD curve for I-FIT Test (IDOT, 2016).

Methodology 49 Equation 9Area r a tlig ( )= − ∗ where Gf = fracture energy (Joules/m2) Wf = work of fracture (Joules) Arealig = ligament area (mm2) r = specimen radius (mm) a = notch length (mm) t = specimen thickness (mm) Laboratory Conditioning of Specimens The recommended aging procedures for the specimens were based on each test method. ASTM D7064 recommends short-term aging of laboratory compacted specimens according to AASHTO R 30, Mixture Conditioning of Hot Mix Asphalt (HMA). This procedure was followed for the Cantabro and permeability test specimens. For all other performance test specimens, with the exception of the TSR testing, loose mix was conditioned per AASHTO R 30 for 4 hours at 135°C (275°F), while being stirred every hour, and then compacted. The OT procedure states in Note 3, “Cure warm-mix asphalt (WMA) mixtures at 275°F for 4 h ± 5 min. before molding,” and requires conditioning all other laboratory mixed specimens for 2 hours at the appropriate compaction temperature. The HWTT test procedure states that the mix must be conditioned according to AASHTO R 30. The I-FIT testing recommends fabri- cating the specimens according AASHTO T 312, which then directs the user to AASHTO R 30. AASHTO R 30 has mixture conditioning methods for: 1. Volumetric mixture design. 2. Mixture mechanical property testing—short term, and 3. Mixture mechanical property testing—long term. The performance testing for the I-FIT Test is a mechanical property test, so it is assumed that option 2 or 3 should be chosen. Short-term aging simulates the effect that production and construction has on the mix, while long-term aging simulates the aging expected of the mix after 7 to10 years post-construction. A summary of the aging procedures used in this study can be found in Table 15. Table 15. Aging procedures for work plan testing. Test Method Aging Requirements Specified Performed Cantabro (Tx-245-F) HMA - 2 h ± 5 min at 150°C WMA - 4 h ± 5 min at 135°C 2 h ± 5 min at 150°C1 Permeability (FM 5-565) Not Provided 2 h ± 5 min at 150°C1 TSR (AASHTO T 283 modified) 16 h ± 1 h at 60 ± 3°C 16 h ± 1 h at 60 ± 3°C 2 h ± 10 min at Comp Temp 2 h ± 10 min at 150°C1 HWTT (AASHTO T 324) 4 h ± 5 min at 135 ± 3°C 4 h ± 5 min at 135 ± 3°C OT (Tx-248-F) HMA - 2 h ± 5 min at 150°C WMA - 4 h ± 5 min at 135°C 4 h ± 5 min at 135 ± 3°C I-FIT (Illinois TP 405) AASHTO T 312 R 30 4 h ± 5 min at 135 ± 3°C 1All mixes were compacted at 150°C with the exception of the PG 82-22 specimens (160°C).

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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 877: Performance-Based Mix Design for Porous Friction Courses presents a proposed mix design method for porous asphalt friction course (PFCs).

PFCs have been used in the United States for many years. Their open aggregate gradations and resultant high air void contents provide PFCs with the ability to quickly remove water from the surface of a roadway, thus reducing the potential for vehicles to hydroplane and improving skid resistance. Splash, spray, and glare are also reduced, improving pavement marking visibility in wet weather. PFCs can also provide additional environmental benefits by reducing the pollutant load of storm water runoff as well as traffic noise.

Despite their many benefits, the use of PFCs has been limited in part because of cost, lack of a standard mixture design method, premature failure by raveling or stripping, and loss of functionality by clogging with debris. In addition to the need to develop improved maintenance methods to address clogging, the performance of PFC mixtures will benefit from the development of a standardized mixture design method that balances durability in terms of resistance to premature failure with functionality in terms of permeability and noise reduction.

The goal of this project was to achieve the required balance in the mix design between PFC durability and functionality.

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