Performance-Based Mix Design for Porous Friction Courses (2018) / Chapter Skim
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From page 5... ...
5 Introduction The use of PFC mixes in the United States severely declined in the 1980s due to design and performance issues and was completely eliminated in some states. While conducting a literature review on PFC mixes, many of the reports and articles encountered were dated prior to this cessation.
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6 Performance-Based Mix Design of Porous Friction Courses reduced the number of fatalities during rainy weather in that country when results were compared to standard dense-graded mix (Figure 3)
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Literature Review 7 reduces the effect of backsplash and spray significantly when compared to dense-graded mixes. A comparison of PFC to dense-graded mix in regards to backsplash and spray shows a dramatic difference (Figure 5)
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8 Performance-Based Mix Design of Porous Friction Courses A typical reduction of 5 decibels dB(A) is expected from a noise wall.
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Literature Review 9 maintain stone-on-stone contact and create a stone skeleton of the coarse particles. Aggregate mineralogy is not specified in national specifications because of limitations and availability of local aggregates.
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10 Performance-Based Mix Design of Porous Friction Courses recommended gradation range as described in ASTM D7064. The agencies surveyed by NCAT that currently use PFC mixes provided their gradation specification ranges for PFC mix designs.
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Literature Review 11 requirement. ASTM D7064 specifies a minimum accepted air void level of 18.0%.
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12 Performance-Based Mix Design of Porous Friction Courses According to ASTM D7064, the mix must also have a draindown percentage less than 0.3%, a tensile strength ratio (TSR) of 0.80 or greater, and a VCAMIX ≤ VCADRC.
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Literature Review 13 most common way to define durability and polish resistance is with the sulfate soundness test and the polish stone value (PSV)
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14 Performance-Based Mix Design of Porous Friction Courses If crushed gravel is used in the design, ASTM requires that 95% of the particles have two or more fractured faces. The criterion for two or more fractured faces ranges from 75% in Spain (Ruiz et al., 1990)
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Literature Review 15 Stabilizing Agents Stabilizing agents come in several forms, the most common of which are fibers. Fibers provide stability to the mix while also preventing draindown of the binder.
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16 Performance-Based Mix Design of Porous Friction Courses Filler/Anti-stripping Agents Hydrated lime is used as a filler material by many agencies. The Netherlands uses a limestone filler but requires that at least 25% of it must be hydrated lime.
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Literature Review 17 the only 12.5 mm (1/2 inch) designs were from Louisiana and Great Britain.
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18 Performance-Based Mix Design of Porous Friction Courses Optimum Binder Content Selection Trial asphalt contents, normally in 0.5% increments, are fabricated and then the properties of the mix are considered; however, there is no specific procedure that requires particular properties of the mixture to be considered. While the ASTM standard suggests a minimum of 18.0% air voids and a draindown of less than 0.3%, it makes all other properties optional.
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Literature Review 19 indicated that 50 gyrations in the SGC provided approximately the same amount of compaction as a 50-blow Marshall design (European PFC design)
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20 Performance-Based Mix Design of Porous Friction Courses that as the asphalt content increases, the durability of the mixture improves; but the risk of draindown is increased. Draindown in the U.S.
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Literature Review 21 Construction and Maintenance of PFC Mixes The main construction-related issues with PFC mixes are raveling and delamination. The following factors are the main influences that lead to issues with PFC pavements during production and construction: • Homogenous mix gradation and temperature; • Asphalt content; • Tack bond strength, rate, and quality of application; • Layer thickness; and • Mixing temperature during placement.
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22 Performance-Based Mix Design of Porous Friction Courses While raveling can be linked to the interface bond, it is also a durability issue that begins at the top of the pavement. Mix temperature is one of the biggest concerns when constructing PFC mixtures.
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Literature Review 23 Performance Testing Moisture Susceptibility The most recognized and widely used performance test for PFC mixes is a moisture susceptibility test. There are three different methods for determining moisture susceptibility of PFC mixes.
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24 Performance-Based Mix Design of Porous Friction Courses prior to testing. In the 2009 survey, Great Britain was the only agency that provided their aging protocol, which stated that the specimens were submerged for 24 hours at 140°F in a water bath prior to testing (Cooley et al., 2009)
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Literature Review 25 system that has a coarse-graded PFC on the lower lift and a finer-graded PFC on the surface. A fixed binder content of 4.5 to 5.5 is also utilized.
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26 Performance-Based Mix Design of Porous Friction Courses skeleton needed to maintain the structural integrity of the pavement. California's design guide for OGFC also maintains that inadequate compaction can cause short-term raveling (Caltrans, 2006)
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Literature Review 27 Top-Down Cracking Cracking of PFC mixes is not as common as raveling, but it does occur. There is much debate about the type of cracking that is predominant in PFC mixes.
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28 Performance-Based Mix Design of Porous Friction Courses the agencies surveyed indicated that field permeability testing was being conducted to track the performance of the PFC mixtures. Testing performed at the NCAT Pavement Test Track showed a decrease in permeability with traffic loading (Figure 21)
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Literature Review 29 Figure 22. NCAT truck-mounted field permeameter.
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30 Performance-Based Mix Design of Porous Friction Courses Loss of Noise Reduction over Time One of the primary reasons for the loss of noise reduction is clogging of the pores with dust, sand, silt, and other types of debris. As noted in the previous section, there are methods for preventing and correcting clogging of the PFC, to a point.
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Literature Review 31 South Africa Illustration Dutch Highway – The Netherlands 2.5 cm 4.5 cm Figure 25. Examples of porous Twinlay pavements (Masondo, 2001)
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32 Performance-Based Mix Design of Porous Friction Courses One of the northern states, Maine, reported that vacuum sweeping is conducted periodically in the winter months to keep the surface pores from clogging. In addition to the increased need for pavement maintenance in winter months, there are other financial costs associated with winter maintenance of PFC pavements.
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Literature Review 33 PFC thickness from 0.5 to 1.25 in. A typical PFC thickness in the U.S.
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34 Performance-Based Mix Design of Porous Friction Courses The NCAT Test Track demonstrated differences in performance of PFC mixes placed at different lift thicknesses (Watson, 2014)
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