Annotated Literature Review for NCHRP Report 640 (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.

219 asphalt layer and by starting earlier in the life that the drainage characteristics could be maintained longer. The authors noted that porous asphalts require more salt per unit area for winter maintenance than does dense-graded HMA surfaces. Brines are generally ineffective because they have a tendency to drain into the porous asphalt layer. Pucher et al state that there is a tendency toward the use of electronic warning systems to assist in selecting the appropriate time for winter maintenance in France and the Netherlands. The authors state that there is a need for a deicing agent that will stay on the surface of porous pavements and not drain into the void structure. They indicated that Calcium Magnesium Acetate (CMA) mixed with another material [this material was not given] should stay at the pavement surface. 1.55.6 Rehabilitation Practices The authors state that as of 1997, very little, if any, recycling of porous asphalt had occurred. However, Pucher et al indicate that both cold-mix and hot-mix recycling are options for porous asphalt pavements. Cold-mix recycling would be a process where the reclaimed porous asphalt would be combined with new asphalt and/or recycling agents to produce cold base mixtures. In contrast, hot-mix recycling would be the process of taking reclaimed porous asphalt and combining with new materials through a hot mix production facility. According to a European point of view, hot-mix recycling would be the highest level of value. Due to expected large amounts of porous asphalt planned by the Dutch, they are placing an emphasis on recycling porous asphalt, both in-plant and in- place. 1.55.7 Performance The authors indicated that the most common distress in porous asphalt pavements is raveling. This problem generally occurs very quickly once the flow of traffic begins and usually originates from placing the porous asphalt at too low of a temperature, incomplete compaction or from segregation of the binder (draindown). Two studies were cited by the authors on service life. One indicted that after 5 to 10 years, porous asphalt slowly degrades. As time increases past this point, the speed of distress development (mostly raveling) also increases. Experience in the Netherlands indicates that the approximate service life of porous asphalt pavements is 10 years while for dense-graded asphalt the service life is 12 years. 1.55.8 Structural Design No specifics on inclusion within structural design were given. 1.55.9 Limitations No specific limitations were given. 1.56 Punith, V. S., S. N. Suresha, A. Veeraragavan, S. Raju and S. Bose. “Characterization of Polymer and Fiber-Modified Porous Asphalt Mixtures.” TRB 2004 Annual Meeting CD-ROM. Transportation Research Board. National Research Council. Washington, D.C. 2004.

220 1.56.1 General Punith et al present the results of a study carried out to evaluate the laboratory performance of different porous mixtures. Performance related to abrasion, moisture- induced damage, fatigue, plastic deformation and the coefficient of friction were evaluated. Punith et al indicate that polymer-modification of the binder enhanced the properties of the porous asphalt mixtures. 1.56.2 Benefits of Permeable Asphalt Mixtures Punith et al describe the different benefits of porous mixtures (also referred in the text as friction or popcorn mixes). These include improvement of surface frictional resistance, minimization of hydroplaning, reduction of splash and spray, improvement of night visibility and lowering pavement noise levels. Punith et al indicate that an additional benefit of using fibers in porous mixtures is increased asphalt binder content and, hence, increased film thicknesses and durability. They also mention that the use of modified binder allows a thicker binder film thickness on the aggregate particles and, hence, reduces oxidation and raveling of aggregate. particles 1.56.3 Materials and Design The different properties of the materials are provided in Table 107. A granite aggregate and three types of asphalt binder – one unmodified and the other two modified (crumb rubber and reclaimed polyethylene) were used in the study. Cellulose fibers were used with the unmodified asphalt binder. Punith et al mention that crumb rubber (CR) is an elastomeric polymer obtained from waste tires, which is added in crumb form to base asphalt under agitation. They also indicate that because of the presence of elastomer and reduced stiffness at low temperatures, the modification of a binder with CR may thus result in a substantial improved fatigue life by reducing fatigue cracking. Punith et al indicate that the Reclaimed Polyethylene was obtained from low-Density Polyethylene (LDPE) carry bags collected from domestic waste, and these bags were shredded into approximately 3mm by 3 mm size. They mention that LDPE is plastomeric polymer which is added to base asphalt with a high-speed stirrer rotating at a speed of 3500 rpm for period of 25 minutes. The authors mention that at high service temperatures, the presence of plastomer improves the stiffness of the mixtures and improved resistance to rutting.

221 Table 107: Properties of Materials and Information on Mix Design Materials/Type Properties Specific Gravity: 2.67 Water Absorption, %: 0.42 Impact Value, %: 16.1 Aggregate/Granite Gradation: Sieve Size, mm Percent Passing 19.0 100 13.2 95 9.50 45 4.75 13 2.36 10 0.075 5 Penetration (770F): 66 Softening Point: 50 Ductility (cm): +75 Specific Gravity: 1.02 Asphalt Binder/60/70 Pen/Unmodified Elastic Recovery (59oF): 5 % Penetration (770F): 64 Softening Point: 64 Ductility (cm): 61 Specific Gravity: 1.021 Asphalt Binder/Modified/12 % Crumb Rubber (CRMB) Elastic Recovery (59oF): 52 % Penetration (770F): 61 Softening Point: 62 Ductility (cm): 57 Specific Gravity: 1.019 Asphalt Binder/Modified/5 % Reclaimed Polyethylene (RPEB) Elastic Recovery (59oF): 40 % Punith et al. mention that the introduction of fibers into bituminous mixtures reinforces the binder system, thus causing an increase in the viscosity of the system. They indicate that the resulting mixture could have greater stability and possibly higher resistance to fatigue cracking, and can also prevent the draindown of the binder in porous mixtures. Cellulose fibers were used at the rate of 0.3 percent based on total mixture weight. 1.56.4 Construction Practices No information is provided on construction practices. 1.56.5 Maintenance Practices No information is provided on maintenance practices 1.56.6 Rehabilitation Practices No information is provided on rehabilitation practices

222 1.56.7 Performance Punith et al provide the results of basket drainage testing carried out on mixtures at mixing temperature of 170˚C (338˚F), 160˚C (320˚F) and 170˚C (338˚F) for CRMB, 60/70-grade binder with fiber and RPEB respectively. The use of fiber did lower the draindown significantly, especially at higher asphalt contents, whereas the use of reclaimed polyethylene only (without fiber) did not lower draindown, as compared to the 60/70 grade binder. For mix design, two types of Marshall compactive efforts were used. In the first type, mixtures at different asphalt binder contents were compacted with 25 blows per face and in the second type, mixtures were compacted with 50 blows on only one face of the specimen by Marshall hammer. Punith et al. mention that the optimum binder content was defined as the binder content that produces the lowest voids in mineral aggregate (VMA). Mix design results are shown in Table 108. Table 108: Results of Mix Design Properties Compactive Effort Mix Asphalt Binder Content, % Theoretical Maximum Density Air voids, % VMA, % VCA, % VFA, % CR Modified 5.2 2.487 18.9 28.3 34.5 34.3 60/70 + Fiber 5.3 2.474 19.1 28.8 34.4 33.6 25 Blow RP Modified 5.0 2.491 18.5 27.9 34.0 33.5 CR Modified 5.2 2.487 18.8 27.9 33.9 35.1 60/70 + Fiber 5.3 2.474 18.7 26. 32.5 38.0 50 Blow RP Modified 5.0 2.491 17.9 27.5 33.4 34.6 Punith et al indicate that the resistance to compacted porous asphalt mixtures to abrasion loss was analyzed by means of the Cantabro test. They mention that this is an abrasion and impact test carried out in the Los Angeles Abrasion Machine (ASTM C131). In this test, the initial mass of compacted sample is recorded as P1. The specimen is then placed in the Los Angeles Rattler without the charge of steel spheres. The operating temperature is usually 250˚C (770˚F). The machine is operated for 300 revolutions at a speed of 30 to 33 rpm. The test specimen is then removed and it’s mass determined to the nearest 0.1 gram P2. The percentage abrasion loss (P) is calculated according to: P = 100 (P1 – P2)/ P1; the recommended maximum permitted abrasion loss value for freshly compacted specimens is 25 percent. Punith et al’s results show that the abrasion loss was the lowest for the RPEB modified mixes, and the highest for the 60/70 Pen mix, with the CRMB mix falling in between.

223 Also, in general, the abrasion loss decreased with an increase in asphalt content and decrease in air voids. A falling-head laboratory permeability test was used to evaluate the permeability of the different mixes. Punith et al indicates that there was a reduction in permeability with an increase in asphalt binder content. It should be noted that an increase in asphalt binder content also caused a lowering of voids, and that the 25 blows mixes showed higher permeability compared to the 50 blows mixes. Considering all the results, the permeability dropped from a value between 500 and 550 liters per day to approximately 400 to 425 liters per day, for an increase in asphalt content of 4.5 to 6.0 percent. Punith et al mention that the stiffness of porous asphalt is less than those of conventional, dense-graded wearing courses, and that these mixtures therefore have less ability to distribute traffic stresses than dense-graded mixtures. They mention that the stiffness of the porous asphalt mixtures are generally about half to two-thirds of dense-graded mixtures depending on the amount of voids within the mixture (the higher the void content, the lower the stiffness of the mixture). Punith et al present the results of different tests conducted in indirect tensile mode – resilient modulus, indirect tensile strength, and calculated tensile strength ratios and fatigue lives for the different mixes. They indicate that the use of binder modified by addition of CRMB and RPEB improve the fatigue resistance of mixtures significantly when compared to mixtures with cellulose fibers for both compactive efforts. Punith et al also show that the tensile strength ratio values of the porous asphalt mixtures with modified binders were significantly higher when compared with asphalt mixtures with fibers. Punith e al indicate that rutting characteristics were studied using Hamburg Wheel Tracking Device (HWTD) at 45˚C (113˚F), using samples compacted with 5.2, 5.3 and 5.0 percent asphalt binder (by mass of aggregates) for the three different asphalt binders (60/70-grade binder with fiber, CRMB and RPEB). They describe the HWTD as a wheel- tracking device consisting of a loaded wheel and a confined mold in which the 300 mm x 150 x 50 mm specimen for porous asphalt mixtures is rigidly restrained on its four sides. A motor and a reciprocating device give the wheel a to and fro motion of 24 passes a minute with a distance of travel of 300 mm. The solid rubber tired steel wheel bears a total load of 31 kg and indents a straight track in the specimen. The depth of the deformation was recorded at the midpoint of its length by means of a rut depth-measuring device. The contact area between the wheel and specimen is about 5.457 sq cm giving a mean normal pressure 566 kPa. Punith et al observed that the resistance to plastic deformation was enhanced (compared to mixes with unmodified binder with fiber) with the use of RPEB and CRMB binders. The authors mention that the use of polymeric bitumen (CRMB or RPEB) can diminish the effect of post compaction by traffic, which is sometimes observed in porous asphalt mixtures.