Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures (2016) / Chapter Skim
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Pages 6-41
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7 materials or the properties of the total asphalt mixture after removing the asphalt from the particulates. Asphalt Content Either the ignition oven (AASHTO T308)
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8 Advantages associated with using the ignition oven method for determining the asphalt content are that test results can be obtained quickly for QC testing and aggregate properties can be determined after the asphalt is removed. Disadvantages include the need for correction factors to account for the mass loss of materials other than asphalt, which may be burned off during testing.
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9 Rotavapor (ASTM D5404) recovery methods.
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10 shows that Scholz' conclusion of a generally linear relationship between changes in critical upper and lower PG temperatures can be replicated with data from other researchers. The upper critical temperature changes almost twice as much as the lower critical temperature.
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11 (i.e., non-Newtonian behavior) of the blends increased with the percentage of RAS at the intermediate temperatures, but not at the upper or lower temperatures.
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12 experience. The calculated effective specific gravity is then used to calculate the bulk specific gravity of the aggregate, Gsb, using: G GG P G sb estimated se se ba b( )
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13 Other information related to asphalt availability factors found in the literature included: • Virgin asphalt content can be reduced by approximately 0.2% for every 1% by weight of RAS (manufacturer's waste) used in a mixture (Mallick and Mogawer 2000)
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14 • The Bonaquist method can be used to estimate if most or all of the recycled material asphalt contributes to the total asphalt content. At this time, this method is primarily a research tool.
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15 SAMPLE PREPARATION FOR MIX DESIGNS Laboratory procedures for material preparation, batching, preheating, mixing, and compacting asphalt mixtures for mix designs were originally developed using virgin aggregates and asphalts. Batching of materials has to consider what portions of the recycled material mass are included in the solid particulate measurements and what part of the mass is included in the determination of the total asphalt content.
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16 variations in the steps used to prepare mix design samples are shown in Table 5. Molenaar et al.
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17 MIXTURE TESTING The volumetric properties of the compacted samples are used as parameters for determining the optimum total asphalt content using the selected aggregate gradation. Performance-based testing of the compacted mixtures is used to evaluate that the likelihood the mixture, as designed, will achieve the design service life.
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18 c = 1.18-mm (No.
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19 usually conducted using at least two different stress or strain levels and the data are analyzed to determine the slope of the stress (or strain) versus the number of cycled to failure relationships (log-log relationships)
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20 to increased strains as temperatures drop. The tensile strength decreases with increases in creep compliance (i.e., inverse relationship)
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21 DSCEf = dissipated stress creep energy at failure (portion of area under stress–strain curve from indirect tensile test) ; and ER = energy ratio.
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22 U = strain energy to failure (i.e., area under deformation- stress curve up to maximum stress) , kJ; a = notch depth, m; and dU/da = change of strain energy with notch depth, kJ.
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23 Another use for this test configuration is measuring the coefficient of thermal contraction (UTSST)
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24 Results for a range of performance testing for RAS mixtures with rejuvenators were found in the literature and are summarized in Table 10. Changes in the mixture properties depend on the percentage and type of rejuvenators used in the studies.
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25 until more is known about the impact of RAS on mixture volumetrics. • Increasing percentages of RAP may: – Increase stiffness and tensile strength, and decrease rutting potential.
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26 RAS clumping in the stockpile can also be minimized by blending with an acceptable source of fine aggregate or with RAP. A ratio of RAP to RAS of either 75:25 or 80:20 can minimize clumping; however, the RAP/RAS blend must be consistent throughout the stockpile to prevent variations in the material properties of the total mixture (Carolina Asphalt Pavement Association 2011; NCAT 2012)
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27 2001; West 2010)
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28 to fractionate the RAP into coarse and fine RAP stockpiles. Because the asphalt content of finer RAP particles is generally higher than for the coarse RAP, fractionating the RAP also helps control the RAP asphalt content.
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29 • Deleterious material retained on each sieve is visually determined and the total percentage of deleterious material is calculated. AASHTO MP23 requires that RAS be certified as conforming to local requirements concerning asbestos when using tearoff shingles.
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30 amount of recycled materials that stick to the belts. When the conveyors are weigh belt scales, metering difficulties through cold feed bins can lead to nonuniform amounts of recycled material being fed into the plant (West and Willis 2014)
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31 fied to increase the percentage of recycled materials added to the mixtures. Counterflow and double drum mix plants are newer designs that accommodate a wider range and higher percentages of recycled materials (Table 15)
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32 the aggregate temperature needs to be increased from about 460°F (no moisture) to almost 700°F if the RAP contains 5% moisture (Brock and Richmond 2007)
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33 – Higher moisture contents and percentages of RAP require significantly higher temperatures, which can damage both the plant and the asphalt material properties. – Higher plant temperatures use significantly more fuel (energy)
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34 pavement performance differences when using a PG 76-22 and a PG 67-22 virgin asphalt in mixtures with 20% RAP. Four test sections were also constructed in 2006, each with a different PG virgin asphalt grade and 45% RAP.
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35 asphalt mixtures with mixtures with up to 30% RAP. Overlays were either less than 2-in.
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36 RAS Pavement Performance The performance of RAS and combinations of RAP and RAS demonstration project test sections placed in eight states was recently evaluated. Information about the general performance of RAS mixtures across the country was discussed in a 2015 FHWA memorandum.
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37 Illinois, Indiana, Iowa, Minnesota, and Wisconsin. Each demonstration project evaluated variables of importance to each state agency and the pavement condition survey results are summarized in Table 17.
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38 Pavement performance results 1 and 1.5 years after placement can be summarized as: • Wisconsin: No distresses seen in test sections (13% RAP/3% RAS)
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39 RAS pavement performance studies show: • Pavement condition surveys conducted fewer than about 1.5 years after construction typically show no or very limited distresses. • Most of the significant distresses witnessed in the limited RAS test sections reported in the literature at this time are related to PCC joints (reflective cracking)
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40 Costvirgin asphalt = Cost of virgin asphalt in mixture, $/ton; CostRAP = Cost of virgin aggregate in mixture, $/ton; Pricevirgin asphalt = Price of virgin asphalt, $/ton of asphalt; Pricevirgin aggregate = Price of virgin aggregate, $/ton of aggregate; PriceRAP = Price of RAP, $/ton of RAP; AC%mix = Total asphalt content of mix, %; AC%RAP = Asphalt content of RAP, %; RAP% = Percentage of RAP in mixture, %; and Agg% = Percentage of aggregate, %. Wet materials can increase production costs because higher temperatures are needed to dry recycled materials.
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41 impact on costs from materials to production (Brock and Richmond 2007)
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42 The objectives of NCHRP Project 9-58, Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios, are to: • Evaluate the effectiveness of recycling agents in HMA and WMA mixtures with high RAS, RAP, or combined RAS and RAP binder ratios through a coordinated program of laboratory and field experiments. • Propose revisions to several relevant AASHTO specifications and test methods.
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