1、Standard Practice for Design Considerations When Using Reclaimed Asphalt Shingles (RAS) in Asphalt Mixtures AASHTO Designation: PP 78-141American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2d PP 78-1 AASHTO Standard Pr
2、actice for Design Considerations When Using Reclaimed Asphalt Shingles (RAS) in Asphalt Mixtures AASHTO Designation: PP 78-1411. SCOPE 1.1. This recommended practice provides guidance for designing asphalt mixtures that incorporates reclaimed asphalt shingles (RAS) from manufactured waste or tear-of
3、f sources. Specific guidance includes design considerations, how to determine the shingle aggregate gradation, and how to determine the performance grade (PG) of the binder. Note 1Refer to MP 23 for baseline information (source requirements, shingle gradation, and deleterious requirements) to consid
4、er when using RAS in asphalt mixtures. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 320, Performance-Graded Asphalt Binder M 323, Superpave Volumetric Mix Design MP 23, Reclaimed Asphalt Shingles for Use in Asphalt Mixtures R 30, Mixture Conditioning of Hot Mix Asphalt (HMA) R 35, Superpave Volu
5、metric Design for Asphalt Mixtures T 27, Sieve Analysis of Fine and Coarse Aggregates T 30, Mechanical Analysis of Extracted Aggregate T 164, Quantitative Extraction of Asphalt Binder from Hot Mix Asphalt (HMA) T 209, Theoretical Maximum Specific Gravity (Gmm) and Density of Hot Mix Asphalt (HMA) T
6、308, Determining the Asphalt Binder Content of Hot Mix Asphalt (HMA) by the Ignition Method T 319, Quantitative Extraction and Recovery of Asphalt Binder from Asphalt Mixtures 3. INTRODUCTION 3.1. RAS has been used as a component in asphalt mixtures for more than 20 years, but it remains as a relati
7、vely new application for many agencies as a cost effective tool in the production of asphalt mixtures. The use of RAS brings with it the need to address design considerations to ensure a well-designed mixture is achieved. Three separate areas are addressed by this recommended practice, with each ela
8、borating on and providing recommendations relative to the following: Design Considerations When Using RAS in Asphalt Mixtures Determining the Shingle Aggregate Gradation and Specific Gravity Determining Adjustment to the New Asphalt Binder Grade 2014 by the American Association of State Highway and
9、Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d PP 78-2 AASHTO 4. DESIGN CONSIDERATIONS WHEN USING RAS IN ASPHALT MIXTURES 4.1. The introduction of shingle aggregate from RAS can have an effect on the gradation properties of the asphalt mixture. The d
10、esigner must determine the particle size and percentage of shingle aggregate present and adjust the new aggregate composition accordingly. 4.2. The introduction of RAS may affect new asphalt binder content requirements. The designer must determine the new asphalt binder content of the asphalt mixtur
11、e as part of the volumetric design procedure. 4.3. Although the amount of RAS in an asphalt mixture design is generally small, typically 3 to 5 percent, the non-asphalt components (aggregates and fibers) can have a significant effect on the mixture. Voids in the mineral aggregate (VMA) will generall
12、y increase due to the hard angular properties of the RAS granules as well as the fibers. Dust content of the RAS causes a reduction in VMA that is generally less than the increase from granules and fibers, resulting in a net VMA increase. Other properties influenced by the shingles include fine aggr
13、egate angularity and dustasphalt ratio. Note 2There are a number of unanswered questions regarding the effects of asphalt shingle binder on asphalt mixtures containing RAS. The properties of the shingle asphalt binder are much stiffer than paving asphalt binder. As a result, agencies typically limit
14、 use of RAS to a maximum of 5 percent by weight of the aggregate. 5. DETERMINING THE SHINGLE AGGREGATE GRADATION AND SPECIFIC GRAVITY 5.1. Collect a representative sample of RAS and proceed in accordance with T 164 or T 319 to extract the shingle asphalt binder. The size of the sample should be such
15、 that the amount of aggregate material recovered will meet the size requirements of the gradation procedure. Note 3Generally, 400 g of RAS is sufficient to provide the 300 g of aggregate needed for T 27. For T 319 extracting 400 g of RAS will meet the minimum sample size requirements. T 308 recommen
16、ds mix samples size of 1200 g, however, the test should be run with 400 g of RAS. If the ignition oven ventilation system cannot handle the exhaust, the sample may need to be run in two parts and the results combined. 5.2. Determine the shingle aggregate specific gravity by determining the theoretic
17、al maximum specific gravity (Gmm) of the RAS according to T 209 and calculating the effective specific gravity (Gse) of the aggregate according to Equation 1. A fine spray of alcohol may help reduce surface tension to allow fine particles to sink when testing according to T 209. 1001001.03=brsebrmmP
18、GPG(1) where: Gse= effective specific gravity of the shingle aggregate; Gmm= theoretical maximum specific gravity of the RAS; and Pbr= percentage of shingle asphalt binder in the RAS by mass, percent. Note 4The use of Gsein place of bulk specific gravity, Gsb, is generally not desired due to the err
19、or this practice can contribute in the calculation of some asphalt mixture volumetric properties; however, the absorption of most shingle aggregate is so low that little difference exists between the bulk and effective specific gravities. Therefore, the Gseof the shingle aggregate may be 2014 by the
20、 American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d PP 78-3 AASHTO substituted for the Gsbin subsequent calculations until more accurate procedures to determine Gsbare developed. 6. DETERMINING ADJUSTMENT TO THE
21、ASPHALT BINDER GRADE 6.1. Perform a volumetric mix design that includes all the components of the mixture including RAS or RAS and RAP according to R 35. Determine the design asphalt binder content (Pb). Asphalt binder contributed by the RAS is determined according to Equation 2: ( )( )bsa s bsP FP
22、P= (2) where: Pbsa= available percentage of asphalt binder in the RAS, expressed as a decimal; F = RAS asphalt binder availability factor, expressed as a decimal (see Note 6); Ps= percentage of RAS in the asphalt mixture, expressed as a decimal; and Pbs= percentage of asphalt binder in the RAS expre
23、ssed as a decimal. Note 5In R 35, non-available asphalt binder from RAS will automatically be included as part of the aggregates. In the equation for VMA, the percent aggregate is calculated as 100 minus the percent of asphalt binder. Percent asphalt binder does not include non-available asphalt bin
24、der from the RAS. Note 6The RAS asphalt binder availability factor is assumed to range from 0.70 to 0.85 for this practice. Additional research is required to define the interaction of asphalt binder from RAS. 6.2. For mixtures containing RAS and/or RAP, determine the percentage of available RAS asp
25、halt binder (Pbst) plus asphalt binder from the RAP present in the mix design asphalt binder content, using Equation 3: ( )( ) ( )( )100+=s bs r brbstbFPP PPPP(3) where: Pbst= percentage of RAS and/or RAP binder in the design asphalt binder content; F = RAS asphalt binder availability factor, expres
26、sed as a decimal (see Note 6); Ps= percentage of RAS in the asphalt mixture, expressed as a decimal; Pbs= percentage of asphalt binder in the RAS, expressed as a decimal; Pr= percentage of RAP in the asphalt mixture, expressed as a decimal; Pbr= percentage of asphalt binder in the RAP, expressed as
27、a decimal; and Pb= design asphalt binder content in the asphalt mixture, expressed as a decimal. 6.3. Adjust the asphalt binder grade using Pbsa(percent available RAS binder in the design asphalt binder content) and/or Pbst(percent available RAS binder and percent RAP binder in the design asphalt bi
28、nder content). Note 7As the percentage of asphalt binder from RAS increases, the combined asphalt binder in the mixture will increase in stiffness. Generally, experience has shown asphalt binder blends containing RAS asphalt binder will stiffen twice as fast as those containing RAP. That is, 5 perce
29、nt asphalt binder from RAS will typically stiffen a new asphalt binder about the same amount as 10 percent asphalt binder from RAP. Agencies should consider this information in determining binder grade adjustments to be used. The binder grade adjustment guidelines in Table 1 have been adapted from M
30、 323 for RAS or RAS+RAP asphalt binder replacement percentages. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d PP 78-4 AASHTO Table 1Binder Grade Adjustment Guidelines for Mixtures with Reclaimed
31、Asphalt Shingles (RAS) Recommended Virgin Asphalt Binder Grade RAS or RAS+RAP Binder Percentage No change in binder selection 25 a The use of blending charts is difficult if the asphalt binder recovered from the RAS is too stiff to properly grade. 7. KEYWORDS 7.1. Asphalt mixtures; binder grade; shi
32、ngle aggregate gradation; RAS+RAP; VMA. APPENDIX (Nonmandatory Information) X1. EXAMPLES FOR EQUATION 3 X1.1. Examples of calculations of the percentage of asphalt shingle binder from Equation 3: X1.1.1. To calculate the percentage of asphalt shingle binder only in the design asphalt binder content,
33、 assuming the following values Pbstis calculated as: ( )( )( ) ( )( )0.85 0.05 0.20 0 0 0.0085100 100 15.45%0.055 0.055+= = =bstPwhere: Pbst= percentage of available RAS binder and RAP binder in the design asphalt binder; F = assumed as 0.85; Ps= 5.0 percent, or 0.05; Pbs= 20 percent, or 0.20; Pr= 0
34、.0 percent, or 0; Pbr= 0.0 percent, or 0; and Pb= 5.5 percent, or 0.055. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d PP 78-5 AASHTO X1.1.2. To calculate the percentage of available RAS asphalt
35、binder with RAP in the design asphalt binder content, assuming the following values Pbstis calculated as: ( )( ) ( )( )0.70 0.03 0.20 0.20 0.045 0.0042 0.009100 100 24%0.055 0.055+= = =bstPwhere: Pbst= the percentage of available RAS binder and RAP binder in the design asphalt binder F = assumed as
36、0.70; Ps= 3.0 percent, or 0.03; Pbs= 20 percent, or 0.20; Pr= 20.0 percent, or 0.20; Pbr= 4.5 percent, or 0.045; and Pb= 5.5 percent, or 0.055. 1This provisional standard was first published in 2014. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.
