1、Standard Practice for Design Considerations When Using Reclaimed Asphalt Shingles (RAS) in Asphalt Mixtures AASHTO Designation: PP 78-171 Technical Section: 2d, Proportioning of AsphaltAggregate Mixtures Release: Group 3 (August 2017) American Association of State Highway and Transportation Official
2、s 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2d PP 78-1 AASHTO Standard Practice for Design Considerations When Using Reclaimed Asphalt Shingles (RAS) in Asphalt Mixtures AASHTO Designation: PP 78-171Technical Section: 2d, Proportioning of AsphaltAggregate Mixtures Release: G
3、roup 3 (August 2017) 1. SCOPE 1.1. This recommended practice provides guidance for designing asphalt mixtures that incorporate reclaimed asphalt shingles (RAS) from manufactured waste or tear-off sources. Specific guidance includes design considerations, how to determine the shingle aggregate gradat
4、ion, and how to determine binder quantity requirements for effective asphalt and binder quality requirements for binder embrittlement. Note 1Refer to MP 23 for baseline information (source requirements, shingle gradation, and deleterious requirements) to consider when using RAS in asphalt mixtures.
5、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 28, Standard Practice for Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV) R 30, Mi
6、xture Conditioning of Hot Mix Asphalt (HMA) R 35, Superpave Volumetric 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 Maximu
7、m Specific Gravity (Gmm) and Density of Hot Mix Asphalt (HMA) T 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 2.2. ASTM Standard: D7643, Standard Practice for Determining
8、 the Continuous Grading Temperatures and Continuous Grades for PG Graded Asphalt Binders 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d PP 78-2 AASHTO 3. INTRODUCTION 3.1. RAS has been used as a
9、component in asphalt mixtures for more than 20 years, but it remains as a relatively 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
10、. Four separate areas are addressed by this recommended practice, with each elaborating 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 Binder Quantity Re
11、quirements for Effective Asphalt Determining Binder Quality Requirements for Binder Embrittlement 4. DESIGN CONSIDERATIONS WHEN USING RAS IN ASPHALT MIXTURES 4.1. The introduction of aggregate from RAS can have an effect on the gradation properties of the asphalt mixture. The designer must determine
12、 the particle size and percentage of shingle aggregate present and adjust the new aggregate composition accordingly. 4.2. The introduction of RAS may affect the asphalt binder content requirements of a mixture. The designer must determine the new asphalt binder content of the asphalt mixture as part
13、 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 by weight of aggregate, the non-asphalt components (aggregates and fibers) can have a significant effect on the mixture. Voids in the mineral aggregate (VMA)
14、 will generally increase due to the hard angular properties of the RAS granules as well as the presence of 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
15、the shingles include fine aggregate angularity and dust to binder ratio. Note 2The properties of RAS binder are much stiffer than paving asphalt binder. As a result, agencies typically limit the use of RAS to a maximum of 5 percent by weight of aggregate. 5. DETERMINING THE RAS AGGREGATE GRADATION A
16、ND SPECIFIC GRAVITY 5.1. Collect a representative sample of RAS and proceed in accordance with T 164 or T 319 to extract the RAS asphalt binder or T 308 to ignite and remove the RAS asphalt binder and recover the RAS aggregate. The size of the sample should be such that the amount of RAS aggregate m
17、aterial 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 recommends a sample size of 1200 g, ho
18、wever, 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 RAS aggregate specific gravity by determining the theoretical maximum specific gravity (Gmm) of
19、the RAS according to T 209 and calculating the effective specific gravity (Gse) of the aggregate according to Equation 1. 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d PP 78-3 AASHTO 1001001.03=
20、brsebrmmPGPG(1) where: Gse= effective specific gravity of the RAS aggregate; Gmm= theoretical maximum specific gravity of the RAS; and Pbr= percentage of RAS asphalt binder in the RAS by mass, percent. Note 4A fine spray of alcohol may help reduce surface tension to allow fine particles to sink when
21、 testing according to T 209. Alternatively, 77C (170F) water can be used during the maximum specific gravity test procedure; however, it must be cooled to 25C (77F) prior to applying the vacuum to the sample. Research has shown that adding 77C (170F) water to the T 209 sample aids in “wetting” the R
22、AS, thus allowing it to sink and making the use of the alcohol spray more effective. Note 5The use of Gsein place of the bulk specific gravity (Gsb) of the aggregate, is generally not desired due to the error this practice can contribute in the calculation of some asphalt mixture volumetric properti
23、es; however, the absorption of most RAS aggregate is so low that little difference exists between the bulk and effective specific gravities. Therefore, the Gseof the RAS aggregate may be substituted for the Gsbin subsequent calculations until more accurate procedures to determine Gsbare developed. 6
24、. BINDER QUANTITY REQUIREMENTS FOR EFFECTIVE ASPHALT 6.1. In order to account for the RAS asphalt binder that does not become available and effective during the asphalt mixture mixing process, it is necessary to increase the amount of asphalt binder in the mixture. The minimum VMA requirement as ide
25、ntified in M 323 should be increased by 0.1 percent for every 1 percent RAS by weight of total aggregate. For example, using 5 percent RAS would result in a required increase in the minimum VMA of 0.5 percent, which would result in an increase of approximately 0.2 percent asphalt binder in the aspha
26、lt mixture. Note 6For agencies that have already adjusted their minimum effective binder contents, either by increasing the minimum VMA requirement or by designing the mixture at a lower air void content, caution should be exercised so as to not over-asphalt the mixture. However, it should be noted
27、that the fibers and angular aggregate in the RAS may help to increase the VMA in the mixture; consequently, this change should have minimal impact on mix designs. 7. BINDER QUALITY REQUIREMENTS FOR BINDER EMBRITTLEMENT 7.1. Impact of RAS Binder on Cracking PropertiesThere has been significant contro
28、versy about the impact of RAS binder on the cracking properties of an asphalt mixture. One approach has been to designate the percentage of the total RAS binder that should be considered available (often referred to as “effective binder”). Whether designated effective or not, the RAS binder is still
29、 present and has an effect on the asphalt binder in the mixture. 7.2. Evaluating Embrittlement Using the Critical Low-Temperature DifferenceInstead of designating the percentage of the total RAS binder that is effective, an alternate approach is to evaluate the embrittlement of the blended binder. 7
30、.2.1. For stiffness (S): ( ) ( )( ) ( )( )11 1212log 300 log10log logcST T TTSS=+ (2) 2017 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 7.2.2. For relaxation (m-value): ( )11 12120.30
31、010cmT T TTmm=+ (3) 7.2.3. From these two values, the critical low-temperature difference (Tc) can be determined as follows: Tc= Stiffness (S) critical temperaturethe Relaxation (m-value) critical temperature 7.2.4. Separate research conducted by Anderson et al. (2011) and Bennert (2015) have indica
32、ted that when Tcis less than or equal to 5.0C, a significant loss of cracking resistance occurs. Additional research has indicated that when determining Tc, material should be used that has been PAV-aged per R 28, with the exception that the aging time is increased to 40 h. Note 7The Tccriteria of 5
33、.0C can be adjusted based on local experience. Note 8In many locations the specified low temperature of the binder grade is below the recommended grade from LTPPBind. (For example, the southeast uses 22C while LTPPBind indicates only 16C or 10C is needed.) This could lead to cases where the Tcof 5.0
34、C may be restrictive. This is because the actual pavement temperature would likely be above the critical low binder temperature during service. Performance data should be collected to evaluate if a lower value of Tccould be used in these cases. 7.3. Testing: 7.3.1. Testing to determine Tcshould be d
35、one on the blended binder, which is the most conservative condition. Disagreements about the amount of blending that occurs between new and reclaimed binder would become moot, since the maximum impact of the aged binder will occur when complete blending occurs. If blending is less than complete, the
36、 impact of the aged binder on stiffening and relaxation is less than what the laboratory would predict. 7.3.2. The critical temperature difference provides a method to evaluate the effect of the RAS binder on the cracking behavior of asphalt mixtures. It provides an alternate way to control the amou
37、nt of RAS asphalt binder entering a mix design rather than trying to determine which portion of the RAS binder is effective. The critical temperature difference quantifies the embrittlement of adding RAS to the mixture. If the final blend is to include both RAP and RAS, both should be considered in
38、the blend for evaluation. 7.3.3. In addition to the Tccriteria, the performance grade of the binder must be determined and meet the appropriate criteria. Note 9A mixture performance test for cracking implemented by an agency is acceptable in lieu of the binder testing for Tc. 7.4. MethodologyThere a
39、re two allowable methods which use Tcin determining the allowable amount of RAS material that can be used in an asphalt mixture: One option is for the agency to develop an appropriate statewide or regional RAS Binder Ratio (RASBR) tier, and the other option is to identify the allowable RAS usage on
40、a mix-by-mix basis. Both options use recovered binder that is PAV-aged for 40 h. Each of these options is outlined below. Note 10An alternative to the binder aging in the PAV is to age the mixture prior to recovering the binder. This approach is described in Appendix X1. 7.5. Procedure for Determini
41、ng a Statewide or Regional Tier Using Binder BlendingIn order to set a statewide or regional tier for allowable RAS contents, multiple blends of RAP binder, if used, and base asphalt binder are blended together with varying levels of RAS binder. The blended binder is then PAV-aged for 40 h. The cont
42、inuous grade of the blended binder and Tcare then determined 2017 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 for each level. Based on this data, the appropriate RASBR is selected th
43、rough interpolating the results such that the minimum Tcis greater than or equal to 5.0C. 7.5.1. A more detailed description to set the allowable RASBR tier is as follows: 7.5.1.1. Obtain components for an asphalt mixture that are typical for the geographic region in question. These components would
44、 include RAS, RAP (if used) and base asphalt binder. Obtain RAS that is representative of the source (manufactured waste versus tear-off). The base asphalt binder can be either the agencys standard binder grade or a softer binder if it was anticipated that a softer binder would be used. For example,
45、 if an agencys standard binder grade were PG 64-22, that material would be used to set the maximum RASBR tier. Or, if it was expected that a softer binder would be used during production to blend with the RAS, such as PG 58-28, then that material would be used rather than the PG 64-22; Note 11Typica
46、l components would be defined as material that is genera lly consistent throughout a particular region. For example, due to the statewide consistency of their climatic and geographic conditions, Florida may have only one geographic region, which would be statewide. Conversely, due to their varying c
47、limatic and geographic conditions, Colorado may have multiple regions. 7.5.1.2. Extract and recover an adequate amount of binder from the RAP and RAS material in order to perform the following testing and analysis; 7.5.1.3. Prepare a blend of three samples with the following RASBRs: 0.00, 0.15, and
48、0.30. If it is anticipated that RAP will be used in addition to the RAS, each blend should include an amount of RAP binder that might be considered appropriate. PAV-age the blended binder as per R 28, with the exception that the aging time is increased to 40 h; 7.5.1.4. After aging, determine Tcof e
49、ach of these blended samples; 7.5.1.5. Based on this data, identify the appropriate RASBR tier (by interpolating the results) such that the minimum Tcis greater than or equal to 5.0C; 7.5.1.6. Fabricate an additional blend at the RASBR tier where the Tccriteria are met. Determine the continuous grade of this blended binder as described in ASTM D7643 to assure that it meets the specified binder requirements. The blended binder should be graded as if it were a
