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performance. Newcomb (8) has summarized these A potential shortcoming of such a large, diverse, questions as follows: and dynamic program is the difficulty of comparing results between laboratory and field studies using Mix design: What modifications to asphalt different experiment designs, conditioning protocols, mix technology, if any, are required for design- and test methods to characterize the material proper- ing WMA? How is the selection of binder per- ties and performance of WMA. To address this short- formance grades impacted by the lower WMA coming, the "Workshop to Coordinate Key WMA production temperatures? Research Projects" was organized with the goal of fos- Long-term performance: How do the short- tering cooperation and coordination among research and long-term performance and durability of studies. Workshop participants sought to (1) identify pavements constructed with WMA compare the laboratory and field-test methods and sample with those constructed with HMA? How are preparation, curing, and conditioning procedures in these qualities affected by WMA technologies use in FHWA-, NCHRP-, state DOT-, and industry- using foaming or chemical additives? Does sponsored research projects and (2) agree on a core WMA present an increased potential for dis- set of methods and procedures that would be com- tresses such as rutting and moisture damage? monly used, insofar as possible, in all present and Cost benefits: What are the cost benefits of future WMA studies. In addition, the workshop the reduced fuel consumption and emissions participants reviewed new and existing WMA field obtained with WMA? pavements included in short- and long-term WMA Plant operations: Is WMA compatible with performance studies to facilitate sharing of their field the high production rates needed in the United materials and data, and developed selection criteria States? for future field pavements. The invited participants Control of mixing process: Given that the included researchers and practitioners from the pub- various WMA mixing processes all differ to a lic sector, academia, and industry, and representatives greater or lesser degree from that of conven- of the sponsoring organizations. tional HMA, are new guidelines needed for proper quality assurance of the mix? WORKSHOP RESULTS Workability at the paving site: Although the WMA may appear workable and easily com- The results of the workshop are presented in tables pactable when produced, does it remain work- on the following pages. These tables present a pro- able at the paving site? posed core set of criteria, methods, and protocols, Quick turnover to traffic: Can WMA pave- including ments be opened to traffic as soon as possible field project selection criteria (Table 1); after construction, in a time frame similar to or specimen preparation methods (Table 2); earlier than conventional HMA pavements? conditioning methods for laboratory-mixed, Answers to many of these questions are being laboratory-compacted (LMLC) specimens, pursued in WMA research studies informally coordi- plant-mixed, laboratory-compacted (PMLC) nated through the FHWA's WMA Technical Work- specimens, and plant-mixed, field-compacted ing Group. For example, more than 15 state DOTs (PMFC) specimens (Table 3); are currently sponsoring WMA research studies, and performance test methods for LMLC, PMLC, the 50 state DOTs are collectively sponsoring NCHRP and PMFC specimens (Table 4, Table 5, projects investigating WMA mix design, the poten- Table 6, and Table 7); and tial moisture susceptibility of WMA pavements, and binder and aggregate test methods (Table 8). whether WMA and HMA pavements provide signifi- These criteria, methods, and protocols were cantly different short- and long-term performance. arrived at through a consensus-building activity NCHRP projects planned for 2012 and later years will involving all the workshop participants. They rep- address the short-term laboratory aging of WMA for resent the participants' collective judgment of the mix design and performance testing, characterization minimum complement necessary to enable correla- of foamed asphalt for WMA applications, and the tion and comparison of results between or among use of recycled asphalt pavement (RAP) and recycled WMA research studies. Use of this core set does not asphalt shingles (RAS) in WMA. (Text continues on p. 14.) 2

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Table 1 Field project selection for short- and long-term performance studies. Project length The minimum test section shall be 1/2 lane-mile in one travel lane located between inter- sections or interchanges. The plant temperature may be increased to produce the HMA control section. Shorter sections may be allowed if they are well planned and documented. Notes: The ideal production per test section is 8001000 tons or 1/2- to 1 day production or 1 tanker load of binder (400600 tons of non-foamed WMA); these amounts will vary depending on the nominal maximum aggregate size (NMAS) of the mix. Although 1 day's production is often possible, test projects with control sections often are difficult to find. Selection of the minimum section length also must consider the type of WMA additive and where it is introduced. Project and NCAT and the University of Minnesota (for cold-climate projects) have developed construction detailed checklists for documenting field projects (see Appendix A). documentation Notes: Key considerations are (1) a condition survey of the existing pavement, (2) the pavement cross-section, (3) evaluation of pavement structural support, and (4) WMA production and compaction temperatures. Control section The HMA control section must be identical to the WMA sections (including any RAP definition or RAS content) in all aspects but the presence of WMA, with the exception that the binder content of the control section may differ if necessary to attain identical air void contents in all sections. Minimum number Minimum two technologies, plus a control. However, this minimum number may be of WMA waived, depending on whether the project is a new pavement or an overlay on an existing technologies pavement. Other key features (1) WMA and control sections must be surface mixes in the same travel lane and with the same pavement support throughout all sections. (2) The correct mix discharge temperatures for the WMA must be verified throughout the project. (3) New projects are favored, but existing projects may be used if the necessary require- ments are met. It is sometimes feasible to work with the state DOT and contractor to add WMA sections to an HMA project through a change order. (4) Specific and systematic performance monitoring plans are required for new versus exist- ing WMA projects. Both plan types should include the provision for forensic analysis when pavements exhibit significant distress. (5) In the event that a WMA project of interest was constructed without a control section, it may be possible to pair the WMA project with an otherwise unconnected HMA project constructed with similar materials, structure, condition, traffic, and climate (e.g., see Von Quintus, Mallela, and Buncher [1]). (6) Future field projects should consider (a) roadway functional classification (average daily traffic [ADT] and trucks per day [% trucks]); (b) a variety of mix types (e.g., stone mas- tic asphalt and open-graded friction courses); and performance in intersections. (7) RAP and RAS are permitted as long as identical control mixes are available. (8) For overlay projects, the WMA and control sections must have comparable levels of existing distress. 3

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Table 2 Specimen preparation methods. WMA binders for Laboratory blending with low shear mechanical stirrer or foaming with laboratory- mix design foamed asphalt plant, per the proposed appendix to AASHTO R 35 (2). Notes: (1) Aggregate coating is the key measure of foaming. Use coating to help guide selection of temperature. (2) Mix design may not require production of foamed binder in laboratory. Rather, it may be feasible to add water and binder to a bucket mixer containing aggregate and obtain comparable results. (3) At present, there are three commercial units for producing foamed asphalt. It is not known how these units compare. Further, it is very difficult to test the properties of foamed binder in bucket during production, and the foaming is typically lost during transfer of the binder for mixing with the aggregate. In practice, however, no problems have been identified with foamed WMA. (4) Future research is needed to better define the requirements for laboratory production of foamed asphalt. WMA binder A procedure such as that of Minnesota DOT is required. In the Minnesota DOT procedure, extraction and asphalt binder extractions are performed using AASHTO T 164 Method A (Centrifuge recovery Method). Toluene is used as the extraction solvent for the first two washes with an 85:15 v/v mixture of toluene and 95% ethanol used for the third wash. ASTM D5404--Standard Practice for Recovery of Asphalt from Solution Using Rotary Evaporator--is followed for the binder recovery method with the following modifications: Bath temperature and vacuum settings for toluene distillation (60C, 100mBar). Fines are removed from the extract by high-speed centrifuging at 2000 RPM for 35 minutes after volume of asphalt extract is reduced to 500ml. Notes: (1) The FHWA memorandum Extraction and Recovery Procedures at TFHRC Asphalt Laboratories (Appendix B) provides detailed information on a preferred method of binder extraction and recovery. (2) The use of trichloroethylene (TCE) as the extraction solvent is discouraged. TCE is known to harden recovered binders beyond the in situ level. (3) Western Research Institute has developed an infrared spectroscopy method for detecting residual solvent in the recovered binder. (4) Research indicates that a higher temperature and vacuum than specified in ASTM D5404 may be required to effectively remove the toluene solvent from the recovered binder. 4

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Table 2 (Continued) LMLC specimens 1. Mix design: 150-mm diameter 115-mm high at Ndesign. for mix design 2. Moisture sensitivity: 150-mm diameter 95-mm high at 7.00.5% air voids. Note: Some researchers may also use complementary lower and higher air voids, e.g., 4.0% and 9.0%. 3. Dynamic modulus and flow number with AMPT: 100-mm diameter 150-mm high cored and sawn from 150-mm diameter 175-mm high specimens at 7.00.5% air voids (per appendix to AASHTO R 35 and 2011 change to AASHTO TP 79). 4. IDT creep and strength: 150-mm diameter 50-mm high prepared from gyratory specimen. Note: It is recommended to cut only one specimen from the center of each 115-mm high gyratory specimen. 5. Hamburg Test: 150-mm diameter 62-mm high prepared from gyratory specimen. 6. Beam Fatigue Test: 380-mm long 63-mm wide 50-mm high beams cut from rolling- wheel compacted slabs. 7. Overlay Test: 150-mm diameter 115-mm high. PMLC specimens 1. Verify mix design: 150-mm diameter 115-mm high at Ndesign. for quality 2. Moisture sensitivity and resilient modulus: 150-mm diameter 95-mm high at 7.00.5% assurance air voids. 3. Dynamic modulus, flow number, and AMPT fatigue: 100-mm diameter 150-mm high cored and sawn from 150-mm diameter 175-mm high specimens; 7.00.5% or field air voids. 4. Indirect Tensile Test (IDT) creep and strength: 150-mm diameter 50-mm high. 5. Hamburg Test: 150-mm diameter 62-mm high. PMFC specimens 1. 150-mm diameter cores: generally suitable for (a) bond strength, (b) in-place density and for quality thickness, (c) air voids analysis, (d) IDT creep compliance and strength, (e) IDT dynamic assurance and modulus, (f) Hamburg Test, (g) Overlay Test, and (h) moisture sensitivity. long-term Notes: performance (1) Some low-temperature IDT testing may be done with 4-in. diameter specimens due to testing load requirements for 150-mm diameter specimens. (2) A core barrel with a 150-mm inside diameter should be used. (3) Due to lift thickness limitations, 150-mm pavement cores are generally not suitable for (a) dynamic modulus and (b) flow number. 5

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Table 3 Required conditioning methods. LMLC SPECIMENS 2 hours at WMA construction For WMA mix design and volumetric analysis, moisture sensitivity (AASHTO compaction temperature. T 283 and T 324), and flow number (AASHTO TP 79). Notes: (1) This is the short-term conditioning recommended by NCHRP Project 9-43 as the best representation of aging at construction (see [2]). (2) This recommendation leads to decreased flow number requirements for WMA compared to HMA and possibly lower binder contents compared to an equivalent HMA mixture, and was based on data from mixtures with aggre- gate absorptions of 1.0% or less. (3) The flow number measured under these conditions may be indicative of a propensity of the mixture to early rutting. (4) For WMA mixtures containing RAP or RAS, the compaction temperature is that for the virgin binder. 2 hrs at WMA construction For WMA and HMA dynamic modulus (AASHTO TP 79), flow number compaction temperature, (AASHTO TP 79), and moisture sensitivity (AASHTO T 283 and T 324) then 16 hours at 140F Notes: (per AASHTO T 283), (1) This conditioning is intended to simulate aging after approximately 1 to 2 then 2 to 2.5 hours at years in service. compaction temperature. (2) Measurement of Gmm after conditioning provides an indication of extended binder absorption. Long-term aging (per For WMA and HMA fatigue testing (AASHTO T 321 and TX-248-F) and low- AASHTO R 30), 5 days at temperature cracking testing (AASHTO T 322). 85C (after conditioning Note: for rutting tests). This conditioning is generally done on bulk specimens, but may be done on cored and sawn specimens if desired. PMLC SPECIMENS 16 hours at 140F (per For WMA and HMA dynamic modulus (AASHTO TP 79), flow number AASHTO T 283), then 2 (AASHTO TP 79), and moisture sensitivity (AASHTO T 283 and T 324). to 2.5 hours at compaction Notes: temperature. (1) This conditioning is intended to simulate aging after approximately 1-2 years in service. (2) The flow number measured before this conditioning may be indicative of the propensity of the mixture to early rutting. 6

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Table 3 (Continued) PMLC SPECIMENS (continued) From ambient temperature, For volumetric analysis. reheat to compaction temperature for a target period of 2.5 hours. For samples not at ambient For volumetric analysis. temperature, note the temperature and reheat to compaction temperature, noting the time. Long-term aging (AASHTO For WMA and HMA fatigue testing (AASHTO T 321 and TX-248-F) and R 30), 5 days at 85C low-temperature cracking testing (AASHTO T 322). (after conditioning for Note: This conditioning is generally done on bulk specimens, but may be done on rutting tests). cored and sawn specimens if desired. Recommended minimum 5 days. time between fabrication and testing. Recommended maximum 20 to 30 days unless specimens are properly vacuum sealed and stored. Record time between fabrication times and temperatures of storage. and testing. PMFC SPECIMENS Drying as needed. Take precautions when drying PMFC specimens at elevated temperatures to avoid damaging them. 7

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Table 4 LMLC specimens: required performance testing for mix design. RUTTING Flow number AASHTO TP 79. Note: Follow the procedure in Section 8.5 of the draft appendix to AASHTO R 35 (2). Hamburg Test AASHTO T 324 performed for moisture sensitivity. Note: Prepare specimens at air voids content of 71% and conduct test at standard conditions: 50C under water. MODULUS Dynamic modulus AASHTO TP 79. Note: Provides necessary input data for pavement analysis with DARWin-ME. FATIGUE CRACKING Beam Fatigue Test ASTM D7460 in strain control. Overlay Test Strong alternative: Tex-248-F, Test Procedure for Overlay Test, January 2009. THERMAL (LOW-TEMPERATURE) CRACKING IDT creep compliance AASHTO T 322. and strength Note: Provides necessary input data for pavement analysis with DARWin-ME. DURABILITY Moisture sensitivity AASHTO T 283. Note: 1 freeze/thaw cycle. Hamburg Test AASHTO T 324. Note: Prepare specimens at air voids content of 71% and conduct test at standard conditions: 50C under water. OTHER Volumetric mix design Per the procedure in the draft appendix to AASHTO R 35 (2). Compactibility Per the procedure in section 8.3 of the draft appendix to AASHTO R 35 (2). Coating AASHTO T 195, in accordance with the guidance in section 8.2 of the draft appendix to AASHTO R 35 (2). Note: Be aware of the inherent variability of the method and potential variability in results between different types of mixers. 8

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Table 5 PMLC specimens: required performance testing for quality assurance. RUTTING Flow number AASHTO TP 79. Hamburg Test AASHTO T 324 performed for moisture sensitivity. Note: Prepare specimens at air voids content of 71% and conduct test at standard conditions: 50C under water. MODULUS Dynamic modulus AASHTO TP 79. Note: Provides necessary input data for pavement analysis with DARWin-ME. FATIGUE CRACKING Beam Fatigue Test ASTM D7460 in strain control. Overlay Test Strong alternative: Tex-248-F, Test Procedure for Overlay Test, January 2009. THERMAL (LOW-TEMPERATURE) CRACKING IDT creep compliance AASHTO T 322. and strength Note: Provides necessary input data for pavement analysis with DARWin-ME. Semi-Circular Strong alternative: Per Li and Marasteanu (4). Bending Test DURABILITY Moisture sensitivity AASHTO T 283. Note: 1 freeze/thaw cycle. Hamburg Test AASHTO T 324. Note: Prepare specimens at air voids content of 71% and conduct test at standard conditions: 50C under water. OTHER Gmm (AASHTO T 209) AASHTO T 209. Volumetric properties AASHTO R 35. Gyratory compaction AASHTO T 312. to Ndesign 9

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Table 6 PMFC specimens: required performance testing for quality assurance and long-term performance. RUTTING Hamburg Test AASHTO T 324 performed for moisture sensitivity. Note: Prepare specimens at air voids content of 71% and conduct test at standard conditions: 50C under water. MODULUS Dynamic modulus by Per the procedure in Kim, Seo, et al. (5). IDT method Spectral analysis of Strong alternative. seismic waves (SASW) FATIGUE CRACKING Overlay Test Strong alternative: Tex-248-F, Test Procedure for Overlay Test, January 2009. THERMAL (LOW-TEMPERATURE) CRACKING IDT creep compliance AASHTO T 322. and strength Note: Provides necessary input data for pavement analysis with DARWin-ME. Semi-Circular Strong alternative: Per Li and Marasteanu (4). Bending Test DURABILITY Hamburg Test AASHTO T 324 performed for moisture sensitivity. Note: Prepare specimens at air voids content of 71% and conduct test at standard conditions: 50C under water. Moisture sensitivity AASHTO T 283. Note: 1 freeze/thaw cycle. Bond strength between For forensic analysis, as necessary. Per the procedure in West, Zhang, and Moore (7). layers PAVEMENT CONDITION Visual distress survey Per the FHWA LTPP Protocol. Rut depth profile In-place thickness and Core or SASW measurements. density Smoothness (IRI) With cooperation of state DOT. FWD As needed for forensic analysis. Per the FHWA LTPP Protocol. Permeability As needed for forensic analysis. Per the method in Cooley (6). Gmb AASHTO T 166 or T 331. Gmm AASHTO T 209. Air voids analysis AASHTO T 269. Absorption (by calculation) DSR torsion bar 10

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Table 7 Summary of performance testing and specimen conditioning. Performance Testing Sample Type Modulus Rutting Fatigue Cracking Low-Temperature Cracking Durability LMLC Dynamic modulus Flow number Beam Fatigue Test IDT Lottman Test PMLC (AMPT) (AMPT) Overlay Test Semi-Circular Bending Test Hamburg Test Hamburg Test PMFC IDT Hamburg Test Overlay Test IDT Lottman Test SASW Semi-Circular Bending Test Hamburg Test Specimen Conditioning Conditioning 2 hrs @ WMA 2 hrs @ WMA compaction temperature compaction temperature 16 hrs @ 140F 16 hrs @ 140F + 2 hrs @ WMA 2 hrs @ WMA + 2 hrs @ WMA compaction temperature Sample Type Test For compaction temperature compaction temperature + 5 days @ 85C LMLC Mix design/volumetric analysis X Modulus X Rutting X X Fatigue cracking X Low-temperature cracking X Durability X X (continued on next page)

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Table 7 (Continued) Conditioning 2 hrs @ WMA compaction temperature 16 hrs @ 140F 16 hrs @ 140F + 2 hrs @ WMA 2 hrs @ WMA + 2 hrs @ WMA compaction temperature Sample Type Test For compaction temperature compaction temperature + 5 days @ 85C PMLC1 Volumetric analysis X Modulus X Rutting X Fatigue cracking X Low-temperature cracking X Durability X Sample Type Test For Conditioning PMFC Volumetric analysis Dry and test Modulus Rutting Fatigue cracking Low-temperature cracking Durability 1For samples of mix at ambient temperature, reheat at WMA compaction temperature for 2.5 hrs. For samples of mix not at ambient temperature, reheat at WMA compaction temperature and note time.

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Table 8 Binder and aggregate testing. BINDERS Continuous performance grade of extracted AASHTO R 29 without RTFO aging. WMA binder Note: Done before and after PAV aging. Use a DSR capable of handling stiff binders. Continuous performance grade of original AASHTO R 29. WMA binder, to include modifiers added Note: Use a DSR capable of handling stiff binders. at the plant Aging Index Multiple Stress Creep Recovery Test AASHTO TP 70. Linear Amplitude Sweep Test Per Hintz, Velasquez, et al. (3). Frequency sweep to develop master curve AGGREGATES Gradation AASHTO T 27. Bulk specific gravity and absorption AASHTO T 84 and T 85. Flat and elongated or AIMS method ASTM D 4791 or use state or contractor data. Sand equivalent AASHTO T 176 or use state or contractor data. Fine aggregate, uncompacted voids AASHTO T 304 or use state or contractor data. Coarse aggregate angularity AASHTO T 335 or use state or contractor data. Stockpile moisture content AASHTO T 255 or use state or contractor data. Geologic type Yes or use state or contractor data. LA Abrasion Test or Micro Deval Test AASHTO T 96 or T 327 or use state or contractor data. Soundness AASHTO T 104 or use state or contractor data. 13