Mix Design Practices for Warm-Mix Asphalt (2011) / Chapter Skim
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From page 8... ...
. Several modifications to current HMA mix design procedures are needed to address the wide range of WMA processes currently available and likely to become available in the future.
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From page 9... ...
Design Binder Content Selection Volumetric Analysis and Criteria • None Specim en Preparation • See considerations above for laboratory batching, mi xing, conditioning, and co mp action. Evaluate Moisture Sensitivity Testing and Analysis • None Specim en Preparation • See considerations above for laboratory batching, mi xing, conditioning, and co mp action.
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From page 10... ...
The revised preliminary procedure was further modified based on the findings of the Phase II laboratory mix design study, field validation study, and fatigue study to produce the draft standards that were the primary products of NCHRP Project 09-43. The preliminary WMA mixture design and analysis procedure was based on AASHTO R 35, Standard Practice for Superpave Volumetric Design for Hot Mix Asphalt (HMA)
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From page 11... ...
The preliminary procedure for WMA mixture design and analysis also included a mandatory evaluation of the design 11 Key Element Included in Preliminary Procedure WMA Process Selection Key considerations for WMA process selection. Binder Grade Selection Concept of high-temperature grade bumping based on WMA production temperature.
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. 2.3.7 Optional Mixture Analysis Tests The preliminary mixture design and analysis procedure for WMA included optional performance tests to evaluate the dynamic modulus, resistance to fatigue cracking, and resistance to thermal cracking.
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This reduced aging may result in increased rutting of pavements produced using WMA processes and it may also result in improved resistance to fatigue and low-temperature cracking. NCHRP Project 09-43 included analysis of an experiment conducted by the FHWA where the effects of WMA production temperatures were simulated using the RTFOT (AASHTO T 240)
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From page 14... ...
2.4.5 RAP Study The primary concern when using RAP in WMA is whether the RAP and new binders mix at the lower temperatures used in WMA. In the preliminary mixture design procedure, it was hypothesized that the allowable RAP content of WMA mixtures would decrease as the production temperature decreased.
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From page 15... ...
2.4.6 Workability Study Phase I also included a screening study to select an appropriate workability device for use in WMA mixture design. To accommodate the wide range of WMA processes currently available and expected in the future, the preliminary procedure proposed evaluating coating, workability, and compactability directly during the evaluation of trial blends and during the optimum binder content selection.
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Modified Nynäs Workability Device Force to push a blade into a loose mix sample. Temperature control at WMA placement and compaction temperatures.
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a laboratory mixture design study, (2) a field validation study, and (3)
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From page 18... ...
For the WMA processes, two mixing and compaction temperatures were used: one above the preliminary grade bumping temperature from the Phase I binder grade study and one below. The HMA mixtures and the WMA mixtures above the grade bumping temperature were made with PG 64-22 binder.
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From page 19... ...
The HMA mixtures required design in accordance with AASHTO R 35, flow number testing, and assessment of compactability at the lower temperature as proposed in the WMA mixture design procedure. Table 14 presents the six mixtures that were included in the mix design study.
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From page 20... ...
The parts of the revised preliminary procedure addressed by the validation included the following: • Binder grade selection • RAP • Short-term oven conditioning • Specimen fabrication and compactability • Moisture sensitivity • Rutting resistance Table 16 summarizes the mixtures that were included in the validation study. Materials from a total of 16 mixtures from six projects were sampled.
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From page 21... ...
Short-Term Conditioning Short-Term Conditioning Study Compare maximum specific gravity and tensile strength of plant mixtures with laboratory mixtures. Process-Specific SpecimenFabrication Procedures Literature Review and Research in Progress Volumetric properties of WMA mixtures.
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From page 22... ...
The HMA mixture was prepared at the recommended viscosity-based mixing and compaction temperatures. The WMA mixtures were prepared at the midpoint of the temperatures used in the mix design experiment.
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