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OCR for page 74
74 Location(s) the binder is used (state, region, etc.). surements. This would allow for testing at higher tempera- Supplier's recommended mixing and compaction tem- ture ranges (closer to mixing and compaction temperatures) peratures. and examination of the binder behavior at the more funda- Equiviscous mixing and compaction temperatures. mental phase angle point of 45 (the point where loss mod- SSF mixing and compaction temperatures. uli and storage moduli are equal). This analysis would provide Phase Angle mixing and compaction temperatures. more points on the phase angle master curve for analysis of Issues with the procedures and/or equipment. the frequency-temperature relationships for determining mix- Comments and observations regarding laboratory mixing ing and compaction temperatures. and compaction. Comments and observations regarding field mixing and Interlaboratory Studies compaction. Interlaboratory studies are useful for improving test meth- This information would allow users and researchers to see ods and determining repeatability and reproducibility infor- how well the methods gain acceptance and if problems occur, mation of the results. A ruggedness study should be conducted where and with what sort of binders. A single organization on new methods to identify what procedural factors have the should be responsible for initial training on the methods, es- greatest influence on the results. The recommended method tablishing the database, trouble-shooting problems, and re- for conducting a ruggedness study is ASTM C1067, Standard porting of the field validation data. This initial field validation Practice for Conducting A Ruggedness or Screening Program for effort should take about 18 months. Test Methods for Construction Materials. Steps for developing a ruggedness study include Refinement of the SSF and Phase Angle Methods 1. Identify seven procedural factors for the test method; Gerald Reinke, developer of the SSF method, has recently 2. Establish high and low levels for each factor; recommended using a higher shear stress of 1000 Pascals com- 3. Design the experiment: normally eight combinations of 14 pared with the 500 Pascals used in this study. The recom- factor levels (7 factors 2 levels) with two replicates for each mended change is evidently to try to reach a better steady state combination; viscosity for some highly modified binders. Since viscosities of 4. Identify at least three laboratories to participate in the such binders decrease at higher shear stresses (shear thinning study; and behavior), the resulting mixing and compaction tempera- 5. Determine three to five materials that cover the range of ma- tures could be expected to be slightly lower for those binders. terials properties to which the test method is applicable. The Reinke's recommended refinement of the SSF method simply selection of the procedural factors should be selected follow- adds one additional stress level to the procedure, so it would ing the independent validation work described above. be relatively easy to analyze the data using both stress levels as part of the independent validation work described earlier. For many test methods used in pavement materials analysis, Although the Phase Angle method developed in this study a second interlaboratory study is conducted to establish preci- is simple, reasonable, and innovative, criticisms of the method sion statistics. The recommended procedure for this type of are (1) that the relationships between phase angle and mixing interlaboratory study is ASTM C802, Standard Practice for and compaction temperatures are too empirical; (2) the selec- Conducting an Interlaboratory Test Program to Determine the tion of frequencies at =86 seems arbitrary; and (3) the com- Precision of Test Methods for Construction Materials. However, mon water-cooled DSRs may not be able to reach the desired given that the purpose of either the SSF method or the Phase phase angle transition region within the temperature range of Angle method would be only to prepare asphalt mixture sam- the water bath. Further research is warranted to explore sev- ples and they would not be used in determining whether a ma- eral possible refinements of the concept. One idea suggested terial met a criteria for the purpose of payment, the repeatabil- by the AI is to simply perform the frequency sweep testing at ity and reproducibility statistics are not critical. Alternatively, only 80C and find the frequency corresponding to the phase a more economical way to obtain useful precision information angle at 86. This could substantially reduce the testing and for either of these procedures would be to include it in the analysis time. Another path of further study should evaluate AMRL proficiency testing program for asphalt binder testing. the use of the phase angle measurements on aged binders (e.g., RTFO or some other aging protocol) since rheological Training behaviors of asphalts change at different rates during plant mixing or lab conditioning protocols. Another idea to evalu- A key final step in implementation of a new method is ate would be to change from the parallel plate geometry to training on the procedure and getting users to understand a cup and bob geometry in the DSR for the phase angle mea- how the results should be used. Multiple avenues should be

OCR for page 74
75 used for delivery of training on using the Phase Angle method tional materials, such as Powerpoint slides with examples, need ranging from traditional instructor-led courses with hands on to be developed and distributed. Online delivery of training ma- workshops to more contemporary methods like self-paced terials is likely to become a very important method for training web-based training. Many technicians can be reached effectively in the near future. Interactive web-based training content is able within existing regional and national binder technician certifi- to reach a broad audience at any time, with self-paced learn- cation programs. To aid in these training venues, simple educa- ing using new media including animation and video.