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33 discharge temperatures. This suggests that it is not necessary to The binder grade study yielded three key findings. First, the evaluate workability at the planned production temperature. high-temperature grade of the binder was significantly affected The evaluation of coating at the planned production temper- by changes in the RTFOT aging temperature. A relationship ature should suffice. It appears that workability and com- among the short-term aging temperature, the aging index of pactability can be evaluated by using the gyratory compactor the binder, and the change in high-temperature grade of the to determine the gyrations to 8-percent air voids at the planned binder was developed and used to provide preliminary guid- field compaction temperature and a second temperature that ance on production temperatures below which the high- is approximately 55F (30C) lower than the planned field temperature binder grade should be increased one grade level. compaction temperature. This will permit an assessment of the This guidance was included in the revised preliminary proce- temperature sensitivity of the workability and compactability dure. The second key finding from the binder grade study was of the mixture. that the changes in the low-temperature grade of the binder that resulted from changes in the RTFOT aging temperature were small and did not warrant recommended changes in low- 3.2 Preliminary Mixture Design temperature binder grade selection for WMA. The third key Procedure Revisions finding was that small improvements in the low-temperature The preliminary mixture design procedure was modified properties could result in increased RAP usage when a blend- based on the findings of the Phase I studies. Table 23 summa- ing chart analysis is conducted. rizes how the findings from each of the Phase I studies were The key finding from the short-term conditioning study used to revise the preliminary mixture design procedure. was that 2 h of conditioning at the compaction temperature The key finding from the sample reheating study was that reasonably reproduced the absorption and binder aging that reheating has a similar stiffening effect on WMA and HMA. occurred during construction. The revised preliminary proce- This finding was not directly incorporated into the revised pre- dure specified 2 h of conditioning at the compaction tempera- liminary mixture design procedure. It was used in analysis of ture for volumetric design and performance testing. data from the other Phase I studies, particularly the selection of The RAP study found that RAP and new binders do mix at a short-term conditioning time for WMA. WMA production and compaction temperatures in a manner Table 23. Summary of preliminary design procedure revisions. Phase I Key Findings Preliminary Design Procedure Revisions Study Sample 1. Reheating has similar stiffening effect for 1. Not directly incorporated. Used in selection Reheating WMA and HMA of tentative short-term conditioning time. 1. The high-temperature binder grade is 1. Preliminary recommendations were included significantly affected by the RTFOT in the binder grade selection to increase the temperature. The temperature effect was high-temperature performance grade based greater for binders with greater short-term on the planned production temperature and Binder aging susceptibility. Table 21. Grade 2. The effect of RTFOT temperature on the 2. No change required. low-temperature binder grade was small. 3. Preliminary recommendations for improving 3. The effect of RTFOT temperature on the the low-temperature grade of the virgin low-temperature grade could affect RAP binder for blending chart analyses were contents when blending charts are used. added based on Table 22. 1. 2 h of oven conditioning at the compaction 1. 2 h at the compaction temperature was Short-Term temperature reasonably reproduced the specified for volumetric design and Conditioning binder absorption and binder stiffening that performance testing. occurs during construction. 1. RAP and new binders mix at WMA 1. Note added that the "as recovered" high- production and compaction temperatures temperature grade of the RAP binder should in a manner similar to HMA. The mixing be less than the planned field compaction depends on the time at elevated temperature. Also, if the mix time at RAP temperature and probably the stiffness of elevated temperature was expected to be less the RAP binder. than 2 h, plant mixing studies should be conducted to verify the degree of mixing of the RAP and new binders. 1. Differences in workability and 1. A workability test was not included in the compactability of WMA could only be revised preliminary procedure. Coating is measured at temperatures that are below evaluated at the planned production WMA production temperatures. temperature. Limits on the gyrations to 92- Workability percent relative density at the planned field compaction temperature and 54F below the planned field compaction temperature were added to control compactability.