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Design of Dense-Graded HMA Mixtures 107 9. Calculate Trial Mix Proportions by Weight and Check Dust/Binder Ratio 10. Evaluate and Refine Trial Mixtures 11. Compile Mix Design Report Most of these steps are straightforward and easily accomplished. However, Steps 8 through 10 are more complicated and require some experience in order to perform them proficiently. The suggested procedures for performing each of these steps are described below, followed by an example. Step 1. Gather Information At the beginning of the mix design process, the technician must gather as much information as possible bearing on the mix design, including the design traffic level, the climate at the place of construction, information on available aggregates and binders, anticipated lift thickness, pavement type (that is, surface, intermediate, or base course), and any special issues pertaining to the mix design or pavement construction. Unfortunately, this information is often incomplete, and the technician must use her or his judgment to fill in the gaps. Frequently, the organization requesting the mix design will provide specific information concerning the aggregates and binders to be used, eliminating these steps from the mix design process and making the process of gathering information somewhat simpler. Generally, the information below is often useful during the mix design process: Site Information Geographic Location Climate Relating to Binder Grade Design Traffic Level Construction Information Lift Thickness Pavement Information Mix type (dense-graded, SMA, or OGFC) Distance from Pavement Surface to Top of Layer Materials Information Information on Available or Recommended Aggregates Nominal maximum aggregate size Gradation Specific gravity and absorption Pertinent specification properties Information on Available or Recommended Asphalt Binders Performance grade (PG) Specification test data, including mixing and compaction temperatures Type of modification, if applicable Other pertinent specification properties Information on Other Mix Materials Anti-strip additives Properties of recycled asphalt pavement (RAP) Properties of other additives such as ground rubber or fibers Special Issues Pertaining To Mix Design Unusual Specification Requirements Use of Special Additives or Recycled Materials Unusual Construction Constraints Unusual Performance Constraints