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I. Special Mixture Design Considerations and Methods for Warm Mix Asphalt (WMA) 5 Table 3. Recommended improvement in virgin binder low-temperature continuous grade for RAP blending chart analysis for WMA production temperatures. Virgin Binder PG Grade 58-28 58-22 64-22 64-16 67-22 Average HMA Production Temperature, oF 285 285 292 292 300 Rate of Improvement of Virgin Binder Low- Temperature Grade per oC Reduction in Plant 0.035 0.025 0.025 0.012 0.025 Temperature Recommended Improvement in Virgin Binder Low- WMA Production Temperature, oF Temperature Continuous Grade for RAP Blending Chart Analysis, oC 300 NA NA NA NA 0.0 295 NA NA NA NA 0.1 290 NA NA 0.0 0.0 0.1 285 0.0 0.0 0.1 0.0 0.2 280 0.1 0.1 0.2 0.1 0.3 275 0.2 0.1 0.2 0.1 0.3 270 0.3 0.2 0.3 0.1 0.4 265 0.4 0.3 0.4 0.2 0.5 260 0.5 0.3 0.4 0.2 0.6 255 0.6 0.4 0.5 0.2 0.6 250 0.7 0.5 0.6 0.3 0.7 245 0.8 0.6 0.7 0.3 0.8 240 0.9 0.6 0.7 0.3 0.8 235 1.0 0.7 0.8 0.4 0.9 230 1.1 0.8 0.9 0.4 1.0 225 1.2 0.8 0.9 0.4 1.0 220 1.3 0.9 1.0 0.5 1.1 215 1.4 1.0 1.1 0.5 1.2 210 1.5 1.0 1.1 0.5 1.3 205 1.6 1.1 1.2 0.6 1.3 200 1.7 1.2 1.3 0.6 1.4 are summarized in Table 4. As discussed in Chapter 8, these compaction levels are under review and could be modified soon. Step 4. Select Nominal Maximum Aggregate Size The same nominal maximum aggregate size mixture should be used when designing the mix- ture as WMA or HMA. Usually, the nominal maximum size is given by the specifying agency. When it is not, the recommendations in Chapter 8 on the ratio of lift thickness to nominal maxi- Table 4. mum aggregate size should be followed. These recommendations are reproduced in Table 5. As Recommended design with HMA, smaller aggregate sizes should be used for wearing course mixtures and where extra compaction levels durability is desired; this will help provide a mix that compacts easily, has low permeability, and for dense-graded resists fatigue cracking. HMA mixtures. Design Traffic Ndesign Step 5. Determine Target VMA and Design Air Voids Values (Million ESALs) In the design procedure presented herein, the target VMA and design air void content are < 0.3 50 0.3 to < 3 75 used to initially calculate the design binder content for the mixture using an assumed value 3 to < 10 100 for binder absorption. Trial mixtures are then prepared using the design binder content to deter- 10 to < 30 100 mine an aggregate gradation that provides the design air void content. Minor adjustments to the 30 125