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70 Brown et al. (179) performed a similar analysis for all of Bulk specific gravity, the granite sections on the east tangent of the track. Coarse- F&E, graded (below the restricted zone [BRZ]), fine-graded (above Uncompacted voids in coarse aggregate, the restricted zone [ARZ]), and gradations passing through Uncompacted voids in fine aggregate (FAA), the restricted zone (TRZ) were included. Each gradation was Sand equivalent, placed with an unmodified PG 67-22 binder as well as with Methylene blue, PG 76-22 binder produced with both SBS (styrene-butadiene- LA abrasion, styrene polymer) and SBR (styrene-butadiene rubber) modi- Micro-deval, and fiers. The interaction between gradation and binder grade is Sulfate soundness. shown in Figure 32. An ANOVA is shown in Table 17. In the case of the east curve data, gradation is a significant Coarse aggregate angularity was not performed even though factor, with the coarse-graded mixes having the largest rut gravel sources were used at the track. The tests were per- depth followed by the mixes passing through the restricted formed on the aggregate stockpiles, and the blend properties zone. The mixes with the fine gradations were the most rut were determined mathematically using a weighted average resistant. Practically speaking, there was little difference (percent of blend and percent coarse or fine aggregate were between the rut depths, and all three gradations would per- used as weighting factors). form well. A stepwise regression was performed using the final-wire line rut depth as the response variable for all of the Superpave 4.4.2 Relationship Between Aggregate sections. When only the aggregate properties shown above Properties and Performance were used as predictor variables, LA abrasion was the first predictor entered followed by percent passing the 0.075-mm The following aggregate tests were performed on the aggre- (No. 200) sieve. However, the relationship was not signifi- gate sources used in the 2000 NCAT Test Track: cant for either variable. Other response variables that were Figure 32. Effect of gradation shape and binder type (east curve) (179). TABLE 17 Results of analysis of variance on effect of modifier and gradation on rut depth (179) Source Degrees Adjusted F-stat p-value Significant?1 of Mean Freedom Squares Gradation (Grad) 2 14.1783 30.18 0.000 Yes Modifier 2 18.9431 40.33 0.000 Yes Grad*Modifier 4 3.082 6.56 0.000 Yes Error 72 0.4697 -- -- -- 1 5% level of significance.