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30 10 130C 9 150C 8 170C 190C 7 6 Opacity, % 5 4 3 2 1 0 0 20 40 60 80 100 120 Time, minutes Figure 17. Example data from a SEP test, opacity measurements versus time for four temperatures. Mixture Tests ment was that in the field, aggregate stockpiles are often wet and the plant's drier may not completely dry the moisture from Mix Coating Tests. Each of the binders was mixed with the coarse aggregate before mixing with the asphalt binder. As the baseline mix using a common bucket-type mixer and a residual moisture escapes the aggregate and expands to steam, laboratory pugmill mixer at four temperatures to evaluate the asphalt binder can be foamed, which greatly increases it coating of the binder on the aggregates. The two mixer types volume and enhances the coating process. The procedure used (bucket and pugmill) were selected because they provide rea- for this experiment was as follows: sonable simulations of the mixing action occurring in drum mix plants and batch plants. Ratings of mix coating were de- 1. The baseline mix with granite aggregate was batched to termined using the Ross count method, ASTM D 2489. Re- 4,600 grams and then split into coarse (+4.75 mm) and sults of the coating tests for both mixer types were analyzed fine fractions. by developing regression equations based on a Sigmoid func- 2. The coarse aggregate fraction was placed in a deep pan, tion of the form: covered with water, then placed in an oven overnight at 210F. The fine aggregate fraction was heated in a separate 1 oven at about 20F above the target mixing temperature, C= (7) 1 + ae - b T either 248F, 284F, 320F, or 356F. 3. The heated coarse and fine aggregate were combined in where C is the percentage coating at any temperature T, and the pugmill mixer, and the combined blend was heated a and b are regression constants. The regressions were used to with a propane blowtorch until the blend reached the tar- estimate the coating percentage of the binders at any tempera- get mixing temperature. For higher mixing temperatures, ture. Using the equiviscous mixing temperatures of the un- the blowtorch heating took as much as 20 minutes. modified binders, baseline coating percentages for the bucket 4. The asphalt was added (161.2 grams) to the aggregate in the mixer and the pugmill mixer were determined to be 98% and mixer and mixing continued for 1 minute. 89%, respectively. The temperatures to achieve these coating 5. The mixture was discharged from the pugmill and imme- percentages for the modified binders were then estimated diately sieved on a 2.36-mm sieve, and the coarse aggregate with the regression equations. Results of the coating percent- particles were retained for later assessment of percentage ages for both mixer types were correlated to mixing tempera- coating in accordance with the Ross count method. tures from the candidate methods. An additional coating experiment was conducted to assess This experiment included four binders selected following the effect of residual aggregate moisture on how well asphalt the main coating experiment as having a wide range of coat- binders coat the aggregate. The motivation for this experi- ing results.