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Test for Mineral Dust In bituminous paving, particles finer than the No. 200 sieve are referred to a mineral dust. To measure the amount of mineral dust in a selected sample, you perform a washed sieve analysis (discussed in the EA3 TRAMAN), using the No. 40 and No. 200 sieves. After all the material possible has passed the No. 200 sieve and has been discarded, the materials remaining on the sieve are returned to the original washed sample, oven-dried, and weighed The amount of mineral dust is then calculated, using the following formula:
Tests for Specific Gravity The specific gravities of aggregates used in bituminous paving mixtures are required in the computation of the percent of air voids and percent of voids filled with bitumens. Apparent specific gravity used with aggregate blends showing water absorption of less than 2 1/2 percent is based upon the apparent volume of the material, which does not include those pore spaces in the aggregate that are permeable to water. Bulk-impregnated specific gravity is used for aggregate blends with 2 1/2 percent or greater water absorption The methods for determining absorption were discussed earlier in this chapter in the discussion of concrete aggregates. The apparent specific gravity can be determined using the methods described in NAVFAC MO-330 for apparent and bulk specific gravity. It may also be determined using the Dunagan apparatus shown in figure 13-34. The procedures are as follows: 1. Select approximately 5,000 grams of aggregate from the sample, not including particles smaller than the 3/8-inch sieve.2. Wash the aggregate to remove any dust or other coating and dry it to constant weight in the oven. Record the total weight of ovendry aggregate on the data sheet, as shown in figure 13-35.3. Immerse the aggregate in water at 15C to 25C for a period of 24 hours.
Figure 13-35.Data sheet for specific gravity of bituminous mix components (DD Form 1216). 4. After soaking the sample, place it in the bucket, which is filled with water. Then turn the bucket and aggregate sharply back and forth to help remove any air.5. Suspend the bucket from the brass hanger and bring the water level up to the overflow pipe.6. Determine the submerged weight using weights placed in the scoop on the right-hand pan. Record the weights in the appropriate spaces on the data sheet. The calculations required for the determination of the apparent specific gravity of coarse aggregate are shown on the data sheet and are self-explanatory.MIX DESIGN TESTS Mixture design tests for bituminous pavement are carried out on samples mixed and compacted in the laboratory to determine the optimum bitumen content, the optimum aggregate content, and gradation required to produce a pavement that will meet given quality specifications. Mixes with various bitumen and aggregate contents and gradations are prepared, compacted to specified density, and tested. From the test results, design engineers determine optimum values. Mix design test procedures vary considerably. this course can give only a general description of typical procedures. Mixture design is more fully discussed in NAVFAC MO-330 and at the EA1 level in Part 2 of this TRAMAN. |
 
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