Figure 13-34.-Dunagan apparatus for specific gravity test.Test for Mineral DustIn bituminous paving, particles finer than the No.200 sieve are referred to a mineral dust. To measure theamount of mineral dust in a selected sample, youperform a washed sieve analysis (discussed in the EA3TRAMAN), using the No. 40 and No. 200 sieves. Afterall the material possible has passed the No. 200 sieveand has been discarded, the materials remaining on thesieve are returned to the original washed sample,oven-dried, and weighed The amount of mineral dust isthen calculated, using the following formula:Tests for Specific GravityThe specific gravities of aggregates used inbituminous paving mixtures are required in thecomputation of the percent of air voids and percent ofvoids filled with bitumens. Apparent specific gravityused with aggregate blends showing water absorptionof less than 2 1/2 percent is based upon the apparentvolume of the material, which does not include thosepore spaces in the aggregate that are permeable to water.Bulk-impregnated specific gravity is used for aggregateblends with 2 1/2 percent or greater water absorptionThe methods for determining absorption were discussedearlier in this chapter in the discussion of concreteaggregates.The apparent specific gravity can be determinedusing the methods described in NAVFAC MO-330 forapparent and bulk specific gravity. It may also bedetermined using the Dunagan apparatus shown infigure 13-34. The procedures are as follows:1. Select approximately 5,000 grams of aggregatefrom the sample, not including particles smaller than the3/8-inch sieve.2. Wash the aggregate to remove any dust or othercoating and dry it to constant weight in the oven. Recordthe total weight of ovendry aggregate on the data sheet,as shown in figure 13-35.3. Immerse the aggregate in water at 15°C to 25°Cfor a period of 24 hours.13-46
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