that has a thermometer running through the stopper, asshown. The flask and contents are heated. As thetemperature rises, distillate is given off in the form ofvapor. A condenser returns the vapor to liquid form, andthe liquid (the distillate) is caught in a volumetric beaker.The test indicates what can be expected in theapplication and use of the materials. The distillationtemperature ranges from 374°F to 680°F for RC asphaltcutbacks, from 437°F to 680°F for MC, and only at680°F for SC. Road tars are distilled at temperatures thatrange from 338°F to 572°F, and tar-rubber blends from170°F to 355°F. The amount distilled is expressed as apercentage of the total. The residue is the differencebetween the distillate and the total. The percentages ofdistillation may be as little as 1 percent for tar-rubberdistilled at 170°C (338°F) to as much as 59 percent whenRC and MC cutbacks and tars are heated to the highertemperatures.Record the volume of bitumen remaining in theflask. If the residue is solid enough to be tested, it issubjected to the penetration test described later in thischapter. If it is solid enough for this test, the residue mustbe asphaltic cement, and the original material was eitherRC or MC. If it is not solid enough for penetrationtesting, the original material was SC.Finally, you can determine the grade by calculatingthe percentage of bitumen and comparing it with theranges previously given.Flash Point TestsThe flash point of a bitumen that contains a volatiledistillate is the temperature at which it begins to give offignitable vapor. The principal purpose of flash-pointtesting is to determine maximum safe mixing andapplying temperatures; however, these tests are an aidto identification as well. Referring again to table 13-6,you see that RC and MC have flash points below 175°F.MC-30 and SC-70 have flash points around 150°F, butthe other grades of SC have flash points above 175°F.Testing for a flash point below 175°F is done withthe tag open-cup equipment shown in figure 13-31.When testing for flash points above 175°F, use theCleveland open-cup equipment shown in figure 13-32.When using either of these testers, you need to followthe procedures described in NAVFAC MO-330. Whilethere are important procedural differences, flash-pointtesting using either equipment is similar in that you usethe equipment to heat the test sample at a prescribed rateof temperature increase. Then, when the temperaturereading on the thermometer nears the estimated flashFigure 13-31.—Tag open-cup flash point tester.point (table 13-6), you use an alcohol torch to beginpassing a flame across the surface of the sample. Theflash point is reached when the test flame produces adistinct flicker or flash on the surface of the sample. Atthis point you read the thermometer and record thetemperature.Penetration TestFigure 13-33 shows an asphalt penetrometer that isused to determine the grade of asphalt cement. Inperforming the test, the needle is carefully brought tocontact with the surface of the sample, then released soas to exert a pressure of 100 grams. The seconds afterthe needle is released, the distance it penetrated thesample is read, to the nearest 0.01 centimeter, on thepenetrometer dial. The reported penetration is theaverage of at least three tests on the same material whosevalues do not differ more than four points betweenmaximum and minimum. Detailed procedures can befound in NAVFAC MO-330.13-44
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