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LABORATORY TESTS OF BITUMENS Laboratory testing provides a more positive identification of bituminous materials than is possible with field testing. That, however, is not the only purpose of the various laboratory tests. For example, specific gravity testing (discussed in NAVFAC MO-330) is sometimes needed for the purpose of other tests and for checking the uniformity of successive asphalt shipments. Other tests are performed for mix design purposes, for checking compliance with project specifications, and for establishing safe handling procedures.Bituminous materials are manufactured to meet specifications established by the federal government, American Association of State Highway and Transportation Oficials (AASHTO), and American Society for Testing and Materials (ASTM). These specifications define the extreme limits permitted in the manufacture of the material and assure the user that the material will possess definite characteristics and fulfill the project requirements. Some of the different tests the EA should be able to perform in the laboratory are discussed below. Other tests that you are less likely to perform, but should be aware of, are discussed in NAVFAC MO-330. The laboratory identification kit for bitumens consists of a number of jars containing samples of bitumens in all the recognized categories. To use this kit, you must bring an unidentified sample to approximately the same temperature as the kit samples, and then, following instructions that come with the kit, make identification on the basis of similarity of color, feel, consistency, and odor.A bituminous material suitable for use in pavement has a considerably higher ductility (which may be roughly defined as stretchability) than one that is suitable only for use as a waterproofer, roofing binder, or crack filler. Any crude method of determining the presence or absence of ductility (such as stretching the material like an elastic) will indicate whether or not the unidentified samples lies somewhere in the category of pavement material. Distillation Test If the unknown bitumen proves to be an asphalt and has an odor that indicates the presence of a distillate (such as the odor of kerosene or naphtha), a distillation test will indicate the character and approximate grade. In making this test, bear in mind that the basic material for RC and MC is asphaltic cement; that is, penetration asphalt. The basis for SC, however, is not asphaltic cement, but an asphalt residual oil too fluid to be penetration-tested for grade.RC, MC, and SC all contain a distillate; that is, a volatile liquid that evaporates during the curing process. For RC and MC, the distillate is highly volatile and evaporates quickly; for SC, it is considerably less volatile. The grade of RC, MC, or SC increases with the ratio of bitumen to distillate. Obviously, the higher the percentage of bitumen, the more solid the material will be, and, therefore, the higher the grade. For RC and MC, the percentage of bitumen for a given grade is the same, as shown in the following example:
These figures mean that for MC-30, for example, the percentage of bitumen is 54the percentage of distillate being determinable, of course, by subtracting the percentage of bitumen from 100. For SC the bitumen percentages are somewhat lower as follows:
From the distillation test, you can determine the bitumen percentage and whether the material is SC, RC, or MC. If it turns out to be RC or MC, the speed with which the distillate evaporates during the test (naphtha or gasoline will evaporate much more rapidly than kerosene) will indicate whether it is RC or MC. Figure 13-30 shows the apparatus used in distillation testing. A measured quantity (measured by volume) of the bitumen is placed in a distillation flask
Figure 13-30.-Apparatus for distillation testing. that has a thermometer running through the stopper, as shown. The flask and contents are heated. As the temperature rises, distillate is given off in the form of vapor. A condenser returns the vapor to liquid form, and the liquid (the distillate) is caught in a volumetric beaker. The test indicates what can be expected in the application and use of the materials. The distillation temperature ranges from 374F to 680F for RC asphalt cutbacks, from 437F to 680F for MC, and only at 680F for SC. Road tars are distilled at temperatures that range from 338F to 572F, and tar-rubber blends from 170F to 355F. The amount distilled is expressed as a percentage of the total. The residue is the difference between the distillate and the total. The percentages of distillation may be as little as 1 percent for tar-rubber distilled at 170C (338F) to as much as 59 percent when RC and MC cutbacks and tars are heated to the higher temperatures.Record the volume of bitumen remaining in the flask. If the residue is solid enough to be tested, it is subjected to the penetration test described later in this chapter. If it is solid enough for this test, the residue must be asphaltic cement, and the original material was either RC or MC. If it is not solid enough for penetration testing, the original material was SC.Finally, you can determine the grade by calculating the percentage of bitumen and comparing it with the ranges previously given. |
 
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