glazed paper. If the material is an RC, most of thevolatiles will evaporate within 10 minutes, and thesurface of the smear will become extremely tacky. Thisis not so for the lighter MC or SC grades, which remainfluid and oily for some time-for hours or days, in somecases. An 800- or 3000-grade MC or SC cutbackhowever, also may become sticky in a few minutes. Thatis because these grades of cutback contain such smallamounts of cutterstock, therefore, you should confirmthe identification of the sample by a prolonged smeartest.A prolonged smear test is used to identify the 800and 3000 grades of MC or SC cutback. In this test, a thinsmear of asphalt cutback is placed on a nonabsorbentsurface and allowed to cure for at least 2 hours. If at theend of that time, the smear is uncured and still quitetacky, the material is an MC or SC; however, if the smearis hard and only slightly tacky, then the material is notan MC or SC. An RC 3000 cutback will cure completelyin 3 hours and an RC 800 in about 6 hours; but, an MCor SC will still be sticky even after 24 hours.The odor given off from a heated cutback helpsdifferentiate an MC (cutback with kerosene) from an SC(cutback with fuel oil). In the heat-odor test, you heatthe unknown sample in a closed container to capture theescaping vapors. (Use MINIMAL heat.) An MCsample will give off a strong kerosene odor. An SCsample will not smell of kerosene, but may have a slightodor of hot motor oil.Tests for Asphalt EmulsionsYou can distinguish asphalt emulsions from otherbitumens in various ways as follows:1. By observing the color of the material.Emulsions are dark brown in color, but other bitumensare black.2. Emulsions mixed in kerosene or some otherpetroleum distillate can be detected by the appearanceof small black globules, or beads, which fall to thebottom of the container.3. When an emulsion is mixed with water, theemulsion will accept the extra water and still remain auniform liquid. Other bitumens will not mix with water.4. Since an emulsion contains water, a small pieceof cloth saturated with it will not burn. Other bitumenswill burn or flame.Once you have established that a bitumen inquestion is an emulsion, you can then determine whetherit is a mixing grade (medium or slow setting) or anonmixing grade (rapid setting). To do so, attempt tomix a small amount (6 to 8 percent by weight) of theemulsion with damp sand, using a metal spoon. Afast-setting (RS) emulsion will not mix with the sand,but a medium-setting (MS) or slow-setting (SS)emulsion will readily mix and completely coat the sand.Identifying the emulsion as a mixing or nonmixing typeis sufficient for field conditions. Difference in viscosityis unimportant since there are so few grades. Nodistinction is necessary between MS and SS emulsionsbecause both are mixing types and are used largely forthe same purpose.Tests for TarsA pour test is used to identify the viscosity gradesof tar. Viscosity grades of road tars are comparable tothe viscosity grades of asphalt cutbacks and asphaltcement, as shown in figure 13-28. RT-1, the most fluid,is similar in viscosity to the MC-30 asphalt cutback.RT-8 is similar to grade 800 asphalt cutback. RT-12 hasthe approximate consistency of asphalt cement; that is,200 to 300 penetration.Referring again to figure 13-28, you see that roadtars RT-4 to RT-7 and road-tar cutbacks RTCB-5 andRTCB-6 have similar viscosities; therefore, if anidentified tar has a viscosity range of RT-4 to RT-7, youmust perform a smear test to distinguish whether it is aroad tar or a road-tar cutback. The test is performed inthe manner previously described for cutback asphalt.Like rapid-curing cutback asphalts, road-tar cutbacksare thinned with highly volatile materials, whichevaporate quickly, leaving a sticky substance within a10-minute period. On the other hand, because the fluidcoal oil in road tars evaporates slowly, road tars willremain at about the same consistency at the end of anidentical period. It is not important to determine whetherthe road-tar cutback is RTCB-5 or RTCB-6 since bothare used under approximately the same conditions.LABORATORY TESTS OF BITUMENSLaboratory testing provides a more positiveidentification of bituminous materials than is possiblewith field testing. That, however, is not the only purposeof the various laboratory tests. For example, specificgravity testing (discussed in NAVFAC MO-330) issometimes needed for the purpose of other tests and forchecking the uniformity of successive asphaltshipments. Other tests are performed for mix designpurposes, for checking compliance with project13-42
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