Figure 8-24.–Smear test of asphalt cutback.Smear TestThe smear test is used to separatean RC from an MC or SC. The test isprimarily based on the fact that RCs arecutback with a highly volatile material(naphtha or gasoline). You can determinewhether a sample is an RC or not bysmearing some of the sample in a thinlayer on a nonabsorbent surface, such as apiece of glazed paper. The volatilesubstance evaporates within a few minutesand the surface becomes so tacky that whentouched, the specimen, paper and all,sticks to your fingers and can be liftedinto the air (fig. 8-24).Checking the reverse side of thepaper, you will find that the RC did notpenetrate through the paper as MCs or SCsdo. MCs and SCs on smear tests remainfluid and oily for time periods that varyfrom hours to days, depending on the typeand grade of material. If an 800 or 3,000grade MC or SC is present, they may becomesticky in a few minutes since there issuch a small amount of cutterstock inthem. When such a viscous grade ispresent, it is well to confirm theidentification of the sample by a prolongedsmear test. Generally, the MCs and SCs willpenetrate through the paper while the RCswill not. You can determine this byobserving the back side of the paper.In a prolonged smear test, a thinsmear is made on nonabsorbent paper andallowed to cure completely. If the viscouscutback is all RC-3000, it will curecompletely in about 3 hours. When the spothas cured completely (the cutterstock hasalmost all evaporated), the smear willbe almost pure asphalt cement (AC) andwill be hard and no longer sticky. Ifthe viscous sample were an MC or SC-800 or 3,000, the spot would still beFigure 8-25.—Stone-coating test for emulsions.uncured and, therefore, very sticky, evenafter 24 hours, while the RC smear willhave become a hard, glazed spot.Heat-Odor TestA heat-odor test is used todistinguish between medium-curing andslow-curing asphalt cutback by identifyingthe cutter stock as kerosene, fuel oil, ordiesel oil. A sample of the material isheated in a closed container to retain thevapors. (CARE MUST BE TAKEN TO AVOID THEUSE OF TOO MUCH HEAT). Medium-curingasphalt cutback will have a strong odor ofkerosene. Slow-curing asphalt cutback willlack the kerosene odor, but a faint odorof motor oil may be present.Field Penetration TestThe field penetration test isperformed to determine the approximatehardness of the asphalt, not to pinpointthe exact penetration number for it. Todetermine if the number falls in the hard,medium, or soft group is sufficient.To perform this test, attempt topush a sharpened pencil or nail into thecontainer of asphalt (at about 77°F),using a firm strong pressure ofapproximately 10 pounds. If only a slightpenetration is made with considerabledifficulty, a hard asphalt cement ispresent. When the penetration is madeslowly but without great difficulty, amedium asphalt cement is present. If thepenetration is made with ease, the asphaltcement is a high penetration scale (a softAC).Stone-Coating TestWhen a material has been tested andfound to be an emulsion, the stone-coatingtest is performed (fig. 8-25). This test isconducted to determine if the emulsion is a8-26
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