Figure 8-26.-Water-mixing test for emulsions.rapid setting emulsion termed a nonmixinggrade or a medium- or slow-settingemulsion termed as mixing grade emulsion.To know which type is present isimportant because the applications ofthe mixing and nonmixing types varygreatly. The test performed todistinguish between these two types ofemulsions is the stone-coating test.This test consists of taking a handfulof damp sand and adding to the sand asmall amount of emulsion (estimate about6 to 8 percent by weight) and attemptingto mix the two materials. Care should beexercised not to add so much emulsionthat the sand becomes saturated.A rapid-setting emulsion will“break” so quickly it will not be possibleto mix it with sand. It breaksimmediately, gumming up the mixing spoonand the aggregate with asphalt cement;otherwise, if the unknown sample is amedium- or slow-setting emulsion whenadded to the damp sand, it will mix easilyand coat all the particles completely aswell as the mixing spoon with a uniformcoating of asphalt. Identification of anemulsion merely as a mixing or nonmixingtype is sufficient for field conditions.The difference in viscosity is unimportantbecause there are so few grades. Nodistinction is necessary between medium-and slow-setting emulsions since both aremixing types used largely for the samepurpose.Another test for emulsions is theWATER-MIXING TEST (fig. 8-26). Becauseemulsions are made with water, more watermay be added to emulsions withoutdisturbing the uniformity of the liquid.None of the other bituminous materialswill dissolve in water.AFLAME TEST can also be used intesting asphalt emulsions. A clothsaturated with asphalt emulsion willsmolder but will not burn or burst intoflame. Other bituminous materials arecombustible.Laboratory Test of Bituminous MaterialsIn addition to the field tests,various tests are performed on bituminousmaterials in the laboratory. These testsusually are made for the purpose ofchecking compliance with the establishedspecifications; however, laboratory testsmay also be made to identify the materialbeyond field identification, to furnishinformation for mix design, or toestablish safe handling procedures.Bituminous materials are produced tomeet the specification established by thefederal government, the AmericanAssociation of State Highway Officials(AASHO), and the American Society forTesting Materials (ASTM). Thesespecifications define the extreme limitspermitted in the manufacture of thematerial and assure the user that thematerial will possess definitecharacteristics and fulfill the projectrequirements. Consult with the EAs for theproper specifications required.ESTIMATION OF MATERIALSMany different combinationsofmaterials are used on bituminous surfaces.Before a bituminous surface is placed, thesurface to be covered normally requiresthe placing of a preliminary treatment: aprime or a tack coat.Prime CoatPrime coats are placed on a dirt orgravel surface. The purpose of priming isto waterproof and dustproof the surface,plug capillary voids, and coat and bondloose particles. A prime coat also hardensor toughens the surface, promotes adhesionbetween the existing surface and the newsurface, and penetrates the surface.The priming material may be one of thefollowing:A low-viscosity tar, such as RT-2,RT-3, or RT-4A low-viscosity asphalt,such as MC-30, -70, -250, orSC-70, -250,-800A diluted asphalt emulsionBituminous materials used for theprime coat should be applied in quantitiesknown as the rate of application (ROA) ofnot less than 0.2 gallon or more than 0.5gallon per square yard. Normally, theconstruction project specifications denotethe ROA for the prime coat application;however, when the ROA is not included inthe project specifications, the NCF usesan ROA of .3 for planning purposes.8-27
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