Table 13-6.-Characteristics of Bituminous Materialscutback asphalt, but differs in many specific properties.It is used as a soil binder and dust palliative.EMULSIONS.ā Emulsification is the third processin which asphalt is liquified. In the emulsificationprocess, hot asphalt cement is mechanically separatedinto minute globules and is dispersed in water that istreated with a small quantity of an emulsifying agent,such as soap, colloidal clay, or one of numerous otherorganic agents. The rate at which the asphalt globulesseparate from the water is called the breaking or settingtime. This rate is generally dependent upon theemulsifier used and the proportion of water to asphalt.Based in the breaking time, emulsions are describedas rapid setting (RS), medium setting (MS), and slowsetting (SS). They are also described by viscositynumbers (fig. 13-28).Emulsions are also grouped according to theirability to mix with damp aggregate. The RS emulsionbreaks so fast that it cannot be mixed; therefore, it iscalled a nonmixing emulsion. The MS and SS emulsionsbreak slowly enough to permit good mixing; that is, eachparticle of the aggregate is uniformly coated. Emulsionsmay be satisfactorily used as a tack coat for bituminouspavements.ROAD TARS.ā Tars are products of thedistillation of coal. No natural sources of tar exist. Coaltar is a general term applied to all varieties of tarobtained from coal. It is produced by one of severalmethods, depending on the desired end product. When.13-38---------- Lā .
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