Table 8-2.-Penetration Grade and AP Number of Asphalt CementTable 8-3.-AsphaIt Cutback Composition (Expressed in Percent of Total Volume)from 40 (hard) to 300 (soft) (table 8-2). The number isderived from a penetration test that is the distance thata standard needle penetrates the asphalt cement under astandard loading weight, in a given time, under knowntemperature conditions.All asphalt cements are solid or semisolid at roomtemperature (77°F) and must be converted to a fluid formixing with aggregate or for spraying. Asphalt cementmust be heated to a temperature ranging from 250°F to350F, depending upon the grade of the asphalt cement.The various penetration grades of asphalt cementare suitable for different uses, such as plant mixes,penetration macadam, and surface treatment. Softpenetration grades of asphalt cement are preferred foruse in cold climates, medium grades in moderateclimates, and had grades in warm climates.Asphalt CutbacksThe special equipment needed to heat asphaltcements is not always available. Since asphalt must bein a fluid condition to spray or to mix with an aggregate,the solid asphalt cement would not be suitable. Asphaltcement (AC) can be made fluid by adding solventscalled Cutterstock or Flux Oil. Cutterstock maybe anyone of the more volatile petroleum distillate products.The resulting combination is called Asphalt Cutback.Exposure to air causes the petroleum distillate toevaporate and leave the asphalt cement to perform itsfunction.The rate of evaporation determines the type ofasphalt cutback that is in the mixture. Gasoline ornaphtha (highly volatile) will produce a rapid-curecutback (RC) with a curing time of 4 to 8 hours; kerosene(medium volatility) will produce a medium-curingcutback (MC) with a curing time of 12 to 24 hours; anda fuel oil (low volatility) will produce a slow-curingcutback (SC) with a curing time of 48 to 60 hours, Table8-3 shows the percentage of components by grade forthe three types of asphalt cutbacks.8-20
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