Table 13-7.—Typical Uses of Bituminous Materialsbituminous coal is destructively distilled, coke and gasare formed, and tar, ammonia, light oils, sulfur, andphenol may be recovered. Coke-oven tar is produced inthe greatest amount, and its chemical, physical, andadhesive characteristics make it most suitable forroad-tar purposes. Water-gas tar is obtained in themanufacture of carbureted (mixed with hydrocarbons)water gas. The nature of the carbureting oil largelydetermines the character of the water-gas tar produced.This tar may vary widely in specific gravities,viscosities, and other physical and chemical properties.Road tars are manufactured in 12 grades of viscosity(figs. 13-27 and 13-28). There are also some specialgrades for use in rubberized-tar binders. Grades 1through 7 are liquid at room temperature, and grades 8through 12 are semisolid or solid. The difference occursbecause of different amounts of the liquid coal distillatesin the tar; the more distillate, the more liquid (or lesssolid) the tar. The road-tar cutbacks(RTCBs) are theproducts of cutting back the heavier or harder gradeswith coal tar distillates. Road-tar cutbacks aremanufactured in two viscosity grades (5 and 6) only.Tar, which is insoluble in petroleum distillates, issometimes mixed with oil-resistant, unvulcanizedrubber to form a rubberized-tar binder material.CHARACTERISTICS ANDUSES OF BITUMENSSelection of a particular bituminous materialdepends upon the type of pavement, climatic conditions,seasonal factors, and availability of equipment. Ingeneral, soft penetration grades of asphalt cement arepreferred for use in cold climates, medium grades inmoderate climates, and hard grades in warm climates.Heavier grades of asphalt cutbacks and tars are normallyused in warm weather and lighter grades in cold weather.Tables 13-6 and 13-7 list the bituminous materials,sources, curing, temperatures, and grades associatedwith bituminous operations.13-39. . .
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