Table 13-7.—Typical Uses of Bituminous Materials
bituminous coal is destructively distilled, coke and gas
are formed, and tar, ammonia, light oils, sulfur, and
phenol may be recovered. Coke-oven tar is produced in
the greatest amount, and its chemical, physical, and
adhesive characteristics make it most suitable for
road-tar purposes. Water-gas tar is obtained in the
manufacture of carbureted (mixed with hydrocarbons)
water gas. The nature of the carbureting oil largely
determines 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 special
grades for use in rubberized-tar binders. Grades 1
through 7 are liquid at room temperature, and grades 8
through 12 are semisolid or solid. The difference occurs
because of different amounts of the liquid coal distillates
in the tar; the more distillate, the more liquid (or less
solid) the tar. The road-tar cutbacks (RTCBs) are the
products of cutting back the heavier or harder grades
with coal tar distillates. Road-tar cutbacks are
manufactured in two viscosity grades (5 and 6) only.
Tar, which is insoluble in petroleum distillates, is
sometimes mixed with oil-resistant, unvulcanized
rubber to form a rubberized-tar binder material.
CHARACTERISTICS AND
USES OF BITUMENS
Selection of a particular bituminous material
depends upon the type of pavement, climatic conditions,
seasonal factors, and availability of equipment. In
general, soft penetration grades of asphalt cement are
preferred for use in cold climates, medium grades in
moderate climates, and hard grades in warm climates.
Heavier grades of asphalt cutbacks and tars are normally
used in warm weather and lighter grades in cold weather.
Tables 13-6 and 13-7 list the bituminous materials,
sources, curing, temperatures, and grades associated
with bituminous operations.
13-39
. . .
