Figure 8-20.Tars obtained from distillation of bituminous coal.
The viscosity grades range from 1 (least
fluid) to 3 (most fluid).
Use of Asphalt Emulsions
treatment, road and plant mixes, and crack
and joint filling. The mixing grades can
be mixed unheated with damp aggregate.
They are preferred over asphalt cutback
when the aggregate is very damp. Cationic
emulsions coat damp aggregate better than
not mix well since the emulsion will
Tars are obtained from the distillation of
bituminous coal (fig. 8-20) and are seldom used in
the NCF. A road tar is designated by the symbol RT
and is manufactured in 12 grades of viscosity
(table 8-5). RT-1, RT-2, and RT-3 are PRIMING
OIL. RT-4 through RT-7 are called COLD TARS
because they are fluid enough to be mixed and
applied at relatively low temperatures. RT-8
through RT-12 are called HOT TARS because they
are solid enough to require high temperatures for
mixing and applying.
The symbol RTCB refers to ROAD TAR
CUTBACK. RTCBs are manufactured only in
viscosity grades 5 and 6. Coal distillate,
naphthalene in benzol, may be used to
cutback the heaviest grades of road tar to
produce both grades of road tar cutbacks.
The viscosity grades of road tars and road