15 May 2001
Cut-back asphalts can be contained in a single tank, and only the standard pipelines and spray bar are
necessary. Additional equipment is necessary for handling the kerosene and asphalt cement, when this
type of binder is produced. Asphalt emulsions are advantageous in that damp aggregate can be used in
the mixing process; whereas, dry aggregates are required for the other binder materials. Mixes made
with asphalt emulsions cannot be stockpiled unless the emulsion has been specifically formulated for
stockpiling purposes. The choice of asphalt material type depends primarily on economics and the type
of equipment to be used. Table 6-6 is provided as a guide to the selection of the proper type and grade
of asphalt cement. The table provides information on asphalt for mixes to be used immediately and on
asphalt for mixes to be stockpiled for later use.
Selection of Asphalt
Cold (less than
or Storage Hot
(above 27EC, 80EF)
Kerosene, gallon per ton mix
RC-70 - RC-250
RC-250 - RC-800
RC-800 - RC-3,000
MS-2 - MS-2h
SS-1 - SS-1h
Note: RC = rapid curing; MS = medium set; SS = slow set.
Amount of kerosene to be added when mixture is to be stockpiled for future use.
Emulsified asphalts are available that are specifically formulated for stockpile use.
d. Design. Several equations based on the surface area of the aggregate are available for
calculating the optimum amount of asphalt cement in the mix. Although these equations give an
approximation of the binder content, they do not properly account for porosity of the aggregate or the
compaction characteristics of the mix and, therefore, can be misleading. The following procedure is
recommended for determining the amount of asphalt cement to be used in the paving mix for plant-mix
cold-laid pavements. This design procedure is similar to the procedure used for designing plant-mix hot-
laid mixes for roads and streets. The laboratory equipment and test procedures shall be determined by
CRD-C 649 and CRD-C 650.
(1) Asphalt contents for specimens. The quantity of asphalt cement required for a particular
aggregate is the most important factor in the design of a paving mixture. An estimate of the optimum
amount of asphalt cement for the aggregate to be tested should be made in order to start the laboratory
tests. Laboratory tests normally are conducted for a minimum of five asphalt cement contents: two
above, two below, and one at the estimated optimum content. Incremental changes of 1 percent may be
used for preliminary work, but increments of 0.5 percent are generally used where the approximate
optimum asphalt cement content is known and for final designs.
(2) Proportioning of aggregates. As a preliminary step in mixture design and manufacture, it is
necessary to determine the approximate proportions of the different available stockpiled materials
required to produce the desired gradation of aggregate. The above-mentioned step is necessary to
determine whether a suitable blend can be produced and, if so, the approximate proportion of
aggregates to be fed from the cold feeders into the dryer. Sieve analyses are conducted on material
from each of the stockpiles. The aggregates are combined as described in chap 2. After a suitable