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(d) If the 1,655 kPa (240 psi), 1-degree, 60 revolutions compaction effort is used for the
mix design, greater field compaction effort will be required by the contractor to achieve the specified
density. Also, the compaction effort to determine the field control density is likely to be greater than the
standard 75-blow compaction effort.
(e) When two or more paving mixes have been investigated, the one used for field
construction should be the most economical mix that satisfies all of the established criteria.
(4) The final evaluation of the design mixture involves a test for moisture susceptibility. The
tensile strength ratio (TSR) of the mixture at the selected optimum will be performed according to ASTM
D 4867. A TSR value of less than 75 percent will require the use of an antistrip additive in the mixture.
d Mixture control.
(1) The aggregates and asphalt must be fed through the plant at a constant rate to obtain
efficient plant operation and to produce a mixture conforming to requirements. The approximate
proportion of aggregates and asphalt to be fed into the plant is determined from the laboratory mix
design. However, some adjustment in these proportions is usually required because gradations of the
stockpile aggregates generally will not entirely duplicate the gradation of the aggregate samples
obtained for laboratory design use; fines may be lost or manufactured while passing through the dryer;
aggregate may degrade in the dryer; and material mixed at an asphalt plant is more uniformly coated
with asphalt than materials mixed in the laboratory.
(2) To evaluate the quality of the material produced and to insure the best possible paving
mixture, a reasonably complete plant laboratory is necessary. The laboratory should be located at the
plant site and should contain about the same equipment listed in CRD C 649 and CRD C 650. Because
of the capacity of most asphalt plants, at least two technicians should be assigned to conduct control
tests; otherwise, all necessary testing cannot be completed in a timely manner.
(3) The heaviest demands on plant laboratory facilities occur at the initiation of plant
production. For batch plants, preliminary computations may be made to determine the weight of
material from each bin that will provide the gradation on which the mixture design is based. However,
the gradation of the aggregate supplied by the plant may not precisely reproduce the desired gradation.
The gradation of the plant-produced aggregate generally approximates the gradation used in design,
within reasonable tolerances, if initial sampling for design purposes has been accomplished properly
and if the plant is operated efficiently. Certain steps should be taken, however, to insure that satisfactory
mixtures are produced from the beginning and throughout the period of plant production. Procedures
subsequently outlined will insure that satisfactory paving mixes are produced.
(4) The aggregates obtained from the hot bins of batch plants sometimes cannot be
proportioned to satisfactorily reproduce the gradation of the aggregate used in the laboratory design. It
is then necessary to redesign the mix using plant-produced aggregates. Specimens are prepared and
tested for the new design in the same manner as for the original design tests. Optimum asphalt content
and acceptability of the mix produced by the plant are determined. Occasions may arise where the
gradation of the plant-produced aggregate will differ from that on which the laboratory design was based
to the extent that specified criteria cannot be met. Necessary steps should be taken to produce a
asphalt mixture meeting the specification requirements. Sufficient additional tests should be
performed to establish optimum asphalt requirements and to insure that the mix will meet
(5) After the aggregate and asphalt binder qualities have been determined to be satisfactory
and a proper mix design has been completed, the next step is to insure that the JMF is produced at the