GENERAL PROCEDURES AND
GUIDELINES
The objective of hot-mix design is to determine the
most economical blend of components that will produce
a final product that meets specified requirements. The
following is a list of general procedures:
1. Prepare a sieve analysis of each of the
aggregates available.
2. Determine the aggregate blend that will achieve
the specified gradation (Paving and Surfacing
Operations, TM 5-337). Plot the selected blend
proportions on a graph with the allowable limits to see
that it conforms.
3. Determine the specific gravity of the
components.
4. Using selected percentages of bitumen (TM
5-337), make trial mixes, and compute the design test
properties of the mix.
5. Plot the test properties on individual graphs
using the selected bitumen percentages. Draw smooth
curves through the plotted points.
6. Select the optimum bitumen content (AC) for
each test property from the curves of the Marshall test
results. For a discussion of the Marshall stability test,
you can refer to chapter 13 of this TRAMAN and to
NAVFAC MO-330.
7. Average the bitumen content values (from Step
6) and, from the graphs, read the test property value
corresponding to this average.
8. Check these read values with the satisfactoriness
of mix criteria.
The selection of the mix ratios of materials is
tentative. The bitumen should be the same as the one to
be used in construction. The aggregates and fillers must
meet definite requirements. In general, several blends
should be considered for laboratory mix-design tests.
Gradation specifications are based on limits
established by the U.S. Army Corps of Engineers as
satisfactory. Within these limits, the following variables
are considerations that will affect the final mix design:
1. Use of mix (surface course, binder course, or
road mix)
2. Binder (asphalt, cement, or tar)
3. Loading (low tire pressure—100 psi and under,
or high tire pressure—over 100 psi)
4. Maximum size of aggregate (in stockpile or
based on thickness of the pavement course)
Once the gradation specifications have been
selected, you should check the available materials to
determine how to proportion the blend to meet these
specifications. You should study sieve analyses of the
available aggregates and compute a series of trial
blends. You may have to make adjustment of the blend
after testing the design and prepared mix. The
considerations for establishing and adjusting the blend
are explained in TM 5-337.
The determination of optimum bitumen content is
based on a definite design and testing procedure known
as the Marshall method. This method is explained in
chapter 13 of this TRAMAN and in NAVFAC MO-330.
The final step is the preparation of a job-mix
formula to be furnished to the construction unit.
It is recognized that at times it will be necessary to
shorten the design procedure as much as possible to
expedite military construction. For additional
information, refer to TM 5-337.
EXAMPLE OF MARSHALL METHOD OF
HOT-MIX DESIGN
A typical mix design is illustrated by the
calculations and graphs shown on figures 17-5 through
17-10.
Aggregate Grading
An aggregate grading chart is shown in figure 17-5
(DD Form 1207). This chart shows the gradation curves
of the three aggregates that are available for the mix.
The sieve analyses are run in the manner as described
in the EA3 TRAMAN. Calculations may be made and
data recorded on standard sieve analysis data sheets
before the curves are drawn. A gradation curve is not
shown for the mineral filler to be used.
Aggregate Blending
The front and back sides of a data and computation
sheet for aggregate blending is shown in figures 17-6A
and 17-6B (DD Form 1217). The gradation of the
available aggregates should be recorded on the
upperpart (fig. 17-6A) of the form. The lower part (fig.
17-6A) may be used for the computation of the trial
blend. Several attempts may be required before a blend
meeting specifications is obtained. The cold feeds
(quantities per batch) of aggregate to the asphalt plant
17-11
