Description of Test
The Marshall Method for hot-mix asphalt concrete mix design is a rational approach to
selecting and proportioning two materials, asphalt cement and mineral aggregates to
obtain the specified properties in the finished asphalt concrete surfacing structure. The
method is intended for laboratory design of asphalt hot-mix paving mixtures.
1.2.
Application of the Test
The objective to be achieved using the Marshall Method for hot-mix asphalt concrete mix
design is to determine an economical blend and gradation of aggregates (within the limits
of project specifications) and asphalt that yields a mix having;
1. Sufficient asphalt cement to ensure a durable asphalt concrete surface course.
2. Sufficient mix stability to satisfy the demands of traffic without distortion or
displacement.
3. Sufficient voids in the total compacted mix to allow for a slight amount of
additional compaction under traffic loading without flushing, bleeding and loss of stability, yet low enough to keep out harmful air and moisture.
4. Sufficient workability to permit efficient placement of the mix without segregation.
5. Characteristics which allow normal construction operating variations without
falling outside of the specified requirements.
1.3.
Units of Measure
The units of measure will be as specified in the individual procedures that are used in the
Marshall Mix Design analysis.
Standard Test Procedures Manual
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TP 204-10
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ASPHALT MIXES MARSHALL MIX DESIGN
Page: 2 of 6 Date: 1993
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2.
APPARATUS AND MATERIALS
2.1.
Equipment Required
Refer to:
STP 204-8 Preparation of Marshall Compaction Specimens
STP 204-9 Theoretical Maximum Specific Gravity
STP 204-11 Marshall Stability and Flow
STP 204-15 Stripping Potential
STP 204-19 Asphalt Film Thickness Determination
STP 204-20 Hveem Stability
STP 204-21 Marshall Compaction Specimens - Density and Void Characteristics
Determination
STP 204-22 Retained Marshall Stability
STP 206-4 Plasticity Index Coarse Grained Soils
STP 206-5 Sand Equivalent
STP 206-7 Specific Gravity - Bulk, Apparent
STP 206-9 Lightweight Pieces in Aggregate
STP 206-14 Percent Fractured Faces in Aggregate
STP 206-15 Clay Lumps and Friable Particles in Aggregate
2.2.
Materials Required
Refer to the Standard Test Procedures as outlined in 2.1 above.
Standard Test Procedures Manual
Standard Test Procedures Manual
TP 204-10
Section
:
Subject
:
ASPHALT MIXES MARSHALL MIX DESIGN
Date: 1993 03 22 Page:
3 of 6
2.3.
Sample to be Tested
Representative samples of all aggregate components to be used on the project and asphalt
cement of the same grade and from the same manufacturer as will be used for the field
work.
2.3.1.
Obtaining Required Gradation For Each Aggregate Component
Dry the samples of aggregate in the oven for approximately 18 hours at 105
o
C to
110
o
C. Separate aggregate into individual sieve sizes by dry sieving. Select the
sieve sizes corresponding to the specifications for the "type" of
Recombine individual aggregate fractions in correct proportions to obtain the
average stockpile gradation which is submitted from the field along with the
sample. Use a trial and error method as described in the following paragraph.
Combine trial percentages of each size, then run a wet sieve and compare the
result to the stockpile average. Adjust the proportions of each size and repeat the
procedure until the desired gradation is achieved. Use the final percentages of
each size to produce specimens as required later in the procedure.
2.4.
Data Required
The following data is required for each proposed aggregate gradation when preparing a
Marshall Mix Design;
Lightweight Pieces in Aggregate
Plasticity Index of the Aggregate
and Equivalent of the Aggregate
Percent Fractured Faces in the Aggregate
Clay Lumps and Friable Particles in Aggregate
Theoretical Maximum Specific Gravity for each asphalt/aggregate combination
Specific gravities for all aggregate fractions
Density, air voids and voids in mineral aggregate determination for each asphalt/aggregate
combination
Standard Test Procedures Manual
Standard Test Procedures Manual
S
TP 204-10
Section
:
Subject
:
ASPHALT MIXES MARSHALL MIX DESIGN
Page: 4 of 6 Date: 1993
03 22
Marshall stability and flow for each asphalt/aggregate combination
Stripping Potential Analysis on the recommended mix design
Hveem stability on the recommended mix design
Retained stability for the recommended mix design
Asphalt film thickness determination for the design aggregate gradation at each asphalt
content evaluated.
3.
PROCEDURE
3.1.
Test Procedure
Prepare two or more initial trial specimens as described in STP 204-8 at an estimated
optimum asphalt content. Use the combined stockpile gradation of the natural split for
one set of molds.
Determine the Marshall Mix Design characteristics using STP 206-7, 204-21, 204-9 and
204-11.
Compare the Marshall properties for the trial molds with SHT specified properties for that
aggregate type and asphalt type.
If the Marshall properties for one of the chosen gradations are satisfactory, proceed with
the full design procedure. If the properties are obviously outside the range, make further
adjustments by changing split combinations or adding blenders/fillers. Estimate by
plotting the gradation on an e
.45
graph and comparing to the theoretical maximum density
line (a line drawn between the origin and the point where the gradation line crosses 90%
passing). Continue until the properties are satisfactory.
Using the procedures previously described, prepare a series of Marshall specimens in
triplicate at four asphalt contents (by weight of dry aggregate) to bracket optimum.
Determine the Marshall properties for each specimen and average the results of the
triplicates at each asphalt content.
On a graph MR-71 or EPS-71, plot the Marshall properties (density, air voids, VMA and
Marshall stability) as a function of asphalt content.
Select optimum asphalt for each property; for density and stability use the peak of the
curves and for VMA use the low point. For air voids, select the optimum asphalt content
Standard Test Procedures Manual
S
TP 204-10
Section
:
Subject
:
ASPHALT MIXES MARSHALL MIX DESIGN
Date: 1993 03 22 Page:
5 of 6
where air voids are 0.5 to 0.75% above the minimum specified value for that particular
asphalt type.
After selecting optimum asphalt from each graph average the values and use this new
asphalt content for further design requirements (Stripping Potential, Hveem stability,
Retained Stability, Asphalt Film Thickness).
4.
RESULTS AND CALCULATIONS
4.1.
Reporting Results
Marshall Mix Designs shall be reported on Form MR-71 or Form EPS-71 whichever is
applicable. Additional information on other options evaluated should be attached to the
formal design as an Appendix
St
