TM 5-822-5/AFM 88-7, Chap. 1
APPENDIX B
DETERMINATION OF FLEXURAL STRENGTH AND MODULUS OF
ELASTICITY OF BITUMINOUS CONCRETE
B-1. Purpose. This appendix describes procedures
compaction until the paving mixture is compacted
for preparation and testing of bituminous concrete
to a 6- by 6-inch cross section. After compaction
to determine flexural strength and modulus of
and while the mixture is still hot, place a 6- by 21-
elasticity. The procedures are an adaptation of tests
inch steel plate on the surface of the paving mixture
conducted on portland cement concrete specimens.
and apply a leveling load of 2,000 pounds to the
plate for 30 minutes. Prepare six beam test
B-2. Applicable Standards. The standard applica-
specimens in the manner described.
ble to this procedure is ASTM C 78.
b. After cooling, remove the beams from the
molds and rotate 90 degrees so that the smooth,
B-3. Apparatus. Apparatuses required are a test-
parallel sides will become the top and bottom.
ing machine capable of applying repetitive loadings
Cement and L-shaped metal tab with quick-setting
for compaction of beam specimens 6 by 6 by 21
epoxy glue to each 6- by 21-inch side of the beams
inches to the design density (an Instron electro-
on the beams' neutral axes at midspan. The tabs
mechanical testing machine meets this requirement);
should be drilled for attachment of the LVDT's.
a steel mold, suitably reinforced to withstand
Cure and condition the beams at 75 + 5 degrees
compaction of specimens without distortion; two
Fahrenheit for 4 days prior to testing and record the
linear variable differential transformers (LVDT's); a
temperature.
5,000-pound load cell; an X-Y recorder; and a
testing machine for load applications conforming to
B-6. Test Procedure. Place the specimens in the
ASTM C 78 (a Baldwin or Tinius Olsen hydraulic
test machine as described in ASTM C 78. Place thin
testing machine is suitable for this purpose).
Teflon strips at the point of contact between the test
specimens and the load-applying and load-support
B-4. Materials. Sufficient aggregate and bitumen
blocks. While the beams are being prepared for
meeting applicable specifications to produce six 6-
testing, place an additional support block at
by 6- by 21-inch test specimens are required. In the
midspan to prevent premature sagging of the beams.
event the proportions of aggregate and bitumen,
Remove this support block immediately prior to the
bitumen content, and density of compacted speci-
initiation of load application. Mount the LVDT's on
mens are not known, additional materials will be
laboratory stands on each side of the beams, and
required to conduct conventional Marshall tests to
attach the LVDT's to the L-shaped tabs on the sides
develop the needed mix design data.
of the beams. Connect the LVDT's and load cell to
B-5. Sample Preparation.
the X-Y recorder. Make final adjustments and
a. Prepare in a laboratory mixer four portions of
checks on specimens and test equipment. Apply
paving mixture for one 6- by 6- by 21-inch beam
loading in accordance with ASTM C 78, omitting
test specimen consisting of aggregate and bitumen
the initial 1,000-pound load.
in the proportions indicated for optimum bitumen
content. The total quantity of paving mixture should
B-7. Calculations.
be such that when compacted to a uniform 6- by 6-
a.
The modulus of rupture R is calculated from
inch cross section, the density of the beam will be as
the following equation (from ASTM C 78)--
specified from previous laboratory mix design tests
or other sources. The temperature of the paving
R=PL/bd2
(eq B-1)
mixture at the time of mixing should be such that
where
subsequent compaction can be accomplished at 250
R = modulus of rupture, psi
+ 5 degrees Fahrenheit. Place two of the four
P = maximum applied load, pounds
portions in the 6- by 6- by 21-inch reinforced steel
L = span length, inches (18 inches)
mold and compact to a 3-inch thickness with a 6- by
b = average width of beam, inches
6-inch foot attached to the repetitive loading
d = average depth (height) of beam, inches
machine. Shift the mold between load applications
to distribute the compaction effort uniformly. Add
the following equation:
the remaining two portions and continue
B-1
Previous Page
