30 June 2001
direction, forcing the beam to return to its original horizontal position and holding it at that position
during the rest period. Adjustable stop nuts installed on the flexure apparatus loading rod prevent
the beam from bending below the initial horizontal position during the rest period.
(2) The dynamic deflection of the beam's center is measured with an LVDT. An LVDT
suitable for this purpose is the Sheavitz type 100 M-L. The LVDT core is attached to a nut bonded
with epoxy cement to the center of the specimen. Outputs of the LVDT and the electrohydraulic
testing machine's load cell, through which loads are applied and controlled, can be fed to any
suitable recorder. The repeated flexure apparatus is enclosed in a controlled-temperature cabinet
capable of controlling temperatures within 0.28 degrees Celsius (2 degree Fahrenheit). A
Missimer's model 100 by 500 carbon dioxide plug-in temperature conditioner has been found to
provide suitable temperature control.
d. Specimen Preparation. Beam specimens 380 millimeters (15 inches) long with 59-
millimeter (3-1/2-inch) depths and 83 millimeter (3-1/4-inch) widths are prepared according to
ASTM D 3202. If there is undue movement of the mixture under the compactor foot during beam
compaction, the temperature, foot pressure, and number of tamping blows should be reduced.
Similar modifications to compaction procedures should be made if specimens with less density are
desired. A diamond-blade masonry saw is used to cut 76-millimeter (3-inch) or slightly less deep
by 76 millimeters (3-inch) or slightly less wide test specimens from the 380-millimeter- (15-inch-)
long beams. Specimens with suitable dimensions can also be cut from pavement samples. The
widths and depths of the specimens are measured to the nearest 0.25 millimeter (0.01 inch) at the
center and at 51 millimeters (2 inches) from both sides of the center. Mean values are determined
and used for subsequent calculations.
e. Test Procedures.
(1) Repeated flexure apparatus loading clamps are adjusted to the same level as the
reaction clamps. The specimen is clamped in the fixture using a jig to position the centers of the
two loading clamps 51 millimeters (2 inches) from the beam center and to position the centers of
the two reactions clamps 165 millimeters (6-1/2 inches) from the beam center. Double layers of
Teflon sheets are placed between the specimen and the loading clamps to reduce friction and
longitudinal restraint caused by the clamps.
(2) After the beam has reached the desired test temperature, repeated loads are applied.
Duration of a load repetition is 0.1 second with 0.4-second rest periods between loads. The
applied load should be that which produces an extreme fiber stress level suitable for flexural fatigue
tests. For fatigue tests on typical bituminous concrete paving mixtures, the following ranges of
extreme fiber stress levels are suggested:
Temperatures, degrees Celsius
Stress Level Range
1.03 to 3.1 (150 to 450)
0.52 to 2.1 (75 to 300)
0.24 to 1.38 (35 to 200)