Page 419 - Mechanics of Asphalt Microstructure and Micromechanics

Characterization and Modeling Anisotropic Proper ties of Asphalt Concrete 411

compressive modulus nor a tensile modulus. More sophisticated analysis is necessary
for interpreting the stress and strain distribution and evaluating the modulus in ten-
sion and compression in the IDT configuration.
Most previous research has measured the moduli in tension and compression by
applying tensile and compressive loads on different sets of asphalt mixture specimens
and investigated the bimodularity by comparing the mean values from these sets. Con-
sidering the limited accuracy for dynamic modulus tests (Table 2 of AASHTO TP62),
and the difficulty in conducting a dynamic modulus test in tension, a more convenient
testing procedure is necessary. It is advantageous to develop an experiment measuring
both moduli from the same specimen and at the same time to minimize experimental
efforts and effects induced due to the use of different samples. This section describes a
study on determining the moduli in tension and compression from a simply supported
asphalt mixture beam.

12.7.1 Testing Setup and Procedure
Li and Wang (2008) developed a testing procedure to use the four-point beam fatigue
test on asphalt mixtures (AASHTO T321) for the simultaneous determination of the
tensile and compressive moduli of asphalt materials (Figure 12.14a). The beam is 381
mm (15 in) long (L), 50.4 mm (2 in) wide (w), and 63.5 mm (2.5 in) high (h) (Figure

FIGURE 12.14 Testing
setup.

(a)

L
V
Load Load
D
T

380 mm 63 mm 50 mm Specimen

Deflection

Return to
Reaction Reaction
Original
(b) Position