the numerical evaluation of stresses, strains, and displacements in a
linear elastic system. He demonstrated that predicted vertical, radial,
and shear stress distribution were noticeably affected by slight changes
in the assumed material moduli. Pichumani's work demonstrated the need
for proper and extensive material characterization.
2.3 Material Characterization Methods
2.3.1 General
The use of multilayered elastic theory has provided the engineer
with a rational and powerful basis for the structural design of pave-
ments, for pavement evaluation, and for overlay design. In this theory,
the complete stress, strain, and displacement pattern for a material
needs only two material properties for characterization, namely the
elastic modulus (E), and the Poisson's ratio (u). Generally, the effect
of Poisson's ratio is not as significant as the effect of the modulus
(133, pp. 280-282; 88; 59, p. 160). Thus, E is an important input
parameter for pavement analysis using the layer theory.
Many tests have been devised for measuring the elastic modulus of
paving materials. Some of the tests are arbitrary in the sense that
their usefulness lies in the correlation of their results with field
performance. To obtain reproducible results, the procedures must be
followed at all times. The various possible methods for determining the
elastic modulus of pavement materials include laboratory tests, destruc-
tive field tests, and in situ nondestructive tests.
Laboratory methods consist of conducting laboratory testing on
either laboratory-compacted specimens or undisturbed samples taken from
the pavement. Yoder and Witzcak (133) describe various laboratory