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