30 June 2001
modulus is computed from the load-deflection curves. The modulus used should be the average
obtained for the three loadings. For bituminous-stabilized materials, the definition of an ultimate load will
be dependent on the rate of application of load and the temperature. Several loads should be selected
that will result in stresses in the outer fibers of the beam, which are less than the values shown in
Table 19-1. One test should be conducted at about 0.34 MPa (50 psi).
Recommended Maximum Stress Levels to Test Bituminous-Stabilized Materials
Maximum Stress Level in
Extreme Fibers, MPa (psi)
(b) An indirect method of obtaining an estimated modulus value for bituminous concrete is
presented in detail in Appendix C. The use of this method requires that the ring-and-ball softening point
and the penetration of the bitumen as well as the volume concentration of the aggregate and percent air
voids of the compacted mixture be determined.
(c) No procedures are provided for determining Poisson's ratio of bound base material. It
is recommended that the values in Table 19-2 be used.
Poisson's Ratio Values for Bound Base Material
0.5 for E < 3,447 MPa (500,000 psi)
0.3 for E > 3,447 MPa (500,000 psi)
c. Unbound (Granular) Bases (Subbases).
(1) General. Unbound granular materials are extremely difficult to characterize. The state of
stress, particularly the confining stress, is the dominating factor in determining load-deformation
properties. Repeated loadings also affect the modulus of granular materials. The general pattern noted
was that repeated loadings increased the stiffness provided shear failure was not progressing. This
implies that the modulus of elasticity is increased.