UFC 3-260-02

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).

Temperature

Maximum Stress Level in

Range, EC(EF)

Extreme Fibers, MPa (psi)

4.4-15.5 (40-60)

3.1 (450)

15.5-27 (60-80)

2.1 (300)

27-38 (80-100)

1.4 (200)

(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.

Material

Poisson's Ratio

Bituminous-stabilized

0.5 for E < 3,447 MPa (500,000 psi)

0.3 for E > 3,447 MPa (500,000 psi)

Chemically stabilized

0.2

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.

19-4

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