71
37.6 0.78114 2 0.96
10
*
10
E* = × G R =
Hz Hz
( 6.7)
79.28 ( ) 0.71735 2 0.93
10
" "
E10Hz = × G Hz R = ( 6.8)
where,
| E*|, | G*| = axial and shear dynamic stiffness, respectively; and
E", G" = axial and shear loss- stiffness, respectively.
The use of equations 6.7 and 6.8 will be elaborated in the following section.
6.6 Shear frequency sweep test for field cores
In the previous section, a relationship between axial stiffness and shear stiffness
was presented. This relationship presents a useful tool for forensic analysis of pavement
sections.
For mechanistic analysis, it is required to evaluate the axial stiffness in laboratory,
or to estimate it using models. However, laboratory evaluation of axial stiffness for field
sample is often a difficult task, especially for pavement sections with thin layers. An
alternate method is to obtain field cores that are tested in shear mode- of- loading to
evaluate the shear stiffness | G*|. Once the shear stiffness of a mix is known, the axial
stiffness can be estimated using equations 6.7 and 6.8. Then, the procedure outlined in
chapter 7 can be used for mechanistic analysis and for determining the fatigue resistance
of pavement section under consideration.
In this study, 6 in. diameter field cores were obtained to conduct shear frequency
sweep test. From each field core, a 2 inch high specimen was obtained for both SP 12.5-
mm and SP 19- mm mixes. Tests were conducted at 15, 20 and 25 ° C. Four specimens
were tested for each mix, and the data are presented in Appendix F. The average air void
content for these mixes varied between 7.5 to 8.1- percent for both mixes.