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computations, because the AC thickness generally exceeded 3.0 in. for
most of the test pavements. Equation 4.19 was used for the SR 24 test
site, while Equation 4.18 was used in the case of SR 12. The base
course modulus, E2, was computed from Equation 4.21, since Equation
4.22, which was more generalized than Equation 4.21, could not be used
because no D0 measurements were made during the FWD data collection. E
was calculated from Equation 4.24. This equation was considered to be
simplified enough and more generalized than Equation 4.23. Equations
4.25, 4.26, and 4.28 were used to make E4 computations. Equations 4.27
and 4.29 could not be used because measurements of D0 were not made
during FWD testing.
Table 6.4 lists the results of layer moduli predictions from the
FWD prediction equations. The asphalt concrete modulus, E seems to be
very high for most of the test sections. High Ex values are generally
typical of pavements tested under cold temperature conditions and/or
composed of very hard or brittle asphalt cements. The reliability or
accuracy of the FWD predicted Ex values, and that of the Dynaflect, are
compared in the next section with that determined from the rheology
tests.
The predicted E2 and E3 values seem to be of the order of magnitude
expected in practice, with the possible exception of SR 26C and SR 715.
For the latter, the high thickness of the base course layer (24.0 in.)
might have caused the peculiar predictions of E2 and E3. There were
also five test sections (SR 24, SR 15B, SR 715, SR 12, and SR 15C) in
which the predicted E2 values were lower than that of E3. Also SR 26C,
I-10A, US 301 and SR 15C test sections predicted considerably low E3
values. Unless the subbase layer of these pavements had failed, such