120
Equations 4.1 through 4.3 are applicable in this range. Therefore,
these equations were used to compute Ex values for asphalt concrete
thicknesses of 3.0, 4.5, and 6.0 in. Predictions were generally very
good and within +10 percent of the actual Ej value when the true value
of E2 was used. In general, the majority of the predicted E values
were within +5 percent, with the maximum error being +22.5 percent.
Pavements with Ex predictions above +10 percent are listed in Table
4.5. It can be seen from the table that these were very few considering
the size of the data set analyzed. Correlation between predicted and
actual E: values resulted in the following:
Ej (Predicted) = 9.988 + 0.933E1 (Actual) Eqn. 4.30
(N = 58, R2 = 0.992)
Attempts to predict outside of the designated thickness range
resulted in errors up to 70 percent. Thus, it is imperative that the E
prediction equations for Case 1 be used for the specified range.
Case 2: 32.0 < E < 85.0 ksi; and 2.0 < t < 6.0 in.
2 l
E: is predicted from Equations 4.1, 4.4, and 4.5. Comparisons between
predicted and actual E1 values indicated that errors up to 90 percent
could be obtained with the use of these equations. The higher errors
occurred in pavements with extreme values of E^ (0.35 and 200 ksi).
When these pavements were deleted, predictive errors were generally
within the range of +20 percent, with a few cases going as high
as +30 percent.