equations for computing pavement layer moduli may be considered to be

very sensitive to small changes in FWD deflections.


 6.4 Estimation of E from Asphalt Rheology Data

 The predicted asphalt concrete modulus, E listed in Tables 6.3

 and 6.4 were noted to be unusually high, considering the test tempera-

 tures, for most of the test pavement sections. The equations used to

 compute these E1 values had a high degree of prediction accuracy from

 their R2 values. For example, Equation 4.20, used for most of the FWD

 predictions, had an R2 value of 0.993. The compatibility of the predic-

 tion equations to the field measured NOT deflections is discussed in

 this and subsequent sections.

 As discussed previously, the resilient characteristics of asphalt

 concrete materials are generally dependent on both temperature and rate

 of loading. The modulus of asphalt concrete pavements are usually

 determined from indirect tensile tests (8) using either laboratory-

 prepared specimens or cored specimens from in-service pavements. An

 indirect method which uses low-temperature rheology tests and previously

 established correlations by Ruth et al. (98) has been found to effec-

 tively predict asphalt concrete modulus, El (96,97,117).

 Asphalt cement samples recovered from the cores taken during NDT

tests were tested to establish their viscosity-temperature relation-

ships. The results of the low-temperature rheology tests performed at

different temperatures are listed in Appendix E. The resulting regres-

sion equations are also shown in Table 5.4. Using the mean pavement

temperature recorded at the time of NOT tests, the corresponding E1

value was calculated using the procedures described by Tia and Ruth