layers, respectively. In Table 6.16, the modulus of the asphalt con-

crete determined from rheology test data (Table 6.5) are also listed for

comparison purposes. The table shows favorable agreement between the

NDT moduli and the indirect method of using low-temperature viscosity

relationship. Slight differences occur at SR 26B in which the rheology

moduli prediction was reduced by about 12 percent in tuning the NDT

deflection basins. In some test sections where there were differences,

it was found that the Dynaflect moduli matched the rheology value while

the FWD required some adjustment in the El or vice versa. These always

occurred with pavements tested at higher temperatures (900F or more).

It is generally believed that the indirect method of estimating El works

best at mean pavement temperatures less than 80F or where E is greater

than 100 ksi.

 The NDT El values listed in Table 6.16 were correlated to the

 respective mean pavement temperatures to establish a simple and rapid

 method of estimating El values for routine applications. The resulting

 relationship is shown in Figure 6.64. The asphalt concrete modulus, El,

 of pavements with no visible cracks can be determined from the mean

 pavement temperature, T, using the following equation


 Log E, = 6.4147 0.0148 T Eqn. 6.3


 In Equation 6.3, El is in psi, and T is in OF, as illustrated in Figure

 6.64. The relationship for considerable cracking in Figure 6.64 can be

 used when pavement cracks are spaced sufficiently to eliminate their

 influence on the NDT deflections. This would apply to pavement sections

 that have uncracked segments within cracked segments. However, if the