-K
E = K (D D ) 2 Eqn. 4.1
1 11 4
where
El = asphalt concrete modulus in ksi,
D D4 = difference in Dynaflect deflections in mils,
K, = intercept, and
K = slope or exponent.
Figures 4.17 and 4.18 show the variation of Ki and K2 with tl,
respectively, for different E2 values. The figures indicate that the
effect of E2 on the regression constants reduces significantly beyond t
values of 6.0 in. Equations were developed for each value of E2 using
curve fitting techniques to obtain the primary constants and coeffi-
cients. It was necessary in several instances to limit the applicable
range of t. to achieve reasonable prediction accuracy. The next step
was to combine some of the regression equations to cover the range of
E2. This process was found to be extremely complex and difficult.
The complexity of obtaining a combined equation for the various
values of El was resolved by developing equations to cover different
ranges in E2 and t1 values. This approach assumed a priori that these
parameters could be estimated for computation of El. Three equations
were developed to represent the range of parameters listed in Table 4.1,
with Equation 4.1 being the basic form. The KI and K2 equations for the
applicable range of parameters are presented below.