99
-K
E = K (D D ) 2 Eqn. 4.1
1114
where
Ex = asphalt concrete modulus in ksi,
Di ~ 4 = d1fference in Dynaflect deflections in mils,
Kl = intercept, and
K2 = slope or exponent.
Figures 4.17 and 4.18 show the variation of Kx and K2 with t ,
respectively, for different E2 values. The figures indicate that the
effect of E2 on the regression constants reduces significantly beyond t1
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 tl 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 Ex 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 E1. Three equations
were developed to represent the range of parameters listed in Table 4.1,
with Equation 4.1 being the basic form. The K2 and K2 equations for the
applicable range of parameters are presented below.