develop methods that account fully for the variation of stiffness in HMA pavements with
vehicle speeds.
The concept behind the complex modulus test is to account not only for the
instantaneous elastic response, without delayed elastic effects, but also the accumulation
of cyclic creep and delayed elastic effects with the number of cycles. Hence, the
fundamental difference between the complex modulus test and the resilient modulus test
is that the complex modulus test does not allow time for any delayed elastic rebound
during the test.
The dynamic modulus (IE*|) relates the cyclic strain to cyclic stress in a sinusoidal
load test. The dynamic modulus test procedure outlined in ASTM D 3497 uses a
standard triaxial cell to apply stress or strain amplitudes to a material at 16 Hz, 4 Hz, and
1 Hz. It also recommends that the test be repeated at 50C, 250C, and 400C (ASTM D
3497). The dynamic modulus is calculated using Equation 2-1 (Yoder & Witczak, 1975).
E*| = o (Eq. 2-1)
go
Where
co is the stress amplitude,
So is the strain amplitude.
This parameter includes the rate dependent stiffness effects in the mixture.
However, it does not provide insight into the viscous components of the strain response.
The dynamic modulus test can be expanded on to find the complex modulus (E*). The
complex modulus is composed of a storage modulus (E') that describes the elastic
component and a loss modulus (E") that describes the viscous component. The storage
and the loss moduli can be determined by the measurement of the lag in the response