Creep-Compliance Test

To predict the blister response accurately, proper characterization of the MA is needed. The viscoelastic properties of MA are measured using either simple

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FIG. 4—Scheme of a material characterization for the finite-element model.

creep tests (time domain) or complex modulus tests (frequency domain). In this study, time domain IDT results are used to describe the viscoelastic properties of the material in ABAQUS. In case of IDTs, a static constant load was applied along the vertical diametrical axis of a temperature-controlled cylindrical speci­men for a specified period of time (100 or 1000 s), while measuring the horizon­tal deformation. The load was controlled such that the upper linear-elastic limit of the specimen, typically 100-500 istr, was not exceeded (see Ref 14).

In this report, the dimensions of the indirect tensile specimens were 100 mm in diameter and 49.8 mm in height. These specimens were cored from MA slabs. Each specimen was tested at 5 °C, 15 °C, and 25 °C temperatures. A load was applied to cause a horizontal strain in the order of 100 istr, so that the electric noise during data acquisition process became insignificant. During the loading period, horizontal deformations were measured on both sides of the specimens using four extensometers.

Different theoretical assumptions are commonly used for evaluating IDT results: homogeneity, isotropy, Poisson’s ratio, coefficient of thermal contrac­tion, and the estimation of relaxation modulus from the creep compliance are important issues in the IDT analysis [15].

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Huang [16] suggested that the Poisson’s ratio for most asphalt-mixture ranges between 0.3 and 0.4. It is stated that it can be appropriate to assume the Poisson’s ratio value rather than determining it from actual tests because the effect of Poisson’s ratio is not significant. Hence, for simplicity, Poisson’s ratio is often assumed to be time independent in spite of the fact that this is not the case in reality [17].