SHRP-A-379 traducir

3. SUMMARY OF METHOD
3.1 This test method consists of two types of tests: a tensile creep test and a tensile
strength test. The tensile strength test can be performed separately (for fatigue cracking
analyses) or in concert with the creep test (for thermal cracking analyses).
3.2 A static load of fixed magnitude is applied along the diametral axis of a
preconditioned specimen for a fixed duration of time, 1,000 seconds. The horizontal and
vertical deformations measured near the center of the specimen are used to calculate a tensile
compliance at a particular duration of time. Loads are selected to keep strains in the linear
viscoelastic range (typically below 300 microstrains). By measuring both horizontal and
vertical strains in regions where the stresses are relatively constant and away from the
localized non-linear effects induced by the steel loading strips, the Poisson's ratio can be
more accurately determined. The Poisson's ratio is then used to better predict threedimensional
stresses and strains.
3.3 The failure portion of the test immediately follows the creep portion. Without
releasing the creep load, a constant rate of vertical deformation (or ram movement) is applied
to the specimen to failure. The failure limits determined can be input into mechanistic-based
models for thermal cracking or used to compare relative qualities of mixtures. The failure
portion of the test method can be performed separately when only the tensile strength
properties are needed.
4. DEFINITIONS
4.1 Creep Compliance--The slow movement of asphalt concrete mixtures under a
sustained load per unit of the applied stress; time-dependent strain (continuing strain) with a
sustained stress level.
5. SIGNIFICANCE AND USE
5.1 The values of creep compliance can be used to evaluate the relative quality of
materials, as well as to generate input for pavement design and evaluation models. From
creep testing, these values include the intercept and straight line slope of log creepcompliance
versus log loading time, or the entire master-compliance curve. The test can be
used to study effects of temperature, load magnitude, binder content, and loading time.
5.2 When used in conjunction with other mixture physical properties, the creep
compliance may contribute to the overall mixture characterization. It is one factor for
determining a mixture's suitability for use as a highway paving material under given traffic
and environmental conditions.
5.3 Reheated, recompacted mixtures may be used in this method, but the resulting
creep compliance values will be higher than for newly prepared mixtures because of changes
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