United States Department of Transportation
i
Characterization of time-dependent changes in strength and stiffness of Florida base materials : final report, October 2008.
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2008-10-01
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[PDF-17.85 MB]
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Edition:Final report.
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Abstract:Resilient modulus and Young’s modulus are parameters increasingly used to fundamentally characterize the behavior
of pavement materials both in the laboratory and in the field. This study documents the small-strain Young’s modulus
and larger-strain resilient modulus response of unbound aggregate base coarse materials to various environmental
conditions. The small-strain Young’s modulus experiments were conducted on laboratory compacted materials and
field core materials by the authors. The State Material Office conducted the resilient modulus experiments on
laboratory compacted materials. The results of both tests are presented in this study. It is shown that the small-strain
Young’s modulus is not constant, even when held at constant moisture, and that significant changes in modulus will
occur with drying and wetting of the material. The response to drying and wetting cycles appears to be repeatable, and
suggests that the underlying mechanism that controls the response is reversible. It is also shown that the larger-strain
resilient modulus demonstrated similar trends with small-strain Young’s modulus, but the rate of change and
magnitude of the effect are different between materials. The material response to drying and wetting cycles appears to
be reasonably repeatable. Comparison of both experiments revealed that the change in Young’s modulus with drying is
much more dramatic than the resilient modulus, indicating that the drying effect is significantly reduced with higher
strain. Lastly, the evidence suggests that these changes can be explained by the science of unsaturated soil mechanics:
changes in moisture or moisture distribution results in changes in internal pore pressure, which affect the effective
confining pressure constraining the material. The influence of this phenomenon is observed but is not as dramatic at
higher strain. Based upon these results it appears that a pavement design process based on resilient modulus for the
base material should account for changes in moisture content anticipated in the base during the life of the pavement
structure. The authors are aware that a procedure for the effects of moisture changes and other seasonal effects on the
resilient modulus of the base material has been implemented in the new Mechanistic-Empirical (M-E) Pavement
Design Guide. It is thus recommended that this procedure be utilized in conjunction with the findings reported herein
to design pavements in Florida.
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