Characterization of Time-Dependent Changes in Strength and Stiffness of Florida Base Materials

摘要

Resilient modulus and Youngs 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 Youngs modulus and larger-strain resilient modulus response of unbound aggregate base coarse materials to various environmental conditions. The small-strain Youngs 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 Youngs 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 Youngs 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 Youngs 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.