Laboratory determination of resilient modulus of granular materials for flexible pavement design

Existing laboratory test procedures used to characterize pavement materials are complex, ambiguous, and vary in approach. The triaxial repeated load resilient modulus test when properly performed offers a reasonably reliable laboratory alternative for characterizing pavement materials. The main objective of this study was to develop a prototype resilient modulus test and to evaluate important experimental factors. Synthetic specimens were used for equipment calibration. Four different materials ranging from clean crushed granular material to gravels with a high soil content were tested. Additional validation testing, was performed on granular material, and stabilized materials as well as different SHRP materials. Several experiments were performed during the resilient modulus testing program. The effect of preconditioning, loading pulse shapes, and the effect of using a scalped and replaced gradation was studied. A quasi-static test was also investigated to determine if it gives similar results to the regular haversine repeated loading triaxial test. The data obtained in the general study was used to determine experimental error, variability, reliability, and repeatability of the experimental procedure. Comparisons were made of the reproductibility and variability of results obtained using LVDTs mounted on clamps, LVDTs extending from the top to bottom, and externally mounted LVDTs. Several resilient modulus models were fitted with the experimental data to determine the one giving best fit. The statistical analyses of the results suggest improvements in the testing procedures and testing equipment, making a more efficient and accurate test. A series of validation tests were performed to determine the improvement in the experimental results when applying the suggested changes in procedure and equipment. Recommendations to the existing resilient modulus test standards are suggested including modifications to the testing systems data acquisition and data reduction procedures.