Impact of Moisture Content and Density on Stiffness-Based Acceptance of Geomaterials

Modulus-based quality management of compacted layers has been considered by a number of highway agencies. Although simple in concept, the paradigm shift from density to modulus has generated some technical challenges. For a given density, for example, the modulus can vary, depending on the moisture content at the time of compaction and at the time of testing. The results of a systematic laboratory study to qualify and to quantify the effect of compaction moisture content, moisture content at the time of testing, and density on the modulus of four diverse geo-materials are reported. For specimens compacted to maximum dry density but with a 2% to 3% variation in compaction moisture content, the changes in modulus at the time of testing can vary by a factor of two or more, depending on the index properties of the material. These changes are exaggerated as the time between compaction and testing increases. Specifying densities less than maximum dry densities has a significant impact on the modulus of the material at the time of testing. Although the findings of this study have been only marginally validated in the field, some preliminary recommendations are provided for consideration in modulus-based specifications.