Impact of moisture content and density on strength and stiffness

Modulus-based quality management of compacted layers has been considered by a number of highway agencies. Even though simple in concept, the paradigm shift from density to modulus for quality acceptance has generated some technical and institutional challenges. One of these complications is that for a given density, the modulus can vastly vary depending on the moisture content at the time of compaction and at the time of acceptance. The results of a systematic study carried out to qualify and quantify the impact of compaction moisture content, moisture content at the time of field testing and density on the modulus and strength of four diverse geomaterials. It was found that for specimens compacted to the maximum dry density but with 2 to 3% variation in compaction moisture contents, the changes in modulus at the time of acceptance can vary by a factor of five or more depending on the index properties of a given material. These changes are further exaggerated as the time between the compaction and field acceptance increases. Also specifying densities less than maximum dry densities have significant impact on the modulus of the material at the time of acceptance. These issues should be incorporated in the modulus-based specifications to maximize the potential for the shift from the less desirable density-based acceptance to more sound modulus-based approach