Pavement base unbound granular materials gradation optimization

Unbound base granular materials must provide adequate bearing capacity to ensure good pavement performance, but they should also have the ability to keep their structural integrity through seasons. The latter is greatly marked by the influence of water on the modulus and through freeze/thaw cycles, emphasizing the importance of drainage capacity. A laboratory study is realized in order to determine the gradation influence on the mechanical behavior and the environmental sensitivity of three typical unbound granular materials. The study allowed the identification of several directly or indirectly related gradation variables closely linked to the studied performance parameters. It was possible to link the environmental sensitivity to one variable related to fine particles content and volumetric influence. Using guidelines on load and environment contributions on the deterioration of typical pavement structures, it was possible to define zones within the grading envelope which ensure optimized behavior.