This paper addresses the impact of particle characteristics on the mechanical behavior of two fine cement kiln dusts (CKD): one freshly generated and one landfilled. While the two materials present similar particle size distribution, differences are observed in the shape and the morphology of the particles. SEM images of the landfilled CKD show evidence of chemical alteration arising from the long term exposure to the environment, and nitrogen adsorption measurements indicate a specific surface area significantly greater than that of the fresh material. The paper highlights how these differences in the CKD particles affect the compaction, one dimensional compression and shear behavior of the two powders.