Evaluation of Moisture Sensitivity of Bituminous Mixtures by a Complex Modulus Approach

Various laboratory tests are used to evaluate the moisture sensitivity of bituminous mixtures. However, most of them are destructive and require a large number of specimens. Consequently, they do not permit continuous monitoring of the deterioration in mechanical performance, much less measurement of the recovery of this performance, as water evaporates during the drying process. Monitoring of the stiffness modulus could provide a clearer picture of the process of deterioration and recovery that occurs during an immersion-drying cycle. However, during the specimen immersion phases, bitumen ages and hardens, and its stiffness modulus increases. Thus, the action of water simultaneously produces deterioration in the bitumen-aggregate bond and hardening of the binder; these two processes lead to opposing responses and prevent making a clear appraisal of the bituminous mixture's ability to withstand the action of water. Evaluating the mechanical characteristics of bituminous mixtures with a Cole—Cole plot or in black space provides new possibilities for isolating the effect of water at the bitumen-aggregate interface from the effect of the binder.