EVIDENCE OF A HARD SOFT RELAXATION IN A P OLYMER-MODIFIED BITUMEN/

A micromechanical relaxation is observed in a heterogeneous Polymer Mo dified Bitumen (PMB). This relaxation, theoritically studied by Frohli ch and Sack, arises when a microscopic elastic deformation develops in dispersed phase particles. Thus, two reinforcement domains are highli ghted when the material is sheared under a low-strain dynamic mechanic al deformation: at low frequency, the polymer-rich dispersed particles are harder than the matrix and behave as hard spheres (undeformable i nclusions). At high frequencies, they are soft (deformable), causing a subsequent decrease in the modulus of the PMB. The hard/soft relaxati on results in a minimum of phase angle versus frequency.