In order to study permanent strains in bituminous mixtures, the division SMIT of LCPC has developed a thermo-controlled triaxial testing device at constant confining pressure. An important work of testing development and verification on measurement has been carried out. The first experimental testing programme, consisting in creep tests at constant stress, has allowed to study the respective influences of the confining pressure, the deviatoric stress and the temperature on the behaviour of our bituminous mixture. These tests have also allowed to validate partially the time-temperature superposition principle in the non-linear field, under triaxial stress. An elasto-visco-plastic model has been developed in order to simulate creep tests under confining pressure. This model aims at reproducing our experimental observations. These results may be applicable for aeronautic and storage bituminous platforms. A second experimental testing programme, consisting in cyclic sinusoidal compression tests has been performed. During these tests, two scales of strains have been measured: strains about 10-4m/m, related to the viscoelastic behaviour of asphalt concretes, and strains about 10-2m/m related to the appearance of permanent strains in asphalt concretes. The respective influences of the confining pressure, the temperature and the frequency have also been studied in this programme. Noteworthy differences in the behaviour of our asphalt concrete during creep tests and cyclic tests have been observed.
Prediction of permanent strains of bitumous mixtures