VISCOELASTIC PROPERTIES OF BITUMINOUS MIXTURES

VISCOELASTIC PROPERTIES OF BITUMINOUS MIXTURES ARE INVESTIGATED THROUGH CREEP AND DYNAMIC TESTS. IN CREEP TESTS A CYLINDRICAL SPECIMEN IS SUBMITTED TO TENSILE OR SHEAR STRESSES AND THE DEFORMATION OF THE SPECIMEN IS RECORDED BY ELECTRONIC DEVICES PREVIOUSLY CALIBRATED. IN DYNAMIC TESTS TWO TYPES OF VIBRATIONS ARE USED' /1/ TRANSVERSAL VIBRATIONS IN WHICH A CANTILEVER BEAM IS SUBMITTED ON ITS HEAD TO A SINUSOIDAL LOAD, AND /2/ LONGITUDINAL VIBRATIONS IN WHICH A CYLINDRICAL SPECIMEN IS SUBMITTED TO AXIAL SINUSOIDAL LOAD. IT IS FOUND THAT BITUMINOUS MIXTURES BEHAVE LINEARLY FOR SMALL DEFORMATIONS, IN THE RANGE OF LINEAR BEHAVIOR BITUMINOUS MIXES ARE THERMORHEOLOGICALLY SIMPLE. MASTER CURVES HAVE BEEN ESTABLISHED FOR CREEP AND MODULUS FUNCTIONS WITH A SHIFTING FACTOR FOLLOWING THE W.L.F. EQUATION. THE RELAXATION DISTRIBUTION SPECTRUM IS CONSISTENT WITH ROUSES THEORY. A RHEOLOGICAL MODEL AND ANALYTICAL EQUATIONS ARE PROPOSED TO REPRESENT THE VISCOELASTIC PROPERTIES OF BITUMINOUS CONCRETE IN CREEP AND DYNAMIC TESTS IN THE RANGE OF LINEAR BEHAVIOR. REDUCED CURVES DETERMINED FOR SEVERAL BITUMINOUS MIXTURES ARE PROPOSED TO REPRESENT MODULUS, CREEP AND RELAXATION V.S. FREQUENCY OR TIME OF FRESHLY LAID BITUMINOUS CONCRETE. THEREFORE VISCOELASTIC PROPERTIES OF BITUMINOUS MIXES COULD BE DESCRIBED THROUGH: THE INSTANTANEOUS MODULUS /FUNCTION OF VOID CONTENT AND TYPE OF BITUMEN/ AND ITS THERMAL SUSCEPTIBILITY DEFINED BY THE SHIFTING FACTOR. FINALLY IN SITU MEASUREMENTS ARE COMPARED WITH THOSE OF LABORATORY TESTS AND IT WAS FOUND THAT IT IS POSSIBLE TO PREDICT THE PERFORMANCE IN SITU FROM LABORATORY EXPERIMENTS.