VISCOELASTIC RESPONSE OF ASPHALTS IN THE VICINITY OF THE GLASS TRANSITION POINT

AN INVESTIGATION IS REPORTED WHICH WAS MADE OF THE EFFECT OF A LOW TEMPERATURE ENVIRONMENT UNDER VISCOELASTIC RESPONSE OF ASPHALT CEMENTS. THE VISCOELASTIC RESPONSE TO STRESS OF FOUR DIFFERENT ASPHALT CEMENTS WAS STUDIED AT DIFFERENT TEMPERATURES FROM 16 F TO 41 F. SPECIMENS OF A CYLINDRICAL SHAPE 2.81 X 1.35 INCHES OF ASPHALT CEMENTS WERE SUBJECTED TO CONSTANT STRESS LEVELS AND STRAIN-TIME DATA WERE COLLECTED AT TEMPERATURES OF 16 F, 25 F, 32 F, AND 41 F. THE CREEP DATA WERE ANALYZED TO OBTAIN VISCOELASTIC PARAMETERS DESCRIBING THE DEFORMATION MECHANISM OF THESE MATERIALS. BY EMPLOYING THE FOURIER TRANSFORMATION, THE DYNAMIC RESPONSE OF THESE MATERIALS AT THE ABOVE TEST TEMPERATURES AND OVER A WIDE RANGE OF FREQUENCIES WERE OBTAINED. IT IS CONCLUDED THAT THE CREEP RESPONSE OF THE ASPHALT STUDIED AS A FIRST APPROXIMATION CAN BE REPRESENTED BY MAXWELL ELEMENT (SPRING AND DASHPOT IN SERIES) AND TWO KELVIN ELEMENTS (SPRING AND DASHPOT IN PARALLEL) BETWEEN THE COMPONENTS OF THE MAXWELL ELEMENT. THIS MODEL IS ALSO CALLED ONE KIND OF BURGER MODEL. SOME INSTANTANEOUS ELASTIC DEFORMATION WAS EXHIBITED BY THE ASPHALT WHICH IS REPRESENTED BY THE SPRING IN THE MAXWELL ELEMENT AT EXTREMELY LOW TEMPERATURES SUCH AS 16 F. AT THE HIGHER TEMPERATURES OF 25 F, 32 F, AND 41 F, NO INSTANTANEOUS ELASTIC DEFORMATION WAS OBSERVED IN THE CREEP RESPONSE. THE DYNAMIC RESPONSE OF ASPHALTS STUDIED SUCH AS THE COMPLEX ELASTIC MODULUD, STORAGE MODULUD, LOSS MODULUS AND THE PHASE ANGLE BETWEEN STRESS AND STRAIN ARE CONSIDERABLY AFFECTED BY TEMPERATURE AND FREQUENCY. IN THE LOW FREQUENCY RANGE, DASHPOT OF THE MAXWELL ELEMENT CONTROLS THE DYNAMIC RESPONSE, WHEREAS AT HIGHER FREQUENCIES THE ELASTIC MODULUS OF THE SPRING IN THE MAXWELL ELEMENT IS OF GREAT SIGNIFICANCE.