Amplitude effect on stiffness of bitumen and bituminous mixes under dynamic conditions

Summary Details are given of tests carried out to measure the dynamic torsional stiffness (or modulus) or bitumen and bituminous mixes at various amplitudes of applied strain.The results show that there is a decrease in stiffness with increasing strain amplitude but the rate of decrease diminishes with increasing amplitude until a minimum value is reached, after which the stiffness remains constant with further increase in amplitude. The magnitude of the strain amplitude at which the stiffness becomes a minimum increases with decreasing stiffness (i. e., dependent on temperature and aggregate content). These measurements indicate the non-linearity of the material under certain conditions.