On the analysis of uniaxial cyclic strain sweep test results to bituminous binders: stiffness-phase angle curve

This paper discusses the analysis of uniaxial tension–compression cyclic strain sweep test results for the characterisation of bituminous materials. The test results of one bitumen and two mastics, at different oxidative ageing levels, at three different temperatures are used in the study. The damage mechanisms leading to failure were shown to vary with the temperature, and the transition from slow to fast damage accumulation could be clearly seen in the evolution plots of different mechanical variables with loading cycles. It was shown that the plot of test results in the Black diagram provides an excellent viewpoint for the damage and non-damage related mechanisms affecting the material’s response to increasing loading amplitude. Before significant damage has accumulated in the specimen, the stiffness modulus-phase angle curve, at different temperatures, follows very closely the linear viscoelastic curve of the undamaged material, and heating was identified as the most important reversible mechanism. The thixotropic effect was clearly observed in mastics. The curve shape during fast progression to failure was related to the level of deformation around the crack zone. The slope of the stiffness modulus-phase angle curve was found to provide a consistent indicator of the material’s resistance to cumulative loading, as it is sensitive to the material’s ageing state and the test temperature, and a unique relationship between this factor and the number of cycles to failure was found for all materials and test conditions.