Nonlinearity, Heating, Fatigue and Thixotropy during Cyclic Loading of Asphalt Mixtures

This paper describes investigation into the change in complex modulus (norm and phase angle) during cyclic tests on bituminous mixtures. The change can be explained by four phenomena: nonlinearity, heating, thixotropy and fatigue. An experimental campaign has been performed at ENTPE laboratory in order to identify and quantify the first three phenomena. The analysis of the results reveals that the two reversible effects (heating and thixotropy) are very important and can not be ignored when interpreting fatigue tests. Nonlinearity, for the rather small strain level amplitudes considered in our experimental campaign (up to 122,mu m/m), is also shown to be reversible. Heating is due to the viscous dissipated energy that heats the specimen. At the beginning of the test, temperature increase in the sample is shown to be proportional with the total dissipated energy. Thixotropy effect is quantified. In addition, it is shown that thixotropy effect can be modeled using an equivalent temperature increase.