General overview of the time-temperature superposition principle validity for materials containing bituminous binder
International Journal of Roads and Airports
Mechanical behavior of bituminous mixtures is very complex. It is also characterized by great thermal sensitivity. In the small strain domain (for strain amplitudes below approximately 10 -4 for mixes and 10 -2 for bitumens) the behavior can be considered as linear, therefore Linear Viscoelastic (LVE) theory can be applied. In addition, Time-Temperature Superposition Principle (TTSP) is verified with a good approximation. In this paper, an overview of TTSP for bituminous materials is given,
... rials is given, both in uni-dimensional and three-dimensional conditions. Thermomechanical behavior is totally characterized by complex modulus and Poisson's ratio master curves of the material, considered as isotropic, at an arbitrary reference temperature. Translation of values over the frequency axis is performed by means of a set of shift factors, depending only on temperature. Test results for very different types of bituminous materials (neat binder, polymer modified binder and mixes, mixtures with ultrafine particles, recycled materials, cementbased mixtures added with recycled asphalt materials) are presented. Williams-Landel-Ferry (WLF) law adequately fits the obtained shift factor values. Shift factors for materials produced from the same binder are shown to be extremely close and they can be considered as identical as a first approximation. This proves that time-temperature dependency of bituminous materials is driven uniquely by the bitumen component, regardless of the aggregate fraction. In a second step, experiments in the non linear domain (considering strains up to some percents) allow to show the validity of TTSP in the non linear domain. A relationship proposed by ENTPE (called "ENTPE transformation") between mix and binder behavior, respecting TTSP, is described. Based on this relationship, it is shown that normalized Black (or Cole-Cole) curves for materials containing the same bitumen (even in small quantities) are very close and can be considered as superimposing.