Cédric Sauzéat

Linear viscoelastic behaviour of bituminous materials: From binders to mixes

ABSTRACT A large experimental campaign on the characterization of the linear viscoelastic behaviour of different bituminous materials was carried out. The goal was to establish the links between the linear viscoelastic properties (which are observed in the small strain domain) of binders and those of bituminous mixes. The linear viscoelastic behaviour of bituminous binders and mixes was studied by performing complex modulus tests at different temperatures and frequencies. A unique rheological model (called “2S2P1D model”) was developed for the modelling of linear viscoelastic properties of both bituminous binders and mixes. This model consists of a generalization of the Huet-Sayegh analogical model. Analyses on test data for five binders and different mastic and mix composition, show that the introduced model fits quite well the measurements. Finally, from our first results, a transformation that is independent of the introduced model allows the mix complex modulus to be predicted easily and efficiently from the binder complex modulus.

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

ABSTRACT 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 μm/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.

From the Behavior of Constituent Materials to the Calculation and Design of Orthotropic Bridge Structures

ABSTRACT A new approach is proposed to determine the global response of an orthotropic bridge structure from the behavior of the constituent materials that are binders, aggregates and steel. Experimental results and modeling using constitutive models (2S2P1D and DBN) developed by ENTPE team are presented for the bituminous materials in the linear domain. From these results, a transformation that is independent of the introduced models allows the bituminous mix complex modulus to be predicted from the bitumen complex modulus. Then, the response of a 3D orthotropic steel deck bridge subjected to moving wheel loads is presented using numerical Finite Element Method (FEM). The influence of temperature and viscous behavior of surfacing layers on the structure response such as deflection and longitudinal stress are emphasized.

Time Temperature Superposition Principle Validation for Bituminous Mixes in the Linear and Nonlinear Domains

AbstractThe mechanical behavior of bituminous mixes is very complex. It is also characterized by great thermal sensitivity. In the small strain domain (for strain amplitudes below approximately 10−4), it can be considered to be linear, therefore the linear viscoelasticity theory can be applied. In addition, the time temperature superposition principle (TTSP) may be assumed, with a good approximation. This has been widely verified regarding the unidimensional behavior of bituminous mixes in the viscoelastic linear domain. This paper provides an overview of TTSP for bituminous materials, and three-dimensional (3D) behavior and nonlinear domain are also considered. The 3D behavior is characterized by measurements of the complex modulus and complex Poisson’s ratio. For both parameters, master curves are plotted to check the validity of TTSP in 3D. Some experiments in the nonlinear domain (considering strains up to some percentages and some crack propagation tests) are also conducted in equivalent conditions o...

Determination of thermal properties of asphalt mixtures as another output from cyclic tension-compression test

This paper describes investigation into the change of temperature of asphalt mixtures during cyclic tests on cylindrical specimens. Tension-compression tests were performed at different strain amplitudes (from 55 μm/m to 133 μm/m). Temperature is measured at the surface and inside the specimen. From the analysis of the experimental results, the thermal conductivity (k) and the convection heat transfer coefficient (h) were determined during the steady temperature phase. The specific heat coefficient (C) of the material was determined during the transient temperature phase. This parameter is also indentified using a finite element simulation of the heat process. A thermal conductivity of 1.35 W/(m.°C) and a specific heat of 820 J/(kg.°C) were found for the asphalt mixtures used in this research. These values are quite realistic when compared to values proposed in the literature that are obtained using the traditional thermo-physical measurements. Furthermore, the thermal parameters obtained from FP2C, a device used for the identification of thermal properties of materials, confirm the results.

Time-temperature superposition principle for bituminous mixtures

ABSTRACT In the small strain domain (amplitudes below about 10−4), when considering 1D approach, the bituminous mixtures behaviour is linear viscoelastic, with a great thermal sensitivity and respects the Time-Temperature Superposition Principle (TTSP). In this paper, the generalisation of the TTSP is proposed for 3D. Measurements of complex Youngs modulus (E*) and complex Poissons ratio (v*) during cyclic loadings are presented. v* is also shown dependent on frequency and temperature and respects the TTSP. A key result is that a very close shift factor is obtained for E* and v*. In a second step, experiments in the non linear domain (considering strains up to some percents) allow to propose a generalisation in the non linear domain of the TTSP. This work is associated with modeling development using the general thermo-viscoplastic model « DBN » (Di Benedetto & Neifar).

Behaviour of asphalt mixtures containing reclaimed asphalt pavement and asphalt shingle

This paper presents the results of laboratory research on asphalt mixtures containing reclaimed asphalt pavement (RAP) and asphalt shingle, including the study of their linear viscoelastic (LVE) behaviour and fatigue characteristics. Complex modulus measurements using the tension-compression test on cylindrical specimens were conducted to determine LVE behaviour. Sinusoidal cyclic loadings with a strain amplitude of approximately 50×10−6 were applied at several temperatures (from−30°C to+40°C) and frequencies (from 0.01 to 10 Hz). In addition to axial stresses and strains, radial strains were also measured. The complex modulus E* and complex Poissons ratio ν* were then obtained and the three-dimensional (3D) LVE behaviour (with isotropy hypothesis) was then completely described. The time–temperature superposition principle was verified with good approximation in uni-dimensional and 3D conditions for the same values of shift factor. Experimental results were modelled using the 2 springs, 2 parabolic creep elements and 1 dashpot model developed at University of Lyon/ENTPE. Fatigue properties were evaluated by tension-compression tests on cylindrical specimens using the same testing device used for complex modulus. Sinusoidal loading at 10 Hz in controlled axial strain mode was applied at 10°C. The variation of complex modulus E* and complex Poissons ratio ν* as a function of the number of cycles was obtained. The fatigue test results were analysed using six different fatigue life criteria. The analysis of the results provided a ranking of the tested materials. The influence of RAP and asphalt shingle contents was quantified.

Influence of reclaimed asphalt pavement content on complex modulus of asphalt binder blends and corresponding mixes: experimental results and modelling

The objective of the presented study is to determine linear viscoelastic (LVE) properties of corresponding binders and mixes and to check how they change with reclaimed asphalt pavement (RAP) content. The investigation is part of a wider on-going research project, in the framework of a PhD thesis, in collaboration between Université de Lyon/École Nationale Travaux Publics de l’État (ENTPE), EIFFAGE Travaux Publics and Beyond Petroleum. Dynamic shear rheometer and tension/compression (using a Métravib device) complex modulus tests were performed on nine different bitumens, produced as blends of two different base bitumens and RAP-extracted bitumen in various proportions. LVE properties of six asphalt mixes, produced with the same materials and proportions of certain bitumen blends among the nine tested ones, were measured in tension/compression mode. 2 Springs, 2 Parabolic Elements, 1 Dashpot model was used to fit experimental data both for binders and mixes. Shift-Homothety-Shift in time-Shift transformation (developed at ENTPE) was applied to verify the correspondence of LVE behaviours of related binders and mixes.

Stiffness of Bituminous Mixtures Using Ultrasonic Wave Propagation

ABSTRACT Wave propagation tests were performed on several specimens of bituminous mixes. Back analysis is made within the framework of linear viscoelastic materials to obtain dynamic moduli. Comparison with moduli obtained from traditional cyclic tension-compression complex modulus test, shows that dynamic tests and cyclic tests results fit very well. A unique master curve is obtained and the time-temperature superposition is validated for very high frequencies (several 10 kHz). Simulation with the model developed at University of Lyon, ENTPE laboratory (2S2P1D) confirms the ability of this model to cover the wide frequency and temperature range. Furthermore, moduli obtained in different directions from dynamic (wave propagation) tests, reveal that different compaction techniques create different types of anisotropy.

Three-dimensional Thermo-viscoplastic Behaviour of Bituminous Materials: The DBN Model

ABSTRACT The DBN model, so called from its authors Di Benedetto and Neifar, has been developed, based on simple rheological elements and experimental results on bituminous materials. This model was developed thanks to the large amount of data obtained during the last two decades in the DGCB laboratory. In previous works, the development of the model has been limited to a unidirectional formulation. Nevertheless, the ability of this model to take into account the complex thermo-viscoplastic behaviour of bituminous material in different domains of loading is shown in this paper. In order to simulate the real behaviour in the pavements, the DBN model has been extended to a 3D formulation, which is described in the paper. The calibration of DBN model is also explained. Numerical simulations are compared with some few available data, considering the 3D behaviour of these materials.