François Olard

General “2S2P1D” Model and Relation Between the Linear Viscoelastic Behaviours of Bituminous Binders and Mixes

ABSTRACT A research including a large experimental campaign on the characterization of the viscoelastic behavior of different bituminous materials was developed. The aim is to establish the links between the viscoelastic properties (which are observed in the small strain domain) of binders and those of bituminous mixes. The viscoelastic behavior of bituminous binders and mixes has been studied by performing complex modulus tests at different temperatures and frequencies. A unique rheological model has been developed for the modeling 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 nine different binders and four mixes, with one mix design, 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 to predict easily and efficiently the mix complex modulus from the binder one.

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.

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.

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.

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.

Viscous Energy Dissipation in Asphalt Pavement Structures and Implication for Vehicle Fuel Consumption

The present paper deals with the energy dissipation induced by the viscous behavior of bituminous materials constituting pavement. An approach to take into account viscous properties of bituminous layers and to quantify this dissipation is explained. First, the behavior of different bituminous materials is investigated. Linear viscoelastic modeling is then proposed using a rheological model previously developed at the Civil Engineering and Buildings Department (DGCB) of the University of Lyon / ENTPE (Ecole Nationale des Travaux Publics de l’Etat). Second, this model is implemented in a finite-element code, which enables simulation of the behavior of any pavement structures under any rolling load. In this paper, these developments, previously validated for orthotropic steel bridge and mix surfacing structures, are applied on a classical French pavement structure. In addition, the calculation of energy dissipation due to the viscous properties of the bituminous materials is allowed. Then an estimation of corresponding fuel consumption excess is given considering a 40-ton truck for different temperatures and speeds. The influence of the base course thickness is investigated as well. The simulation results show that energy dissipation in bituminous pavement due to the rolling weight of the considered 40-ton truck may induce a fuel consumption excess of a few percents age points in very unfavorable climatic conditions.

Linear Viscoelastic Properties of Bituminous Binders and Mixtures at Low and Intermediate Temperatures

ABSTRACT Within the framework of a partnership between the DGCB of the ENTPE, Appia and Eurovia, a research program including a large experimental campaign on the viscoelastic behavior of different bituminous materials was developed. The aim is to establish the links between the viscoelastic properties of binders and those of bituminous mixes at low temperatures. The viscoelastic behavior of binders was evaluated using cyclic tests (frequency domain) and Bending Beam Rheometer tests (time domain). The viscoelastic behavior of bituminous mixes has been studied by performing complex modulus tests in tension/compression. Some pertinent links between bituminous binder and mix properties are established. Characteristics which are pertinent and discriminating enough with regard to the low temperature properties of bituminous mixes are presented.

Quantification of biasing effects during fatigue tests on asphalt mixes: non-linearity, self-heating and thixotropy

Various phenomena other than fatigue (so-called “biasing effects”) occur during laboratory fatigue tests on asphalt mixes because of cyclic loading applications, thus altering experimental results and leading to misleading conclusions. The purpose of the study is to isolate and quantify biasing effects, therefore isolating real fatigue damage. In particular, non-linearity, self-heating and thixotropy (defined as a recoverable viscosity reduction after shear application) were evaluated. Six different mixes were produced using three distinct asphalt binders. Tests were performed in tension/compression mode on cylindrical samples. A particular test procedure was followed, consisting of two parts. In the first part, complex modulus measurements were performed at temperatures from 8°C to 14°C and strain amplitudes from 50 to 110 µm/m, at 10 Hz. Regression equations were fitted in order to evaluate variations of norm of complex modulus and phase angle caused by temperature and strain-level changes around common fatigue test conditions (10°C, 100 µm/m). In the second part of the test, five partial fatigue tests (each one consisting of 100,000 cycles at a 100 µm/m strain amplitude) were performed at 10°C, 10 Hz. After each fatigue lag, a 24 hour rest period was imposed. During rest periods, short complex modulus measurements were performed (10°C, 10 Hz) in order to monitor the recovery of mechanical properties. Surface and internal temperature of samples were constantly measured throughout the entire test, in order to monitor self-heating due to repeated loading. A significant temperature increase was observed during each fatigue lag, while, during rest periods, temperature rapidly decreased to the initial value. Self-heating was observed to be correlated to viscoelastic energy dissipation. The procedure used in the study allowed quantitatively estimating biasing effects. Therefore, unrecovered mechanical properties, due to damage accumulation, were obtained. Ninety per cent of total complex modulus and phase angle variations observed during each fatigue lag were found to be completely reversible. Non-linearity and thixotropy appear to influence mechanical properties variations more importantly than self-heating.

GB5 mix design: high-performance and cost-effective asphalt concretes by use of gap-graded curves and SBS modified bitumens

Aggregate packing concepts developed in the field of high-performance cement concretes, initially by Caquot (1937) then by contemporary researchers since the 1970s, were transposed to the field of asphalt concretes. These concepts, associated with the use of the gyratory compactor on aggregates only, enabled the development of a new laboratory design procedure of dense high-modulus asphalt concretes. These mixes are characterized by single or double gap-graded curves, great coarse aggregate interlock and no need for low penetration grade bitumens to fulfil the European EME2 specification requirements, in particular the 14,000 MPa stiffness modulus value at 15°C. In addition, the use of polymer modified binders (PMBs), at a content of about 4% up to 4.5%, combined with such an optimized aggregate packing leads to the design of the so-called high-performance asphalt concretes (HPAs) characterized by great compactability, very high stiffness modulus and high fatigue resistance in a single formulation, allowing for reduced pavement thickness and increased longevity. Moreover, the proposed mix design and the 4–4.5% binder content makes PMBs use affordable in base courses. Laboratory assessment of such materials consisted in the evaluation of compactability, moisture resistance, rutting resistance at 60°C, complex stiffness modulus at 15°C and fatigue resistance at 10°C. Apart from these results, the paper also addresses the successful application of this new material on different job sites, located mainly in France. The proposed HPA material may be potentially considered as a relevant solution for sustainable long life pavements that do not deteriorate structurally, needing only timely surface maintenance.

On the Optimization of the Aggregate Packing Characteristics for the Design of High-Performance Asphalt Concretes

ABSTRACT In the framework of a partnership between the European EIFFAGE Travaux Publics Group and the Ecole de Technologie Supérieure (ETS) from Montreal (Québec), some basic concepts associated with granular combinations and aggregate packing characteristics enabled the development and design of high-performance self-blocking asphalt concretes. The aggregate packing methods first developed in the field of high-performance cement concretes were successfully transposed to the field of asphalt concretes. Laboratory assessment in both laboratories of the ETS and EIFFAGE Travaux Publics consisted in the evaluation of the compactin g ability using the French gyratory shear compactor (GSC), the resistance to moisture using the so-called Duriez test, the resistance to rutting thanks to the French wheel tracking tester at 60°C, the secant stiffness modulus at 15°C and the fatigue resistance at 10°C. The paper concludes that the grading analysis concepts allow the design engineer new insights into the structure of aggregates. The proposed principles can be used to develop more specific guidelines for aggregate structure selection of high-performance asphalt concretes.