Simon Pouget

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 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).

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.

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.

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.

Thermo-mechanical behaviour of mixtures containing bio-binders

The objective of the presented study is to develop an approach to assess the linear viscoelastic (LVE) properties and the low-temperature behaviour during thermal ageing of semi-coarse asphalt concrete (SCAC) containing bio-binders. The investigation is part of a wider ongoing research project in EIFFAGE Travaux Publics Research Center. Tension/compression complex modulus tests, direct tensile strength tests at low temperatures and thermal stress-restrained specimen tests were performed on SCAC, containing three different clear binders. The first one is a reference petroleum-based clear binder, the two others are bio-binders, manufactured from renewable raw materials and fit in with the ideas of sustainable development. The analogical LVE 2S2P1D model (2 springs, 2 parabolic elements, 1 dashpot) was used to fit experimental data for the three mixtures. This method seems to be very relevant to compare rheological properties of mixtures made with bio-binders, for which evolution of low-temperature behaviour with ageing is very discriminatory.

Viscoelastic Behaviour Characterization of a Gap-graded Asphalt Mixture with SBS Polymer Modified Bitumen

A characterization of the linear thermo-viscoelastic behaviour of a gap-graded bituminous mixture with SBS-polymer modified bitumen and RAP aggregates is presented in this paper. A comparison was made, in terms of their viscoelastic behaviour, between this innovative mixture and two commonly used well-graded base-course French mixtures made with pure bitumen. The materials were also compared in terms of viscous dissipated energy. Complex modulus tests on cylindrical samples were performed for each mixture. The viscoelastic behaviour of the materials was modelled using the 2S2P1D (2 springs, 2 parabolic elements, 1 dashpot) constitutive model which was developed in the Laboratory of Civil Engineering and Construction (LGCB) of the ENTPE, University of Lyon. The tests results allowed validating the time-temperature superposition principle for the studied mixtures. Experimental and modelled complex modulus (|E*|) master curves were built for each material. The gap-graded mixture was found to present higher stiffness values at low frequency/high temperature conditions, lower viscous behaviour and lower values of viscous dissipated energy compared to the conventional mixtures. Complex modulus tests were also carried out on the polymer modified bitumen of the gap-graded mixture. A link between the viscoelastic behaviour of both binder and mixture could be established thanks to the SHStS transformation developed by the ENTPE team.

Linear viscoelastic properties of high reclaimed asphalt content mixes with biobinders

The use of high Reclaimed Asphalt (RA) content mixtures together with binders produced from renewable resources (biobinders) is one of the current challenges in pavement engineering research. On the one hand, RA has been used for decades, but there are still some concerns about its performance, especially when high contents are used (>30%). On the other hand, biobinders are relatively new materials, which have to be deeply characterised and studied in order to develop good practices for their use. In this paper, linear viscoelastic properties of biobinders and bio-mixtures manufactured with high RA content and biobinders are analysed and discussed. High-modulus mixtures with 50% RA were selected for the mix design. Binders and mixtures were tested over a wide range of asphalt service temperatures and frequencies by means of Dynamic Shear Rheometer and two-point bending tests, respectively. Results show that biobinders have an important effect on mixtures behaviour. However, no direct links between their linear viscoelastic properties were found. Bio-asphalt mixtures still need further development for commercial exploitation; however, the take-away fact of this investigation is that it is possible to manufacture asphalt-like mixtures with acceptable viscoelastic properties while being composed only of RA and non-petroleum-based binders.

Complex modulus and fatigue performances of bituminous mixtures with reclaimed asphalt pavement and a recycling agent of vegetable origin

The paper focuses on the investigation of the effects of a recycling agent on mechanical performances of bituminous mixtures produced with reclaimed asphalt pavement (RAP). Twenty-one different bituminous mixtures were produced and tested, using three distinct virgin binders (15/25, 35/50 and 70/100 penetration grades), with RAP contents varying from 0% to 60%. Seven of the mixtures were produced by adding a recycling agent of vegetable origin (its content was fixed equal to 3.5% by weight of the RAP binder). One of the mixtures is a 100% RAP mixture, produced only with RAP-extracted binder and aggregates issued from RAP material. Another one is a “perfect” mixture, produced by perfectly blending 70/100 base binder with 60% RAP-extracted binder and using this blend to coat virgin and RAP aggregates. Material properties were investigated using classical tests commonly performed by the road paving industry in Europe, in order to assess the impact of the addition of the recycling agent according to the current standard procedures. In particular, complex modulus |E*| (at 15°C and 10 Hz) and fatigue parameters 6 and 1/b (at 10°C and 25 Hz) were determined by means of two-point bending tests on trapezoidal samples. The addition of the recycling agent was observed to generally lower |E*| and improve fatigue performances of mixtures with a RAP content equal or greater than 40%.

Effect of Vehicle Speed on the Millau Viaduct Response

This paper deals with the influence of a bituminous mix surfacing on orthotropic deck bridges. These researches are part of a French national project “Orthoplus,” which is briefly introduced. The approach to take into account the surfacing and to develop calculation tools is explained. First, the behavior of the different bituminous constituent materials is investigated. A linear viscoelastic modeling is proposed with a rheological model, previously developed at the Civil Engineering and Buildings Dept. (“DGCB”) of the University of Lyon/ENTPE. This model is implemented in a Finite Elements code, which enables the simulation of any orthotropic structures. To validate the proposed numerical tool, the highest bridge in the world, the Millau Viaduct (France) is studied. In situ measurements were especially carried out on the Millau Viaduct. Focus is made on comparisons between experimental data and simulations results. Influence of vehicle speed on bridge response is also analyzed.