Thixotropic behaviour of paving grade bitumens under dynamic shear

A material exhibits a thixotropic behaviour if its apparent viscosity decreases in time under stress, and if it progressively recovers its initial viscosity when the stress is released. Methods for characterizing thixotropy for fluids are relatively well known, the situation is more difficult for viscoelastic materials. For bituminous binders, it corresponds to a decrease of material stiffness under cyclic loading by modification of its internal structure and to a recovery of this stiffness after rest. This property has been highlighted by simple shear tests, carried out using a controlled stress rheometer. An experimental procedure has been defined for studying the thixotropic behaviour of binders in dynamic mode. Then, it has allowed describing the corresponding curves of complex modulus versus the set stress and the rest period at different conditioning times of samples. This study has also permitted to demonstrate that stiffness variations are linked to re-arrangement of molecular structure and not to cracks formation and healing. Finally, based on specific indicators, it has been possible to compare different bituminous binders in order to estimate the ability of materials to restore their internal structures

Comportement et étude des graves-émulsion: Coopération public-privé. Méthodologie de préparation, d'instrumentation et de suivi de chantiers expérimentaux d'enrobés à froid à l'émulsion de bitume

Les mélanges à l'émulsion de bitume sont des techniques à fort potentiel environnemental. Cependant, leur formulation, fabrication et dimensionnement relèvent encore de démarches empiriques issues, bien souvent, de compétences locales. Pour caractériser les performances spécifiques de ces matériaux et aboutir à terme à des méthodologies d'optimisation, de formulation et de dimensionnement, il est nécessaire d'évaluer leur comportement in situ. Pour répondre à ces objectifs, il convent donc de suivre l'évolution des caractéristiques mécaniques et physiques du matériau tout au long des étapes de fabrication, de mise en oeuvre et en conditions de service au moyen d'une instrumentation adaptée et implantée dans la chaussée. Ce type d'instrumentation n'ayant jamais été utilisé en France sur grave-émulsion, une méthodologie appropriée doit être définie. C'est l'objet du présent article qui met en avant les spécificités d'un chantier expérimental instrumenté de grave-émulsion. Il décrit et justifie la méthodologie suivie, les capteurs employés, leur implantation, de même que les moyens de reconnaissance des pathologies des structures de chaussées utilisés. Il présente les indicateurs retenus pour évaluer le comportement des matériaux et de la structure

Comportement et étude des graves-émulsion Coopération public-privé. Chantier expérimental de la RD 44: Suivi du comportement dans le temps

La section expérimentale de la RD 44 près de Rennes, réalisée en collaboration entre l'IFSTTAR, le RST, l'URSIF et le conseil général d'Ille-et-Vilaine vise à suivre l'évolution des caractéristiques mécaniques et physiques du matériau tout au long des étapes de fabrication, de mise en oe½uvre et de service, au moyen d'une instrumentation adaptée et implantée dans la chaussée. Cet article est le second de la série consacrée à la section. Il présente les investigations effectuées en laboratoire sur le matériau prélevé sur chantier ainsi que le suivi temporel du comportement in situ de la grave-émulsion et de la structure mise en place grâce à des auscultations internes et externes

The Comet Interceptor Mission

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule

France's Perspective on the use of RAP Practice Research needs and results

-In a way : Making new material from old stuff. In the sustainable development context. Resources saving. Energy saving (especially with in place recycling) While keeping at least the same global performances as new materials ones. Need for global analysis (technical, environmental and economical) on these materials

Innovation in road Infrastructures with R5G T: the 5th generation road

The modal part of road transport still accounts in France for approximately 80% among all available transport modes. Even if a shift to other modes of transport is wished for, this situation is not likely to change radically in the next coming years. Indeed, the road network has developed over thousands of years: emerging from the track to the paved road, then to the smooth road and on to the continuous road. However, the environmental cost of current road infrastructures is still too important. As a consequence, the development of road infrastructures is not a priority anymore and as a matter of fact excluded from ambitious greening politics. There is then a need of strong innovation in this sector to solve these issues. The 5th Generation Road program (R5G for French Route de 5ème Génération) aims at changing the image of road infrastructures by designing, constructing and operating full scale demonstrators, which implement innovative solutions, ready for testing in research centres. To consider all aspects of this issue, the program is elaborated though a systemic approach and is organized around four emblematic conceptual elements: the adaptable road, the automated road, the resilient road and the acceptable road. The potential benefits of such a program are numerous: Maintaining the RAMS (Reliability, Availability, Maintainability and Safety) of road networks at existing levels, reinforcing industrial leaderships and targeting societal objectives (education, employment, and environment). The coming months will be devoted to the development and the implementation of the program at the National and European levels

Mix design of bituminous materials including reclaimed asphalt pavement

Reclaimed asphalt, obtained by milling of asphalt road layers can be re-used at once or stored. In the case of storage, an heterogeneity issue may occur when several types of materials, with different origins are mixed. At the scale of a storage zone or a stock pile, composition and properties of the reclaimed asphalts will be different, including variations of the final material properties, constraints for the stock manager, and the necessary adaptation of the manufacturing process. The reclaimed asphalt heterogeneity issue and the specific manufacturing process used in drum mixer asphalt plants have to be taken into account in ordre to optimize the laboratory mix design study as well as the physical, chemical and environmental criteria set in European legislation. The objective of this research work is to estimate the RAP heterogeneity in a material stockpile, as well as to improve the laboratory mixing procedure in order to better reproduce in laboratory the specific manufacturing process which can be found in drum mixer asphalt plants for these materials. The most relevant parameters are identified and a parametric study is carried out to estimate their level of influence on the behavior of the final bituminous material

Comportement et étude des graves-émulsion :Coopération public-privé : Acquis, perspectives et suites proposées

L'article résume les connaissances acquises au cours de la coopération IFSTTAR/RST/URSIRF axée sur les graves-émulsions. Dans l'optique de définir une méthodologie d'étude complète, des procédures ont été définies pour la fabrication en laboratoire, la maniabilité et la cohésion, la compactabilité, la résistance en compression, la tenue à l'eau, l'extraction et la caractérisation du liant

Recyclage des matériaux bitumineux : Expérience européenne - Besoins de recherche

-Economie de ressources. Economie d'énergie (retraitement en place)avec des performances comparables aux matériaux neufs Nécessité d'une analyse globale sur ces matériaux. Le contexte français. Grenelle de l'environnement. Engagements actuels sur les agrégats d'enrobés. Matériaux et structures économes en ressources non renouvelables (orientation du LCPC depuis 2004). Situation actuelle. Expérience ancienne en France (années 70). Nécessité d'un «coup d'accélérateur», formalisation, fiabilisation des solutions

Influence of the compaction process on the air void homogeneity

The effectiveness of laboratory compaction methods, for reproducing asphalt mixtures specimens with the same characteristics as on the actual building site, remains relatively unknown. The present paper in aimed at investigating the variability in air void content, therefore in compaction level, of three asphalt mixture types : a continuously-graded mix, an open-graded asphalt