Retour d'expérience sur le comportement de matériaux alternatifs en construction routière

Les matériaux alternatifs placés dans différents contextes routiers sont soumis à des contraintes mécaniques, thermiques et hydriques, susceptibles de modifier leurs propriétés physiques et chimiques, donc leur comportement à long terme. Bien que fondamentale, l'analyse du retour d'expérience à partir d'ouvrages routiers réalisés avec des matériaux alternatifs n'a jusqu'à maintenant pas été véritablement réalisée. Peu de données étant disponibles aujourd'hui sur ces ouvrages, un panel de 17 cas d'études français, parmi lesquels des ouvrages classiques et des plots expérimentaux, a été recensé. L'analyse de ces cas comprend la description de la structure de l'ouvrage, des caractéristiques du matériau alternatif utilisé, des facteurs locaux susceptibles d'avoir une influence sur le comportement des matériaux, et des réponses mécaniques et environnementales du matériau et de la structure routière. Des recommandations pour une meilleure conduite de futures expériences sont proposées

Les convertisseurs électromécaniques d'énergie : des systèmes mécatroniques

International audienceLes actionneurs ou générateurs électriques modernes sont par essence des systèmes mécatroniques, ils sont en effet des objets fondamentalement mécaniques, ils exploitent des principes électromagnétiques pour la conversion d'énergie, de l'électronique de puissance pour son optimisation, des capteurs et de l'électronique de signal pour le contrôle. Après une synthèse du principe de conversion électromagnétique, deux exemples, issus de travaux de recherche effectués en collaboration entre électrotechniciens et mécaniciens, sont présentés. Ces dispositifs, utilisant des nouvelles structures de machines électriques, mettent en évidence l'imbrication forte de compétences nécessaires dès la conception initiale de l'objet pour en faire un produit performant et bien intégré. Modern electric actuators or generators are inherently mechatronic systems. They are mechanical things that exploit electromagnetic principles for energy conversion, power electronics for conversion optimization, sensors and control electronics. We present a synthesis of electromagnetic energy conversion, then we give two examples leading to of research works of electrical engineering and mechanical staffs. These examples are a flywheel energy storage accumulator and an electrical jack. Both are conceived of new electrical machines. They underscore strong interweaving necessary immediately from design step. This interweaving permits to conceive high performance, integrated and cost effective electromechanical products

Assessment of french design method for flexible pavement by mean of the LCPC's ALT facility

One of the three rings of the LCPC's ALT facility has been equipped in 2002 with a 3 meters high waterproof concrete pit and a pumping station, making possible to completely control the water table level in the soil supporting the experimental pavement. The pit has been filled by clayey-silty sand, which the modulus varies from 110 to 85 MPa according to the water content. This soil has been chosen for its water-content susceptibility, but also for its permeability properties, making possible to rise the water-table from the buttom of the pit to the top and saturate the soil within a time of about one week. The first experiment using this new installation has concerned the design of flexible pavements. The objective was to improve the taking into account of the hydraulic condition of the subgrade in flexible pavements design. Four different flexible pavements and one bituminous reference structure have been tested. The different structures were designed for a service life varying from 0.25 to 1.5 millions of 130 kN French standard loads. During the first stage, the water-table level in soil was maintained at its lowest level (-2.80m) and the mean radius of rotation of the load was fixed at 19 meters. During the second stage, the water-table level was maintained at its upper level (-0.70 meter) and the radius of rotation of the load was 16 meters. In total 1.5 million of 65 kN dual-wheel loading were applied during each stage. The different structures supported this traffic without suffering any particular major failure, except for the thinnest one which had to be reinforced after 250 000 passes during the second phase. The experiment led to globally confirm the current French rational design method for flexible pavement. However, it was also observed that the design model doesn't completely take into account the damaging factors ; mainly the rutting of unbound granular aggregates. It is ignored by the design model, but it significantly contributes to the total permanent deformation of the structure

Full-scale experimentations on alternative materials in roads : Analysis of study practices

In France beginning in the 1990s, the topic of road construction using various alternative materials has given rise to several studies aimed at clarifying the technical and environmental feasibility of such an option. Although crucial to understanding and forecasting their behaviour in the field, an analysis of feedback from onsite experiences (back analysis) of roads built with alternative materials has not yet been carried out. The aim of the CAREX project (20032005) has been to fill this gap at the national scale. Based on a stress-response approach applied to both the alternative material and the road structure and including the description of external factors, a dedicated standardised framework for field data classification and analysis was adopted. To carry out this analysis, a set of 17 documented field experiments was identified through a specific national survey. It appears that a great heterogeneity exists in data processing procedures among studies. The description of material is acceptable while it is generally poor regarding external factors and structure responses. Structure monitoring is usually brief and mechanical loads too weak, which limits the significance of field testing. For future full-scale experiments, strengthening the realism within the testing conditions would be appropriate

The LCPC's ALT facility contribution to pavement cracking knowledge

International audienceThe full scale observation of damage and failure mechanisms of pavements dueto traffic is quite essential for the improvement of road materials and construction methods, aswell as for the development and the validation of modelling tools and pavement design methods.An alternative to the survey of real roads over long periods consists in performing acceleratedpavement tests (APT). LCPC has today more than 20 years of experience in APT applied to studyof pavement deterioration and cracking. Since 2006, in relation with an LCPC research programto update the French pavement design method, a detailed analysis of existing data of LCPC APTtests is being carried out. The objective of this work is to improve the understanding and modellingof the development of rutting and fatigue in different types of pavements. This paper presents thefirst conclusions of this synthesis, in relation to fatigue cracking, for the purpose of the RILEMTechnical Committee – Cracking in Asphalt Pavements (TC-CAP)

Detecting Unbounded Interface with Non Destructive Techniques

International audienc

Stripping phenomenon in thick pavement top layers

International audienceMost of the heavily trafficked French roads, like thick pavement structures, are now thirty or forty years old. Since construction, top layers only, have undergone one or more repair operations. Traditional rehabilitation works consist in overlaying the old wearing course or in milling it before covering it with a new overlay. For a few years, unusual deteriorations in highway structures, like pothole series or top layer delamination, have appeared. These phenomena generally occur after winter and more precisely during rainy events. The purpose of this paper is to investigate three cases of degradations observed for both rehabilitation types. The mechanics of the action causing upper layer deteriorations has to do with freeze-thaw processes combined with humidity and traffic. Nevertheless, other causes can add further to pavement degradation long before any surface deteriorations appear. The presence of water near the surface, for instance, can explain some of the damages observed. The fatigue of the layers during hot weather periods can also be at the origin of damages, even though rutting is more traditionally expected as a consequence of fatigue. Deterioration processes are discussed and illustrated by results from a study conducted on the LCPC's circular test track facility revealing some fatigue phenomenon at the level of the first interface when the weather is hot, which, combined with traffic and rainy, wintry conditions,can weaken top layers and lead to their quick degradation

The LCPC's ALT facility contribution to pavement cracking knowledge

International audienceThe full scale observation of damage and failure mechanisms of pavements dueto traffic is quite essential for the improvement of road materials and construction methods, aswell as for the development and the validation of modelling tools and pavement design methods.An alternative to the survey of real roads over long periods consists in performing acceleratedpavement tests (APT). LCPC has today more than 20 years of experience in APT applied to studyof pavement deterioration and cracking. Since 2006, in relation with an LCPC research programto update the French pavement design method, a detailed analysis of existing data of LCPC APTtests is being carried out. The objective of this work is to improve the understanding and modellingof the development of rutting and fatigue in different types of pavements. This paper presents thefirst conclusions of this synthesis, in relation to fatigue cracking, for the purpose of the RILEMTechnical Committee – Cracking in Asphalt Pavements (TC-CAP)