Influence of porosity network on the chemo-mechanical evolution of low-pH cementitious materials subjected to calcareous attack

International audienceThis paper presents a study which aims to understand the degradation mechanisms induced in a low-pH cementitious matrix by a calcareous attack and then, to evaluate the porosity network influence on the degradation scenario. To reach these goals, three experimental campaigns were carried out in parallel. Hardened low-pH cement paste samples were made in laboratory-controlled conditions, then immersed in calcareous water containing a small amount of water. Concrete samples were then cast in industrial conditions, cured in a controlled environment, then immersed in the same experimental device. Finally, massive concrete blocks were cast and cured outside with industrial processes before immersion in the attack water. Chemo-mechanical characterizations (SEM, µCT, micro/nano-indentation) were performed to estimate the degradation state of the samples. Geochemical modelling was performed to validate experimental observations. Calcium and magnesium enrichment are the main phenomena in all cases. However, the degradation scenario changes with the curing protocol. Porosity closing is observed in samples cured in a controlled environment, whereas industrial curing conditions induce non-negligible chemical alteration due to a skin effect

La situation des récifs coralliens des îles Éparses françaises de l’océan Indien

The status of the coral reefs of French Scattered Islands in the Indian Ocean. — Together with La Réunion and Mayotte Islands, Scattered Islands make up French Indian Ocean Territories (FIOT) which all possess highly ecologically sensitive natural habitats of major value for migrant species (turtles, seabirds, mammals). As a contribution to the national action plan of IFRECOR (French initiative on coral reefs) we set up during the period 2002-2005 a survey and monitoring program in order to increase the knowledge of the still poorly known coral reefs of these islands scattered from North to South in the Mozambique Channel and in central Indian Ocean. Results were particularly focused on the geomorphological mapping of shallow marine habitats and on a structural and functional approach of fish, coral and mollusc communities. Additional approaches with rapid assessment methods remained non exhaustive but nevertheless allow a first integrated diagnosis of the patrimonial value of the coral sanctuaries of Scattered Islands and to propose decision-making tools for identifying applied and fundamental axes of research as well as actions of monitoring adapted particularly to vulnerability factors and global warming.Avec l’île de la Réunion et Mayotte, les îles Éparses constituent les îles Françaises de l’océan Indien, lesquelles possèdent toutes des milieux naturels à sensibilité écologique forte et d’intérêt majeur pour des espèces migratrices (tortues, oiseaux marins, mammifères). Dans un contexte de mauvaise connaissance des récifs coralliens de ces îles éparpillées du Nord au Sud du canal du Mozambique et au centre de l’océan Indien occidental, nous avons réalisé de 2002 à 2005 un programme axé sur la connaissance et la surveillance des récifs, en vue de contribuer au plan d’action national de l’Initiative Française sur les Récifs Coralliens (IFRECOR). Les résultats concernent tout particulièrement la cartographie géomorphologique des milieux marins peu profonds ainsi qu’une approche structurelle et fonctionnelle des peuplements de poissons, coraux et mollusques. Les approches complémentaires menées selon des protocoles d’évaluation rapide restent non exhaustives mais permettent aujourd’hui de disposer d’un premier diagnostic intégré de la valeur patrimoniale des sanctuaires coralliens des îles Éparses et de proposer une aide à la décision pour identifier des axes de recherche appliquée et fondamentale, des mesures de gestion adaptées notamment aux facteurs de vulnérabilité tel que le réchauffement global.Quod Jean-Pascal, Barrère Alain, Chabanet Pascale, Durville Patrick, Nicet Jean-Benoît, Garnier R. La situation des récifs coralliens des îles Éparses françaises de l’océan Indien. In: Revue d'Écologie (La Terre et La Vie), tome 62, n°1, 2007. pp. 3-16

The R&D PERFROI project on Thermal mechanical and thermal hydraulics behaviors of a fuel rod assembly during a Loss Of Coolant Accident

International audienceThe safety principle in case of a LOCA is to preserve the short and long term coolability of the core. The associated safety requirements are to ensure the resistance of the fuel rods upon quench and post-quench loads and to maintain a coolable geometry in the core. An R&D program has been launched by IRSN with the support of EDF, to perform both experimental and modeling activities in the frame of the LOCA transient, on technical issues such as: - flow blockage within a fuel rods bundle and its potential impact on coolability, - fuel fragment relocation in the ballooned areas: its potential impact on cladding PCT (Peak Cladding Temperature) and on the maximum oxidation rate, - potential loss of cladding integrity upon quench and post-quench loads. The PERFROI project (2014-2019) focusing on the first above issue, is structured in two axes: 1. axis 1: thermal mechanical behavior of deformation and rupture of cladding taking into account the contact between fuel rods; specific research at LaMCoS laboratory focus on the hydrogen behavior in cladding alloys and its impact on the mechanical behavior of the rod; and, 2. axis 2: thermal hydraulics study of a partially blocked region of the core (ballooned area taking into account the fuel relocation with local over power), during cooling phase by water injection; More detailed activities foreseen in collaboration with LEMTA laboratory will focus on the characterization of two phase flows with heat transfer in deformed structures

Linear and nonlinear resonant ultrasonic techniques applied to assess delayed ettringite formation on concrete samples

International audienc