Model for predicting the UHPFRC tensile hardening response

Ultra High Performances Fibre Reinforced Concretes (UHPFRC) are characterised by an ex-tremely low permeability and outstanding mechanical properties. These characteristics make UHPFRC suitable for locally “harden” reinforced concrete structures subjected to aggressive environments and/or mechanical stresses. Results from uni-axial tensile tests on different UHPFRC materials and cast in different directions have shown a variety of mechanical behav-iour. In particular, the hardening behaviour ranges from 0.1-0.4 % but is, in some cases, not existent. A meso-mechanical model is developed to predict the UHPFRC tensile response as a function of the volume, aspect-ratio, distribution and orientation of the fibres and the mechanical properties of the matrix. The model allows determining the effect of two parameters, the coeffi-cient of orientation and the volume of fibre, on the hardening behaviour

Status of the LHC Superconducting Cable Mass Production

Six contracts have been placed with industrial companies for the production of 1200 tons of the superconducting (SC) cables needed for the main dipoles and quadrupoles of the Large Hadron Collider (LHC). In addition, two contracts have been placed for the supply of 470 tons of NbTi and 26 tons of Nb sheets. The main characteristic of the specification is that it is functional. This means that the physical, mechanical and electrical properties of strands and cables are specified without defining the manufacturing processes. Facilities for the high precision measurements of the wire and cable properties have been implemented at CERN, such as strand and cable critical current, copper to superconductor ratio, interstrand resistance, magnetisation, RRR at 4.2 K and 1.9 K. The production has started showing that the highly demanding specifications can be fulfilled. This paper reviews the organisation of the contracts, the test facilities installed at CERN, the various types of measurements and the results of the main physical properties obtained on the first batches. The status of the deliveries is presented

Competitiveness and communication for effective inoculation byRhizobium, Bradyrhizobium and vesicular-arbuscular mycorrhiza fungi

After a short summary on the ecology and rhizosphere biology of symbiotic bacteria and vesicular-arbuscular (VA) mycorrhiza fungi and their application as microbial inocula, results on competitiveness and communication are summarized. Stress factors such as high temperature, low soil pH, aluminium concentrations and phytoalexins produced by the host plants were studied withRhizobium leguminosarum bv.phaseoli andRhizobium tropici onPhaseolus beans. Quantitative data for competitiveness were obtained by usinggus + (glucoronidase) labelled strains, which produce blue-coloured nodules. ForPhaseolus-nodulating rhizobia, a group specific DNA probe was also developed, which did not hybridize with more than 20 other common soil and rhizosphere bacteria. Results from several laboratories contributing to knowledge of signal exchange and communication in theRhizobium/Bradyrhizobium legume system are summarized in a new scheme, including also defense reactions at the early stages of legume nodule initiation. Stimulating effects of flavonoids on germination and growth of VA mycorrhiza fungi were also found. A constitutive antifungal compound in pea roots, -isoxazolinonyl-alanine, was characterized

Regulatory nodD1 and nodD2 genes of Rhizobium tropici strain CIAT 899 and their roles in the early stages of molecular signaling and host-legume nodulation

BACKGROUND: Nodulation and symbiotic nitrogen fixation are mediated by several genes, both of the host legume and of the bacterium. The rhizobial regulatory nodD gene plays a critical role, orchestrating the transcription of the other nodulation genes. Rhizobium tropici strain CIAT 899 is an effective symbiont of several legumes—with an emphasis on common bean (Phaseolus vulgaris)—and is unusual in carrying multiple copies of nodD, the roles of which remain to be elucidated. RESULTS: Phenotypes, Nod factors and gene expression of nodD1 and nodD2 mutants of CIAT 899 were compared with those of the wild type strain, both in the presence and in the absence of the nod-gene-inducing molecules apigenin and salt (NaCl). Differences between the wild type and mutants were observed in swimming motility and IAA (indole acetic acid) synthesis. In the presence of both apigenin and salt, large numbers of Nod factors were detected in CIAT 899, with fewer detected in the mutants. nodC expression was lower in both mutants; differences in nodD1 and nodD2 expression were observed between the wild type and the mutants, with variation according to the inducing molecule, and with a major role of apigenin with nodD1 and of salt with nodD2. In the nodD1 mutant, nodulation was markedly reduced in common bean and abolished in leucaena (Leucaena leucocephala) and siratro (Macroptilium atropurpureum), whereas a mutation in nodD2 reduced nodulation in common bean, but not in the other two legumes. CONCLUSION: Our proposed model considers that full nodulation of common bean by R. tropici requires both nodD1 and nodD2, whereas, in other legume species that might represent the original host, nodD1 plays the major role. In general, nodD2 is an activator of nod-gene transcription, but, in specific conditions, it can slightly repress nodD1. nodD1 and nodD2 play other roles beyond nodulation, such as swimming motility and IAA synthesis. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12864-015-1458-8) contains supplementary material, which is available to authorized users

MEASUREMENT AND MODELLING OF FIBRE DISTRIBUTION AND ORIENTATION IN UHPFRC

Ultra High Performance Fibre Reinforced Concretes (UHPFRC) combine outstanding protective (extremely low permeability) and mechanical (high tensile strength and significant tensile strain hardening) properties. These materials can be used in composite UHPFRC-reinforced concrete members to provide long term durability and improved structural performance. However, their processing at fresh state and geometric boundary effects can induce significant anisotropic fibre distributions that must be considered when evaluating material characterisation test results or designing structural members to reliably benefit from their strain hardening properties. The fibre distribution and the coefficient of orientation have been measured in UHPFRC tensile specimens cast in forms with different casting directions, and fibre length. A large-scale UHPFRC-reinforced concrete composite structural member has also been investigated to link tensile specimen test results and structural element performance. Relationships have been found between the fibre distribution and orientation as a function of the form size vs. fibre length ratio, casting direction and the resulting mechanical properties. Furthermore, an original model for characterizing the fibre orientation from the determined number of fibres within three orthogonal cuts was developed, tested and successfully employed

Comportement en traction d'éléments en Béton de Fibres Ultra Performant combiné aces des barres d'armature

L’objectif des interventions sur des ouvrages d’art est d’améliorer la durabilité et d’augmenter la résistance pour assurer la sécurité structurale. La combinaison de BFUP avec des armatures, peuvent répondre à ces exigences. Le comportement à la rupture de tirants en BFUP a donc été étudié. Deux paramètres ont été testés, il s’agit du taux d’armature et de la nuance d’acier. Les résultats montrent l’effet favorable de la combinaison d’armatures avec du BFUP que ce soit pour l’amélioration du comportement à la fissuration ou de la capacité portante de l’élément tendu. La conclusion de cette étude est que la combinaison BFUP-armature présente un potentiel élevé pour le renforcement d’ouvrage