Abstract: Sands produced from limestone rock deposits in Algeria contain high proportions of fine 0/100 μm particles (named filler hereafter), which are available in large quantities. This study aims to identify the maximum filler amount which may be added to cementitious materials without performance loss. Performance is quantified here as related to varied properties, either microstructural (density, porosity, pore size distribution, capillary absorption, Klinkenberg effect), mechanical (Young's modulus, compressive and flexural strengths), or indicative of durability (intrinsic gas permeability, drying shrinkage and mass loss). To that purpose, mortars with various amounts of filler, ranging from 15 to 45% sand mass (i.e. 45 to 135% cement mass), have been formulated, tested and compared to a reference mortar. As recommended by J. Baron [J. Baron, Les additions normalisées pour le Béton, Les bétons - Bases et données pour leur formulation, Association technique - industrie des liants hydrauliques (in French), Eyrolles Ed., Paris, 1996, pp. 47-57], substitution to sand is privileged, whereby cement proportion and workability are kept constant while water need varies with increasing filler amount. Preliminary XRD analysis of filler powder shows no other minerals than calcite CaCO3 and traces of dolomite CaMg(CO3)2. Results point out the existence of an optimal performance value and a high effect of filler addition. In particular, for high filler amounts, total porosity increases while bigger pore populations diminish. This is confirmed by SEM examinations of the microstructure as well as by the increase of Klinkenberg coefficient β determined from gas permeability measurements, and by capillary absorption results. Moreover, intrinsic gas permeability, compressive and flexural strengths remain remarkably high whatever the filler proportion. Drying shrinkage and mass loss are not impacted dramatically either.

Abstract: Argillite is considered a privileged candidate for long term nuclear waste storage. Yet argillite rock drilling often induces surface cracks that locally modify its permeability. This phenomenon located in a so-called Excavation Damaged Zone (EDZ) is of importance since permeability increase means lesser confinement capacity of the argillite rock. Potentially influencial phenomena occur when argillite is subjected simultaneously to normal stress variations and fluid seepage. Therefore, this extensive experimental study (6 month duration) on macro-cracked Callovo-Oxfordian argillite is aimed at distinguishing the contribution to rock permeability of mechanical loading (crack opening and closing) on one part and of chemically active fluid seepage (water) on the other. Steady state gas flow tests show that permeability K mainly depends upon crack closure cc, with values on the order of 10−14 m2. Permeability from transient water flow tests varies with test duration from 10−18 to 10−21 m2. In both test types, K also depends upon confining pressure Pc, mainly during the first three loading–unloading phases. A difference between water injection tests and gas injection tests is that the water-saturated rock sample swells. Swelling does not contribute to unload the crack zone but rather creates additional closure and pressure in the crack area. Indeed, water permeability is shown to depend upon cumulated crack closure ac, which sums up swelling and confinement-induced crack closure. Finally, this study outlines the strong effect of water upon crack closure amplitude and permeability. After a relatively short time (on the order of ten days), water flow within the crack drives the permeability back to very low values close to sound rock permeability (10−21 m2). This reflects a complete self-sealing of the macro-crack, which is an important factor for nuclear waste repository safety.

Abstract: This paper is aimed at describing the evolution of newly formed bone density and microarchitecture after implantation of an Injectable Bone Substitute (IBS). Cancellous bone growth (rabbit) is described as dependent of IBS formulation parameters. Possible improvements to the IBS formulation are finally discussed.

Abstract: To better understand the behaviour of sugar within industrial centrifuges or silos, drained triaxial tests were performed on loose, dry or moist sugar aggregates under low confining pressures (15–90 kPa). Particular attention is paid to test reproducibility and grain damage level. Rowe's stress-dilatancy theory is used to improve characterisation of the critical state, at which the aggregate of grains could participate in frictional flow at constant volume. The effects of strain rate, mean grain size and moisture upon internal friction and dilatancy are each investigated. Additionally, initial elastic properties are identified.

Abstract: A multiaxial failure criterion is validated for a brittle orthotropic composite, namely a tridirectional carbon–carbon composite (3D C---C). It is aimed at designers of 3D C---C structures. The composite is subjected to a triaxial strain state along its reinforcement axes, which is representative of its in-service loading conditions. A multiaxial test rig is designed in order to reproduce this required strain state. Its mock-up dimensions are optimised by combining Taguchi experimental strategy with tridimensional finite element modelling. Comparison of experimental results with numerical modelling shows that failure occurs due to the required strain state; failure is brittle and corresponds to simultaneous breakage of carbon yarns along the three reinforcement axes. Subsequently, the experiment validates a failure criterion, which assumes linear coupling between the three principal strains.

Abstract: This paper investigates the effect of finite specimen size upon the tensile failure of a tridirectional carbon-carbon composite along each reinforcement axis. Asymmetry in the position of load-bearing axial yarns across the cross-section is generated randomly by machining. This yields parasitic bending of the specimen, and thereby premature failure of the yarns subjected to the maximum bending stress. However, bending effects become negligible at final failure. Additionally, the composite failure strength sgr F is determined from the cross-sectional area of the actually load-bearing axial yarns, using both symmetrical and asymmetrical specimens. Results are in good agreement with previous work, and we show that the variability of sgr F is small.

Abstract: Among diversified industrial uses, see for instance [Koch, Appl.Clay Sci., (21) 2002], compacted bentonite blocks are potential candidates for sealing nuclear waste repositories. Indeed, when put in place in a wet environment such as that considered for nuclear waste repositories, sodium bentonite swells. Following positive in situ experiments, bentonite is reputed ensuring proper repository tunnel sealing. As requested by ANDRA (French Agency for Nuclear Waste Management) and complementarily to in situ experiments, an original experimental labora- tory set-up was designed in order to reproduce the introduction and swelling of bentonite plugs inside an argillite host rock. Once the argillite/bentonite interface is established, an increase in storage tunnel gas pressure is simulated and the interface gas migration pressure (or gas critical pressure) is evaluated. More precisely, a first experimental set-up provides bentonite swelling pressure and kinetics (i.e. mainly hydraulic cut-off, time to reach asymptotic swelling pressure and value of asymptotic swelling pressure) at given initial compaction and saturation rate. This phase is preparatory to devising an experimental set-up and procedure which reproduce the introduction and subsequent swelling of a bentonite plug inside the argillite host rock, measures water permeability through the argillite/bentonite interface and finally the gas critical pressure. Experimental results upon MX80 compacted bentonite associated to Bure Callovo-Oxfordian argillite are provided.