Impact of carbonation on unsaturated water transport properties of cement-based materials

International audienceIn unsaturated conditions, the durability of concrete structures is strongly dependent on the evolution of the amount of free water within concrete porosity. Reliable durability assessment of concrete structures in relation to their environment thus requires accurate unsaturated water transport description as well as reliable input data. The effect of carbonation on water transport remains poorly studied and data are lacking. It was then the purpose of this article to acquire all the data needed to describe unsaturated water transport in carbonated cementitious materials (porosity, water retention and unsaturated permeability). Four hardened pastes made with four different binders were carbonated at 3% CO2 to ensure representativeness with natural carbonation. Beyond the modification of the water retention curve and porosity clogging, significant microcracking due to carbonation shrinkage was observed. The consequence on permeability highlighted a competition between porosity clogging and microcracking that was dependent on the initial mineralogical composition

Atmospheric trace element concentrations in total suspended particles near Paris, France

International audienceTo evaluate today’s trace element atmospheric concentrations in large urban areas, an atmospheric survey was carried out for 18 months, from March 2002 to September 2003, in Saclay, nearby Paris. The total suspended particulate matter (TSP) was collected continuously on quartz fibre filters. The TSP contents were determined for 36 elements (including Ag, Bi, Mo and Sb) using two analytical methods: Instrumental Neutron Activation Analysis (INAA) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The measured concentrations were in agreement within the uncertainties with the certified values for the polycarbonate reference material filter SRM-2783 (National Institute for Standard Technology NIST, USA). The measured concentrations were significantly lower than the recommended atmospheric concentrations. In 2003, the Pb atmospheric level at Saclay was 15 ng/m3, compared to the 500 ng/m3 guideline level and to the 200 ng/m3 observed value in 1994. The typical urban background TSP values of 1–2, 0.2–1, 4–6, 10–30 and 3–5 ng/m3 for As, Co, Cr, Cu and Sb, respectively, were inferred from this study and were compared with the literature data. The typical urban background TSP concentrations could not be realised for Cd, Pb and Zn, since these air concentrations are highly influenced by local features. The Zn concentrations and Zn/Pb ratio observed in Saclay represented a characteristic fingerprint of the exceptionally large extent of zinc-made roofs in Paris and its suburbs. The traffic-related origin of Ba, Cr, Cu, Pb and Sb was demonstrated, while the atmospheric source(s) of Ag was not identified

He NMR measurements on palladium samples aged under tritium

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Impact of alkali on the passivation of silicate glass

International audienceAmorphous silica-rich surface layers, also called gels, can passivate silicate glass and minerals depending on environmental conditions. However, several uncertainties remain on the mechanisms controlling the formation of these layers. In this paper, the influence of exogenous ions supplied by solutions is studied, both on the formation and on the properties of the gel formed on international simple glass (ISG). ISG was altered at 90 °C, pH$_{90°C}$ 7, in silica-saturated solutions containing various alkaline cations separately (Li$^+$ , Na$^+$ , K$^+$ , and Cs$^+$). The alteration kinetics observed with Li and Na in the solution is similar to that observed with no ions, while K and Cs in the solution tend to decrease glass alteration. Furthermore, for K or Cs ions, the kinetics decreases as the ionic strength of the solution increases. The passivation layer formed in these solutions shows a selectivity toward cations following the series K > Cs > Na >> Li. These alkalis replace Ca from pristine glass in the altered structures, leading to differences in [AlO$_4$] − units charge compensation. Importantly, exchange between Ca and alkali also affects the total quantity of water inside each gel and this effect is well correlated with the observed drop in glass alteration

Inorganic Pollution in PM10 Particles Collected Over Three French Sites Under Various Influences: Rural Conditions, Traffic and Industry

International audiencePM10 particles were collected over three sites in France. The first one, Montagney was a rural site that was considered as a reference site. The second site Saclay, close to a highway, was used to study the influence of the traffic. The third site was Dunkerque, one of the most industrial areas in France for the production of steel, aluminium and petroleum refinement. More than 50 element concentrations were determined by instrumental neutron activation analysis and inductively coupled plasma–mass spectrometry. Comparisons between Saclay and Montagney shown that some elements, considered as crustal elements had similar concentration variations and weak (close to 1) enrichment factors. Elements with enrichment factors higher than 10 shown in Montagney correlated variations, with a Winter maximum, that should be due to Winter heating sources. Over Saclay, most of elements with high enrichment factors were attributed to the dense traffic of the highway. This is particularly true for Mn, Fe, Zn, Ba, Sb, Cu. Some additional elements correlated also, without a particular origin that can be ascertained. In Dunkerque, the most important industry is steel production. Correlation studies shown that Tl, Cs, Ba, Ag, Cu, Rb, Se, Mn, Pb concentration variations were closely associated to the Fe concentration variations. The second polluting industry is aluminium production. Correlation studies allowed to associate Ni, Y, Co, V, rare earth elements, Ti, Sr, Th, U, Ca, Sc, concentration variations to the aluminium concentration variations. A third important industry is petroleum refinement. The only element observed here and that is suspected to be emitted more specifically is La, used in cracking processes. An important enrichment of La with respect to Ce is observed. A strong decrease of the ratio Cl/Na was observed over the three sites, between the beginning of the experiment in Autumn 2005, and its end in Spring 2006. This was attributed to a release of gaseous HCl, produced by acidification of aerosols by other pollutants like NOx and SOx, that should have been oxidized to NO2 and SO3, then dissolved in the aerosols. The effects responsible for the loss of Cl, represents a large surface and long-term pollution event over the North of France. This work allowed a characterization of the heavy metal concentrations of the aerosol that will sustain results published in a companion paper, and that concerned the bio-accumulation of metals by Scleropodium purum, simultaneously exposed in the same sites

Rare-earth silicate crystallization in borosilicate glasses: Effect on structural and chemical durability properties

International audiencea r t i c l e i n f o Due to their low solubility, some elements, such as lanthanides, can lead to crystalline phases in borosilicate glass during cooling. The impact of rare earth (lanthanum and neodymium) silicate crystallization on glass structural configuration as well as on glass chemical durability was investigated in soda-lime borosilicate glasses. Partially crystallized glasses containing a single Ca 2 RE 8 (SiO 4) 6 O 2 (RE = La, Nd) phase (ranging from 1 to 36 wt.%) were synthesized by heat treating homogeneous glasses. Structural characterizations of vitreous and crystalline parts were carried out by 29 Si, 11 B, 23 Na and 17 O MAS and MQMAS NMR. The crystallization leads to a reorganization of the cation distribution around the rare earth elements. By keeping a part of the lanthanum and the calcium , crystallization causes a decrease in the number of NBOs in the vitreous part. A part of the sodium, initially near the lanthanum, becomes available to form Si–O–Na bonds and to convert trihedral boron into tetrahedral boron. Through the study of the alteration of different materials – homogeneous, crystallized and surrounding glasses, rare earth silicate ceramics, and separated mixtures of glass and crystals – a precise description could be made of the influence of the presence of crystals has on chemical durability. For the various alteration regimes, it was thus shown that the alteration kinetics increase proportionally to the crystal content, and that apatite-type crystals do not lead to a composition gradient on the glass–crystal interface. Although the crystals formed were more durable than the vitreous matrix, the chemical durability of partially crystallized glasses depends on the composition and structure of the surrounding glass

The role of alkalis on the incorporation of iodine in simple borosilicate glasses

International audienceThe purpose of this study was to identify incorporation mechanisms and saturation levels of iodine in borosilicate glasses that are simplified versions of compositions used for nuclear waste containment. Several series of glasses with different alkali contents (22 or 35 mol% Na$_2$O, or 22 mol% of a mixture of Na$_2$O + Li$_2$O, K$_2$O or Cs$_2$O) were loaded with iodine (from 1 000 to 10 000 ppm at.) at 1100 °C in a specially-designed closed system. When the incorporation limit of iodine was reached, alkali iodide crystals were observed (e.g. NaI, KI…). Crystal-free pools of glass were studied by Electron Probe Micro-Analysis (EPMA) to measure the incorporation limit of iodine, which ranges from 892 ppm at. for a cesium–bearing glass to 7260 ppm at. for the glass with 35 mol% Na$_2$O. The composition of the crystals was analyzed by Inductively Coupled Plasma spectroscopy (ICP) and it was systematically found that crystals are enriched in the heavy alkali compared to the bulk composition. Correlations exist between the saturation level and the composition of the crystals. It is concluded that high alkali content in general and high concentration of Na$_2$O in particular is favorable for iodine incorporation

Borosilicate glass alteration in vapor phase and aqueous medium

International audienceA Na-alumino-borosilicate glass and its Ca-doped counterpart were altered in vapor phase (98% relative humidity) and aqueous medium at 90 °C. Both the alteration media were enriched in 17 O. Characterization of the altered samples pointed out some differences between glass alteration in aqueous medium and vapor phase in terms of the alteration kinetics, the effect of Ca-doping on glass chemical durability, the behavior of elements in the gel layer, and the structure of the gel layer. Some of the key results are the recondensation of boron in the gel layer formed in the vapor phase and the utility of Rotation Echo DOuble Resonance Nuclear Magnetic Resonance spectroscopy to qualitatively distinguish between signals from the pristine glass and hydrated gel layer within a sample that was not altered to the core. The results gave rise to inferences about glass alteration mechanisms in both the alteration media and the differences between them

Heavy metal bioaccumulation by the bryophyte Scleropodium purum at three French sites under various influences: rural conditions, traffic, and industry

International audienceAn active biomonitoring of the heavy metals pollution experiment was undertaken by means of the bryophyte species Scleropodium purum transplanted at three different sites exposed to rural, traffic, or industrial influences. Concentrations of about 40 elements in S. purum were determined by instrumental neutron activation analysis and inductively coupled plasma mass spectrometry. Accumulation rates of heavy metals were determined in the three sites. These accumulation rates in polluted sites were matched together and also to those recorded at the rural site. The changes of the accumulation rate of heavy metals in S. purum versus their concentrations in PM10 particles simultaneously collected above show some different accumulation properties of S. purum according to elements and sites. S. purum has a weak efficiency in the three sites to accumulate elements like V, Cr, Cu, Zn, As, Se, Sb, and Pb originating from atmospheric hot sources generally enriched in particulates matter (PM10), whereas it is particularly high for Br, Th, and Rb. For other elements, Co, La, Ce, and Hf, and rare earth elements, Fe, Sr, Nb, Ti, Al, and Sc, the collection efficiency by S. purum is intermediate. In the industrial site Dunkerque, a magnification of the collection efficiency by S. purum for elements originating from steel and aluminum productions and petroleum refinement suggests that these metals could be enriched in coarse particles with a better accumulation by the bryophyte with respect to PM10

Bulk Li mobility enhancement in Spark Plasma Sintered Li(7−3x)AlxLa3Zr2O12 garnet

International audienceLi (7−3x) Al x La 3 Zr 2 O 12 (LLAZO) Al-doped garnets display high ionic conductivity in the range of ~10-4 S.cm-1 at room temperature and are thus envisioned for future solid-state batteries. In this study, LLAZO powders with two doping levels were synthetized using a solid-state route and sintered using Spark Plasma Sintering (SPS). Both pristine and SPS crushed pellet powders were investigated using X-Ray Diffraction (XRD) confirming the formation of the most conducting cubic phase. Ionic conductivity measurements were performed using electrochemical impedance spectroscopy. Li and Al distributions among available sites were identified using Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) experiments, and Li mobility was explored using 7 Li static wideline NMR spectroscopy. Results show that SPS treatment, beyond producing highly densified pellets, mainly modifies Al distribution and strongly impacts the bulk Li + mobility