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Le present travail est une seconde etape faisant partie de notre travail de recherche sur l'influence des parametres de composition sur le comportement des betons autoplacants (BAP) a l'etat frais et durci. Il concerne l'etude de l'effet des rapports eau sur ciment et fines sur ciment sur le comportement du BAP a l'etat durci. Plusieurs essais ont ete realises tels que l'etalement, la boite en L, la stabilite au tamis, le ressuage, les resistances mecaniques, le retrait libre (retrait de sechage et retrait endogene) et une etude microstructurale (caracterisation mineralogique, distributions porometriques) afin de comprendre les roles joues par les differents constituants susceptibles d'entrer dans la formulation d'un BAP a base de materiaux locaux et chercher a mieux cerner les mecanismes qui regissaient les comportements vis-a-vis du retrait. Nous avons mis en evidence le role du reseau poreux et de la microstructure des hydrates. Les resultats obtenus offrent de belles perspectives pour optimiser les BAP en Algerie. Notre etude a permis de developper une variete de formulations de betons autoplacants repondant aux criteres rheologiques (bonne deformabilite, moins de ressuage, absence de segregation, meilleures performances mecaniques). Mots-cles: betons autoplacants, fines calcaires, porosimetre, retrait de sechage, retrait endogene, resistances mecaniques. This paper describes the second phase of our research project on the influence of the composition parameters on the behaviour of unset and hardened self-compacting concrete (SCC). It studies the impact of the water/cement ratio and the fores/cement ratio on the behaviour of hardened SCC. Several tests were carried out, such as surface settlement, L box, sieving, bleeding, mechanical strengths, free shrinkage (drying shrinkage and autogeneous shrinkage) and a microstructure study (mineralogical characterization, pore space distribution), to better understand the roles of the various possible SCC components made with local materials and to identify the mechanisms governing shrinkage. We highlighted the role of the pore network and the microstructure of the hydrates. Results show good SCC optimization potential in Algeria. Our study helped develop several SCC formulations meeting the rheological criteria (good deformability, less bleeding, no segregation, better mechanical performance). Key words: self-compacting concrete, limestone fines, porosimeter, drying shrinkage, autogeneous shrinkage, mechanical strengths., 1. Introduction Les betons autoplacants (BAP), developpes depuis une vingtaine d'annees, sont encore a l'heure actuelle qualifies de << nouveaux betons >>, car leur utilisation reste modeste bien qu'ils possedent [...]

The isotopic composition of water in hydrated minerals, such as gypsum and jarosite, has numerous applications in studies of recent climate change, ore formation, and soil development. However, oxygen and hydrogen isotope analysis of water of crystallization is currently a complex procedure. Commonly used techniques involve offline extraction of water from hydrated minerals and subsequent isotope analysis. Such methods are time-consuming, require relatively large sample sizes, and the stepwise procedure has to be carried out with extreme caution to avoid erroneous results. We present a novel online method for the oxygen and hydrogen isotope analysis of water of crystallization in hydrous minerals. Gypsum (CaS[O.sub.4] x 2[H.sub.2]O) samples, 2 mg in size, are reacted in a simply modified carbon reducing furnace connected to a continuous-flow mass spectrometer system. Analysis time is less than 10 min/sample. The precision (2 std dev mean) of our method for 2-mg gypsum (30 [micro]mol of [H.sup.2]O) samples is 0.3 [per thousand] for oxygen and less than 1.4 [per thousand] for hydrogen isotope measurements. For oxygen isotope analysis alone, samples as small as 0.2 mg of gypsum can be analyzed with a precision of 0.3 [per thousand].

We study crustal thermal evolution by examining heat flow patterns along a convergent boundary from a young subduction zone to a more structurally mature collision zone. More than 8000 km of seismic profiles covering an offshore region of 45,000 [km.sup.2] in southern Taiwan show widespread bottom-simulating reflectors (BSRs). We derived 1107 BSR-based heat flows before combining 42 additional, published, offshore thermal probe data and 86 on-land heat flow data to document the shallow forearc thermal structures from the subduction zone to the collision zone. In the subduction zone, the geothermal gradient ranges mostly within 30-80 [degrees] C/km, and decreases toward the arc due to slab cooling, intensive dewatering at the toe, sediment blanketing, topographic effects, and other processes. The geothermal gradient ranges mostly from 30 to 90 [degrees] C/km in the collision zone, and increases, instead of decreases, toward the arc, possibly caused by exhumation, erosion, topographically induced groundwater circulation, and some upper mantle processes related to collision. Heat flow in the collision zone ranges from 80 to 250 mW/[m.sup.2]. The high heat flow in the collision zone correlates with a shallower seismicity zone and high seismic attenuation, while the lower heat flow in the subduction zone might allow the earthquakes to rupture to greater depth. The heat flow increases along the topographic high from subduction to collision zone due to increasing geothermal gradients and higher thermal conductivities of the exhumed basement rocks. This heat flow variation may generate an artificial exhumation rate pattern, if a conventional 30 [degrees] C/km geothermal gradient was used in fission-track studies. Keywords: bottom-simulating reflector, hydrates, geothermal gradient, heat flow, Taiwan, subduction, collision, seismogenic zone, fission-track dating.

Guanacoite with high Mg content from the type locality (El Guanaco mine, Chile) was investigated to elucidate the crystal-chemical characteristics of this arsenate mineral. In this study, WDS X-ray intensity maps revealed that guanacoite single crystals from the investigated specimen show distinct and characteristic compositional zoning, which varies cyclically along [100], which is in the direction of the elongation of the prismatic crystals (Witzke et al. 2006); the boundaries separating different compositional regions lie perpendicular to the prism faces. The crystal structure of a selected fragment [a = 5.459(2), b = 16.808(9), c = 6.917(3) [Angstrom], [beta] = 100.44(1)[degrees], V = 624.1(5) [[Angstrom].sup.3], [P2.sub.1]/c, and Z = 2], was solved using direct methods and refined to an R index of 3.09% for 1385 observed [[I.sub.o] > 4[sigma]([I.sub.o])] reflections measured at 103 K using MoK[alpha] X-radiation. The chemical formula based on the refinement is [([Cu.sub.0.85][Mg.sub.0.15]).sub.2] [Mg.sub.2]([Mg.sub.0.83][CU.sub.0.17])[(OH).sub.4][([H.sub.2]O).sub.4] [(As[O.sub.4]).sub.2]. The structure model obtained is in good agreement with the previous structure determination, although the occupancies of the three M sites (M = Mg or Cu) are distinctly different, i.e., the sites are considerably richer in Mg, especially M1 and M3. These structural results suggest that guanacoite's chemical formula should be enlarged from the Cu-rich composition [Cu.sub.2] [Mg.sub.2](Mg,Cu)[(OH).sub.4][([H.sub.2]O).sub.4][(As[O.sub.4]).sub.2] to [(Cu,Mg).sub.2][Mg.sub.2](Mg,Cu)[(OH).sub.4][([H.sub.2]O).sub.4] [(As[O.sub.4]).sub.2] to include the Mg-rich members (Mg up to 3.395 apfu). It appears that the chemical variability of guanacoite is mainly due to Mg-Cu substitution on the M1 and M2 sites. Keywords: Guanacoite, copper magnesium arsenate hydrate, crystal structure, chemical analysis, Jahn-Teller distortion

Numerical simulations and geologic studies suggest that high thermal anomalies beneath, within, and above thermally insulating layers of buried hydrated salts and gas hydrates could have triggered and sustained hydrologic processes on Mars, producing or modifying chaotic terrains, debris flows, gullies, and ice-creep features. These simulations and geologic examples suggest that thick hydrate deposits may sustain such geothermal anomalies, shallow groundwater tables, and hydrogeologic activity for eons. The proposed mechanism may operate and be self-reinforcing even in today's cold Martian climate without elevated heat flux. Keywords: Mars, heat flow, hydrous sulfates, clathrate hydrates, Aram Chaos. doi: 10.1130/G23783A.1

The features of the clathrate hydrate equilibria in mesoporous media are discussed in terms of a conceptual model, with the aim of resolving current inconsistencies concerning experimental and interpretative methods employed in studies of such systems. It is concluded that the Gibbs-Thomson (or Kelvin) relationship used to model clathrate inhibition in porous media must be modified correctly to reflect the hysteries between growth and dissociation.

The kinetics of methane hydrate formation prepared from polycrystalline deuterated ice are investigated. In-situ time-of-flight neutron powder diffraction is used for this purpose.