Search

Highlights • Isostatic graphite (IG) waste powder from the milling of molds for EDM, can be use as filler in advanced cement composites. • Mechanical properties and thermal conductivity are increased with IG in cementitious composites. • Carbonation of cementitious composites is increased with IG. • IG-Cement Composite showed a sealed microstructure and close interphase by SEM analysis. • IG used as addition can be new source for low-cost multifunctional cement-based materials. Abstract The following research work presents a characterization of cement pastes and mortars with Isostatic graphite (IG). This addition is a carbon-based addition from waste origin obtained after the mill of graphite blocks from synthetic origin to produce Electrical Discharge Machining (EDM). This carbon-based material presents a great carbon purity and a crystalline structure. The effects of IG addition on the fresh and hardened properties of cementitious composites have been studied. The microstructure of the composites and their mechanical and physical properties have been analyzed. IG addition modifies the fresh behavior of the composites, and later the physical properties, such as density and porosity. Moreover, the possibilities of using IG in cementitious materials have been highlighted in this work, thanks to the increase of the compressive and flexural strength, thermal conductivity and CO 2 entrapping capacity. [ABSTRACT FROM AUTHOR]

This paper studies the rheological properties in aerated cement pastes in order to develop an aerated sprayed mortar with low thermal conductivity. For this purpose, different mixtures of cement with additions of metakaolin (MK) and sepiolite (SP) were tested. In addition, influence of yield stress on build-up thickness, as well as expansion speed and pore network were studied using cement pastes aerated with aluminum powder. At the same time, the volume increase during expansion, water retention and yield stress of the fresh foamed cement pastes were studied to characterize the fresh mortar. Results obtained show that the incorporation of siliceous fly ashes (SFA) in ordinary Portland cement together with additions of MK or/and SP provided the largest expansion speed increase and the lowest density of the aerated mortar. Pastes with greater yield stress show higher thermal conductivity but are better to be pneumatically gunited due to its bigger build up thickness. The most suitable paste from all them was selected, sprayed and aerated over ceramic bricks, checking the results on site. Results obtained by means of these tests confirm that is possible to spray an aerated mortar over vertical surfaces. In addition, this mortar has acceptable thermal insulation properties to be used in chambers of building façades and for external wall thermal insulation systems (EWIS). [ABSTRACT FROM AUTHOR]

Few high-resolution paleoclimate proxy records exist in the region located under the direct influence of the Intertropical Convergence Zone (ITCZ) in South America and most of them were retrieved from the Cariaco Basin off the coast of Venezuela. Here we present new ẟ18O and ẟ13C records of Venezuelan speleothems collected in caves adjacent to Cariaco, covering the mid- and late-Holocene. We document previously undetected secular-to multidecadal-scale climate variability in the core region of the ITCZ, which is compared to other high-resolution records from the North Atlantic, Caribbean and tropical South America. Over the mid-Holocene our record exhibits broad swings between periods of reduced (8.3–8.0, 6.5–5.0, 4.1–3.6 ka BP) and increased (8.5, 8.0–6.5, 4.9–4.2 ka BP) rainfall. In particular, between 5.5 and 5.0 ka BP, increases in polar and subpolar North Atlantic ice rafted debris and a reduction in North Atlantic Deep Water (NADW) formation might have contributed to the southward displacement of the North Atlantic Subtropical High (NASH) and the ITCZ, which led to severe dry conditions in north central Venezuela and an enhancement of the South American Monsoon System (SAMS). During the late-Holocene, contrary to data from Cariaco reported in previous studies, our results point to drier conditions during the Medieval Climate Anomaly (MCA, 900–1100 CE), which were further amplified during positive Atlantic Multidecadal Oscillation (AMO) phases. Wet conditions, however, prevailed during the first part of the Little Ice Age (LIA, 1400–1500 CE). No speleothem deposition occurred during the main LIA period, which might be related to drier conditions in response to a southward displacement of the ITCZ that led to major moisture convergence over the SASM domain. Our new records from Venezuela provide a reliable proxy for ITCZ behavior over the Atlantic – South America domain and document past dynamics in relation to other climate systems (NASH and SAMS), while providing new evidence of ITCZ – North Atlantic teleconnections during the Holocene. • ẟ18O and ẟ13C speleothem records from northern Venezuela for mid- and late- Holocene. • ITCZ meridional migration proxy nearby Cariaco Basin. • Evidence of IRD and NADW forcings on ITCZ rainfall between 6000 and 5000 years BP. • Northern Venezuela presents dry MCA and wet first part of the LIA. • MCA dry conditions further amplified during positive AMO phases. [ABSTRACT FROM AUTHOR]

The study here exposed was developed in order to contribute to the recycling and re-valorization of isostatic graphite powder as filler in gypsum pastes. Graphite powder is a waste product obtained from isostatic graphite blocks ground for mold production. The design of these molds is previously processed by Computer-Aided Manufacturing (CAM) and CAD/CAM software applications that uses a tool path for three-dimensional modeling to assist computer-numerically controlled (CNC). In order to contribute to the knowledge of this material as filler, this paper describes and assesses the microstructure of gypsums with graphite, through the use of a Scanning Electron Microscope and an Energy Dispersive X-ray Spectroscopy (SEM/EDX). Furthermore, the density, water absorption, and mechanical properties of gypsum pastes with addition of graphite filler have been analyzed. In order to deepen on the knowledge of the influence in the behavior of gypsum commonly used in building, several series of gypsum pastes with 0–5–10–15–20–25% of graphite filler by weight replacement of gypsum, and three different water/gypsum ratios – one of them with plasticizer – have been tested. It was observed that isostatic graphite powder from milled molds for Electrical Discharge Machining (EDM) significantly increases the mechanical properties of the gypsum pastes, more than other conventional fillers. This has been achieved by the great compatibility of the gypsum microstructure and the graphite micro-grains, which fill the microstructure of the pastes and increase the density of the hardened paste. The progressive increase of the amount of graphite influences the pastes properties, increasing their density and their mechanical resistances and reducing their porosity. [ABSTRACT FROM AUTHOR]

Early age shrinkage and cracking, water permeability and carbonation depth of concretes with natural Pozzolans blended cement (NPC) were investigated in order to assess the combined effect of Polypropylene short fibers (PPF) and Silica Fume (SF) on some durability parameters. The addition of 10% of SF increased compressive strength, shrinkage and cracking, permeability and carbonation depth. But, the combination of 10% SF and 0.07% PPF volumetric fraction mitigated early age cracking and significantly reduced water permeability and carbonation depth. The use of PPF in NPC concrete combined with SF can be recommended to reduce long-term impact of early age cracking, and enhance durability. However, cement should not be reduced when SF is added to mixtures without PPF, because lower CaO reserves may affect final pH, leading to concretes more sensible to carbonation. [ABSTRACT FROM AUTHOR]

Abstract: A parametric experimental study of the effects of Polypropylene fibers (PPF) on early cracking due to drying shrinkage in concretes with Natural Pozzolan Cement (NPC) and its influence on its durability is presented. Concrete composites containing natural pozzolan (toba trachite), point shaped crushed aggregates and different fiber volume fractions of PPF (0.03%, 0.06%, 0.09%, and 0.12%) were studied. This mixture is characterized by high permeability and carbonation ranges. Early age cracking control ability and drying shrinkage of PPF in NPC concretes were measured under dry setting conditions. The cracked area due to drying shrinkage was measured to establish the positive effect of the different PPF volume fractions in concretes. Besides, bulk density and water permeability depth were determined. Finally these specimens were stored for two years and tested afterwards, measuring the natural carbonation depth. Then the cracking area was again measured to assess the control ability of PPF on this parameter after long time. Finally a relationship of these indicators is analyzed to understand future lifespan of these concrete composites. The results indicate that a volume fraction of 0.07% of PPF reduces cracking area due to drying shrinkage of NPC a 66%, but larger volume fractions did not increased linearly this effect, and even worse results were obtained. The increment of PPF volume fraction reduces the water permeability depth and even the carbonation depth. A reduction of the cracked area, due to early shrinkage, of a 66% in NPC concretes may reach in these concretes a 32% lower water permeability indicators (enclosed wet area) and a 43% shorter minimum carbonation depth attending to the results obtained. So it can be considered that the cracking control ability of fibers on the exposed concrete surface reduced water permeability and CO2 diffusion. However the use of fiber increased porosity and reduced bulk density and ultrasonic modulus of NPC concretes. In conclusion NPC concretes with low amounts of PP fibers (upper to 0.07% volume fraction) are less permeable and the CO2 diffusion is slower in time due to early age cracking control, producing more durable concretes. [Copyright &y& Elsevier]

1:1 and 1:2 cobalt complexes of bis(benzimidazol-2-ylmethyl)amine (bbma) bis(benzimidazol-2-ylmethyl)sulfide (bbms), bis(benzimidazol-2-ylethyl)sulfide (bbes) and diethylenetriamine (dien) were prepared and their spectral and redox behavior studied. Two geometrical isomers pink-[Co(bbes)2]2+ and blue-[Co(bbes)2]2+ were obtained when the complexes were prepared by using with bbes and they were separated manually and recrystallized. The octahedral structure of pink-[Co(bbes)2]2+ was resolved by X-ray analysis. The electronic spectra show the presence of two geometrical isomers for Co(bbes)22+ in the solid state; for example, the spectral bands of pink-[Co(bbes)2]2+ differs markedly with those of blue-[Co(bbes)2]2+. This is consistent with the results obtained from magnetic measurements (5.10 BM for pink-Co(bbes)22+ and 4.72 BM for blue-[Co(bbes)2]2+). Further, the behavior of the ligands (bbma, bbms, bbes) at different pH conditions was determined on the basis of 13C NMR studies. The redox potentials [Co(II)/Co(I)] of the complexes follow the trend [Co(bbma)2]2+ < [Co(bbms)2]2+ ≈ [Co(bbes)2]2+ which demonstrates the stabilization of the Co(II) ion is more by both weak σ-donor and weak π-acceptor ligands rather than by σ-donor ligand. [Copyright &y& Elsevier]

This paper sets out to explore and promote the use of a hydrokinetic microturbine module designed to obtain energy from water streams. It is made up of a hydrokinetic rotor, a permanent magnet generator, power electronic stages and a microcontroller to regulate power production. It is further complemented by a control strategy focused on maximizing the electrical power produced when varying different water velocities. This method is based on three operating zones defined by the electrical frequency produced by the generator, and where different values of direct current set points are defined. It is set in motion in a boost converter power stage, using a maximum current control, with constant off time in the power switch, and continuous or discontinuous mode of operation depending on the current value required. The control strategy has been validated though the use of dynamic simulations. The microturbine modules are suitable for alignment in rows to increase the power produced. The modules connected in smart grids define the hydrokinetic smart grid concept. A global control strategy for hydrokinetic smart grids has also been proposed and tested. [ABSTRACT FROM AUTHOR]

The high-spin states of 80Y have been studied with the reactions 24Mg(58Ni, pnγ) at 180 MeV and 58Ni(24Mg, pnγ) at 77 MeV. Gamma-ray transitions in this nucleus have been unambiguously assigned by using the GASP detector array in conjunction with the recoil mass spectrometer CAMEL and the ISIS Silicon detector ball. These transitions have been arranged into several rotational bands extending up to an excitation energy of about 12 MeV and spin 24 ℏ. The bands are discussed within the framework of the interacting boson–fermion–fermion and cranked shell models. [Copyright &y& Elsevier]

NanoXplore is the European pioneer vendor to develop ITAR-free radiation-hardened SRAM-based FPGAs. This work is the first to explore dynamic SEE tests in the NG-Medium FPGA device. The reliability-performance analysis of an embedded unmitigated design is performed under heavy ion-induced errors. Moreover, the improvements of additional user level fault-tolerance techniques, such as redundancy and scrubbing, are explored. The design sensitiveness is evaluated through dynamic cross section, mean fluence to failure, and empiric reliability. Results obtained demonstrate the best tradeoff between area, performance, and reliability is achieved combining full design redundancy, periodic scrubbing, arithmetic functions implemented in DSPs, logical resets between executions, and area-oriented application execution. [ABSTRACT FROM AUTHOR]