Développement des bétons autoplaçants à faible teneur en poudre, Éco-BAP: formulation et performance

Abstract : Although concrete is a relatively green material, the astronomical volume of concrete produced worldwide annually places the concrete construction sector among the noticeable contributors to the global warming. The most polluting constituent of concrete is cement due to its production process which releases, on average, 0.83 kg CO[subscript 2] per kg of cement. Self-consolidating concrete (SCC), a type of concrete that can fill in the formwork without external vibration, is a technology that can offer a solution to the sustainability issues of concrete industry. However, all of the workability requirements of SCC originate from a higher powder content (compared to conventional concrete) which can increase both the cost of construction and the environmental impact of SCC for some applications. Ecological SCC, Eco-SCC, is a recent development combing the advantages of SCC and a significantly lower powder content. The maximum powder content of this concrete, intended for building and commercial construction, is limited to 315 kg/m[superscript 3]. Nevertheless, designing Eco-SCC can be challenging since a delicate balance between different ingredients of this concrete is required to secure a satisfactory mixture. In this Ph.D. program, the principal objective is to develop a systematic design method to produce Eco-SCC. Since the particle lattice effect (PLE) is a key parameter to design stable Eco-SCC mixtures and is not well understood, in the first phase of this research, this phenomenon is studied. The focus in this phase is on the effect of particle-size distribution (PSD) on the PLE and stability of model mixtures as well as SCC. In the second phase, the design protocol is developed, and the properties of obtained Eco-SCC mixtures in both fresh and hardened states are evaluated. Since the assessment of robustness is crucial for successful production of concrete on large-scale, in the final phase of this work, the robustness of one the best-performing mixtures of Phase II is examined. It was found that increasing the volume fraction of a stable size-class results in an increase in the stability of that class, which in turn contributes to a higher PLE of the granular skeleton and better stability of the system. It was shown that a continuous PSD in which the volume fraction of each size class is larger than the consecutive coarser class can increase the PLE. Using such PSD was shown to allow for a substantial increase in the fluidity of SCC mixture without compromising the segregation resistance. An index to predict the segregation potential of a suspension of particles in a yield stress fluid was proposed. In the second phase of the dissertation, a five-step design method for Eco-SCC was established. The design protocol started with the determination of powder and water contents followed by the optimization of sand and coarse aggregate volume fractions according to an ideal PSD model (Funk and Dinger). The powder composition was optimized in the third step to minimize the water demand while securing adequate performance in the hardened state. The superplasticizer (SP) content of the mixtures was determined in next step. The last step dealt with the assessment of the global warming potential of the formulated Eco-SCC mixtures. The optimized Eco-SCC mixtures met all the requirements of self-consolidation in the fresh state. The 28-day compressive strength of such mixtures complied with the target range of 25 to 35 MPa. In addition, the mixtures showed sufficient performance in terms of drying shrinkage, electrical resistivity, and frost durability for the intended applications. The eco-performance of the developed mixtures was satisfactory as well. It was demonstrated in the last phase that the robustness of Eco-SCC is generally good with regards to water content variations and coarse aggregate characteristics alterations. Special attention must be paid to the dosage of SP during batching.

Evaluation of frozen ground conditions along a coastal topographic gradient at Byers Peninsula (Livingston Island, Antarctica) by geophysical and geoecological methods

Geophysical surveying and geoelectricalmethods are effective to study permafrost distribution and conditions in polar environments. Geoelectrical methods are particularly suited to study the spatial distribution of permafrost because of its high electrical resistivity in comparison with that of soil or rock above 0 °C. In the South Shetland Islands permafrost is considered to be discontinuous up to elevations of 20–40ma.s.l., changing to continuous at higher altitudes. There are no specific data about the distribution of permafrost in Byers Peninsula, in Livingston Island, which is the largest ice-free area in the South Shetland Islands. With the purpose of better understanding the occurrence of permanent frozen conditions in this area, a geophysical survey using an electrical resistivity tomography (ERT)methodologywas conducted during the January 2015 field season, combined with geomorphological and ecological studies. Three overlapping electrical resistivity tomographies of 78meach were done along the same profile which ran from the coast to the highest raised beaches. The three electrical resistivity tomographies are combined in an electrical resistivitymodel which represents the distribution of the electrical resistivity of the ground to depths of about 13malong 158m. Several patches of high electrical resistivity were found, and interpreted as patches of sporadic permafrost. The lower limits of sporadic to discontinuous permafrost in the area are confirmed by the presence of permafrost-related landforms nearby. There is a close correspondence between moss patches and permafrost patches along the geoelectrical transect.

Resistivity imaging of a reconfigurable phantom with circular inhomogeneities in 2D-electrical impedance tomography

Resistivity imaging of a reconfigurable phantom with circular inhomogeneities is studied with a simple instrumentation and data acquisition system for Electrical Impedance Tomography. The reconfigurable phantom is developed with stainless steel electrodes and a sinusoidal current of constant amplitude is injected to the phantom boundary using opposite current injection protocol. Nylon and polypropylene cylinders with different cross sectional areas are kept inside the phantom and the boundary potential data are collected. The instrumentation and the data acquisition system with a DIP switch-based multiplexer board are used to inject a constant current of desired amplitude and frequency. Voltage data for the first eight current patterns (128 voltage data) are found to be sufficient to reconstruct the inhomogeneities and hence the acquisition time is reduced. Resistivity images are reconstructed from the boundary data for different inhomogeneity positions using EIDORS-2D. The results show that the shape and resistivity of the inhomogeneity as well as the background resistivity are successfully reconstructed from the potential data for single or double inhomogeneity phantoms. The resistivity images obtained from the single and double inhomogeneity phantom clearly indicate the inhomogeneity as the high resistive material. Contrast to noise ratio (CNR) and contrast recovery (CR) of the reconstructed images are found high for the inhomogeneities near all the electrodes arbitrarily chosen for the entire study. (C) 2010 Elsevier Ltd. All rights reserved.

Studying the resistivity imaging of chicken tissue phantoms with different current patterns in Electrical Impedance Tomography (EIT)

A current injection pattern in Electrical Impedance Tomography (EIT) has its own current distribution profile within the domain under test. Hence, different current patterns have different sensitivity, spatial resolution and distinguishability. Image reconstruction studies with practical phantoms are essential to assess the performance of EIT systems for their validation, calibration and comparison purposes. Impedance imaging of real tissue phantoms with different current injection methods is also essential for better assessment of the biomedical EIT systems. Chicken tissue paste phantoms and chicken tissue block phantoms are developed and the resistivity image reconstruction is studied with different current injection methods. A 16-electrode array is placed inside the phantom tank and the tank is filled with chicken muscle tissue paste or chicken tissue blocks as the background mediums. Chicken fat tissue, chicken bone, air hole and nylon cylinders are used as the inhomogeneity to obtained different phantom configurations. A low magnitude low frequency constant sinusoidal current is injected at the phantom boundary with opposite and neighboring current patterns and the boundary potentials are measured. Resistivity images are reconstructed from the boundary data using EIDORS and the reconstructed images are analyzed with the contrast parameters calculated from their elemental resistivity profiles. Results show that the resistivity profiles of all the phantom domains are successfully reconstructed with a proper background resistivity and high inhomogeneity resistivity for both the current injection methods. Reconstructed images show that, for all the chicken tissue phantoms, the inhomogeneities are suitably reconstructed with both the current injection protocols though the chicken tissue block phantom and opposite method are found more suitable. It is observed that the boundary potentials of the chicken tissue block phantoms are higher than the chicken tissue paste phantom. SNR of the chicken tissue block phantoms are found comparatively more and hence the chicken tissue block phantom is found more suitable for its lower noise performance. The background noise is found less in opposite method for all the phantom configurations which yields the better resistivity images with high PCR and COC and proper IRMean and IRMax neighboring method showed higher noise level for both the chicken tissue paste phantoms and chicken tissue block phantoms with all the inhomogeneities. Opposite method is found more suitable for both the chicken tissue phantoms, and also, chicken tissue block phantoms are found more suitable compared to the chicken tissue paste phantom. (C) 2012 Elsevier Ltd. All rights reserved.

Studies on thin film based flexible gold electrode arrays for resistivity imaging in electrical impedance tomography

Practical phantoms are essential to assess the electrical impedance tomography (EIT) systems for their validation, calibration and comparison purposes. Metal surface electrodes are generally used in practical phantoms which reduce the SNR of the boundary data due to their design and development errors. Novel flexible and biocompatible gold electrode arrays of high geometric precision are proposed to improve the boundary data quality in EIT. The flexible gold electrode arrays are developed on flexible FR4 sheets using thin film technology and practical gold electrode phantoms are developed with different configurations. Injecting a constant current to the phantom boundary the surface potentials are measured by a LabVIEW based data acquisition system and the resistivity images are reconstructed in EIDORS. Boundary data profile and the resistivity images obtained from the gold electrode phantoms are compared with identical phantoms developed with stainless steel electrodes. Surface profilometry, microscopy and the impedance spectroscopy show that the gold electrode arrays are smooth, geometrically precised and less resistive. Results show that the boundary data accuracy and image quality are improved with gold electrode arrays. Results show that the diametric resistivity plot (DRP), contrast to noise ratio (CNR), percentage of contrast recovery (PCR) and coefficient of contrast (COC) of reconstructed images are improved in gold electrode phantoms. (C) 2013 Elsevier Ltd. All rights reserved.

Projection Error Propagation-based Regularization (PEPR) method for resistivity reconstruction in Electrical Impedance Tomography (EIT)

A novel Projection Error Propagation-based Regularization (PEPR) method is proposed to improve the image quality in Electrical Impedance Tomography (EIT). PEPR method defines the regularization parameter as a function of the projection error developed by difference between experimental measurements and calculated data. The regularization parameter in the reconstruction algorithm gets modified automatically according to the noise level in measured data and ill-posedness of the Hessian matrix. Resistivity imaging of practical phantoms in a Model Based Iterative Image Reconstruction (MoBIIR) algorithm as well as with Electrical Impedance Diffuse Optical Reconstruction Software (EIDORS) with PEPR. The effect of PEPR method is also studied with phantoms with different configurations and with different current injection methods. All the resistivity images reconstructed with PEPR method are compared with the single step regularization (STR) and Modified Levenberg Regularization (LMR) techniques. The results show that, the PEPR technique reduces the projection error and solution error in each iterations both for simulated and experimental data in both the algorithms and improves the reconstructed images with better contrast to noise ratio (CNR), percentage of contrast recovery (PCR), coefficient of contrast (COC) and diametric resistivity profile (DRP). (C) 2013 Elsevier Ltd. All rights reserved.

Characterization of metallic electrical contacts to SnO2 thin films lightly doped with Eu3+ ions, and photo-induced resistivity

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

The effect of red blood cell orientation on the electrical impedance of pulsatile blood with implications for impedance cardiography

Impedance cardiography is an application of bioimpedance analysis primarily used in a research setting to determine cardiac output. It is a non invasive technique that measures the change in the impedance of the thorax which is attributed to the ejection of a volume of blood from the heart. The cardiac output is calculated from the measured impedance using the parallel conductor theory and a constant value for the resistivity of blood. However, the resistivity of blood has been shown to be velocity dependent due to changes in the orientation of red blood cells induced by changing shear forces during flow. The overall goal of this thesis was to study the effect that flow deviations have on the electrical impedance of blood, both experimentally and theoretically, and to apply the results to a clinical setting. The resistivity of stationary blood is isotropic as the red blood cells are randomly orientated due to Brownian motion. In the case of blood flowing through rigid tubes, the resistivity is anisotropic due to the biconcave discoidal shape and orientation of the cells. The generation of shear forces across the width of the tube during flow causes the cells to align with the minimal cross sectional area facing the direction of flow. This is in order to minimise the shear stress experienced by the cells. This in turn results in a larger cross sectional area of plasma and a reduction in the resistivity of the blood as the flow increases. Understanding the contribution of this effect on the thoracic impedance change is a vital step in achieving clinical acceptance of impedance cardiography. Published literature investigates the resistivity variations for constant blood flow. In this case, the shear forces are constant and the impedance remains constant during flow at a magnitude which is less than that for stationary blood. The research presented in this thesis, however, investigates the variations in resistivity of blood during pulsataile flow through rigid tubes and the relationship between impedance, velocity and acceleration. Using rigid tubes isolates the impedance change to variations associated with changes in cell orientation only. The implications of red blood cell orientation changes for clinical impedance cardiography were also explored. This was achieved through measurement and analysis of the experimental impedance of pulsatile blood flowing through rigid tubes in a mock circulatory system. A novel theoretical model including cell orientation dynamics was developed for the impedance of pulsatile blood through rigid tubes. The impedance of flowing blood was theoretically calculated using analytical methods for flow through straight tubes and the numerical Lattice Boltzmann method for flow through complex geometries such as aortic valve stenosis. The result of the analytical theoretical model was compared to the experimental impedance measurements through rigid tubes. The impedance calculated for flow through a stenosis using the Lattice Boltzmann method provides results for comparison with impedance cardiography measurements collected as part of a pilot clinical trial to assess the suitability of using bioimpedance techniques to assess the presence of aortic stenosis. The experimental and theoretical impedance of blood was shown to inversely follow the blood velocity during pulsatile flow with a correlation of -0.72 and -0.74 respectively. The results for both the experimental and theoretical investigations demonstrate that the acceleration of the blood is an important factor in determining the impedance, in addition to the velocity. During acceleration, the relationship between impedance and velocity is linear (r2 = 0.98, experimental and r2 = 0.94, theoretical). The relationship between the impedance and velocity during the deceleration phase is characterised by a time decay constant, ô , ranging from 10 to 50 s. The high level of agreement between the experimental and theoretically modelled impedance demonstrates the accuracy of the model developed here. An increase in the haematocrit of the blood resulted in an increase in the magnitude of the impedance change due to changes in the orientation of red blood cells. The time decay constant was shown to decrease linearly with the haematocrit for both experimental and theoretical results, although the slope of this decrease was larger in the experimental case. The radius of the tube influences the experimental and theoretical impedance given the same velocity of flow. However, when the velocity was divided by the radius of the tube (labelled the reduced average velocity) the impedance response was the same for two experimental tubes with equivalent reduced average velocity but with different radii. The temperature of the blood was also shown to affect the impedance with the impedance decreasing as the temperature increased. These results are the first published for the impedance of pulsatile blood. The experimental impedance change measured orthogonal to the direction of flow is in the opposite direction to that measured in the direction of flow. These results indicate that the impedance of blood flowing through rigid cylindrical tubes is axisymmetric along the radius. This has not previously been verified experimentally. Time frequency analysis of the experimental results demonstrated that the measured impedance contains the same frequency components occuring at the same time point in the cycle as the velocity signal contains. This suggests that the impedance contains many of the fluctuations of the velocity signal. Application of a theoretical steady flow model to pulsatile flow presented here has verified that the steady flow model is not adequate in calculating the impedance of pulsatile blood flow. The success of the new theoretical model over the steady flow model demonstrates that the velocity profile is important in determining the impedance of pulsatile blood. The clinical application of the impedance of blood flow through a stenosis was theoretically modelled using the Lattice Boltzman method (LBM) for fluid flow through complex geometeries. The impedance of blood exiting a narrow orifice was calculated for varying degrees of stenosis. Clincial impedance cardiography measurements were also recorded for both aortic valvular stenosis patients (n = 4) and control subjects (n = 4) with structurally normal hearts. This pilot trial was used to corroborate the results of the LBM. Results from both investigations showed that the decay time constant for impedance has potential in the assessment of aortic valve stenosis. In the theoretically modelled case (LBM results), the decay time constant increased with an increase in the degree of stenosis. The clinical results also showed a statistically significant difference in time decay constant between control and test subjects (P = 0.03). The time decay constant calculated for test subjects (ô = 180 - 250 s) is consistently larger than that determined for control subjects (ô = 50 - 130 s). This difference is thought to be due to difference in the orientation response of the cells as blood flows through the stenosis. Such a non-invasive technique using the time decay constant for screening of aortic stenosis provides additional information to that currently given by impedance cardiography techniques and improves the value of the device to practitioners. However, the results still need to be verified in a larger study. While impedance cardiography has not been widely adopted clinically, it is research such as this that will enable future acceptance of the method.

Partial melt processing and electrical properties of Bi-Sr-Ca-Cu-o superconducting thick films on (100) MgO substrates

Superconducting thick films of Bi2Sr2CaCu2Oy (Bi-2212) on single-crystalline (100) MgO substrates have been prepared using a doctor-blade technique and a partial-melt process. It is found that the phase composition and the amount of Ag addition to the paste affect the structure and superconducting properties of the partially melted thick films. The optimum heat treatment schedule for obtaining high Jc has been determined for each paste. The heat treatment ensures attainment of high purity for the crystalline Bi-2212 phase and high orientation of Bi-2212 crystals, in which the c-axis is perpendicular to the substrate. The highest Tc, obtained by resistivity measurement, is 92.2 K. The best value for Jct (transport) of these thick films, measured at 77 K in self-field, is 8 × 10 3 Acm -2.

Electrical property and characterization of nano-SnO2/wollastonite composite materials

Nano-tin oxide was deposited on the surface of wollastonite using the mixed solution including stannic chloride pentahydrate precursor and wollastonite by a hydrolysis precipitation process. The antistatic properties of the wollastonite materials under different calcined conditions and composite materials (nano-SnO2/wollastonite, SW) were measured by rubber sheeter and four-point probe (FPP) sheet resistance measurement. Effects of hydrolysis temperature and time, calcination temperature and time, pH value and nano-SnO2 coating amount on the resistivity of SW powders were studied, and the optimum experimental conditions were obtained. The microstructure and surface properties of wollastonite, precipitate and SW were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), specific surface area analyzer (BET), thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier translation infrared spectroscopy (FTIR) respectively. The results showed that the nano-SnO2/wollastonite composite materials under optimum preparation conditions showed better antistatic properties, the resistivity of which was reduced from 1.068 × 104 Ω cm to 2.533 × 103 Ω cm. From TG and XRD analysis, the possible mechanism for coating of SnO2 nanoparticles on the surface of wollastonite was proposed. The infrared spectrum indicated that there were a large number of the hydroxyl groups on the surface of wollastonite. This is beneficial to the heterogeneous nucleation reaction. Through morphology, EDS and XPS analysis, the surface of wollastonite fiber was coated with a layer of 10–15 nm thickness of tin oxide grains the distribution of which was uniform.

Investigation on Temperature-Dependent Electrical Conductivity of Carbon Nanotube/Epoxy Composites for Sustainable Energy Applications

Composites with carbon nanotubes are becoming increasingly used in energy storage and electronic devices, due to incorporated excellent properties from carbon nanotubes and polymers. Although their properties make them more attractive than conventional smart materials, their electrical properties are found to be temperature-dependent which is important to consider for the design of devices. To study the effects of temperature in electrically conductive multi-wall carbon nanotube/epoxy composites, thin films were prepared and the effect of temperature on the resistivity, thermal properties and Raman spectral characteristics of the composite films was evaluated. Resistivity-temperature profiles showed three distinct regions in as-cured samples and only two regions in samples whose thermal histories had been erased. In the vicinity of the glass transition temperature, the as-cured composites exhibited pronounced resistivity and enthalpic relaxation peaks, which both disappeared after erasing the composites’ thermal histories by temperature cycling. Combined DSC, Raman spectroscopy, and resistivity-temperature analyses indicated that this phenomenon can be attributed to the physical aging of the epoxy matrix and that, in the region of the observed thermal history-dependent resistivity peaks, structural rearrangement of the conductive carbon nanotube network occurs through a volume expansion/relaxation process. These results have led to an overall greater understanding of the temperature-dependent behaviour of conductive carbon nanotube/epoxy composites, including the positive temperature coefficient effect.

Effect of Coulomb blockade, gold resistance, and thermal expansion on the electrical resistance of ultrathin gold films

Controlling the electrical resistance of granular thin films is of great importance for many applications, yet a full understanding of electron transport in such films remains a major challenge. We have studied experimentally and by model calculations the temperature dependence of the electrical resistance of ultrathin gold films at temperatures between 2 K and 300 K. Using sputter deposition, the film morphology was varied from a discontinuous film of weakly coupled meandering islands to a continuous film of strongly coupled coalesced islands. In the weak-coupling regime, we compare the regular island array model, the cotunneling model, and the conduction percolation model with our experimental data. We show that the tunnel barriers and the Coulomb blockade energies are important at low temperatures and that the thermal expansion of the substrate and the island resistance affect the resistance at high temperatures. At low temperatures our experimental data show evidence for a transition from electron cotunneling to sequential tunneling but the data can also be interpreted in terms of conduction percolation. The resistivity and temperature coefficient of resistance of the meandering gold islands are found to resemble those of gold nanowires. We derive a simple expression for the temperature at which the resistance changes from non-metal-like behavior into metal-like behavior. In the case of strong island coupling, the total resistance is solely determined by the Ohmic island resistance.

Structural, optical and electrical properties of Al-doped ZnO transparent conducting oxide for solar cell applications

Al-doped zinc oxide (AZO) thin films are deposited onto glass substrates using radio-frequency reactive magnetron sputtering and the improvements in their physical properties by post-synthesis thermal treatment are reported. X-ray diffraction spectra show that the structure of films can be controlled by adjusting the annealing temperatures, with the best crystallinity obtained at 400°C under a nitrogen atmosphere. These films exhibit improved quality and better optical transmittance as indicated by the UV-Vis spectra. Furthermore, the sheet resistivity is found to decrease from 1.87 × 10-3 to 5.63 × 10-4Ω⋅cm and the carrier mobility increases from 6.47 to 13.43 cm2 ⋅ V-1 ⋅ s-1 at the optimal annealing temperature. Our results demonstrate a simple yet effective way in controlling the structural, optical and electrical properties of AZO thin films, which is important for solar cell applications.

Low-temperature electrical conductivity of LaNi1-xFexO3

We report the electrical conductivity between 2 and 300 K for LaNi1-xFexO3 across the composition-controlled metal-insulator (m-i) transition. Using a method first suggested by Mobius, we identify the critical concentration x(c) to be 0.3 for the m-i transition. The negative temperature coefficient of resistivity observed at low temperatures in the metallic phase follows a temperature dependence characteristic of disorder effects. The semiconducting compositions (x greater than or equal to 0.3) do not show a simple activation energy but exhibit variable-range hopping at high temperatures confirming that the m-i transition in this system is driven by increasing disorder effects.

Phase conversions in calcium manganites with changing Ca/Mn ratios and their influence on the electrical transport properties

The phase-interconversions between the spinel-, brownmillerite-, defect rocksalt and perovskite-type structures have been investigated by way of (i) introducing deficiency in A-sites in CaxMn2-xO3 (0.05 <= x <= 1) i.e., by varying Ca/Mn ratio from 0.025 to 1 and (ii) nonstoichiometric CaMnO3-delta (CMO) with 0.02 <= delta <= 1. The temperature dependence of resistivity (rho-T) have been investigated on nonstoichiometric CaMnO3-delta (undoped) as well as the CMO substituted with donor impurities such as La3+, Y3+, Bi3+ or acceptor such as Na1+ ion at the Ca-site. The rho-T characteristics of nonstoichiometric CaMnO3-delta is strongly influenced by oxygen deficiency, which controls the concentration of Mn3+ ions and, in turn, affects the resistivity, rho. The results indicated that the substitution of aliovalent impurities at Ca-site in CaMnO3 has similar effects as of CaMnO3-delta ( undoped) annealed in atmospheres of varying partial pressures whereby electron or hole concentration can be altered, yet the doped samples can be processed in air or atmospheres of higher P-O2. The charge transport mechanisms of nonstoichiometric CaMnO3-delta as against the donor or acceptor doped CaMnO3 (sintered in air, P-O2 similar to 0.2 atm) have been predicted. The rho (T) curves of both donor doped CaMnO3 as well as non-stoichiometric CaMnO3-delta, is predictable by the small polaron hopping (SPH) model, which changes to the variable range hopping (VRH) at low temperatures whereas the acceptor doped CaMnO3 exhibited an activated semiconducting hopping ( ASH) throughout the measured range of temperature (10-500 K).