Study of the Effect of Siliceous Species in the Formation of a Geopolymer Binder: Understanding the Reaction Mechanisms among the Binder, Wood, and Earth Brick.

International audienceIn building construction, geopolymer binder or mortar can interact with the structural materials and thus modify the binder formation mechanisms. In a geopolymer binder, the availability and amount of siliceous species is a preponderant parameter influencing the nature of networks formed after consolidation. In this study, the interactions between the binder and structural materials (wood and earth bricks) were investigated by 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) and Fourier transform infrared spectroscopy (FTIR) during and after the consolidation. Then, the effect of the amount and nature of the siliceous species available in the reaction medium were analyzed. According to the siliceous species available, it is possible to form different types of materials (hardening or sedimented materials). By corroborating these results with MAS NMR and FTIR analyses, a formation scheme of the binder in contact with the materials was proposed

Interictal Functional Connectivity of Human Epileptic Networks Assessed by Intracerebral EEG and BOLD Signal Fluctuations

In this study, we aimed to demonstrate whether spontaneous fluctuations in the blood oxygen level dependent (BOLD) signal derived from resting state functional magnetic resonance imaging (fMRI) reflect spontaneous neuronal activity in pathological brain regions as well as in regions spared by epileptiform discharges. This is a crucial issue as coherent fluctuations of fMRI signals between remote brain areas are now widely used to define functional connectivity in physiology and in pathophysiology. We quantified functional connectivity using non-linear measures of cross-correlation between signals obtained from intracerebral EEG (iEEG) and resting-state functional MRI (fMRI) in 5 patients suffering from intractable temporal lobe epilepsy (TLE). Functional connectivity was quantified with both modalities in areas exhibiting different electrophysiological states (epileptic and non affected regions) during the interictal period. Functional connectivity as measured from the iEEG signal was higher in regions affected by electrical epileptiform abnormalities relative to non-affected areas, whereas an opposite pattern was found for functional connectivity measured from the BOLD signal. Significant negative correlations were found between the functional connectivities of iEEG and BOLD signal when considering all pairs of signals (theta, alpha, beta and broadband) and when considering pairs of signals in regions spared by epileptiform discharges (in broadband signal). This suggests differential effects of epileptic phenomena on electrophysiological and hemodynamic signals and/or an alteration of the neurovascular coupling secondary to pathological plasticity in TLE even in regions spared by epileptiform discharges. In addition, indices of directionality calculated from both modalities were consistent showing that the epileptogenic regions exert a significant influence onto the non epileptic areas during the interictal period. This study shows that functional connectivity measured by iEEG and BOLD signals give complementary but sometimes inconsistent information in TLE

A geopolymer mortar for wood and earth structures

International audienceIn building construction, because of the hygroscopic nature of wood and earth brick and the low adhesion between these materials, cracks are formed at their interface when they are assembled. Geopolymer binder has been show to create strong bonds between wood and earth brick. Assemblies of wood and extruded earth brick with geopolymer binder were manufacture and tested. Double shear tests at two scales were carried out that provided evidence of good adhesion and information about the influence of the type of brick on shear behavior. The workability of the binder was improved by adding siliceous aggregates. The mortar obtained has an improved compressive strength, ranging from 3 to 8 MPa, depending on the aggregate size. FTIR measurements and thermal analysis were performed to determine the reaction mechanis

New mortar for clay masonry structures

International audienceConstruction system using timber frame with earth brick infill shows the formation of cracks at their interface with the fluctuation of temperature and humidity. Geopolymer binder has been identified to create good adhesion between these two materials. The aim of the study is to characterize the pullout and shear mechanical behavior of laboratory masonry assemblies of wood, geomaterial binder and extruded earth brick. Compression test on the brick were also performed. Full-field deformation of double shear test sample werecarried-out by digital image correlation (DIC) in order to better describe and understand the mechanical behavior. The geopolymer binder show good adhesion properties with mean shear test results around 1.5 MPa and pullout test result around 0.82MPa. © (2013) Trans Tech Publications, Switzerland

Mechanical behavior of an assembly of wood-geopolymer-earth bricks

International audienceTimber frame construction with earth brick infill is a sustainable design that is promising in the building construction field. However, cracks form at the interfaces of the bricks and frame with temperature and humidity fluctuations. A geopolymer binder can create stronger bonds between these two materials than traditional mortar, potentially preventing crack formation. This study focuses on the pull-out and shear mechanical behavior of laboratory assemblies of wood, geomaterial binder and two different types of earth brick. The full-field displacements of double-shear test samples were also obtained by digital image correlation (DIC) to better describe and understand the mechanical behavior of the system. The results show that the geopolymer binder provides good adhesion of approximately 1.5 MPa or 2 MPa, depending on the type of brick. Failure localization is also different for each assembly, occurring inside the brick and binder or only inside the binder. This result is confirmed by DIC analysis. The microstructure of the brick has been correlated with the mechanical behavior of the assembly. First results show that the geopolymer binder can be used as a joint in wood and earth masonry. © 2012 Elsevier Ltd. All rights reserved

Experimental evaluation of hydric performances of masonry walls made of earth bricks, geopolymer and wooden frame

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Study of the Effect of Siliceous Species in the Formation of a Geopolymer Binder: Understanding the Reaction Mechanisms among the Binder, Wood, and Earth Brick

In building construction, geopolymer binder or mortar can interact with the structural materials and thus modify the binder formation mechanisms. In a geopolymer binder, the availability and amount of siliceous species is a preponderant parameter influencing the nature of networks formed after consolidation. In this study, the interactions between the binder and structural materials (wood and earth bricks) were investigated by ²⁹Si magic angle spinning nuclear magnetic resonance (MAS NMR) and Fourier transform infrared spectroscopy (FTIR) during and after the consolidation. Then, the effect of the amount and nature of the siliceous species available in the reaction medium were analyzed. According to the siliceous species available, it is possible to form different types of materials (hardening or sedimented materials). By corroborating these results with MAS NMR and FTIR analyses, a formation scheme of the binder in contact with the materials was proposed

Characterization of the coupled hygrothermal behavior of unfired clay masonries: Numerical and experimental aspects

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Physical-chemical characterization of Tunisian clays for the synthesis of geopolymers materials

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What is the significance of interictal water diffusion changes in frontal lobe epilepsies ?

International audienceThe aim of this study was to better understand the significance of interictal changes in water molecule diffusivity defined by diffusion-weighted imaging (DWI) in frontal lobe epilepsy (FLE), as well as to test the accuracy of interictal DWI in the definition of the epileptogenic zone (EZ).DWI was carried out in 14 patients with refractory FLE (9 negative-MRI) as well as in 25 controls. Statistical mapping analysis (SPM2) of diffusivity maps was used to detect, for each subject, significant diffusivity alterations. We then studied the relationships between diffusion and depth recorded electrical abnormalities. Clinical correlates of the extent of diffusivity changes were also tested. We found areas of significantly increased diffusivity (SID) in 13 patients. Eight had SID in the EZ, 9 within the irritative zone (IZ) and 12 outside, mainly in connected areas. We found a correlation between the extent of SID and the duration of epilepsy (p corrected = 0.026, R = 0.621). In addition, SID was significantly less widespread in negative-MRI patients (p = 0.028). However, we found no significant differences concerning either seizure frequency (p = 0.302), seizure generalization (p = 0.841), history of status (p = 0.396), or surgical outcome (p = 0.606). We suggest that SID in normal appearing areas is not a specific signature of epileptogenicity in FLE, and is more likely to reflect multifactorial and potentially evolving neuro-glial injuries