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The present paper is concerned with the simulation of the Casagrande test carried out on a rammed earth material for wall-type structures in the framework of Limit Analysis (LA). In a preliminary study, the material is considered as a homogeneous Coulomb material, and existing LA static and kinematic codes are used for the simulation of the test. In each loading case, static and kinematic bounds coincide; the corresponding exact solution is a two-rigid-block mechanism together with a quasi-constant stress vector and a velocity jump also constant along the interface, for the three loading cases. In a second study, to take into account the influence of compressive loadings related to the porosity of the material, an elliptic criterion (denoted Cohesive Cam–Clay, CCC) is defined based on recent homogenization results about the hollow sphere model for porous Coulomb materials. Finally, original finite element formulations of the static and mixed kinematic methods for the CCC material are developed and applied to the Casagrande test. The results are the same than above, except that this time the velocity jump depends on the compressive loading, which is more realistic but not satisfying fully the experimental observations. Therefore, the possible extensions of this work towards non-standard direct methods are analyzed in the conclusion section.

Reducing energy consumption for future buildings using bio-based insulation materials is currently one of the most attractive research pursuits. The specific purpose of this research was to optimize thermo-pressing conditions for new low-environmental-impact bio-insulation fiberboards from bamboo fibers and protein-based bone glues. The microstructure, thermal insulation, water sensitivity, and mechanical properties of these fiberboards were investigated in this study. As illustrated by the results, protein-based bone glue acts as a good internal binder for bamboo fiberboards when 30% (w/w) of glue was added and elaborated under specific thermo-pressing conditions (150 kgf/cm2, 160 °C) during 15 min. Indeed, this board presents the best mechanical properties and water resistance due to the effective adhesion of the proteins. The thermal conductivity of all the fiberboards is in a low range, between 0.0582 and 0.0812 (W.m−1K−1) at 57% RH and 25 °C, and it changes according to relative humidity levels and moisture content variation. The bamboo fibers have great potential for buildings thermal insulation with a thermal conductivity below 0.082 Wm−1K−1.

The present study evaluates the performances of a rammed earth (RE) structure under seismic loading and its reinforcement by using finite element simulations . First, the pertinence of the numerical model was evaluated through the simulation of an experimental test conducted on a 0.5-scale house and presented in the literature. A full 3D model, based on solid elements, and a 3D surface model based on shell elements were conducted. The effects of interface stiffness on the natural frequencies and on the non-linear dynamic behavior were examined. It was found that the interfaces played an important role to well reproduce the experimental results. Reinforcement techniques, such as horizontal reinforced concrete belt beam at the top or/and the middle height, and the internal reinforced concrete columns were also simulated and their benefits under seismic loading were conducted. The results obtained showed that these reinforcements enhanced the seismic capacity of RE house . The Rayleigh damping, which has been rarely addressed in the rammed earth structures, was also investigated.

The development of electrocatalyst for large-scale production of hydrogen and oxygen via water electrolysis with low overpotential is highly necessary. In this research, a novel electrocatalyst of sulfur-doped nickel cobalt phosphide nanosheets coating over structure of the conductive carbon cloth (CC) (S–NiCoP/CC) was synthesized via a facile electrodeposition method followed by a phosphidization step. Such hierarchical nanostructure with excellent porosity offered rich active sites and high electrical conductivity, thereby accelerating electrocatalyst activities for HER and OER in 1.0 KOH electrolyte. The S–NiCoP/CC required small overpotentials of 90 at 10 mA cm−2 for HER and 320 mV at 20 mA cm−2 for OER. In addition, an electrolyzer based on S–NiCoP/CC electrodes showed a cell voltage of 1.61 V at 20 mA cm−2 along with good stability in 1.0 M KOH electrolyte. The successful synthesis of S–NiCoP/CC prospectively opened a new aspect for developing effective electrocatalyst in water splitting application.

Rammed earth (RE) construction is attracting renewed interest throughout the world thanks to its sustainable characteristics: very low embodied energy, advantageous living comfort due to substantial thermal inertia, good natural moisture buffering and an attractive appearance. This is why several studies have recently been conducted to investigate RE. However, there have not yet been sufficient studies on the seismic performance of RE buildings. This paper presents an experimental study on the static nonlinear pushover method and its application to the seismic performance of RE structures. Several walls with different height/length ratios were built and tested to obtain nonlinear shear force–displacement curves. By transposing these shear force-displacement curves to an acceleration–displacement system and using the standard spectra presented in Eurocode 8, the performance points were determined, making it possible to assess the seismic performance of the walls studied in different conditions (seismicity zones and soil types).

Rammed earth (RE) is a soil-based construction material which attracts scientific researches because of its sustainable properties. This paper presents a numerical study to investigate the in-plane seismic behaviour of RE walls. First, an in-situ RE wall was modelled by the discrete element method (DEM). The robustness of the model was checked by comparing dynamic properties of the model with the experimental values. Then, an earthquake excitation was introduced to the model to assess the seismic behaviour of the RE wall studied. The signal was scaled at different amplitudes to assess the damages following different earthquake intensities. The drifts were recorded and the seismic behavior was discussed.

Rammed earth (RE) is a construction material manufactured from the soil. This material attracts the attention of numerous scientific investigations during the past decade due to its sustainable properties. The performance of RE buildings under horizontal loadings remains an important topic to be investigated. This paper presents an experimental study which identifies the limit states for the in-plane seismic assessment of RE walls. Four RE walls were tested under bi-axial loading: first a vertical force was applied on the top of the wall to simulate the dead and live loads in a building; then a horizontal force pushed at the top the walls to simulate a seismic action. The cracking evolution was recorded by using the DIC (digital image correlation) technique in which the displacement fields were determined by comparing the images taken after and before the loading. Based on the damage evolution observed during the tests and on a similar approach of unreinforced masonries, the present paper proposed four limit states for RE walls corresponding to the inter-storey drift δ: no damage (before LS1) and slight damages (before LS2): δ

International audience; Rammed earth (RE) is a construction material which is made by compacting the soil in a formwork. This material is attracting the attention of the scientific community due to its sustainable characteristics. Among different aspects to be investigated, the seismic performance remains an important topic which needs advanced investigations. The existing studies in the literature have mainly adopted simplified approaches to investigate the seismic performance of RE structures. The present paper adopts a numerical approach to investigate the seismic behavior of RE walls with an L-form cross-section. The 3D FEM model used can take into account the plasticity and damage of RE layers and the interfaces. The model was first validated by an experimental test presented in the literature. Then, the model was employed to assess the seismic performance of a L-form wall of a RE house at different amplitudes of earthquake excitations. Influences of the cross-section form on the earthquake performance of RE walls were also investigated. The results show that the L-form cross-section wall has a better seismic performance than a simple rectangular cross-section wall with similar dimensions. For the L-form cross-section wall, the damage observed concentrates essentially on the connection between two flanges of the wall.

This paper presents an experimental investigation on the mechanical properties and microstructure of geopolymer concrete mixed using class F fly ash (FA), ground granulated blast-furnace slag (GGBS) and high-magnesium nickel slag (HMNS). An optimal combination of FA, GGBS and HMNS was determined using the compressive strength tests of geopolymer (GP) pastes mixed with various different replacements of FA with GGBS and/or HMNS. It was found that the replacement of FA with 20% of GGBS and 10% of HMNS in GP concrete increases the 28-day compressive strength by 100% and the 28-day splitting tensile strength by 58%. The microstructure analysis of the GP concrete using SEM, XRD, and FTIR showed the formation of aluminosilicate amorphous phase in a three-dimensional network. The SEM images revealed a fully compact and cohesive geopolymer matrix, which explains the reason why the mechanical properties of the FA based GP concrete with both GGBS and HMNS are improved.

Using in-situ soils for building constructions is attractive in the sustainable development because these materials have low embodied energy and present an interesting hygro-thermal behavior. Several researches have been recently carried out to study soil materials. However, the variability of soil characteristics on each construction site makes that the use of an unique construction technique (soil concrete, rammed earth, adobe, …) becomes difficult to satisfy several exigencies of the modern regulations (mechanical, thermal performances, durability and earthquake resistance), and the economic criterion. This paper introduces firstly a strategy which can facilitate the use of in-situ soils for building constructions. Relevant techniques corresponding to several in-situ soil types are proposed. Then, the application of the proposed approach is showed with a case study on a building project using a soil concrete. Several aspects are investigated: material optimization, architectural design, structural-thermal performances and life cycle analysis.

Electrochemical nonenzymatic sensor has achieved numerous attentions from analytical chemistry communities. A facile and direct synthesis route for developing high-performance electrocatalyst is essential to improve efficiency of sensor in terms of cost and catalytic activities for reliable analysis applications. In this research, we introduced an easy synthesis approach for the in-situ fabrication of iron sulfide nanosheets (Fe–S NSs) vertically grown on a nickel foam (NF) via an electrodeposition step. Such a self-supported Fe–S NSs/NF demonstrated sensitive and selective determination towards hydrogen peroxide (H2O2) with a wide sensing region ranging from 10 μM to 3.3 mM in 0.1 M KOH medium. Besides, it’s excellent sensitivity of 4.48 μA μM−1 cm−2, low detection limit of 7.9 μM, good reproducibility, and stability have been successfully demonstrated as well. The facile fabrication process of Fe–S NSs/NF opened a novel and effective avenue for the development of non-precious metal-based electrocatalysts in analytical chemistry.

A facile two-step approach has been developed to fabricate blackberry-like gold nanostructure uniformly depositing on surface of reduced graphene oxide/three-dimensional nickel foam (Au-rGO/3DNF). The hybrid material has been successfully applied as a free-standing biosensor for nonenzymatically detecting H2O2 in 0.1 ​M PBS medium. The results indicated that the sensor could detect H2O2 a low detection limit of 1.06 ​μM, wide linear detection range of 1–296 ​μM, and high sensitivity of 51.28 μA/(μM ⋅ cm2). In addition, the sensor showed excellent selectivity to H2O2 without poisonous influence from coexisting interferents, including ascorbic acid, dopamine, uric acid, urea, and KCl. Furthermore, the sensor also exhibited excellent repeatability, reproducibility and stability towards H2O2 detection. This may be due to the formation of a unique 3D nanoarchitecture, in which gold catalysts was effectively deposited on superconductive rGO to produce synergistic effect that efficiently improve electroactive sites, charge transfer ability, and mass diffusion. The achieved results may imply a highly potential method to develop a novel sensor with the enhanced performance for H2O2 sensing applications.

The development of anodic catalysts for direct methanol fuel cell applications has recently been concerned in both academy and energy industries. In this study, we successfully developed an efficient electrocatalyst based on ultra-small platinum nanoparticles (Pt NPs) deposited reduced graphene oxide (rGO) supported by a three-dimensional (3D) framework. The catalyst was directly used as a self-supported and binder-free electrode for electrocatalytically catalyzing methanol oxidation (MOR). The achieved results showed the enhanced catalytic behavior of Pt-rGO/3DF towards MOR along with an excellent stability, superior to another electrode catalyst based on commercial Pt-C product. Our findings implied that growth of the Pt NPs on rGO nanosheets supported by a three-dimensional (3D) foam could impressively increase the catalytic performance of the resulting catalyst material towards MOR in alkaline environment. This study may open a novel and efficient option for creating highly catalytic hybrid towards MOR in fuel cell applications.

Fabrication of efficient electrocatalysts for hydrogen evolution reaction (HER) is important to produce hydrogen fuel on a large scale via electrocatalytic water splitting. In this research, a novel electrocatalyst based on star-like molybdenum phosphide structure vertically grown on highly conductive graphene supported by a three-dimensional nickel foam (MoP/GR/NF) was synthesized via a facile hydrothermal method followed by a phosphidization strategy at 300 °C. The exclusive hierarchical nanostructure with abundant porosity was beneficial for enhancing active site numbers and electrical conductivity. In particular, the formation of Mo–P impressively changed electronic structure of the resulting material, thereby accelerating electrocatalytic activity for HER in 1.0 M KOH medium. The MoP/GR/NF required small overpotentials of 95 and 189 mV to deliver current densities of 10 and 50 mA cm−2, respectively. In addition, it also demonstrated a Tafel slope of 54 mV dec−1, which was significantly smaller than that of the GR/NF, Mo–O/GR/NF, and Mo–P/NF. Furthermore, there was negligible decrease of current response and overpotential for a continuous HER during long-term operation, implying its excellent stability. The prospective catalytic activity and good stability of the MoP/GR/NF material could prospectively open a new aspect for developing effective electrocatalyst for hydrogen production in water splitting application.

Rammed earth (RE) is a construction material manufactured by compacting the soil by layers in a formwork. This material has been the focus of numerous scientific researches in the last decades because of its sustainable properties and the heritage of RE buildings throughout the world. Several studies were performed to investigate different aspects of this material, however, there were few studies investigating on the capacity of nails on RE walls. Indeed, this resistance is important when occupants want to hang furniture (photo frames, kitchen cabinets…). This paper presents firstly an experimental study on the capacity of smooth steel nails (without dowel) horizontally fixed on RE specimens to carry vertical loads. Different types of nails with different diameters (from 3.1 to 5 mm) were tested, at different anchorage lengths into the RE specimens (from 65 to 120 mm). The results showed that one nail could hang 200–1000 N of vertical load, depending on the type of nail, the anchored length and the loading rate. It was worth noting that the steel nails were excessively deformed after the test. A numerical model was developed to analyze the results. The numerical results showed that RE was first plasticized in certain zones and then the steel nails were also plasticized. Influences of the creep phenomenon was also observed and analyzed.

In this study, we successfully prepared a highly sensitive hydrogen peroxide sensor by directly growing heterostructure of cobalt oxide-sulfide nanosheets on three-dimensional foam. As a self-supporting sensor, it exhibited good activity and excellent stability for hydrogen peroxide detection with a sensitivity of 0.059 mA μM−1 cm−2, wide detection range of 2 to 954 μM, and low detection limit of 0.890 μM. In addition, such sensor also displayed outstanding selectivity and good current response retention of around 87.1% after long-term operation of 1500 s. The achieved results may be due to the synergistic effects generated by the formation of metallic oxide-sulfide heterostructure and unique hierarchical 3D structure, which improved electroactive surface area, electron transfer, and electrolyte/ion diffusion, thereby resulting in the enhancement of catalytic performance. Our research may introduce a promising option for fabricating highly catalytic electrocatalyst towards hydrogen peroxide detection in analytical applications.

In this study, we developed a sensitive glucose sensor by hybridizing abundant gold nanoparticles on surface of copper sulfide nanosheets supported three-dimensional framework. The sensor showed high activity and long-term stability towards glucose oxidation. In this context, is was recognized an adequate sensitivity of 0.059 mA μM−1 cm-2, wide linear detection range of 1.98–976.56 μM, along with low LOD of 7.62 μM. Besides, the sensor also presented high selectivity and good retention of around 85.9% after long-term operation of 1800s. These results may be assumed to the synergistic effects produced by the combination between gold nanoparticles and copper sulfide nanosheets, as well as the formation of hierarchical 3D architecture, which promoted electroactive surface area, charge transfer, electrolyte penetration, and ion diffusion, thereby leading to the enhancement of catalytic activity. Our work may open a new option for developing highly catalytic material for glucose sensor in analytical purposes.

In this study, we developed a novel nanoneedle-like structure of zinc-doped cobalt hydroxide supported by three-dimensional porous architecture (Zn-Co-OH/3DNF) via a facile approach. The hybrid was successfully applied as a binder-free and self-supported sensor for nonenzymatic glucose detection in alkaline medium. The hybrid can detect glucose with a wide linear detection range of 10–3535 μM, low detection limit of 8.33 μM, and an acceptable sensitivity of 0.0061 mA μM−1 cm-2. In addition, the hybrid exhibited good selectivity, long-term stability, and durability. The obtained results may be due to the synergistic effect produced by the combination between zinc and Co-OH in the form of large-area nanoneedle-like structures, together with the high conductivity and large surface area of 3D supporting material; thereby improving electroactive sites, charge conductivity, and electrolyte diffusion. The achieved results suggested a novel approach for developing potential sensor with the improved performance towards glucose detection in analytical applications.

International audience; A new concept for the soil nail walls is here proposed and validated through experimental and numerical approaches. This process, based on the use of precast elements that are easier to install, is cheaper and more aesthetic than the classical methods, but the main advantage is reducing the cement consumption which conducts to divided carbon footprint by three. In order to characterize the structural capacity of this new process, this article present an investigation on two in-situ representative walls, one in shotcrete which is the old way of construction, and the other, consisting the precast reinforced concrete slabs, which is the new process. We thus have a demonstrator on a real scale, and perfectly representative, since the constructive modes, as well as the mechanical, thermal, and hydric loadings are the real ones associated with the environment in situ. Substantial instrumentation has been realized over a long period (nearly 2 years), enabling to follow the evolution of the displacements of each wall and the efforts in the anchor nails. To determine the bearing capacity of the constituent element of the precast nail wall, an experimental study coupled with a numerical simulation has been conducted in the laboratory on a single precast slab. This study allows the evaluation of the load associated to crack initiation and the bearing capacity associated to the ultimate state, at the scale of the constituent elements. Finally, in order to evaluate the behaviour of the two concepts of nail walls in the case of extreme solicitation, a dynamic loading induced by an explosion has been conducted on the site.

Beam-column joints are critical regions for reinforced concrete (RC) frames subjected to earthquakes. The steel reinforcement is, in general, highly concentrated in these zones. This is why in many cases, headed bars are used. A headed bar is a longitudinal steel reinforcement whose end has a special button added to reduce the bonding length of the steel rebar. This paper establishes a formula predicting the shear strength of exterior RC beam-column connections where the beam longitudinal reinforcements use headed bars. A database was collected, which contained 30 experimental data about the exterior beam-column joints using headed bars and subjected to quasi-static cyclic loading. First, from the collected database, a statistical study was carried out to identify the most influencing parameters on the shear strength of the beam-column joints tested. The three most important parameters were identified and an empirical modified formula was developed based on the formula existing in the standards. The study showed that the results obtained from the modified formula proposed in the present study were closer to the experimental results than that obtained from the formula existing in the standards. Finally, a numerical study was performed on two T-form RC structures and the numerical results were compared with the prediction calculated from the modified formula proposed. For two investigated cases, the proposed formula provided the results in the safety side and the differences with the numerical results were less than 20%. Thus, the proposed formula can be used for a rapid assessment of the shear strength of RC joints using headed bars.

Rammed earth (RE) is a construction material which is manufactured from the soil. The soil is dynamically compacted at its optimum water content, inside a formwork to build a monolithic wall. The RE wall is composed of several layers, about 10–12 cm thick. In the last decades, RE material has been the focus of numerous scientific researches because of sustainable properties of this material: low embodied energy, positive hygrothermal behavior and a particular esthetic aspect. In several situations, nondestructive methods are needed to assess the mechanical characteristics of RE material, for both old and new RE constructions. This paper presents how in situ vibrational measurements can be used to identify the dynamic behavior of RE walls and to determine the Young’s modulus of the RE walls measured. To determine Young’s modulus from the dynamic characteristics, an analytical model based on Timoshenko’s beam theory is presented, both for flexural and torsional modes. Then, the proposed analytical model is verified with measurements on several walls having different cross-sectional forms: rectangle and L-shape. The walls’ natural frequencies were identified from the dynamic measurements by using the Frequency Domain Decomposition method. In parallel, for comparison, the Young’s modulus of the RE material studied was also determined by classical static measurements (on the walls, prismatic and cylindrical specimens). The displacements were measured by using the Image Correlation technique. The comparisons showed that the results from the proposed analytical method provided high accuracies and better than that obtained by measurements on the usual specimens (prismatic and cylindrical).

Rammed earth (RE) is attracting renewed interest throughout the world thanks to its “green” characteristics in the context of sustainable building. In this study, the ageing effects on RE material are studied on the walls which have been constructed and exposed for 22 years to natural weathering. First, mechanical characteristics of the “old” walls were determined by two approaches: in-situ dynamic measurements on the walls; laboratory tests on specimens which had been cut from the walls. Then, the walls’ soil was recycled and reused for manufacturing of new specimens which represented the initial state. Comparison between the compressive strength, the Young modulus of the walls after 22 years on site and that of the initial state enables to assess the ageing of the studied walls.

Beam-column joints are commonly considered critic regions for RC frames subjected to earthquake. That is why assessing the beam-column joint capacity is an important topic, especially for structures constructed before the modern seismic design codes, or for buildings in post-seismic situations. Among the in-situ structural assessment methods, the vibrational testing is currently mentioned. The authors have developed an analytical method to assess the damage evolution of a structure in function of its dynamic characteristics. The method consists of two main steps and the first one necessitates a robust model which can reproduce the static behavior of the studied structure. For this purpose, the authors try and assess the relevancy of existing numerical models to choose the most relevant for the second step. This paper presents an assessment of the CDP (Concrete Damage Plasticity) model implemented in the Abaqus software. First, an experimental study on a RC beam-column frames is presented. Unloading-reloading cycles were performed during the tests and the displacement fields were recorded by using the image correlation technique. The experimental data are used to assess the relevancy of the CDP model, but these data can be useful also for the further studies to verify and improve the accuracy of the numerical or analytical models.

The shear design of concrete slabs is still an unsolved problem. The following study presents experimental and numerical investigations on the shear behaviour of reinforced concrete slabs (without shear reinforcement) under concentrated loads. The small thick slabs of 10 cm were tested in this study. Experimental tests were conducted to quantify the shear strength and the associated failure modes. The influence of several variables was addressed such as the influence of boundary conditions, four supported side slabs instead of two supported side slabs, the influence of loading plate length. A series of eight tests on six slabs were presented. The experiments are firstly used to evaluate the pertinence of Eurocode 2 and Model Code 2010 formulations using the levels of approximation LoA I and LoA II for the shear design of reinforced concrete slabs without shear reinforcement in comparison with the French approach, and secondly validated numerical modelling using the non-linear finite element method. The proposed numerical model showed good agreement with the experimental results in terms of slab behaviour.; La conception au cisaillement de dalles en béton reste encore un problème irrésolu. L'étude suivante présente des investigations numérique et expérimentale sur le comportement au cisaillement de dalles en béton armé (sans renforcement au cisaillement) sous charge localisée. Des dalles de faible épaisseur (10cm) ont été testées dans cette étude. Les essais ont permis de quantifier la résistance au cisaillement et les modes de rupture associés. L'influence de plusieurs paramètres a été étudiée telles que les conditions-limites ou les dimensions du plateau de chargement. Une série de 8 essais sur 6 dalles est présentée. Les expériences ont été dans un premier temps, utilisées pour évaluer la pertinence des formules de l'Eurocode 2 et du ModelCode 2010 en utilisant les niveaux d'approximation LoAI et LoAII pour le dimensionnement au cisaillement de dalles en béton armé sans renforcement au cisaillement en comparaison de l'approche française. Dans un second temps, les résultats ont été validés numériquement par une méthode aux éléments finis non-linaires. Le modèle numérique proposé a montré une bonne adéquation avec les résultats expérimentaux en termes de de comportement de dalle.

In several cases where high quantities of steel reinforcements are needed at reinforced concrete (RC) beam-column joints, headed bars are employed as a solution to facilitate the placing of reinforcement bars. This paper establishes a new formula for the prediction of the shear strength of exterior RC beam-column joints where beam longitudinal reinforcements use headed bars. A database was collected, which contains most of available test data of exterior beam-column connections using headed bars and subject to quasi-static cyclic loading. First, influences of the key parameters for the joint shear strength of the connections were evaluated by using the collected database. Then, three most important parameters were chosen to develop a formula for the prediction of the joint shear strength. The accuracy of the proposed formula was evaluated by comparing the predicted joint shear strength using the proposed formula and that of 30 experimental exterior connections collected from different sources, and also with predicted values using two existing analytical models. This evaluation showed a better relevancy of the proposed model in predicting exterior joint shear strength, compared to the existing formulas

Earth is an ancient building material which has been recently the focus of scientific research due to its sustainable properties. The disadvantage of earthen material is its low strength and its sensibility to the water content. To enhance the durability and the mechanical characteristics of earthen material, hydraulic binders are currently added (cement or lime) which have high embodied energy and therefore increase the embodied energy of the stabilized earth material. This paper presents an exploratory study which uses geopolymer as a stabilizer for earthen material. Geopolymers are inorganic binders with polymeric structure obtained by alkaline activation of raw materials containing silicon and aluminum; they are obtained by dissolution/precipitation reactions at low temperature. The present study proposes to use blast furnace slag as geopolymer raw material, which was mixed with an alkaline solution activator to obtain the stabilizer for earthen material. The geopolymer effects were investigated on two types of earthen material: rammed-earth (RE, soil dynamically compacted) and soil-geopolymer-concrete (soil poured with more water content). The results show that geopolymer had more effects in soil-concrete than in rammed-earth. Indeed, RE specimens stabilized by geopolymer did not present a significant improvement of compressive strength comparing to the unstabilized RE specimens. Soil-geopolymer-concrete specimens had double compressive strength comparing to soil-cement-concrete specimens.

Thermal power plants (TPP) generates wastes (bottom and fly ashes) which become a serious environmental problem in Vietnam. Indeed, although in several countries fly ash can be used for cement industry, fly ash from actual TPP in Vietnam does not have enough good quality for cement production, because the fly ash treatment phase has not yet included in the generations of existing Vietnamese TPP. That is why bottom ash and fly ash purely become wastes and their evacuation is an urgent demand of the society. This paper presents an investigation using fly and bottom ashes in the manufacturing of construction materials. The aim of this study is to propose a possibility to reduce environmental impacts of fly and bottom ashes, and manufacture construction materials having low embodied energy by using less cement. Several proportions of fly ash, cement, gravel, sand and water are tried to manufacture low strength concretes which can be used for non-load-bearing walls. Specimens are tested in uniaxial compressions. Results show that with a reasonable cement amount (4–8% by weight), by replacing cement by fly ash or replacing sand by bottom ash at 10-30%, the obtained materials can be used for non-bearing materials or low strength structural materials.

Rammed-earth (RE) is a construction material manufactured from the soil. The soil is compacted at its optimum water content, inside a formwork to build a monolithic wall. RE material is attracting renewed interest throughout the world thanks to its sustainable characteristics: low embodied energy, substantial thermal inertia, and natural regulator of moisture; on the other hand, the existing historic RE buildings is still numerous. This is why several research studies have been carried out recently to study different aspects of this material. However, few investigations have been carried out to explore the possibility of applying the nondestructive techniques on RE walls. This paper presents an assessment of the well-known rebound hammer test on RE walls. The calibration curves of the rebound hammer test have been established for conventional concrete where the rebound number is more than 20. For RE material with lower compressive strengths, a new calibration curve must be established. In the present study, two soils were used and different homogenized specimens with different dry densities were manufactured and tested, to plot a general calibration curve. Then, this calibration curve was applied to RE specimens; different results at different positions in an earthen layer were observed, due to the inhomogeneity of the material. The final results showed an acceptable accuracy of the calibration curve in the prediction of the compressive strength of RE material.

Bamboo is a natural material having a fast reproduction and high mechanical strengths. However, when a bio-based material in general, and bamboo in particular are expected to be a construction material, their sensitivity to moisture and their durability are usually questionable. Indeed, it is well known that these materials do not possess the same performance in the long-term, when compared to industrial materials. Sustainable solutions for the bamboo treatment still need to be investigated. The present study explores the oil-heated treatment with different types of oils, like flax or sunflower oils. The present investigation concentrates on mechanical properties and durability of treated bamboos to assess the effectiveness of these kinds of treatment. First, bamboo specimens were treated to decrease their sensitivity to moisture and improve their durability. Different conditions of treatment were tested: treatment at 100 °C or 180 °C; with flax oil, sunflower oil, or without oil; treatment durations of 1 h, 2 h, or 3 h; and, different cooling methods and cooling durations. Then, mechanical and durability tests were carried out on untreated and treated bamboos: uniaxial compression tests, 3 points bending tests, water immersion tests, and humidity tests. The results showed that some tested treatment methods could increase both the durability and the compressive strength of treated specimens, compared to untreated bamboo. The best results were observed on specimens treated at 180 °C during 1 h or 2 h without oil, and then cooled in 20 °C sunflower oil.

In this paper, influence of moisture content on the mechanical characteristics of rammed-earth has been studied. Samples from different soils (sandy, clayey, stabilised) were manufactured and tested in unconfined compression at several moisture contents. Compressive strength, elastic modulus and Poisson's ratio were determined. A simplified method to measure the suction within rammed earth samples has been developed and validated. The variation of mechanical characteristics related to moisture content and suction are presented. This paper shows that a slight increase in the moisture content of dry rammed-earth is not followed by sudden drop in wall strength. Qualitative explanations at the nano-scale are presented.

In present work, we proposed a novel nanohybrid based on hierarchical molybdenum dichalcogenide nanosheets uniformly assembled over surface of nitrogen-doped graphene (MoS2 NSs/N-Gr) via a facile and cost-effective synthesis approach. The developed material was applied for highly sensitive dopamine (DA) detection. It was demonstrated that the MoS2 NSs/N-Gr nanohybrids displayed excellent sensitivity towards DA sensing with an outstanding detection range of 3.2 μM–5.68 mM, low detection limit of 11.9 μM (S/N = 3), and very fast response (~1.5 s). In addition, the proposed sensor also exhibited long-term stability and good selectivity for the target analyte. Remarkably, it can successfully perform accurate detection of DA in human blood serum samples. Therefore, the results suggest that such nanohybrid-based sensor may be a potential candidate for electrochemical detection of DA in practical analysis.

A hierarchical nanohybrid based on vertical cobalt oxide nanorods shelled with nickel oxide supported on a three-dimensional foam was prepared by a simple synthetic procedure. The unique nanoarchitecture along with superior conductivity and synergistic effect between components made hybrid become as a sensitive non-binder and free-standing sensor for non-enzymatic glucose detection at low concentration. In this regard, the hybrid exhibited excellent electrocatalytic activity towards glucose oxidation with a wide linear detection range of 1 μM to 2 mM, excellent sensitivity of 4.86 μA/(mM ⋅ cm2), low detection limit of 1.07 μM, and rapid response time of

Here we propose a novel nanohybrid of bimetallic nickel‑tungsten sulfides nanostructures uniformly distributed on nitrogen-doped graphene with efficient ORR performance in 0.1 M KOH electrolyte. The material exhibits high limit current density, positive onset potential (+0.97 V) and half-wave potential (+0.82 V), and a small Tafel slope of 101 mV/dec, which are comparable to a commercial Pt/C (20 wt%). In addition, the material also shows superior stability, durability, and methanol tolerance than those of the Pt/C. The good performance can be credited to the synergistic effects of bimetallic nickel‑tungsten sulfides, which lead to the modification of electronic structure with the enhanced electroactive sites for ORR. In addition, the large surface area and high conductivity of nitrogen-doped graphene stably disperse active metals with good interaction to effectively avoid reaggregation/agglomeration and promote the charge transfer at the interface. The achieved results of this work present efficient and durable electrocatalyst, highly potential towards ORR in alkaline fuel cell applications.

The performance of an electrochemical sensor for detecting small biomolecules can be greatly upgraded by properly controlling the chemical nanostructure of electrocatalyst. In this study, we successfully prepared a unique hierarchical three-dimensional nanoarchitecture based on gold nanocrystals supported cobalt nanorods on foam substrate via a facile synthesis approach. The Au-Co NRs/3DNF hybrid has been effectively utilized as a novel binder-free self-supported electrochemical sensor for hydrogen peroxide detection with wide linear detection range of 2–799 μM, low limit of detection of 1.42 μM, long-term stability, and very excellent selectivity. Besides, the hybrid precisely detected hydrogen peroxide in real samples. The achieved results can be explained by the synergistic effect produced by the combination between gold and one-dimensional Co NRs. In addition, the 3D nanostructure with self-supported ability, large surface area, and without the use of any polymer binder, leads to the enhanced electroactive sites, conductivity, electrolyte penetration, and ion diffusion, thereby promoting the sensing performance. The results imply that the hybrid may open a prospective way for developing electrochemical sensor towards efficient detection of hydrogen peroxide.

International audience; Rammed earth (RE) is attracting renewed interest throughout the world because of its low embodied energy and its interesting hygric-thermal behavior. Several studies have recently been carried out to investigate this material. However, the seismic behavior of RE walls is still an important subject that needs to be more thoroughly investigated. The present study assesses the seismic performance of RE walls by using the discrete element modeling (DEM) and the nonlinear pushover method. Firstly, nonlinear “force–displacement” curves of the studied wall were obtained by DEM. Secondly, the standard “acceleration–displacement” curves were carried out following Eurocode 8. Thirdly, the above curves were superimposed to determine the intersection point (target point) which enabled to assess the seismic performance of the studied wall in the corresponding conditions (vertical load, seismic zone). The results show that the studied walls can have satisfactory resistance in seismicity zones ranging from “very low” to “moderate” (according to Eurocode 8). For “medium” seismicity zones, the studied structures should only be constructed on A-type soils (very good soil). For B-type soils, wall reinforcement techniques would be necessary. Without special reinforcements, studied RE structures seem unsuitable for “strong” seismicity zones, for all soil types.

International audience; Rammed earth is attracting renewed interest throughout the world thanks to its “green” characteristics in the context of sustainable development. Several research studies have thus recently been carried out to investigate this material. Some of them attempted to simulate the rammed earth’s mechanical behavior by using analytical or numerical models. Most of these studies assumed that there was a perfect cohesion at the interface between earthen layers. This hypothesis proved to be acceptable for the case of vertical loading, but it could be questionable for horizontal loading. To address this problem, discrete element modeling seems to be relevant to simulate a rammed earth wall. To our knowledge, no research has been conducted thus far using discrete element modeling to study a rammed earth wall. This paper presents an assessment of the discrete element modeling’s robustness for rammed earth walls. Firstly, a brief description of the discrete element modeling is presented. Then the parameters necessary for discrete element modeling of the material law of the earthen layers and their interfaces law following the Mohr–Coulomb model with a tension cut-off and post-peak softening were given. The relevance of the model and the material parameters were assessed by comparing them with experimental results from the literature. The results showed that, in the case of vertical loading, interfaces did not have an important effect. In the case of diagonal loading, model with interfaces produced better results. Interface characteristics can vary from 85 to 100% of the corresponding earthen layer’s characteristics.

In the cloud computing context, performance isolation is enforced by giving to each VM a given fraction of each resource, namely a fraction of physical memory, a fraction of the CPU capacity and a fraction of IO bandwidth. However, micro architecture-level resources such as processor caches cannot be divided and allocated to VMs: they are globally shared between all VMs, which compete for their use, and it can lead to cache contention. Therefore, performance isolation and predictability are compromised. In this paper, we propose a software solution (called Kyoto) to this issue, inspired by the polluters pay principle. A VM is said to pollute a cache if it provokes significant cache replacements, which affect the performance of other VMs. We rely on hardware performance counters to monitor the cache activities of VMs and measure their level of cache pollution. Each VM is allocated a given pollution permit. A VM, which exceeds its permitted pollution, has its CPU capacity reduced accordingly. We present the implementation of Kyoto in the Xen system and its evaluation with several benchmarks.

Rammed earth construction is attracting a renewed interest throughout the world thanks to its “green” characteristics in the context of sustainable development. Several studies have been carried out to investigate this material and evaluate its durability along with its mechanical, thermal and earthquake capacities. This paper presents a study on the parameters needed for the seismic design of rammed earth buildings in accordance with current earthquake standards. First, the dynamic parameters of buildings such as natural frequencies and damping ratios–which were necessary to determine the equivalent static seismic force–were identified using in-situ dynamic measurements. Then, these experimental values were compared with the values calculated by empirical formulas suggested in Eurocode 8 to demonstrate that these formulas were applicable for the cases of rammed earth structures. Then, modeling was done to find a simple suitable model for rammed earth structures. Laboratory experiments were developed to measure the Poisson’s ratio which was necessary for the models. The results provided by the shear-beam model were close to that of in-situ experiments, which showed a shearing behavior of rammed earth structures. Elements which influenced the dynamic behavior of this structural type were also discussed. Understanding the dynamic characteristics of rammed earth structures will help engineers in their design of new rammed earth buildings but also in earthquake analyses of existing rammed earth buildings.

Thermal power plants (TPP) generates wastes (bottom and fly ashes) which become a serious environmental problem in Vietnam. Indeed, although in several countries fly ash can be used for cement industry, fly ash from actual TPP in Vietnam does not have enough good quality for cement production, because the fly ash treatment phase has not yet included in the generations of existing Vietnamese TPP. That is why bottom ash and fly ash purely become wastes and their evacuation is an urgent demand of the society. This paper presents an investigation using fly and bottom ashes in the manufacturing of construction materials. The main aims of this study is to reduce environmental impacts of fly and bottom ashes, and to test another non-conventional binder to replace cement in the manufacture of unburnt bricks. Several proportions of fly ash, bottom ash, cement, gravel, sand and water were tested to manufacture concretes. Then, geopolymer was prepared from the fly ash and an activator. Specimens were tested in uniaxial compressions. Results showed that the cement concrete tested had the compressive strengths which could be used for low rise constructions and the material using geopolymer could be used for non-load-bearing materials (unburnt bricks).

Rammed earth construction is an ancient technique that is attracting renewed interest throughout the world today. Since it is carried out by stacking layers of rammed earth, it is possible that the rammed earth material is anisotropic. This paper presents the first study of this anisotropy, carried out on two scales. The first is the scale of Representative Volume Elements (RVEs) of the rammed earth material, with dimensions close to those of the walls on site, manufactured and tested in the laboratory. The second is the microscopic scale, for which tests were carried out on equivalent Compressed Earth Blocks (CEBs). A conventional homogenization procedure was carried out to determine the relationships of the microscopic scale and the RVE scale. The compressive strengths, elasticity moduli and failure moduli are similar in both directions of the material: perpendicular and parallel to the layers. The sum of these results allows us to propose the hypothesis that the rammed earth material is an isotropic material of the first order, if the layers remain adherent to each other.

This paper presents a study on the durability of different types of stabilised and unstabilised rammed earth walls. These rammed earth walls were constructed and exposed for 20 years to natural weathering, in a wet continental climate. None of these walls have shown complete collapse to date. A method to measure the rammed earth walls erosion by stereo-photogrammetry has been developed. The result shows that the mean erosion depth of the studied walls is about 2 mm (0.5% wall thickness) in the case of rammed earth wall stabilised with 5% by dry weight of hydraulic lime and about 6.4 mm (1.6% wall thickness) in the case of unstabilised rammed earth walls. The stabilisation enables to not use any plaster to protect the walls. In the case of the unstabilised rammed earth walls, an extrapolated lifetime longer than 60 years can be assessed. This shows a potential for the use of unstabilised rammed earth in the similar climatic conditions with this study. The method of stereo-photogrammetry used to measure the erosion of rammed earth walls on site may also help to calibrate and develop more pertinent laboratory test to assess the durability of rammed earth wall.

In order to give an example of a scientific approach adapted to non-industrial materials, we chose to study a structural element: a load-bearing building wall made of rammed earth material. Rammed earth construction is an ancient technique which is attracting renewed interest throughout the world today. Although rammed earth is currently regarded as a promising material in the construction sector in the context of sustainable development, it is still difficult to quantify its durability, as well as its thermal and mechanical performances, which discourages people from using it. This paper is devoted to the study of the last problem. Three different scales were studied. The first is the scale of in-situ walls. Dynamic measurements were carried out on site to determine the Eigen frequencies of the walls. The elastic modulus was determined from the frequencies measured by using a finite element model. The second is the scale of a representative volume element (RVE). Rammed earth RVE samples with dimensions similar to those of the walls on site were manufactured and tested in the laboratory. Finally, at the last scale, called the micro-mechanical scale, tests were performed on equivalent compressed earth blocks (CEBs), which can replace the rammed earth RVE samples to facilitate laboratory tests.

International audience; Après un événement (séisme, modifications du voisinage, ...), une structure BA peut être endommagée. La capacité résistante de cette structure peut être évaluée par des mesures vibratoires. A l'heure actuelle, ce type de mesures permet le diagnostic à l'échelle globale (toute la structure) et de manière qualitative alors que la localisation et la quantification des endommagements restent encore à approfondir. Dans le cadre de cette recherche, le diagnostic à l'échelle locale d'une structure poteaux-poutres béton armé instrumentée en laboratoire est étudié. Ce travail s'insère dans un contexte national de réévaluation des structures existantes. En première partie, le travail de recherche a commencé par une expérimentation en laboratoire sur une structure poteaux-poutres de type H (deux poteaux et une poutre). Différentes sollicitations croissantes ont été imposées au milieu de la poutre correspondant à différents états d'endommagement. Des mesures de champs de déplacement de toute la structure et des mesures vibratoires par accéléromètres ont été effectuées. A partir des mesures vibratoires, les caractéristiques dynamiques de la structure ont été identifiées (fréquences propres, déformées modales). Ces caractéristiques ont permis de caler un modèle numérique EF simplifié (établi par Matlab), qui utilise les éléments « barres » et les connexions semi-rigides entre les poteaux et les poutres. Les rigidités de ces connexions ont été identifiées par des boucles d'optimisation pour trouver les résultats qui s'approchent le plus des résultats expérimentaux. Les rigidités identifiées des connexions sont utilisées pour calculer des facteurs de rigidités qui varient entre 0 (rotule parfaite) et 1 (encastrement parfait). Ils apportent des informations sur l'état d'endommagement des connexions étudiées. Par conséquent, l'évaluation des connexions par des mesures dynamiques, à l'échelle du laboratoire, est possible. En deuxième partie, pour pouvoir vérifier l'influence des endommagements locaux sur d'une part, la réponse dynamique globale de la structure et d'autre part, sur la capacité structurelle globale de toute la structure, un code EF plus complexe (Castem) a été utilisé. Des éléments poutres multifibres ont été utilisés pour modéliser la structure du type portique. Dans un premier temps, les paramètres des matériaux (« béton » et « acier ») ont été identifiés en fonction des résultats expérimentaux sur les matériaux. Ensuite, le résultat numérique sur le portique est comparé avec l'expérimentation. La pertinence du modèle numérique dans l'évaluation de la capacité de la structure après les premiers endommagements est discutée.