Overview on bio-based building material made with plant aggregate

Global warming, energy savings, and life cycle analysis issues are factors that have contributed to the rapid expansion of plant-based materials for buildings, which can be qualified as environmental-friendly, sustainable and efficient multifunctional materials. This review presents an overview on the several possibilities developed worldwide about the use of plant aggregate to design bio-based building materials.  The use of crushed vegetal aggregates such as hemp (shiv), flax, coconut shells and other plants associated to mineral binder represents the most popular solution adopted in the beginning of this revolution in building materials.  Vegetal aggregates are generally highly porous with a low apparent density and a complex architecture marked by a multi-scale porosity.  These geometrical characteristics result in a high capacity to absorb sounds and have hygro-thermal transfer ability.  This is one of the essential characteristics which differ of vegetal concrete compared to the tradition mineral-based concretes.  In addition, the high flexibility of the aggregates leads to a non-fragile elasto-plastic behavior and a high deformability under stress, lack of fracturing and marked ductility with absorbance of the strains ever after having reached the maximum mechanical strength.  Due to the sensitivity to moisture, the assessment of the durability of vegetal concrete constitutes one of the next scientific challenging of bio-based building materials

Processing the vane shear flow data from Couette analogy

The original contribution is available at http://www.ar.ethz.ch/International audienceA new procedure is described to convert the vane torque and rotational velocity data into shear stress vs shear rate relationships. The basis of the procedure consists in considering locally the sheared material as a Bingham fluid and computing a characteristic shear rate from Couette analogy. The approach is first applied to experimental vane data of Newtonian fluid, then used to process vane experimental data of non-Newtonian and yield stress materials. Results, which are favourably compared with torsional flow, show that the approach correctly predicts the rheological behaviour of the materials investigated

Courbes d'écoulement en géométrie Couette par une approximation de Bingham

National audienceUne méthode simple pour identifier la courbe d'écoulement d'un fluide en cisaillement dans une géométrie Couette est développée. Elle consiste à considérer le fluide en écoulement comme étant un fluide de Bingham, et à évaluer la vitesse de cisaillement caractéristique du fluide partiellement et/ou complètement cisaillé. La pertinence et l'intérêt pratique de la méthode sont examinés en analysant les résultats générés par des données numériques en géométrie Couette de fluides de propriétés fixées, en variant la taille de l'entrefer, puis en l'appliquant aux données expérimentales en géométrie Couette et vane d'un fluide visqueux newtonien et d'une suspension de Carbopol

Fatigue behavior of damaged concrete beams repaired with composite material

By the present paper, an analytical model was developed to study the cracked FRP-strengthened reinforced concrete beams subjected to fatigue loading. In order to follow the distribution of interfacial shear stresses causing the debonding phenomenon, a new analytical model based on the cohesive zone (CZ) approach was developed. The present model has the possibility to describe the evolution of the shear stress in the three zones (elastic, microcrack and debonding) and the bearing capacity of the repaired structure. Interface damage scenarios were evaluated for a fatigue load estimated to 90% of the elastic load and another at 60% of the ultimate load Pu.  Results obtained are in good agreement with those given by the literature. The results showed that the shear strength developed by the repaired beam is sensitive to the variation of the mechanical properties (Concrete, FRP and Adhesive layer), the fatigue load ratio and the number of cycles. These parameters can be considered as indicators of damage affecting the health status of the structure repaired during fatigue. The debonding at the FRP-concrete interface noticeably reduced the strength and lifespan of the repaired structure.&nbsp

Structural build-up of rigid fiber reinforced cement-based materials

International audienceThe structural build-up of rigid fiber reinforced cement-based materials is studied. It has recently been shown that the behaviour of fiber reinforced concrete depends on the orientation of the fibers that has to be optimized during casting. As a result, there is a great interest to study the rheology of fiber reinforced concrete. One of the most important characteristics of modern fresh concretes is the structural build-up which is involved in many recent issues of concrete casting. This characteristic depends on the cement pastes chemical activity. This present work shows that structural build-up modelling used for common concretes can be generalized to fiber reinforced concretes. It can be shown that, if the inclusions percolation threshold is not reached, the structural build-up rate Athix is amplified by the addition of fibers and aggregates. Finally, this amplification of the structuration is estimated using modelling initially developed for spherical inclusions and aggregates

Utilization of air granulated basic oxygen furnace slag as a binder in belite calcium sulfoaluminate cement: A sustainable alternative

Basic oxygen furnace (BOF) slag negatively impacts ordinary Portland cement performance when replacement levels exceed 5%. This necessitates the exploration of alternative applications for the slag. Simultaneously, a high-volume slag utilization is desired to benefit slag recycling as supplementary cementitious materials. Therefore, this study aims to optimize the air granulated BOF slag substitution potential in belite calcium sulfoaluminate cement by investigating the hydration products in standard mortar. The reactivity of the novel binder is correlated with workability, and mechanical performance by thermal, mineralogical, and microstructure analysis. Consequently, the 10–30% replacement delays the final setting time by inhibiting the ettringite formation leading to a decrease in mechanical performance till 28 days. At later ages (28–180 days), the 30–50% substitution exhibited the synergy in mechanical performance, which is attributed to the hydrogarnet, calcium silicate hydrate, and strätlingite formation. Moreover, all the mortar samples exhibited heavy metals’ leaching and drying shrinkage below the permissible limit.</p

Etude statistique et Caractérisation Mécanique des Bétons Polymères Sollicités en Flexion (S06)

Le travail proposé est une étude expérimentale du comportement mécanique d'un béton polymère sollicité en flexion 3- points. Le béton élaboré est constitué d'une matrice en résine polyester renforcée par la poudre de marbre et des granulats de sable. Sept types de formulation d'échantillons composites sont préparés et dimensionnés selon la norme ASTM C580-02 où la matrice polymère est prise constante représentant 14% de la masse totale. Vu les dispersions des résultats des analyses statistiques par la variance Anova et par les distributions de Weibull à 2 et à 3-paramètres ont été utilisées. L'analyse des résultats obtenus montre que le taux de la poudre de marbre et des granulats de sable ont un effet significatif sur la résistance du béton polymère et que la distribution de Weibull à 2-paramètres décrit mieux les résultats expérimentaux que celle à 3-paramètres

Réhabilitation des Poutres en Béton Armé Rompues au Cisaillement à l'aide des Matériaux Composites (S06)

L'objectif de cette étude est de développer une nouvelle technique d'approche pour la réparation des poutres en béton armé chargées en flexion 4-points et rompues par cisaillement. Cette technique utilise des matériaux composites dans la zone critique de la poutre. Pour ce faire un programme d'essais a été entrepris afin d'en juger la faisabilité, les performances, le comportement et la rupture de poutres en béton armé. De plus, les résultats obtenus par cette méthode ont montré une supériorité dans la capacité de charge et un changement du mode de rupture du cisaillement à la flexion comparativement avec des travaux antérieurs des auteurs qui consistaient à faire des réparations des poutres par collage de composites en forme de U

Impact of Bio-Aggregates Properties on the Chemical Interactions with Mineral Binder, Application to Vegetal Concrete

Plant concretes were developed and are currently used as filling material in a timber frame. Their properties are strongly related to the bio-aggregates characteristics. In addition, since hemp shiv, the reference bio-based aggregate, has a limited availability, it is necessary to consider alternative bio-aggregates largely and locally available. Thus, this paper focused on identifying and understanding mechanisms of interaction between different bio-aggregates and mineral binders. To address this issue, the first objective was to determine the properties of five hemp shives and two alternative bioaggregates for vegetal lightweight concrete: corn and sunflower bark particles. The study of the chemical interactions between bio-aggregates and a pozzolanic binder was conducted on model pastes mixed with filtered solutions containing bio-aggregates extractives. The mechanical properties of the paste, as well as their hydration and their mineralogical evolution were studied. In the last part, the mechanical behavior of vegetal concretes was assessed. The results highlight a strong relation between the mechanical behavior of pastes and concretes and the extractive content of the different tested bio-aggregates. Finally, pastes appeared as a relatively good model to predict the behavior of concretes by following their early age performances: setting delay and 3-day mechanical strength

Repair of reinforced concrete beams in shear using composite materials PRFG subjected to cyclic loading

Nowadays, finding new approaches to attenuate the effects of the catastrophic shear failure mode for reinforced concrete beams is a major challenge. Generally the bending failure is ductile. It allows a redistribution of the stresses providing an early warning, whereas the rupture by shear is fragile and sudden which can lead to detrimental consequences for the structures. This research focuses on the repair of deep beams in reinforced concrete shear subjected to 4-point bending. After being preloaded at different levels of their ultimate loads, the beams are repaired by bonding a composite material made of an epoxy resin reinforced by glass fibers. The main objective of this study is to contribute to the mastery of a new method developed by the authors that consists by banding the cracks in critical zones in order to avoid fragile ruptures due to the shear force. This new technique led to better results in terms of mechanical properties when compared to conventional methods, notably the absence of the debonding of the composite found in the case of the repairs of the beams by bands or U-shaped composites. The feasibility, the performances and the behavior of the beams have been examined. The experimental approach adopted using this new technique has shown the influence of the type of loading on the fatigue behavior. In addition, the repair performed led to a considerable improvement in the fatigue durability of the preloaded beam