Experimental characterization of an earth eco-efficient plastering mortar

Earthen plastering mortars are becoming recognized as highly eco-efficient. The assessment of their technical properties needs to be standardized but only the German standard DIN 18947 exists for the moment. An extended experimental campaign was developed in order to assess multiple properties of a ready-mixed earth plastering mortar and also to increase scientific knowledge of the influence of test procedures on those properties. The experimental campaign showed that some aspects related to the equipment, type of samples and sample preparation can be very important, while others seemed to have less influence on the results and the classification of mortars. It also showed that some complementary tests can easily be performed and considered together with the standardized ones, while others may need to be improved. The plaster satisfied the requirements of the existing German standard but, most importantly, it seemed adequate for application as rehabilitation plaster on historic and modern masonry buildings. Apart from their aesthetic aspect, the contribution of earthen plasters to eco-efficiency and particularly to hygrometric indoor comfort should be highlighted.EMBARRO Ld

Assessment of durability of biobased earth composites

Bio-based earth composites present various environmental benefits, such as usable wastes, coproducts, abundant or renewable materials, etc. Moreover, the incorporation of bioaggregates in the earth matrix allows the buildings to act as an effective carbon sink. A growing number of studies are now focusing on the mechanical and hygrothermal properties of bio-based earth building materials. However, the durability of these types of material is a major concern, and knowledge of their various aspects is essential to anticipate maintenance and sustain the performance levels. Here, the durability of compressed earth composites, valorizing discarded earth containing 3% of barley straw, hemp shiv, or rice husk, is investigated. Due to the lack of internationally recognized standards to assess the durability of earthen materials and products, we proposed some testing procedures and discussed their relevance. The addition of these three bioaggregates decreases stiffness, as estimated by ultrasound velocity, and improves the resistance to impact and erosion by water. However, water absorption under low pressure is increased, and dry abrasion resistance is decreased. Moreover, the rice husk composite presents the best compromise.publishersversionpublishe

Characterization of the microbiome associated with in situ earthen materials

Background The current increase in public awareness of environmental risks is giving rise to a growth of interest in the microbiological safety of buildings. In particular, microbial proliferation on construction materials can be responsible for the degradation of indoor air quality that can increase health-risk to occupants. Raw earth materials are still widely used throughout the world and, in some cases, are linked to heritage habitats, as in the southwest of France. Moreover, these building materials are currently the subject of renewed interest for ecological and economic reasons. However, the microbial status of earthen materials raises major concerns: could the microbiome associated with such natural materials cause disease in building occupants? Very few analyses have been performed on the microbial communities present on these supports. Characterizing the raw earth material microbiome is also important for a better evaluation and understanding of the susceptibility of such materials to microbial development. This study presents the distribution of in situ bacterial and fungal communities on different raw earth materials used in construction. Various buildings were sampled in France and the microbial communities present were characterized by amplicon high-throughput sequencing (bacterial 16S rRNA gene and fungal ITS1 region). Bacterial culture isolates were identified at the species level by MALDI-TOF mass spectrometry. Results The major fungal and bacterial genera identified were mainly associated with conventional outdoor and indoor environmental communities, and no specific harmful bacterial species were detected on earthen materials. However, contrary to expectations, few human-associated genera were detected in dwellings. We found lower microbial alpha-diversity in earthen material than is usually found in soil, suggesting a loss of diversity during the use of these materials in buildings. Interestingly enough, the main features influencing microbial communities were building history and room use, rather than material composition. Conclusions These results constitute a first in-depth analysis of microbial communities present on earthen materials in situ and may be considered as a first referential to investigate microbial communities on such materials according to environmental conditions and their potential health impact. The bacterial and fungal flora detected were similar to those found in conventional habitats and are thought to be mainly impacted by specific events in the building’s life, such as water damage

Potential of X-ray tomography for the exploration of vegetal concretes’ porous structure

International audienceVegetal concretes offer promising perspectives as building materials thanks to their low environmental impact and interesting hygrothermal behavior. Their insulating properties and moisture buffering capacity are largely controlled by their microstructure. In this context, X-ray tomography is a promising technique as it enables inner inspection of the microstructure in three dimensions in a non-destructive fashion. Geometrical characteristics, such as the overall porosity and the aggregate volume ratio, can be quantified within the limits of the accuracy of the technique. The present study focuses on a vegetal concrete obtained by combining a metakaolin-based pozzolanic binder with sunflower bark chips. Our measurements show that the vegetal concrete exhibits an open and interconnected pore space, with pore sizes varying over multiple orders of magnitude. The arrangement of the particles is clearly affected by their elongated shape in combination with the compacting force applied during settlement. The material also exhibits shrinkage-induced cracks at the interface between bio-aggregates and binder paste. These observations demonstrate the potential and limitations of X-ray tomography applied to bio-based concretes. The three-dimensional datasets yield more insight compared to typical two-dimensional digital imaging methods such as SEM. Moreover, the non-destructive nature of the method could allow to monitor ageing mechanisms of bio-based concretes by scanning the same sample at different points in time. Similar to other techniques such as SEM, high-resolution tomographic scans can only be obtained on relatively small samples, which raises the question about the representativeness of the specimens in view of the high heterogeneity of vegetal concretes. Nevertheless, the non-destructive nature of the method enables performing multiple scans of different locations within the same sample and to combine the data. X-ray tomography is thus a powerful tool, which can easily be combined with other techniques and contribute to characterize the microstructure of vegetal concretes

How Properties of Kenaf Fibers from Burkina Faso Contribute to the Reinforcement of Earth Blocks

Physicochemical characteristics of Hibiscus cannabinus (kenaf) fibers from Burkina Faso were studied using X-ray diffraction (XRD), infrared spectroscopy, thermal gravimetric analysis (TGA), chemical analysis and video microscopy. Kenaf fibers (3 cm long) were used to reinforce earth blocks, and the mechanical properties of reinforced blocks, with fiber contents ranging from 0.2 to 0.8 wt%, were investigated. The fibers were mainly composed of cellulose type I (70.4 wt%), hemicelluloses (18.9 wt%) and lignin (3 wt%) and were characterized by high tensile strength (1 ± 0.25 GPa) and Young’s modulus (136 ± 25 GPa), linked to their high cellulose content. The incorporation of short fibers of kenaf reduced the propagation of cracks in the blocks, through the good adherence of fibers to the clay matrix, and therefore improved their mechanical properties. Fiber incorporation was particularly beneficial for the bending strength of earth blocks because it reinforces these blocks after the failure of soil matrix observed for unreinforced blocks. Blocks reinforced with such fibers had a ductile tensile behavior that made them better building materials for masonry structures than unreinforced blocks

Etude du potentiel des écorces de tournesol et de maïs comme granulats végétaux dans la formulation de bétons légers

International audienceABSTRACT. Bio-aggregate based building materials offer promising perspectives thanks to their low environmental impact and interesting hygrothermal behaviour. As one of the high-potential agricultural resources, hemp has been extensively investigated for the last 15 years. This article aims to evaluate the potential of two other vegetal aggregates as a raw material to design bio-aggregate based concrete. Being locally available, the use of sunflower and maize bark particles could reduce transport and the associated carbon dioxide emissions. This study focuses on assessing the porous structure of bio-aggregates by X-ray tomography, their hygric sorption capacities (vapour and liquid water) as well as their chemical interactions with mineral binder and their effects on setting. The results underline the high transfer and storage capacities of these materials. Hence, the findings demonstrate that sunflower and maize bark particles are high-potential plant aggregates to design bio-aggregates based concrete.L'association de particules biosourcées à un liant minéral permet de formuler des bétons végétaux légers à faible impact environnemental et aux propriétés hygrothermiques intéressantes. Ces dernières années, les travaux de recherche se sont principalement focalisés sur l'utilisation du chanvre comme granulat végétal. L'étude présentée s'intéresse au potentiel d'autres agroressources disponibles localement afin de réduire le coût environnemental lié au transport des matières premières. Les travaux menés ont visé à caractériser l'arrangement granulaire des particules (granulométrie et densité), leur structure poreuse par tomographie à rayons X, leur comportement hydrique (vis-à-vis de l'eau liquide comme de la vapeur d'eau) et les interactions chimiques entre les hydrosolubles des agroressources et une matrice minérale. L'analyse de ces résultats met en évidence des capacités de transfert et de stockage de l'humidité élevée pour les particules de tournesol et de maïs. Les travaux menés révèlent les perspectives prometteuses des écorces de maïs et de tournesol comme granulats végétaux

Les enduits de terre crue de deux fosses antiques

Une fouille réalisée à Prades (Pyrénées-Orientales) a mis au jour deux fosses antiques (ier siècle de notre ère) de forme quadrangulaire. Elles sont enduites d’un épais revêtement de terre crue. Des analyses physiques, chimiques et minéralogiques ont permis de déterminer la nature et les proportions des éléments présents dans le limon naturel ainsi que dans les enduits de revêtement des fosses. Ces analyses sont complétées par une recherche de phytolithes qui nous renseigne sur la présence de graminées et de taxons ligneux. La fonction initiale de ces creusements pourrait être la conservation de végétaux, peut-être du fourrage.Excavations undertaken at Prades (Pyrénées-Orientales) have revealed two quadrangular pits dated to the first century AD. They were lined with a thick layer of clay. Physical, chemical and mineralogical analyses have enabled us to identify the types and proportions of the elements present in the natural clay-silt and in the lining of the pits. In addition, an examination of the phytoliths indicates that grasses (gramineae) and ligneous taxa (tree species) were present. The pita may have originally been used to store vegetable matter, perhaps fodder.Una excavación llevada a cabo en Prades (departamento de Pirineos Orientales) dejó al descubierto dos fosas antiguas de forma cuadrangular del siglo I de nuestra era, mamposteadas con un espeso revestimiento de barro. Análisis físicos, químicos y mineralógicos han permitido determinar la naturaleza y las proporciones de los elementos presentes en el lodo natural, así como de las argamasas de revestimiento de las fosas. La búsqueda de fitolitos, que determina la presencia de gramíneas y de taxones leñosos, ha permitido completar los análisis. La función inicial de estas cavaduras puede haber sido la conservación de vegetales, presumiblemente de forraje

Kinetic Control in the Chiral Recognition of Three-Bladed Propellers

The ion pair of the stereolabile C3-symmetric, i+o proton complex [1⋅H]+ of diaza-macropentacycle 1 and the configurationally stable Δ-TRISPHAT ([Δ-3]−) anion exists in the form of two diastereomers, namely, [Δ-(1⋅H)][Δ-3] and [Λ-(1⋅H)][Δ-3], the ratio of which, in terms of diastereomeric excess (de) decreases in the order [D8]THF (28 %)>CD2Cl2 (22 %)>CDCl3 (20 %)>[D8]toluene (16 %)>C6D6 (7 %)>[D6]acetone (0 %) at thermodynamic equilibrium. Except in the case of [D6]acetone, the latter is reached after a period of time that increases from 1 h ([D8]THF) to 24 h (CDCl3). Moreover, the initial value of the de of [1⋅H][Δ-3] in CDCl3, before the thermodynamic equilibrium is reached, depends on the solvent in which the sample has been previously equilibrated (sample “history”). This property has been used to show that the crystals of [1⋅H][Δ-3] formed by slow evaporation of CH2Cl2/CH3OH mixtures had 100 % de, which indicates that [1⋅H][Δ-3] has enjoyed a crystallization-induced asymmetric transformation. Structural studies in solution (NMR spectroscopy) and in the gas phase by calculations at the semiempirical PM6 level of theory suggest that the optically active anion is docked on the i+ (endo) external side of the proton complex such that one of the aromatic rings of [Δ-3]− is inserted into a groove of [1⋅H]+, a second aromatic ring being placed astride the outside i+ pocket. Solvent polarity controls the thermodynamics of inversion of the [1⋅H]+ propeller. However, both polarity and basicity control its kinetics. Therefore, the rate-limiting steps correspond to the ion-pair separation/recombination and [1⋅H]+/1 deprotonation/protonation processes, rather than the inversion of [1⋅H]+, the latter being likely to take place in the deprotonated form (1)

Earth blocks stabilized by cow-dung

WOS:000379589500010International audienceIn developing countries, most of the population cannot afford conventional building blocks made with the sand-cement mixture. In addition, these blocks do not provide thermal comfort and have a high embodied energy compared to vernacular materials. The main objective of this work was to produce low cost, resistant and durable (good resistance to water) blocks with a thermal behaviour enabling quality comfort indoor. For that purpose, the effects of cow-dung on microstructural changes in earth blocks (adobes) are investigated by means of X-ray diffraction, thermal gravimetric analyses, scanning electronic microscopy coupled with energy dispersive spectrometry, and video microscopy. The effects of these changes on the physical properties (water absorption and linear shrinkage) and mechanical properties (flexural and compressive strengths) of adobe blocks are evaluated. It is shown that cow-dung reacts with kaolinite and fine quartz to produce insoluble silicate amine, which glues the isolated soil particles together. Moreover, the significant presence of fibres in cow-dung prevents the propagation of cracks in the adobes and thus reinforces the material. The above phenomena make the adobe microstructure homogeneous with an apparent reduction of the porosity. The major effect of cow-dung additions is a significant improvement in the water resistance of adobe, which leads to the conclusion that adobes stabilized by cow-dung are suitable as building materials in wet climates

Experimental analysis of Pressed Adobe Blocks reinforced with Hibiscus cannabinus fibers

WOS:000331424400009International audienceThere is an intense on-going search for less polluting materials and technologies, which consume little energy in their production, construction and/or utilization. Attention of the researchers has turned to materials, which found applications in engineering in pre-industrial times: local vegetable fibers and earth composites are one of the promising materials. This paper presents the results of an investigation in establishing the physical and mechanical properties of Hibiscus cannabinus fibers which have been used in the fabrication of Pressed Adobe Blocks (PABs). The PABs have been reinforced with 0.2-0.8 wt.% of 30 mm and 60 mm lengths of H. cannabinus fibers. The microstructural characteristics of the PABs composites were investigated using X-ray diffraction (XRD), thermal gravimetric analyses (TGA), scanning electronic microscopy (SEM) and video microscopy. It was established that the addition with 0.2-0.6 wt.% of 30 mm long fibers reduced the dimensions of the pores in the PABs with the improvement of their mechanical properties. However, the addition of 0.8 wt.% of 60 mm fibers had negative effects on the compressive strength. The elaborated Pressed Adobe Blocks specimens were suitable as building material with contribution for thermal comfort. (C) 2013 Elsevier Ltd. All rights reserved