Hygro-thermo-mechanical properties of earthen materials for construction : a literature review

Although earth has been used for construction for millennia and is still one of the most widely used building materials in the world, it is still difficult to find reliable values for the hygro-thermal and mechanical properties of earthen materials. Only little scientific research has been conducted on this material compared to the huge literature available concerning cementitious materials. Considering the literature available on earthen materials, a majority of studies deal with cement or lime stabilized earth for compressed earth blocks or rammed earth, and less has been done about natural unstabilized earth. The only existing comprehensive overview on the hydro-thermal and mechanical properties of earthen materials was authored by CRAterre-ENSAG and published 25 years ago. Now, for the second time in its thirty years of existence, CRAterre-ENSAG has undertaken the task of reactualizing this synthetic knowledge by writing a comprehensive review of the existing literature on the subject, thanks to the CRAterre laboratory documentation centre, which is the most complete source of information on earthen construction and architecture in the world (more than 20.000 references). In the present work, we intend to compile the most reliable experimental data on the hygro-thermal and mechanical properties of natural earth. We will inventory the performances determined by several research teams for rammed earth, compressed earth blocks, adobe, cob and mortar. We will discuss the reliability of the experimental techniques used. We will provide an overview on the state of knowledge concerning the different properties as well as on the lacking data. Finally, this literature review will also give some orientations for further scientific research

Hygro-thermo-mechanical properties of earthen materials for construction : a literature review

Although earth has been used for construction for millennia and is still one of the most widely used building materials in the world, it is still difficult to find reliable values for the hygro-thermal and mechanical properties of earthen materials. Only little scientific research has been conducted on this material compared to the huge literature available concerning cementitious materials. Considering the literature available on earthen materials, a majority of studies deal with cement or lime stabilized earth for compressed earth blocks or rammed earth, and less has been done about natural unstabilized earth. The only existing comprehensive overview on the hydro-thermal and mechanical properties of earthen materials was authored by CRAterre-ENSAG and published 25 years ago. Now, for the second time in its thirty years of existence, CRAterre-ENSAG has undertaken the task of reactualizing this synthetic knowledge by writing a comprehensive review of the existing literature on the subject, thanks to the CRAterre laboratory documentation centre, which is the most complete source of information on earthen construction and architecture in the world (more than 20.000 references). In the present work, we intend to compile the most reliable experimental data on the hygro-thermal and mechanical properties of natural earth. We will inventory the performances determined by several research teams for rammed earth, compressed earth blocks, adobe, cob and mortar. We will discuss the reliability of the experimental techniques used. We will provide an overview on the state of knowledge concerning the different properties as well as on the lacking data. Finally, this literature review will also give some orientations for further scientific research

A proposed new approach to light rail safety management in Spain and other countries

[Abstract:] The light rail transit (LRT) has experienced considerable growth in Spain since 1994; to date, this has led to the installation of more than 200 km of light rail lines and LRT operations in 11 metropolitan areas. Nevertheless, its institutional and regulatory framework have not been developed accordingly. Thus, in this paper, an approach for managing the LRT safety in Spain is proposed. The approach is based on the French model and could be applied to any other country that is interested in improving its LRT safety management. The paper explains the current situation of LRT safety management in Spain and provides a critical review. A comparison of the situations in several European countries is presented. Moreover, the paper presents details pertaining to the French framework and tool as the most adequate model for managing the LRT safety; a critical review is also included in order to propose ways for improving it. Finally, the main points of the proposed LRT safety management approach include the following: (1) development of a National Light Rail Safety Act, which would create the National Light Rail Safety Body; (2) implementation of a light rail safety database, which is created through the codification of light rail lines in homogenised sections from the safety point of view and the standardised light rail accident/incident reports, to be filled in by light rail operators directly; (3) management of the database by the National Light Rail Safety Body in order to improve safety based on the conclusions obtained

Projet : Béton d'Argile Environnemental (B.A.E.): Rapport scientifique

Rapport scientifiqueLa terre est un matériau à changement de phase naturel, localement disponible, à faible énergie griseet recyclable. Ces qualités en font un matériau de construction d’avenir.La physique et la mécanique de la matière divisée (et ultra divisée) sont des domaines en plein essor.L’éclosion des nanosciences offre un nouvel éclairage sur les comportements mécaniques, thermiques,hygrométriques et rhéologiques du matériau terre, en particulier aux échelles physico-chimiques lesplus fines des argiles.A cet apport de connaissances théoriques s’ajoute un savoir-faire industriel très élaboré pour la miseen oeuvre de matériaux offrant de nombreux points communs avec la terre, véritable béton d’argile.Ainsi, les méthodes appliquées à la confection de bétons de ciment toujours plus performants d’unepart et celles appliquées au coulage des crus des céramiques industrielles d’autre part sonttransférables au matériau terre.D’autre part, le marché spécialisé de la construction en terre s’organise et se développe rapidement. Acela s’ajoute une demande sociétale toujours plus forte qui conduit par exemple les industriels de labrique cuite à proposer des briques crues. Les carrières de granulats souhaitent quant à elles valoriserleurs importants volumes de coproduits de carrières (fines argilo-calcaires).Les conditions sont donc réunies pour mettre en place à l’échelle nationale, à l’instar de la filière bois,une filière terre qui s'appuie sur des bases scientifiques et techniques approfondies.L’enjeu scientifique réside notamment dans une meilleure compréhension des propriétés mécaniqueset thermiques du matériau terre en liaison avec son comportement hygrométrique d’une part et unemeilleure connaissance des systèmes argile/eau en vue du coulage du matériau terre à l’état liquided’autre part. Il réside également dans une meilleure compréhension de la cohésion du matériau et del’amélioration de cette cohésion par ajout de polymères : les nanocomposites argile/polymère sont, dece point de vue, exemplaires.ObjectifsLe projet s’articule autour de 6 objectifs :1. établir un état de l’art et une synthèse des caractéristiques mécaniques, thermiques ethygrométriques du matériau terre en vue de l’élaboration de règles professionnelles.2. étudier l’influence de la densité, de l’organisation spatiale du réseau poreux et de l’humidité relativesur les caractéristiques mécaniques et thermiques : ce sont 3 paramètres clés de la dispersion desvaleurs données par la littérature.3. transférer d’une part la technologie des superplastifiants du béton de ciment afin de mettre enoeuvre la terre à l’état liquide et d’autre part la Direct Coagulation Casting (DCC) de l’industriecéramique afin de solidifier la terre après coulage par coagulation des argiles.4. formuler de nouveaux liants argiles / biopolymères pour la confection de nouveaux bétons, briques,enduits et peintures très écologiques.5. Evaluer l’intérêt de l’ajout de particules végétales poreuses pour optimiser les performances(mécaniques et thermiques) de ces bétons.6. Valoriser les coproduits de carrières de granulats en les transformant en matériaux de constructionterre innovants

Poured Earth as concrete

International audienceIn order to pour an earthen material in a liquid state, as a concrete, technologies used by concrete and ceramic industries can be transferred to the field of earthen construction. Two different methods should be employed simultaneously. The first relates to theories of grain packing that have led to models of Apollonian packing and spaced packing, commonly used for the development of cement concrete (ultra high performance concrete and self-leveling concrete). It concerns the optimization of the granular skeleton of natural materials. The second relates to the dispersion of the colloidal fraction of earthen materials. In natural soils, clays are organized as porous aggregates composed of several tens of particles. These aggregates trap water that is not used to liquefy the mixture. The dispersion of these aggregates, releasing this interstitial water, liquefies the earthen material without adding water. This dispersion is obtained by adding a small proportion (on the order of a few tenths of a percent by mass relative to the dry material) of deflocculating agents such as those commonly used for the development of industrial ceramics. The combined action of these two methods leads to a solid material that does not crack while drying, and can easily be implemented at a viscosity comparable to that of vibrated concrete with the same tools than those employed by the concrete industry (cement mixer, shuttering, vibrating needle). This new technique is particularly suited for the implementation of slabs and other horizontal surfaces, and also for vertical walls

Circuitry rewiring directly couples competence to predation in the gut dweller Streptococcus salivarius

Small distortions in transcriptional networks might lead to drastic phenotypical changes, especially in cellular developmental programs such as competence for natural transformation. Here, we report a pervasive circuitry rewiring for competence and predation interplay in commensal streptococci. Canonically, in streptococci paradigms such as Streptococcus pneumoniae and Streptococcus mutans, the pheromone-based two-component system BlpRH is a central node that orchestrates the production of antimicrobial compounds (bacteriocins) and incorporates signal from the competence activation cascade. However, the human commensal Streptococcus salivarius does not contain a functional BlpRH pair, while the competence signaling system ComRS directly couples bacteriocin production and competence commitment. This network shortcut might underlie an optimal adaptation against microbial competitors and explain the high prevalence of S. salivarius in the human digestive tract. Moreover, the broad spectrum of bacteriocin activity against pathogenic bacteria showcases the commensal and genetically tractable S. salivarius species as a user-friendly model for competence and bacterial predation

Poured Earth as concrete

International audienceIn order to pour an earthen material in a liquid state, as a concrete, technologies used by concrete and ceramic industries can be transferred to the field of earthen construction. Two different methods should be employed simultaneously. The first relates to theories of grain packing that have led to models of Apollonian packing and spaced packing, commonly used for the development of cement concrete (ultra high performance concrete and self-leveling concrete). It concerns the optimization of the granular skeleton of natural materials. The second relates to the dispersion of the colloidal fraction of earthen materials. In natural soils, clays are organized as porous aggregates composed of several tens of particles. These aggregates trap water that is not used to liquefy the mixture. The dispersion of these aggregates, releasing this interstitial water, liquefies the earthen material without adding water. This dispersion is obtained by adding a small proportion (on the order of a few tenths of a percent by mass relative to the dry material) of deflocculating agents such as those commonly used for the development of industrial ceramics. The combined action of these two methods leads to a solid material that does not crack while drying, and can easily be implemented at a viscosity comparable to that of vibrated concrete with the same tools than those employed by the concrete industry (cement mixer, shuttering, vibrating needle). This new technique is particularly suited for the implementation of slabs and other horizontal surfaces, and also for vertical walls

The fast milk acidifying phenotype of Streptococcus thermophilus can be acquired by natural transformation of the genomic island encoding the cell-envelope proteinase PrtS

In industrial fermentation processes, the rate of milk acidification by Streptococcus thermophilus is of major technological importance. The cell-envelope proteinase PrtS was previously shown to be a key determinant of the milk acidification activity in this species. The PrtS enzyme is tightly anchored to the cell wall via a mechanism involving the typical sortase A (SrtA) and initiates the breakdown of milk casein into small oligopeptides. The presence or absence of PrtS divides the S. thermophilus strains into two phenotypic groups i.e. the slow and the fast acidifying strains. The aim of this study was to improve the milk acidification rate of slow S. thermophilus strains, and hence optimise the fermentation process of dairy products

Oviductal microenvironment: role in canine oocyte maturation in vivo and in vitro

In most mammals, oocytes are ovulated at the metaphase II stage, and the meiosis inhibition is then lifted by fertilization. In bitches and other Canidae species however, oocytes are released at the prophase I stage, and another 48 to 72h are necessary for themtomature into themetaphase II stage and become fertilizable. This specificity is currently hindering the development of reproductive biotechnologies in these species. In vitro maturation rates of canine oocytes are very low, as only 10 to 30%will reach the metaphase stage after 72h in culture. In bitches, nuclear maturation occurs in the oviduct, and tubal derivatives (culture media, such as Synthetic Oviductal Fluid, oviductal explants, coculture on tubal cell layers) were used to improve the yield, but so far not very successfully. This failure may be due to the lack of data on the composition of oviductal fluid in bitches. Further studies on the oviductal microenvironment of bitches are therefore necessary, as it is probably quite different from the oviductalmicroenvironment of other females, e.g. the presence of preovulatory luteinisation in bitches only. Creating a maturation medium based on the composition of oviductal fluid could be an interesting avenue to explore to improve in vitro maturation rates.Chez la plupart des mammifères, les ovocytes sont bloqués en métaphase II au moment de l'ovulation et cette inhibition de la méiose est ensuite levée par la fécondation. Chez les chiennes et les autres femelles de canidés, les ovocytes sont libérés au stade de prophase I, et il faut encore attendre 48 à 72 heures pour qu'ils atteignent le stade de métaphase II et deviennent fécondables. Cette particularité constitue aujourd'hui un frein au développement des biotechnologies de la reproduction chez les canidés. En effet, dans les essais de maturation in vitro d'ovocytes canins, seuls 10 à 30 % des ovocytes atteignent le stade de métaphase au bout de 72 heures de culture. Chez la chienne, la maturation nucléaire se produisant dans l'oviducte, des substituts de l'oviducte (milieux de culture comme le Synthetic Oviductal Fluid, explants d'oviductes, cultures sur tapis de cellules tubaires) ont été utilisés pour les cultures d'ovocytes in vitro, afin d'en améliorer le rendement, mais sans grand succès jusqu'à maintenant. Cet échec peut être dû au manque de données sur la composition du liquide tubaire de la chienne. L'étude de ce microenvironnement prend donc tout son intérêt, celui-ci étant probablement assez différent de celui des autres femelles, ne serait-ce que par l'existence du processus de lutéinisation préovulatoire dans cette espèce. À terme, la conception d'un milieu de maturation sur la base de la composition du liquide tubaire pourrait être une voie intéressante pour augmenter les taux de maturation in vitro

Enantioselective regulation of lactate racemization by LarR in Lactobacillus plantarum.

Lactobacillus plantarum is a lactic acid bacterium that produces a racemic mixture of l- and d-lactate from sugar fermentation. The interconversion of lactate isomers is performed by a lactate racemase (Lar) that is transcriptionally controlled by the l-/d-lactate ratio and maximally induced in the presence of l-lactate. We previously reported that the Lar activity depends on the expression of two divergently oriented operons: (i) the larABCDE operon encodes the nickel-dependent lactate racemase (LarA), its maturases (LarBCE), and a lactic acid channel (LarD), and (ii) the larR(MN)QO operon encodes a transcriptional regulator (LarR) and a four-component ABC-type nickel transporter [Lar(MN), in which the M and N components are fused, LarQ, and LarO]. LarR is a novel regulator of the Crp-Fnr family (PrfA group). Here, the role of LarR was further characterized in vivo and in vitro. We show that LarR is a positive regulator that is absolutely required for the expression of Lar activity. Using gel retardation experiments, we demonstrate that LarR binds to a 16-bp palindromic sequence (Lar box motif) that is present in the larR-larA intergenic region. Mutations in the Lar box strongly affect LarR binding and completely abolish transcription from the larA promoter (PlarA). Two half-Lar boxes located between the Lar box and the -35 box of PlarA promote LarR multimerization on DNA, and point mutations within one or both half-Lar boxes inhibit PlarA induction by l-lactate. Gel retardation and footprinting experiments indicate that l-lactate has a positive effect on the binding and multimerization of LarR, while d-lactate antagonizes the positive effect of l-lactate. A possible mechanism of LarR regulation by lactate enantiomers is proposed