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

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

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