Matériaux De Construction En Terre Stabilisés Aux Biopolymères

Les constructions en terre crue, soit fabriquées à partir de sol, sont considérées comme des constructions durables en raison de leur faible empreinte environnementale : les matériaux de construction à base de terre crue non stabilisée ont une faible énergie intrinsèque, d'excellentes propriétés hygroscopiques et un fort potentiel de recyclage. Cependant, sous cette forme, les matériaux sont susceptibles de se détériorer au contact de l’eau. Ainsi, les éléments de constructions modernes en terre crue utilisent du ciment pour améliorer leur durabilité, mais entachent de ce fait leurs propriétés hygroscopiques et leur potentiel de recyclable. Il est donc impératif de développer des solutions alternatives à l’incorporation de ciment, pouvant améliorer la résistance à l’eau sans pour autant compromettre les propriétés qui constituent les atouts de ces matériaux durables. Ces travaux de doctorat étudient l'utilisation de deux biopolymères, la gomme de guar et le xanthane, comme stabilisants naturels pour les matériaux de construction en terre crue. Dans un premier temps, une campagne expérimentale a été menée pour comprendre le mécanisme de stabilisation de la terre par ces biopolymères et optimiser cette technique. Les résultats révèlent que la nature intrinsèque des biopolymères induit la formation d’hydrogels qui participent à renforcer le matériau et à modifier les phénomènes de succion. L’addition d’environ 2,0 % de biopolymère en masse de sol sec est suffisant pour obtenir un comportement mécanique comparable à la stabilisation au ciment à un taux de 8,0 %. Afin de mieux caractériser l’influence des biopolymères, les propriétés hydrauliques et mécaniques des sols ainsi stabilisés ont été étudiées. Les tests de caractérisation prouvent que, pour une même gamme de teneur en eau, la succion des sols stabilisés par les biopolymères est supérieure à celle des sols non stabilisés. Les courbes de rétention d'eau sol démontrent que la valeur d'entrée d'air est augmentée en présence des biopolymères, ce qui affecte la distribution de la taille des vides. Les paramètres de résistance au cisaillement ont été obtenus par des essais triaxiaux à teneur d’eau constante. Les deux biopolymères ont un effet significatif, et pourtant différent, sur la cohésion du sol et l'angle de friction interne. Dans le temps, la modification de résistance des sols stabilisés à la gomme de guar est liée à la variation de la composante de friction, tandis que pour les sols stabilisés à la gomme de xanthane cette variation est pilotée par la cohésion du sol. L'analyse microstructurale par micro tomographie X-RCT montre que les biopolymères favorisent l’agglomération des particules de sol, ce qui modifie la porosité globale. Les courbes de distribution de la taille des vides obtenues par balayage XRCT confirment les résultats des essais de succion. Pour finir, les performances en termes de durabilité de ces matériaux de construction stabilisés aux biopolymères en présence d'eau ont été validées par différents tests ainsi que leur potentiel de recyclage. Il apparait donc que l'utilisation de ces biopolymères comme stabilisant améliore la résistance mécanique des matériaux en terre crue et leur durabilité ; et que contrairement à la stabilisation au ciment le comportement hygroscopique est conservé - voire amélioré-, ainsi que le potentiel de recyclage.Earthen structures (i.e. structural units manufactured from soil) are often regarded as sustainable forms of construction due to their characteristically low carbon footprint. Unstabilised earthen construction materials have low embodied energy, excellent hygroscopic properties and recycling potential. However, in this form, the material is susceptible to deterioration against water ingress and most modern earthen construction materials rely on cement to improve their durability properties. Using cement leads to compromises in hygroscopicproperties and recyclability potential. In this situation, it is imperative to look for alternatives to cement, which can address these issues without compromising on the desired engineering properties of these materials. This thesis explores the use of biopolymers, namely guar and xanthan gum, as stabilisers for earthen construction materials. As an initial step, an experimental campaign was undertaken to understand biopolymer stabilisation and optimise their use to stabilise earthen construction materials. The results from this campaign reveal that biopolymer stabilised soils derive their strength through a combination of soil suction and hydrogel formation. The intrinsic chemical properties of the biopolymer affect the nature of hydrogel formation and in turn strength. In a subsequent campaign of experimental work, hydraulic and mechanical properties of these biopolymer stabilised soils were determined. The hydraulic properties of the biopolymer stabilised soils indicate that for the range of water contents, the suction values of biopolymer stabilised soils are higher than unamended soils. The soil water retention curves suggest that both biopolymers have increased the air entry value of the soil while affecting the void size distribution. Shear strength parameters of biopolymer stabilised soils were obtained through constant water triaxial tests, and it was noted that both biopolymers have a significant and yet different effect on soil cohesion and internal friction angle. With time, guar gum stabilised soils derive strength through the frictional component of the soil strength, while xanthan gum stabilised soil strength has a noticeable contribution from soil cohesion. Macrostructural analysis in the form of X-RCT scans indicate that both biopolymers form soil agglomerations and increase overall porosity. The void size distribution curves obtained from XRCT scanning complement the findings of the suction tests. As a final study, the performance of biopolymer stabilised earthen construction materials was assessed as a building material. Durability performance of these materials against water ingress was evaluated, and it was noted both biopolymers provide satisfactory stabilisation to improve the erosional resistance of the material. In conclusion, unlike cement, biopolymer stabilised earthen materials do not compromise on hygroscopic properties and have better mechanical performance than unamended earthen construction materials. Finally, recyclability tests suggest that apart from improving the strength, durability and hygroscopic properties of the material, biopolymer stabilised earthen construction materials have a better potential for recycling without any environmental concerns

Biopolymer Stabilised Earthen Construction Materials

Earthen structures (i.e. structural units manufactured from soil) are often regarded as sustainable forms of construction due to their characteristically low carbon footprint. Unstabilised earthen construction materials have low embodied energy, excellent hygroscopic properties and recycling potential. However, in this form, the material is susceptible to deterioration against water ingress and most modern earthen construction materials rely on cement to improve their durability properties. Using cement leads to compromises in hygroscopic properties and recyclability potential. In this situation, it is imperative to look for alternatives to cement, which can address these issues without compromising on the desired engineering properties of these materials. This thesis explores the use of biopolymers, namely guar and xanthan gum, as stabilisers for earthen construction materials. As an initial step, an experimental campaign was undertaken to understand biopolymer stabilisation and optimise their use to stabilise earthen construction materials. The results from this campaign reveal that biopolymer stabilised soils derive their strength through a combination of soil suction and hydrogel formation. The intrinsic chemical properties of the biopolymer affect the nature of hydrogel formation and in turn strength. In a subsequent campaign of experimental work, hydraulic and mechanical properties of these biopolymer stabilised soils were determined. The hydraulic properties of the biopolymer stabilised soils indicate that for the range of water contents, the suction values of biopolymer stabilised soils are higher than unamended soils. The soil water retention curves suggest that both biopolymers have increased the air entry value of the soil while affecting the void size distribution. Shear strength parameters of biopolymer stabilised soils were obtained through constant water triaxial tests, and it was noted that both biopolymers have a significant and yet different effect on soil cohesion and internal friction angle. With time, guar gum stabilised soils derive strength through the frictional component of the soil strength, while xanthan gum stabilised soil strength has a noticeable contribution from soil cohesion. Macrostructural analysis in the form of X-RCT scans indicate that both biopolymers form soil agglomerations and increase overall porosity. The void size distribution curves obtained from XRCT scanning complement the findings of the suction tests. As a final study, the performance of biopolymer stabilised earthen construction materials was assessed as a building material. Durability performance of these materials against water ingress was evaluated, and it was noted both biopolymers provide satisfactory stabilisation to improve the erosional resistance of the material. In conclusion, unlike cement, biopolymer stabilised earthen materials do not compromise on hygroscopic properties and have better mechanical performance than unamended earthen construction materials. Finally, recyclability tests suggest that apart from improving the strength, durability and hygroscopic properties of the material, biopolymer stabilised earthen construction materials have a better potential for recycling without any environmental concerns

Effect of enzymes on plasticity and strength characteristics of an earthen construction material

Abstract In this study, a commercially available enzyme which is used popularly to improve sub-grade material for pavements was used as a potential stabilizer to improve soil properties used for earthen construction. As a preliminary study, the interaction of this enzyme with the soil was assessed by evaluating the plasticity and strength characteristics of enzyme treated soil with ageing. From the research findings, it was observed that with ageing, the liquid limit of soil decreased, while plastic and shrinkage limits increased, leading to reduced plasticity and shrinkage indices. The reduced plasticity and shrinkage indices indicate that soil has become relatively more volumetrically stable and less susceptible to crack formation. Further, strength characteristics under two different curing conditions were evaluated, and it was found that under sealed curing conditions, the treated soil had better compressive strength. The improvement of plasticity, shrinkage and strength characteristics due to the addition of enzymes can be advantageously used for development of lightly stabilized durable earthen construction material, and thus, eliminating the necessity of using conventional energy-intensive stabilizers. The findings from this study bring the immense potential of eco-friendly enzymatic stabilization in the development of modern sustainable earthen materials

Potential Use of Enzymes in the Preparation of Compressed Stabilized Earth Blocks

Compressed stabilized earth blocks (CSEBs) prepared with an enzyme along with a combination of cement and lime have been shown to have a nearly 50% increase in wet compressive strength after two years of aging compared with blocks prepared without enzymes. The influence of enzymes in improving the property of the blocks is confirmed by the changes induced at the microlevel as evidenced by scanning electron microscope (SEM) views. Furthermore, CSEBs prepared with enzymes are also durable and could be beneficial when used as a unit in building construction. The increased strength of the blocks with the use of microdoses of enzymes would lead to a substantial reduction in the quantity of routinely used conventional stabilizers to manufacture blocks of comparable strength and other properties

A non-hysteretic simplification to the Glasgow Coupled Model (GCM)

The Glasgow Coupled Model (GCM) is an established elasto-plastic constitutive model developed to capture the coupled hydro-mechanical response of unsaturated soils. This study highlights the unique capabilities of the GCM in modelling the water retention and mechanical behaviour of unsaturated soils. Namely, its ability to capture the scanning, main wetting and main drying water retention responses, the mechanical response (including volume change and shear strength), and the coupling between the water retention and mechanical behaviour. However, due to the multiple yielding scenarios that a given stress path can trigger, numerical integration of the model is challenging and adjustments towards a more simplified approach are desirable if the model is to be used in geotechnical practice. For this purpose, the capabilities of a simplified non-hysteretic version of the GCM, designed to streamline its formulation, are investigated in this paper. The non-hysteretic model requires less parameters and simplifies the identification of the elasto-plastic mechanism activated by a stress path, at the expense of limiting some of the original modelling abilities

Advances in the Use of Biological Stabilisers and Hyper-Compaction for Sustainable Earthen Construction Materials

International audienceIn the majority of cases, earthen construction materials for real buildings require amendment to deliver suitable material properties, which could be some additional strength or resilience to erosion. In modern earthen construction, in India, Australia and other parts of the world, cement and lime have been successfully used as stabilisers, providing both strength and durability benefits. However, the use of cement is detrimental to the green credentials of earthen construction materials, due to the large carbon footprint of that material's manufacture and, for some time, researchers have been motivated to find more appropriate stabilisers and manufacturing methods. In this paper, we present recent findings from two projects that are linked by this motivation and involve the study of bio-based stabilisers and alternative manufacturing methods for in situ and unit-based materials. Results are presented from laboratory testing of strength and durability of a range of materials, bio-stabilisers and manufacturing processes, indicating that there could be viable alternatives to cement and lime, certainly for many current uses of earthen construction materials

Mechanical properties of biopolymer-stabilised soil-based construction materials

Soil-based construction materials are of interest as structural building materials due to their green credentials, as well as being present in many historical structures. For effective conservation of the latter, and to motivate greater uptake for new construction, understanding of the mechanical and hydraulic properties of these materials is in need of improvement. Earthen construction materials can be considered to be manufactured unsaturated soils, and advances in understanding can be made by considering them from a geotechnical point of view. This paper presents initial results from a major programme of testing, seeking improved properties for earthen construction materials, where unusual organic compounds have been employed as stabilisers. Two gums (guar and xanthan) used as stabilisers for a soil mixture are shown to have significant effects on certain mechanical properties, some of which can be explained, and other aspects which are in need of further investigation

Advances in the Use of Biological Stabilisers and Hyper-compaction for Sustainable Earthen Construction Materials

In the majority of cases, earthen construction materials for real buildings require amendment to deliver suitable material properties, which could be some additional strength or resilience to erosion. In modern earthen construction, in India, Australia and other parts of the world, cement and lime have been successfully used as stabilisers, providing both strength and durability benefits. However, the use of cement is detrimental to the green credentials of earthen construction materials, due to the large carbon footprint of that material’s manufacture and, for some time, researchers have been motivated to find more appropriate stabilisers and manufacturing methods. In this paper, we present recent findings from two projects that are linked by this motivation, and involve the study of bio-based stabilisers and alternative manufacturing methods for insitu and unit-based materials. Results are presented from laboratory testing of strength and durability of a range of materials, bio-stabilisers and manufacturing processes, indicating that there could be viable alternatives to cement and lime, certainly for many current uses of earthen construction materials