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

A review of factors affecting undrained strength of fine-grained soils at consistency limits.

Estimation of remoulded undrained shear strength of fine-grained soils over a wide range of water content encountered in civil engineering practice is very essential for geotechnical design. Engineers predict the strength through simple index properties, namely consistency limits, rather than using strength evaluated using poor quality soil samples. Though shear strength at two characteristic water contents of practical significance, namely, liquid and plastic limit has found to vary quite significantly, for convenience, strength at these limits has been assumed to be unique. Since, liquid and plastic limit of any soil are nothing but water holding capacity at different states of consistency, undrained strength for different soils having varying liquid limit or plastic limit cannot be expected to have a unique value. In addition to this, recent findings have also brought out the fact that mobilization of strength of soils depends on clay mineralogy and particle gradation. Hence, considering un-drained strength of soils to be unique at any consistency limits of soil is not correct. A critical re-examination of factors contributing to the strength and reasons for its non-uniqueness is presented in this paper based on review of data from various well cited articles reported in the literature

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

Planning with Tradable Reservations in Mobile Assistants operating in Resource Constrained Environments

(Under the direction of Peter Wurman) Mobile devices are hand held devices used to deliver time sensitive and locale specific information to the users. In multi-user environments with limited resources, agents running on mobile devices as assistants to their users improve the social welfare in the presence of tradable reservations. The purpose of this research is to show the benefits of planning in such an environment. By conducting various experiments we study the effects, when complex plans are generated to satisfy the user specified constraints and environment enforced constraints. We observe that with tradable reservations the social welfare increases with increase in planning horizon. We also observe that tradable reservations and clairvoyance help the users satisfy their preferences and constraints imposed by environment without loss in social welfare

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

Experiments with planning and markets in multi-agent systems. SIGecom Exchanges

Mobile devices are hand-held devices used to deliver time sensitive and locale specific information to the users. Users of multi-user environments with limited resources can be enabled with agents running on mobile devices as assistants to improve their ability to plan activities in the space. This paper discusses experiments to characterize the benefits of planning in such an environment, particularly when the resources can be reserved and the reservations traded in a market. We observe that with tradable reservations the social welfare increases with increase in planning horizon. We also observe that tradable reservations and clairvoyance help the users satisfy their preferences and the constraints imposed by environment

Evaluation of recycling capabilities of bio-stabilised earth building materials

Earth building materials are considered sustainable due to the inherent low embodied and operational energies, the ability to buffer hygrothermal fluctuations and the recycling potential. Despite these advantageous attributes, they are not employed in mainstream construction mainly because of their vulnerability to water. To improve durability in humid environments, earth is often stabilised with chemical binders, such as cement, which results in similar mechanical properties to those of conventional building materials. It has been reported that the addition of about 8-12% of cement to the earth is sufficient to obtain the same mechanical performance of fired bricks1. Cement stabilisation was initially adopted for the manufacture of compressed earth blocks, but it has now become a norm for other forms of earthen construction like adobe. The addition of cement increases durability but also contributes to carbon emissions while increasing embodied energy. Studies have shown that cement-stabilised earthen materials have the same net carbon emissions as lean concrete and, therefore, relatively poor green credentials. Furthermore, cement stabilisation negatively impacts other aspects of material performance by reducing both hygroscopicity and ease of recycling2. Reduced hygroscopicity leads to a poorer ability to buffer hygrothermal fluctuations and, hence, higher levels of operational energy for ensuring adequate levels of indoor comfort. The loss of recycling potential means instead that demolished materials cannot experience a full lifecycle but are either downcycled or dumped in landfills. To reinstate the original sustainability of the material without compromising on durability, it is necessary to look for alternative stabilisation techniques that can ensure engineering performance while retaining hygroscopic and recycling advantages

Geotechnical characterisation of recycled biopolymer-stabilised earthen 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 materials can easily be recycled or disposed, however, modern earthen structures rely on cement to obtain desirable strength and durability. This lowers both green credentials and recyclability potential of the material. With growing global interest in sustainability, it becomes imperative to explore alternatives to chemical stabilisers which can address these issues without compromising on the desired engineering properties of earthen construction materials. It has been reported that, earthen material treated with biopolymers, namely guar and xanthan gums have improved strength and durability properties. This study reports a preliminary assessment of the recyclability potential of these biopolymer treated earthen materials. Geotechnical properties of the recycled soil mixture such as particle size gradation, Atterberg limits and linear shrinkage were compared with the original unamended soil mixture to assess the changes due to recycling. Findings from this study provide an insight on the recyclability potential of biopolymer treated earthen materials and any associated environmental concerns relating to their disposal