Using small-angle X-ray scattering to investigate the compaction behaviour of a granulated clay

The compaction behaviour of a commercial granulated clay (magnesium aluminium smectite, gMgSm) was investigated using macroscopic pressure-density measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray microtomography (XμT) and small-angle X-ray scattering (SAXS). This material was studied as a potential compaction excipient for pharmaceutical tabletting, but also as a model system demonstrating the capabilities of SAXS for investigating compaction in other situations. Bulk compaction measurements showed that the gMgSm was more difficult to compact than polymeric pharmaceutical excipients such as spheronised microcrystalline cellulose (sMCC), corresponding to harder granules. Moreover, in spite of using lubrication (magnesium stearate) on the tooling surfaces, rather high ejection forces were observed, which may cause problems during commercial tabletting, requiring further amelioration. Although the compacted gMgSm specimens were more porous, however, they still exhibited acceptable cohesive strengths, comparable to sMCC. Hence, there may be scope for using granular clay as one component of a tabletting formulation. Following principles established in previous work, SAXS revealed information concerning the intragranular structure of the gMgSm and its response to compaction. The results showed that little compression of the intragranular morphology occurred below a relative density of 0 · 6, suggesting that granule rearrangements or fragmentation were the dominant mechanisms during this stage. By contrast, granule deformation became considerably more important at higher relative density, which also coincided with a significant increase in the cohesive strength of compacted specimens. Spatially-resolved SAXS data was also used to investigate local variations in compaction behaviour within specimens of different shape. The results revealed the expected patterns of density variations within flat-faced cylindrical specimens. Significant variations in density, the magnitude of compressive strain and principal strain direction were also revealed in the vicinity of a debossed feature (a diametral notch) and within bi-convex specimens. The variations in compaction around the debossed notch, with a small region of high density below and low density along the flanks, appeared to be responsible for extensive cracking, which could also cause problems in commercial tabletting

Remediation of desiccation cracking in clayey soils through bio-cementation and bottom ash

Desiccation cracking considerably impairs the hydraulic and mechanical properties of clayey soils and is critical to the long-term performance of infrastructure foundations and earth structures. Classical crack remediation methods are associated with high labor and maintenance costs or the usage of environment-unfriendly chemicals. Recycling waste materials and developing bio-mediated techniques have emerged as green and sustainable soil stabilization solutions. The objective of this study is to investigate the feasibility of soil crack remediation through the usage of microbial-induced calcite precipitation (MICP) and bottom ash admixtures. We carry out monotonic drying and cyclic drying-wetting tests to characterize the effects of bottom ash and MICP on the desiccation cracking of clayey soils. The desiccation cracking patterns captured by a high-resolution camera are quantified using image processing and digital image correlation techniques. We also resort to scanning electron microscopy for microstructural characterizations. MICP treatment improves the soil strength due to the precipitation of calcite crystals on soil particle surface and inside inter-particle pores. Adding bottom ash into clay reduces the plasticity of the mixture, promotes the flocculation of clay particles by cation exchange, and also provides soluble calcium to enhance calcite precipitations. This study demonstrates the potential of using bottom ash and MICP for crack remediation and brings new insights into the design and assessment of sustainable infrastructures under climate changes

Summary Report: Project Terra Research Meeting

Developing the conservation of earthen architectural Heritage -- as a science, a field of study, a professional practice, and a social endeavor -- is the overall objective of Project Terra

Measuring and accounting for community capabilities in Kordofan, Sudan:

"Parallel to the growing attention being devoted to the relationship between empowerment and development, an increasing number of tools are being developed to measure empowerment and determine the link between these two phenomena. This paper details the methodological processes used to construct, test and possibly refine one such instrument, the Community Capability Index, an innovative tool to measure community capabilities in the domain of natural resource governance. Empirical reference is made to research conducted in 85 villages in North and South Kordofan, Sudan. Following this, the paper presents findings from analyses of the determinants of community capabilities, including geographic, economic, and institutional variables. The results suggest that in Kordofan a number of factors influence capabilities. Possessing a village market, proximity to the nearest town, and access to credit are economic variables that have a significant and highly positive effect on community capabilities. Regarding the environment, capabilities are found to be greater where there is more rainfall, but access to groundwater from lower-quality aquifers and cracking clay soils have negative impacts on capabilities. War shocks, as might be expected, have a negative and significant effect. Particularly interesting is the generally weak correlation found between capabilities and wealth, along with strong correlations between institutional and social dimensions of community capabilities and participation in donor-funded projects. This combination suggests that development interventions must take into account the non-identity of poverty reduction and empowerment processes, at least when the targeted agents are communities rather than individuals or households. The findings reveal areas for further investigation into the relationship between the determinants and dimensions of capabilities, and the potential significance of the relationship for some dimensions suggests context-specific interventions to strengthen the relevant capabilities." from Authors' AbstractCapabilities, Community Capabilities Index, Empowerment, methodologies, Social capital,

First GIS analysis of modern stone tools used by wild chimpanzees (Pan troglodytes verus) in Bossou, Guinea, West Africa

Stone tool use by wild chimpanzees of West Africa offers a unique opportunity to explore the evolutionary roots of technology during human evolution. However, detailed analyses of chimpanzee stone artifacts are still lacking, thus precluding a comparison with the earliest archaeological record. This paper presents the first systematic study of stone tools used by wild chimpanzees to crack open nuts in Bossou (Guinea-Conakry), and applies pioneering analytical techniques to such artifacts. Automatic morphometric GIS classification enabled to create maps of use wear over the stone tools (anvils, hammers, and hammers/anvils), which were blind tested with GIS spatial analysis of damage patterns identified visually. Our analysis shows that chimpanzee stone tool use wear can be systematized and specific damage patterns discerned, allowing to discriminate between active and passive pounders in lithic assemblages. In summary, our results demonstrate the heuristic potential of combined suites of GIS techniques for the analysis of battered artifacts, and have enabled creating a referential framework of analysis in which wild chimpanzee battered tools can for the first time be directly compared to the early archaeological record.Leverhulme Trust [IN-052]; MEXT [20002001, 24000001]; JSPS-U04-PWS; FCT-Portugal [SFRH/BD/36169/2007]; Wenner-Gren Foundation for Anthropological Researc

Experimental analysis of soil cracking due to environmental conditions

This thesis presents an experimental approach on the subject of cracking in soils due to changes in environmental conditions, where research is mainly directed to the soil-air interface and the effect of boundary conditions. At the theoretical level, hypotheses put forward by various authors on the cracking of soils in terms of origin and crack propagation are considered, which serve as a reference to describe the behavior obtained from the tests. The objectives of the thesis belong to a line of research dedicated to studying the desiccation of soils and their implications in engineering works. The work consisted in the implementation of a one-year-long field test, subjected to natural environmental conditions, instrumented to monitor and record the main variables within the soil (temperature, volumetric water content, suction) and others very close to the ground-air interface area (wind speed and direction, temperature, relative humidity, solar radiation, rain intensity). For the laboratory experiments, significant improvements have been made in the existing environmental chamber to allow wetting of the specimens, and the automatic control of drying and wetting cycles. The cycles of humidity in the environmental chamber and the periods of rain and drought selected from the one-year-long field test measurements have been devised to study the behavior of the cracks in response to the variation of water content in the soil. Several types of soil have been used for the development of the tests. One of the soils was a silty clay from the Campus Nord of the UPC in Barcelona, already well characterized in works already published. Another soil, used in both laboratory and field experiments, is a silty clay from the Agròpolis agricultural campus in Viladecans. This clay is characterized in depth in this thesis. To study the cracking of soils as an effect of suction and contraction, mixtures of Jeddah sand (Saudi Arabia) with Gordon’s Kaolinite (United States) have been used. The analysis of the results is based on concepts of classical soil mechanics and unsaturated soil mechanics, notions of agro-meteorology, application of techniques for image analysis and concepts previously developed in the research group. Some theoretical analysis has been carried out to explain the results obtained and to reach conclusions on the proposed objectives. In general, the results of the laboratory experiments confirm some hypotheses and coincide with observations from previous published studies. The modified soil classification system RSCS has worked well as a tool to anticipate the transition of the capillarity phenomenon and the tendency to cracking by drying according to the input parameters required by that classification system. The combination of laboratory and field experiments has led to the conclusion that drying in the field is more efficient than in the environmental chamber, despite an extreme decrease of the relative humidity, given that there are natural variables that affect the boundary conditions and may have effects on the process of cracking in the ground.Esta tesis presenta un enfoque experimental sobre el tema de agrietamiento en suelos debido a cambios en las condiciones medioambientales, donde la investigación se dirige principalmente a la interface suelo-aire y al efecto del contorno. A nivel teórico se consideran hipótesis expuestas por diversos autores sobre el agrietamiento de suelos en términos de origen y propagación de grietas, que sirven de referencia para describir el comportamiento obtenido de los ensayos. Los objetivos de la tesis se enmarcan dentro de una línea de investigación dedicada a estudiar la desecación de suelos y sus implicaciones en obras de ingeniería. El trabajo ha consistido en la implantación de un ensayo en campo a largo plazo, de un año de duración, sometido a las condiciones ambientales naturales, instrumentado para el registro de variables dentro del suelo (temperatura, contenido de humedad volumétrico, succión) y otras muy cercanas a la zona de la interface suelo-aire (velocidad y dirección del viento, temperatura, humedad relativa, radiación solar, intensidad de la lluvia). En el ámbito experimental de laboratorio se han hecho mejoras importantes en la cámara ambiental existente para permitir reproducir la humectación de las muestras y el control automático de ciclos de secado y humedecimiento. Los ciclos de humedad en cámara ambiental y periodos de lluvia y sequía seleccionados del año de medición al aire libre se plantean para estudiar el comportamiento de las grietas como respuesta ante la variación del contenido de agua en el suelo. Para el desarrollo de los ensayos se han utilizado varios tipos de suelo. Uno ha sido la arcilla limosa del Campus Nord de la UPC en Barcelona, ampliamente estudiada en trabajos ya publicados. Otro suelo, utilizado tanto en experimentos de laboratorio como en campo, es una arcilla limosa del campus agrario Agròpolis en Viladecans. Esta arcilla se caracteriza en profundidad en la presente tesis. Para estudiar el agrietamiento de suelos como un efecto de la succión y la retracción se han utilizado mezclas de arena de Jeddah (Arabia Saudí) con Caolinita de Gordon (Estados Unidos). El análisis de los resultados se basa en conceptos de la mecánica de suelos clásica y mecánica de suelos no saturados, nociones de agro-meteorología, aplicación de técnicas para el análisis de imagen y fundamentos definidos en trabajos previos del grupo de investigación. Se ha llevado a cabo un tipo de análisis teórico para explicar los resultados obtenidos y concluir sobre los objetivos planteados. En general los resultados de los experimentos de laboratorio confirman algunas hipótesis planteadas y coinciden con observaciones de estudios previos publicados. El sistema modificado de clasificación de suelos RSCS ha funcionado como una herramienta para anticipar la transición del fenómeno de capilaridad y la tendencia al agrietamiento por desecación según los parámetros de entrada que requiere el sistema de clasificación mencionado. La combinación de experimentos en laboratorio y en campo han llevado a concluir que el secado en campo es más eficiente que en la cámara ambiental, aunque se extreme la disminución de la humedad relativa, dado que hay variables naturales que afectan las condiciones de contorno y pueden llegar a tener efectos en el proceso de formación de grietas en el suelo.Aquesta tesi presenta un treball experimental sobre el tema d'esquerdament en sòls a causa de canvis en les condicions mediambientals, on la investigació es dirigeix principalment a la interfície sòl-aire i a l'efecte de les condicions de contorn. A nivell teòric es consideren hipòtesis exposades per diversos autors sobre l'esquerdament de sòls en relació a la formació i propagació d'esquerdes, que serveixen de referencia per descriure els comportaments obtingut dels assajos. Els objectius de la tesi s'emmarquen dins d'una línia de recerca dedicada a estudiar la dessecació de sòls i les seves implicacions en obres d'enginyeria. El treball ha consistit en la implantació d'un assaig en camp a llarg termini, d'un any de durada, sotmès a les condicions ambientals naturals, instrumentat per al registre de variables dins del sòl (temperatura, contingut volumètric d'humitat, succió) i altres molt properes a la zona de la interfície sòl-aire (velocitat i direcció del vent, temperatura, humitat relativa, radiació solar, intensitat de la pluja). En l'àmbit experimental de laboratori s'han fet millores importants en la cambra ambiental existent per permetre reproduir la humectació de les mostres i el control automàtic de cicles d'assecat i humitejament. Els cicles d'humitat en cambra ambiental i els períodes de pluja-sequera seleccionats de l'any de mesurament a l'aire lliure es plantegen per estudiar el comportament de les esquerdes com a resposta davant la variació del contingut d'aigua en el sòl. Per al desenvolupament dels assajos s'han utilitzat diversos tipus de sòl. Un tipus de sòl és l'argila llimosa del Campus Nord de la UPC a Barcelona, àmpliament estudiada en treballs ja publicats. Un altre sòl, utilitzat tant en experiments de laboratori com en el de camp, és una argila llimosa del campus agrari Agròpolis a Viladecans. Aquesta argila s'ha caracteritzat en profunditat en la present tesi. Per estudiar l'esquerdament de sòls com un efecte de la succió i la retracció s'han utilitzat mescles de sorra de Jeddah (Aràbia Saudita) amb caolinita de Gordon (Estats Units). L’anàlisi dels resultats es basa en conceptes de la mecànica de sòls clàssica i mecànica de sòls no saturats, nocions d'agro-meteorologia, aplicació de tècniques per a l’anàlisi d'imatge i altres conceptes definits en treballs previs del grup de recerca. S'ha dut a terme un tipus d’anàlisi teòrica per explicar els resultats obtinguts i concloure sobre els objectius plantejats. En general els resultats dels experiments de laboratori confirmen algunes hipòtesis plantejades i coincideixen amb observacions d'estudis publicats prèviament. El sistema modificat de classificació de sòls RSCS ha funcionat com una eina per anticipar la transició del fenomen de capil·laritat i la tendència a l'esquerdament per dessecació segons els paràmetres d'entrada que requereix el sistema de classificació esmentat. La combinació d'experiments en laboratori i en camp han portat a la conclusió que l'assecat en camp és més eficient que a la cambra ambiental, malgrat la disminució extrema de la humitat relativa, atès que hi ha variables naturals que afecten les condicions de contorn i poden arribar a tenir efectes en el procés de formació d'esquerdes en el sòl

Desiccation and cracking behaviour of clay layer from slurry state under wetting-drying cycles

International audienceLaboratory tests were conducted to investigate the effect of wetting-drying (W-D) cycles on the initiation and evolution of cracks in clay layer. Four identical slurry specimens were prepared and subjected to five subsequent W-D cycles. The water evaporation, surface cracks evolution and structure evolution during the W-D cycles were monitored. The effect of W-D cycles on the geometric characteristics of crack patterns was analyzed by image processing. The results show that the desiccation and cracking behaviour was significantly affected by the applied W-D cycles: the measured cracking water content c, surface crack ratio Rsc and final thickness hf of the specimen increased significantly in the first three W-D cycles and then tended to reach equilibrium; the formed crack patterns after the second W-D cycle were more irregular than that after the first W-D cycle; the increase of surface cracks was accompanied by the decrease of pore volume shrinkage during drying. In addition, it was found that the applied W-D cycles resulted in significant rearrangement of specimen structure: the initially homogeneous and non-aggregated structure was converted to a clear aggregated-structure with obvious inter-aggregate pores after the second W-D cycle; the specimen volume generally increased with increasing cycles due to the aggregation and increased porosity. The image analysis results show that the geometric characteristics of crack pattern were significantly influenced by the W-D cycles, but this influence was reduced after the third cycle. This is consistent with the observations over the experiment, and indicates that the image processing can be used for quantitatively analyzing the W-D cycle dependence of clay desiccation cracking behaviour

Can electrical resistivity tomography describe soil structure evolution?

Variations of soil structure is significant for the understanding of water and gas transfer in soil profiles. In the context of arable land, soil structure can be compacted due to either agriculture operation (wheel tracks), or hardsetting and crusting processes. As a consequence, soil porosity is reduced which may lead to decrease water infiltration and to anoxic conditions. Porosity can be increased by cracks formation due to swelling and shrinking phenomenon. We present here a laboratory experiment based on soil electrical characteristics. Electrical resistivity allows a non destructive three dimensional and dynamical analysis of the soil structure. Our main objective is to detect cracks in the soil. Cracks form an electrical resistant object and the contrast of resistivity between air and soil is large enough to be detected. Our sample is an undisturbed soil block 240mm*170mm*160mm with an initial structure compacted by wheel traffic. Successive artificial cracks are generated. Electrodes built with 2 mm ceramic cups permit a good electrical contact at the soil surface whatever its water content. They are installed 15 mm apart and the electrical resistivity is monitored using a dipole-dipole and wenner multi-electrodes 2D imaging method which gives a picture of the subsurface resistivity. The interpreted resistivity sections show the major soil structure. The electrical response changes with the cracks formation. The structure information extracted from the electrical map is in good agreement with the artificially man-made cracks. These first results demonstrate the relevance of high resolution electrical imaging of the soil profile. Further experiments need to be carried out in order to monitor natural soil structure evolution during wetting-drying cycles