Nowadays, new approaches to fabricate high-performance electrode materials are of vital importance in the renewable energy field. Here, we present a facile synthesis procedure of 3D Ni(OH)2/graphene hybrids for supercapacitors via synchronous electrochemical-assisted exfoliation and assembly of graphene on 3D Ni(OH)2 networks. With the assistance of an electric field, the electrochemically exfoliated high-quality graphene can be readily, uniformly assembled on the surfaces of 3D Ni(OH)2. When serving as electrode materials for supercapacitors, the resulting 3D Ni(OH)2/graphene composites exhibited excellent specific capacitance (263 mF cm−2 at 2 mA cm−2), remarkable rate capability and super-long cycle life (retention of 94.1% even after 10 000 continuous charge–discharge cycles), which may be attributed to their highly porous, stable 3D architecture as well as uniform, firm anchoring of ultrathin graphene on their surfaces. Therefore, our approach provides a facile strategy for the large-scale synthesis of high-quality graphene based composites towards various applications.

No description available.

Bridge decks are commonly subjected to harsh environmental conditions that often lead to serious corrosion problems triggered by blisters under the hot mix asphalt bridge deck surfacing and secretly evolving during weather exposure until damage is often detected too late. Blisters may form under both the waterproofing dense mastic asphalt layer or under the waterproofing membrane which is often applied as additional water protection under the mastic asphalt (MA). One of the main technical issues is the formation of blisters under the membrane and asphalt-covered concrete structures caused by a complex mechanism governed by bottom-up pressure and loss of adhesion. A linear viscoelastic finite-element model was developed to simulate time-dependent blister growth in a dense mastic asphalt layer under uniformly applied pressure with and without temperature and pressure fluctuation. A finite element model was developed using ABAQUS with linear viscoelastic properties and validated with a closed form solution from first-order shear-deformation theory for thick plates. In addition, the blister test was conducted on different samples of MA in the laboratory and digital image correlation measurement technique was used to capture the three-dimensional vertical deflection of the MA over time. It was found that the blister may grow continuously under repeated loading conditions over subsequent days. With respect to blistering under waterproofing membranes, mechanical elastic modeling and experimental investigations were performed for three different types of membranes under in-plane stress state. The orthotropic mechanical behavior of a polymer modified bitumen membrane (PBM) was determined from biaxial test data. Finally, blister tests by applying controlled pressure between orthotropic PBMs and concrete plates were performed for studying the elliptical adhesive blister propagation using digital 3D image correlation. The energy calculated from elliptical blister propagation was found comparable to the adhesive fracture energy from standard peeling tests for similar types of PBMs. This indicates that the peeling test assists to evaluate and rank the adhesive properties of different types of membranes with respect to blister formation at room temperature without conducting time consuming and complicated pressurized blister propagation tests using digital 3D image correlation. / <p>QC 20130625</p>

Cedar, represented by Western redcedar (Thuja plicata) and Yellow Cedar (Chamaecyparis nootkatensis) was known as the “Tree of Life” to the Nuu-chah-nulth on Vancouver Island’s west coast, and most other groups of the Pacific Northwest. This thesis investigates the Culturally Modified Trees (CMTs), or more specifically Tapered Bark Strips (TBS), created through the extraction of cedar bark removed for all manner of material goods. CMTs are now the most common archaeological site type within British Columbia. Current regional chronologies have inherent biases that make interpretations difficult. The chronologies created through Archaeological Impact Assessments (AIAs) are weighted heavily to the contact period and the highest frequency of use corresponds with indigenous population collapse rather than peak. Investigations are made into the true distribution of existing CMT features. This thesis details the survey of 16 recent old growth cedar clearcuts which found extensive unrecorded CMT features that have recently been logged throughout the southern Nuu-chah-nulth study region. Half of all TBS scars in exposed stumps were found embedded within healed trees, otherwise invisible to archaeologists. Comparing all AIA report dates (surveyed prior to logging activity) with all post-impact assessments surveys it was found the latter contain a greater and older distribution of scarring events corresponding to high First Nations populations before the contact period. The study also compares CMT chronologies with local histories, investigates the antiquity of Northwest Coast CMTs and the indigenous management of cedar trees to maximize bark harvests. The findings of this research hint at the expanded extent of anthropogenic forests in the Northwest Coast, the inadequate recording and heritage protections of CMTs, and what it all means for Aboriginal Land Rights in British Columbia. / Graduate / 0324 0740 0329 / kinze.earnshaw@gmail.com

Le renforcement de structures ou d'éléments de structure par collage de plats PRF (polymères renforcés de fibres) est une technique actuellement reconnue et utilisée dans le monde entier. Il permet d'augmenter la durée de vie des structures existantes ce qui est très intéressant du point de vue développement durable et est souvent plus intéressant d'un point de vue économique. La première partie de ce travail s'intéresse au renforcement de poutres béton armé par des plats PRF. En effet, ce type de renforcement peut engendrer une rupture prématurée de type peeling-off. Ce mode de ruine très fragile résulte du décollement du béton d'enrobage qui reste collé au matériau de renforcement. Pour une conception optimale d'un renforcement en flexion par collage, il est important d'être en mesure de prévoir ce type de rupture et d'en tenir compte dans le dimensionnement. Pour cela, un modèle numérique fiable de type élasto-plastique est dans un premier temps présenté qui permet de prévoir la rupture de type peeling-off. Ce modèle est validé à l'aide de résultats d'essais expérimentaux. Les paramètres principaux affectant l'efficacité du renforcement sont ensuite mis en évidence dans le cadre d'une étude paramétrique. Les résultats de cette étude sont mis en parallèle avec des résultats d'essais de la littérature prouvant ainsi l'efficacité du modèle proposé. Enfin, plusieurs mesures sont proposées pour améliorer la performance du renforcement et éviter la rupture prématurée de peeling-off. La deuxième partie de ce travail s'attache quant à elle à l'étude de renforcement de tabliers de ponts soumis aux efforts éventuels d'impact d'un véhicule sur une barrière de sécurité. Une campagne expérimentale composée de différentes configurations de dalles est d'abord réalisée. Un modèle numérique s'inspirant du modèle proposé précédemment est ensuite présenté. La confrontation des résultats expérimentaux et numériques montre une concordance encourageante avant la fissuration majeure de la dalle. Enfin, les résultats mettent en relief l'efficacité du renforcement par des plats PRF dans le cas de glissières de sécurité

No description available.

The Atomic Force Microscope (AFM) is an instrument that is capable of measuring intermolecular forces between single molecules. Multi-Parameter Force Spectroscopy (MPFS) is a technique that uses the AFM. MPFS enables the acquisition of force curves and thermal resonance of the system under investigation. This technique can shed light on the mechanical behavior at the molecular level. Improvements described herein have enhanced the sensitivity of MPFS over background noise. This investigation focuses on the mechanical and interfacial properties of three carbon nanostructures: long nanotubes, nanocoils, and nanoloops. Different types of adhesion are encountered, measured and discussed: friction, rupture, and peeling. The elastic modulus of long carbon nanotubes is calculated from frequency shifts when the system is put into tension. An elastica model is applied to the post-buckled carbon nanotubes, which enables the estimation of the static coefficient of friction on chemically modified surfaces. The compression of a nanocoil at large contact angles reveals that changes in oscillation amplitude do not occur from damping, but from adding stiffness into the systems measured herein. This result is counter to the assumptions of dynamic force spectroscopy. Finally, carbon nanoloops are brought into and out of contact with several different surfaces. The force curve and frequency response of the system shows the difference between rupture and peeling. The results presented herein lead to a better understanding of the mechanical and tribological properties of the carbon nanostructures.

Aging bridges in the United States demand effective, efficient, and economical strengthening techniques to meet future traffic requirements. One such technique is to bond steel or fiber reinforced polymer (FRP) plates to the tension faces of reinforced concrete bridge beams with adhesives to strengthen them in flexure. However, beams that have been flexurally strengthened in this manner often fail prematurely, in particular by plate end peeling. The benefits of flexural strengthening by externally bonded reinforcement can only be fully realized by preventing premature failure modes so as to allow the development of composite action between the beam and the external reinforcement. With this goal in mind, several critical limit states of externally reinforced beams are examined in this thesis. Models developed by Roberts (1989) and by Colotti, Spadea, and Swamy (2004) that predict premature plate end debonding are examined in depth using data from previously conducted experimental programs that employed both steel and FRP external reinforcement. In addition, various parameters of the concrete beam, adhesive, and external reinforcement are analyzed in each model to determine the role of each parameter in failure prediction. A critical appraisal of the performance of the models using existing experimental data leads to the selection of the Roberts (1989) model. This model is used to develop recommended design guidelines for flexurally strengthening reinforced concrete bridge beams with externally bonded FRP plates and for preventing premature plate peeling.

No description available.

The three main components of wood, namely, cellulose, hemicellulose, and lignin, can be used in various areas. However, since lignin covalently crosslinks with wood polysaccharides creating networks that is an obstacle for extraction, direct extraction of different wood components in high yield is not an easy matter. One potential approach to overcome such obstacles is to treat the wood with specific enzymes that degrade the networks by specific catalysis. However, the structure of wood is so compact that the penetration of the wood fibers by large enzyme molecules is hindered. Thus, the pretreatment of wood prior to the application of enzymes is necessary, for “opening” the structure. One pretreatment method that was performed in this thesis is based on kraft pulping, which is a well-established and industrialized technique. For untreated wood, the wood fibers cannot be attacked by the enzymes. A relatively mild pretreatment was sufficient for wood polysaccharides hydrolyzed by a culture filtrate. A methanol-alkali mixture extraction was subsequently applied to the samples that were pretreated with two types of hemicellulases, Gamanase and Pulpzyme HC, respectively. The extraction yield increased after enzymatic treatment, and the polymers that were extracted from monocomponent enzyme-treated wood had a higher degree of polymerization. Experiments with in vitro prepared lignin polysaccharide networks suggested that the increased extraction was due to the enzymatic untying. However, the relatively large loss of hemicellulose, particularly including (galacto)glucomannan (GGM), represents a problem with this technique. To improve the carbohydrate yield, sodium borohydride (NaBH4), polysulfide and anthraquinone were used, which increased the yields from 76.6% to 89.6%, 81.3% and 80.0%, respectively, after extended impregnation (EI). The additives also increased the extraction yield from approximately 9 to 12% w/w wood. Gamanase treatment prior to the extraction increased the extraction yield to 14% w/w wood. Sodium dithionite (Na2S2O4) is an alternative reducing agent for the preservation of hemicelluloses because it is less expensive than metal hydrides and only contains sodium and sulfur, which will not introduce new elements to the recovery system. Moreover, Na2S2O4has the potential to be generated from black liquor. Na2S2O4 has some preservation effect on hemicelluloses, and the presence of Na2S2O4 also contributed to delignification. The extraction yield increased to approximately 15% w/w wood. Furthermore, Na2S2O4 has been applied in the kraft pulping process of spruce. The yield and viscosity increased, while the Klason lignin content and kappa number decreased, which represents a beneficial characteristic for kraft pulp. The brightness and tensile strength of the resulting sheets also improved. However, the direct addition of Na2S2O4 to white liquor led to greater reject content. This problem was solved by pre-impregnation with Na2S2O4 and/or mild steam explosion (STEX) prior to the kraft pulping process. Following Na2S2O4 pre-impregnation and mild STEX, the obtained kraft pulp had substantially better properties compared with the properties exhibited after direct addition of Na2S2O4 to the white liquor. The wood structure opening efficiency of mild STEX alone was also tested. The accessibility of the wood structure to enzymes was obtained even at very modest STEX conditions, according to a reducing sugar analysis, and was not observed in untreated wood chips, which were used as a reference. The mechanical effect of STEX appears to be of great importance at lower temperatures, and both chemical and mechanical effects occur at higher STEX temperatures. / <p>QC 20140903</p>