47 research outputs found
Cellular decision making at the nanoscale
No full textThe well-established dependence of cell traction forces on the compliance of supporting matrices has been attributed to levels of force exerted on components in focal contacts. Here, use of novel, force-limited nanoscale tension gauges revealed that both force and substrate deformations govern cell decision-making during initial attachment to compliant substrates. We propose a mechanical model consistent with observed behavior. Upon formation of stable cell contacts, bond tension and tether rupture govern cell attachment, spreading, and focal adhesion maturation at force levels on individual receptors predicted by prior studies.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2019-08-01The student, Zainab Rahil, accepted the attached license on 2016-04-27 at 06:49.The student, Zainab Rahil, submitted this Thesis for approval on 2016-04-27 at 06:55.This Thesis was approved for publication on 2016-04-29 at 14:30.DSpace SAF Submission Ingestion Package generated from Vireo submission #9538 on 2017-09-29 at 11:12:58Made available in DSpace on 2017-09-29T17:52:42Z (GMT). No. of bitstreams: 2
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Previous issue date: 2016-04-29Embargo set by: Colleen Fallaw for item 103531
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Development of Eco-friendly and High-Strength Lime-Hemp Concrete (LHC)
No full textThere is a growing demand for eco-friendly alternatives to Portland cement (PC) in the construction industry, primarily driven by the global push to achieve net-zero carbon emissions by 2050. Lime-hemp concrete (LHC), or hempcrete, presents a promising solution to replace traditional, carbon-intensive Portland cement (PC) based construction materials. However, its adoption has been constrained by its limited mechanical strength, with compressive strength ranging from approximately 0.4 to 3.2 MPa and flexural strength ranging from 0.06-1.2 MPa depending on dry density, as reported in several studies. Despite its impressive net carbon-negative potential (around -135 kg CO₂/m³) and other remarkable properties, this limitation has hindered its widespread appeal within the construction industry. This study focuses on developing LHC, with improved mechanical strength while maintaining its advantageous properties, including breathability, insulation, and hygrothermal performance. By incorporating Polyvinyl Acetate (PVAc) adhesive into the LHC system, we developed a mix with a weight ratio of 1:0.3:0.3:0.6 of lime, hemp stalk particles (SP), PVAc, and water. This resulted in a relatively high 28-day compressive strength of 9.9 ± 0.31 MPa and a flexural strength of 5.0 ± 0.25 MPa, demonstrating promising potential for further improvement to make it suitable for load-bearing applications in the future. The optimized LHC has a dry density of 841.61±5.22 kg/m³, dry thermal conductivity of 0.061±0.0006 W/mK, dry specific heat capacity of 1883.38 J/kgK, vapor permeability of 47.83 perm-inch, and a Moisture Buffer Value (MBV) of 1.50 g/m²%RH. Later, a composite wall block was designed based on this mix for further improvement of thermal and hygrothermal properties, which achieved a vapor permeability of 60.65 perm-inch, thermal conductivity of 0.050±0.00145 W/mK, and an MBV of 1.35 g/m²%RH. In the second phase of this project, calcined tailings from the Tailing Solvent Recovery Unit (CTSRU) were used as a lime replacement material (LRM), replacing 30 wt.% of the lime. This approach could reduce the carbon footprint, cost and environmental impact of the developed LHC further by replacing a significant portion of lime with waste calcined tailings. The substitution not only mitigated the environmental impact associated with the replaced lime production and tailings management but also preserved comparable mechanical performance, attaining a compressive strength of 9.3 ± 0.85 MPa at a dry density of 939.44 ± 11.20 kg/m³. This indicates that the material retained its mechanical performance despite the use of waste materials as LRM component. According to our study, X-ray diffraction (XRD) and differential thermogravimetric (DTG) analyses showed no significant pozzolanic activity in CTSRU, as no pozzolanic reaction products were observed in XRD or increased portlandite consumption by DTG analysis. Therefore, it is considered an LRM rather than a supplementary cementitious material (SCM), which requires notable pozzolanic or hydraulic activity. The comparable strength in the presence of 30 wt% CTSRU was attributed to pore refinement, evidenced by reduced porosity, a denser microstructure, a change in pore types, reduced microcracking, and enhanced interfacial adhesion between lime-hemp particles, as confirmed by X-ray computed tomography (X-CT) and scanning electron microscopy-energy dispersive X-ray (SEM-EDS) analyses. The composite wall block made from LHC core with CTSRU achieved a dry thermal conductivity of 0.052±0.000124 W/mK, vapor permeability of 44.38 perm-inch, and an MBV of 1.28 g/m²%RH. X-CT imaging revealed around 50% porosity in the composite, while SEM-EDS analysis confirmed a denser microstructure with CTSRU. This research highlights the potential of LHC as a high-strength material with improved mechanical and hygrothermal performance, offering an eco-friendly alternative for Portland cement-based wall blocks in the future, especially as load-bearing wall applications
Effect of Masterbatch Type and Concentration on Carbon Nanotube Reinforced Polyolefin Blend Nanocomposites
No full textThe use of polymer mixtures filled with conductive nanofillers, i.e. polymer blend nanocomposites (PBN), has increased greatly due to a high demand for advanced conductive materials. The new requirements are based on materials that are lightweight, easy to process, easy to shape, and less expensive than metals so that they can be used in electrical applications (e.g. automotive, electronics, aircraft). A great number of PBN are immiscible, leading to phase-separated structures (e.g. co-continuous morphology), which influences the final properties of the PBN. One of the main challenges when producing PBN is obtaining a homogeneous dispersion of fillers within the polymer, which is required for excellent electrical properties. Among the plethora of conductive nanofillers, high aspect ratio fillers such as multi-walled carbon nanotubes (MWCNT) are the most preferred fillers when the aim is to achieve low electrical percolation threshold and high electrical conductivity in the material. A masterbatch (MB) (polymer incorporated with a high concentration of MWCNT) is often used and the MB is diluted into the pure polymer to prepare the nanocomposite. This technique has been shown to improve dispersion and achieve low electrical percolation threshold in PBN. In this thesis, we control the final morphology in the multiphase polymer materials, particularly we are interested in how to manipulate localization of MWCNT in one of the phases in polyolefin blends (i.e. High density polyethylene/polypropylene HDPE/PP). This is a powerful technique to reduce filler content and tune electromagnetic interference (EMI) shielding properties. Two major studies were conducted to better understand how to successfully design polyolefin blends nanocomposites: 1) effect of order of addition of MWCNT by using different types of masterbatches (MB) (i.e. PE-MB and PP-MB) on the filler localization, final morphology and electrical conductivity; and 2) effect of MWCNT concentration in the MB (20 and 5.6 vol%) on the morphology development and EMI shielding performance. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and optical microscopy (OM) were used to characterize the MWCNT filler localization, phase morphology and MWCNT state of dispersion, respectively. Incorporation of MWCNTs resulted in a modification of the morphology and electrical properties. For instance, MWCNT induced continuity of PE phase, which led to enormous improvement in electrical properties via double percolation. The order of addition of MWCNTs into the blend also had an enormous effect on the blend microstructure. If the MWCNTs were first pre-mixed with HDPE and then diluted in HDPE/PP blend, the tendency was to decrease the domain size of the droplets, regardless of HDPE used. However, when MWCNTs were first pre-mixed with PP, and then diluted into HDPE/PP blends, an increase in domain size due to increased coalescence was observed. Moreover, MWCNTs were located in PE phase, due to higher PE/MWCNT affinity, regardless of whether MWCNTs were pre-mixed first with PP phase or type of masterbatch used (LDPE-5.6 MB or LDPE-20 MB). This result is contrary to predictions using wetting coefficients, which are widely used in the literature. Blends prepared with the less concentrated MB (5.6 vol% MWCNT) showed higher conductivity and EMI shielding due to double percolation and an optimum state of MWCNT dispersion. This indicates that double percolation in blends of polyolefins is a powerful way to enhance electrical properties
Towards High-Strength and Low-Carbon Concrete Masonry Blocks Using Locally Available Materials
No full textHigh-strength concrete masonry blocks are attracting attention to be used for loadbearing applications, such as tall walls. Such blocks can be achieved via modification of the dry mixture design and production methods. These modifications, however, may increase the carbon footprint of the concrete masonry blocks upon manufacturing. Careful selection of the mixture parameters is, therefore, necessary for the production of concrete blocks that have higher compressive strengths yet low carbon footprints. This study explored the effectiveness of using locally available materials for the production of dry concrete mixtures that can be used for the masonry block manufacturing. First, the suitability of utilizing pumice, sourced in British Columbia, as an alternative for Class F fly ash to partially replace the Portland cement in the concrete mixtures was studied. That was important as the availability of Class F fly ash is declining in Alberta and finding alternative replacements is imperative. To overcome the lower reactivity and strength development of pumice, a performance enhancing chemical admixture was used. Finally, recycled aggregates were obtained by crushing and pulverizing concrete masonry blocks that were used for structural testing in the laboratory. The so-produced aggregates were used as a replacement for the natural aggregates in the production of the dry concrete mixtures without and with pumice and chemical admixture. The resulting dry concrete mixtures were categorized into different classes of 30, 35, 40, and 50 MPa based on their average compressive strength at the age of 28 days in the laboratory conditions. Their mixture proportion with respect to their cement intensity (cement content per unit of strength) and application was discussed, and recommendations for future research were made. It is worth noting that although the results of this study were obtained for producing dry concrete mixtures, they can be extended for other concrete applications
Durability of Novel C-S-H-based Nanocomposites and Secondary Hydrated Cement Phases
No full textIssues concerning mechanisms of durability of hydrated cement phases in aggressive environments were studied. The possibility of using organic compounds in order to modify the micro- and nanostructure of the calcium-silicate-hydrate (C-S-H) phases was also investigated. Pure cement-based hydrated phases were synthesized and characterized by several analytical techniques such as X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy and scanning electron microscopy. Compacted samples of the synthetic hydrated cement phases were also prepared and used for the assessment of durability and mechanical properties. This doctoral thesis is comprised of several research chapters which can be categorized into two main parts. The first part focuses on the development of novel organically modified C-S-H systems. The second part involves the mechanisms underlying the volume stability of phase pure sulfoaluminate and related phases. A brief description of each part is as follows:
- development of novel organically modified C-S-H systems: The mechanisms of interaction of organic compounds with the nanostructure of C-S-H systems were studied. A model for the nanostructure of the resulting composite systems was proposed. In addition, the organically modified systems were tested for length-change, calcium-ion leaching and diffusion of isopropanol. Dynamic mechanical analysis and microindentation techniques were also used to determine the mechanical performance. Evidence of the superior engineering performance of the novel organically modified C S-H systems was provided.
- mechanisms of the volume stability of sulfoaluminate and related phases: Volume stability and change in the microstructure of the synthetic ettringite, monosulfate and thaumasite was critically examined in de-ionized water as well as in highly concentrated gypsum- or lime-water. A new dissolution-based mechanism for the expansion of these phases was proposed. The volume stability of multicomponent systems comprised of the C-S-H-based system (prepared in part I) and these sulfate-based hydrated phases was also investigated. It was suggested that the systems containing the modified C-S-H rather than the phase pure C-S-H had better resistance to crack growth and disintegration originating from the presence of ettringite or thaumasite
Assessment of Various Natural Pozzolans, Recycled Glass Powder, and Reclaimed Fly Ash as Supplementary Cementitious Materials for Concrete Mixtures
No full textThe increasing demand for reducing the CO2 emissions associated with Portland cement production in the concrete industry has increased the need for the use of supplementary cementitious materials (SCMs) to partially replace the Portland cement. Such a demand, in addition to the decline in the availability of Class F fly ash, necessitates exploring alternative SCMs. This study aimed to fill this gap by assessing the performance of different natural pozzolans and industrial wastes/by-products as SCMs for concrete mixtures. The SCMs included a medium- and a high-grade metakaolin (MMK and HMK), diatomaceous earth (DE), pumice, wollastonite, recycled glass powder (RGP), and reclaimed fly ash (RFA), all sourced from North America. The research first explored the effect of these SCMs in cement paste and mortar, when used at 20% by weight of cement, with DE at 10%. The rheology and heat of reaction were measured in cement paste, and the flow table and compressive strength were assessed in mortar. Reactivity of these SCMs was also tested according to RILEM TC 267-TRM. The SCMs that met the threshold for the 7-day heat release and bound water content were then used in concrete at the same content as that used in cement paste and mortar. The concretes were tested for fresh properties, compressive strength, and durability parameters, including depth of water penetration, water sorptivity, chloride penetrability, and bulk and surface electrical resistivity. The results showed that the selected natural pozzolans (MMK, HMK, and DE) had similar or improved compressive strengths over the reference concrete with no SCMs at all testing ages (3 to 91 days), however, they reduced the workability of the concrete. Concretes with these natural pozzolans also had the highest resistance to water and chloride penetration out of all the concretes tested, indicating improved durability. Concretes with RFA and RGP had reduced early-age strength, however, achieved comparable late-age strengths to the reference concrete and the concrete containing Class F fly ash, with improved or similar workability to the reference concrete. The concrete with RGP did not perform as well as the concretes with the natural pozzolans, however, it provided enhanced strength and durability compared to the concretes with RFA and Class F fly ash. The findings from this research contribute to a deeper understanding of the effectiveness of these SCMs across various applications in the concrete industry
Effect of alternative crosslinking agents on the thermo-rheological properties of SBS-modified asphalts
No full textCurrent industrial practices rely on the modification of asphalt by thermoplastic elastomers, particularly styrene-butadiene-styrene, crosslinked with a small amount of sulfur. This technology allows the formation of a three-dimensional polymer network with a significant impact on thermo-rheological and engineering properties. However, gelation of the material and potential development of harmful sulfur emissions may occur. This work concentrates on the mechanism of modification and development of thermo-rheological properties of styrene-butadiene-styrene modified asphalt crosslinked by novel sulfur-based and sulfur-free crosslinkers. The properties of crosslinked modified asphalts were studied by Superpave binder specification tests and rheological tests conducted in the linear and non-linear viscoelastic region. The results were compared with currently used crosslinking technology employing elemental sulfur as well as with the technology without any crosslinking agent. The results from Superpave binder specification showed that the samples crosslinked with novel sulfur-based crosslinking agents were less sensitive to thermo-oxidative degradation than the sample crosslinked with elemental sulfur. This behavior was confirmed by the thermogravimetric analysis which also provided insights about decomposition and combustion behavior. In addition, modified asphalts crosslinked with sulfur and sulfur-based crosslinkers had the highest values of %Recovery_3.2kPa. The appearance of the “shoulder” on the master curves of G'(ω) and the local maximum followed by the local minimum on the master curves of tanδ(ω) suggested exceptional resistance of modified asphalts crosslinked by sulfur and sulfur-based crosslinkers to deformation. The development and strength of polymer network were evaluated by the presence of viscosity overshoots and stress overshoots in the steady-state viscosity and start-up of steady shear measurements, respectively. The effects of crosslinking technologies were also evaluated via mechanical glass transition temperature and modulated differential scanning calorimetry. Obtained results point to a considerable difference in the crosslinking mechanism which was also reflected by significant differences in morphology of prepared modified asphalts at ambient temperature. Although sulfur and sulfur-based crosslinking systems had superior performance, the non-sulfur-based crosslinking systems could play a significant role in the reduction of odor and sulfur emissions in densely populated areas
Effect of Ultrafine Slag and Metakaolin Blend on the Properties of High-strength Dry-mix Concrete for Potential Application in Concrete Masonry Unit Production
No full textThis study aimed to develop a high-strength and low-Portland cement content dry-mix concrete with properties important for concrete block masonry unit manufacturing. First, the effect of six aggregate gradations on the compressive strength of dry-mix concretes made with a commercial Portland/Portland limestone cement was studied. Then, the aggregate that provided the highest strength was selected to prepare a dry-mix concrete that contained 50% of that cement together with an ultrafine granulated blast furnace slag (UFS) and a locally available medium-grade metakaolin (MK). Another binder that contained commercial slag combined with MK was also considered for comparison. The concretes were tested for the compressive strength, water absorption, permeable voids volume, bulk electrical resistivity, and freeze-thaw resistance. Results showed that the concrete incorporating MK-UFS achieved a 28-d compressive strength of ~70 MPa while that with MK-slag reached ~56 MPa. The concrete with MK-UFS also exhibited reduced water absorption and improved freeze-thaw resistance.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Durability of Novel C-S-H-based Nanocomposites and Secondary Hydrated Cement Phases
No full textIssues concerning mechanisms of durability of hydrated cement phases in aggressive environments were studied. The possibility of using organic compounds in order to modify the micro- and nanostructure of the calcium-silicate-hydrate (C-S-H) phases was also investigated. Pure cement-based hydrated phases were synthesized and characterized by several analytical techniques such as X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy and scanning electron microscopy. Compacted samples of the synthetic hydrated cement phases were also prepared and used for the assessment of durability and mechanical properties. This doctoral thesis is comprised of several research chapters which can be categorized into two main parts. The first part focuses on the development of novel organically modified C-S-H systems. The second part involves the mechanisms underlying the volume stability of phase pure sulfoaluminate and related phases. A brief description of each part is as follows:
- development of novel organically modified C-S-H systems: The mechanisms of interaction of organic compounds with the nanostructure of C-S-H systems were studied. A model for the nanostructure of the resulting composite systems was proposed. In addition, the organically modified systems were tested for length-change, calcium-ion leaching and diffusion of isopropanol. Dynamic mechanical analysis and microindentation techniques were also used to determine the mechanical performance. Evidence of the superior engineering performance of the novel organically modified C S-H systems was provided.
- mechanisms of the volume stability of sulfoaluminate and related phases: Volume stability and change in the microstructure of the synthetic ettringite, monosulfate and thaumasite was critically examined in de-ionized water as well as in highly concentrated gypsum- or lime-water. A new dissolution-based mechanism for the expansion of these phases was proposed. The volume stability of multicomponent systems comprised of the C-S-H-based system (prepared in part I) and these sulfate-based hydrated phases was also investigated. It was suggested that the systems containing the modified C-S-H rather than the phase pure C-S-H had better resistance to crack growth and disintegration originating from the presence of ettringite or thaumasite
Optimization and characterization of asphalts modified with isocyanate modifier
No full textWith the increase of traffic volumes, higher axle loads and harsh climate conditions, the paving industry relies on the use of polymer modified asphalts. With the progress of polymer science and technology, new polymer modified asphalt technologies have emerged. Among the most innovative modification technologies belong the use of B2last, a commercial product of BASF. Unlike other polymer modifiers, B2last is characterized as reactive mono- and oligomeric aromatic diisocyanate. Besides the formation of covalent bonds with polar species present in asphalt, the conversion of B2last into polymer could also be anticipated. In this thesis, a soft conventional asphalt was modified by B2last. The development of modification technology and the effect of B2last on the properties of asphalt was investigated by Superpave binder specification and Fourier-transform infrared spectroscopy (FTIR). The initial Superpave results suggested that B2last had a significant effect on maximum service temperature and resistance to the effects of short-term aging. This could be attributed to the reactive nature of the modification, as the additional oxygen and high temperatures could have led to further conversion of B2last and formation of heavier molecules. Due to the poor performance of B2last modified asphalt in the Multiple Stress Creep and Recovery experiment, the formulations of ternary modified asphalts containing B2last and vulcanized SBS were studied via the Design of Experiments. A positive interaction between the materials was found at high service temperatures, where the thermo-oxidative sensitivity of crosslinked SBS was generally mitigated by the presence of B2last. Lastly, the effect of B2last in paving mixes was evaluated and compared to the performance of hot mix asphalts containing asphalts prepared by a variety of modification technologies. The formulations included asphalt modified with B2last, vulcanized SBS, straight run asphalt with low Pen grade, catalytically oxidized asphalt, and optimized ternary blends containing SBS and B2last. While the samples modified with only vulcanized SBS had a superior performance in several tests, some of the ternary blends showed similar properties while using reduced amounts of total modifiers by weight, leading to the potential formulation of superior performing asphalt mixes with a reduced total content of polymer modifiers
