published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Acrylic bone cement is widely used as a structural material in orthopaedics, dentistry, and orofacial surgery. Although bone cement celebrates four decades of success, it remains susceptible to fatigue fracture. This type of failure can directly lead to implant loosening, revision surgery, and increased healthcare expenditures. The mechanism of fatigue failure is divided into three stages: 1) fatigue crack initiation, 2) fatigue crack propagation, and 3) fast, brittle fracture. Adding reinforcing fibers and particles to bone cement is a proposed solution for improving fatigue performance. The mechanical performance of these reinforced bone cements is limited by fiber ductility, fibermatrix de-bonding, elevated viscosity, and mismatch of fiber size and scale of fatigue induced damage. In this dissertation, I report that adding small amounts (0% - 10% by weight) of multiwall carbon nanotubes (MWNTs) enhances the strength and fatigue performance of single phase bone cement. MWNTs (diameters of 10-9 10-8 m; lengths of 10-6 10-3 m) are a recently discovered nanomaterial with high surface area to volume ratios (conferring MWNT bone cement composites with large interfaces for stress transfer) that are capable of directly addressing sub-microscale, fatigue induced damage. MWNTs (2wt%) significantly increased the flexural strength of single phase bone cement by a modest 12%; whereas, similar additions of MWNTs dramatically enhanced fatigue performance by 340% and 592% in ambient and physiologically relevant conditions, respectively. Comparing the fatigue crack propagation behaviors of reinforced and unreinforced single phase bone cements revealed that the reinforcing mechanisms of MWNTs are strongly dependent on stress intensity factor, K, a numerical parameter that accounts for the combinatorial effect of the applied load and the crack size. As the crack grows the apparent stress at the crack tip intensified and the MWNTs lost their reinforcing capabilities. For that reason, it is likely that the predominant role of the MWNTs is to reinforce the bone cement matrix prior to crack initiation and during the early stages of crack propagation. Therefore, MWNTs are an excellent candidate for improving the clinical performance of bone cement, thereby improving implant longevity and reducing patient risk and healthcare costs.

Statybos pramonėje, mišiniuose vis plačiau naudojamas įvairus tiek natūralių tiek sintetinių ceolitų spektras. Atliktuose tyrimuose buvo naudojamas sintetinis ceolitas – hidrosodalitas (Na6+x(SiAlO4)6(OH)x•nH2O), modifikuotas hidrosodalitas ir fero silicio gamybos atlieka - SiO2 mikrodulkės. Su pastaraisiais pucolaniniais priedais tiriama sąveika su cementu, nustatyta kaip keičiasi cemento stiprio, tankio ir įgėrio savybės. Tyrimai atlikti ruošiant bandinius su 2%, 5%, 10% ir 15% pucolaninių priedų masės santykiais. Atlikus tyrimus nustatyta, kokia daroma įtaka cementinės masės hidratacijos temperatūrai. Nustatytas bandinių stiprumas, tankis po 3, 7 ir 28 parų. Nustatytas bandinių įgėris po 28 parų. Cementinio akmens gniuždomasis stipris nenaudojant priedo ir ilginant hidratacijos trukmę nuo 3 iki 28 parų didėja nuo 59 iki 80 MPa. Panaši priklausomybė stebima ir cementiniuose bandiniuose su pucolaniniais priedais. Ilgėjant hidratacijos trukmei stipriai gniuždant didėja. Tirtose sąlygose didžiausią stiprį gniuždant turėjo bandiniai su 10 % modifikuoto hidrosodalito priedo po 28 parų, gniuždomasis stipris padidėja iki 101 MPa. Galima daryti prielaidą, kad hidrosodalito, modifikuoto hidrosodalito ir SiO2 mikrodulkių pucolaninės savybės pasireiškia ne iš karto, bet išryškėja po ilgesnes hidratacijos trukmės, t. y. po 28 parų. Vykstant hidratacijai nuo 16 iki 28 parų, įgėris sumažėja nuo 13,41% iki 9,04% (esant 2% hidrosodalito kiekiui). Naudojant 5% SiO2 mikrodulkių kiekį... [toliau žr. visą tekstą] / Construction industry is increasingly being used in combination and variety of natural and synthetic zeolites spectrum. A study carried out using synthetic zeolite - hydrasodalite (Na6 + x (SiAlO4) 6 (OH) x • nH2O) modified hydrasodalite silicon production and Fair play - fume SiO2. With the recent pozzolanic additives investigated the interaction with cement, concrete changes in the strength, density and retention properties. Studies carried out in the preparation of the samples with 2%, 5%, 10% and 15% by weight of pozzolanic additives relations. It was determined, which affect the weight of cement hydration temperature. Fixed specimens the strength and the density of 3, 7 and 28 days. Set of samples absorption after 28 days. Compressive strength of cement stone without the use of additive and longer duration of hydration from three to 28 days increased from 59 to 80 MPa. A similar dependence is observed in samples with cement and pozzolanic additives. Hydration with increasing duration of the compressive strength increases. To examine the conditions had the highest compressive strength of samples with 10% modified hydrasodalite additives after 28 days, compressive strength increases to 101 MPa. It can be assumed that hydrasodalite, and SiO2 modified hydrasodalite fume pozzolanic properties are not immediate, but come on after a longer duration of hydration, etc. Y. after 28 days. During the hydration from 16 to 28 days, absorption decreases from 13.41% to 9.04% (at 2%... [to full text]

Existing specifications for asphalt cement employ insufficient aging and conditioning times prior to testing and low strains during the actual test which are insufficient to predict asphalt performance, especially if the materials are modified with additives such as those used for warm mix technology. However, slightly modified protocols, like increasing the conditioning time in the bending beam rheometer (BBR) test and increasing the aging duration in the pressure aging vessel (PAV), predict asphalt performance better than the current Superpave™ specification. These improved protocols are published as new test standards through the collaborative effort between the Ontario Ministry of Transportation and Queen’s University. In this study, the effects of warm mix and other additives on rheological, aging and failure properties are investigated. The properties are measured by regular tests and by modified protocols. The latter include the extended BBR test (LS-308) and the double-edge-notched tension (DENT) test (LS-299). Changes in ductile strain tolerance within base asphalts due to the various additives as measured with the DENT test were found to be very significant. The DENT results like essential work of fracture, we, plastic work of fracture term, βwp, and critical crack tip opening displacement, CTOD, are usually helped to correlate with the cracking distress survey results of the pavement in service. The addition of amide and polyethylene waxes risks increasing the cracking susceptibility in the pavement. They show a negative effect on strain tolerance in the ductile state, which is likely to show up as premature and/or excessive cracking in service which is similar to their physical hardening behavior from low temperature grading and extended BBR testing. / Thesis (Master, Chemistry) -- Queen's University, 2013-02-26 11:10:41.08

South African cement manufacturers are under financial pressure. Sales have declined due to the 2008 recession and electricity costs have tripled from 2005 to 2012. Electricity cost savings are therefore more important than ever. Unfortunately retrofitting highly energyefficient equipment is not ideal. These installations are costly and take a long time to implement. Alternative strategies that can produce quick results in reducing electricity costs are needed. One such alternative is a programme called Demand Market Participation (DMP). The DMP programme was implemented by Eskom, South Africa’s national electricity utility, to reduce electricity demand during supply shortages. This programme offers potential cost savings for clients with excess production capacity. Clients such as cement plants can switch off non-essential production equipment in Eskom’s peak demand periods for a financial incentive. To maximise the benefits for both the clients and Eskom, accurate electricity forecasting is needed, as are systems enabling a quick response to load reduction requests. In this study DMP opportunities on typical cement plants were identified. A DMP strategy to assist cement plants was developed to achieve maximum cost savings without influencing production, quality and safety. An existing energy management system (EnMS) was adapted to incorporate the new DMP participation strategy. The new EnMS and DMP strategy were implemented at a South African cement plant, resulting in savings of R220 000 per month. This translates into an annual cost-saving potential of R2-million for the plant, and an R13- million cost-saving potential for the total South African cement industry. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

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In dieser Arbeit wird das Revisionsverhalten kanülierter, fenestrierter Pedikelschrauben evaluiert. Dies erfolgt zum einen anhand von Messungen des Drehmoments bei dem Entfernen von Pedikelschrauben aus osteoporotischen Wirbelkörpern eines Kadermodells. Hierbei werden Werte nicht zementierter und zementierter, kanülierter Pedikelschrauben erhoben, verglichen und ausgewertet. Während der Schraubenexplantation werden etwaig auftretende Rotationsbewegungen des Zements im Wirbelkörper radiografisch detektiert. Darüber hinaus wird das Revisionsverhalten kanülierter, fenestrierter Pedikelschrauben nach Zementaugmentation in vivo anhand monozentrisch, retrospektiv erhobener Patientenbeispiele aus dem klinischen Alltag beurteilt. Im Rahmen der Drehmomentmessungen bei Entfernung der kanülierten, fenestrierten Pedikelschrauben nach vorangeganger Zementierung konnte keine Destruktion des Wirbelkörpers beobachtet werden. Auch in den untersuchten Fallbeispielen des klinischen Alltags konnten die zementaugmentierten Pedikelschrauben komplikationslos entfernt werden.

The third generation of hip resurfacing commenced in the U.K. in the 1990’s with the Birmingham Hip Resurfacing system and is now becoming more commonplace as an attractive alternative for young and active patients due to premature failure in total hip replacement in this patient group. However the Swedish National Hip Arthroplasty Register (2010) suggests that premature failure of resurfacing arthroplasty may be more prevalent than first expected. The aim of this study is to investigate, through Finite Element Analysis, the short, medium and long term performance of Poly Methyl Methacrylate (PMMA) bone cement of the femoral component in hip resurfacing arthroplasty. The study takes a forensic engineering approach, analysing the performance of PMMA bone cement in order to provide understanding, awareness and an insight into lifestyle options. Finite Element Analysis explores and models the effect of resting periods during daily activities, patients’ bone quality and PMMA bone cement Young’s modulus on the PMMA bone cement stresses within the femoral hip resurfacing component. Mechanical tests are used to illustrate the use of the Finite Element Analysis results. Contributing to knowledge, this study verifies the significance of high metal-on-metal friction due to resting periods, developing a dynamic FEA model to quantify the premature fatigue failure of PMMA bone cement, within the femoral component of hip resurfacing arthroplasty. A decrease in bone quality added to the effect of resting periods increase the risk of PMMA fatigue failure and PMMA-metal interface failure due to an increase of PMMA tensile and shear stresses, suggesting that patients with low bone quality should avoid hip resurfacing procedures. The use of low PMMA Young’s modulus could greatly enhance the long term success of hip resurfacing arthroplasty generally and specifically reduce the risk of interface failure and PMMA bone cement failure due to resting periods and patient bone quality. Moreover, this study shows that the consequence of PMMA fatigue failure and PMMA-metal interface failure must be included in the design, patient selection, screening process, post-operative rehabilitation and long term lifestyle attributes. This study suggests that occupational therapists and patients with hip resurfacing arthroplasty should be aware of high metal-on-metal friction situations, which could lead to early failure indicated by this research. The deleterious effect of resting periods indicated by this research could be alleviated by appropriate re-initiation of synovial lubrication by movement prior to full loading. Recommendations for further work include the compilation of a PMMA bone-cement fatigue properties database and further development of the FEA modelling technique for application upon other arthroplasty procedures.

The first detailed systematic investigation of a cement plant with various carbon capture technologies has been performed. The calcium looping (Ca-looping) process has emerged as a leading option for this purpose, since this process applied to a cement plant provides an opportunity to use the CaO purge for clinker production. The Ca-looping process is comprised of two interconnected reactors where the carbonator captures CO2 from flue gases and the calciner regenerates the CaCO3 into CaO by oxy-combustion. Fully integrated process flowsheets have been developed and simulated in UniSim Design Suite from Honeywell. The detailed carbonator model has been implemented using Matlab and incorporated into UniSim to provide a full flowsheet simulation for an exemplary dry-feed cement plant as a user-defined operation. The base cement plant simulation was also modified to integrate three different carbon capture processes: membrane; indirect calcination; and amine-scrubbing. Furthermore, an advanced configuration of Ca-looping process has been investigated where the energy intensive air separation unit was replaced with a chemical looping combustion (CLC) cycle. Each case has been optimised to minimise its energy consumption and compared in terms of levelised cost of cement and its resulting cost of CO2 avoided at the same CO2 avoidance rate. The proposed integration of the Ca-looping process is capable of achieving over 90% CO2 avoidance with additional fuel consumption of 2.5 to 3.0 GJth/ton CO2 avoided. By using an advanced configuration of the Ca-looping process with a CLC cycle, the additional fuel consumption can be reduced to 1.7 GJth/ton CO2 avoided, but the cost of the oxygen carrier is the major concern for this system. Among the other CO2 capture options, the membrane process is a promising alternative for the Ca-looping process since it has a potential of achieving the target CO2 avoidance rate and purity requiring lower energy consumption. The indirect calcination process provides moderate levels of CO2 avoidance (up to 56%) without a need of an external capture process whereas the integration of the amine process in a cement plant is challenging as a result of the requirement of steam for solvent regeneration. Furthermore, considering zero net CO2 emissions associated with biomass combustion systems, a novel concept has been analysed to capture of CO2 in-situ with the Ca-looping process while operating the combustor of a dedicated biomass power plant at sufficiently low temperature. This process is capable of achieving 84% overall CO2 capture rate with an energy penalty of 5.2% when a proper heat exchanger network is designed with the support of a pinch analysis. The techno-economic performance of the biomass power plant with in-situ Ca-looping CO2 capture process was compared with that of the alternative biomass-air-fired and biomass-oxy-fired power plants.

Dans le circuit primaire des réacteurs nucléaires à eau pressurisée, le bore participe au contrôle des réactions de fission. Le traitement de cette solution génère des déchets aqueux contenant une forte concentration en bore (de 1 à 3 mol/L). Le conditionnement de ces déchets à l'aide d'un ciment silico-calcique est compliqué par le fort pouvoir retardateur des ions borate sur l'hydratation du liant. Un traitement des déchets à la chaux est nécessaire pour précipiter les ions borate sous forme d'hexahydroborite. Cette stratégie, si elle limite le retard d'hydratation, ne le supprime pas. Par ailleurs, l'hexahydroborite est instable en milieu cimentaire et se convertit dans le temps en boroaluminate de calcium. Une autre approche pourrait consister à utiliser un ciment sulfoalumineux bélitique à forte teneur en ye'elimite. Ce liant présente en effet l'avantage de former en quantité importante des phases de type AFm et/ou AFt lors de son hydratation, phases qui peuvent incorporer des ions borate dans leur structure.Au cours de ce travail, l'hydratation de ciments sulfoalumineux par des solutions de borate de sodium a été étudiée au jeune âge et à plus long terme (sur une durée de 2 ans) dans l'objectif de préciser l'influence d'un ensemble de paramètres (pH du déchet, concentration en bore, taux de gypse du ciment) sur la vitesse d'hydratation du liant, la nature des hydrates formés, et les propriétés du matériau obtenu (résistance mécanique, stabilité dimensionnelle). Pour ce faire, une démarche analytique, procédant par complexification progressive des systèmes étudiés, a été mise en œuvre. Ainsi ont été successivement abordées la spéciation du bore en solution alcaline, l'étude des phases précipitant au sein des systèmes {CaO, B2O3, Na2O, H2O}, {CaO, B2O3, Al2O3, H2O} et {CaO, Al2O3, B2O3, SO3, H2O}, puis celle des pâtes de ciment gâchées avec une solution boratée simulant le déchet. L'approche expérimentale a été complétée par des modélisations thermodynamiques s'appuyant sur une base de données spécialement développée pour les besoins de l'étude.Il apparaît que le gypse joue un rôle primordial dans le contrôle de la réactivité du ciment. L'ajout de gypse fixe, par un mécanisme indirect, le pH de la solution interstitielle à une valeur proche de 11, ce qui favorise la précipitation transitoire d'un composé boraté faiblement cristallisé, l'ulexite. La dissolution des phases anhydres du ciment est alors fortement ralentie jusqu'à l'épuisement du gypse, conduisant ainsi à des retards de prise considérables. En l'absence de gypse, le retard à l'hydratation est de plus faible amplitude. Dans ces conditions, le pH de la solution interstitielle atteint des valeurs plus élevées, ce qui permet de déstabiliser rapidement l'ulexite. A plus long terme, les ions borate sont incorporés au sein d'une phase de type AFt, en solution solide avec les ions sulfate. Les résultats obtenus permettent de conclure que ce sont les ciments sulfo-alumineux contenant une faible teneur en gypse qui sont les plus adaptés au conditionnement de solutions à forte concentration en bore. / In the primary circuit of pressurized water reactors, boron helps controlling the fission reactions. The treatment of this solution produces aqueous low-level or intermediate-level and short lived radioactive with a high boron concentration (up to 1 to 3 mol/L). Stabilization/solidification of such wastes with calcium silicate cement is complicated by the strong retarding effect of borate ions on cement hydration. A calcium hydroxide addition is required to precipitate borate ions into hexahydroborite. With this approach, the hydration delay is limited, but not suppressed. Besides, hexahydroborite is unstable in the cement paste and is progressively converted into a hydrated calcium boroaluminate phase. Another strategy may consist in using belite calcium sulfoaluminate cement with high ye'elimite content. During hydration, this binder forms indeed large amounts of AFm and/or AFt phases which can incorporate borate ions into their structure.In this work, hydration of calcium sulfoaluminate cement by borated solutions was investigated at early age, and over a 2-year period, in order to determine the influence of a set of parameters (boron concentration and pH of the waste, gypsum content of the cement) on the hydration rate of the binder, on the phase assemblage formed, and on the properties of the resulting material (mechanical strength, volume change). An analytical approach was adopted, based on a progressive increase in the complexity of the investigated systems. The focus was successively placed on the speciation of boron in alkaline solution, on the study of the phases formed within the {CaO, B2O3, Na2O, H2O}, {CaO, B2O3, Al2O3, H2O} and {CaO, Al2O3, B2O3, SO3, H2O} systems, and on the characterization of cement pastes prepared with a borate solution which mimicked the waste. The experimental approach was completed by thermodynamic modelling using a database specially developed for the needs of the study. Gypsum appears to play a key role in controlling the reactivity of cement. The gypsum addition sets, by an indirect mechanism, the interstitial solution pH at a value close to 11, which promotes the precipitation of a poorly crystallized borated compound, ulexite. Dissolution of the anhydrous phases is strongly slowed down until the exhaustion of gypsum, and major delays are observed. Without any gypsum, the hydration delay is shorter. Under these conditions, the pore solution pH reaches higher values after mixing. Ulexite is consequently quickly destabilized. Borate anions are then incorporated into a mixed borate/sulphate AFt type phase. It appears that calcium sulfoaluminate cements with low gypsum contents should be recommended to solidify borated solutions.