The manufacturing and characterisation of piezoelectric textile fibres are described in this thesis. A piezoelectric material is one that generates an electric voltage when deformed, a property which exists in a number of materials. The polymer with the strongest known piezoelectric effect today is poly(vinylidene fluoride) (PVDF), however it must be processed under certain conditions to become piezoelectric. This study shows that piezoelectric bicomponent PVDF-based fibres can be produced by melt spinning, which is a common and relatively simple fibre spinning method. The melt spinning process must include cold drawing, as this introduces a polar crystalline structure in the polymer. The fibres must also be electroded, which is done by producing bicomponent fibres with a core-and-sheath structure. The core is electrically conductive and constitutes an inner electrode consisting of a carbon black/polymer compound, whereas the sheath is PVDF and constitutes the piezoelectric component. Being sensitive to both deformation and temperature changes, these fibres are anticipated to be useful in a number of sensor applications. The flexibility and small size of the fibres makes it possible to include them as miniature-sensors in structures or garment without affecting the shape or comfort.

La réhabilitation parasismique de piliers de ponts et de poteaux de bâtiments en béton armé peut être réalisée efficacement par le confinement à l'aide de polymères renforcés de fibres de carbone (PRFC), ce qui a été étudié dans le présent projet par des essais en compression-flexion sur huit poteaux, dont quatre ont été réhabilités avec des PRFC. Les ponts, viaducs et bâtiments canadiens construits selon les codes de conception datant d'avant les années 1970 sont propices à subir d'importants dommages lors d'un séisme et même à poser un risque pour la sécurité des utilisateurs/occupants. Depuis, les normes parasismiques ont été grandement améliorées. De plus, avec le vieillissement des infrastructures, des dilemmes importants forcent les décideurs à choisir entre la réhabilitation et la reconstruction. Il importe de quantifier l'amélioration de la performance sismique apportée par le confinement des poteaux avant d'adopter cette technique à grande échelle. Pour cela, il faut étudier la ductilité et la résistance des poteaux confinés et non confinés et évaluer l'amélioration de la capacité de dissipation de l'énergie sismique. Les résultats ont de plus été comparés aux prédictions du modèle de confinement de Eid et Paultre afin d'évaluer la précision de ce modèle. Pour répondre à ces objectifs, huit spécimens ont été construits, quatre ont été réhabilités et tous les poteaux ont été testés par chargements axial constant et latéral cyclique. L'espacement des étriers, le niveau de charge axiale ainsi que l'usage de confinement ont été étudiés. Des courbes d'hystérésis ont ensuite été tracées afin de calculer les gains en capacité de dissipation d'énergie sismique. L'hypothèse de départ était que les poteaux confinés reprendraient une charge latérale maximale légèrement plus élevée, mais surtout qu'ils se déformeraient davantage et qu'ils dissiperaient plus d'énergie avant la rupture. Cette recherche vient combler un manque criant de données expérimentales sur le comportement en flexion-compression des poteaux confinés à l'aide de PRF. Les prochaines recherches pourront se baser sur ces résultats pour explorer d'autres paramètres expérimentaux et éventuellement proposer des articles de normes.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Macro synthetic fibres are known to significantly improve the toughness and energy absorption capacity of conventional concrete in the short term. However, since macro synthetic fibre are flexible and have relatively low modulus of elastic compared to steel fibres, it is uncertain if the improved toughness and energy absorption could be sustained over a long time, particularly under sustained tensile loadings. The main goal of this study is to investigate the time-dependent crack mouth opening response of macro synthetic fibre reinforced concrete (FRC) under sustained uniaxial tensile loadings, and to simulate the flexural creep behaviour. For the purpose of simulating the in-service time-dependent condition, all specimens were pre-cracked. Experimental investigations were carried out at three levels (macro, single fibre and structural) to investigate the time-dependent behaviour and the mechanisms causing it. At the macro level, compressive strength, uniaxial tensile strength and uniaxial tensile creep test at 30 % to 70 % stress levels of the average residual tensile strength were performed. To understand the mechanism causing the time-dependent response, fibre tensile test, single fibre pullout rate test, time-dependent fibre pullout test and fibre creep test were done. Flexural test and flexural creep test were done to simulate the structural level performance. The results of this investigation have shown significant drop in stress and increase in crack width of uniaxial tensile specimens after the first crack. The post cracking response has shown significant toughness and energy absorption capacity. Under sustained load at different stress levels, significant crack opening has been recorded for a period of 8 month even at a low stress level of 30 %. Creep fracture of specimens occurred at 60 % and 70 % indicating that these stress levels are not sustainable for cracked macro synthetic FRC. The single fibre level investigations have revealed two mechanisms responsible for the time-dependent crack widening of cracked macro synthetic FRC under sustained loading: time-dependent fibre pullout and fibre creep. In all cases of investigation, fibre failure was by complete pullout without rupture. Flexural creep results have shown that the crack opening increases over time. After 8 months of investigation, the total crack opening was 0.2 mm and 0.5 mm at 30 % and 50 % stress levels respectively. Since the crack opening of tensile creep and flexural creep specimens cannot be compared due to differences in geometry, specimen size, load transfer mechanisms and stress distribution in the cracked plane, a finite element analysis (FEA) was conducted. Material model parameters obtained from the uniaxial tensile test and viscoelastic parameters from curve fitting to experimental uniaxial creep results have been implemented to successfully predict the time-dependent crack opening of specimens subjected to sustained flexural loading. Analyses results correspond well with experimental result at both 30 % and 50 % stress levels. / AFRIKAANSE OPSOMMING: Makro sintetiese vesels is bekend daarvoor dat dit die taaiheid en energie absorpsie van konvensionele beton beduidend verbeter in die kort termyn. Aangesien makro sintetiese vesels buigsaam is met 'n relatiewe lae styfheidsmodulus in vergeleke met staalvesels, is dit onseker of die verhoogde kapasiteit vir energie absorpsie en taaiheid volgehou kan word oor die langer termyn, veral in gevalle waar dit aan volgehoue trekkragte blootgestel is. Die hoofdoel van die studie is om die tydafhanklike-kraakvergrotingsgedrag van makro sintetiese veselversterkte beton (VVB) wat blootgestel is aan volgehoue trekkragte te ondersoek asook die simulasie van die kruipgedrag in buig. Ten einde die werklike toetstande te simuleer is al die proefstukke doelbewus gekraak in 'n beheerde manier voor die aanvang van die toetse. Die eksperimentele ondersoek is uitgevoer op drie vlakke (makro, enkelvesel en strukturele) om die tydafhanklike gedrag sowel as die meganismes verantwoordelik vir hierdie gedrag te ondersoek. Op die makro-vlak is druktoetse gedoen saam met eenassige trek- en eenassige kruiptoetse met belastings tussen 30 % en 70 % van die gemiddelde residuele treksterkte. Om die meganisme wat die tydafhanklike gedrag veroorsaak te verstaan is veseltoetse, enkel vesel uittrektoetse, enkel vesel uittrek kruiptoetse asook kruiptoetse op vesels gedoen. Buigtoetse en buig kruiptoetse is ook gedoen om die gedrag op die strukturele vlak te ondersoek. Die resultate van hierdie ondersoek wys dat daar 'n beduidende val in spanning is en dat daar gepaardgaande kraak opening in die eenassige trek proefstukke plaasgevind het na die vorming van 'n kraak. Die na-kraak gedrag wys beduidende taaiheid en energie absorpsie kapasiteit. Gedurende die volgehoue trekbelasting by verskillende spanningsvlakke is beduidende kraakvergroting opgemerk, selfs by 30 % belasting na 8 maande. Kruipfaling het plaasgevind by proefstukke met belastings van 60 % en 70 % wat daarop wys dat hierdie spanningsvlakke nie geskik is vir gekraakte makro sintetiese VVB nie. Op die enkel veselvlak is twee meganismes geïdentifiseer wat verantwoordelik is vir die kraakvergroting oor tyd vir gekraakte makro sintetiese VVB met volgehoue trekbelasting: tydafhanklike vesel uittrek en vesel-kruip. In alle gevalle in hierdie ondersoek was die falingsmeganisme vesels wat uittrek. Buig kruiptoets resultate wys dat die krake vergroot oor tyd. Na 8 maande van ondersoek was die kraakwydtes 0.2 mm en 0.5 mm by 30 % en 50 % spanningsvlakke onderskeidelik. Aangesien die kraak opening van eenassige trek kruiptoetse en die buig kruiptoetse nie direk met mekaar vergelyk kan word nie weens die verskille in geometrie, proefstuk grootte en spanningsverdeling in die kraakvlak, is 'n eindige element analises (EEA) gedoen. Materiaal eienskappe is bepaal deur gebruik te maak van die eenassige kruip trektoets se resultate en viskoelastiese parameters is bepaal deur middel van kurwepassing van die resultate. Dit was gebruik om suksesvol die buig kruip kraak opening gedrag te simuleer. Die analises se resultate vergelyk goed met die eksperimentele data by beide 30 % en 50 % spanningsvlakke.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: FRC (Fibre-reinforced concrete) has become a common form of secondary and even primary reinforcing in some applications throughout the world. In South Africa, the structural applications are limited primarily to steel fibres while cheaper, lighter and more durable synthetic fibres have been side-lined due to low stiffnesses. The purpose of this research project is to investigate the behaviour of synthetic fibre-reinforced concrete (SynFRC) using fibres which are locally available in South Africa, and to propose a performance-based specification and test method for the use of these fibres. In order to achieve this, single fibre pull-out tests were performed on four locally available polypropylene fibres. It was found that the average bond stresses of the fibres are influenced primarily by the fibre cross sectional shape, longitudinal geometry and surface treatment, and secondarily by the aspect ratio. The W/C ratio had little effect on the single fibre performance of non-treated fibres, but appeared to have a slight effect on the single fibre performance of the surface treated fibre. From the experimental results, the highest fibre bond stress will be generated by using a fibre with an X-shaped cross section, longitudinal crimping and applying a surface treatment to this fibre. It also appears that the bond stress distribution for flat fibres is close to uniform, while the bond stress distribution for non-flat crimped fibres has a high mechanical interlock component at the surface end. Macro-mechanical performance tests were performed by means of the BS EN 14651 (2007) three point beam bending test and the ASTM C1550 (2012) Round Determinate Panel Test (RDPT). These tests were selected following a thorough literature review. The RDPT was found to be more consistent and able to identify trends which the three point beam bending test could not. In addition, the three point beam bending test’s most popular output, the Re,3 value tended to be misleading with varying W/C ratios, and it is recommended that the equivalent flexural tensile strength be used instead if the three point beam bending test is used. The macro-mechanical testing showed that increasing the fibre dosage did increase post-cracking performance. The flat fibres’ performance was significantly better than that of the non-flat fibres, and also increased at a faster rate with increasing fibre dosage. The post-cracking performance decreased with increasing W/C ratios and increasing aggregate sizes. The macro-mechanical performance was inversely proportionate to the single fibre performance. The macro-mechanical performance decreased with increasing fibre bond stress, and increased with increasing equivalent diameter, which equates to fewer fibres in a set volume of fibres. Finally, basic principles were developed from the data. These principles were used to predict the RDPT and three point beam bending test performance parameters based on fibre dosage, single fibre properties (bond stress and equivalent diameter), W/C ratio and aggregate size from the available data. The principles can be further refined with more experimental data. / AFRIKAANSE OPSOMMING: Vesel-gewapende beton word regoor die wêreld as ’n algemene vorm van sekondêre en selfs primêre versterking gebruik. In Suid-Afrika is die strukturele toepassings hoofsaaklik tot staal vesels beperk, terwyl goedkoper, ligter en meer duursame sintetiese vesels vermy word as gevolg van lae styfhede. Die doel van hierdie navorsingsprojek is om die gedrag van sintetiese-veselversterktebeton (SynFRC) te ondersoek deur gebruik te maak van vesels wat in Suid-Afrika beskikbaar is, en 'n prestasie-gebaseerdespesifikasie en toetsmetode vir die gebruik van sintetiese vesels voor te stel. Enkelveseluittrektoetse is op vier plaaslik beskikbare polipropileen vesels uitgevoer. Daar is gevind dat die gemiddelde verbandspanning van die vesel hoofsaaklik deur die vesel deursnee vorm, lengte meetkunde en oppervlak behandeling beïnvloed word, en tweedens deur die aspek verhouding beïnvloed. Die W/C-verhouding het min effek op die enkelveselprestasie van nie-behandelde vesels, maar het 'n effek op die enkeleveselprestasie van die oppervlak-behandelde vesel gehad. Die eksperimentele resultate wys dat die hoogste vesel verbandspanning deur 'n vesel met 'n X-vormige deursnit, lengte krimping en toepassing van 'n oppervlak behandeling gegenereer sal word. Dit blyk ook dat die verbandspanningverspreiding vir ’n plat vesel naby aan uniform is, terwyl die verbandspanningverspreiding vir ’n nie-plat gekrimpde vesel 'n hoë meganiese grendeling komponent op die oppervlak ente het. Makro-meganiese prestasietoetse is uitgevoer deur middel van die BS EN 14651 (2007) driepuntbalkbuigtoets en die ASTM C1550 (2012) RDPT. Hierdie toetse is ná ’n deeglike literatuuroorsig gekies. Die RDPT is meer konsekwent en is in staat om neigings te identifiseer wat die driepuntbalkbuigingtoets nie kan nie. Daarbenewens, met wisselende W/C verhoudings, is die driepuntbalkbuigtoets se gewildste resultaat, die Re,3-waarde geneig om misleidend te wees. Dit word aanbeveel dat die ekwivalentebuigtreksterkte in plaas van die Re,3-waarde as die drie punt balk buig toets resultaat gebruik word. Die makro-meganiesetoets het getoon dat die verhoging van die veseldosis ’n toename in na-krakingprestasie veroorsaak. Die plat vesels se prestasie was aansienlik beter as die van nie-plat vesels, en het met 'n toenemende veseldosis teen 'n vinniger koers verhoog. Die na-krakingprestasie het met toenemende W/C en die verhoging van die klip grootte afgeneem. Die makro-meganieseprestasie was omgekeerd eweredig aan die enkelveselprestasie. Die makro-meganieseprestasie het met toenemende vesel band stres verminder, en het met 'n toenemende gelykstaande deursnee (wat gelykstaande is aan minder vesel in 'n stel volume van vesel) vergroot. Ten slotte is basiese beginsels uit die data ontwikkel. Hierdie beginsels is gebruik om die RDPT en driepuntbalkbuigtoets prestasieparameters gebaseer op veseldosis, enkelveseleienskappe (verbandspanning en ekwivalentediameter), W/C-verhouding en klip grootte van die beskikbare data te voorspel. Die beginsels kan met meer eksperimentele data verder verfyn word.

<p>The adsorption of cationic polyacrylamide (C-PAM) and silicananoparticles onto a model surface of silicon oxide wascompared with the adsorption of C-PAM to fibres and theirinfluence on flocculation of a fibre suspension. An increase inionic strength affects the polyelectrolyte adsorption indifferent ways for these two systems. With the silica surface,an increase in the ionic strength leads to a continuousincrease in the adsorption. However, on a cellulose fibre, theadsorption increases at low ionic strength (1 to 10 mM NaCl)and then decreases at higher ionic strength (10 to 100 mMNaCl). It was shown that the adsorption of nanoparticles ontopolyelectrolyte-covered surfaces has a great effect on both theadsorbed amount and the thickness of the adsorbed layer. Theresults showed that electrostatic interactions were thedominating force for the interaction between both the fibresand the polyelectrolytes, and between the polyelectrolytes andthe silica particles. Furthermore, at higher NaClconcentrations, a significant non-ionic interaction between thesilicon oxide surface/particles and the C-PAM was observed.</p><p>The adsorption rate of C-PAM onto fibres was rapid andquantitative adsorption was detected in the time range between1 and 8 s at polyelectrolyte addition levels below 0.4 mg/g.Conversely, an increase in the amount of added polymer leads toan increased polymer adsorption up to a quasi-static saturationlevel. However, after a few seconds this quasi-staticsaturation level was significantly lower than the level reachedat electrostatic“equilibrium”. The adsorbed amountof charges at full surface coverage after 1 to 8 s contact timecorresponded to only 2 % of the total fibre charge, whereasafter 30 minutes it corresponded to 15 % of the total fibrecharge. This shows that a full surface coverage at shortcontact times is not controlled by surface charge. Based onthese results, it is suggested that a combination of anon-equilibrium charge barrier against adsorption and ageometric restriction can explain the difference between theadsorption during 1 to 8 s and the adsorption after 30 minutes.With increasing time, the cationic groups are neutralised bythe charges on the fibre as the polyelectrolyte reconforms to aflat conformation on the surface.</p><p>The addition of a high concentration of C-PAM to a fibresuspension resulted in dispersion rather than flocculation.This behaviour is most likely due to an electrostericstabilisation of the fibres when the polyelectrolyte isadsorbed. Flocculation of the fibre suspension occurred at lowadditions of C-PAM. A maximum in flocculation was found ataround 50 % surface coverage and dispersion occurred above 100% surface coverage. It was also shown that for a given level ofadsorbed polymer, a difference in adsorption time between 1 and2 seconds influenced the flocculation behaviour. An optimum inflocculation at 50 % surface coverage in combination with theimportance of polymer reconformation time at these shortcontact times showed that the C-PAM induced fibre flocculationagrees with La Mer and Healy’s description of bridgingflocculation.</p><p>A greater degree of flocculation was observed with theaddition of silica nanoparticles to the fibre suspension thanin the single polyelectrolyte system. Flocculation increased asa function of the concentration of added nanoparticles until0.5 mg/g. At higher additions the flocculation decreased againand this behaviour is in agreement with an extended model formicroparticle-induced flocculation. An increase in flocculationwas especially pronounced for the more extended silica-2particles. This effect is attributed to the more extendedpolyelectrolyte layer, since the adsorbed amount wasessentially the same for both silica particles.</p><p>Finally it was found that fines from the wood fibres had asignificant effect on the flocculation. When fines were added,a greater degree of flocculation was detected. Furthermore, itwas also more difficult to redisperse the fibres with polymerin the presence of fines.</p><p><b>Keywords:</b>Adsorption, bridging, cationic polymers,cellulose fibres, electrosteric stabilisation flocculation,ionic strength, nanoparticle, polyelectrolyte, reconformation,retention aids and silica</p>

No description available.

This thesis investigates the constant pressure cake filtration of interacting cellulose fibre/TiO2 (rutile) mixtures, and involved experimental studies using an automated pressure filtration apparatus. The influence of suspension composition, filtration pressure and solution environment on filtration has been discussed in relation to cake properties such as average cake porosity and specific resistance. To help interpret the filtration results, sedimentation data were also obtained. The average porosities of filter cakes formed from pure rutile and fibre suspensions in deionised water were approximately 0.6 and 0.75, respectively, and a steady and progressive increase in porosity with fibre fraction was generally observed. With filtrations at 450 kPa, the average specific cake resistances for pure fibre and rutile in deionised water were approximately 9.4x1013 and 4.2x1012 m kg-1 respectively, with the variation of specific resistance with solids composition showing a minimum. Similar trends were observed at other tested filtration pressures with suspensions in deionised water but not with filtrations of suspensions in 0.2 M NaCl and 0.1 M CaCl2 solutions. The minima in average specific cake resistance with solids composition for feeds in deionised water was attributed to rutile-fibre interactions. Abrupt transitions in cake structure were evident part way through some filtrations, and resulted in unexpected filtrate flow behaviour. This is an interesting phenomenon, and not only were the changes in cake structure relatively reproducible, but also the nature of the change could be altered by changes in filtration pressure, solids composition and/or solution environment. The study of fibre/particle binary filtration behaviour, in particular the porosity and specific cake resistance trends, were substantiated by relevant theoretical treatment and modelling analysis. With the porosity trends, an additive porosity concept seemed to represent the data better than interparticle penetration models. With the specific cake resistance trends, a semi-empirical equation was proposed which appeared to represent a wide range of binary mixture filtration data. A mathematical framework was also developed in an attempt to understand the underlying physical mechanisms which led to filter cake restructuring, and possible explanations were postulated.

We study a number of non-equilibrium models of interest to both active matter and biological physicists. Using microscopic agent-based simulation as well as numerical integration of stochastic PDEs, we uncover the non-trivial behaviour exhibited when active transport, or an advection field, is added to out of equilibrium systems. When gravity is included in the celebrated Fisher-Kolmogoro Petrovsky Piscouno (F-KPP) equation, to model sedimentation of active bacteria in a container, we observe a discontinuous phase transition between a `sedimentation' and a `growth' phase, which should in principle be observable in real systems. With the addition of multiplicative noise, the resulting model contains, as its limits, both the bacterial sedimentation previously described and the fluctuating hydrodynamic description of Directed Percolation (DP), an important and well-studied non-equilibrium system whose physics incorporate many universal features which are typical of systems with absorbing states. We map out the phase diagram describing all the systems in between these two limiting cases, finding that adding an advection term, however small, immediately lifts the resulting system out of the DP universality class. Furthermore, we find two distinct low-density phases separated by a dynamical phase transition reminiscent of a spinodal transition. Finally, we attempt to improve the current diffusion-limited model for the growth of filopodia, which are intriguing networks of actin fibres used by moving cells to sense their environment. By the addition of directed transport of actin monomers to the fibre tip complex by myosin molecular motors, we show that, under appropriate conditions, the resulting dynamics may be more efficient that transport by diffusion alone, which would result in filopodial lengths better corresponding to experimental observation.

It is crucial for a building to maintain structural stability when subjected to multiple and sequential extreme loads. Safety and economic considerations dictate that structures are built to resist extreme events, such as a earthquakes, impacts, blasts or fires, without collapse and to provide adequate time for evacuation of the occupants. However, during such events, some structural damage may be permissible. Design codes do not account for the scenario where two extreme events occur consecutively on a structure nor do they address the situation of the structure having some initial damage prior to being subjected to a fire load. This work begins by detailing the major inconsistancies between designing reinforced concrete structures for extreme mechanical loads and designing for fire. The material behaviour and traits of the constitutive parts (i.e. the concrete and the steel), including post yielding behaviour, thermal relationships and their interaction with each other are all explored in detail. Comprehensive experimental and numerical investigations are undertaken to determine whether, and to what extent, phenomena such as tensile cracking and loss of the concrete cover affect the local and global fire resistance of a member or structure. The thermal propagation through tensile cracks in reinforced concrete beams is examined experimentally. A comparison is made between the rate of thermal propagation through beams that are undamaged and beams that have significant tensile cracking. The results show that, although small differences occur, there is no significant change in the rate of thermal propagation through the specimens. Consequently, it is concluded that the effects of tensile cracking on the thermal propagation through concrete can be ignored in structural analyses. Significantly this means that analyses of heated concrete structures which are cracked can be carried out with heat-transfer and mechanical analyses being conducted sequentially, as is currently normal and fully-coupled thermo-mechanical analyses are not required. The loss of concrete cover and the impact on the thermal performance is examined numerically. A comparison is made of the thermal propagation, beam deflections and column rotations between structures that are undamaged and structures that have partial cover loss in a variety of locations and magnitudes. Results show that any loss of cover can lead to unsymmetrical heating, causing larger deflections in both vertical and horizontal directions, which can result in a more critical scenario. It is concluded that the effect of cover loss on the thermal performance of the structure is extremely significant. A new approach to numerically simulating the loss of cover by mechanical means from a member is developed. This new approach provides the user with an extremely flexible yet robust method for simulating this loss of cover. The application of this method is then carried out to show its effectiveness. A large experimental study carried out at the Indian Institute of Technology, Roorkee and separately numerically modelled at the University of Edinburgh. Unfortunately, due to unforseen circumstances, the experimental data available is limited at this time and as a result the validation of the numerical simulation is limited. Through these investigations it is clear that it is necessary to develop a method in enhance the stability and integrity of the concrete when subjected to the scenario of a fire following another mechanically extreme event. Therefore, finally a method is proposed and experimentally investigated into the use of fibres to increase the post crushing cohesiveness of the concrete when subjected to thermal loads. Results show that the fibrous members display an increased thermal resistance by retaining their concrete cover through an enhanced post crushing cohesion. From this investigation, it is concluded that the use of fibrous concrete is extremely beneficial for the application of enhancing the performance under extreme sequential mechanical and thermal loading.

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