Magister Scientiae Dentium - MSc(Dent) (Paediatric Dentistry) / The use of glass ionomer cement (GIC) restorative materials assists in the prevention of dental caries due to its long-term fluoride release. However, poor physical strength is one of the main drawbacks of GIC. A surface coating is recommended to improve the physical strength and is considered necessary during the overlapping stages of setting reactions of GIC restorative materials. The development of resin based coatings has improved the properties of the material but the effect on fluoride release needs investigation.

From initial contact with water until hardening, and deterioration, cement and concrete materials are subjected to various chemical and physical transformations and environmental impacts. This thesis focuses on the properties during the fresh state, shortly after mixing until the induction period. During this period flow history, including shearing and resting, and hydration both play big roles in determining the rheological properties. The rheological properties of cement and concrete not only affect the casting and pumping process, but also very critical for harden properties and durability properties. Compared with conventional concrete, self-consolidating concrete (SCC) can introduce many advantages in construction application. These include readiness to apply, decreasing labor necessary for casting, and enhancing hardened properties. However, challenges still remain, such as issues relating to formwork pressure [1-7] and multi-layer casting [8]. Each of these issues is closely related to the property of thixotropy. From the microstructural point of view, thixotropy is described as structural buildup (flocculation) under rest and breakdown (deflocculation) under flow. For SCC, as well as other concrete systems, it is about balancing sufficient flowability during casting and rate of structural buildup after placement for the application at hand. For instance, relating to the issue of SCC formwork, it is ideal for the material to be highly flowable to achieve rapid casting, but then exhibit high rate of structural buildup to reduce formwork pressure. This can reduce the cost of formwork and reduce the risk of formwork failure. It is apparent that accurately quantifying the two aspects of thixotropy, i.e. structuration and destructuration, is key to tackling these challenges in field application. Thus, the overall objective of my doctoral study is to improve quantification of key parameters tied to thixotropy that we have identified to be important: static yield stress, cohesion and degree of shear-induced particle migration. The two main contributions are as follows: Firstly, I quantified structuration of fresh paste and mortar systems by measuring static yield stress. After an extensive review of various rheological methods to probe viscoelastic properties of yield stress fluids, I selected, developed, and implemented a creep recovery protocol. Creep results were supplemented by low-amplitude oscillatory shear results, and supported that the measured static yield stress corresponds to the solid-liquid transition. This improved quantification of static yield stress can help better understand the effect of mix composition on SCC formwork pressure development, as well as static segregation and stability [9]. Since the static yield stress is measured before the structure is broken down, the effects of sand migration are eliminated. This study also analyzed effects of other supplementary cementitous materials such as nanoclay and fly ash. Results showed that nanoclay effectively increases static yield stress and structuration rate, while fly ash decreases static yield stress. To complement this investigation, I studied cohesion using the probe tack test, as cohesion is widely cited to be closely related to formwork pressure. I verified that probe tack test is a quick and useful method to measure static cohesion. Results showed that nanoclay increased cohesion dramatically while fly ash did not have an apparent effect on cohesion. Secondly, I developed an empirical model to fit the stress decay process under constant shear rate, For mortar systems, the stress decay can be attributed to two mechanisms: colloidal destructuration and sand migration. Such a model could be used to characterize particle migration and dynamic segregation [10], a critical issue for casting applications. In addition, shear induced particle migration is a widely recognized challenge in characterizing mortars and concretes through shear rheological methods [11-13]. Therefore this model can help determine the range of shear rates within which migration can be minimized to guide the design of protocols for dynamic rheological characterization and to ultimately develop design strategies to minimize mitigation. Compared with currently existing methods, this model provides a faster approach to quantify the sand migration process, including kinetics.

Cement has three sequential states in most applications: fluid, setting and hardened. This thesis focuses on the effect of nanoclays and diutan gum on rheological, chemical and mechanical properties corresponding to the three states. Water transport properties are critically important in many applications, such as oil well cementing and 3D concrete printing. The effect of nanoclays and diutan gum on water transport properties of cement pastes were investigated. Bleeding, water retention under suction pressure, and evaporation under air flow were measured. The nanoclay was found to reduce bleeding but had no effect on water retention or evaporation. The diutan gum was found to reduce bleeding, improve water retention, and decrease evaporation loss. The rheological properties of the pastes and their interstitial solution were also characterized to resolve the mechanisms underlying the water transport behaviors. Good correlation between the measured rheological parameters and water transport properties was found. In addition to water retention, the static yield stress build-up plays a major role in the successful oil well cementing and 3D concrete printing. Linear models are commonly used to describe the early structural build-up of cement-based materials. However, some studies have shown that there exists a faster non-linear phase before the linear phase. A simple non-linear thixotropy model is presented to describe the structural build-up process. It was quantified using static yield stress and storage modulus, which are measured through the stress growth protocol and small amplitude oscillatory shear (SAOS) tests, respectively. The effect of pre-shear, rest condition and nanoclay and diutan gum on the build-up behavior are studied. The results showed distinctly different trends between static yield stress and storage modulus. This may be attributed to the two different structures of fresh cement pastes, i.e. floc structures and C-S-H structures, measured by the stress growth protocol and SAOS test, respectively. Phase characterization of cement paste was performed through synchrotron x-ray diffraction technique. This allowed for real-time, in-situ measurements of x-ray diffraction patterns to be obtained, and subsequently the continuous formation and decomposition of select phases over time (up to 8 hours). Phases of interest included alite, ferrite, portlandite, ettringite, monosulfate, and jaffeite (crystalline form of calcium silicate hydrate). The effects of elevated temperatures at elevated pressure, as well as the effect of nanomaterial addition were investigated. Rate of conversion of ettringite to monosulfate increased with increasing temperature, and monosulfate became unstable when temperatures reached 85ºC. The synchrotron x-ray diffraction setup appeared to have captured the seeding effect of nano-sized attapulgite clays at 0.5% addition by mass of cement, where acceleration in the rate of formation of portlandite and jaffeite was observed. Finally, the investigated system was upscaled from cement paste to cement mortar incorporating the fly ash and the slag. The effect of the nanoclays on the mechanical properties was evaluated in comparison with the carbon nanotube. Compressive strength and tensile strength were evaluated. Results indicated that although the nanoclays are utilized primarily as a rheological modifier, they can also enhance mechanical properties.

Fluid-tight obturation of the root canal space is an important requirement for successful root canal treatment. Gutta percha, used as a core material in combination with different sealers, is the most commonly used root filling material and is considered the gold standard. However, it does not possess all the properties of the ideal obturation material. Mineral trioxide aggregate (MTA) is a cement material based on calcium silicates (CSC). It sets by hydration, provides excellent sealing ability, is biocompatible/bioactive and has performed successfully in different clinical applications. The use of MTA as an orthograde obturation material has been proposed. However, MTA is difficult to handle and very little is known about the most appropriate technique to ensure good compaction within the shaped root canal. This research aims to investigate the performance of MTA when used as an orthograde obturation material. The effect of different times of ultrasonic activation of unset material on the incidence of voids in root canals was investigated. Manual compaction of MTA using hand pluggers without ultrasonic activation resulted in minimal void formation. Ultrasonic activation resulted in significantly higher incidence of voids. The removal of the smear layer prior to obturation with MTA resulted in a significantly reduced push-out bond strength between the MTA and radicular dentine. The apical sealing ability of MTA orthograde filling was assessed in comparison with gutta percha and sealer using a dye leakage model. It was concluded that MTA provides a better apical seal against dye penetration over a 30-day observation period. The ability of MTA to reinforce the remaining root structure in comparison with gutta percha and sealer was investigated. MTA significantly increased the resistance to vertical root fracture after one month of storage in synthetic tissue fluid. The radiopacity of MTA together with new calcium silicate cements was assessed and it was concluded that MTA was more radiopaque than gutta percha but less radiopaque than AH-plus sealer. The use of MTA as an orthograde obturation material has shown some potential of enhanced clinical performance in comparison with gutta percha and sealer in terms of sealing ability and bioactivity. However, there are certain disadvantages for obturation with this category of materials in its present form. It is important to point out that MTA is still in its early stages of development. With further improvements to its physical properties, MTA can present a valuable option for obturation of the root canal space.

O presente trabalho contempla um estudo experimental de análise do comportamento de concretos projetados por via seca, através de ensaios indicadores dos principais parâmetros de durabilidade, constantes de especificações nacionais e internacionais. A pesquisa envolve a avaliação comparativa entre quatro tipos de cimento especialmente formulados para uso em concreto projetado, em relação a outros dois tipos de cimento tradicionalmente empregados na composição de misturas projetáveis, no que se refere ao atendimento aos requisitos relativos à durabilidade, normalmente especificados para o material. Os concretos projetados, elaborados com consumos de cimento de 300 kg/m³, 350 kg/m³, 400 kg/m³ e 450kg/m³ foram inicialmente caracterizados, no estado fresco, com base em ensaios de consistência e depois produzidas amostras, em condições similares às de obra e estas submetidas aos ensaios balizadores de parâmetros de durabilidade adotados neste estudo, a saber: Absorção por Imersão e Fervura, Índice de Vazios, Massa Específica Real; Absorção de Água por Capilaridade; Migração de Íons Cloreto; Resistividade Elétrica; Penetração de Água sob Pressão e Carbonatação Acelerada. Como alguns dos ensaios supracitados não são destrutivos, foi possível aproveitar corpos-de-prova, que foram depois submetidos a ensaios de resistência à compressão axial e à tração através da compressão diametral, que também contribuíram para caracterização do material. De um modo geral, os resultados foram satisfatórios e atenderam às especificações vigentes. Contudo, os concretos elaborados com cimentos especiais, formulados com granulometria mais fina e adição de metacaulim, apresentaram indicadores de durabilidade consideravelmente superiores aos dos concretos elaborados com cimentos convencionais ou mesmo cimentos especiais formulados com aditivos, inclusive para consumos relativamente baixos. Apesar de não ter sido o foco principal deste trabalho, vale ressaltar os surpreendentes resultados dos ensaios de resistência mecânica, obtidos para os concretos elaborados com cimentos especiais formulados com granulometria mais fina e adição de metacaulim, que atingiram valores de resistência à compressão nunca antes observados, fato que pode tornar o material bastante promissor. / The present work involves an experimental study with dry-mix shotcrete aiming at the behavior analysis, through indicative testing of the main durability parameters of national and international specifications. The research involves the use of four cement types especially formulated for use in shotcrete use in comparison with two other cements that are traditionally used in mix production for shotcrete spraying. The shotcrete mixtures were elaborated with cement consumptions of 300 kg/m³, 350 kg/m³, 400 kg/m³ and 450kg/m³. They were characterized initially, in the fresh state, in terms of stiffness tests, and later, cores were extracted to produce samples, in similar conditions and submitted to ordinary durability tests: Water Absorption, Volume of Voids, Specific Weight; Water Absorption by Capillarity; Chloride Migration; Electric Resistivity; Water Penetration under Pressure and Accelerated Carbonatation. As some of the tests are not destructive, some of the samples was used for compressive and tensile (Brazilian Test) strength determination, what also contributed to additional characterization of the material. In general, the results were very satisfactory and they fit to the specifications requirements. However, the shotcretes elaborated with special cements, formulated with finer gradation and metakaolin addition, presented a much better behavior in terms of durability indicators comparing to the shotcretes produced with conventional cements and cements formulated with accelerators, even when, relatively low consumption of cement was used. Despite not being the main focus of this work, it is worth mentioning the surprising results of the testing of mechanical resistance, obtained for the shotcretes elaborated with special cements formulated with finer gradation and metakaolin addition, which reached resistance values to the compression never observed, making it a promising material.

With the pressure on the construction industry to lower CO2 emissions it has become increasingly important to utilise materials that supplement Portland cement (CEM I) in concrete. These include additions such as ground granulated blast-furnace slag (GGBS) and fly ash, which have found greater use due to the benefits they provide to many properties of the material (in addition to environmental impact). While studies have investigated these materials in binary blends with CEM I, little work has examined the effect of combining materials in ternary blend concretes. A wide-ranging study was, therefore, set up to examine this for the range of more commonly available additions. This thesis reports on research carried out to investigate the effects of cement combinations based on CEM I / GGBS with either fly ash or limestone. The experimental programme investigated these materials in both paste and concrete and covered fresh properties, compressive strength, permeation and durability properties (using standard water curing for the latter three) and considered, for the hardened properties, how these may be balanced with environmental cost. The mixes covered a range of w/c ratios (0.35. 0.50 and 0.65), which was the main basis of comparison, and combinations of CEM I with GGBS (at levels of 35%, 55% and 75%), and fly ash and LS part-replacing this (at levels of 10 to 20 % and 10 to 35% respectively), after consideration of the relevant standards and related research. The initial phase of the study examined the characteristics of the materials, which indicated that they conformed to appropriate standards and were typical of those used in the application. Studies with cement paste (0.35 and 0.50 w/c ratio) indicated that there were reductions in water demand with the use of addition materials (binary and ternary) compared to CEM I. The setting times of the cement pastes were also affected, generally increasing with GGBS level for the binary mixes, although the effect was influenced by w/c ratio. Whilst fly ash and limestone delayed setting at the higher w/c ratio, the opposite occurred as this reduced, compared to the binary mixes. It was also found that the yield stress increased with GGBS level and further with the addition of ternary materials (particularly limestone) compared to CEM I. The superplastiser (SP) dosage requirement in concrete was found to decrease with increasing w/c ratio, and ternary additions reduced this compared to binary and CEM I concrete with the effect most noticeable at low w/c ratio. Early strength development was less than CEM I for binary concretes and differences increased with GGBS level. Improvements with the introduction of fly ash compared to the binary concretes were noted with increasing GGBS levels and w/c ratio. In general, the addition of LS gave reduced early strength for all concretes. Although at the 35% GGBS level binary concretes achieved similar strength to those of CEM I, the others generally gave reductions at all ages to 180 days, with differences increasing with GGBS level. However, with increasing w/c ratio and GGBS level improved strength development of ternary concretes, was noted compared to those of CEM I from 28 days. Permeation (absorption (initial surface absorption and sorptivity) and permeability (water penetration and air permeability)) and durability properties (accelerated carbonation and chloride ingress) of the test concrete were also investigated. At 28 days, for low GGBS levels, the binary concretes gave reduced absorption properties compared to CEM I, while the reverse occurred at high level. The effect of the ternary concretes gave further improvements at the lower GGBS levels and with increasing w/c ratio and curing time compared to CEM I. At the higher GGBS level the effect of the ternary additions was less noticeable but, in the case of limestone, improvements were still seen with increasing w/c ratio compared to CEM I. Similar effects were noted for the sorptivity results. The air permeability results gave higher values at 28 days for the binary and ternary concretes compared to CEM I, but significant improvements in the long-term at the lower GGBS level across the range of w/c ratios compared to CEM I concrete. Similar trends were found with water penetration tests. Accelerated carbonation increased with GGBS level for binary concretes compared to CEM I. These differences increased further with the introduction of fly ash and LS, particularly the former. In contrast rapid chloride tests indicated improvements with increasing GGBS levels compared to CEM I and further benefits with the inclusion of fly ash and limestone. Embodied CO2 (ECO2) was calculated based on published British Cement Association (BCA) values for each component of the mix and was shown to reduce with increasing w/c ratio and addition level in concrete. For concrete of an equal strength of 40N/mm2 the ECO2 could be almost halved (reduced from 343 kg/m3 for the CEM I to 176 kg/m3) for the ternary concretes at higher GGBS levels. These combination concretes also gave enhanced durability with regard to chloride ingress and at the lower w/c ratio comparable properties to CEM I in the case of carbonation. Overall, the results suggest that there is potential for ternary concretes to be used in the concrete industry given their ability to reduce ECO2, without compromising strength, permeation and durability properties of concrete.

A pesquisa aborda os métodos ASTM C 1152 e ASTM C 114, para determinação de cloretos em concreto. Os ensaios foram realizados em dois laboratórios, o da Escola Politécnica da USP, em São Paulo e o da Universidade de Pernambuco, em Recife. Foram preparados concretos com 5 tipos de cimento Portland. O estudo teve como objetivo fazer um levantamento de trabalhos publicados sobre métodos de determinação de cloretos total e solúvel, em concretos, especificamente, discutir a influência do tipo de cimento no teor de cloreto combinado e livre, em amostras de concreto. Foi também objetivo, determinar como se distribui o íon cloreto, solúvel e combinado ao longo da altura de corpos-de-prova de 10x20 cm de diâmetro e apresentar sugestões ao método proposto visando a sua normalização. Paralelamente foram realizados análises químicas e físicas dos cimentos, pela ABCP. O método proposto apresentou boa reprodutibilidade entre os dois laboratórios, através dos cálculos estatísticos, confirmando sua atualidade e, adequação para outros laboratórios. É importante no entanto dizer que este método é demorado, exige dedicação, equipamentos sensíveis e a resposta é lenta. Os cálculos encontram-se informatizados através de planilha interativa de cálculos, facilitando a sua aplicação. A metodologia pareceu adequada para elaboração de norma técnica nacional. / The aim of this research was the application of ASTM method for determination of chlorides in concrete. The tests were made by two laboratories, the EPUSP in São Paulo and POLI in Recife, on concretes prepared with five types of Portland cement. The purpose of this study was to make a survey of published works about the methods of determination of total and soluble chlorides in Portland cement concrete, to discuss the influence of each kind of cement on chlorides, combined and free, in samples of concrete. The purpose was too, determine how the free and linked chlorides are distributed through the height of the specimens of 10x20 diameter and to present suggestions to the standardization of this method. The method presented good results among the two laboratories, the statistical tests demonstrating the method\'s actuality and, adequate to anothers laboratories. It is important to say that this method is slow, needs dedication and specific facilities. The mix-proportion calculations from chemical analysis were made with a spreadsheet software. The methodology seemed to be adequated for the elaboration of a National Standard.

The use of plastic concrete for cutoff walls in dams for remediation of seepage issues has become more widely used in the past 25 years, however, the in-situ material properties are still not well understood. The research presents a new testing procedure that combines two existing testing methods, triaxial shear and permeability testing. By developing this laboratory testing method, material properties of the cutoff wall backfill material can be more accurately examined and explained using changes in the permeability of the material to discern the ductility and stiffness.

>Magister Scientiae - MSc / Introduction: Together with bonding to both enamel and dentine, an ideal restorative material would display physical properties similar to that of natural tooth tissue and would not be prone to degradation as a result of the oral environment. This includes changes in colour. Glass ionomer technology has undergone many changes to its original chemistry since it was developed in the early 1970’s. In 1988 resin-modified glass ionomers were introduced and in 2008, nano-ionomers were introduced. As a result of the progression in material sciences and the use of more sophisticated techniques and methods in restorative dentistry, it is possible to accomplish much improved aesthetics and functional durability of a restoration, both anteriorly and posteriorly. However, for as long as aesthetic restorations have been available, and in spite of advances in material structure and performance, one of the greatest challenges facing clinicians still remains that aesthetic restorations have to be replaced relatively frequently as staining and discolouration is a common problem. Aim of the study: The aim of this study was to determine the stainability of four resin-modified glass ionomers and one glass ionomer cement when exposed to a staining broth. Objectives: To record any change in colour before and after exposing the sample with the staining broth using a spectrophotometer, to compare the stainability, to examine the depth of staining using a light microscope and to observe the particle size of the powder and the surface texture using Scanning Electron Microscopy of the four resin- modified glass ionomer cements and one glass ionomer cement. Materials and Methods: Four resin-modified glass ionomers (one nano-ionomer) and one glass ionomer (zinc-reinforced ionomer) were selected. All were shade A2, except for Vitremer™ which was not available in A2. 15 discs of each material were prepared. The discs were 15 mm in diameter and 2 mm in thickness. All the materials were handled and cured according to the manufacturers’ instructions. After curing, only one side of each disc was polished using Sof-Lex™ discs (3M ESPE, USA). The unpolished side of each disc was designated as a matrix finish. The specimens were all immersed in distilled water at 37 °C for one week. They were then immersed in a staining broth for a period of one week and readings were taken after a period of 2 hours, 4 hours, 8 hours, 24 hours and one week. Colour was read on each side of each disc at the indicated intervals with a spectrophotometer. The colour difference was calculated using the CIELAB colour co-ordinates. Sample discs were then sectioned to determine the depth of staining. An additional sample disc of each material was made for observation with the SEM and was therefore not stained. Also, an unmixed sample of each material was prepared for examination with the SEM. Results: In general, for all materials there was an increase in staining when assessed with the colour difference between the baseline colour and the 7 day reading. Ketac™ N100, showed the highest total colour change of 43.84 for the unpolished surface followed by Riva™ which showed the total colour change of 28.55 for the unpolished surface. This was similar to Fuji II LC® which had a total colour change of 28.16 for the unpolished surface. For Vitremer™, the total colour change increased to 18.07 for the unpolished surface. For the unpolished surfaces, ChemFil™ Rock showed the least colour difference from baseline to 7 days (ΔE*ab = 10.45), followed by Vitremer™ (ΔE*ab = 18.07). Both Fuji II LC® and Riva™ Light Cure showed similar colour change from baseline to 7 days for unpolished surfaces (ΔE*ab of 28.16 and 28.55 respectively). Ketac™ N100 showed the highest staining after 7 days in the staining broth with a colour difference of 43.84. For the polished surfaces, the colour change for Fuji II LC® was 25.72 which was similar to Riva™ Light Cure which was 22.44 and Ketac™ N100 which showed a colour change of 22.79 on the polished surface. ChemFil™ Rock showed the least colour change of 17.69 for the polished surface followed by Vitremer™ which showed a colour change of 23.63 for the polished surface. Thus, for both the unpolished and polished surfaces there was a similar staining pattern. Conclusion: In this study it was demonstrated that all products evaluated in this study showed some degree of staining when exposed to a staining broth when evaluated using the ΔE*ab CIELAB colour evaluation. Ketac™ N100 showed the highest colour change compared to the other materials, but the reason for this was not explored. Both Vitremer™ and ChemFil™ Rock showed similar patterns of staining. / 2020-09-01

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