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The microstructure and performance of calcium sulfoaluminate (CSA) cements are described. CSA cements contain C₄A<sub>3S, 4CaO.3Al₂O₃.SO₃,and are interground with gypsum/anhydrite. They have been used structurally in China for more than 20 years and elsewhere as special cements in non-structural applications. Their long-term behaviour of depends on ettringite, a relatively fragile substance, and a novel matrix former compared with Portland cement. The mineralogy, evolution of hydrate and microstructure of CSA cement pastes and concretes were studied to relate hydration products and microstructure with performances. Samples taken from in-service structures in China, ranging from several to 25 years old, were investigated. Drying methods for cement pastes affect experimental results, especially for ettringite-based materials and are reported. Calorimetry, X-ray diffraction, microprobe and porosimetry are used to investigate early (<24 hours) and late hydration processes in different curing regimes. A "shrinking sphere" model is proposed to explain hydration processes. At early stages, mineralogy differs between inner and outer products: the former contain mainly AFm and C-S-H while the latter contains mainly ettringite and gibbsite. At 25°C, these differences persist but inner products densify the paste. At 55°C, and at 85°C, substantial siliceous hydrogarnet, forms after ~3 d. It is a major inner product. This results in a volume decrease and coarsening of pores. Long-term exposure to higher temperatures ~85°C is harmful. The impact of water:cement ratios on hydration mechanisms is reported. Depths of carbonation of CSA cement concrete are reported: results show similar resistance Portland cement concrete. Pipe immersed in seawater for 16 years shows that CSA cement has excellent resistance to seawater attack. The steel in the pipe is uncorroded even though chloride ions have penetrated the cover. Long-term exposure to high temperatures, 85°C, of CSA cement should be avoided but under normal in-service conditions its long-term behaviour is satisfactory.

Currently in the UK, composite blends of Portland cement (PC) and blastfurnace slag (up to 90%) are commonly used for the encapsulation of low and intermediate level wastes. The high volume replacement of PC is considered necessary in order to to reduce the high heat generation resulting from cement hydration in 500 litre waste packages. While suited to the majority of waste streams, the high pH environment in such systems (usually around 12.5 -13), will cause the corrosion of certain waste metals such as aluminium. Since aluminium is only passive between pH4 - 8.5, the use of an alternative low-pH cement system could serve to reduce/inhibit the corrosion. However, before such cements can be considered, two main research problems must be addressed, as follows: (1) quantitative evaluation of alternative cement systems based on their corrosion performance with aluminium; (2) high heat generation due to the rapid rate of hydration. The research in this thesis was thus divided into two strands, as follows: (1) The design and development of a novel, scientifically robust testing facility for the quantitative monitoring of aluminium corrosion in cement pastes; (2) the development of novel cement composites based on weakly alkaline calcium sulfoaluminate (CSA) cement for the encapsulation of aluminium from nuclear wastes. The output from this research is considered to be of interest to the UK nuclear industry.

Calcium sulfoaluminate (CSA) cement was used to cast a prestressed voided deck slab bridge girder. The rapid-set properties of CSA cement allowed the initial concrete strength to reach the required 4300 psi needed in order to cut the prestressing strands 6.5 hours after casting. Prestress losses were monitored long-term using vibrating wire strain gages cast into the concrete at the level of the prestressing strands and the data was compared to the American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO LRFD) predictions for prestress losses. AASHTO methods for prestress loss calculation were overestimated compared to the vibrating wire strain gage data. Material testing was performed to quantify material properties including compressive strength, tensile strength, static and dynamic elastic modulus, creep, and drying and autogenous shrinkage. The material testing results were compared to AASHTO predictions for creep and shrinkage losses. The bridge girder was tested at midspan and a distance 1.25 times the depth of the beam from the face of the support until failure. Midspan testing consisted of a crack reopening test to solve for the effective prestress in the girder and a test until failure. The crack reopen effective prestress was compared to the AASHTO prediction and AASHTO appeared to be effective in predicting losses based on the crack reopen data. The midspan failure was a shear failure, as accurately predicted by AASHTO. The 1.25d test resulted in a bond failure, which was accurately predicted by the AASHTO bond model for prestressed concrete. Funding for this project was provided by The Mountain Plains Consortium.

Since the energy crisis in 1970’s, research on low energy cements with low CO2-emissions has been increasing. Numerous solutions have been investigated, and the goal of this original research is to create a viable hybrid cement with the components of both Ordinary Portland cement (OPC) and calcium sulfoaluminate cement (CSAC), by forming a material that contains both alite and calcium sulfoaluminate clinker phases. Furthermore, this research focuses on keeping the cost of this material reasonable by reducing aluminum requirements through its substitution with iron. The aim of this work would produce a cement that can use large amounts of red mud, which is a plentiful waste material, in place of bauxite known as an expensive raw material. Modified Bogue equations were established and tested to formulate this novel cement with different amounts of ferrite, from 5% to 45% by weight. This was followed by the production of cement from reagent chemicals, and from industrial by-products as feedstocks (fly ash, red mud and slag). Hydration processes, as well as the mechanical properties, of these clinker compositions were studied, along with the addition of gypsum and the impact of a ferric iron complexing additive triisopropanolamine (TIPA). To summarize this research, the influence of the addition of 5-45% by weight of ferrite phase, was examined with the goal of introducing as much red mud as possible in the process without negatively attenuate the cement properties. Based on this PhD dissertation, the production of high-iron alite-calcium sulfoaluminate-ferrite cements was proven possible from the two sources of raw materials. The hydration processes and the mechanical properties seemed negatively affected by the addition of ferrite, as this phase was not hydrated entirely, even after 6 months of curing. The usage of TIPA counteracted this decline in strength by improving the ferrite hydration and increasing the optimum amount of gypsum required in each composition. The mechanical data were equivalent to OPC strengths for some compositions with 25% ferrite. This preliminary work constitutes the first research phase of this novel cement and requires additional research for its improvement. Topics for additional research are identified in this dissertation.

One of the benefits of calcium sulfoaluminate (CSA) cements is that these materials gain strength rapidly, where strength development is often measured in hours instead of days. This property makes these materials desirable for use in temporary, non-reinforced repairs of roadways, airfields, and navigable locks. The rapid repair of these infrastructure elements is critical to transporting supplies into regions devastated by disaster. In these austere environments, potable water may not be available in sufficient quantities to make vital repairs, and the use of impure water in the production of CSA cement-based concrete would be advantageous. However, the hydration products formed by CSA cement are substantially different from those formed by portland cement and may react differently to impurities that water sources may contain. This Thesis investigates the impact of various salts and impure water sources on the early-age strength development of commercially-available CSA cement-based concrete.

Les mélanges de ciment sulfoalumineux et de ciment Portland sont des liants hydrauliques innovants permettant de moduler les propriétés des bétons, telles que la vitesse de montée en résistance ou la stabilité dimensionnelle. Les performances du liant peuvent ainsi être ajustées pour de nombreuses applications. Au-delà de cet avantage, les émissions de dioxyde de carbone liées à la production du ciment sulfoalumineux sont significativement réduites comparées à celles du ciment Portland traditionnellement utilisé. La diversité des propriétés de ces liants résulte de la variété des mélanges pouvant être réalisés à partir des deux constituants de base. Chaque mélange présente alors une cinétique d'hydratation et des propriétés qui lui sont propres. Par exemple, certains liants sont expansifs mais présentent une montée en résistance progressive, tandis que d'autres sont stables dimensionnellement alors que leur résistance stagne après quelques jours d'hydratation. L'identification et le contrôle des paramètres à l'origine de ces comportements sont donc nécessaires pour garantir des propriétés spécifiques à un usage donné : chape, mortier de réparation, élément préfabriqué, etc. C'est l'objectif de cette étude qui s'attache à déterminer la cinétique, la minéralogie et les propriétés associées à l'hydratation de trois mélanges contenant 85 %, 70 % et 40 % de ciment Portland. Les essais entrepris ont aussi permis d'aboutir à une modélisation thermodynamique des mécanismes d'hydratation. L'impact de la composition du ciment Portland est également étudié. Enfin, il est montré que l'anhydrite et la chaux sont deux leviers qui modifient radicalement le processus d'hydratation et permettent ainsi d'adapter les propriétés d'un mélange aux exigences de son utilisation / Blends of ordinary Portland cement and sulfoaluminate cement are innovative hydraulic binders allowing control of concrete properties such as hardening speed or dimensional stability for specific applications. Moreover, carbon dioxide emissions linked to sulfoaluminate cement are significantly reduced compared to ordinary Portland cement. The binder properties can be adjusted due to the diversity of blends conceivable with these two constituents. Each blend has its own hydration kinetic and properties. For example, some blends are expansive and the hardening is progressive whereas other mixtures are dimensionally stable but their strength stagnates after few days. Identification and control of the parameters responsible of these comportments are necessary in order to guaranty specific properties for each application: screed, repairing mortar, etc. This is the aim of this study which described the hydration kinetic, the properties and composition of three blends containing 85 %, 70 % and 40 % of Portland cement. These experiments are completed by thermodynamic modeling of the hydration mechanisms. The effect of the Portland cement composition has also been tested. Finally, it's shown that anhydrite and calcium hydroxide are two key parameters which modify radically the hydration process and allow the properties adjustment required for the blend used

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.

Embora o uso do cimento Portland com altos teores da fase alita [silicato tricálcico - C3S – (CaO)3.(SiO2)] seja difundido mundialmente, argumentos ambientais indicam a fabricação de cimentos com baixos teores desta fase e altos teores da fase belita [silicato dicálcico - C2S, (CaO)2.(SiO2)] justamente ao contrário do que é produzido atualmente. A alita tendo mais cálcio que a belita, libera mais CO2 para a atmosfera quando ocorre a decomposição do calcário (CaCO3 CaO + CO2 ) durante sua fabricação. Além disso, o C2S é formado a uma temperatura mais baixa (800 a 900ºC) que a temperatura em que o C3S (1350 a 1450ºC) é formado, necessitando desta forma, menos combustível e produzindo um cimento de moagem mais facilitada, tornando-o mais eco-eficiente. Um aspecto negativo dos cimentos belíticos é que os mesmos atingem seu nível máximo de resistência em idades mais avançadas, e este comportamento não é considerado adequado na indústria da construção civil atual, que busca alta produtividade em um curto espaço de tempo. Uma maneira de eliminar este problema seria acelerando as reações iniciais de hidratação e endurecimento. Uma alternativa à esta questão é combinar estes clínqueres belíticos com agentes expansivos de base sulfoaluminato ou em uma produção simultânea no clínquer, tais como os sulfoaluminato de cálcio belítico (CSAB), sendo estes ligantes considerados de baixo impacto ambiental. No entanto, o cimento CSAB requer uma maior quantidade de alumina, que geralmente é provinda da bauxita na sua fabricação. Devido ao elevado custo da bauxita para a produção deste cimento, a utilização de resíduos ricos em alumina é uma opção que pode agregar valor ao resíduo e aumentar a disponibilidade de ligantes de reduzido impacto ambiental. Desta forma, este trabalho apresenta uma alternativa para utilização do resíduo na produção do cimento CSAB. Foi realizada a caracterização físico-química do resíduo estudado, e são apresentados os resultados da produção de clínqueres CSAB formados a partir de três misturas, com variações no teor deste resíduo. As propriedades físico-mecânicas destes clínqueres foram avaliadas e comparadas com um clínquer referência e um cimento Portland comercial, da mesma forma, técnicas de difração de raio X, calorimetria e termogravimetria foram utilizadas para verificar a formação dos produtos de hidratação de pastas. Desta maneira, foi demonstrado que o aproveitamento do resíduo de anodização do alumínio para a produção do cimento CSAB é viável tecnicamente. O produto gerado possui características especiais, apresentando elevado desenvolvimento da resistência mecânica nas primeiras horas de hidratação. / Although currently Portland cement with high alite [(CaO)3.(SiO2)] content is the most used globally, environmental advices call for changes on the production for cements with lower alite and higher belite [(CaO)2.(SiO2)] contents. Alite, having more calcium than belite, releases more CO2 to the atmosphere in the course of cement manufacture, due to limestone decomposition (CaCO3 CaO + CO2 ). Besides, belite is formed at lower temperatures (800- 900ºC) than alite (1350-1450ºC), and for this reason less fuel is necessary for the process. Additionally, clinker is easier to grind, resulting in a less energy demanding and more sustainable process. However, belite cements reach the maximum strength level at later ages, drawing back the fast and active civil construction industry, which aims high productivity in a short time spam. In order to minimize this problem it is possible to accelerate the initial hydration reactions and hardening by combining the belite clinkers with expansive sulfoaluminate base agents, or in a simultaneous clinker production, such as calcium sulfoaluminate belite cements (CSAB). These binders have lower environmental impact. However, CSAB cement requires a higher amount of alumina, which comes from bauxite. As this material is costly, the use of alumina-rich residues comes as an option to aggregate value to the residue and to increase the availability of low environmental impact binders. This work presents an alternative use for alumina-rich residues in CSAB cement production. Physicochemical characterization of the aluminium anodizing sludge is presented together with results of the production of CSAB clinkers from 3 mixtures, with different residue content. Properties of the produced clinkers were evaluated and compared to a control clinker and to an ordinary Portland cement. X-ray diffraction, calorimetry and thermogravimetry analysis track the formation of hydration products in the cement pastes. The use of aluminium anodizing sludge to produce CSAB cement was proved to be technically viable, as the generated product has special characteristics, presenting high mechanical strength development at the first hours of hydration.

Embora o uso do cimento Portland com altos teores da fase alita [silicato tricálcico - C3S – (CaO)3.(SiO2)] seja difundido mundialmente, argumentos ambientais indicam a fabricação de cimentos com baixos teores desta fase e altos teores da fase belita [silicato dicálcico - C2S, (CaO)2.(SiO2)] justamente ao contrário do que é produzido atualmente. A alita tendo mais cálcio que a belita, libera mais CO2 para a atmosfera quando ocorre a decomposição do calcário (CaCO3 CaO + CO2 ) durante sua fabricação. Além disso, o C2S é formado a uma temperatura mais baixa (800 a 900ºC) que a temperatura em que o C3S (1350 a 1450ºC) é formado, necessitando desta forma, menos combustível e produzindo um cimento de moagem mais facilitada, tornando-o mais eco-eficiente. Um aspecto negativo dos cimentos belíticos é que os mesmos atingem seu nível máximo de resistência em idades mais avançadas, e este comportamento não é considerado adequado na indústria da construção civil atual, que busca alta produtividade em um curto espaço de tempo. Uma maneira de eliminar este problema seria acelerando as reações iniciais de hidratação e endurecimento. Uma alternativa à esta questão é combinar estes clínqueres belíticos com agentes expansivos de base sulfoaluminato ou em uma produção simultânea no clínquer, tais como os sulfoaluminato de cálcio belítico (CSAB), sendo estes ligantes considerados de baixo impacto ambiental. No entanto, o cimento CSAB requer uma maior quantidade de alumina, que geralmente é provinda da bauxita na sua fabricação. Devido ao elevado custo da bauxita para a produção deste cimento, a utilização de resíduos ricos em alumina é uma opção que pode agregar valor ao resíduo e aumentar a disponibilidade de ligantes de reduzido impacto ambiental. Desta forma, este trabalho apresenta uma alternativa para utilização do resíduo na produção do cimento CSAB. Foi realizada a caracterização físico-química do resíduo estudado, e são apresentados os resultados da produção de clínqueres CSAB formados a partir de três misturas, com variações no teor deste resíduo. As propriedades físico-mecânicas destes clínqueres foram avaliadas e comparadas com um clínquer referência e um cimento Portland comercial, da mesma forma, técnicas de difração de raio X, calorimetria e termogravimetria foram utilizadas para verificar a formação dos produtos de hidratação de pastas. Desta maneira, foi demonstrado que o aproveitamento do resíduo de anodização do alumínio para a produção do cimento CSAB é viável tecnicamente. O produto gerado possui características especiais, apresentando elevado desenvolvimento da resistência mecânica nas primeiras horas de hidratação. / Although currently Portland cement with high alite [(CaO)3.(SiO2)] content is the most used globally, environmental advices call for changes on the production for cements with lower alite and higher belite [(CaO)2.(SiO2)] contents. Alite, having more calcium than belite, releases more CO2 to the atmosphere in the course of cement manufacture, due to limestone decomposition (CaCO3 CaO + CO2 ). Besides, belite is formed at lower temperatures (800- 900ºC) than alite (1350-1450ºC), and for this reason less fuel is necessary for the process. Additionally, clinker is easier to grind, resulting in a less energy demanding and more sustainable process. However, belite cements reach the maximum strength level at later ages, drawing back the fast and active civil construction industry, which aims high productivity in a short time spam. In order to minimize this problem it is possible to accelerate the initial hydration reactions and hardening by combining the belite clinkers with expansive sulfoaluminate base agents, or in a simultaneous clinker production, such as calcium sulfoaluminate belite cements (CSAB). These binders have lower environmental impact. However, CSAB cement requires a higher amount of alumina, which comes from bauxite. As this material is costly, the use of alumina-rich residues comes as an option to aggregate value to the residue and to increase the availability of low environmental impact binders. This work presents an alternative use for alumina-rich residues in CSAB cement production. Physicochemical characterization of the aluminium anodizing sludge is presented together with results of the production of CSAB clinkers from 3 mixtures, with different residue content. Properties of the produced clinkers were evaluated and compared to a control clinker and to an ordinary Portland cement. X-ray diffraction, calorimetry and thermogravimetry analysis track the formation of hydration products in the cement pastes. The use of aluminium anodizing sludge to produce CSAB cement was proved to be technically viable, as the generated product has special characteristics, presenting high mechanical strength development at the first hours of hydration.