Dissertations / Theses on the topic 'Carbonation'

Iron and steel production is a rapidly growing industry with global outputs increasing 65% over the last ten years (World Steel Association, 2012). Unfortunately, it is also the largest industrial source of atmospheric CO2, accounting for a quarter of the CO2 emissions from industrial sources (International Energy Agency (IEA), 2007).Mineral carbonation provides a robust method for permanent sequestration of CO2 that is environmentally inert. Larnite (Ca2SiO4), the major constituent of steel slag, reacts readily with aqueous CO2 (Santos et al., 2009). Consequently, its carbonation offers an important opportunity to reduce CO2 emissions at source. A potential added benefit is that this treatment may render steel slag suitable for recycling. This study investigates the impact of temperature, fluid flux and reaction gradient on the dissolution and carbonation of steel slag, and is part of a larger study designed to determine the conditions under which conversion of larnite, and other calcium silicates, to calcite is optimized. Experiments were conducted on 2 – 3 mm diameter steel slag grains supplied by Tata Steel RD&T. A CO2-H2O mixture was pumped through a steel flow-through reactor containing these grains. For a given experiment, temperature was fixed at a value between 120°C and 200°C, pressure was 250 bar, and the fluid flux was fixed at 0.8 mL/cm2min or 6 mL/cm2min. Reactions were also carried out in a batch reactor at 180°C and 250 bar, corresponding to a condition of zero flux. The duration of experiments ranged from 3 to 7 days. The CO2-H2O fluid reacted with the steel slag grains to form phosphorus-bearing Ca-carbonate phases. At high fluid flux, 6 mL/cm2min, these phases dissolved at the edges of slag grains, leaving behind a porous rind of aluminum and iron oxides. Increasing temperature increased the rate of this reaction. At low fluid flux, 0.8 mL/cm2min, the extent of carbonation was increased. At the edge of grains, instead of being transformed to porous rinds, primary Ca minerals were replaced by phosphorus-bearing Ca-carbonate phases. As a result of the greater length of reactor used in these experiments, a reaction gradient was observed along which the fluid remained supersaturated with respect to the calcium carbonate, coating the surfaces of the slag grains. Steel slag exposed to the CO2-H2O fluid in the batch reactor was less carbonated; incongruent dissolution of the slag followed by surface coating of the grains by calcium carbonate inhibited further interaction of the slag with the fluid, limiting the extent of possible carbonation.The results of this study show that carbonation of steel slag by aqueous CO2 is feasible using relatively large grains, and that it can be optimised by varying fluid flux. Experiments of the type described above will contribute to the eventual global reduction of industrial CO2 emissions.
L'industrie du fer et de l'acier est en pleine croissance et sa production mondiale a augmenté de 65% au cours des dix dernières années (World Steel Association, 2012). Malheureusement, elle est également responsable d'un quart des émissions industrielles de CO2 ce qui en fait la plus importante source industrielle de CO2 atmosphérique (International Energy Agency (IEA), 2007).La carbonatation minérale fournit une méthode robuste pour la séquestration permanente du CO2 sous une forme écologiquement inerte. La larnite (Ca2SiO4), constituant principal des scories d'acier, réagit aisément avec le CO2 aqueux (Santos et al., 2009). Par conséquent, sa carbonatation offre une importante occasion de réduire à la source les émissions de CO2. Un avantage potentiel supplémentaire de ce traitement est de rendre les scories d'acier convenables pour le recyclage. Cette étude examine l'impact de la température, le flux molaire surfacique du fluide carbonaté, et d'un gradient de réaction sur la dissolution et la carbonatation des scories d'acier. Elle s'inscrit dans une étude plus large visant à déterminer les conditions optimisant la conversion de la larnite, et d'autres silicates de calcium, à la calcite.Des expériences ont été menées sur des grains de scories d'acier d'un diamètre de 2 à 3 mm fournis par Tata Steel RD&T. Un mélange de CO2-H2O a été pompé à travers un réacteur continu contenant ces grains et maintenu à une température entre 120°C et 200°C, une pression de 250 bar et à des flux molaires surfaciques de 0.8 à 6 mmol/cm2min. Chaque expérience a duré de 3 à 7 jours. Le fluide CO2-H2O a réagi avec les grains de scories d'acier et a formé des minéraux de carbonate de calcium contenant du phosphore. À flux molaire surfacique élevé, soit 6 mL/cm2min, ces phases sont dissoutes aux bords des grains, laissant place à une bordure poreuse d'oxydes d'aluminum et de fer. Une augmentation de la température a augmenté la vitesse de cette réaction. A valeur intermédaire de flux molaire surfacique, 0.8 mL/cm2min, le degré de carbonatation a augmenté. Au lieu laisser des bordures poreuses d'oxydes, les minéraux de calcium primaires en marge des grains ont plutôt été remplacés par des phases de calcium carbonate contenant du phosphore. En plus, l'usage d'un réacteur plus long a créé un gradient de réaction et maintenu la supersaturation du fluide relative au carbonate de calcium qui a enrobé les grains. Les scories d'acier exposées au fluide dans un réacteur discontinu (sans flux de fluide) ont été moins carbonatées; la dissolution non-congruente de la scorie a pris place suivie par l'enrobage des grains de scories par le carbonate, et ce dernier a réduit la surface de réaction de la scorie avec le fluide.Les résultats de cette étude démontrent que la carbonatation par le CO2 aqueux des scories d'acier à granulométrie relativement grossière est possible et qu'elle peut être optimisée en variant le flux molaire surfacique du fluide. Les expériences de ce type contribueront à la réduction éventuelle des émissions industrielles globales de CO2.

Accelerated carbonation involves exposing a material to a concentrated atmosphere of carbon dioxide, and can be used to treat hazardous wastes and soils and create new construction materials. The present work examines the use of accelerated carbonation to reduce the hazardous properties of wastes as a means of reducing the costs of disposal to landfill, and then develops the process to manufacture aggregate from the waste removing it from landfill disposal completely . A range of thermal wastes, including those from cement, metallurgical and paper processes, were found to be reactive with carbon dioxide. Many of these wastes are hazardous on account of their alkaline pH, which carbonation partially neutralizes, effectively allowing reclassification of the materials as stable non-reactive hazardous wastes under the Landfill Regulations. Cement and paper wastes were highly reactive with carbon dioxide, and were considered for use as cement substitutes to reconstitute non-reactive wastes into aggregate. Previous work had suggested that carbonation and pelletising were not compatible due to differing optimum conditions. This issue was investigated by considering the effects of the mix formulations and machinery parameters. The pelletising and carbonation processes require widely different moisture contents. The disparity is due to the need for total saturation of the material to form bonds between grains during pelletising, and an open pore network for carbon dioxide to penetrate. To achieve the two simultaneously, several methods were investigated. Chemical catalysts including sodium hypochlorite and sodium sulfite increased carbonation in a saturated material. However, curing the formed aggregates in carbon dioxide was found to be the most economic solution. A pilot scale process was developed based upon the laboratory results. A bespoke rotary carbonation reactor was developed to produce aggregate in bulk for commercial testing. Aggregate which was subjected to accelerated carbonation, has enhanced strength and durability compared to aggregate exposed to natural carbonation. The aggregate was successfully used to produce lightweight concrete with comparable strength to concrete made from commercial lightweight aggregate. Aggregate was also supplied for a research project to investigate the use of recycled materials as a horticultural growing medium.

Fluidized bed combustion (FBC) ash from the combustion of high-sulphur fuels with limestone addition can contain from 15 to 25% quick lime content. This excess calcium oxide gives the ash numerous undesirable properties such as strong exothermicity on wetting and high-pH leachate that must be treated before discharge. It also leads to the formation of ettringite with significant deleterious expansion in the landfill. In consequence, carbonation of FBC ash is desirable in order to reduce its alkalinity and improve its disposal characteristics. The current technique to reduce the exothermic character of the ash involves hydrating the ash in two stages, leading to the consumption of large quantities of water. Sonication along with simultaneous carbonation of the ash yields a product suitable for direct disposal in landfills with the minimum of water addition (to achieve the optimum proctor levels for maximum compaction of the ash in the landfill site). This work explores the use of sonochemical-enhanced carbonation of FBC ash. Tests have been conducted using four ashes, two of which differ in age only and are from the Nova Scotia Power 183 MWe CFBC (circulating fluidized bed combustor) boiler. The other two ashes are from the CFBC boilers at A/C power and Piney Creek, U.S.A. Tests with additives such as sodium chloride (at levels comparable with that in seawater) and seawater from Nova Scotia have also been carried out. Tests were carried out at low (20°, 40°C) and high (60°, 80°C) temperatures. Sonicated samples were also analyzed using TGA (Thermogravimetric analysis), TGA-FTIR (Thermogravimetric and Fourier transform infra red spectroscopy analysis) and XRD (X-ray diffraction) techniques to determine the influence of other calcium compounds (OCC). The size reduction brought about by sonication was quantified using wet sieving. The ash reactivity displays a strong temperature dependency with almost complete carbonation of the ashes being achieved in minutes at higher temperatures. Additives were found to increase the level of hydration of the ashes in line with previous work; however, carbonation levels were unaffected. TGA, TGA-FTIR and XRD analysis of the samples indicated that other calcium compounds (OCC) were also formed during hydration.

Solidification technology can be an effective process for treating a variety of difficult to manage waste materials containing heavy metals prior to reuse or disposal. There are numerous commercial solidification techniques spanning a spectrum of technical complexity and cost. The most common methods include those based on cement or cement/pozzolanic materials. These materials, which are used in many solidification processes, make the technology appear simple and inexpensive. However, there are significant challenges to the successful application of this technique. The morphology and chemistry of the solidified waste forms are complex, specially when the waste streams used contain components other than the metals that are likely to be effectively immobilised. Also, the selection of the binder, depends upon an understanding of the chemistry of both the contaminants and the binder itself, to ensure efficient and reliable results. Nevertheless,a number of complex interactions are known to cause significant retardation on normal hydraulic reactions of cement-based materials, causing numerous and controversial problems. In recent years there has been renewed interest in elucidating the binding mechanisms responsible for the fixation of waste species. Carbonation, which is known to affect a wide range of cementitious materials, is a phenomenon observed by many scientists and has received very little attention. The aim of this work has been to investigate the effects of natural and accelerated carbonation on the development of mechanical and microstructural properties of solidified products as well as on the binding of metallic waste components. Particular emphasis was paid to examine the influence of different binders on the properties of carbonated solidified waste forms. The kinetics of the carbonation reaction was thoroughly examined, particularly when mix parameters such as binder/waste type and water content were varied. An examination of the resulting products showed that carbonated solidified waste materials had improved mechanical properties and increased metal binding capacity, when compared to specimens cured in nitrogen or normal atmospheric conditions. Microstructural analysis showed that large amounts of calcite where characteristics of carbonated samples. The increased formation of calcite as a result of carbonation appeared to be directly linked with the development of strength and enhanced metals fixation. NMR and FTIR spectroscopy indicated that carbonation has a significant influence on the hydration of waste forms by increasing the degree of polymerisation of the silicate hydration phases, with a consequent acceleration of the hydration of the cement paste. Examination by SEM analysis confirmed an acceleration of C3S hydration, typified by a de-calcified hydration rims and a matrix of dense calcite intergrowth infilling porosity. Some metals appeared to be incorporated in the silica-rich rims and others in the calcite rich matrix, suggesting precipitation of metal as both carbonates, silicates and complex double-salts. An examination of the kinetic of the carbonation reaction revealed that the reactivity of the different cements was different in the presence of carbon dioxide, and that when metal wastes were added the susceptibility of the paste to react with carbon dioxide increased. In general the results of this work indicate the potential of carbon dioxide for incorporation into the treatment of wastes during solidification. However, further work is necessary to establish the long-term performance of these carbonated waste forms as well as the behaviour of carbon dioxide upon different waste streams.

Accelerated carbonation technology (ACT) could be used for the stabilisation of hazardous wastes, remediation of contaminated soils and re-use/recycling of various waste streams. ACT has also potential for storing anthropogenic CO2 emissions into mineral silicates and alkaline waste residues via mineral or waste carbonation. Compared to ocean and geological storage, mineral and waste carbonation offer several advantages such as long-term storage and low monitoring requirements. Currently, the biggest challenge of mineral carbonation is the low conversion rate of calcium and magnesium-based minerals into thermodynamically stable carbonates under ambient temperature and pressure. Also, literature offers little information about physical techniques or chemical substances that could enhance the efficacy of accelerated carbonation of alkaline wastes. In this study, various carbonation techniques were applied for increasing the carbonation reactivity of magnesium hydroxide. The experiments were conducted under low temperature and pressure, while the maximum reaction time was 24 hours. Under these conditions the associated costs are kept to a minimum. The possibility of producing monolithic products with value-added was investigated by using blended mixtures of magnesium and calcium hydroxide. These mixtures were cured in carbon dioxide for 7 and 28 days and their physical properties were measured and compared with the properties for normal and lightweight concrete. Moreover, several alkaline residues were carbonated with the aid of ultrasound and four candidate catalysts (acetic acid, ethanol, sodium hypochlorite and sodium nitrite) and their CO2 uptake was measured. During sonication the variables: ultrasonic frequency, water content and treatment time were examined, while the applied chemicals were added at three different molarities (0.1 M, 0.5M and 2.5M). Throughout this work a number of analytical techniques were used for the characterisation of the raw and carbonated materials. These techniques included XRay fluorescence, X-ray diffraction, wet laser analysis, total organic carbon analysis and scanning electron microscopy. The results showed that the CO2-reactivity of Mg(OH)2 was low due to thermodynamic constraints that inhibited the rapid diffusion of CO2 into the system. The mixtures composed of pure Mg showed improved compressive strength and bulk density. In addition, sonication at low water content was weak, as there was lack of enough water to facilitate cavitation. On the other hand, at high water content the achieved CO2 uptake of the products increased by up to four times, as the wet conditions enhanced the cavitation of the solid particles. Finally, it was found that ethanol and acetic acid promoted the hydration rate of CO2 during accelerated carbonation, while minerals phase analysis did not reveal the formation of toxic by-products. In conclusion, the findings of this study proved that sonication depends highly on water content and is favoured at wet conditions. Furthermore, acetic acid and ethanol are two chemicals with potential to ameliorate the accelerated carbonation of various industrial wastes without the formation of un-desired or toxic compounds.

Incineration can reduce the mass and volume of municipal waste significantly but produces solid waste in the form of bottom ash and air pollution control (APC) residues. Landfill is currently the most commonly used disposal option for these ash residues, however, the impact of hazardous compounds in these wastes on the environment during landfilling is becoming more widely appreciated and cheaper, alternative, management options need to be explored. In this research, the treatment of these municipal solid waste incinerator (MSWI) residues by accelerated carbonation is investigated and compared with naturally aged ashes. Both bottom ash and APC residues were carbonated in an atmosphere composed of gaseous CO2. It was found that the carbonation of calcium oxides/hydroxides resulted in the rapid formation of calcium carbonate and that silicate compounds were hydrated. The reduction of pH from 12-12.5 to 7-9 observed upon carbonation was associated with a reduction in availability of soluble salts and meals. Carbonated ash had a higher buffering capacity to acid attack when compared to the untreated, non-carbonated, ash. The bottom and APC ashes sequestrated between 6% and 13% CO2 (w/w dry weight), respectively upon carbonation; and this may be important where the reduction of greenhouse emissions to the atmosphere is concerned.

This PhD study aims to understand the carbonation mechanism of slag-rich waste forms and consequently benefits assessing the long term efficiency of immobilising waste materials with cementitious disposals. Three phases of experiments had been managed to achieve the aim. The first was an examination of three 20-year-old alkali-activated neat slag pastes. This section supplied the information about the immobilisation mechanism of alkaline metal cations within a cement system. The second was a characterisation of four 20-year-old water- activated slag-bearing pastes with curing at 40°C for the initial five years. This part concerned the effects of aging and heating treatment in cement hydration. The third was the accelerated and gentle testing of the water-activated pastes. The carbonation mechanism was mainly drawn by the micro-structural and nano- structural features of carbonated pastes and comparison to those of hydrated pastes. The obtained experimental data for the alkali-activated pastes confirmed the outstanding suitability of slag for fixing metal cations. It was because the formed C- S-H gel had been verified to be entirely tobermorite-based and possess a high substitution degree of bridging Si tetrahedra by Al tetrahedra. Meanwhile, the main fixation mechanism has been proved to be the incorporation of metal cations into the structure of the C-S-H through balancing the charges caused by the substitution. Thus, the significant incorporation of Ae+ within the structure of the C-S-H could be advantageous of immobilising alkaline cations through charge-balancing. The collapse of the C-S-H structure during carbonation has been observed due to not only decalcification, but also dealumination. Thus, according to the above findings, the carbonation is very likely to negatively affect the fixation of waste materials within cement systems. It was because, along with the extraction of the bridging Al tetrahedra, the charge-balancing cations were not needed and possibly would eventually be released. A conceptual model of carbonation occurring in hardened cement pastes has been proposed at the end of the chapter conclusion. More findings about the efficiency of different activators on hydration and the effects of curing temperature and aging on hydration have been discussed in details in the following chapters.

This research advances the current understanding of the carbonation reaction in porous materials by investigating pH changes during the hardening process of lime, the role of pore-water in the dissolution process of calcium hydroxide and the effects of pore size on precipitation of calcium carbonate solid phases. To achieve this, carbonation is studied within a thin film of an aqueous solution of calcium hydroxide, that simulates the conditions existing in porous media once most of the liquid water has evaporated. The research introduces novel approaches such as the use of specially manufactured micro-electrodes used to measure pH variations during the carbonation process. The effect of pore size on the solid phases precipitated by carbonation is investigated using a novel lime based material called nano-lime. Influence of pore-water on the hardening process of lime is studied in formulated lime using impedance spectroscopy: an electrochemical technique which is new in the study of lime based materials. Overall, results demonstrate that the micro-electrodes can operate reliably in very alkaline environments such as those produced by the dissolution of lime. Their potentiometric response, in fact, was found to be Nernstian up to pH 14. Furthermore, the electrode response proved to be sufficiently sensitive and reproducible to differentiate, on the basis of pH, between the formation of calcite and vaterite. It is likely that these micro-electrodes are currently the only analytical tools capable of monitoring high pHs in confined places and, for this reason, they can be considered highly valuable for the study of chemical processes involving very alkaline waters. The study on the role of pore-water in the hardening process of formulated lime has, instead, demonstrated the potential of impedance spectroscopy as a non-destructive technique for real time in situ monitoring of the reaction between lime and hydraulic additives.

The Durability Index (DI) approach has been developed in South Africa, in order to improve the durability performance of reinforced concrete structures. The DI approach is based on durability index tests, which are linked to transport mechanisms related to particular deterioration processes (Alexander et al., 1999a). Carbonation of concrete is governed, inter alia, by the microstructure and the transport characteristics of the concrete. A carbonation model with permeability coefficient (k) from the Oxygen Permeability Index (OPI) test as the key material variable was developed by Salvoldi (2010) using accelerated carbonation test data. The main aim of this research is to further develop the carbonation model by adopting the modelling framework of Salvoldi (2010) using natural carbonation data. For the experimental work, a total 48 different concrete mixes were produced by with different water: binder ratios (w/b), cement types, cement extender (addition) type and curing regime. The OPI test was conducted on all the concretes, and their corresponding permeability coefficients were determined. A set of 48 concrete specimens were exposed to five different sites for natural carbonation, and carbonation depths were measured periodically. Based on the modelling framework of Salvoldi (2010) and using the natural carbonation data between 150- 850 days, a model predicting the depth of natural carbonation was developed. However, in the case of concrete exposed to rain, drying/wetting is a major factor influencing the rate of carbonation. Therefore, the carbonation model was further modified taking into account the influence of drying/wetting cycles, by coupling it with a moisture model. For the development of the moisture model, the concrete specimens were exposed to a laboratory environment maintained at constant temperature and relative humidity (RH). The internal RH of the concrete specimens at varying depth was measured at different time intervals. Based on the measured RH data, the moisture model was also developed with ‘k' from the OPI test as the key input parameter. The moisture model was then coupled with the carbonation model developed. This provides an integrated and powerful solution for predicting carbonation of concrete both sheltered and exposed to rain by using only one main material input parameter ‘k', which is one of the major contributions of this research.

La corrosion de l’acier par carbonatation du béton est un phénomène de dégradation majeur des structures en béton armé, qui débute par la dépassivation de l'acier due à l'abaissement du pH de la solution interstitielle, se concrétise par une initiation effective avant de se propager. Nous nous sommes focalisé sur la dépassivation et l'initiation effective. Une large campagne expérimentale a permis de comprendre l'incidence des conditions d'exposition, de la nature des ciments utilisés dans les bétons et des conditions de carbonatation de l'enrobage, sur la dépassivation des armatures et le démarrage effectif de la corrosion. Au total 27 configurations ont été étudiées. Le potentiel libre de corrosion et la résistance de polarisation ont été mesurés au cours de l'expérimentation sur une durée voisine d'une année. Parallèlement, à échéances régulières, les coefficients de Tafel et la masse de produits de corrosion ont été également mesurés. L'ensemble des données a été analysé pour conduire, à partir du calcul des probabilités de bonne ou de mauvaise alarme, aux seuils de détection du démarrage effectif de la corrosion associés aux paramètres électrochimiques ainsi que la masse seuil de produits de corrosion correspondant à cette détection. Alimentée par les résultats des essais de caractérisation des bétons, une simulation numérique par éléments finis du démarrage de la corrosion a été développée permettant de corroborer de façon satisfaisant les résultats expérimentaux
The steel corrosion induced by carbonation is a major cause of degradation of the reinforced concrete structures. Two stages arise: the steel depassivation due to the decrease of pH of the pore solution and the effective initiation, and then the propagation. A wide experimental study was carried out focusing on the first stage, in order to emphasize the effect of the exposure conditions, the type of cement and the concrete mixes, and the carbonation conditions of the concrete cover. In all a set of 27 configurations was investigated. The free potential of corrosion and the resistance of polarization were measured in the course of the experiment during one year. Regularly the Tafel coefficients along with the mass of corrosion products were also measured. The set of data was analyzed in order to derive the detection thresholds of the effective onset of corrosion associated with the electrochemical parameters, from the calculation of the probabilities of good or bad alarm. The threshold of the mass of corrosion products corresponding to this detection was also derived. The tests on concrete probes (porosity, permeability, etc.) supplied data that were used to calibrate a finite element model of the onset of corrosion: this model was found in fairly good agreement with the experimental results

Static and dynamic carbonation curing at early age was developed for ordinary Portland cement (OPC) and Portland limestone cement (PLC) concrete masonry units (CMU) production. It is intended to replace conventional steam curing, improve the CMU performance, reduce energy consumption, and permanently sequester carbon dioxide in concrete. Concrete slabs representing the face shell of a 20-cm CMU as well as full sized CMU were used throughout the carbonation process. In static carbonation, it was found that initial air curing was vital to maximize carbonation reaction. After a procedure of casting, air curing, carbonation curing, and water compensation in subsequent hydration, carbonated CMUs had shown equivalent strength to steamed CMU but much better resistance to freeze-thaw damage. Carbonate-reinforced cement matrix played a critical role in improving freeze thaw resistance. In dynamic carbonation, the initial air curing was combined with carbonation with controlled relative humidity. The production cycle was significantly reduced to avoid initial air curing. The process proved to be a valid replacement of the static system in terms of CO2 uptake and compressive strength. While both OPC and PLC concretes displayed the hydration and carbonation products, only OPC concrete demonstrated an intermix of these products in the form of calcium silicate hydrocarbonate and a phase transformation of poorly crystalline aragonite and vaterite into well crystalline calcite. Based on 24% CO2 uptake, the CMU production in US and Canada is capable of sequestering 2 million tons CO2 per year. It is equivalent to 2.5% carbon emission reduction for US and Canada cement industry.
La carbonatation par méthode statique et dynamique a été développée pour la cure rapide de blocs de bétons composés à partir de ciment Portland ordinaire ainsi que de ciment Portland à base de calcaire. Cette approche vise à remplacer le procédé traditionnel de cure de blocs de bétons par étuvage afin d'améliorer leur performance, réduire la consommation d'énergie, et séquestrer le dioxyde de carbone de manière indéfinie. La façade extérieure d'un bloc de béton de 20-cm, représenté par une dalle de béton, ainsi qu'un bloc de pleine taille, ont été utilisés durant le procédé de carbonatation. Les résultats indiquent qu'il est essentiel de curer les blocs par air contrôlé avant d'employer la carbonatation statique. Suivant la procédure de moulage, cure à l'air, carbonatation, et compensation de l'eau à travers hydratation suivie, les blocs de bétons carbonatés ont témoigné une résistance comparable à celle de blocs durcis à la vapeur, cependant une résistance supérieure aux dégâts de gel-dégel. La microstructure du ciment carbonaté-renforcé a joué un rôle crucial dans l'amélioration de la résistance du gel-dégel. Dans la carbonatation dynamique, le durcissement initial par étuvage a été combiné avec carbonatation sous une humidité relative contrôlée. Afin de réduire le cycle de production, le durcissement initial par étuvage a été éliminé. La carbonatation dynamique s'est avérée être un remplacement valable du système statique en termes d'absorption de CO2 et résistance à la compression. Bien que le ciment Portland ordinaire ainsi que le ciment Portland à base de calcaire ont confirmé des produits d'hydratation et de carbonatation, seul le ciment Portland a fait preuve de la capacité de ses produits d'hydratation et de carbonatation de se mélanger sous la forme de calcium hydrocarbonate silicate . De plus, de l'aragonite mal cristallisé et de la vatérite ont subi une transformation de phase dérivant en calcite cristalline. Basé sur une capacité d'absorption de CO2 de 24%, la production de blocs de bétons aux États-Unis et au Canada a le potentiel annuel de séquestrer 2 millions de tonnes de CO2. Ce fait signifie que la réduction d'émissions de dioxyde de carbone de ces deux pays dans l'industrie de ciment est égale à 2.5%.

Rapid anthropogenic climate change is one of the greatest challenges that human civilisation will face in the 21st century. A 25-180 % increase in atmospheric carbon dioxide content since the early 1800’s and a predicted increase of 2-3% each year will lead to a 2-6°C rise in tropospheric temperatures. The consequences of increased atmospheric temperatures are profound and would put unsustainable strain on human infrastructure, which was conservatively estimated in the Stern Review (2006) to cost approximately 20% of GDP. Given the political, technical, economic and social barriers preventing the transition to a low carbon economy, there is an unequivocal need to research ‘geoengineering’ technologies that can bridge the gap between carbon emission reduction targets and actual emissions. Soil mineral carbonation is one such technology. The atmosphere is one of the smallest carbon pools at the Earth’s Surface (depending on how each pool is demarcated). Soils turn over the quantity of carbon in the atmosphere in under a decade and collectively form one of the largest carbon pools (3-4 times the quantity of carbon in the atmosphere). Land use change since the agricultural revolution has released 256 GtC (40 % of anthropogenic emissions). Research investigating the potential for carbon accumulation in soils is primarily focused on restoring organic carbon concentration to pre-agricultural values through modification of farming practices. The research presented in this thesis is the first that explores the potential of increasing the inorganic carbon pool as an emissions mitigation technology. Inorganic carbon accumulation is promoted by introducing divalent cation rich (predominantly calcium and magnesium) silicate and hydroxide minerals into the soil, which weather and supersaturate the soil solution with respect to carbonate minerals (predominantly calcite, aragonite, magnesite and dolomite). The carbon in the resultant precipitate is derived from the atmosphere. This is analogous to mineral carbonation technologies which induce carbonate precipitation from silicate weathering in industrial scale reactors at elevated temperatures and pressures. However, carbonation in soil exploits natural weathering processes to the same effect with minimal energy and infrastructure input. The research presented in this thesis broadly investigates soil mineral carbonation by contributing work towards the fundamental issues associated with application of soil mineral carbonation technology. Research activity described herein covers a range of laboratory batch weathering experiments, field work, geochemical modelling, plant growth trials, soil microcosm experiments and literature reviews. While eclectic, all work packages contribute to the same goal of describing the efficacy, effectiveness and potential impacts of soil mineral carbonation. The efficacy of mineral carbonation technology is primarily limited by the availability of appropriate silicate bearing material. A literature search suggests that approximately 15-16 Gt a- 1 of silicate rich ‘waste’ materials are produced as a consequence of human activity. This has a carbon capture potential between 190 and 332 MtC a-1, which is equivalent to other emissions mitigation strategies. Quarrying silicate specifically for carbonation is a suggested strategy that may be able to store on the order of 102 GtC a-1 (based on two sites in the US). Therefore, mineral carbonation may form part of global mitigation strategies collectively equivalent to 14 GtC a-1 to stabilise the CO2 concentration of the atmosphere at 500 parts per million by volume. Considering that the potential capacity of soil mineral carbonation is sufficient to act as a substantial emissions mitigation strategy it was appropriate to investigate issues associated with the application of such a technology. In the first instance, sites known to contain silicates were investigated. These include soils developed on natural silicates (on the Whin Sill in Northumberland), construction and demolition waste (at a brownfield site and waste transfer stations) and slag (at a former steelworks). Interpretation of fieldwork results suggests that inorganic carbon accumulation is rapid (up to 38 gC kg-1(soil) a-1), and is orders of magnitude xxv greater than organic carbon accumulation in natural soils. The average concentration of inorganic carbon (20-30 Kg m-3) is equivalent to organic carbon in natural soils. The unusually light carbon and oxygen isotope ratios of the carbonate (-3.1 ‰ and -27.5 ‰ for δ13C and -3.9 ‰ and -20.9 ‰ for δ18O) were used to determine that up to 55% of the carbon was derived from the atmosphere. The rate of carbon capture, which is the same as the precipitation rate of carbonate, is a function of solution chemistry. The more supersaturated a solution is with respect to a carbonate mineral, the more rapid the precipitation rate. Saturation of a solution is a function of divalent cation and carbonate anion concentration. Therefore, the supply of each of these components was investigated in laboratory experiments. Batch weathering experiments were used to investigate the supply of calcium from artificial silicates (hydrated cement gel). Up to 70-80 % of the calcium contained in the mineral was removed, which is consistent with efficiencies reported for conventional mineral carbonation. The log rate of weathering was between -10.66 and -6.86 mol Ca cm-2 sec-1, which is several orders of magnitude greater than that usually reported for natural silicates. Microcosm experiments were conducted to investigate the rate of supply of carbonate from the organic carbon mineralisation in high pH solutions. The research clearly demonstrates that high pH solutions inhibit the breakdown of organic carbon as a function of nutrient supply. Where organic carbon was successfully mineralised the log rates (-3.4 mmol g-1(field moist soil) sec-1) were equivalent to that found in previous studies. While the influx of dissolved carbonate mineral components into the soil solution is the primary controlling step in the rate of carbon accumulation, there is a complex relationship between soil physical properties and geochemistry. This was highlighted in a numerical model that was constructed for this thesis, which suggests that soil pore volume and particle size distribution are important variables. An additional numerical model was constructed to investigate the transportation of silicate material to the application site. This model suggests that an economics of soil mineral carbonation is a function of transport costs, the value of the silicate material and the price of carbon. Field observations, growth trials, microcosm experiments and previous research suggest a complex interaction between biology, weathering and carbonate precipitation. Additional work is required to investigate carbonate precipitation mediated by plant and microorganism activity and the degree to which soil mixed with silicates impact on ecosystem functioning. This research has demonstrated that mineral carbonation in soils could form a substantial emissions mitigation strategy, but additional work is required in a number of areas to which this thesis provides a suitable foundation.

Lime has been used in construction for millennia, and its value, especially in the field of conservation architecture, has only recently been rediscovered. Lime mortars harden through carbonation, and this thesis is a study of that process. The research conducted has resulted in the development of two novel techniques for the measurement and detection of carbonation. The first technique is a method of thermogravimetric analysis which allows the carbonation profile to be measured within an acceptable time-frame. The second technique is the use of drilling resistance measurement to visualise the carbonation profile. The potential of elemental analysis to measure the carbonation profile has also been identified. It has been demonstrated that the lime/water ratio has less impact on the compressive strength of air lime mortars than had previously been supposed. The change in the pore size distribution of air lime mortars caused by carbonation has been studied, and a theory has been proposed to explain this phenomenon. Five different forms of air lime binder were studied. The impact of these on the structural performance of the resultant mortars has been assessed. It was concluded that mortars made with lime putties perform better than mortars made with dry lime hydrate. Mortars made with dispersed hydrated lime appear to perform as well as mortars made with lime putties, but at a slower rate of strength growth. The use of extra mature lime putty does not appear to confer structural performance benefits when compared with ordinary lime putty. It has been shown that the use of calcitic aggregates can produce air lime mortars which perform as well as moderately hydraulic lime mortars. It is theorised that this phenomenon is not directly related to carbonation, but rather to a complex interaction of the granulometry, mineralogy, chemistry and porosity of the aggregate with the binder.

The world’s exponential growth in urbanisation has placed significant pressure on the construction industry to support development by expanding its provision of infrastructure. There is expected to be a rapid increase in the consumption of structural concrete to meet the associated requirements. This increase in concrete consumption has adverse effects on the environment. Firstly, the production of cement, one of the main components of concrete, is regarded as a system of energy-intensive processes. Secondly, the production of Portland cement (PC) releases a substantial amount of greenhouse gases (such as carbon dioxide), which in turn contributes to the global warming phenomenon. In addition to the change in demand for concrete over time, its composition and mix proportions have indeed also undergone a significant evolution. Concrete is becoming more sophisticated and complex. The construction industry has introduced mineral admixtures as partial replacement of PC in the attempt to mitigate the negative environmental impact of cement production. The use of mineral admixtures has positive economic and environmental benefits. In the context of concrete durability, the use of mineral admixtures has the potential to improve the performance of concrete by mitigating the deterioration processes occurring in concrete structures, such as reinforcement corrosion. Reinforcement corrosion is one of the most pervasive concerns within the construction industry. Carbonation is considered as of the main causes contributing to the corrosion phenomenon. The carbonation mechanism entails the reaction between atmospheric carbon dioxide and the cement paste and leads to an altered chemistry within concrete, which eventually causes the depassivation of steel reinforcement. The deterioration of the concrete caused by carbonation can be predicted using the oxygen permeability index (OPI) test results as an input parameter in the appropriate carbonation prediction model. While South Africa has developed carbonation durability prediction models that can predict the performance of conventional concrete mixes (concrete containing 30% fly ash, 50% slag, 10% silica fume) relatively well, this formulation of the carbonation model was instituted approximately twenty years ago and is considered outdated. Therefore, this research seeks to investigate whether the previously established correlation between carbonation and oxygen permeability is still relevant for modern South African concretes. In this study, concrete constituting of different mineral admixtures at varying PC replacement levels or the use of chemical admixtures is defined as modern concrete. The experimental work included investigating the permeability and carbonation performance of modern concretes made with modern binder types at varying binder replacement levels and binder combinations, including binary and ternary cement blends at two water:binder ratios of 0,50 and 0,65. This included addition of fly ash (FA) (20%-50% in 10% increments), blast furnace slag (BS) (20%- 60% in 10% increments), Corex slag (CS) (20%-60% in 20% increments), and limestone (10% and 20%). For ternary blends, the concrete was limited to three mixes, that is, 5% SF with either 25% FA, 25% BS or 25% CS. Furthermore, two commercial blended cement products were tested namely CEM II A-L, and CEM Il B-M (L-S) 42,5N, referred to as A-L and B-M. A-L and B-M cement nominally contain 8% L, and 8% L coupled with 25% CS respectively. The OPI test was conducted after 28-days of wet curing. The accelerated carbonation tests were conducted using a phenolphathein indicator solution at 6, 9 and 12 weeks of exposure. Prior the testing, the samples were wet cured for seven days and underwent a preconditioning regime in attempt to minimise the influence of the internal moisture of the concrete affecting the carbonation depth results. A statistical analysis was done on both OPI and the accelerated carbonation results to determine the significance in results with the increase in binder replacement percentage, different binders of the same binder replacement percentage and significance of using ternary mixes in comparison to binary mixes. In conclusion it was found that, generally, mineral admixtures had a statistical insignificant influence on the permeability. This can be attributed to the fact that the control mixes already possessed a high permeability performance i.e. concretes exhibiting relatively low permeabilities. Therefore, the inclusion of a mineral admixture would result in a minor influence on the performance. Regarding carbonation depths, the inclusion of mineral admixtures resulted in a decrease in carbonation performance, as expected. This is attributed to the dilution effect and the pozzolanic effect to some degree, which decreased the amount of carbonatable material that is calcium hydroxide, subsequently decreasing the concrete’s resistance to carbonation. Finally, reasonable correlations were identified between carbonation depth and permeability when all concrete mixes were considered. The direction of the trend showed a positive and negative association when the carbonation coefficient was plotted against k-permeability and OPI respectively. Further investigation of the correlation between carbonation depth and a singular binder type regardless of the replacement level showed an increased in correlation strength between permeability and carbonation. It was concluded that using this approach may provide reasonable correlations for carbonation prediction modelling. However, more testing would be required to confirm the previous statement.

Thesis (M.S.)--West Virginia University, 2003.
Title from document title page. Document formatted into pages; contains viii, 65 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 60-64).

La carbonatation est l’un des processus initiateurs de la corrosion des armatures du béton armé. Sa cinétique est souvent utilisée pour modéliser la durabilité des ouvrages. La carbonatation résulte de la réaction en présence d’eau entre le dioxyde de carbone contenu dans l’air et les phases hydratées de la pâte de ciment. Elle donne du carbonate de calcium et provoque une baisse du pH qui induit la dépassivation des armatures et leur corrosion. La carbonatation des matériaux à base de ciment a été largement étudiée ces dernières années mais les données de la littérature sont extrêmement contradictoires sur la plupart des évolutions qu’elle engendre tant au niveau microstructural qu’à l’échelle macroscopique. Notre travail a eu pour objectif d’étudier les conséquences microscopiques et macroscopiques de la carbonatation sur deux mortiers standards simples à base de ciment CEM I et CEM II. Nous avons mené une étude expérimentale approfondie sur deux mortiers normalisés à base de ciment CEM I et CEM II pour comprendre les mécanismes physico-chimiques de la carbonatation. Nous avons utilisé les techniques suivantes pour examiner les conséquences de la carbonatation sur les caractéristiques microstructurales de la matrice cimentaire : analyse thermogravimétrique, diffraction de rayons X, pycnométrie à l’hélium, adsorption – désorption d’azote et de vapeur d’eau. Comme ces modifications observées au niveau de la microstructure induisent à leur tour des évolutions significatives au niveau des propriétés macroscopiques d’usage et des indicateurs de durabilité, nous avons examiné les conséquences de la carbonatation sur la perméabilité au gaz, la vitesse de propagation des ondes ultrasonores, la conductivité thermique et la résistivité électrique de surface. Notre étude a également porté sur la contribution de la carbonatation à la cicatrisation des mortiers endommagés thermiquement. Enfin, nos résultats expérimentaux ont été utilisés comme base de données pour élaborer un modèle sur la propagation de CO2 dans la matrice cimentaire
Carbonation is one of the most important factors that initiate the corrosion of steel bars in reinforced concrete. Its kinetics are often used to model the durability of structures. Under the action of carbon dioxide from the air and with the presence of water in the pores, several hydrated phases of the cement paste are carbonated and form calcium carbonate. This process causes a decrease in pH of the pore water, which subsequently induces the depassivation and corrosion of the rebars. Although the carbonation of cementitious materials has been extensively studied in recent years, results in literature about changes in both micro and macroscopic levels are extremely contradictory. The aim of this work is to study the micro and macroscopic effects of carbonation on two standard cement mortars CEM I and CEM II. A wide experimental campaign was conducted on two standard mortars CEM I and CEM II in order to apprehend the physicochemical mechanisms of the carbonation. The following techniques were used to examine the impacts of carbonation on the microstructural characteristics of the cementitious matrix : thermogravimetric analysis, X-ray diffraction, helium pycnometry, nitrogen and water vapor adsorption-desorption. As changes observed in the microstructure could consequently induce significant modifications in the macroscopic properties and the sustainability indicators, we examined the effects of carbonation on the gas permeability, the ultrasonic waves velocity, the thermal conductivity and electrical resistivity. Our work also studied the self-healing effect caused by carbonation of thermally damaged mortars. Finally, our experimental results were used as a database to elaborate a model of the propagation of CO2 in the cementitious matrix

Alkaline industrial wastes are considered potential resources for the mitigation of CO2 emissions by simultaneously capturing and sequestering CO2 through mineralization. Mineralization safely and permanently stores CO2 through its reaction with alkaline earth metals. Apart from natural formations, these elements can also be found in a variety of abundantly available industrial wastes that have high reactivity with CO2, and that are generated close to the emission point-sources. Apparently, it is the applicability and marketability of the carbonated products that define to a great extent the efficiency and viability of the particular process as a point source CO2 mitigation measure. This project investigates the valorization of iron- and steel-making slags through methods incorporating the carbonation of the material, in order to achieve the sequestration of sufficient amounts of CO2 in parallel with the formation of valuable and marketable products. Iron- and steel-manufacturing slags were selected as the most suitable industrial byproducts for the purposes of this research, due to their high production amounts and notable carbonation capacities. The same criteria (production amount and carbonation capacity) were also used for the selection of the iron- and steel-making slag types that are more suitable to the scope of this work. Specifically for the determination of the slag types with the most promising carbonation capacities, the maximum carbonation conversions resulting from recent publications related to the influence of process parameters on the conversion extent of iron- and steel-manufacturing slags, were directly compared to each other using a new index, the Carbonation Weathering Rate, which normalizes the results based on particle size and reaction duration. Among the several iron- and steel-manufacturing slags, basic oxygen furnace (BOF) and blast furnace (BF) slags were found to combine both high production volumes and significant affinity to carbonation. In the context of this research, two different procedures aiming to the formation of value added materials with satisfactory CO2 uptakes were investigated as potential BF and BOF slags valorization methods. In them, carbonation was combined either with granulation and alkali activation (BOF slag), or with hydrothermal conversion (BF slag). Both treatments seemed to be effective and returned encouraging results by managing to store sufficient amounts of CO2 and generating materials with promising qualities. In particular, the performance of the granulation-carbonation of BOF slag as a method leading to the production of secondary aggregates and the sequestration of notable amounts of CO2 in a solid and stable form, was evaluated in this work. For comparison purposes, the material was also subjected to single granulation tests under ambient conditions. In an effort to improve the mechanical properties of the finally synthesized products, apart from water, a mixture of sodium hydroxide and sodium silicate was also tested as a binding agent in both of the employed processes. According to the results, the granules produced after the alkali activation of the material were characterized by remarkably greater particle sizes (from 1 to 5 mm) compared to that of the as received material (0.2 mm), and by enhanced mechanical properties, which in some cases appeared to be adequate for their use as aggregates in construction applications. The maximum CO2 uptake was 40 g CO2/kg of slag and it was achieved after 60 minutes of the combined treatment of alkali activated BOF slag. Regarding the environmental behavior of the synthesized granules, increased levels of Cr and V leaching were noticed from the granules generated by the combination of granulation-carbonation with alkali activation. Nevertheless, the combination of granulation with alkali activation or that of granulation with carbonation were found not to worsen, if not to improve, the leaching behaviour of the granules with regards to the untreated BOF slag. The formation of a zeolitic material with notable heavy metal adsorption capacity, through the hydrothermal conversion of the solid residues resulting from the calcium- extraction stage of the indirect carbonation of BF slag, was also investigated in this project. To this end, calcium was selectively extracted from the slag by leaching, using acetic acid of specific concentration (2 M) as the extraction agent. The residual solids resulting from the filtration of the generated slurry were subsequently subjected to hydrothermal conversion in caustic solution of two different compositions (NaOH of 0.5 M and 2 M). Due to the presence of calcium acetate in the composition of the solid residues, as a result of their inadequate washing, only the hydrothermal conversion attempted using the sodium hydroxide solution of higher concentration (2 M) managed to turn the amorphous slag into a crystalline material, mainly composed by a zeolitic mineral phase (detected by XRD), namely, analcime (NaAlSi2O6·H2O), and tobermorite (Ca5(OH)2Si6O16·4H2O). Finally, the heavy metal adsorption capacity of the particular material was assessed using Ni2+ as the metal for investigation. Three different adsorption models were used for the characterization of the adsorption process, namely Langmuir, Freundlich and Temkin models. Langmuir and Temkin isotherms were found to better describe the process, compared to Freundlich model. Based on the ability of the particular material to adsorb Ni2+ as reported from batch adsorption experiments and ICP-OES analysis, and the maximum monolayer adsorption capacity (Q0 = 11.51 mg/g) as determined by the Langmuir model, the finally synthesized product can potentially be used in wastewater treatment or environmental remediation applications.

Includes bibliographical references (leaves 220-227).
The rate of carbonation for the localities of the Cape Peninsula, Durban (i.e. Durban - KwaZulu Natal South Coast) and Johannesburg (i.e. the motorway system and between Heidelberg Road and Geldenhuis interchanges on the N3 freeway) were studied in order to derive carbonation prediction models for each of these localities. The derivation of the prediction models was based on field carbonation data measured from approximately 30 in-service bridges in each locality. One of the uses of the derived models was to allow the preparation of maintenance plans so as to avoid carbonation-induced corrosion for structures in these localities. Since the rate of carbonation depends strongly on material and environmental factors, the carbonation data from each locality were analysed separately on the grounds that these localities have different climatic conditions. The data within each locality represent different material and exposure conditions, and the data were therefore grouped according to the concrete strength grade (as a measure of concrete quality) and exposure conditions, prior to statistical analysis. Based on the method of least squares, as well as integration of the understanding of the process of carbonation and knowledge of climatic conditions of each locality, carbonation prediction models for a variety of concretes for each locality were derived. Results show that bridge structures in the Johannesburg locality have the highest carbonation rate due to the relatively dry environment throughout the year. Bridges in Durban locality exhibit a lower carbonation rate than Johannesburg bridges, but higher than Cape Peninsula bridges owing to shorter rainfall duration and higher temperature. In addition, the carbonation rates of both exposed and sheltered elements with similar concrete strength grades for bridges in Durban are very similar, i.e. exposure condition has little influence on carbonation rate for these elements. The same is true for bridges in the Johannesburg locality. It is surmised that short precipitation times and high relative humidity in Durban locality make the near surface moisture content of exposed and sheltered elements very similar. Likewise, it is surmised that short rainfall duration and low relative humidity in Johannesburg locality result in essentially the same near surface moisture content of concrete elements throughout the exposure time. The data in Durban locality show that old concretes have a slower carbonation rate than modem concretes with the same concrete strength grade. This is likely due to the changes in cement properties over the years, related to the need for fast track development for modem structures. This finding indicates that the prediction models are not suitable for carbonation predictions for future structures (produced by modem cements) as the rates of carbonation will be different. Oxygen Permeability Index (OPI) was investigated in an attempt to predict the rate of carbonation. According to the philosophy and testing procedures for OPI, it is considered that early age OPI may be superior to concrete strength grade for carbonation predictions because of better characterisation of the permeability of (cover) concrete. However, due to the lack of early age OPI information for the data, using OPI as a carbonation prediction tool was not entirely successful. Further research in this regard is worthwhile.

Chemistry
Ph.D.
Carbon dioxide (CO2) is formed when fossil fuels such as oil, gas and coal are burned in power producing plants. CO2 is naturally found in the atmosphere as part of the carbon cycle, however it becomes a primary greenhouse gas when human activities disturb this natural balanced cycle by increasing levels in the atmosphere. In light of this fact, greenhouse gas mitigation strategies have garnered a lot of attention. Carbon capture, utilization and sequestration (CCUS) has emerged as a possible strategy to limit CO2 emissions into the atmosphere. The technology involves capturing CO2 at the point sources, using it for other markets or transporting to geological formations for safe storage. This thesis aims to understand and probe the chemistry of the reactions between CO2 and iron-bearing sediments to ensure secure storage for millennia. The dissertation work presented here focused on trapping CO2 as a carbonate mineral as a permanent and secure method of CO2 storage. The research also explored the use of iron-bearing minerals found in the geological subsurface as candidates for trapping CO2 and sulfide gas mixtures as siderite (FeCO3) and iron sulfides. Carbon dioxide sequestration via the use of sulfide reductants of the iron oxyhydroxide polymorphs lepidocrocite, goethite and akaganeite with supercritical CO2 (scCO2) was investigated using in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The exposure of the different iron oxyhydroxides to aqueous sulfide in contact with scCO2 at ~70-100 ˚C resulted in the partial transformation of the minerals to siderite (FeCO3). The order of mineral reactivity with regard to siderite formation in the scCO2/sulfide environment was goethite < lepidocrocite ≤ akaganéite. Overall, the results suggested that the carbonation of lepidocrocite and akaganéite with a CO2 waste stream containing ~1-5% H2S would sequester both the carbon and sulfide efficiently. Hence, it might be possible to develop a process that could be associated with large CO2 point sources in locations without suitable sedimentary strata for subsurface sequestration. This thesis also investigates the effect of salinity on the reactions between a ferric-bearing oxide phase, aqueous sulfide, and scCO2. ATR-FTIR was again used as an in situ probe to follow product formation in the reaction environment. X-ray diffraction along with Rietveld refinement was used to determine the relative proportion of solid product phases. ATR-FTIR results showed the evolution of siderite (FeCO3) in solutions containing NaCl(aq) concentrations that varied from 0.10 to 4.0 M. The yield of siderite was greatest under solution ionic strength conditions associated with NaCl(aq) concentrations of 0.1-1 M (siderite yield 40% of solid product) and lowest at the highest ionic strength achieved with 4 M NaCl(aq) (20% of solid product). Based partly on thermochemical calculations, it is suggested that a decrease in the concentration of aqueous HCO3- and a corresponding increase in co-ion formation, (i.e., NaHCO3) with increasing NaCl(aq) concentration resulted in the decreasing yield of siderite product. At all the ionic strength conditions used in this study, the most abundant solid phase product present after reaction was hematite (Fe2O3) and pyrite (FeS2). The former product likely formed via dissolution/reprecipitation reactions, whereas the reductive dissolution of ferric iron by the aqueous sulfide likely preceded the formation of pyrite. These in situ experiments allowed the ability to follow the reaction chemistry between the iron oxyhr(oxide), aqueous sulfide and CO2 under conditions relevant to subsurface conditions. Furthermore, very important results from these small-scale experiments show this process can be a potentially superior and operable method for mitigating CO2 emissions.
Temple University--Theses

Les bétons de chanvre associent un granulat végétal issu du chanvre, appelé « chènevotte », et une matrice minérale. Ce sont des matériaux isolants répondant particulièrement bien aux nouvelles problématiques environnementales du secteur du bâtiment. Pourtant, leur développement est freiné par d'occasionnels désordres de mise en œuvre et des propriétés mécaniques relativement faibles qui pourraient résulter d'interactions complexes développées entre la chènevotte et le liant. Dans ce contexte, l'objectif des travaux a été de préciser la nature de ces interactions et d'identifier par quels mécanismes celles-ci peuvent modifier la prise du liant et les propriétés finales du matériau. Pour cela, l'évolution de mélanges de matières premières (chènevottes et liants) de natures différentes a été étudiée par des techniques de biochimie, de spectroscopie, de physico-chimie et de mécanique. Cette approche multi-échelle a ainsi permis de mettre en évidence le puissant pouvoir retardateur des produits extraits de la chènevotte sur la prise des liants hydrauliques. Ce retard peut conduire à une absence totale de prise du liant, lorsque celui-ci est couplé à des phénomènes de dégradation de la chènevotte, de migration de ces produits dans la matrice et d'évaporation d'eau. En outre, il a été démontré que les caractéristiques de la chènevotte (composition chimique), la nature du liant (ciment pur ou additionné de chaux), ainsi que les conditions de cure (présence ou non de CO2) sont des facteurs pouvant moduler les effets délétères sur la prise et les propriétés mécaniques du matériau formé. Ils constituent donc des paramètres potentiels d'optimisation des bétons de chanvre
The hemp concretes, combine a plant aggregate, called “shiv” with a mineral binder. They are insulating materials particularly suited to face the new environmental problems of the building sector. However, their development is hampered by the occasional implementation problems and their relatively low mechanical properties that could result from complex interactions between the shiv and the binder. In this context, the objective of the presented work was to clarify the nature of these interactions and to identify the mechanisms by which they can impact the setting of the binder and the final properties of the material. To do so, the evolution of mixtures of the initial components (shiv and binders) differing by their nature was studied by biochemical, spectroscopic, physical chemistry and mechanical techniques. This multi-scale approach enabled us to highlight the powerful set retarding action of shiv-extractable products on hydraulic binders. This delay can even lead to a total failure of the binder setting when this one is coupled to simultaneous degradation of the hemp aggregate, migration of the formed products in the matrix and water evaporation. Finally, it has been demonstrated that the characteristics of the shiv (chemical composition), the nature of the binder (pure cement or lime added), and the curing conditions (presence or absence of CO2) represent factors that may modulate the deleterious effects on the setting and the mechanical properties of the formed material. They hence constitute potential parameters for the optimization of hemp concretes

The potential success of integrating mineral carbonation, as a pathway to CO₂ sequestration, in mining projects, is dependent on the mineralogical composition and characteristics of its waste rock and tailings. Ultramafic rocks have proven the best potential substrate for mineral carbonation and their ability to alter and to convert CO₂ into its carbonate mineral form is dependent on the original mineralogy and particle surface area. CO₂ conversion kinetics is complex and with the application of appropriate comminution technologies, its efficiency can be enhanced. The objective of this research is to evaluate mechanical activation to enhance the carbonation storage capacity of mine waste material. Three approaches were taken in this research. The first approach was to characterize the microstructure of the mechanically-activated mineral olivine, a predominant mineral constituent of ultramafic rocks, using X-ray diffraction patterns and line profile analysis methods with full pattern fitting method. The second approach was to compare the structural and chemical changes of mine waste with pure olivine, both of which were activated by various mechanical forces under both wet or dry conditions and subsequently carbonated in a direct aqueous carbonation process. Regardless of milling conditions, forsterite (Mg₂SiO₄), the olivine mineral variety in the mine waste, was found to be the main mineral being mechanically-activated and carbonated. It was determined that lizardite (Mg₃(Si₂O₅)(OH)₄), a hydrated magnesium silicate also common in ultramafic hosted mineral deposits, acted as catalyzer assisting forsterite reaching high levels of activation. This condition generated a greater CO₂ conversion to carbonate than that of pure olivine with the equal specific milling energy input. The stirred mill proved to be the most efficient form of mechanical activation vis-a-vis the direct aqueous carbonation process, followed by the planetary mill and the vibratory mill. The third approach analyzes the feasibility of mechanical activation in an integrated mineral carbonation process in a nickel mine considering the life cycle of the process. The minimum operating cost for 60% CO₂ sequestration efficiency was 105-107 $/t CO₂ avoided. At this point, the Turnagain project can potentially sequester 238 Mt/y CO₂ using its waste during the 28-year life of mine.
Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate

Carbon dioxide (CO2) is the dominant greenhouse gas resulting from many anthropogenic activities, mainly combustion of fossil fuels. One of the strategies to mitigate CO2 emissions is considered to be carbon dioxide capture and storage (CCS). The current storage methods focus on enhanced oil recovery, underground geological storage, disposal in deep oceans, and ex situ mineral carbonation of abundant metal oxide minerals such as olivine, serpentinite and wollastonite.During mineral carbonation, a gas stream rich in CO2 is reacted with mineral metal oxides to form thermodynamically stable carbonates. These carbonated minerals, however, store CO2 but do not produce any materials that are of value. Accelerated carbonation curing of concrete can be used as a mineral sequestration method with the advantage of producing a value-added concrete product. During accelerated carbonation curing of concrete, CO2 is reacted with cement and stored as a solid calcium carbonate in concrete construction products. Among the concrete products, non-reinforced precast concrete, such as blocks and bricks, can be used for carbonation curing. In previous studies, pressurized chambers have been used for accelerated CO2 curing of concrete, where a high pressure of CO2 is required for sufficient gas diffusion in concrete and homogeneous carbonation. In this research, a flow-through carbonation reactor was used for concrete curing and the rate and extent of CO2 uptake by concrete was studied. One of the advantages of the carbonation reactor applied in this study is that significantly less energy for gas mixture compression is required compared to a CO2 pressure chamber.The overall objective of this thesis was to develop and assess the performance of an accelerated carbonation curing reactor for concrete using an advective flow of flue gas. The rate and extent of CO2 uptake by concrete in a 1-D flow-through carbonation reactor were studied and compared with the published results on CO2 uptake in pressurized chambers using diffusive flow of CO2. The factors limiting the CO2 uptake were studied through experimental observation as well as mathematical modeling of CO2 transport and reaction in concrete during accelerated carbonation curing. Carbonation efficiencies of 16-20% attained in the flow-through reactor were comparable to those obtained for static CO2 pressure chambers. The extent of CO2 uptake was limited by formation of solid calcium carbonate in micro-scale pores. Intermittent carbonation experiments showed that the carbonation efficiency was limited in part by slow dissolution and/or diffusion of dissolved reactive components in the concrete matrix. The electron microprobe imaging technique used in this study also confirmed formation of solid calcium carbonate which filled up the narrow pores (<4 µm). The uptake efficiency reached 67% when cement was carbonated in an aqueous suspension in a completely mixed flow-through reactor where the effect of pore blockage was eliminated and a higher percentage of reacting surface area was exposed to dissolved CO2. However, formation of a calcium carbonate layer still inhibited diffusion of dissolved calcium and CO2 through this layer. In the presence of the calcium carbonate layer and other carbonation products like silica (SiO2 gel), and at partial pressure of CO2 used for carbonation, the aqueous solution reached a chemical equilibrium and carbonation ceased before the maximum theoretical uptake could be achieved. The effect of physico-chemical processes on CO2 uptake during carbonation curing was also studied using a mathematical model. Equations describing the CO2 transport by advection and dispersion in concrete pore space, dissolution in pore water and reaction with reactive cement species were solved numerically. The initial concentration of cement species were calculated based on a hydration model which was developed to simulate the 4 hours of hydration time before carbonation starts.
Le dioxyde de carbone (CO2) est le gaz d'effet de serre dominant, résultat des plusieurs activités anthropogènes, dont le plus important est la combustion des combustibles fossiles. Une des stratégies qui a pour but d'atténuer des émissions de CO2 est le captage et le stockage du dioxyde de carbone (CCS en anglais). Les méthodes courantes de stockages incluent la récupération assistée du pétrole, le stockage géologique souterrain, la disposition sous les océans profonds, et la carbonatation minérale ex situ des gisements abondants des oxydes métalliques, comme l'olivine, la serpentinite et la wollastonite. Pendant la carbonatation minérale, un jet de gaz riche en CO2 est mis à réagir avec les oxydes des métaux minéraux pour former des carbonates thermodynamiquement stables. L'élimination des minerais carbonatés, cependant, stocke le CO2 mais ne produit pas des matériaux de valeurs ajoutées. La carbonatation accélérée pour murir du béton peut être employée comme une méthode de la séquestration minérale avec l'avantage de produire un produit de béton à valeur ajoutée. Pendant la carbonatation accélérée pour murir du béton, le CO2 est mis à réagir avec le ciment et stocké comme carbonate de calcium solide dans les produits de béton utilisés en construction. Les produits en béton non-armés et préfabriqués tel que les blocs et les briques sont ceux qui peuvent être faits avec la méthode carbonatation pour murir le béton. Lors des études précédentes, des chambres sous pression ont été employées pour accélérer le durcissement du CO2 au béton, où une haute pression de CO2 est exigée pour une diffusion suffisante de gaz et une carbonatation homogène. Dans cette recherche, un écoulement à travers le réacteur de carbonatation a été utilisé pour le durcissement du béton; le taux et l'ampleur de la prise de CO2 par le béton ont été également étudiés. Un des avantages du réacteur de carbonatation appliqué dans cette étude est que l'énergie exigée est nettement inférieure, comparé à une chambre sous pression de CO2. L'objectif global de cette thèse est de développer et d'évaluer la performance de l'exécution d'une carbonation accélérée traitant le réacteur pour le béton en utilisant un flux advectif des émissions gazeuses. Le taux et l'ampleur de la prise de CO2 par le béton dans un écoulement unidimensionnel (1-D) à travers le réacteur de carbonation ont été étudiés et comparés aux résultats publiés sur la prise de CO2 dans les chambres pressurisées en utilisant l'écoulement diffusif du CO2. Les facteurs limitant la prise de CO2 ont été étudiés à travers l'observation expérimentale ainsi que la modélisation mathématique du transport et de la réaction du CO2 dans le béton durant le traitement accéléré de la carbonation. Les efficacités de carbonatation de 16-20% atteintes dans l'écoulement à travers le réacteur sont comparables à celles obtenues pour les chambres de pression statiques de CO2. L'ampleur de la prise de CO2 a été limitée par la formation du carbonate de calcium solide dans des micro et macro-pores. Les expériences intermittentes de carbonatation ont prouvé que l'efficacité de carbonatation a été limitée en partie par la dissolution et/ou la diffusion lente des composants réactifs dissous dans la matrice de béton. La technique d'imagerie du micro-probe d'électron utilisé dans cette étude a également confirmé la formation du carbonate de calcium pendant la carbonatation, qui a rempli les micropores. L'efficacité de prise a atteint 67% quand le ciment a été carbonaté sous la forme de boue dans un réacteur qui contienne un mélange de suspension aqueux (à travers du quel écoule le CO2), où l'effet du colmatage des pores a été éliminé et un pourcentage plus élevé de la superficie de surface de réaction a été exposé au CO2 dissous. Cependant, la formation d'une couche de carbonate de calcium empêchait encore la diffusion du calcium dissous et du CO2 à travers cette couche.

Carbonation curing of concrete products has shown potentials for CO2 capture and storage with environmental, technical and economical benefits in global greenhouse gas mitigation exercise. The primary objective of this study is to investigate the effect of early age carbonation on mechanical performance and pH of concrete in an attempt to understand the process and promote large scale applications.
It was found that significant early strength was developed in cement and concrete through early age carbonation curing. The early strength could be maintained and improved due to subsequent hydration. Twenty-eight-day strength of carbonated cement and concrete was comparable to that of hydrated reference if subsequently cured in the air in a sealed bag, but was lower if subsequently cured in water. Treatment with either internal curing using lightweight aggregates or chemical admixture can effectively enhance late strength development in carbonated concrete.
For three typical cement-based products including cement paste compacts, concrete compacts and precast concrete, two-hour carbonation reduced pH value from 12.8 to 11.8 as the lowest and subsequent 28-day hydration could slightly increase pH by 2% as maximum. At any time pH of early age carbonated concrete was always higher than 11.5, a threshold value under which the corrosion of reinforcing steel is likely to occur in concrete. The high pH in early-age carbonated concrete was likely attributed to the fact that early age carbonation was an accelerated hydration process, which was totally different from weathering carbonation in which pH of concrete could be neutralized due to the decomposition of calcium hydroxide and calcium silicate hydrates gel. Therefore, early age carbonation technology is applicable not only to concrete products such as masonry units and paving stones, but possibly to precast concrete with steel reinforcement as well.

Pervious concrete is an innovative material with several environmental advantages. Studies on the properties and performance of ordinary Portland cement (OPC) pervious concrete have been done worldwide. Portland limestone cement (PLC) has recently been introduced into the Canadian market as a greener option than OPC. This thesis explores the possibility of using PLC in pervious concrete to achieve technical and environmental benefits.Since the major application of pervious concrete is pavements, it is important to find a way to accelerate the concrete curing process, as one of the most important factors in determining the cost and impact of road work is the construction time. Pervious concrete is the ideal material to cure by carbonation in a feasible way. It is usually designed without reinforcement, so the reduction of the concrete pH value resulting from the process has no impact. Additionally, the open massive pore structure provides a larger surface to optimize CO₂ penetration during the curing process. This study focuses on the effect of carbonation on early age strength and freezing and thawing durability of PLC pervious concrete. It was found that, under the same conditions, PLC pervious concrete shows lower compressive strengths and higher absorption than the OPC counterpart. The optimization of the mixture proportion by including admixtures would permit the use of PLC to generate a pervious concrete with strengths equivalent to OPC pervious concrete. Carbonation curing of PLC pervious concrete increased early age compressive strength, and maintained a comparable final strength. In addition, carbonation curing increased resistance to absorption, but decreased the resistance to freezing and thawing cycles in saline solution. Therefore, carbonation curing of pervious concrete is not recommended for cold climates.
Le béton drainant est un matériau innovant avec plusieurs avantages environnementaux. Des études portant sur les propriétés et la performance du béton drainant au ciment Portland ordinaire (CPO) ont été réalisées internationalement. Le ciment Portland au calcaire (CPC) a fait son arrivée sur le marché canadien récemment et s'avère une option plus écologique que le CPO. Cette thèse explore la possibilité d'utiliser CPC en béton drainant pour obtenir avantages techniques et environnementaux. Une des applications majeures du béton drainant est le pavage. Pour cette raison, c'est important de trouver une façon d'accélérer le processus de durcissement du béton, puisque le temps de construction est l'un des facteurs les plus importants déterminant le coût et l'impact des travaux routiers. Le béton drainant est le matériau idéal à mûrir au carbone de manière faisable. Il est fabriqué sans armature et donc, la réduction du pH du béton résultant du processus de carbonatation n'a aucun impact. De plus, la structure ouverte massive des pores offre une surface plus grande permettant d'optimiser la pénétration de CO₂ au cours du processus de mûrissement. Cette étude a pour but de déterminer l'effet de la carbonatation sur la résistance à jeune âge et la durabilité au gel/dégel du béton drainant fabriqué avec le CPC. Les résultats indiquent que, pour les mêmes conditions, il y a une réduction de la résistance à la compression et une meilleure absorption avec le béton drainant au CPC comparé avec ceux au CPO. L'optimisation du dosage par l'inclusion d'ajouts cimentaires et chimiques, permettrait l'utilisation du CPC pour générer un béton drainant avec des résistances équivalentes au béton drainant au CPO. Le mûrissement au carbone du béton drainant au CPC a augmenté la résistance à la compression à jeune âge, et a maintenu une résistance finale comparable. De plus, le mûrissement au carbone a augmenté la résistance à l'absorption, mais a réduit la résistance aux cycles de gel/dégel en solution saline. Par conséquent, le mûrissement au carbone du béton drainant n'est pas recommandé pour les climats froids.

Moist calcium silicate minerals are known to readily react with carbon dioxide (CO2). The Accelerated Carbonation of hazardous wastes is a controlled accelerated version of the naturally occurring process. The solid mixture is carbonated under a gaseous, CO2 rich environment at slightly positive pressures (3 bar), which promotes rapid stiffening of the non-hydrated product into a structural medium within minutes. In addition, an increased binding of toxic metals occurs as the solid carbonates. Today, Accelerated Carbonation is a developing technology, which may have potential for the treatment of wastes and contaminated soils and for the sequestration of CO2, an important greenhouse gas. The consequent significant improvement in the properties of certain treated materials can facilitate reuse in a variety of construction applications. Accelerated Carbonation represents a potential solution to sustainable waste management, the problem of decreasing landfill space in the UK, rising CO2 emission levels and the depletion of natural aggregate resources. This thesis reports on the application of Accelerated Carbonation for the treatment of Municipal Solid Waste Incinerator residues (MSWIr). The treatment imparts chemical and mineralogical changes to the residues, which reduce their environmental impact through encapsulation of hazardous components and cementation by carbonate precipitation. Given the viability of carbonation as a process to treat MSWIr, this investigation focused on optimising the fundamental parameters determining the extent and quality of carbonation of these residues. Major attention was also given to the modelling of the kinetics and mechanism of the carbonation reaction of Air Pollution Control Residues (APCr). The kinetics were studied in a batch carbonation rig designed and built at University College London. In addition, the major physical and chemical changes in APCr and Bottom Ashes (BA) after carbonation were evaluated using various analytical techniques. In addition, a commercial feasibility study has been carried out which confirmed the considerable and immediate potential for the commercialisation of Accelerated Carbonation technology for the treatment of municipal MSWIr. This conclusion was reached by analysing the market and industry for waste management, competing innovations and the capacity of Accelerated Carbonation to enable the recycling and reuse of CO2 and solid wastes. This work provides a fundamental understanding of the Accelerated Carbonation reaction of APCr essential to further ascertain the scale-up parameters required for the design of a large scale continuous process.

The work presented in this thesis is aimed at evaluating the potential for using supercritical carbonation (SCC) in conjunction with novel processing techniques, to fabricate new blended calcareous matrix composites with superior engineering properties and lower environmental impacts than conventional cement-based materials. Taking combinations of waste materials such as steel slag (SS) and fuel ash (PFA), binders such as hydrated and cement and various aggregate types to manufacture green forms and exposing them to supercritical carbon dioxide has produced a number of promising ceramic materials. The project looked at novel ways to process the ‘green forms’ from these composites, such as dry- and wet-compression moulding, 3-D printing and hand lay up technique that was adapted from the fibre-reinforced polymer industry. Work concentrated on optimising mix designs, green processing and SCC conditions to produce the highest strength materials. Three main avenues were explored. The effects of mix design, different curing regimes and SCC treatment, on the microstructure and chemistry of the composites was investigated using SEM, TSP, DTA, XRD, helium pycnometry and other techniques. Investigation showed that SCC process significantly enhances the mechanical and microstructural properties of carbonated products. It was shown that SCC treatment activates materials such as steel slag, that in the unground state are not activated by high temperature curing, to form useful composites. It was revealed that the relationship between the ‘degree of carbonation’ and strength is not straightforward and the order in which the various phases in the concrete react is important. Microstructural investigations hinted that the bond between carbonate limestone aggregate and the carbonated matrix was much stronger and more intimate (less porous) than for other aggregates. Chemical analysis also determined how much carbon dioxide could be ‘locked-up’ in the samples and this data was then used in the life-cycle assessment (LCA) of potential products. LCA was used to assess the green credentials of the SCC process and results were encouraging; a net reduction in CO2 emission of around 50% can potentially be achieved. Overall, the project has made many significant advances both in the practical application of SCC to ceramic composite manufacture and in the science of the reaction between sc-CO2 and cementitious phases. The technology could now be exploited by the manufacturing industry as a lowtemperature, rapid, low raw material cost and a sustainable route for manufacture of a wide range of ceramics.

L'élaboration de stratégies économiquement viables pour le stockage à long terme du dioxyde de carbone est devenue depuis quelques années un enjeu majeur en réponse aux préoccupations liées au réchauffement planétaire. Le captage et stockage du carbone (CSC) est considéré comme l'un des scénarios possibles visant à contrer le phénomène du réchauffement planétaire en ciblant le CO₂ atmosphérique. La carbonatation minérale – dans des plateformes de CCS – devrait être une option privilégiée pour la capture et le stockage permanent du carbone, connaissant la réactivité de matériaux alcalins tels que les silicates de magnésium et la brucite avec le dioxyde de carbone pour former des carbonates stables et respectueux de l'environnement. La carbonatation minérale passive des minéraux contenus dans les rejets ultramafiques pourrait être considérée comme une option économiquement attrayante en raison de la disponibilité de grandes quantités de rejets miniers riches en magnésium, de granulométrie très fine et hautement réactifs. De plus, les réactions impliquées dans la carbonatation minérale se font relativement facilement dans les conditions ambiantes. Le CO₂ est principalement dissous dans l'eau provenant de la pluie et de la fonte des neiges pour former des ions HCO₃₋ et CO₃²⁻. Des ions métalliques tels que le Mg²⁺ et le Ca²⁺ sont également lessivés dans l'eau permettant ainsi la formation de carbonates métalliques. Des travaux expérimentaux de laboratoire ont été réalisés afin d'identifier la dynamique de la carbonatation minérale passive dans des conditions environnementales qui prévalent généralement dans les régions du Québec, au Canada. Une cellule de carbonatation à diffusion différentielle a été développée pour suivre la cinétique de carbonatation minérale dans des conditions ambiantes. Les mesures cinétiques ont révélé le rôle complexe de l'eau à la fois dans le milieu réactionnel et en partie dans les processus de carbonatation. L'analyse par diffraction aux rayons X en fonction du temps et les observations au microscope électronique à balayage révèlent la formation de carbonates de magnésium intermédiaires, poreux et métastables qui ont ensuite évolué en couches de nesquehonite moins poreuses. Ces minéraux secondaires sont responsables de la passivation des surfaces malgré la disponibilité d’une partie de la brucite qui n’avait pas encore réagie. Cependant, les résultats ont montré que l'abrasion des surfaces de rejets préalablement carbonatés peut permettre l’exposition de surfaces fraiches permettant ainsi une carbonatation supplémentaire des résidus. Des essais de carbonatation à température variable ont été effectués dans les plages de température chaude (35 ± 1 ° C), de laboratoire (23 ± 2 ° C), faible (5 ± 1 ° C) et de congélation (-5 ± 2 ° C) pour considérer les différences saisonnières. Les résultats suggèrent que la température a un effet notable sur la cinétique de carbonatation et une baisse de la température a provoqué un ralentissement de la réaction, bien que la carbonatation soit, d’un point de vue thermodynamique, définie comme une réaction exothermique. De plus, il a été observé que le séchage et les cycles de gel/ dégel étaient à l'origine d'un effet thermomécanique de "pelage" qui induit des microfractuations des couches de carbonates secondaires permettant à l'eau et au gaz de migrer et de réagir avec des sites donneurs de Mg. L'analyse par spectroscopie FTIR a révélé que des carbonates de magnésium hydratés tels que la nesquehonite se forment parallèlement à la dissolution de la brucite pendant la carbonatation minérale des résidus miniers de nickel riches en brucite. Cependant, les résultats suggèrent aussi que la nesquehonite n'est pas le produit final de carbonate de magnésium hydraté. En effet, une surveillance à long terme (sur 2 ans) d'un matériau déjà carbonaté a révélé que la nesquehonite initiale a évolué en dypingite et en hydromagnésite, dépendamment de l'âge, des cycles de mouillage/séchage et de la profondeur où le carbonate initial s'est formé. Néanmoins, la nesquehonite pourrait maintenir sa stabilité sur des périodes prolongées si elle n'est pas soumise à des conditions humides.
Developing economically feasible strategies for long-term storage of carbon dioxide has become over the past few years a major stake in response to the concerns over global warming. Carbon capture and storage (CCS) is widely believed to be one of the possible scenarios aimed in challenging the global warming phenomenon by targeting the atmospheric CO₂ content. Mineral carbonation – in the platform of CCS – is anticipated to be a premium option for permanent carbon capture and storage owing to the known reactivity of alkaline materials such as magnesium silicates and brucite with carbon dioxide to form stable and environmentally benign carbonates. Passive mineral carbonation of ultramafic mine waste and tailing minerals could be considered as an economically attractive option owing the availability of large amounts of magnesium-rich mining wastes, which are regarded to be virtually free, typically fine grained and highly reactive. Moreover, the energy input of nature is employed in passive mineral carbonation which is likewise free. In this way, CO₂ is mainly dissolved in water resulting from rain and snow season. Metal ions such as Mg²⁺ and Ca⁺ are also leached into the water allowing the formation of metal bicarbonate and consequently formation of metal carbonates. Laboratory experimental works were done in order to identify the dynamics of passive mineral carbonation under environmental conditions prevailing the Quebec region, Canada. A differential diffusion carbonation cell was developed to monitor the kinetics of mineral carbonation under ambient conditions. The kinetic measurements revealed the complex role of water both as reacting medium and moiety in the carbonation pathway. Time-dependent X-ray powder diffraction analysis and scanning electron microscopy reveal formation of transitional, metastable porous, flaky magnesium carbonates which subsequently evolved into less porous nesquehonite layers, which are shown to be responsible for surface passivation despite availability of unreacted brucite. However, surface abrasion was shown to liberate previously carbonated NIMT particles resulting in further carbonation on freshly exposed surfaces. Temperature dependent carbonation tests were performed in the ranges of hot (35 ± 1 °C), laboratory (23 ± 2 °C), low (5 ± 1 °C), and freezing (-5 ± 2 °C) to mimic different seasonal conditions. Temperature had a notable effect on the carbonation kinetics and lowering temperature caused a reaction slowdown despite carbonation is thermodynamically defined as an exothermic reaction. Moreover, it was observed that drying and freeze/thaw cycles were at the origin of a thermomechanical “peel-off” effect which inflicted micro–fractures to the carbonate product layers enabling water and gas to engulf beneath and react with freshly unearthed Mg donor sites. FTIR spectroscopy analysis revealed that hydrated magnesium carbonates such as nesquehonite are being formed parallel to brucite dissolution during mineral carbonation of brucite-rich nickel mining tailings. However, it was observed that nesquehonite is not the ultimate hydrated magnesium carbonate product. Long–term monitoring over 2 years of an already carbonated material revealed that the initial nesquehonite has evolved into dypingite and hydromagnesite depending on age, wetting/drying history and the depth where initial carbonate has been formed. Nonetheless, nesquehonite could maintain its stability over prolonged times if not being subjected to wet/ humid environmental conditions.

The importance of carbonation-induced corrosion has grown in recent years owing to the increasing age of reinforced concrete structures. Among the various remedial treatments for the alleviation of the deterioration process, applications of corrosion inhibitors and surface coatings are highlighted in this thesis owing to their ease of practical application to such structures as railway viaducts. The factors that may enhance the effectiveness of the above two methods in terms of retardation of embedded steel corrosion have investigated as follows: (1) Electrochemical injection of corrosion inhibitors into concrete and (2) Fatigue resistance of surface coatings. (1) After the concentration threshold of electrolytes of three organic base corrosion inhibitors, namely ethanolamine, guanidine, and arginine, required for steel passivation had been investigated by steel immersion tests, the inhibitors were injected into fully/partially carbonated cement-based materials from external electrolytes under the influence of an electrical field. The penetrations of the three inhibitors into the embedded steel cathode were satisfactory in terms of steel inhibition. The field-induced penetration was markedly affected by the pK. values of the inhibitors and the pore solution pH. When the electrochemical treatment was applied to partially carbonated cementitious materials, adequate accumulation of the inhibitors was also attained at the cathode for steel passivation; however, the migration of cationic inhibitors was found to be discouraged in the carbonated region by the lowered current densities effectively applied to this region owing to its large resistivity. Mathematical modelling was performed for simulation of the proposed electrochemical inhibitor injection. A model based on the Nernst-Planck equation, taking account of dissociation equilibria and solubility products of the relevant species, and activity coefficient of molecules, yielded a reasonable agreement with the experimental data. In the application of this model to the 2-D cases, representing the domain with a resistor network that could simulate the current distribution within the material resulted in good prediction of concentrations of the species observed in the experiments. The long-term effectiveness of the electrochemical inhibitor injection was monitored for a reasonably long period, whilst the treated concrete specimens were exposed to cyclic wet/dry conditions. As a result, the injected corrosion inhibitors were found to be effective in promoting steel passivation, and ethanolamine showed the best performance with the smallest steel corrosion rates observed during the experiment. (2) For the investigation of properties of surface coatings affecting their long-term fatigue resistance, fatigue tests with a total of 18 million cycles were carried out under varied temperatures for several coatings bridging a substrate crack whose properties( width and dynamic amplitude) were determined by on-site survey methods. It was found that the thickness and the composition are two important properties of surface coatings that significantly influenced their long-term durability when they were exposed to varied environmental temperatures.

Kyoto University (京都大学)
0048
新制・論文博士
博士(工学)
乙第11664号
論工博第3856号
新制||工||1352(附属図書館)
23477
UT51-2005-D582
京都大学大学院工学研究科材料化学専攻
(主査)教授 檜山 爲次郎, 教授 大嶌 幸一郎, 教授 中條 善樹
学位規則第4条第2項該当

Synthetic and naturally occurring calcium and magnesium carbonate minerals are widely used in a range of industrial and environmental applications where the mineral quality and purity is often critical for their intended use. Hence accurate characterisation of the mineral assemblages is essential. Equally important is an understanding of the chemical and physical pathways leading to mineral formation and their roles in carbon sequestration from greenhouse gases. This study investigates the application of Raman and infrared spectroscopies to Ca-Mg carbonate analysis. A full quantitative calibration has been achieved for quaternary mixtures by Raman spectroscopy (RS) employing monovariable and multivariable methods. The method was validated by X-ray powder diffraction (XRD). The lowest error on component values was obtained by Principal Component Regression with application of Standard Normal Variate. The quantifications show that RS is comparable to XRD. The effect of particle size on the fundamental vibrations of the [CO32-] anion in calcite is investigated by mid-infrared and RS. While the effect of particle size on the infrared signature of internal modes of the [CO32-] anion is well documented, this thesis documents associated changes in Raman spectra as a function of particle size. With decreasing size spectral contrast diminishes and changes in the relative ratios of the internal modes occur. For RS the turnaround from optically thick to thin material occurs in the 42-59 μm size range with further changes occurring at ≤ 5 μm. RS was also utilized to monitor carbonate reaction kinetics after dissolution of [Mg(OH)2] by CO2 sparging in the presence of calcium salts at 35 °C, 30 days duration. Four experiments employing different calcium salts, Ca:Mg ratios and effect of hydromagnesite [Mg5(CO3)4(OH)2.xH2O] seeding were examined utilizing vibrational spectroscopies, XRD and SEM. Results suggest that carbonate mineral paragenesis is driven by geochemical feedback between a range of calcium and magnesium carbonate dissolution-precipitation events where decomposition of nesquehonite [Mg(HCO3,OH)∙2H2O] leads to formation of magnesium carbonate hydrates [Mg5(CO3)4(OH)2.xH2O]. XRD confirmed that these hydrated phases contain 8 and/or 5 molecules of crystalline water. However, RS cannot distinguish these phases. Traces of barringtonite [Mg(CO3)∙2H2O] found at the end of experiments were interpreted as an indicator of incongruent dissolution of nesquehonite. Findings suggest that the Raman active ν1 mode of barringtonite is situated at ca. 1094-1095 cm-1. The limitations of Raman analysis in the context of mineral assemblage quantification, short range ordering and particle size effects are discussed in the context of these findings.

The cement and concrete industry stand for approximately 8% of the global CO2 emissions. The demand of concrete and cement is expected to increase rapidly with the growing world population and increased urbanization. This makes it of the utmost importance for the industry to try to mitigate its emissions. One way to reduce the industry’s environmental impact is by mineral carbonation curing through which CO2 can be sequestered in the concrete. This investigation studied the CO2 uptake of wollastonite (CaSiO3) which can be used for mineral carbonation. The CO2 uptake of different brands of wollastonite powders for different temperatures, pressures and water to solid ratios were tested through carbonation, and the samples were then analyzed through XRD, SEM and particle size analysis. The results showed large differences in CO2 uptake between the brands of wollastonite powders. They also indicate that lower temperatures lead to higher CO2 uptake but also possibly slow down the reaction rate and that higher CO2 pressures seem to increase CO2 uptake though the effect is small. There was significant variation of the effects of the water to solid ratios on CO2 uptake between the tested brands. The morphology of the powders also seemed to be of little relevance as an amorphous and crystalline powder were the two best performing powders, similarly particle size is not indicated by the result to have a large effect on CO2 uptake, though further studies are required to fully determine the effect of the morphology and particle size.
Cement- och betongindustrin står för cirka 8% av de globala koldioxidutsläppen. Efterfrågan på betong och cement förväntas öka snabbt med den växande världsbefolkningen och ökad urbanisering. Detta tyder på hur viktigt det är för industrin att minska sina utsläpp. Ett sätt att minska industrins miljöpåverkan är genom härdning av betongen via mineral karbonatisering, en process som binder in koldioxid i betong. I detta arbete studerades koldioxidupptagningen av mineralen wollastonit (CaSiO3) som kan användas för mineral karbonatisering. Olika märken av wollastonitpulvers koldioxidupptag vid olika temperaturer, koldioxidtryck och vattenhalter testades genom karbonatisering och proverna analyserades därefter genom XRD-analys, SEM-analys och partikelstorleksanalys. Resultaten visade stora skillnader i koldioxidupptagning mellan varumärkena av wollastonitpulver. De visar även att lägre temperaturer leder till högre upptag av koldioxid, men att reaktionshastigheten potentiellt saktar ner vid låga temperaturer. Högre koldioxidtryck verkar öka koldioxidupptagningen men effekten är liten. Det fanns signifikant variation av effekterna av vattenhalterna på koldioxidupptagning mellan de testade varumärkena. Pulvrens morfologi verkade inte ha en stor effekt då ett av de två bäst presterande pulvren var amorft och det andra kristallint. På samma sett verkade partikelstorleken inte ha en stor påverkan på koldioxidupptaget men ytterligare studier krävs för att fullständigt kunna bestämma effekten av morfologin och partikelstorleken.

Le reazioni di carbonatazione di specifiche tipologie di minerali e materiali di diversa origine, come ad esempio malte cementizie o calce, costituiscono un ben noto processo naturale che produce una serie di significativi effetti sugli stessi materiali alcalini, ed in particolare: lo stoccaggio di CO2 mediante la formazione di una fase carbonatica solida e termodinamicamente stabile, la riduzione del pH e modifiche del comportamento alla lisciviazione del materiale, oltre alla variazione di alcune proprietà fisiche e meccaniche. Dato che le cinetiche di reazione sono in genere molto lente in condizioni naturali, per sfruttare alcuni dei sopradetti effetti dell’invecchiamento chimico, come la stabilizzazione chimica di alcune tipologie di residui e lo stoccaggio minerale di CO2, sono stati investigati e sviluppati specifici processi di carbonatazione accelerata selezionando e controllando le condizioni operative in modo tale da incrementare significativamente le cinetiche di reazione. In funzione dell’applicazione del processo e della tipologia di materiale selezionato, sono state sperimentate diverse condizioni operative e differenti tipologie di trattamento (gas-solido, ad umido, ecc.). Il principale obiettivo della presente tesi di dottorato è stato quello di studiare sperimentalmente i processi di carbonatazione accelerata applicati sia a minerali che a residui industriali, così da ottenere nuove indicazioni relative ai meccanismi fondamentali influenzanti il processo per ogni tipologia di materiale analizzato. Lo studio del processo di carbonatazione accelerata di minerali ha riguardato in particolare gli effetti della presenza di CO2 ad alta pressione (fino a 100 bar) e di alcuni sali sulla cinetica di dissoluzione dell’olivina a 120 °C in un reattore agitato a flusso continuo per analizzare se queste sostanze esercitino un effetto positivo o al contrario limitante nei confronti della cinetica di dissoluzione del Mg. Esperimenti di carbonatazione in modalità batch su materiale umidificato (con rapporti liquido/solido <1 l/kg) sono stati eseguiti in condizioni operative blande (temperatura di 30-50 °C e pressione di CO2 pari a 1-10 bar) su residui di incenerimento di rifiuti solidi, in particolare scorie di fondo e ceneri volanti, e su scorie della produzione di acciaio inossidabile. Gli obiettivi di questo lavoro sono stati essenzialmente: la stima della capacità di sequestro ottenibile per ogni tipologia di residuo industriale correlata alla dimensione granulometrica e alla composizione chimica del campione; lo studio dell’influenza dei principali parametri operativi (temperatura, pressione e rapporto liquido solido) sulla cinetica di reazione; e ad ultimo l’analisi degli effetti della carbonatazione sulla mineralogia ed il comportamento alla lisciviazione dei residui. Lo studio della cinetica di dissoluzione dell’olivina ha mostrato che, per tutte le condizioni operative esaminate (pH variabile tra 3 e 8), l’unico fattore controllante il tasso specifico di dissoluzione è risultato essere il pH della soluzione. Dunque la pressione parziale dell’anidride carbonica e la salinità hanno mostrato di influenzare la cinetica di dissoluzione solo indirettamente, variando il valore finale del pH della soluzione. Questo risultato appare significativo, poiché implica che la precipitazione dei carbonati, che ha luogo in presenza di CO2 ad elevata pressione e valori di pH maggiori di 6, e la dissoluzione dell’olivina potrebbero essere teoricamente essere eseguiti nello stesso reattore, senza effetti di inibizione sulla cinetica di dissoluzione del magnesio. Per quanto concerne gli effetti della carbonatazione accelerata sul comportamento alla lisciviazione dei residui alcalini esaminati, significativi risultati sono stati ottenuti in particolare per i residui di incenerimento; per entrambi i materiali, la carbonatazione accelerata ha mostrato di esercitare un importante effetto di immobilizzazione nei confronti di Pb, Zn e Cu, i quali sono risultati essere elementi critici in termini di rilascio per entrambe le tipologie di residui tal quali. Per le ceneri volanti, i risultati ottenuti dalla modellazione geochimica dei dati ricavati dai test di lisciviazione condotti a pH variabile hanno mostrato una variazione nelle fasi minerali controllanti la solubilità di vari elementi tra campioni tal quali e campioni carbonatati. Per le ceneri trattate con CO2, il rilascio di metalli è risultato chiaramente controllato da una varietà di fasi carbonatiche, indicando la potenzialità di questo processo di convertire le iniziali fasi minerali contenenti i metalli in fasi carbonatiche meno solubili, con positive implicazioni per il comportamento ambientale di questa tipologia di residui. Significativi sequestri di CO2 sono stati ottenuti in particolare per le ceneri volanti (250 g/kg residuo); comunque, data l’esiguità dei quantitativi di questo materiale rispetto alle emissioni complessive di CO2 generate tipicamente negli impianti di incenerimento, il processo di carbonatazione su questa tipologia di residui, come sulle scorie di fondo, non risulta essere un processo efficace per lo stoccaggio di CO2. La carbonatazione accelerata di scorie di acciaieria è risultata invece una tecnica potenzialmente molto interessante per il sequestro minerale dell’anidride carbonica generata dallo stesso impianto industriale, per quanto condizioni operative più severe rispetto a quelle adottate nel presente studio dovrebbero essere applicate per incrementare il sequestro di CO2.
Carbonation of specific types of minerals and anthropogenically derived products, such as cement or lime binders, is a well known naturally occurring process which exerts several significant effects on alkaline materials, including specifically: CO2 uptake by formation of a solid and thermodynamically stable carbonate phase, pH decrease and modifications of the leaching behaviour of the material, besides variations of some of its physical and mechanical properties. Since the kinetics of this reaction is very slow at ambient conditions, to exploit some of the above mentioned effects of chemical weathering for developing specific engineered processes, such as waste chemical stabilization and CO2 mineral storage, carbonation processes carried out under selected and controlled operational conditions have been developed, in order to significantly increase the kinetics of the reactions involved. Depending on the application of the process and the selected material, different operating conditions have been employed and several process routes have been tested. The main objective of this doctoral thesis was to investigate the accelerated carbonation process applied both to minerals and industrial residues in order to gain new insight on the key reaction mechanisms for each type of material. Regarding accelerated carbonation of minerals, the effects of the presence of high pressure CO2 (up to 100 bar) and salinity on olivine dissolution kinetics at 120 °C in a stirred flow-through reactor were specifically investigated, in order to assess whether these parameters may exert an enhancing or inhibiting effect on the kinetics of Mg dissolution. Batch carbonation experiments on humidified material (with liquid to solid ratios < 1 l/kg) at mild operating conditions (temperature of 30-50 °C and CO2 pressure of 1-10 bar) were specifically carried out on waste incineration residues such as bottom ash (BA) and air pollution control (APC) residues, as well as on stainless steel slag. The objectives of this study were essentially threefold: to assess the CO2 storage capacity achievable for each type of industrial residue correlating it to the particle size and to the chemical composition of the samples; to study the influence of the main operational parameters (temperature, pressure and liquid to solid ratio) on reaction kinetics; and finally to investigate the effects of carbonation on the mineralogy and leaching behaviour of the residues. The study on olivine dissolution kinetics showed that, under all the examined operating conditions (pH range 3-8), the only factor governing the specific dissolution rate was the pH of the solution. Hence CO2 pressure and salinity appeared to influence olivine dissolution kinetics only indirectly, by affecting the final pH of the solution. This is a significant finding, since it implies that carbonate precipitation, which occurs in presence of high pressure CO2 at pH values above 6, and olivine dissolution could theoretically be carried out in the same reactor without inhibition effects on Mg dissolution kinetics. As for the effects of accelerated carbonation on the leaching behaviour of the studied alkaline residues, significant results were obtained in particular for the BA and APC residues; for both types of materials, accelerated carbonation showed to exert a strong immobilization effect on Pb, Zn and Cu, which were among the critical elements in terms of heavy metal leaching for both types of untreated residues. For APC ash, chemical speciation modelling indicated a change in the solubility-controlling minerals from the untreated to the carbonated ash. For the latter, metal release was found to be clearly controlled by a number of carbonate minerals, indicating the potential of the carbonation process to convert the initial metal-containing minerals into generally less soluble carbonate forms, with positive implications on the environmental behaviour of the ash. Significant CO2 uptakes were achieved in particular for the APC ash (250 g/kg residue); however, owing due to the meagre quantities of this material generated in incineration plants compared to CO2 emissions, accelerated carbonation of this type of industrial residues, as well as of bottom ash, does not appear to be a feasible process for CO2 storage. Accelerated carbonation of stainless steel slag instead, appears to be an interesting technique for carrying out mineral storage of carbon dioxide in industrial facilities using part of the waste streams generated in the same plant, although more severe operating conditions than those used in this work should be applied in order to increase the CO2 uptake of the slag.

La corrosion de l'acier par carbonatation du béton est un phénomène de dégradation majeur des structures en béton armé, qui débute par la dépassivation de l'acier due à l'abaissement du pH de la solution interstitielle. Un modèle est été développé pour estimer la profondeur de carbonatation du béton. Le modèle proposé est un approfondissement de modélisations antérieures, notamment afin de prendre en considération dans les simulations l'effet de la température, tant par l’équation de transfert que par des termes de thermo-activation venant modifier les grandeurs de diffusion de dioxyde de carbone et des ions calcium en phase liquide, la solubilité des hydrates, la viscosité de l’eau, ainsi que l’isotherme hydrique. L’objectif étant d’inscrire la modélisation dans un cadre probabiliste, et donc coûteux en terme de calculs, il a fallu réduire la dimension stochastique du problème. Une méthodologie de choix des paramètres intervenant dans le modèle, basée sur une étude de sensibilité, a été proposée. Un modèle de substitution a été construit, à partir du modèle initial, pour déterminer les grandeurs intervenant dans les expressions des états-limites de dépassivation et d’initiation de la corrosion, s’appuyant sur des développements en chaos polynomiaux.Avec une définition de la probabilité d’amorçage de la corrosion et des modèles de substitution pour la profondeur carbonatée et pour l’amplitude de la variation annuelle du taux de saturation au voisinage des armatures, l’analyse fiabiliste proprement dite a été menée, notamment par rapport à l’incidence des conditions climatiques sur la fiabilité des ouvrages en béton vis-à-vis de la durabilité
Corrosion of the steel by concrete carbonation phenomenon is a major degradation of reinforced concrete structures, which starts with the depassivation of the steel due to the lowering of the pH of the pore solution.A model was developed to estimate the depth of carbonation of concrete. The proposed model is a deepening of previous models, particularly to be considered in the simulations the effect of temperature, both by the transfer equation in terms of thermo-activation that modify dioxide diffusion of sizes carbon and calcium ions in the liquid phase, the solubility of hydrates, the viscosity of water and the water isotherm.The aim is to include in a probabilistic modeling framework, and therefore costly in terms of calculations, it was necessary to reduce the stochastic dimension of the problem. A methodology for the selection of parameters involved in the model, based on a sensitivity analysis, was proposed. An alternative model was built, from the original model, to determine the quantities involved in the expressions of borderline depassivation and corrosion initiation, based on developments in polynomial chaos.With a definition of the boot likelihood of corrosion and substitution patterns for carbonated depth and the amplitude of the annual variation in the degree of saturation in the vicinity of frames, reliability engineer the actual analysis was conducted, including compared to the impact of weather on the reliability of the fabricated vis-à-vis sustainability concrete

La carbonatation minérale est une technique alternative de capture et stockage du CO2 anthropique. L'abondance des matériaux carbonatables sur terre en fait une solution à fort potentiel. En particulier, la carbonatation directe en voie aqueuse a été présentée dans la littérature comme la voie la plus intéressante d'un point de vue énergétique pour la carbonatation minérale ex-situ, à la condition que les cinétiques naturellement lentes de dissolution des silicates magnésiens en phase aqueuse puissent être accélérées de plusieurs ordres de grandeur. Cette thèse étudie en détail les verrous et mécanismes de cette réaction en présence d'additifs organiques tels que l'oxalate, connus pour leur capacité à accélérer la dissolution des silicates magnésiens. Dans un premier temps, la carbonatation en voie aqueuse sans additif d'une olivine modèle est étudiée de manière à mettre en évidence la nature des phénomènes limitants. Ensuite le travail se concentre sur l'étude du rôle de l'additif oxalate à travers des essais spécifiques et une analyse fine de la phase solide. Il est démontré que pour différentes concentrations de suspension et sous 20 bar de CO2, cet additif conduit à la formation de complexes aqueux stables du magnésium avec l'oxalate et à la précipitation de MgC2O4,2H2O (glushinskite), qui empêchent toute précipitation quantitative de magnésite. La simulation géochimique complète du système a été réalisée et a permis d'expliquer les résultats des essais par un mécanisme de dissolution à grain rétrécissant. L'extension de l'étude à un autre silicate (harzburgite) et à d'autres ligands organiques accélérateurs de la dissolution des silicates tels que le citrate et l'EDTA n'a pas non plus permis d'obtenir la formation quantitative de carbonate, à cause d'une forte complexation en phase aqueuse du Mg extrait du minerai. Ces travaux remettent en doute la perspective de développement d'un procédé industrialisable de minéralisation du CO2 en présence d'additifs organiques.

Les principaux objectifs de cette thèse étaient d'évaluer la formulation et la durabilité des géopolymères à base de métakaolin utilisés comme liants dans des matériaux de construction. Les géopolymères sont des matériaux à activation alcaline faisant l'objet d'études de plus en plus nombreuses de la communauté internationale car ils représentent une alternative aux ciments Portland traditionnels. La première partie de cette étude a donc été dédiée à la formulation de ces matériaux réalisés exclusivement à partir de métakaolin flash et de silicate de sodium et a permis de mettre en évidence des performances comparables à un CEM I 52.5. Une caractérisation physico-chimique ainsi qu'une étude du réseau poreux a souligné les différences entre ces deux matériaux et a permis l'élaboration d'une base de donnée sur les caractéristiques du matériau. La réalisation de béton, allant jusqu'à la fabrication en usine de préfabrication, a montré la capacité des géopolymères à remplacer totalement les liants hydrauliques connus, en terme de mise en œuvre et de performances mécaniques. Les questions de durabilité liées au fort taux d'alcalins dans cette matrice ont été traitées par des études sur la réaction alcali-silice et sur la carbonatation. Les résultats obtenus ont permis de conclure que la réaction alcali-silice ne serait pas préjudiciable dans une matrice de métakaolin activé par du silicate de sodium, et que la réaction très rapide des alcalins de la solution interstitielle des pâtes de géopolymère avec le CO2 atmosphérique ne conduirait pas à une chute de pH significative, préjudiciable dans les matrices cimentaires, mais faciliterait l'apparition d'efflorescences
The main objectives of this thesis were to assess the formulation and durability of metakaolin-based geopolymers as a binder for civil engineering materials. Geopolymers are alkali-activated materials; they are increasingly studied by the international community as they represent an alternative to traditional Portland cement. The first part of this study has been dedicated to the formulation of these materials, exclusively made from flash metakaolin and sodium silicate, which has shown performances comparable to a CEM I 52.5. A physicochemical characterization and a study of the porous network have highlighted differences between these two materials and allowed developing a database on the characteristics of the material. The achievement of concrete, up to precast plant, showed their ability to completely substitute known hydraulic binders, in terms of workability and compressive strength. Durability issues related to the high alkali content in this matrix were assessed by studies on alkali-silica reaction and carbonation. The results obtained have concluded that the alkali-silica reaction would not be detrimental in a matrix of metakaolin activated by sodium silicate, and that the very rapid reaction of the alkalis in the geopolymer pastes pore solution with atmospheric CO2 do not lead to a significant drop of the concrete pH, which could be detrimental in cement matrix, but could lead to the appearance of efflorescence on the surfaces of geopolymer

Thesis (M.Sc.)--University of Waterloo, 2003.
"A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Master of Science in Earth Sciences". Includes bibliographical references.

Carbonation is a naturally-occurring process whereby Ca-containing cement phases lose their hydration water and are converted to carbonate minerals by reaction with atmospheric CO₂. As these secondary minerals develop in the microstructure of hydrated cement, porosity, pore-size distribution and permeability are decreased. These are all considered desirable properties in a wasteform. The objective of this study was to examine the effect of carbonation and different pozzolans on the leach performance and mechanical strength of ordinary Portland cement (OPC) wasteforms. Two methods of accelerated cement carbonation were used:

1. A vacuum carbonation method, where wasteforms are placed in an evacuated, sealed cell and subjected to small additions of CO₂ over several days at near vacuum conditions; and
2. A one-step carbonation method, where CO₂ gas is added to the wasteform paste as it is being mixed.

Thirteen elemental constituents of interest to the safety assessments of long-term management of Ontario Power Generation's radioactive waste (Cl, N, S, Se, 13C, Th, Pb, Co, Ni, Cu, Sr, Ba and Cs) were stabilised/solidified via cement mix water. Wasteforms were produced with only OPC, OPC and fly ash, or OPC and silica fume. Most wasteforms were carbonated using one of the carbonation methods. Some wasteforms were not carbonated and served as controls. Wasteforms were subjected to either standard leach tests or compressive strength tests. The extent of carbonation was found to be about 20% for vacuum carbonation method, substantially higher than that for one-step treatment (up to about 10%). For vacuum carbonated wasteforms, carbonation occurred at the outer selvages of the wasteforms, whereas one-step treatment resulted in homogenous carbonation. Generally, compared to uncarbonated OPC wasteforms, vacuum carbonation increased leaching of elements that are anionic in cementitious conditions (Cl, N, S, Se, 13C, Th), decreased leaching of large metal cations (Sr, Ba, Cs, Pb) and had negligible effect on the leaching of the elements that form hydroxyl complexes (Co, Ni, Cu). 13C was the only anionic element whose leachability was reduced by vacuum carbonation, as it may be precipitated in the form CO32- in the large quantity of secondary carbonate minerals produced during the vacuum carbonation process. One-step carbonation did not result in substantial reductions in leachability, compared to uncarbonated OPC wasteforms. However, it had an interesting inverse effect on large metal cation leachability from fly ash- and silica fume-containing wasteforms. A model is presented that proposes that porewater pH changes can have an effect on waste element leachability because 1) the C-S-H Ca/Si ratio is dependent on the equilibrating porewater pH and 2) the degree of ion sorption on C-S-H is dependent on the C-S-H Ca/Si ratio. This model should be tested experimentally as it has important implications on wasteform design. Because of this inverse behaviour, overall neither pozzolan outperformed the other with respect to leachability. Generally, for uncarbonated wasteforms, OPC retained the elements more effectively than OPC with pozzolans. For pozzolans, the leachability of these elements from OPC with fly ash was lower than that of OPC with silica fume. Leaching of Cs was anomalously low from uncarbonated OPC wasteforms, but follow-up experimentation did not corroborate this anomaly. Further testing of these wasteforms to determine how the mineralogical fate of Cs can differ between wasteforms is recommended. All wasteforms tested were of acceptable strength (<0. 689 MPa). Fly ash, and, to a greater degree, silica fume, improved wasteform strength when compared to OPC wasteforms. Carbonation treatments had little effect on wasteform strength. This study has provided much information about the leaching characteristics of a representative set of waste elements from several cement-based wasteform treatments. Although it has not indicated a wasteform design that is ideal for all elements studied, it does suggest that some treatments may be effective for certain groups of elements. Most notably, vacuum carbonation shows promise in improving the immobilisation of isotopes of large metal cations such as Sr, Ba, Cs and Pb as well as 14C (as suggested by 13C here) in cement-based wasteforms.

Intensification of the greenhouse effect from anthropogenic emissions of carbon dioxide and other greenhouse gases have, and will continue to increase the Earth's average global temperature. Intergovernmental demand to minimize human's influence on the global climate was entered into force in 2005, requiring participating industrialized countries to reduce collective greenhouse gas emissions by 5.2% compared to 1990 values. Along with clean energy and efficient system design, carbon dioxide sequestration becomes one of the critical measures in global greenhouse gas mitigation exercises.
Carbon dioxide sequestration through carbonation curing of concrete has the potential to reduce atmospheric carbon dioxide emissions. In the presence of water, carbon dioxide gas readily reacts with the calcium silicate compounds of cement to form calcium carbonate. In this manner, early-age concrete exposed to recovered carbon dioxide could be used as a sink for CO2 storage. The focus of this study was to investigate the potential for carbon dioxide sequestration through carbonation curing of cement paste and concrete compacts, as well as their durability performance in structural applications.
To determine the feasibility of such a method, research was conducted on the carbon dioxide absorption potential and durability of carbonation cured concrete products. Carbonation curing was characterized by the mass of carbon dioxide absorbed, mass of water lost, peak sample temperature, dimensional stability, compressive strength, depth of carbonation and microstructure. Further testing was performed on the carbonation cured products to assess the long-term durability. Long-term durability was characterized by the mass of carbon dioxide absorbed, dimensional stability, freeze/thaw resistance and compressive strength in simulated service exposure. Carbon dioxide absorption in the order of 10% by mass was recorded during early-age carbonation curing. Weathering carbonation shrinkage of concrete samples was reduced by approximately 33% in carbonated samples as oppose to those hydrated. It was also found that carbonation curing reduced the mass loss during freeze/thaw durability testing by 90% over hydration curing.

CO2 absorption behaviour of four commonly used cement based building products: cement paste, concrete block, expanded polystyrene bead (EPB) and cement-bonded cellulose fiberboard are studied. Cement products are manufactured following industry formulation and process, and carbonation curing takes place in a chamber under a pressure of 0.5 MPa, at ambient temperature, for durations of mostly 2 to 8 hours with both pure carbon dioxide gas and flue gas. The flue gas of 13.8% CO2 content is collected from a typical cement kiln without separation. Influencing factors on carbon uptake, long-term strength as well as microstructure development are studied.
It is found that the CO2 uptake ability of those cement-based products follows the same order when exposed to either pure gas or flue gas: fiberboard has the highest uptake capacity, followed by cement paste, bead board and concrete. For fiberboard, the best CO2 uptake in flue gas is 8.1%, it reaches 23.6% if pure gas used. Introduction of cellulose fiber in the fiberboard significantly increases voids volume and cement paste surface area through dispersing the paste onto fiber surface, effectively increasing carbonation reaction sites and thus CO2 uptake.
For pure gas carbonation with high reaction rate, it takes longer time for carbonated products to further develop strength from subsequent hydration, due to the high water loss during carbonation, the densified cement matrix structures and even fast decalcified cement minerals. Fast carbonation with pure gas is detrimental to cement paste in its long-term strength. For flue gas carbonation, both immediate strengths and long-term strength of the products are comparable with those by pure gas carbonation, although with less CO 2 uptake ability.
Five CO2 uptake determination methods are evaluated. Weight gain method is suitable for both pure gas and flue gas carbonation systems. Mass curve method is more suited for pure gas carbonation. For flue gas carbonation, CO2 concentration method agreed well with the weight gain method. Pressure drop method is relatively less accurate because of water vapor generation during carbonation.

The specifications for concrete patch repair mortars usually entail mechanical properties such as compressive strength and tensile strength. However, these properties may not directly relate to the desired performance in relation to durability and prevention of reinforcement corrosion. In addition, the literature does not show any direct relationship between compressive strength and durability properties of concrete and mortars in natural exposure conditions. Relevant performance requirements, such as carbonation resistance and chloride resistance, are usually not considered despite the fact that they have a direct influence on the durability performance of concrete repair mortars. The widespread premature failure of patch repairs which meet the existing compressive strength criteria implies that the use of compressive strength as a performance indicator may not provide a reliable measure of the durability performance. Therefore it can be argued that modern concrete repairs should be based on durability considerations, rather than compressive strength. In this study, an experimental investigation was conducted to determine the durability performance of patch repair mortars. Experimental results were analysed to investigate the correlations that exist between (i) electrical conductivity (Chloride Conductivity Index test) and rate of chloride-ion diffusion (bulk diffusion test), and (ii) gas permeability (Oxygen Permeability Index test) and rate of carbonation (accelerated carbonation test) in patch repair mortars. Eight mortar mixes were used in the investigation, including four commercially available repair mortars and four laboratory-made mortar mixes. To vary the pore structure of the laboratory mixes, different water/binder ratios (0.45 and 0.60) and binder types (100% Portland cement and 50/50 blend of Portland cement/blast furnace slag) were used to make the mortar specimens. Two curing conditions (dry and moist) were adopted with the aim of investigating the influence of curing on durability performance of patch repair mortars. Test results indicate good correlations between electrical conductivity and rate of chloride diffusion (correlation coefficient of 0.9112), and between oxygen permeability and rate of carbonation (correlation coefficient of 0.6751). This correlation was mainly attributed to the fact that these material properties largely depend on the pore structure (specifically the size, connectivity and tortuosity of pores). The good correlation further implies that electrical conductivity and oxygen permeability of repair mortars as evaluated by the CCI and OPI tests may provide a reasonable measure of chloride resistance and carbonation resistance respectively. However, the prediction of chloride ingress and carbonation depth from the electrical and gas permeability properties respectively, ought to be implemented within the range where reasonable correlation can be established. The results also showed that the durability performance of repair mortars in terms of chloride and carbonation resistance is sensitive to material factors, such as w/b ratio, curing type and binder type, which directly influence penetrability. Service life models for predicting chloride ingress and carbonation in the patch repair mortars used in this study were developed based on modified Fickian equations. The prediction profiles for chloride penetration were developed from a modified solution to Fick's second law of diffusion, while the carbonation depth prediction profiles were developed from the square-root-of-time law. Chloride penetration and carbonation depth could be predicted using the developed profiles. Though several assumptions that should be verified and/or modified in future work were made, the modelling results of this study serve as useful framework for evaluating the resistance to chloride ingress and carbonation in patch repair mortars.

Thaumasite form of sulfate attack is having great attention since its discovering in series of foundations supporting motorway bridges in the UK in the late nineties of the last century. This is mainly due to its destructive effect on concrete structures, and the lack of information about its formation mechanisms. This research conducted a study on the effect of wetting and drying, carbonation and the effect of water to cement ratio on the thaumasite formation, and whether these effects are linked with other parameters such as cement type and sulfate concentration or not. 10 different mixes were produced based on four binder types in this study namely 100% CEM I, 90% CEM I + 10% Limestone filler, 50% CEM I + 50 %PFA and 30% CEM I +70%GGBS. A series of mortar samples of two types were prepared 50 mm cubes and 40 × 40 × 160 mm prisms. The samples were kept in three different solutions contain BRE DS3,DS4 based on magnesium sulfate MgSO4.7H2O in addition to deionised water. Two different temperatures 5°C and 20°C were also used to confirm the formation of thaumasite at ambient temperatures (20°C) and to accelerate its formation at 5°C. The effect of wetting and drying cycles on thaumasite formation was studied and compared with samples immersed continuously in the same solutions for 12 months. Powder-sulfate interaction and its effect on thaumasite formation was studied by grinding mortar samples to a fine powder, thus eliminating the permeability effect and enabling physical factors that affect the rate at which solutions can be transferred through the mortar to be separated from chemical factors that affect the rate at which the chemical reactions take place. Visual observations, mass and length changes were used to assess the mortar deterioration, along with X-ray diffraction, infra-red spectroscopy and SEM that were used to determine the mineralogy of deterioration products. For the cyclic wetting and drying exposure regime the results showed that wetting and drying cycles significantly delayed thaumasite formation compared with control specimens. For powder samples, it is found that thaumasite is readily formed in these powders after 3 months of exposure to sulfate solutions including GGBS and PFA samples, on the other hand cubes and prisms, exposed to the same solutions for 24 months showed no signs of deterioration. Thermodynamic modelling was used to predict the deterioration products for powders samples and good agreement between predicted and observed results was found.

Thaumasite formation in carbonated Ordinary Portland Cement (OPC) and carbonated Portland Limestone Cement (PLC) was investigated. The study was motivated by the question of whether or not the carbonation curing of concrete would make final concrete products more vulnerable to low temperature sulphate attack. The Thaumasite Form of Sulphate Attack (TSA) was discovered in concrete containing limestone powder exposed to sulphates in cold and damp environments. Carbonation curing of concrete could produce a large quantity of calcium carbonates in OPC and PLC, making them analogous to the concretes containing limestone powder. The vulnerability of carbonated concretes to thaumasite formation was thus studied. It was surprisingly found that carbonation curing at early age had significantly improved the resistance to TSA in both OPC and PLC. The improved resistance of carbonated cements was attributed to a decrease in pH at the surface of the specimens, a reduction in calcium hydroxide due to the carbonation reaction, the highly crystalline nature of calcium carbonates produced by carbonation, and the improved resistance to gas permeability.
La formation de thaumasite dans du ciment Portland ordinaire et du ciment Portland comportant du carbonate de calcium qui furent sujet à la carbonatation fut vérifiée. La motivation de la recherche est de déterminer si le béton carboné est vulnérable à une attaque chimique en présence de sulfates, lorsque exposé à de basses températures. La formation de thaumasite fut remarquée dans du béton contenant du ciment Portland comportant du carbonate de calcium. La carbonatation du béton produit aussi une grande quantité de carbonate de calcium, ce qui peut rendre ce type de béton plus vulnérable à la formation de thaumasite. La vulnérabilité du béton sujet à la carbonatation et exposé au thaumasite fut donc étudiée. Il fut surprenant de trouver que le béton sujet à la carbonatation avait une résistance améliorée à la formation de thaumasite. L'amélioration de la résistance du béton carboné fut attribuée à une réduction du pH à la surface des spécimens, une diminution de l'hydroxyde de calcium présent dans le ciment due à la réaction de carbonatation, la structure cristalline des carbonates formés par carbonatation, et la nature moins perméable des spécimens sujets à la carbonatation.

L'objectif principal de ce travail est de développer un essai accéléré de corrosion dans le béton armé capable de bien représenter les conditions de développement de la corrosion en environnement réel. Le test reproduit les phases d'initiation et de propagation. La phase d'initiation correspond à la période durant laquelle les agents agressifs (le CO2 ou les ions chlorure) pénètrent à travers le béton d'enrobage jusqu'à atteindre l'armature. La phase de propagation se produit une fois que le béton entourant les armatures est totalement pollué par les agents agressifs et les conditions nécessaires étant réunies, la corrosion de l'acier démarre. Dans cette étude la phase d'initiation est accélérée en exposant le béton dans une enceinte avec un taux de CO2 de 50% et une humidité relative de 65%. Dans la phase de propagation la corrosion de type galvanique est accélérée en augmentant le rapport de surface entre cathode et anode. Les échantillons utilisés sont composés de deux cylindres de béton imbriqués. Le cylindre interne contient une seule armature et le béton d'enrobage est entièrement carbonaté. Autour de cette éprouvette un cylindre externe de béton est alors coulé avec quatre armatures régulièrement réparties sur sa périphérie. Le béton du cylindre externe est préservé de la carbonatation. Les barres externes sont donc dans un état passif et la barre interne dans un état actif. La distance entre chaque barre du cylindre externe et la barre du cylindre interne est identique. La connexion entre une ou plusieurs barres passives et la barre active génère un courant galvanique qui va entraîner la corrosion de la barre active. En jouant sur le nombre de barres passives connectées on peut donc faire varier l'intensité du courant galvanique et donc accéléré ou ralentir la corrosion. Pour éviter de réaliser un trop grand nombre d'essais en laboratoire, la conception de l'essai et la définition de sa sensibilité sont effectuées par le biais de simulations numériques à l'aide du logiciel commercial COMSOL Multiphysics(r) qui utilise les éléments finis. La vitesse de corrosion de l'acier dans le béton est déduite de la densité de courant à la surface de l'acier, qui est elle-même reliée au potentiel. La modélisation numérique de la corrosion dans le béton implique la résolution de deux équations simultanément, l'équation du transfert de charge et la loi d'Ohm, avec des conditions aux limites appropriées. Le comportement du système électrochimique est décrit par l'équation de Butler-Volmer pour les aciers actifs et passifs. Les paramètres nécessaires à l'implémentation des équations de Butler-Volmer (constantes de III)
This work presents the results of an experimental and numerical study of an accelerated corrosion test, performed in laboratory. The acceleration of corrosion in reinforced concrete is due to the elimination of initiation phase by an artificial environment technique. The initiation phase takes years to undergo, if it is accelerated, the studies can be focused on the kinetics of steel corrosion in concrete. For acceleration of initiation phase the concrete samples were kept in a carbonation chamber set at 50% CO2 and 65% RH. The geometry used in this test is comprised of two concrete cylinders. The inner concrete cylinder is carbonated and has a steel bar in the center, the bar is depassivated and acts as anode (A). The outer cylinder comprised of non-carbonated concrete, casted around the inner carbonated cylinder. Four steel bars are embedded around centered bar at given distance in non-carbonated concrete; these bars are in passive state and act as cathodes (C). The presence of these passive bars will allow changing the cathode surface and hence C/A ratio, by connecting different number of bars to active bar. The geometry for the test is defined by numerical simulations using COMSOL Multiphysics(r) software, and its sensitivity in particular the effect of C/A ratio, is defined by numerical experiments. In order to provide reliable inputs for the model the corrosion parameters are measured. Once the geometry of the samples is defined an extensive experimental program involving 15 samples is carried out. Despite the higher resistivity of carbonated concrete layer, the measurements of macrocell current revealed high levels of galvanic corrosion rate even in case of low C/A ratio. With the increase in C/A ratio the higher macrocell current levels are achieved in propagation phase. The importance of galvanic coupling in carbonationinduced corrosion is therefore also experimentally demonstrated. The accordance between numerical and experimental results is demonstrated regarding both potential field and C/A influence on macrocell current. This coherence highlights the relevance of the numerical modeling

L’encrassement biologique des revêtements de façade constitue un problème esthétique et économique. Parmi les microorganismes impliqués, les algues sont les plus répandues. Ce travail avait pour but d’étudier expérimentalement l’influence des paramètres intrinsèques (porosité, rugosité et carbonatation) de mortiers à base de ciment sur leur bioréceptivité et de modéliser le développement du biofilm d’algues.Pour étudier l’effet de ces paramètres sur la biodétérioration des mortiers, un essai accéléré de laboratoire a été développé. Les travaux ont été réalisés avec l’algue verte Klebsormidium flaccidum fréquemment identifiée dans les prélèvements réalisés sur des façades colonisées. Les résultats montrent qu’une augmentation de rugosité et une diminution du pH de surface par carbonatation favorisent l’encrassement des mortiers par les algues.Un modèle inspiré de la loi d’Avrami a permis de modéliser le phénomène de colonisation par les algues. Deux processus interviennent dans le mécanisme de colonisation : l’accrochage (ou « germination ») et la croissance des algues. Les paramètres cinétiques représentant ces processus ont été déterminés et révèlent l’importance de la rugosité et de la carbonatation sur la constante de vitesse de « germination ».L’exposition d’échantillons en extérieur a été également réalisée. Les résultats obtenus permettent de retrouver partiellement le comportement des matériaux en laboratoire même si le démarrage de la colonisation semble être affecté par les conditions climatiques
Biofouling of wall coatings is an aesthetic and economic problem. Among microorganisms involved, the algae are the most involved. This work aimed to study experimentally the influence of intrinsic parameters (porosity, roughness and carbonation) of a cement-based mortar on its bioreceptivity and to model the development of algae.To study the algal biodegradation, an accelerated laboratory test was developed. This work was carried out with the green alga Klebsormidium flaccidum frequently identified in samples taken on colonized facades. The results show that an increase in roughness and a decrease in surface pH by carbonation of mortars promote fouling by algae.A model based on Avrami's law was used to simulate the algal colonization. Two processes involved in the mechanism of colonization: the attachment (or "germination") and the growth of algae. The kinetic parameters representing these processes have been determined and reveal the importance of the roughness and the carbonation on the constant rate of "germination".Exposure of samples in nature was also carried out. The results obtained allow recovering partially the behavior of materials in the laboratory test even if the start of colonization seems to be affected by weather conditions

Le béton armé est sans conteste le matériau le plus utilisé dans la construction, et permet de réaliser la plupart des infrastructures dans tous les pays du monde. Cependant, sa durabilité peut être compromise de façon prématurée par la corrosion des aciers, qui est la pathologie considérée comme la plus dangereuse vis-à-vis du maintien de l'intégrité des ouvrages de Génie Civil. Afin d'obtenir une meilleure résistance face au risque de corrosion, l'acier conventionnel (AC) peut être soumis à divers traitements, dont les plus connus sont le recouvrement superficiel par d'autres matériaux métalliques à base de zinc (AG), ou par des revêtements doubles métal-polymères (AD). Cependant, il existe aussi des barres d'acier thermiquement traitées (ATT) qui ne sont actuellement quasiment pas utilisées en tant qu'armatures. De ce fait, leur comportement face aux mécanismes de détérioration comme la corrosion en milieu cimentaire causée par les chlorures ou la carbonatation est encore très peu connu. Dans ce travail, le comportement des différentes barres d'acier mentionnées ci-dessus a été étudié. Des éprouvettes prismatiques de béton, incluant ces types d'armatures, ont été fabriquées avec deux rapports E/C : 0,45 et 0,65. Avant leur utilisation, les barres ont été caractérisées mécaniquement et métallographiquement. Ensuite, les éprouvettes ont été placées dans différentes conditions d'exposition : un environnement urbain/industriel ou côtier, et un environnement contrôlé en laboratoire. Des mesures du potentiel de corrosion, de résistance de polarisation linéaire, et de spectroscopie d'impédance électrochimique ont été mises en œuvre durant la période d'exposition. Pour chaque série, la teneur critique en chlorures a été déterminée, et la progression de la profondeur de carbonatation a été suivie. En outre, en induisant un couple galvanique par effet de la carbonatation, des mesures originales du comportement électrochimique de ces barres ont été effectuées puis une analyse, en s'appuyant sur une modélisation en éléments finis, en a été faite. Dans l'environnement contrôlé en laboratoire, l'ordre de dépassivation des différentes barres exposées a été observé de façon similaire pour les deux rapports E/C, à savoir : ATT, AC, AG et enfin AD. Une teneur critique en chlorures plus élevée a été obtenue pour les barres AG et AD. Cependant, lors de l'inspection visuelle, les dommages causés sur les armatures AG étaient plus élevés que sur les autres types de barres. Enfin, durant l'étape de propagation, la densité de courant de corrosion des barres ATT et des barres AG s'est révélée inférieure
Corrosion of reinforcing bars in concrete is considered as the most important problem that affects the integrity of the civil structures. In order to obtain a better resistance to corrosion, various superficial processes as coatings with zinc (AG) or such as the dual covering metallic-polymeric (AD) are applicate to ordinary steel bars (AC). On the other hand, steel bars with thermal treatments (ATT), principally developed as an alternative to improve the mechanical properties without the use of ferroalloys, are not used in concrete. The behavior of these kinds of bars in front of mechanisms of deterioration as the corrosion induced by chlorides or carbonation has not yet been studied. In this work, all these various steel bars (AG, AD, AC and ATT) were embedded in prismatic specimens of concrete made with two ratio water/cement: 0.45 and 0.65. Previously, steels bars were characterized by mechanical tests and metallographic identifications. Then, specimens were placed in several sites of exposition: urban/industrial environment, or coastal environment, or controlled atmosphere in laboratory. During these expositions, measurements of corrosion potential, linear polarization resistance, and electrochemical impedance spectroscopy were regularly carried out. For each type of steel bar, chloride threshold level and progress of the carbonation depth were determined. Furthermore, by means of the induction of a galvanic couple during design of new samples, the electrochemical behavior of the steels bars AC, ATT and AG was followed up experimentally and then analyzed with finite element model. It was founded that the different steels bars exposed in controlled atmosphere of laboratory followed a same sequence in depassivation for both ratios water/cement: ATT, AC, AG and AD. The chloride thresholds were higher for steels bars AG and AD. However, visual inspection showed that the morphology of damages caused on AG bars was most important compared with the other steel bars. In the propagation phase, the corrosion current density of the ATT bars was lower, even to that obtained by the AG bars