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 CO&#8322;. 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: <ol> <li>A vacuum carbonation method, where wasteforms are placed in an evacuated, sealed cell and subjected to small additions of CO&#8322; over several days at near vacuum conditions; and <li>A one-step carbonation method, where CO&#8322; gas is added to the wasteform paste as it is being mixed. </ol> 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.

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 CO&#8322;. 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: <ol> <li>A vacuum carbonation method, where wasteforms are placed in an evacuated, sealed cell and subjected to small additions of CO&#8322; over several days at near vacuum conditions; and <li>A one-step carbonation method, where CO&#8322; gas is added to the wasteform paste as it is being mixed. </ol> 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.

The use of lime mortars with pozzolanic additives is of special importance for the repair of historic masonry. In this study, the effect of pozzolanic materials on the final characteristics of mortars was investigated. Metakaolin, fly ash and historic brick powder were used as pozzolanic materials in mortar mixes with varying binder:pozzolan:aggregate ratios. Historic mortar samples from rubble stone masonry of Kahta Castle, a medieval structure in close vicinity of the Nemrut Dag Monument, were also investigated to serve as a starting point for the preparation of repair mortars. Physical and physicomechanical tests, optical microscopy, chemical tests, SEM-EDX and XRD analyses were used to assess the properties of the historic mortars and repair mortars. Fat lime was found to be used in historic mortars with a high binder/aggregate ratio. They were observed to have relatively low density and high porosity with an average compressive strength of 7.4 MPa. Historic mortars were determined to have relatively high water vapour permeability and low water impermeability characteristics. In repair mortars setting was found to be predominantly due to carbonation along with pozzolanic reactions. However, abundant presence of stratlingite in mortars with added metakaolin indicated that the pozzolanic reactions preceded carbonation in those mortars. Use of pozzolanic materials increased the uniaxial compressive strength and modulus of elasticity of mortars compared with control samples. Using the same binder:pozzolan:aggregate ratio, highest increase was observed on mortars prepared with added fly ash at the end of 90 days. Durability parameters of repair mortars defined as wet to dry compressive strength were in the very good to excellent range according to Winkler&rsquo / s classification. By using fly ash, design of lime mortars with high water impermeability and high water vapour permeability characteristics was accomplished.

Devido à preocupação com a durabilidade das estruturas de concreto armado surgiram novas linhas de pesquisa destacando-se, dentre elas, a previsão de vida útil. Estes estudos deram origem a diversos modelos que tentam estabelecer o comportamento do concreto quando exposto a ambientes agressivos durante um determinado período. Existem várias maneiras de se modelar este comportamento: com base em resultados obtidos em experiências anteriores; a partir de ensaios de degradação acelerados; por métodos determinísticos e probabilísticos ou estocásticos. A estimativa de vida útil das estruturas de concreto empregando dados de ensaios acelerados é recomendada pela ASTM E-632 (1996) desde que estes sejam correlacionados com resultados de ensaios não acelerados ou naturais. A correlação entre estes ensaios possibilita a determinação dos coeficientes de aceleração, os quais expressam o número de vezes em que o ensaio acelerado representa o fenômeno de degradação natural. Dentro deste contexto o presente trabalho avalia a carbonatação do concreto com e sem adição de sílica ativa exposto a degradação natural e acelerada, verificando também a influência do teor desta adição e da relação água/aglomerante na carbonatação. Em paralelo foram determinados os coeficientes de carbonatação (kc) e de aceleração (αa). Os concretos estudados possuem relação água/aglomerante de 0,30; 0,35; 0,45; 0,60 e 0,80 e teor de adição de 0; 5; 10; 15e 20%. A carbonatação natural das amostras foi avaliada após 7 anos de exposição ao CO2, tendo como ambiente de degradação a cidade de Porto Alegre, RS. Os dados de carbonatação acelerada foram obtidos aos 7, 28, 63 e 98 dias de exposição ao CO2 com concentração de 5%, temperatura de 25°C e umidade relativa (UR) de 70%. Para o ensaio acelerado, baseado em análise estatística por meio de regressão múltipla não-linear, os resultados apontaram que a adição de sílica ativa em dosagens com relação água/aglomerante elevada aumenta a profundidade de carbonatação do concreto. Para a relação água/aglomerante de 0,80 com 0 e 20% de adição de sílica ativa, os coeficientes de aceleração obtidos foram de 31,15 e 35,49, respectivamente. / New researches has been appeared with the concern of reinforced concrete structures durability, standing out the service life prediction. These studies creates some models that establish the concrete performance when exposed to an aggressive environment. There are several ways to modeling this performance: with results obtained in previous tests; with accelerated degradation tests; or deterministic and stochastic methods. The concrete structures service life prediction using short term test data are recommended by ASTM E-632 (1996) since these are correlated with long term test results. The correlation among these tests makes possible the acceleration coefficient determination, which express how the accelerated tests represents the natural degradation phenomenon. In this sense, this work evaluate the concrete carbonation with and without silica fume exposed to natural and accelerated test, verifying the influence of silica fume tenor in this material and water – binder ratio in the carbonation. In addition to this, were determined the carbonation (kc) and acceleration coefficients (αa). The concretes studied has a 0,30; 0,35; 0,45; 0,60 and 0,80 water-binder ratio and 0; 5; 10; 15 and 20% addition tenor. The samples natural carbonation was analyzed after 7 years of CO2 exhibition from Porto Alegre city environment degradation. The accelerated carbonation data were obtained in 7, 28, 63 and 98 days of CO2 exhibition with 5% concentration, temperature of 20°C and humidity of 60%. In accelerated tests, based on statistical analysis through nonlinear estimation multiple regression, the results showed that the silica fume addition in high water-binder ratio mixtures increases the concrete carbonation depth. For water-binder ratio 0,80 with silica fume addition of 0 and 20%, the acceleration coefficients obtained were 31,15 and 35,49, respectively.

L’objectif de ce travail de thèse porte sur le stockage chimique du CO2 émis par l’industrie sidérurgique. Le processus de carbonatation directe de l’olivine et l’influence des conditions opératoires est évaluée afin d’optimiser le rendement de la réaction. Cependant, pour une acceptabilité environnementale et une rentabilité économique du projet, la récupération et la valorisation des produits de la carbonatation doivent toutes deux être considérées. La séparation des particules de chromite contenues dans l’olivine et inertes au cours de carbonatation, est tout d’abord étudiée par flottation en amont de la carbonatation. L’expérience de carbonatation montre qu’il est également possible d’extraire la chromite par séparation magnétique. Le rendement de carbonatation étant limité à 40 %, la séparation gravimétrique par sédimentation est alors envisagée pour récupérer les particules d’olivine résiduelle contenues dans les produits de la réaction, afin de les recycler dans le processus de carbonatation. Le tamisage des produits permet ensuite de concentrer les carbonates de métaux dans la fraction de particules de taille inférieure à 40 µm, tandis que la fraction comprise entre 40 et 106 µm contient davantage de silice. Cependant, la coprécipitation de carbonates mixtes liée à la présence de fer et de nickel inclus dans la matrice de magnésium compromet la purification et la valorisation optimale des produits de la carbonatation. De plus, la formation d’une couche de passivation en surface des particules limite la conversion de l’olivine. Un prétraitement de l’olivine est alors envisagé pour la lixiviation sélective du nickel en solution ammoniacale. Enfin, la carbonatation indirecte qui consiste en la dissolution préliminaire de l’olivine et la précipitation sélective des espèces avec un contrôle du pH de la solution se révèle être une alternative intéressante, imaginée pour l’augmentation du rendement de la carbonatation et l’obtention de produits de pureté satisfaisante / This work deals with the study of direct carbonation of olivine in solution, for the chemical transformation of CO2 emitted by the industries. The influence of operating conditions is evaluated in order to optimize the yield of the reaction. However, for environmental acceptability and economic viability of the project, the beneficiation of recoverable metals and products is considered. Chromite particles contained in olivine are unreactive during the carbonation reaction: the separation is developed by flotation upstream of the reaction. According to the results, the extraction of chromite by magnetic separation is also conceivable. Gravimetric separation by sedimentation is considered to recover residual olivine in the reaction products, in order to recycle them in the carbonation process. Products sieving allowed to concentrate carbonates (less than 40 µm) and silica (between 40 and 106 µm). However, the co-precipitation of mixed carbonates due to the presence of iron and nickel included in the magnesium matrix, compromises the purification and the optimal valorization of the solids. Moreover, the formation of a passivation layer on the particles surface limits the conversion of olivine. Pretreatment of olivine is envisaged for the leaching of nickel in ammoniac solution. Besides, preliminary dissolution of olivine and selective precipitation of species with pH control of the solution can be an interesting alternative for higher carbonation extent and more efficient purification of the products

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. / Mineral carbonation is an interesting option for mitigation of anthropogenic CO2 emissions. Direct aqueous mineral carbonation has been presented by many as a promising strategy for ex-situ mineral carbonation, on the basis that organic additives such as oxalate increase the rate and extent of dissolution of magnesium silicates several folds. This thesis discusses and extends the current understanding of this process through geochemical modelling and detailed solid characterization. First, mineral carbonation is investigated in water alone, without additives, in order to understand and quantify the actual limitations of the process with specific magnesium silicate ores. Dissolution kinetics being critical with this process, the role of disodium oxalate as a dissolution accelerating agent is thoroughly examined with olivine, through dedicated experiments and comprehensive analysis of both solid and liquid phases. Under 20 bar of CO2, and irrespective of the conditions used, it is found that the formation of strong oxalate-magnesium complexes in solution and precipitation of MgC2O4,2H2O (glushinskite) impede any chance of precipitating significant amounts of magnesium carbonate. Geochemical modelling permits successful simulation of the dissolution kinetics of magnesium silicate using a shrinking particle model. Other promising ligands from a dissolution perspective, namely citrate and EDTA, were also investigated. Contrary to oxalate, these do not form any solid by-products with magnesium, and yet they do not produce better carbonation results. The results and findings from this work cast strong doubts about the possibility of developing a viable direct aqueous mineral carbonation process using organic salts.

Dans le cadre du développement des réacteurs nucléaires à neutrons rapides refroidis au sodium, des études sont menées sur les conséquences d’un feu de sodium, et sur l'impact toxicologique de rejets éventuels d’aérosols vers l’atmosphère. La carbonatation des aérosols issus d’un feu de sodium entraîne une diminution de leur toxicité, à partir de leur rejet sous forme d'hydroxyde de sodium (NaOH). L’objectif est de développer et de valider expérimentalement un modèle cinétique de carbonatation des aérosols de NaOH. L’adaptation d’un modèle cinétique basé sur l'absorption réactive du CO2 atmosphérique et par la théorie du double film permet de décrire la carbonatation des aérosols de NaOH, initialement sous forme de gouttelettes de soude. Ce modèle définit les caractéristiques initiales des aérosols de soude en équilibre avec l'atmosphère. Il a été appliqué en considérant l'absorption du CO2 à la surface externe des particules. L’ensemble des variables du modèle ont été décrites et leurs équations explicitées. La validation du modèle cinétique a motivé la mise en place d’un dispositif expérimental dédié au suivi du comportement chimique d’aérosols issus d’un feu de sodium, dans des conditions contrôlées d’atmosphère réactive et de prélèvement d’aérosols. L’exploitation des nouvelles données expérimentales montre la compétition entre l’influence de la température, de la pression partielle en eau et en CO2. La confrontation des résultats expérimentaux avec le modèle développé a permis de le valider pour des humidités relatives supérieures à 30%. Enfin, le modèle cinétique a été explicité sous la forme d’une expression analytique pour une utilisation associée aux calculs de dispersion atmosphérique. / As part of the development of 4th generation Sodium cooled Fast Reactors, studies are conducted on the consequences of a sodium fire, including the toxicological impact of possible releases of aerosols into the atmosphere. The carbonation of aerosols from a sodium fire results in a decreased toxicity, from their release point in sodium hydroxide (NaOH). The objective is to develop and experimentally validate a kinetics model of NaOH aerosols carbonation. The kinetic model based on the reactive absorption of atmospheric CO2 and using the double film theory enables to describe the carbonation of NaOH aerosols, initially formed as soda droplets. This model defines the initial aerosol characteristics of soda in equilibrium with the atmosphere. It is applied by considering the absorption of CO2 at the particle’s external surface. All the model variables are described and their equations explained. The validation of this kinetic model has motivated the development of an experimental device dedicated to the monitoring of physicochemical behavior of aerosols from a sodium fire with a better control of conditions of reactive atmosphere and of aerosols sampling. The new experimental data show the competition between the influence of temperature, partial pressure of water and of CO2. The comparison between the experimental results validates the kinetic model based on reactive absorption for relative humidity over 30%. Finally, the kinetic model was adapted into the form of an analytic expression for its use in association with the atmospheric dispersion calculation.

Este trabalho apresenta um estudo de corrosão da armadura induzida por carbonatação em concretos com elevados teores de cinza volante, utilizando-se para isso a técnica de resistência de polarização. Selecionou-se para a pesquisa quatro relações água/aglomerante (0,44, 0,48, 0,55 e 0,65) e quatro teores de substituição de cimento (clínquer + gesso) por cinza volante (0,15, 30 e 45%). Foi também escolhido para comparação o cimento CPIV 32. Os corpos-de-prova foram curados por 28 dias, sazonados por 22 dias e então carbonatados em ambientes com 5 e com mais de 50% de CO2, por um período 223 dias. Após, os concretos foram parcialmente imersos durante 35 dias. Os ensaios de resistência de polarização foram feitos durante todo o período de carbonatação e imersão parcial. Paralelamente, romperam-se corpos-de-prova por compressão axial, determinou-se profundidades carbonatadas e monitorou-se as massas dos corpos de prova usados para ensaio de resistência de polarização. Realizou-se também análises complementares de microestrutura, utilizando-se as técnicas de difração por raios-X, fluorescência de raios-X, microscopia eletrônica de varredura por elétrons retroespalhados, análises com EDS (Energy Dispersive Spectroscopy) e espectroscopia Raman. Os experimentos realizados possibilitaram identificar o efeito significativo da variação do teor de cinza volante para a corrosão da armadura. Os resultados assim obtidos também permitiram constatar o efeito significativo do teor de CO2 para os resultados de potencial de corrosão e de densidade de corrente de corrosão. Os resultados obtidos neste trabalho evidenciaram a importância de cada vez mais se buscar a realização de ensaios que reproduzam o máximo possível condições de exposição das estruturas no ambiente. / This work presents a study of corrosion of reinforcing steel induced by carbonation in concretes containing fly ash. Four water-binder ratios (0,44; 0,48; 0,55 and 0,65) and four clinker (clinker + gypsum) replacements of fly ash (0;15; 30 and 45%) were selected. It was also chosen CPIV 32 cement to study. After 28 days kept in the moist curing room, the samples were carbonated during 223 days in a CO2 atmosphere with 5% and more than 50% of CO2 After the carbonation period, the concretes samples were partially immersed during 35 days in potable water. Linear polarization resistance tests were made during the whole carbonation and partial immersion periods. Moreover, compressive strength tests were made, depth of carbonation in concretes were determined and the masses of samples used in linear polarization resistance tests were monitored. Even microstructure complementary analyses were made using X-ray diffraction (DRX) techniques, X-ray fluorescence (FRX), electronic microscopy using backscattered electrons and energy dispersive spectroscopy analyses and Raman spectroscopy. Based on the accomplished tests it’s possible to identify the significant effect of the fly ash level replacement in concrete on the reinforcing steel corrosion. The thus gotten results also had of allowed evidencing the significant effect of the CO2 concentration on the results of corrosion potential and corrosion current density.

Devido à preocupação com a durabilidade das estruturas de concreto armado surgiram novas linhas de pesquisa destacando-se, dentre elas, a previsão de vida útil. Estes estudos deram origem a diversos modelos que tentam estabelecer o comportamento do concreto quando exposto a ambientes agressivos durante um determinado período. Existem várias maneiras de se modelar este comportamento: com base em resultados obtidos em experiências anteriores; a partir de ensaios de degradação acelerados; por métodos determinísticos e probabilísticos ou estocásticos. A estimativa de vida útil das estruturas de concreto empregando dados de ensaios acelerados é recomendada pela ASTM E-632 (1996) desde que estes sejam correlacionados com resultados de ensaios não acelerados ou naturais. A correlação entre estes ensaios possibilita a determinação dos coeficientes de aceleração, os quais expressam o número de vezes em que o ensaio acelerado representa o fenômeno de degradação natural. Dentro deste contexto o presente trabalho avalia a carbonatação do concreto com e sem adição de sílica ativa exposto a degradação natural e acelerada, verificando também a influência do teor desta adição e da relação água/aglomerante na carbonatação. Em paralelo foram determinados os coeficientes de carbonatação (kc) e de aceleração (αa). Os concretos estudados possuem relação água/aglomerante de 0,30; 0,35; 0,45; 0,60 e 0,80 e teor de adição de 0; 5; 10; 15e 20%. A carbonatação natural das amostras foi avaliada após 7 anos de exposição ao CO2, tendo como ambiente de degradação a cidade de Porto Alegre, RS. Os dados de carbonatação acelerada foram obtidos aos 7, 28, 63 e 98 dias de exposição ao CO2 com concentração de 5%, temperatura de 25°C e umidade relativa (UR) de 70%. Para o ensaio acelerado, baseado em análise estatística por meio de regressão múltipla não-linear, os resultados apontaram que a adição de sílica ativa em dosagens com relação água/aglomerante elevada aumenta a profundidade de carbonatação do concreto. Para a relação água/aglomerante de 0,80 com 0 e 20% de adição de sílica ativa, os coeficientes de aceleração obtidos foram de 31,15 e 35,49, respectivamente. / New researches has been appeared with the concern of reinforced concrete structures durability, standing out the service life prediction. These studies creates some models that establish the concrete performance when exposed to an aggressive environment. There are several ways to modeling this performance: with results obtained in previous tests; with accelerated degradation tests; or deterministic and stochastic methods. The concrete structures service life prediction using short term test data are recommended by ASTM E-632 (1996) since these are correlated with long term test results. The correlation among these tests makes possible the acceleration coefficient determination, which express how the accelerated tests represents the natural degradation phenomenon. In this sense, this work evaluate the concrete carbonation with and without silica fume exposed to natural and accelerated test, verifying the influence of silica fume tenor in this material and water – binder ratio in the carbonation. In addition to this, were determined the carbonation (kc) and acceleration coefficients (αa). The concretes studied has a 0,30; 0,35; 0,45; 0,60 and 0,80 water-binder ratio and 0; 5; 10; 15 and 20% addition tenor. The samples natural carbonation was analyzed after 7 years of CO2 exhibition from Porto Alegre city environment degradation. The accelerated carbonation data were obtained in 7, 28, 63 and 98 days of CO2 exhibition with 5% concentration, temperature of 20°C and humidity of 60%. In accelerated tests, based on statistical analysis through nonlinear estimation multiple regression, the results showed that the silica fume addition in high water-binder ratio mixtures increases the concrete carbonation depth. For water-binder ratio 0,80 with silica fume addition of 0 and 20%, the acceleration coefficients obtained were 31,15 and 35,49, respectively.

Este trabalho visa à quantificação da carbonatação em argamassas de cimento branco em comparação à carbonatação de argamassas de cimento cinza convencional. O estudo experimental foi dividido em 2 fases distintas. Na primeira foram produzidos 12 cimentos pela substituição de 0, 5, 10 e 20% de 3 clínqueres de diferentes procedências por um calcário calcítico. Nesta etapa do trabalho o clínquer e o calcário foram moídos conjuntamente, de forma que não havia controle sobre a granulometria do calcário e do clínquer individualmente. Na segunda fase foram produzidos 21 cimentos, os quais foram constituídos pela adição ao clínquer de 0, 5 10 e 20% do mesmo calcário da primeira fase e de um fíler quartzoso moído de forma a possuir a mesma granulometria do calcário. Nesta etapa os materiais foram previamente moídos, de forma que sua granulometria inicial era controlada, constituindo-se, portanto, 21 cimentos com a mesma finura e 21 argamassas com a mesma relação água/aglomerante. Os resultados dos ensaios de carbonatação, resistência à compressão, porosimetria, termogravimetria, difração de raios-X e análise do pH da solução aquosa dos poros indicam que o calcário tem um efeito potencializador da hidratação das argamassas, com efetivo refinamento da estrutura porosa. Entretanto, a comparação entre os resultados de ambas as fases do estudo mostra que a melhora do desempenho de cimentos acrescidos de calcário não se deve apenas ao efeito de fíler desta adição, mas a uma melhora na eficiência dos cimentos compostos, possivelmente pelo maior moabilidade da mistura clínquer-calcário induzida pelo calcário, isto é, o calcário, quando co-moído com o clínquer, faz com este atinja uma maior superfície específica, aumentando, desta forma, a sua reatividade. Argamassas feitas com cimentos brancos apresentaram menor carbonatação do que argamassas feitas com cimentos cinzas, considerando uma mesma relação água/aglomerante e uma mesma superfície inicial. Os resultados indicam algum tipo de interação química do calcário com a pasta que aumenta a carbonatação, mas este efeito é perceptível para teores elevados de adição. / The present study aims to quantify white cement mortars carbonation when compared to carbonation of conventional gray cement mortars. In the first part of the research, 12 cements were produced by substitution of 0, 5, 10 and 20% of 3 different clinkers by limestone. Clinker and limestone were ground together, so that there was no control over the fineness of limestone and clinker individually. In the second stage of the research 21 cements were produced, which were formed by adding to clinker 0, 5, 10 and 20% of limestone and a crushed quartz filler with the same fineness of limestone. In this second part of the research the materials were first milled, so that their initial particle size was controlled, criating therefore 21 cements with the same finess and 21 mortars with the same water / binder ratio. The test results of carbonation and porosimetry show that limestone has a potentiating effect on mortars hydration with effective refinement of the porous structure. However, the results show that the performance improvement of cement with limestone is not only due to the limestone effect as a filler, but also due to an improvement in the efficiency of blended cements, possibly due to greater efficiency of the clinkers that were milled together with limestone. White cement mortars showed less carbonation than gray cement mortars, assuming the same water / binder ratio and the same initial specific surface. The results show a possible chemical interaction between limestone and the cement paste that eventually increase carbonation depth. This effect was only observable with high addition contents.