Dissertations / Theses on the topic 'Ciment – Corrosion'

Les laitiers de haut-fourneaux (LHF) sont utilisés dans les ciments notamment en raison de l'amélioration globale de la durabilité qu'ils confèrent aux matériaux de construction. Cependant, les liants à forte teneur en laitiers présentent une hydratation plus lente et donc un développement de résistances mécaniques moins rapide que les ciments portland (CP). Des solutions existent pour accélérer le durcissement des liants à base de LHF, notamment l'emploi d'activants chimiques à base de chlorures. Les effets de l'activation des systèmes CP/LHF sur les développements de résistances mécaniques sont abordés dans la littérature, mais leur durabilité est assez peu étudiée. Cette thèse a donc pour but d'évaluer les conséquences de l'utilisation d'activants chlorés sur la durabilité des liants contenant 50% de LHF. D'abord, une analyse des indicateurs de durabilité permet de voir comment l'activant modifie les propriétés de transfert du matériau durci ainsi que sur la structuration du réseau poreux. Cela permet de vérifier que l'activation à jeune âge n'hypothèque pas la durabilité des bétons avec laitier à long terme. Ensuite, une étude de l'état de corrosion des aciers dans ces mélanges est entreprise afin d'évaluer l'impact des activants chlorés, reconnus pour créer de la corrosion dans le béton armé. Des essais électrochimiques couplés à de l'observation directe ainsi qu'une étude microstructurale sur le devenir des chlorures au sein de la matrice cimentaire est effectuée. La faculté des mélanges à base de laitier à fixer les chlorures dans les hydrates est notamment étudiée. Enfin, le comportement des chlorures fixés est analysé, dans le cas où la carbonatation viendrait déstabiliser les hydrates. L'impact d'un relargage éventuel de chlorures est évalué à l'aide d'un modèle couplé carbonatation/diffusion des chlorures
Ground granulated blast-furnace slags (GGBS) are used in cements in particular because of the overall improvement in the durability of building materials. However, binders with a high content of GGBS have a slower hydration and thus a development of mechanical strength slower than Portland cements (PC). Solutions exist to accelerate the hardening of GGBS-based binders, including the use of chemical activators based on chlorides. The effects of activation on the mechanical strength developments of PC/GGBS blends are discussed in the literature, but the durability of these systems is not very developed. This thesis aims to evaluate the consequences of the use of chlorides activators on the durability of binders containing 50% of GGBS. Firstly, an analysis of the durability indicators shows how the activator modifies the transfer properties of the hardened material as well as the structuring of the porous network. This allows to verify that the activation at early age does not decrease the long-term durability of concretes with GGBS. Then, a study of the corrosion state of steels in these blends is realized to evaluate the impact of chlorides activators, known to initiate corrosion in reinforced concrete. Electrochemical tests coupled with direct observation as well as a microstructural study on how interact chlorides in the cement matrix are carried out. The ability of GGBS-based blends to bind chlorides in hydrates is studied in particular. Finally, the behavior of binded chlorides is analyzed, in the case where the carbonation would destabilize the hydrates. The impact of a possible release of chlorides is evaluated using a coupled model carbonation / chloride diffusion

Les principaux phenomenes physiques et chimiques, intervenant entre les armatures corrodees et le beton qui les enrobe, sont etudies sur un modele experimental associant acier corrode et pate de ciment et sur des melanges simples entre les produits de corrosion de l'acier et les composants du ciment. La couche des produits de corrosion sur l'acier, en raison de son importance porosite ouverte, absorbe par capillarite une fraction de l'eau de la pate fraiche provoquant la perturbation de l'hydratation du ciment dans une epaisseur trois fois plus importante que celle de la couche de corrosion sur l'acier. L'absorption d'eau s'accompagne par un degagement de l'air occlus dans la couche de corrosion formant des vides a la limite de presence de la pate et creant, ainsi, une zone de faible resistance entre l'acier et la pate. Des les premiers jours de cure, les produits de corrosion de l'acier reagissent avec l'hydroxyde de calcium et l'eau de la pate pour former un ferrite de calcium hydrate hexagonal et un ferrite de calcium hydrate cubique. La presence d'ions carbonates ou chlorures accelere les reactions precedentes et conduit a la formation de carboferrite de calcium hydrate ou de solutions solides entre ferrite et chloroferrite de calcium hydrate. En presence d'ions sulfates, le monosulfoferrite et le trisulfoferrite de calcium hydrate se forment. La cristallisation de ces produits dans la zone de transition entre l'acier corrode et la pate de ciment se traduit par une amelioration locale des proprietes mecaniques de la liaison

Dans la foulée de la mondialisation, le développement agricole a été axé selon un seul critère, celui de l’intensification des facteurs de production. Ce qui est responsable du paradigme de l’agriculture intensive au détriment des considérations environnementales. Les effluents stockés dans des ouvrages de rétention en béton subissent des transformations sous l’action des bactéries et sont le siège de la production d’acide organique, agents potentiellement agressifs pour la matrice cimentaire. Ce travail avait pour vocation principale la détermination de la formulation adéquate du liant résistant en milieu agricole. L’ensemble des essais réalisés vise à décortiquer les paramètres contrôlant la durabilité de la matrice cimentaire face à l’agressivité des acides organiques des effluents d’élevage. À cette fin, des échantillons de pâtes et/ou mortiers de liants ordinaires et spéciaux ont été immergés dans une solution d’acide acétique simulant l’agressivité des effluents d’élevage. L’influence des ajouts cimentaires suivants : laitier, métakaolin, fumée de silice et cendre volant, a été mis en œuvre. Des essais de lixiviation et d’immersion ont été réalisés. Dans un premier temps, nous nous sommes intéressés à la résistance chimique des pâtes tout en décortiquant les mécanismes de dégradation des matrices cimentaires. Des analyses par porosimétrie au mercure, absorption atomique, diffraction des rayons-x (DRX) ont été réalisées. Les résultats montrent que l’attaque se traduit par une zonation chimique et minéralogique. La durabilité des liants ordinaires ainsi que du ciment alumineux est limitée sachant que l’effet de la durée de cure s’avère primordiale surtout pour les liants à hydratation latente. Dans un second temps, nous nous sommes intéressés à la quantification des phases anhydres et des hydrates des liants présentant les meilleures performances chimiques. La quantification des anhydres a été réalisée par dissolution chimique, résonance magnétique nucléaire (R.M.N.) et traitement d’images. Par contre, la quantification des hydrates a été réalisée par thermogravimétrie (T.G.A.). Les résultats montrent que la stabilité des phases est dépendante des leurs compositions chimiques. L’évaluation de la résistance à la compression de cubes de mortiers sains et dégradés en solution acide a montré une amélioration nette principalement du mortier contenant du métakaolin par rapport au mortier ordinaire. Le suivi du temps d’initiation de la corrosion des armatures des mortiers au laitier et des mortiers au métakaolin a été réalisé par des mesures électrochimiques non-destructives (potentiel de corrosion, polarisation linéaire). Les mortiers au métakaolin présentent les temps d’initiation les plus longs contrairement à ceux au laitier où la forte porosité des échantillons favorisant des chemins de percolation de la solution agressive même à des cures avancées, rend l’initiation de la corrosion des armatures presque immédiate.
In the wake of the globalization, agricultural development has focused on a single criterion, the intensification of production factors. Therfore, the paradigm of intensive agriculture at the expense of environmental considerations was founded. Effluent stored in concrete retention structures are transformed under the action of bacteria to organic acids, potentially aggressive agents to the cement matrix. This work was mainly designed to determine the adequate formulation of the resistant binder in an agricultural environment. All the realized tests aim to define parameters that control the durability of the cement matrix submitted to the aggressiveness of organic acid of manure. Cement pastes and/or mortars samples of ordinary and special binders was immersed in an acetic acid solution simulating the aggressiveness of manure. The influence of mineral additions include: slag, metakaolin, silica fume and fly ash has been implemented. Leaching and immersion tests have been achieved. Initially, we were interested on the chemical resistance of pastes by analyzing the degradation mechanisms of cement matrix. The analyses were performed by mercury intrusion porosimetry, atomic absorption and x-ray diffraction (XRD). The results show that acidic attack results in a chemical and mineralogical zonation. The durability of ordinary binders and alumina cement is limited given that the effect of the curing period is essential especially for binders having a latent hydration. We were also interested to the quantification of the anhydrous and hydrate phases for binders having the best chemical performance. The quantification of the anhydrous phases was realized by chemical dissolution, nuclear magnetic resonance (NMR) and image processing. However, the quantification of the hydrates was realized by thermogravimetry (T.G.A.). The results show that stability of phases is dependent on their chemical compositions. The evaluation of the compressive strength of sound and altered mortar cubes showed a marked improvement mainly for mortar containing metakaolin compared to the ordinary mortar. The evolution of corrosion of reinforced mortars containing slag or metakaolin was followed by non-destructive electrochemical measurements (corrosion potential and linear polarization). Metakaolin mortars present the best resistance to initiation of corrosion. However, the high porosity of samples containing slag, favoring paths of percolation of acid solution even in advanced cured time, makes the initiation of reinforcement corrosion almost immediately.

Une dès causes les plus importantes de dégradation des ouvrages en béton armé est la corrosion des armatures. Cette dernière est aggravé par la présence d'agents agressifs tels que les chlorures,les acides. Notre recherche concerne l'étude de la possibilité de corrosion des aciers placés dans des mortiers réalisés avec divers types de liants. Le liant de référence est le ciment ÇPA_55,. . Les six autres liants – son des mélanges de 70% de CPA55 et de 30% de pouzzolanes rtificielles. Les éprouvettes sont conservées dans de l'eau permutée ou dans une solution contenant 5% de MgC12. Deux méthodes d'étude de la corrosion sont utilisées: la voltampérométrie et la chronopotentiométrie : L'ensemble des paramètres de ces méthodes a été ajusté par des essais préliminaires effectués sur des éprouvettes en mortier. Afin de mieux interpréter les résultats électrochimiques, l'évolution de la microstructure est étudiée par analyse thermique différentielle et spectrométrie infrarouge. Le facteur de porosité et la distribution poreuse des mortiers sont également présentés. La méthode chronopotentiométrique fournit de meilleurs renseignements sur la corrosion des aciers. Dans la solution contenant le MgC12, seul le liant contenant 30% de métakaolin ne conduit pas à la dépassivation de l'acier
One of the most important damages of reinforced concrete constructions is the corrosion of steel reinforcement ; this last is aggravated by the presence of aggressive agents: acids, chlorides… Our research concern the study of corrosion possibility of steel reinforcement in motars made with different types of binders. We used artificial protland cement (CPA 55) as reference and the others binders are mixture of 70% CPA55 and 30 % of artificial pouzzolanic materials mainly calcined clay, fly ash, metakaolin, and slag. The specimens are cured in water or in solution containing 5% of MgCl 2 in order to study the influence of chlorides. Two methods are used to study the corrosion: voltamperometrical and chronopotentiometrical methods. In order to interpret electrochemical results, the evolution of microstructure is studied with physico chemical methods (ATD,IR, porosimetry. ) Chronopotentiometrical method give better informations with regard to steel corrosion in mortar. In solution containing MgC12, only the binder with 30% of metakaolin don't depassivate the reinforcement

Ce travail s'inscrit dans la problématique de la dégradation des prothèses de hanche cimentées par fretting corrosion. L'endommagement de l'acier inoxydable 316L, alliage constituant la tige fémorale, par frottement contre du polyméthacrylate de méthyle (PMMA), composé modèle du ciment chirurgical, a été particulièrement étudié. Deux types d'expériences ont été envisagées : à sec et en solution de Ringer voisine, par sa teneur en chlorures, de la composition du liquide physiologique. Dans un premier temps, à partir des conditions expérimentales choisies de déplacement et de force normale, la carte de fretting a été tracée pour le contact 316L/PMMA permettant de fixer des conditions reproductibles de glissement total pour un déplacement sinusoïdal de demi-amplitude égale à 40 μm et des forces normales comprises entre 42,5 N et 170 N. Ensuite, l'étude, à sec, du fretting entre l'acier inoxydable et du PMMA a permis de quantifier le volume d'usure du PMMA, seul matériau à se dégrader, en fonction de l'énergie dissipée. Le phénomène de stick-slip a été nettement mis en évidence lors du glissement et augmente en fonction de la force normale de contact. Grâce à la transparence du PMMA, la production et l'évolution des débris ont pu être isolées et commentées en cours de fretting. De plus, les analyses infrarouges des débris de PMMA, à la surface de l'acier inoxydable, ont amené des informations sur le changement de configuration au cours du processus de dégradation. En solution de Ringer, milieu corrosif, l'acier inoxydable se dégrade d'une manière très significative pendant le fretting contre du PMMA et du ciment chirurgical. Au cours du processus de dissolution à potentiel libre, la réaction de réduction des ions oxoniums semble s'ajouter à la réduction du dioxygène. L'acier inoxydable 316L présente une forme particulière d'usure en ‘W'. Un effet de crevasse permet de proposer un mécanisme d'endommagement assisté par le fretting. De plus, l'énergie dissipée varie en fonction du potentiel imposé. Une analyse des courants a montré l'existence d'une réaction cathodique supplémentaire. Enfin, les expériences effectuées à l'air ambiant et en solution de Ringer ont fourni des données quantitatives d'usure du PMMA et du 316L.

La pénétration des ions chlorures dans les bétons provoque la corrosion des armatures. L'objectif de ce travail est la modélisation de l'électrodiffusion des ions chlorures au travers des matériaux cimentaires, en régime transitoire, selon une approche multi-espèces intégrant les phénomènes de double couche électrique se développant aux interfaces du milieu poreux. Les équations de transport, issues de la théorie des processus irréversibles, sont résolues par une méthode numérique afin de simuler l'évolution du courant électrique enregistré lors d'un essai accéléré. La confrontation entre courant simulé et courant expérimental, obtenu sur des mortiers, montre une très nette amélioration par rapport à un modèle se basant sur la notion de diffusibilité. Le recouvrement important des couches diffuses chargées négativement, dans les pores de faible diamètre, est à l'origine d'un effet retardateur dans l'évolution du courant, rapprochant ainsi courant électrique simulé et mesuré
Chloride penetration in concrete initiates corrosion of the reinforcement. The aim of this work is to model the chloride ion transport in cement based-materials in non-steady state, according to a multi-species approach, and integrating electrical double layer phenomena occurring at the interfaces of the porous media. Equations of transfer, obtained by the thermodynamic theory of irreversible processes are solved by a numerical method in order to simulate the electrical current evolution recorded during an accelerated test. Comparison between simulated and experimental currents obtained on mortars shows a great improvement compared to a purely geometrical model, based on the concept of diffusibility. A significant overlapping of negatively charged diffuse layers within the small pores is the cause of a slowing effect of the electrical current evolution

L'objectif principal du travail présenté est la compréhension de la relation liant le flux de chlorures mesuré expérimentalement en régime stationnaire lors d'un essai de diffusion-migration à travers un échantillon de mortier, à la valeur de courant associé. Une approche expérimentale, basée sur un protocole d'essai spécifique, a permis de comparer les courbes de chrono-ampérométries obtenues lors d'essais de diffusion-migration pour des mortiers d'épaisseurs différentes préparés à partir de différents dosages en eau. Tous les essais ont montré que la densité surfacique de courant évoluait en deux phases après ajout d'une solution contenant le chlorure de sodium : 1. Une diminution malgré la présence d'une solution plus conductrice. 2. Une augmentation, malgré un flux constant, d'autant plus importante que les pores sont d'un rayon moyen plus important. Un protocole de mesure de l'impédance électro-chimique des échantillons soumis au test de diffusion-migration a fait apparaître une modification des caractéristiques électriques de ces derniers lors des polarisations en présence de chlorures de sodium. La mesure d'impédance électrochimique du matériau a permis d'accéder au taux de surface d'échange solide-liquide. Ces observations ont conduit au développement d'un modèle théorique nouveau qui permet le calcul d'un coefficient de diffusion apparent en prenant en considération les phénomènes de double couche à l'interface solide-solution, la géométrie de la matrice poreuse, les interactions ioniques, et les cinétiques de réactions hétérogènes. La confrontation des résultats théoriques aux mesures expérimentales valide les hypothèses retenues dans le modèle et souligne la prépondérance des effets électro-capillaires sur la valeur de ce coefficient de diffusion apparent.

Ce travail porte sur le conditionnement de déchets radioactifs dans une matrice cimentaire. Il vise plus particulièrement à évaluer la compatibilité chimique entre un mortier à base de ciment phospho-magnésien et l’aluminium métallique. Dans un premier temps, les processus physico-chimiques responsables de la prise et du durcissement du ciment phospho-magnésien sont étudiés : la diffraction des rayons X (DRX), la thermogravimétrie (ATG) et la résonance magnétique nucléaire (RMN-MAS du 31P et 11B) permettent d’identifier les phases solides précipitant au cours de l’hydratation du ciment ; la spectroscopie à plasma à couplage inductif (ICP-AES), la conductimétrie et la pH-métrie apportent des informations sur la composition de la solution porale. Dans un second temps, la corrosion de l’aluminium dans des mortiers phospho-magnésiens est étudiée par suivi du potentiel d’équilibre (OCP) et par spectroscopie d’impédance électrochimique (SIE).Le ciment phospho-magnésien est préparé à partir d’oxyde de magnésium (MgO) et de dihydrogénophosphate de potassium (KH2PO4). En présence d’eau, il s’hydrate selon un processus de dissolution / précipitation. La dissolution des réactifs conduit principalement à la formation de K-struvite (MgKPO4.6H2O), précédée par celle de deux hydrates intermédiaires : la phosphorrösslerite (MgHPO4.7H2O) et la phase Mg2KH(PO4)2.15H2O. L’acide borique retarde l’hydratation du ciment en ralentissant la formation des hydrates. La précipitation initiale d’un ou plusieurs composés boratés et phosphatés amorphes ou très mal cristallisés ainsi que la stabilisation des cations en solution (magnésium, potassium) pourraient en être la cause. Par comparaison avec une matrice à base de ciment Portland, la corrosion de l’aluminium dans le mortier phospho-magnésien est fortement limitée.Le pH de la solution interstitielle, proche de la neutralité, est en effet situé dans le domaine de passivation de l’aluminium. La corrosion dépend de plusieurs paramètres : elle est favorisée pour un rapport massique eau/ciment (e/c) très supérieur à la demande chimique en eau du liant (e/c = 0.51) ainsi que par la présence d’acide borique. Au contraire, le nitrate de lithium ajouté à l’eau de gâchage agit comme un inhibiteur de corrosion. Un mécanisme de corrosion en 4 étapes permet de modéliser les diagrammes d’impédance. L’évolution de la vitesse de corrosion et de la production de dihydrogène qui lui est associée peut alors être calculée au cours du temps. Les résultats obtenus sont en bon accord avec les mesures expérimentales du dihydrogène relâché par des plaques d’aluminium enrobées dans un mortier phospho-magnésien
This work deals with the stabilization / solidification of radioactive waste using cement.More particularly, it aims at assessing the chemical compatibility between metallic aluminum and mortars based on magnesium phosphate cement. The physical and chemical processes leading to setting and hardening of the cement are first investigated. X-ray diffraction (XRD), thermogravimetry (TGA) and nuclear magnetic resonance spectroscopy (31P and11B MAS-NMR) arefirst used to characterize the solid phases formed during hydration, while inductively coupled plasma atomic emission spectroscopy analysis (ICP-AES), electrical conductimetry and pH measurementsprovide information on the pore solution composition. Then,the corrosion of metallic aluminum in magnesium phosphate mortars is studied by monitoring the equilibrium potential and by electrochemical impedance spectroscopy (EIS).Magnesium phosphate cement is prepared from a mix of magnesium oxide (MgO) and potassium dihydrogen orthophosphate (KH2PO4). In the presence of water, hydration occurs according to a dissolution – precipitation process. The main hydrate is K-struvite (MgKPO4.6H2O). Its precipitation is preceded by that of two transient phases: phosphorrösslerite (MgHPO4.7H2O) and Mg2KH(PO4)2.15H2O. Boric acid retards cement hydration by delaying theformation of cement hydrates. Two processes may be involved in this retardation: the initial precipitation of amorphous or poorly crystallized minerals containing boron and phosphorus atoms, and/or the stabilization of cations (Mg2+, K+) in solution.As compared with a Portland cement-based matrix, corrosion of aluminum is strongly limited in magnesium phosphate mortar. The pore solution pH is close to neutrality and falls within the passivation domain of aluminum. Corrosion depends on several parameters: it is promoted by a water-to-cement ratio (w/c) significantly higher than the chemical water demand of cement (w/c = 0.51), and by the addition of boric acid. On the contrary, lithium nitrate, dissolved in the mixing solution, acts as a corrosion inhibitor.A 4-step mechanism makes it possible to model the impedance diagrams. The evolution of the corrosion rate and of the amount of dihydrogen released with ongoing hydration is then calculated The results are in good agreement with the experimental determination of the H2 production by aluminum sheets embedded in magnesium phosphate mortar

La technique de précontrainte permet de réaliser les architectures les plus audacieuses, tout en garantissant leurs solidités. Cependant, au fil des années d’exploitation des ouvrages en béton précontraint, certaines structures ont présenté des fragilités, au niveau des gaines contenant les torons, dans lesquelles du coulis de ciment avait été injecté pour les protéger de la corrosion, pouvant conduire à la rupture de torons. Les expertises réalisées sur des câbles rompus sur site ont mis en évidence que le phénomène de corrosion sous contrainte était responsable de ces ruptures. Dans le cadre de notre travail, le couple métal-milieu d’étude est constitué d’un acier de précontrainte et d’un coulis de ciment siège d’une ségrégation entraînant un pH élevé. Après l’étude du comportement en termes de corrosion de ce milieu vis-à-vis de l’acier, celui-ci a été assimilé à une solution de soude. L’étude de la susceptibilité de l’acier de précontrainte a été déterminée à l’aide de deux méthodes électrochimiques, précisément Parkins et méthode de Fang & Staehle. Le travail a été réalisé dans des milieux de concentration différente en soude afin d’observer l’influence du pH de la solution de corrosion. Le rôle des paramètres métallurgiques de l’acier comme l’état de surface, la microstructure a également été étudié, ainsi que l’influence de la température. Le traitement des résultats des essais a montré qu’à partir de 0,96 mol/kg, il y a un risque de CSC et au-dessus de 4 mol/kg la corrosion généralisée est prépondérante. Pour des solutions de concentration inférieure à 0,07 mol/kg, les critères des méthodes prédictives ne sont pas adaptés pour déterminer une susceptibilité à la CSC.

Le béton est le matériau le plus utilisé dans le monde. Son succès vient de son accessibilité et ses performances mécaniques, surtout lorsqu'il est renforcé par de l'acier. Dans le béton, l'acier doux est naturellement protégé par la formation d'une couche d'oxyde protectrice. Ceci est possible avec l'alcalinité du béton résultant de l'hydratation du ciment Portland.Cependant, la fabrication du ciment Portland est responsable de 5 à 7% des émissions anthropiques mondiales de CO2. Le développement du ciment Belite-Ye'elimite-Ferrite (BYF) comme liant alternatif est une solution prometteuse avec une diminution de 20 à 30% des émissions de CO2 par rapport à la production de ciment Portland. Les propriétés sont en cours d'évaluation et la possibilité d'utiliser l’acier doux en renfort sans corroder en fait partie.Cette thèse traite de la corrosion de l'acier incorporé dans des matériaux à base de ciment BYF sous différents angles. Tout d'abord, une étude d'hydratation détaillée a été effectuée pour comprendre l'évolution de l'électrolyte, c'est-à-dire de la solution interstitielle et de l'assemblage de phases. Ensuite, la passivation des barres d'armature d'acier ordinaire intégrées dans des mortiers renforcés a été étudiée. De plus, des analyses ont été effectuées avec des échantillons d'acier immergés dans des extraits aqueux de pâtes de ciment équivalentes pour caractériser la structure et l'épaisseur du film passif. Enfin, l'impact des chlorures initiaux sur la corrosion des mortiers renforcés a été évalué.L'hydratation a été caractérisée par plusieurs techniques, au jeune âge et pendant un an, avec des techniques telles que la calorimétrie isotherme, la spectroscopie d'émission optique par plasma à couplage inductif, la thermogravimétrie, la diffraction des rayons X et la porosimétrie par intrusion au mercure. L'évolution de l'acier dans les mortiers a été évaluée avec des techniques électrochimiques. L'applicabilité des techniques non destructives courantes (potentiel de demi-cellule, résistance à la polarisation linéaire, et l'impédance électrochimique) a été validée par des mesures de polarisation potentiodynamique large et une inspection visuelle. Le film passif formé dans des extraits aqueux des mortiers a été caractérisé par des techniques électrochimiques couplées aux mesures de spectroscopie de photoélectrons aux rayons X. Une fois que la passivation établi, l'impact des chlorures initiaux sur les mortiers renforcés a été évalué.Pour le BYF, le processus d'hydratation et les assemblages de phases hydratées sont différents du ciment Portland, mais la solution interstitielle est finalement très basique après un jour (pH de 13). La principale différence est le pH qui est inférieur (10.6) avant la prise. Les mesures ont montré que l'acier se passive avec le même niveau de protection qu’avec le ciment Portland. La différence est le temps nécessaire pour atteindre le meilleur niveau de protection (28 jours avec le ciment BYF au lieu de 7 jours avec le ciment Portland). Les échantillons d’acier immergés dans des extraits aqueux de ciment Portland et BYF après 28 jours d’hydratation ont présenté une épaisseur et une composition similaires, indiquant que le milieu BYF est aussi protecteur que celui de Portland. L'acier passive dans les mortiers BYF (E/C = 0.5) contenant 0.4% de chlorures par masse de ciment, ce qui ne remet pas en question, pour ce nouveau ciment, la limite imposée par la norme européenne EN-206 aux bétons armés
Concrete is the most widely used material in the world. The success lies on its affordability and mechanical performance, especially when reinforced with steel. Once embedded in the concrete, mild steel is naturally protected by the formation of a protecting oxide layer. This is possible thanks to the alkalinity of the concrete which results from the hydration of the Portland cement.However, Portland cement manufacturing is responsible of about 5 to 7% of the global anthropogenic CO2 emissions. The development of Belite-Ye’elimite-Ferrite (BYF) cement as alternative binder is a promising solution with a decrease of 20 to 30% in CO2 emissions compared to Portland production. The properties are being evaluated and the possibility of using mild steel reinforcement without corroding is part of it.This thesis approaches the corrosion of steel embedded in BYF cement based materials from various angles. First, a detailed hydration study was performed to understand the evolution of the “electrolyte”, i.e. of the pore solution and of the phase assemblage. Second, the passivation of ordinary steel rebar embedded in reinforced mortars was investigated. In addition, analyzes were carried out with steel samples immersed in aqueous extracts of equivalent cement pastes to characterize the structure and the thickness of the passive film. Finally, the impact of the initial chlorides on corrosion of reinforced mortars was evaluated.The hydration was characterized by several techniques, at early-age and then over one year, with techniques such as isothermal calorimetry, inductively coupled plasma optical emission spectroscopy, thermogravimetry, X-ray diffraction and mercury intrusion porosimetry. The evolution of steel embedded in mortars was evaluated with several electrochemical techniques. The applicability of current non-destructive techniques (half-cell potential readings, linear polarization resistance and electrochemical impedance spectroscopy) has been validated by large potentiodynamic polarizations and visual inspection. The passive film formed in aqueous extracts of the mortars was characterized with electrochemical techniques coupled to X-ray photoelectron spectroscopy measurements. Once the passivation understood, the impact of the initial chlorides on the reinforced mortars was evaluated.For the BYF, the hydration process and the hydrated phase assemblages are different from Portland cement, but the interstitial solution is finally very basic after one day (pH of 13). The main difference is the pH that is lower (10.6) before setting. The measurements showed that steel was effectively passivated in BYF mortars with the same level of protection as with Portland cement. The difference between the BYF and Portland cement is the time required that to reach the greatest level of protection (28 days instead of 7 days), probably because of initial lower pH value. The steel immersed in Portland and BYF aqueous extracts obtained after 28 days of hydration exhibited similar thickness and composition of protective layer, indicating that BYF media was as protective as Portland ones. Steel passivates in BYF mortars (W/C = 0.5) containing 0.4% chlorides by cement mass which is in agreement with the limit imposed by the European Standard EN-206 to reinforced Portland concretes

La dégradation des structures en béton armé par la corrosion des aciers est l'une des principales causes de la réduction de la durée de vie des ouvrages. La corrosion est due à la pénétration des chlorures qui peuvent atteindre les armatures par les fissures ou par la porosité. Le transport ionique dans la solution interstitielle des matériaux cimentaires dépend de l'état de saturation de ces matériaux. Le cas non saturé reflète plus la réalité des ouvrages marins, même s'il est moins abordé dans la littérature. L'objectif principal de ce travail est de proposer un modèle de transfert qui tient compte du couplage du transfert d'humidité et des ions de la solution interstitielle des matériaux cimentaires. Le travail est divisé en trois parties principales: la première est consacrée à l'approche théorique du problème pour établir les équations permettant de décrire le transfert ionique dans les matériaux insatures. La deuxième partie est numérique, elle consiste à résoudre les équations traduisant le transport ionique au sein du matériau soumis à une ambiance marine en cycles d'humidification et de séchage. La dernière partie est expérimentale, elle est consacrée d'une part à la mesure des paramètres d'entrée du modèle et d'autre part à sa validation. Cette dernière est réalisée pour le cas d'un matériau en situation de marnage. Le modèle est également confronté à des résultats expérimentaux de la littérature concernant des mesures d'imbibition - séchage obtenu sur des mortiers
Reinforced concrete structures degradation as a result of steel corrosion is one of the most important causes for the construction service life reduction. Corrosion is due to chlorides penetration which can reach the reinforcement thought cracks or porosity. The ionic transport in the pore solution of the cement based materials depends on the saturation level of those materials. The case of unsaturated materials reflects better the reality of the marine concrete strucures even if this approach is less treated in the literature. The present study has the main objective to propose a transfer model which take into account the coupling between the transport of moisture and ions in cementitious materials. This study is divided in to three principal parts: in first part, we present the theoretical approach in order to establish the transfer equations in unsaturated materials. The second part is a numerical one, and it consists in solving the transport equations within the materials submitted to the marine environment through wetting and drying cycles. The last parts is experimental, it has a goal to validate to define the inputs of the model. The validation was done in laboratory simulator where concretes were submitted to the tidal zones cycles. We have shown a good agreement between the model and the experimental results. The model is also validated by using results of literature carried out mortars submitted to imbibitions drying cycles

Les travaux menés dans le cadre de cette thèse abordent la biodétérioration des mortiers armés par les bactéries du genre Acidithiobacillus thiooxidans connues pour rapidement altérer les mortiers et bétons dans les égouts. Les objectifs ont visés à mettre au point un dispositif expérimental permettant de quantifier et de comprendre les mécanismes bio-physico-chimiques impliqués, et à développer un test accéléré permettant de tester différentes formulations de mortiers, notamment, des aluminates de calcium (CAC) et des ciments Portland (OPC). Le dispositif expérimental est basé sur un essai de biolixiviation de mortiers armés par une suspension bactérienne de A. thiooxidans à pH inférieur à 2. Une étude approfondie des conditions de croissance de A. thiooxidans dans un milieu spécifique à cette bactérie ont été nécessaire pour disposer d’un essai de biolixiviation reproductible. A la fin des tests de biolixiviation, les mortiers armés CAC et OPC présentent deux zones altérées à leur surface ayant différentes minéralogies : une zone endommagée très altérée à l’extérieur et une zone intermédiaire moins altérée entre la zone altérée et le cœur sain. L’état de dégradation à été estimé par un indice d’attaque permettant de confirmer quantitativement que les mortiers armés CAC sont moins biodétériorés que ceux à base de ciment OPC. L’essai de biolixiviation mis en place pourrait donc servir de test pour évaluer la performance de diverses formulations de matériaux cimentaires. Les résultats électrochimiques des armatures incorporées dans les mortiers ont montré un effet protecteur plus important du ciment CAC, avec une intensité de corrosion plus faible que celle du ciment OPC
The aim of this PHD is to study the biodeterioration of reinforced mortar by bacteria of the gender A. thiooxidans known for its fast alteration of mortar and concrete in sewer system. The objectives of this study consisted on the development of a new experimental device that allow on one hand to understand and quantify the different biological, chemical and physical mechanisms that may take place in concrete biodeterioration, and on the other hand to serve as basic reactor for an accelerated biodeterioration test allowing the discrimination of new reinforced mortar formulations mainly Portland cement (OPC) and calcium aluminate cement (CAC) formulations. The experimental device consists of a biolixivation of reinforced mortar by a A. thiooxidans bacterial suspension at pH lower than 2. A study of growth conditions of A. thiooxidans in a specific media for this bacterial strain was necessary to procure a reproducible biolixivation essay. At the end of the biolixiviation test the CAC and OPC mortar presented different mineralogy deteriorated zones. One deeply distorted zone in contact with bacterial suspension, a second intermediate zone less damaged than the first one and the cement untouched core. An estimated attack index confirmed that CAC mortars are much more resistant to biodeterioration than OPC cement. Hence the performed biolixivation essay helped to evaluate the performance of various cementitious material formulations in order to prevent biodeterioration by A. thiooxidans. Electrochemical analysis of mortar incorporated armatures demonstrated that CAC mortar composition shows a more protective effect than OPC cement displaying lower corrosion intensity

Nous avons étudié le passage d'une onde alcaline issue d'une matrice cimentière à tràvers l'argilite (à une profondeur de -480m) du Laboratoire Meuse Haute-Marne composée principalement de quartz, micas, calcite et d'un interstratifié I/S. Une technique dynamique en colonne a été utilisée pour caractériser les diverses interactions entre le fluide alcalin et le milieu argileux. Cette technique repose sur un couplage entre l'étude des courbes de percée des différents ions du système et une caractérisation du solide extrait des colonnes. Cette méthodologie nous a permis de caractériser deux types de phénomènes ayant des temps caractéristiques de réaction très différents: Des réactions de surface rapides: nous avons caractérisé des réactions d'adsorption de cations par ionisation de sites sur l'argilite qui sont à l'origine de l'effet tampon des argiles. Par ailleurs nous avons mis en évidence une réaction originale de condensation d'un composé calcique dans l'interfoliaire des argiles gonflantes. Tous ces processus ont été modélisés et leur simulation à l'aide du code de calcul IMPACT montre que l'on obtient un modèle très satisfaisant. Des processus de dissolution/précipitation fortement limités cinétiquement : Nous avons mis en évidence la dissolution principalement du quartz et de l'interstratifié I/S et la précipitation de phases secondaires type C(A)SH et zéolithes. Après le passage du fluide alcalin à une température de 60ʿC pendant 6 mois, le matériau est largement amorphisé mais seulement 20 à 30% du quartz et de l'interstratifié I/S est dissous. Enfin à partir de l'ensemble des expériences nous avons déterminé les cinétiques de dissolution des phases primaires ainsi que les produits de solubilité des principales phases secondaires.

La carbonatation est une pathologie qui affecte les matériaux à base de ciment tels que les bétons et lesmortiers. Les zones carbonatées du matériau deviennent fragiles et perdent ainsi leur pouvoir deprotection des aciers contre la corrosion. Les produits de corrosion engendrent alors une dégradation dubéton pouvant aboutir à la ruine de la structure.Six types de bétons adjuvantés et deux pâtes de ciments ont été formulés grâce à une étude rhéologiqueafin d’étudier l’effet de la carbonatation accélérée et naturelle sur la durabilité des bétons et des pâtesde ciments à base de ressources algériennes. Pour ce faire, plusieurs méthodes d’investigation sontutilisées, aussi bien à l’échelle macroscopique que microscopique.En conclusion, le modèle rhéologique empirique développé peut être utilisé pour formuler des bétonsrésistants à la carbonatation. L’étude de la carbonatation démontre que le protocole accéléré, peut serévéler moins agressifs que la carbonatation naturelle, notamment pour des pâtes de ciment denses.Dans ce cas, la carbonatation accélérée de la surface tend à combler la microporosité superficielle dubéton, freinant ainsi la diffusion du dioxyde de carbone, contrairement à la carbonatation naturelle quiagit de manière plus diffuse sans totalement obstruer la porosité. Moins les bétons sont compacts, plusle protocole accéléré s’avère effectif
The carbonation is a pathology which affects cement-based materials such as concretes and mortars.The carbonated skin of material becomes brittle and losses the protection of inner steels againstcorrosion. The corrosion products generate a degradation of the concrete which may lead to thecollapse of the structure.Six types of adjuvant concretes and two cement pastes have been designed by a rheological study inorder to study the effect of accelerated and natural carbonation on the sustainability of concretes andcement pastes based on algerian resources. For this purpose, several investigation methods were usedwith both macroscopic and microscopic scales.In conclusion, the empirical rheological model developed herein can be used to formulate concretesresistant to carbonation. The study of carbonation shows that the accelerated protocol may be lessaggressive than the natural one, especially for dense cement pastes. In this case, the acceleratedcarbonation of the surface tends to fill up the superficial microporosity of the concrete, slowing downthe production of carbon dioxide, contrary to the natural carbonation which acts more diffusely withoutcompletely obstructing the pores. The lesser compact is the concrete, the more effective is theaccelerated protocol

La carbonatation est une pathologie qui affecte les matériaux à base de ciment tels que les bétons et lesmortiers. Les zones carbonatées du matériau deviennent fragiles et perdent ainsi leur pouvoir deprotection des aciers contre la corrosion. Les produits de corrosion engendrent alors une dégradation dubéton pouvant aboutir à la ruine de la structure.Six types de bétons adjuvantés et deux pâtes de ciments ont été formulés grâce à une étude rhéologiqueafin d'étudier l'effet de la carbonatation accélérée et naturelle sur la durabilité des bétons et des pâtesde ciments à base de ressources algériennes. Pour ce faire, plusieurs méthodes d'investigation sontutilisées, aussi bien à l'échelle macroscopique que microscopique.En conclusion, le modèle rhéologique empirique développé peut être utilisé pour formuler des bétonsrésistants à la carbonatation. L'étude de la carbonatation démontre que le protocole accéléré, peut serévéler moins agressifs que la carbonatation naturelle, notamment pour des pâtes de ciment denses.Dans ce cas, la carbonatation accélérée de la surface tend à combler la microporosité superficielle dubéton, freinant ainsi la diffusion du dioxyde de carbone, contrairement à la carbonatation naturelle quiagit de manière plus diffuse sans totalement obstruer la porosité. Moins les bétons sont compacts, plusle protocole accéléré s'avère effectif.

La séquestration géologique du dioxyde de carbone (CO2) et du sulfure d'hydrogène (H2S) est une solution envisagée par l'industrie pétrolière pour stocker durablement ces gaz indésirables. Elle consiste à les injecter via des puits dans des réservoirs géologiques profonds. Les puits, constitués par des tubes d'acier entourés d'une gaine de ciment, peuvent être dégradés et ainsi constituer un chemin de fuite des gaz vers la surface qui auraient des conséquences humaines et environnementales sérieuses. Diverses expérimentations en laboratoire ont simulé le vieillissement de ces deux matériaux dans des conditions de séquestration géologique. Pour ce faire, un protocole expérimental et analytique spécifique a été mis en place. La simulation numérique du vieillissement du ciment a également été abordée. Le ciment et l'acier ont été altérés au contact de diverses phases fluides à 500 bar-120°C et 500 bar-200°C : une saumure, une saumure chargée en H2S-CO2, un mélange saumure+phase supercritique à H2S-CO2 et une phase supercritique à H2S-CO2 en l'absence d'eau liquide. Dans tous ces cas, on observe deux réactions découplées : la carbonatation du ciment par le CO2 et la sulfuration de l'acier par le H2S. Il apparaît que la carbonatation est maximale et que la sulfuration est au contraire minimale au sein de la phase supercritique en l'absence d'eau liquide. Les propriétés texturales et de porosité du ciment sont peu ou pas affectées par tous les traitements à 120°C. La porosité est même réduite en présence de H2S-CO2. Par contre, à 200°C, ces propriétés sont affectées par le fait de la présence d'eau liquide dans le milieu. A cette température, seul le vieillissement du ciment au sein de la phase supercritique sans eau liquide améliore ses propriétés. Dans toutes les conditions testées, l'acier est toujours corrodé, il est donc le matériau le plus vulnérable des puits.

As argamassas e concretos de cimento Portland são materiais de construção duráveis, relativamente baratos que, embora apresentem boa rigidez e adequada resistência à compressão, têm outras propriedades deficientes, tais como: resistência à tração, ao impacto, à fadiga, além de baixa tenacidade e ductilidade. Uma considerável melhora destas propriedades pode ser obtida com adição de fibras, em quantidades adequadas, na composição destes materiais. A utilização de fibra de vidro convencional (tipo E) no reforço das argamassas de cimento Portland, pode ser viável uma vez contornado o ataque do meio alcalino à fibra, principalmente o hidróxido de cálcio Ca(OH)2, produzido na hidratação do cimento. No presente trabalho foi obtida uma menor intensidade de ataque alcalino às fibras de vidro E, por meio da modificação com látex Estireno Butadieno, da adição de sílica ativa em substituição ao cimento Portland e da utilização de ambos concomitantemente. Outro procedimento utilizado, visando uma maior durabilidade das fibras de vidro, foi a proteção da superfície desta fibra com uma película de látex Estireno Butadieno e de uma mistura deste látex e sílica ativa. A eficiência de um e outro procedimento foi verificada por meio da comparação dos resultados de ensaio à tração e flexão, em amostras submetidas a processo de hidratação convencional e acelerado e observações pro meio de microscopia óptica.
Portland cement mortar and concrete are durable building materials, relatively cheap and, despite they display a good rigidity and an adequate compressive strength, they have other deficient properties such as tensile strength, impact, fatigue, beyond low toughness and ductility. A considerable improvement of these properties can be obtained adding fibers, in adequate quantities, in the composition of the materials. The use of conventional glass fiber (E-glass) in the reinforcement of Portland cement mortar can be possible if the attack of the alkaline environment, produced by cement hydration (chiefly by calcium hydroxide), to the fiber is controlled. In this work, a lesser intensity of alkaline attack on the E-glass fibers was succeded through the modification of the Portland cement matrix by styrene butadiene latex, the addition of silica fume or through the utilization of both additives at the same time. Another proceeding, aiming at a greater durability of the E-glass, has been the protection of the fiber surface with a styrene butadiene latex coating or with a mixture of this same latex and silica fume. The efficiency of each proceeding was verified by the comparison of tensile strength and flexural strength in samples submitted to accelerate and conventional hydration processes and by the observation of the interface glass/matrix with optical microscopy.

Lorsqu'une structure en béton est soumise à des sollicitations du type séchage ou hautes températures, différents mécanismes interviennent aux différentes échelles d'étude possibles de ce matériau, induisant le comportement global de la structure. Deux mécanismes sont ici distingués : les gradients (hydriques ou thermiques) à l'échelle macroscopique et les incompatibilités de déformations pâte de ciment/granulat à l'échelle mésoscopique. Les travaux présentés visent à déterminer l'effet de ces deux mécanismes. Les simulations réalisées sur le logiciel aux Eléments Finis Cast3M montrent ainsi l'apport d' "essais virtuels" en complément des expériences réelles pour permettre la séparation et la quantification des différents mécanismes intervenant dans la dégradation des propriétés mécaniques. Ces travaux s'appuient sur l'association des deux approches mésoscopique et macroscopique, utilisant deux maillages différents, homogène (considérant une phase unique, le béton) et hétérogène (considérant les deux phases pâte de ciment et granulats). L'influence du modèle mécanique adopté lors des simulations sur l'endommagement et la chute des propriétés mécaniques est également étudié.

Dans le concept actuel de stockage de déchets radioactifs en couche géologique profonde tel qu’envisagé par l’Andra (projet CIGEO), les colis de déchets sont placés dans des alvéoles creusées dans l’argilite du Callovo-Oxfordien (COx) dont le chemisage est en acier faiblement allié. Le COx, et en particulier les pyrites qui le composent, peuvent s’oxyder lors du creusement. Grâce à un montage expérimental original, impliquant plusieurs mélanges pyrite/minéral et un réacteur couplé à un micro chromatographe en phase gazeuse, il est démontré, sur la base de la consommation d'O2 mesurée, qu'à 100°C en présence de calcite, moins de 50% de la pyrite est oxydée. Cette oxydation implique une acidité susceptible de corroder le chemisage des alvéoles. L’Andra a donc développé et breveté un coulis cimento-bentonitique bas pH (9
In the current concept of radioactive waste deep geological disposal planned by Andra (CIGEO project), waste containers are stored into disposal cells drilled into the Callovo-Oxfordian claystone (COx) and encircled by a carbon steel liner. COx and in particular its pyrites, can be oxidized during the drilling of cells. Thanks to an original experimental set-up, involving several pyrite/mineral mixtures and a reactor coupled to a micro gas chromatograph, it is demonstrated, based on the measured O2 consumption that at 100°C in presence of calcite, less than 50% of the pyrite is oxidized. This oxidation induces a transient acidic plume and consequently the corrosion of the steel liner. Andra has developed and patented a low-pH (9

Este trabalho apresenta um estudo sobre a confecção de concretos estruturais com baixo consumo de cimento Portland e avalia algumas das suas propriedades no estado fresco e endurecido, tanto em termos mecânicos como de durabilidade. O uso de concretos de baixo consumo de cimento Portland tem por objetivo possibilitar maior sustentabilidade da indústria da construção baseada no concreto, como maior longevidade de jazidas, reduções na emissão de \'CO IND.2\' e no consumo de energia e menores custos de transporte. Possibilita também diversas melhorias técnicas, como menor retração, fissuração e calor de hidratação. Com base em conceitos de empacotamento e dispersão de partículas, uso de adições minerais e fílers e escolha adequada dos materiais, obtiveram-se concretos com baixo consumo de cimento e alta resistência, com consumo relativo de materiais aglomerantes inferior a 5 kg/\'M POT.3\' para produzir 1 MPa de resistência à compressão. Avaliaram-se diversos parâmetros relacionados à durabilidade destes concretos com base em ensaios de absorção de água por imersão, absorção de água por capilaridade, permeabilidade, abrasão, carbonatação e potencial de corrosão. Os resultados obtidos indicam que os concretos de baixo consumo de cimento obtidos podem ter durabilidade comparável ou até superior a concretos usualmente considerados como de bom desempenho. Observou-se que a durabilidade é dependente do tipo de cimento empregado e que deve ser avaliada especificamente com relação ao tipo de ação agressiva a que o concreto estará exposto.
This dissertation presents a study on the development of structural concrete with low Portland cement consumption and evaluates some of its fresh and hardened properties, in mechanical and durability terms. The use of low concrete Portland cement consumption is intended to enable greater sustainability of the construction industry based on concrete, as increased longevity of deposits, reductions in \'CO IND.2\' emissions and energy consumption and lower transportation costs. It also allows several technical improvements, such as reduced shrinkage, cracking and hydration heat. Based on particle packaging and dispersion, use of mineral additives and fillers and appropriate choice of material, concrete with low cement content and high strength was obtained, with relative consumption of binder materials below 5 kg/\'M POT.3\' to produce 1 MPa compressive strength. Various durability parameters were evaluated based on tests such water absorption by immersion, water absorption by capillarity, permeability, abrasion, corrosion potential and carbonation. The results indicate that the low cement consumption concretes may have achieved comparable or superior durability to concrete usually regarded as good performance. It was observed that the durability is dependent on the type of cement used and that durability should be assessed specifically with regard to the type of aggressive action that the concrete will be exposed.

A corrosão por cloretos é considerada por muitos pesquisadores a mais severa das manifestações patológicas que atacam as armaduras. O objetivo principal deste trabalho é avaliar a presença de cloretos livres em concreto de cimento Portland pelo método de aspersão de solução de nitrato de prata. A verificação de ataque por cloreto na estrutura é normalmente feita através de exames laboratoriais, demorados em que apresentam um custo muito alto. Pesquisando a aplicabilidade do método de aspersão de nitrato de prata in loco, em materiais à base de cimento Portland como indicador com capacidade de informar a presença ou não de contaminação por cloretos, evitando assim de imediato o teste laboratorial. Para que os resultados destes ensaios tivessem credibilidade quanto à presença de cloretos livres nas amostras, foi realizado, paralelamente à aspersão de nitrato de prata, um acompanhamento das amostras através de ensaios eletroquímicos. Observou-se com os resultados experimentais da pesquisa que a aplicabilidade do método de aspersão de solução de nitrato de prata vem a ser de grande relevância para o meio técnico, por ser um método qualitativo, de fácil aplicação, barato e provendo informações rápidas para que os profissionais da área de engenharia possam diagnosticar com segurança as estruturas com corrosão contaminadas por cloreto
The corrosion by chlorides is considered by a number of researchers the most dangerous pathological manifestation attacking concrete reinforcements. The assessment of the attacks to the structure by sodium chloride is usually done in the laboratory, takes too long and costs too much. The.main reason for this work is to assess the presence of free chlorides in Portland cement concrete and mortar through the silver nitrate aspersion method, which is justified by the fact that Our objective is to evaluate the applicability of the silver nitrate aspersion method in loco, in Portland-cement-based materials as indicators capable of showing the presence or not of contamination by chlorides, avoiding the immediate need for lab tests. So as to give credibility to the test for presence of free chlorides in the samples, these were checked by means of electrochemical tests in parallel with the silver nitrate aspersion. The experimental results of these tests showed that the applicability of the silver nitrate aspersion method seems to be of great relevance in the technical environment, as it is a qualitative method, easily applicable, inexpensive and capable of providing quick information so that professionals can safely diagnose the levels of chloride corrosion in the structures

A indústria cimenteira busca alternativas para economia de recursos no processo produtivo, em especial envolvendo o uso de materiais residuais no cimento, como escórias siderúrgicas. A escória de aciaria, em particular, apresenta composição desfavorável para aplicação in natura, porém há metodologias na literatura de modificação do material para aplicações cimentícias. No entanto, ainda não se encontram avaliações da corrosão de armaduras de aço em compósitos cimentícios com essa adição, seja em meio sólido ou líquido (água de poro). Esse estudo avaliou, através de curvas de polarização e da espectroscopia de impedância eletroquímica (EIE), a resistência à corrosão do aço CA-50 em soluções representativas de águas de poro extraídas por pressão de pastas de cimento com 25 % de escória de aciaria in natura ou modificada por processo pirometalúrgico. Para efeitos comparativos, foi feita também a avaliação do desempenho do aço em meios de águas de poro indicadas na literatura como representativas de cimento Portland comum e de escória de alto forno. O efeito da presença de espécies agressivas na resistência à corrosão do aço foi avaliado adicionando-se 1,0 % de NaCl em massa às soluções estudadas. Nas águas de poro sem 1,0 % de cloreto, o aço CA-50 apresentou-se passivo e não mostrou indícios de corrosão nos ensaios nem de polarização nem de EIE durante 120 h de imersão. Entretanto, os ajustes dos diagramas com circuito elétrico equivalente (CEE) apontaram que as características de proteção da camada passiva formada nas águas de poro de cimento com escória de aciaria foram superiores, resultando em maior resistência à corrosão do aço CA-50 nestes meios. Por sua vez, nos meios com 1,0 % de NaCl, após polarização e EIE até 120 h, o aço sofreu corrosão para as águas de poro de cimento comum e escória de alto forno, porém não corroeu nas águas de poro representativas de cimentos com escórias de aciaria, cujo melhor desempenho foi associado à maior alcalinidade destes meios. A caracterização microestrutural por microscopia eletrônica de varredura após os ensaios de polarização anódica e de imersão mostrou que o principal produto de corrosão formado foi a lepidocrocita (?-FeOOH), comum em ataque do aço por cloretos.
The cement industry seeks alternatives to save resources in production processes, especially involving the use of residual materials in cements, such as slags. Steel slags present unfavorable composition for application as cement additions in natura, but there are methodologies in the literature for modifying this material for commercial application. However, there are no evaluations of the corrosion of steel reinforcements in cementitious composites with steel slags, either in solid or liquid medium (pore water). The present study employed polarization curves and electrochemical impedance spectroscopy (EIS) to evaluate the corrosion resistance of CA-50 steel in pore water solutions representative of cement pastes with 25 % steel slag in natura or modified by a pyrometallurgical process. For comparison purposes, the performance of CA-50 steel in the pore waters indicated in the literature as representatives of Portland cement and blast furnace slag activated with cement were also evaluated. The effect of aggressive species on the corrosion resistance of the steel was assessed by adding 1.0 % NaCl by mass to the pore water solutions. Without 1.0 % chloride addition, CA-50 steel exhibited good performance and showed no evidences of corrosion in all of the investigated media, both in anodic polarization and in EIS tests performed up to 120 h immersion. However, the fitting of the EIS diagrams with equivalent electric circuit (EEC) revealed that the protectiveness of the passive layer formed in pore waters representative of cements with steel slags were superior, indicating better corrosion resistance of CA-50 steel in these media. Conversely, when 1.0 % chloride was added to the pore waters, CA-50 steel presented pitting corrosion, and impedance decreases with immersion in the pore waters representative of pure cement and blast furnace slag, whereas no corrosion was detected by both methodologies in pore waters representatives of cements with steel slags, which superior performance was ascribed to their higher alkalinity. Microstructural characterization by scanning electron microscopy (SEM) after anodic polarization and immersion tests showed that the main corrosion product formed was lepidocrocite (?-FeOOH), usual of chloride attack of steel.

O concreto normalmente oferece um alto grau de proteção contra a corrosão ao aço, devido à formação de uma fina película protetora na sua superfície, causada pela alta alcalinidade do concreto. Entretanto, essa película pode ser rompida tanto pela diminuição do pH da solução dos poros do concreto (por carbonatação, por exemplo) ou pela penetração de íons agressivos (como cloretos, por exemplo) até a superfície do aço. O presente trabalho tem por objetivo comparar o desempenho de concretos feitos com diferentes tipos de cimento Portland normalizados no Brasil frente à ação de íons cloreto provenientes de fontes externas. O programa experimental foi realizado com cinco diferentes tipos de cimento (CPII-E, CPII-F, CPIV, CPV ARI e CPV ARI-RS), com e sem adições, e cinco relações água/aglomerante (0,30; 0,35; 0,45; 0,60 e 0,80) em ensaios acelerados de despassivação por cloretos, por meio de ciclos de imersão e secagem dos corpos-de-prova em solução contendo 3,5% de cloreto de sódio. O método de Potencial de Eletrodo foi utilizado para monitorar a corrosão ao longo do tempo. Paralelamente foram realizados ensaios de resistência à compressão do concreto aos 28 dias, de perda de massa da armadura e de teor de cloretos livres no cobrimento da armadura. Os resultados obtidos mostraram que a escolha do tipo de cimento tem influência tanto na resistência à compressão simples quanto na resistência à corrosão das armaduras, verificada através dos ensaios de potencial de eletrodo, de perda de massa gravimétrica da armadura e de teor de cloretos livres. No entanto não houve um tipo de cimento que apresentasse os melhores resultados para todos os tipos de ensaio.
Concrete usually provides a high level of protection against steel corrosion, due to the formation of a fine protecting film on its surface, caused by concrete alkalinity. However, this film can be torn both as a result of the decrease in the pH of the solution of the concrete pores (by carbonation, for example) or as a result of the penetration of aggressive ions (such as chlorides, for example) up to the surface of the steel. The present work has the objective of comparing the performance of concrete made with different kinds of Portland cement regulated in Brazil before the action of chloride ions derived from external sources. The experimental program was performed with five different types of cement (CPII-E, CPII-F, CPIV, CPV ARI and CPV ARI-RS), with and without additions, and five water/agglomerative relations (0.30; 0.35; 0.45; 0.60 and 0.80) in acceleration assays of inactivation by chlorides, by means of immersion cycles and drying of proof bodies in a solution contained 3.5% of sodium chloride. The method of Electrode Potential was used to monitor corrosion over time. Concomitantly, resistance tests were performed as to the compression of the concrete at 28 days, from the loss of mass of the armature and content of free chlorides in the armature coating. The results obtained showed that the selection of the kind of cement has an impact both on the simple compression resistance and on the resistance to armature corrosion, verified through tests of electrode potential, of armature gravimetric mass loss and free chloride content. However, there was not a kind of cement presenting the best results for all types of assay.

A durabilidade dos edifícios em concreto armado só pode ser alcançada se for atendido um conjunto de requisitos e critérios nas etapas de projeto, execução e manutenção, nas quais os materiais envolvidos precisam ser adequadamente especificados, produzidos e empregados, de acordo com as respectivas rotinas dessas etapas. Assim, o requisito genérico de proteção das armaduras de aço carbono, para a durabilidade de estruturas, é contemplado por vários critérios, desde a etapa de projeto. Esta dissertação trata dos critérios pertinentes à qualidade do concreto e visou contribuir para a evolução de procedimentos para o controle tecnológico de concretos estruturais de cimento Portland, em atmosferas marítimas e urbanas, em clima tropical, com vistas à proteção de armaduras de aço carbono. O programa experimental estudou três lotes diferentes de concretos estruturais, semelhantes quanto a especificações básicas de abatimento: 10 ± 2 cm, de fck 30 MPa e para ambiente classe III da NBR 6118 (2003). O objetivo foi caracterizar e analisar a influência de propriedades físicas do estado fresco sobre o estado endurecido de concretos, dentro da faixa de consistência citada, com ênfase nas propriedades relacionadas ao teor de ar das misturas e suas respectivas resistências à carbonatação e ao ingresso de íons cloreto. A amostragem, os ensaios no estado fresco e a moldagem dos corpos-de-prova foram realizados durante três concretagens conduzidas em duas obras de edifícios de múltiplos andares, na cidade de João Pessoa/PB. As composições e a produção dos lotes ficaram a cargo da central dosadora e fornecedora do concreto em cada obra. O lote inicial serviu para o treinamento da equipe, em campo e laboratório, com amostragem de seis caminhões. Os outros dois lotes, identificados como 1 e 2, foram caracterizados em condições bastante semelhantes, sempre pela mesma equipe, e representados pela amostragem de cinco e seis caminhões, respectivamente. As propriedades medidas no estado fresco foram: abatimento do tronco de cone pela ABNT NBR NM 67 (1998); teor de ar por método pressométrico da ABNT NBR 47 (2002); massa específica pela ABNT NBR 9833 (2008); relação água/materiais secos por analogia à ABNT NBR 9605 (1992); e compactabilidade dos concretos adensado e não adensado, por adaptação da BS EN 12350-4 (2008). Para o estudo das propriedades no estado endurecido, os corpos-de-prova eram cilíndricos, com 10 cm de diâmetro e 20 cm de altura, e foram maturados por dois métodos adaptados do Tipo A da ASTM C 684 (1999). Certas propriedades foram ainda caracterizadas para condições normais de cura da ABNT NBR 5738 (2003). As propriedades estudadas no estado endurecido foram: resistência à compressão pela ABNT NBR 5739 (2007); resistência à tração por compressão diametral pela ABNT NBR 7222 (1994); absorção de água por capilaridade pela ABNT NBR 9779 (1995); absorção de água total e índice de vazios pela ABNT NBR 9778 (2005); resistência à carbonatação em câmara com CO2 (5%; UR 65 + 10 %; 23 + 3 °C); e resistência à penetração de cloretos e CO2, por três ciclos de um dia de molhagem e 27 dias de secagem, entre sete e 91 dias. De modo complementar, foram moldados corpos-de-prova específicos de aço e concreto, para medidas de potencial de circuito aberto, com vistas à continuidade de pesquisas sobre envelhecimento acelerado. A maioria das propriedades foram medidas por duas repetições, constando os resultados individuais em apêndices. A análise inicial dos resultados dos três lotes foi descritiva e resumiu em tabelas o valor médio, desvio padrão, valor máximo, valor mínimo, a amplitude e o coeficiente de variação de cada lote. As propriedades de cada lote também foram comparadas por análise de variância e, ao final, foram correlacionadas de modo conjunto, independentemente do lote de origem. Nesse caso, foram destacadas as melhores correlações entre propriedades, independentemente dos materiais constituintes de cada concreto. Entre as propriedades do estado fresco, destacaram-se as seguintes: a) o abatimento do tronco de cone apresentou correlação forte e inversa (r² = -0,802, para lotes 1 e 2) com resistência à compressão após um dia de cura acelerada em temperatura moderada, em método similar ao Tipo A da ASTM C 684 (1999); b) o teor de ar pelo método pressométrico apresentou correlações de razoáveis a fortes com a resistência à compressão a 28 dias (r² = -0,698, para lotes 1 e 2), com a resistência à tração por compressão diametral por cura acelerada a sete dias (r² = -0,818, para lotes 1 e 2), com a profundidade de carbonatação em câmara de CO2 (r² = 0,699, para lotes 1 e 2) e com a profundidade de penetração de cloretos por três ciclos de imersão e secagem (r² = 0,625, para lotes 1 e 2); c) as medidas de compactabilidade do concreto adensado, ainda que realizadas em condições de campo, apresentaram várias correlações moderadas com outras propriedades do estado fresco e endurecido. No estado endurecido, destacaram-se as seguintes correlações: a) r² da ordem de -0,75 para a resistência à compressão a um dia dos concretos dos lotes 1 e 2, com cura acelerada de 0/24 horas em temperatura moderada, e a profundidade de carbonatação em câmara de CO2 (5%) e a de penetração de cloretos por três ciclos de imersão e secagem, ambas analisadas a 91 dias, tendo os corpos-de-prova recebido cura inicial acelerada de 24/48 h, em temperatura moderada, seguida de imersão normal por até sete dias; b) r² de -0,682 entre a resistência à tração por compressão diametral, com cura acelerada de 24/48h em temperatura moderada seguida de cura normal por até sete dias, e a profundidade de ingresso de íons cloreto, para os três lotes submetidos aos ciclos citados; c) valores de r² entre 0,521 e - 0,561 para as correlações entre a absorção de água por capilaridade, em corpos-de-prova submetidos à cura inicial acelerada em temperatura moderada por 24/48 h e em temperatura normal por até sete dias, e a resistência à carbonatação para os lotes submetidos aos ciclos citados. Assim, esta pesquisa conclui e propõe que, além do teor de ar no estado fresco, as resistências à compressão e à tração por compressão diametral entre um e sete dias, por cura acelerada do Tipo A da ASTM C 684 (1999) ou por duração adaptada da mesma, sejam propriedades que passem a ser avaliadas em concretos, com vistas a melhorar e controlar a sua resistência a agentes agressivos. Nesta pesquisa, a microestrutura nas primeiras idades do concreto mostrou ser mais determinante da rede de conexão de poros e do transporte de agentes agressivos do que a microestrutura em idades mais avançadas de hidratação; e trabalhos futuros devem confirmar esta interpretação. Espera-se que estes resultados possam estimular novas práticas de qualificação de concretos em estudos de dosagem ou no ato do recebimento de concretos pré-misturados, especialmente em ambientes mais agressivos às armaduras, com vistas à futura evolução de procedimentos da ABNT NBR 12655 (2006).
Durability of reinforced concrete buildings can only be achieved if a set of requirements and criteria is met in the design, execution and maintenance phases, in which the materials must be properly specified, manufactured and employed, according to the respective procedures of these phases. Therefore, the general requirement of protection of carbon steel reinforcements, for structural durability, is contemplated by several criteria as early as the design phase. This thesis addresses the relevant criteria concerning concrete quality and its objective was to contribute to the evolution of technological control procedures for Portland cement structural concretes, in urban and maritime atmospheres in tropical climate, aiming at the protection of carbon steel reinforcements. The experimental program studied three different batches of structural concrete that were similar in terms of slump test basic specifications: 10 ± 2 cm, fck = 30 MPa and class III of ABNT NBR 6118 (2003) environmental classification. The goal was to characterize and analyze the influence of physical properties of fresh concrete on hardened concrete, within the previously mentioned consistency range, with emphasis on those properties related to air content of the mixtures and their respective carbonation and chloride ion penetration resistances. Sampling, fresh concrete tests and specimen molding were conducted during three cast-in-place concretes in two construction sites of multi-storey buildings in the city of João Pessoa, state of Paraíba, in Brazil. The batch plant supplying the concrete for each construction site was responsible for batch composition and production. The initial batch was used to train the team, in the field and laboratory, with a sample of six trucks. The other two batches, identified as 1 and 2, were characterized under very similar conditions, always by the same team, and the samples consisted of five and six trucks, respectively. The properties measured in fresh concrete were: slump test according to Brazilian norm ABNT NBR NM 67 (1998); air content by the pressure method of ABNT NBR 47 (2002); bulk density according to ABNT NBR 9833 (2008); water/dry material ratio by analogy with ABNT NBR 9605 (1992); and compactability of compacted and non-compacted concretes, by adaptation of BS EN 12350-4 (2008). In order to study the properties of hardened concrete, the specimens were cylindrical, measuring 10 cm in diameter and 20 cm in height, and were matured by using two methods adapted from Type A of ASTM C 684 (1999). Some properties were also characterized for normal curing conditions according to ABNT NBR 5738 (2003). The properties studied in hardened concrete were: compressive strength according to ABNT NBR 5739 (2007); splitting tensile strength as per ABNT NBR 7222 (1994); capillary water absorption according to ABNT NBR 9779 (1995); water absorption by immersion and void ratio following ABNT NBR 9778 (2005); carbonation resistance in CO2 chamber (5%; 65 + 10 % RH; 23 + 3 °C); and chloride and CO2 penetration resistance, using three one-day wet and 27-day dry cycles, between seven and 91 days. As a complement, specific steel and concrete specimens were molded to measure open circuit potential, aiming at the continuity of researches on accelerated ageing. Most properties were measured twice and the individual results are presented in appendices. Preliminary analysis of results from the three batches was descriptive and summarized in tables the mean value, standard deviation, maximum value, minimum value, amplitude and coefficient of variation for each batch. The properties of each batch were also compared using analysis of variance and, at the end, were correlated as a whole, regardless of the batch of origin. In this case, the best correlations among properties were highlighted, regardless of the materials used in each concrete. Among the properties of fresh concrete, the following are noteworthy: a) the slump test presented strong and inverse correlation (r² = -0.802, for batches 1 and 2) with compressive strength after one day of accelerated curing at moderate temperature, using a method similar to Type A of ASTM C 684 (1999); b) air content in the pressure method presented reasonable to strong correlations with compressive strength at 28 days (r² = -0.698, for batches 1 and 2), with splitting tensile strength with accelerated curing at seven days (r² = - 0.818, for batches 1 and 2), with carbonation depth in CO2 chamber (r² = 0.699, for batches 1 and 2) and with chloride penetration depth after three immersion-drying cycles (r² = 0.625, for batches 1 and 2); c) compactability measurements of compacted concrete, despite being taken in field conditions, presented several moderate correlations with other properties of fresh and hardened concrete. In hardened concrete, the following correlations should be highlighted: a) r² was -0.75 for compressive strength at one day of the concretes from batches 1 and 2, with 0/24- hour accelerated curing at moderate temperature, and carbonation depth in CO2 chamber (5%) and chloride penetration depth after three immersion-drying cycles, both analyzed at 91 days, after the specimens underwent 24/48-hour initial accelerated curing at moderate temperature, followed by normal immersion for up to seven days; b) r² was -0.682 between splitting tensile strength, with 24/48-hour accelerated curing at moderate temperature followed by normal curing for up to seven days, and chloride ion penetration depth, for the three batches submitted to the aforementioned cycles; c) r² values between 0.521 and - 0.561 for the correlations between capillary water absorption, in specimens submitted to initial accelerated curing at moderate temperature for 24/48h and at normal temperature for up to seven days, and carbonation resistance for the batches submitted to the aforementioned cycles. Therefore, this research concludes and proposes that, besides air content in fresh concrete, compressive strength and splitting tensile strength between one and seven days, using accelerated curing of Type A of ASTM C 684 (1999) or for a duration adapted from that norm, are properties that should be evaluated in concrete, with the purpose of improving and controlling resistance to aggressive agents. In this research, the microstructure of the early ages of concrete proved to be more determinant of the pore structure connection and of the transport of aggressive agents than the microstructure at later ages of hydration; and future studies should confirm this interpretation. It is expected that these results will encourage new practices for the qualification of concrete in mixture proportion studies or when ready mixed concrete is received at construction sites, especially in environments that are more aggressive to reinforcements, with a view to developing future procedures of ABNT NBR 12655 (2006).

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Neste trabalho o fen?meno da carbonata??o do cimento Portland ? investigado por diferentes abordagens, por?m convergindo para o mesmo objetivo: aprofundar o conhecimento dos processos e os efeitos do CO2 na matriz ciment?cia. Esse fen?meno ocorre atrav?s de rea??es qu?micas entre o ?cido carb?nico, formado pela rea??o do CO2 com a ?gua, e alguns produtos hidratados do cimento. Em subsuperf?cie, devido ao incremento de temperatura e press?o o meio se torna mais danoso, sendo assim, na ?rea de petr?leo e g?s, principalmente a cimenta??o, tem um grande interesse por esta problem?tica. Frente ao exposto, neste trabalho foram desenvolvidos e publicados tr?s artigos intitulados: [Artigo I] Efeitos do di?xido de carbono no cimento Portland: uma rela??o entre a sedimenta??o est?tica e a carbonata??o, [Artigo II] Carbonata??o em cimento Portland para po?os de petr?leo: influ?ncia do tempo de hidrata??o antes do contato com o CO2 e [Artigo III] Estudo sobre a carbonata??o em uma matriz de cimento Portland classe G em ambientes supercr?tico e saturado. No primeiro estudo foi proposto um modelo para o comportamento da sedimenta??o e da carbonata??o ocorrido em uma pasta inst?vel, onde a sedimenta??o est?tica baseia-se na mec?nica dos fluidos. No segundo estudo foram investigadas tr?s pastas com a mesma formula??o, por?m curadas durante per?odos de tempos de 8 horas, 7 dias e 28 dias antes do contato com o CO2. Os resultados mostraram processos distintos, mas com efeitos similares de carbonata??o ao final. E no ?ltimo estudo as amostras foram expostas ao mesmo tempo em CO2 supercr?tico e saturado. As an?lises mostraram resultados significativamente distintos, onde as amostras expostas ao meio saturado sofreram um ataque 35% superior ?quelas submetidas ao CO2 supercr?tico. Este trabalho apresenta estudos que buscam promover uma maior compreens?o da fenomenologia da a??o do CO2 e ao mesmo tempo dar subs?dios para o desenvolvimento de tecnologias que combatam a carbonata??o.
In this study the phenomenon of Portland cement carbonation is investigated by different approaches, but converging towards the same objective: to deepen the knowledge of the processes and the effects in the cement matrix. The phenomenon occurs through chemical reactions between carbonic acid, formed by the reaction of CO2 with water, and some hydrated products of cement. In subsurface due to the increase of temperature and pressure the medium becomes more damaging, being therefore, in the area of oil and gas, mainly cementing, has a great interest by this problematic. In view of the above, in this study three articles were developed and published entitled: [Article I] Effects of carbon dioxide in Portland cement: a relation between static sedimentation and carbonation, [Article II] Carbonation in oil well Portland cement: Influence of hydration time prior to contact with CO2 and [Article III] Study of carbonation in a class G Portland cement matrix at supercritical and saturated environments. In the first study, a model was proposed for sedimentation and carbonation behavior in an unstable slurry, the static sedimentation based on fluid mechanics. In another study, three slurries of the same formulation were investigated, but were cured for periods of 8 hours, 7 days and 28 days before CO2 contact. The results showed distinct processes, but with similar carbonation effects at the end. In addition, in one last study samples were exposed at the same time in supercritical and saturated CO2. The analyzes showed significantly different results, where the samples exposed to the saturated medium suffered a 35% higher attack. This work presents studies that seek to promote a greater understanding of phenomenology and give subsidies for the development of technologies that combat carbonation.

Orientador : Prof. Dr. Marcelo Henrique Farias de Medeiros
Co-orientador : Prof. Dr. Juarez Hoppe Filho
Dissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Construção Civil. Defesa: Curitiba, 24/04/2014
Inclui referências
Area de concentração : Materiais e estruturas
Resumo: A incorporação de adições minerais na composição do cimento Portland é imprescindível, pois reduz o impacto ambiental da indústria cimenteira, além de destinar, adequadamente, resíduos de outros setores industriais, possibilitando vantagens econômicas e ambientais, além de interferir na microestrutura da matriz hidratada, alterando a durabilidade de concretos e argamassas. A hipótese deste trabalho é de que as normas brasileiras atualmente em vigor apresentam inconsistências, classificando erroneamente algumas pozolanas. Desta forma, o programa experimental consistiu na aplicação das técnicas de investigação de pozolanicidade de adições minerais, sendo elas normatizadas ou não no Brasil, utilizando adições minerais: cinza de casca de arroz, metacaulim, sílica ativa, fíler quartzoso, fíler calcário e material cerâmico com diferentes graus de moagem e calcinação em forno mufla. Foram realizados ensaios de caracterização das amostras e a atividade pozolânica foi determinada pelos ensaios de índice de atividade pozolânica (IAP) em argamassa com cimento Portland (NBR 5.752) e com cal hidratada (NBR 5.751), ensaio Chapelle modificado (NBR 15.895) e difração de raios - X (DRX) de pastas idênticas às utilizadas nas argamassas preconizadas pelas normas, que permitem analisar o consumo de portlandita, um indicativo imprescindível da atividade pozolânica. A análise conjunta do IAP com a DRX visou demonstrar que algumas pozolanas apresentam baixo desempenho quando avaliadas por intermédio da resistência à compressão de argamassas, porém são capazes de fixar grande quantidade de cal na formação de compostos hidratados. As normas não consideram parâmetros importantes para a atividade pozolânica, como a área específica, as características físico-químicas, o teor de materiais amorfos e a taxa de reação ao longo do tempo, os quais interferem na resistência da argamassa. Palavras-Chave: atividade pozolânica, adições minerais, resistência à compressão.
Abstract: The incorporation of mineral additions into the Portland cement composition is indispensable, because it reduces the environmental impact of the cement industry and also destine, properly, residues from others industrial segments. This measure brings environmental and economic advantages, apart from interfering in the microstructure of the hydrated matrix, altering the durability of concretes and mortars. The hypothesis of this work is that Brazilian norms currently in vigor present inconsistencies by misclassifying some pozzolanes. Therefore, the experimental program consisted in applying investigation techniques of pozzolanicity of mineral additions, these being normalized or not in Brazil, using: rice husk ashes, metakaolin, silica fume, quartzose filler, calcarium filler and ceramic materials with different milling degrees (0,5; 1,0; 1,5 hour) and calcination in mufla oven. Characterization trials of the samples were made and the pozzolanic activity was determined by tests of the index pozzolanic activity (IPA) in Portland cement mortars (NBR 5.752) and mortar with hydrated lime, modified Chapelle test (NBR 15.895) and X-ray diffraction (XDR) of pastes identic to those used in mortars recommended by standards, which allows analyzing portlandite consumption, a very important indicative of pozzolanic activity. The analysis of IPA and XDR aims to demonstrate that some pozzolanes present low performance when evaluated through mortar compressive strength but are able to fasten high quantities of lime through the formation of hydrated compounds. The standards ignore important for the pozzolanic activity parameters such as specific area, physicochemical characteristics, the amorphous content and reaction rate over time, which interfering in the mortar compressive strength. Key words: pozzolanic activity, mineral additions, compressive strength.

Orientador : Prof. Dr. Kleber Franke Portella
Coorientadora : Dra. Mariana D'Orey Galvão Portella Bragança
Dissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia e Ciência dos Materiais - PIPE. Defesa: Curitiba, 22/02/2017
Inclui referências : f. 114-121
Área de concentração: Engenharia e ciência de materiais
Resumo: A reação álcali-agregado (RAA) é um mecanismo de degradação que ocorre em diversas estruturas de concreto submetidas a condições frequentes de umidade. De forma geral, trata-se de uma reação fundamentada em interações químicas entre os minerais constituintes do agregado e os álcalis presentes no cimento Portland, em presença de água. O produto formado é um gel sílico-alcalino que se expande na presença de umidade e pode impulsionar processos de fissuração nas estruturas de concreto devido ao aumento das tensões confinantes no interior dos poros do mesmo. Atualmente, já estão disponíveis várias metodologias para indicar a presença da RAA em estruturas degradadas e avaliar previamente o potencial reativo dos agregados empregados nas obras civis. Dentre os métodos de investigação mais comuns, pode-se citar por exemplo: a análise petrográfica do agregado; a microscopia eletrônica de varredura associada à espectroscopia por energia dispersiva de raios X; e o mais comum dos métodos: a avaliação da RAA envolvendo os ensaios laboratoriais normatizados pela NBR 15577 (ABNT, 2008), que permitem o diagnóstico desta manifestação patológica por meio do monitoramento da expansão de corpos-de-prova submetidos a meios agressivos. Desta forma, utilizando os métodos descritos na normativa, a intenção deste trabalho foi estudar a influência da incorporação de nano-Fe3O4 na reatividade de agregados em argamassas e concretos de cimento Portland, quando expostos a condições ambientais desfavoráveis. Além deste estudo, também foi possível verificar a relação entre a expansão experimentada pelos CP's ensaiados e a absorção de água no decorrer do ensaio, por meio do monitoramento periódico das massas das amostras; a fim de observar a expansão devido à saturação dos materiais submetidos à condição de umidade excessiva, e avaliar a sua utilização como um método de investigação da RAA. Simultaneamente a estes estudos, concretos com adição de 1% de nano-magnetita foram investigados quanto às suas propriedades físicas e mecânicas, e a conclusão obtida foi de que, com 1 ano de idade, a adição apresentou indícios de reação com o meio cimentício e diminuiu a produção de gel de RAA no interior destes; além disso, todos os resultados apresentaram parâmetros condizentes com as recomendações normativas. As conclusões obtidas nesta pesquisa evidenciaram a possibilidade de expansão do estudo da técnica de adição de nano-magnetita para concretos, que por serem ensaiados em condições de menor agressividade tendem a reagir com a adição nanométrica, mesmo que lentamente. Além disso, os dados obtidos para o monitoramento da variação mássica nos prismas, permitiram comprovar que a técnica pode ser utilizada de forma complementar a metodologia normativa de avaliação da expansão, pois, para o monitoramento ao longo de 365 dias, o ensaio de variação dimensional indicou a ausência de reação. Os produtos formados no interior dos concretos tendem, inicialmente, a acumular-se nos poros e vazios, desta forma, a expansão dos prismas pode ocorrer apenas para idades mais avançadas, muito embora já haja formação inicial de gel, identificada pela variação de massa. Palavra-Chave: Reação álcali-agregado. Manifestação patológica. Métodos de investigação. Nano-magnetita. Variação mássica.
Abstract: Alkali-aggregate reaction (AAR) is a degradation mechanism that occurs in several concrete structures subject to constant humidity conditions. In general, it is a reaction based on chemical interactions among the aggregate mineral components and alkalis contained in Portland cement, in presence of water. The formed product is a silico-alkaline gel that expands in the presence of moisture and may boost cracking processes at concrete structures due to increased confined stress inside their pores. Currently, several methods are available to diagnose the presence of AAR in degraded structures and perform a prior evaluation of the reactive potential of aggregates used in engineering works. Amongst the more common methods of investigation, some are worth mentioning, such as: aggregate petrographic analysis, scanning electron microscope associated with energy dispersive spectroscopy X-ray and the most common method: evaluation of AAR involving NBR 15577 standardized laboratory tests (ABNT, 2008), that allows the diagnosis of pathological manifestations by monitoring the expansion on samples subjected to aggressive environments. Thus, using the methods described in the normative, the primary intention was to study the influence of nano-Fe3O4 embedding in the reactivity of aggregates in Portland cement mortars and concretes when exposed to unfavorable environmental conditions. Aside from this study, it was also possible to verify the relationship between the expansion experienced by the samples tested and the water absorption during testing, by periodic monitoring of the sample masses; in order to observe the expansion due to saturation of the samples subjected to excessive moisture conditions, and evaluate its use as an additional method of AAR investigation. Simultaneously, concretes with a 1% addition of nano-magnetite were investigated as to their physical and mechanical properties, and it was concluded that, within 1 year, the addition didn't show any signs of reaction with cement and decreased the production of AAR gel on the inside of these samples; besides, all results presented parameters fitting with standardized recommendations. The conclusions obtained from this study shows the possibility of expanding the study of nano-magnetite additions techniques for concrete, which, because they are tested in less aggressive conditions, tend to react with nanometric additions, even if slowly. Furthermore, the data obtained for monitoring the mass variations in the prisms, proved that the technique can be utilized, complementarily to the standard expansion evaluation methodology, since, for the 365 days monitoring, the dimensional variance test indicated the absence of reaction. The products formed within the concrete tend at first to accumulate in the pores and voids, thus the expansion of the prisms can occur only for more advanced ages, although there are already initial gel formation, identified by mass variation. Keywords: Alkali-aggregate reaction. Pathological manifestation. Investigation methods. Nano-magnetite. Mass variation.t

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The study aims to analyze the influence of the presence of CaCO3 in the corrosion behavior of low carbon steel (API 5L – grade B), in order to simulate the presence of carbonated cement in contact with the oil well casing in an interstitial CO2-rich brine solution. The water composition represents a scenario of Tupi oil-field in the Santos Basin (offshore) above the geological layer of the pre-salt: solution saturated with CO2, NaCl and CaCO3 and a solution saturated with CO2 and NaCl at temperature of 80°C and pressure of 15 MPa. In this study were analyzed the corrosion films on the steel surface with respect to corrosion rate, morphology, chemical composition and chemical stability. The uniform corrosion was predominant and there was small heterogeneities in the corrosion film influenced by preferential dissolution of ferrite present in the steel microstructure. The main corrosion product in presence of CaCO3 in solution was a calcium enriched siderite and the average corrosion rate observed was about 0. 67mm/y over the first 72 hours of reaction. As opposed to fresh cement, the experimental results indicate that initially the carbonated cement does not passivate standard carbon steel, despite the high carbonate alkalinity in solution. Besides, the presence of calcium as a substitucional element promoted a distortion on the crystalline lattice of the calcium enriched siderite film formed on the steel surface, which may contribute to decreased resistance of this film.
Este estudo visa analisar a influência da presença de CaCO3 na corrosão do aço baixo carbono (API 5L - grau B), a fim de simular a degradação da pasta de cimento em contato com os tubos de revestimento em aço de poços de petróleo em soluções ricas de CO2 e NaCl. A composição da solução foi baseada no cenário geológico do campo de petróleo de Tupi na Bacia de Santos sobre a camada geológica do pré-sal: solução saturada com CO2, NaCl e CaCO3 e solução com CO2 e NaCl em uma temperatura de 80°C e uma pressão de 15 MPa. Neste estudo foram analisados os filmes de produtos de corrosão na superfície do aço no que diz respeito à taxa de corrosão, morfologia, composição química e estabilidade química. A corrosão uniforme foi predominante e observaram-se pequenas heterogeneidades no filme de produtos de corrosão, influenciadas pela dissolução preferencial da ferrita presente na microestrutura do aço. O principal produto de corrosão, na presença do CaCO3 em solução, foi o carbonato de ferro enriquecido de cálcio e a taxa de corrosão média observada foi de 0,67 mm/ano durante as primeiras 72 horas de reação. Ao contrário do cimento fresco, os resultados experimentais indicam que o cimento degradado (carbonatado) não impede a corrosão inicial do aço, apesar da sua degradação promover elevada quantidade de carbonatos alcalinos em solução. Além disso, a presença do cálcio como elemento substitucional proporcionou distorção na rede cristalina do filme de carbonato de ferro enriquecido de cálcio formado na superfície do aço, o que pode contribuir para uma menor resistência do filme.

Orientador : Gladis Camarini
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil
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Resumo: A durabilidade de estruturas de concreto armado é um assunto de crescente interesse, principalmente devido aos altos custos de manutenção apresentado por estruturas em envelhecimento. Um dos principais fatores determinantes da durabilidade é a qualidade do concreto de cobrimento das armaduras, cujas propriedades são reguladas pela dosagem de materiais, qualidade de execução e procedimentos de cura. O presente trabalho teve por objetivo investigar os efeitos da cura térmica a vapor sob pressão atmosférica e temperatura máxima de 60°C na durabilidade de concretos com diferentes teores de adição de escória de alto-fomo, comparando-os com os efeitos da cura úmida por 7 dias em temperatura ambiente. Foram analisadas a absorção capilar, permeabilidade ao ar, absorção de cloretos, carbonatação natural e carbonatação acelerada de concretos de relação água cimento 0,42, produzidos com cimentos com 53%, 27% e 0% de adição de escória de alto-fomo. Também as resistências à compressão e à tração foram determinadas, para caracterização dos concretos. De acordo com os resultados obtidos, os concretos com adição de escória apresentaram os melhores desempenhos contra o ataque de cloretos, independente da cura empregada, enquanto o cimento sem adição apresentou o melhor desempenho contra a carbonatação, onde a cura mostrou ser um diferencial. Entre outros pontos, concluiu-se que a resistência dos concretos estudados não está relacionada à sua durabilidade e que o emprego do cimento adequado pode minimizar os efeitos da cura térmica...Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital
Abstract: Reinforced concrete structures' durability has been an issue of great interest, due to the high cost of aging structures recuperation. One of the main determinant characteristics of durability is the reinforcement cover concrete's quality, whose properties are controlled by materiaIs proportion, quality of execution and curing procedures. The aim of this work was to investigate the effects of steam thermal curing, under atmospheric pressure and maximum temperature of 60°C, on the durability of concretes with different blast-furnace slag contents, comparing them with the effects of wet curing for 7 days in ambient temperature. Capillary absorption, air permeability, chloride ions absorption, natural carbonation and accelerated carbonation were determined in concretes of waterlcement ratio of 0,42, produced with Portland cements with slag contents of 53%, 27% and 0%. Compressive and tensile strength were also determined. According to results, slag cements concretes have presented the best performances against chloride attack, despite the curing procedure employed, while slag free cement has presented the best performance in front of carbonation, to which curing procedure has demonstrated to have a major effect. Among other points, it was concluded that concretes' compressive strength is not related to its durability and that the adequate cement employment can reduce thermal curing effects...Note: The complete abstract is available with the full electronic digital thesis or dissertations
Mestrado
Edificações
Mestre em Engenharia Civil

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The emission of greenhouse gases to the environment can be reduced by the adoption of the technology of geological storage of carbon. However, the materials usually employed in the construction of CO2 injection wells do not resist the acid attack by the CO2 in the presence of brine and suffer degradation in longer exposure times. Field and laboratory studies indicate that degradation of the materials occurs mainly at the interface between the cement paste and the steel casing. In this work, experiments that simulate the conditions of CO2 storage in saline aquifers of the Paraná Basin at a depth of 1500 m were conducted to investigate the chemical integrity of Class G cement paste and API N80 steel, involving a failure at interface steel-cement paste in different times (48h, 380h and 720h). The degradation of the cement paste was evaluated in terms of characteristics and depth of the region chemically modified. The corrosion films formed on steel were characterized in terms of morphology and thickness. The influence of these films on the steel corrosion resistance was evaluated by electrochemical measurements of open circuit potential and potentiodynamic polarization. The results indicate that the degradation or corrosion processes depend on the media that the system steel- cement paste was submitted and the exposure time. The degradation of the cement paste involved the formation of two zones, carbonated zone of high density and bicarbonate zone of high porosity, and the latter zone is critical since it can provide a path to CO2 leakage. The films of corrosion product formed on the steel are composed by iron-calcium complex carbonates and they have protective characteristics to the steel casing considering the experimental conditions used in this work.
A emissão gases de efeito estufa ao meio ambiente pode ser reduzida pela adoção da tecnologia de armazenamento geológico de carbono. Contudo, os materiais usualmente empregados na construção de poços injetores de CO2 não resistem ao meio ácido formado pelo CO2 na presença de água das formações geológicas, sofrendo degradação em longos tempos de exposição. Estudos de campo e de laboratório indicam que a degradação dos materiais ocorre principalmente na interface entre a pasta de cimento e o tubo de revestimento de aço. Neste trabalho, experimentos que simulam as condições de armazenamento de CO2 em aquíferos salinos da Bacia do Paraná a uma profundidade de 1500 m foram conduzidos para investigar a integridade química da pasta de cimento classe G e do aço API N80, envolvendo uma falha de ligação na interface pasta de cimento-aço em diferentes tempos (48h, 380h e 720h). A degradação da pasta de cimento foi avaliada em termos de características e profundidade da camada alterada quimicamente. Os filmes de produto de corrosão formados no aço foram caracterizados em termos de morfologia e espessura. A influência desses filmes na resistência à corrosão do aço foi avaliada por medidas eletroquímicas de potencial de circuito aberto e polarização potenciodinâmica. Os resultados obtidos indicam que a degradação ou corrosão depende do meio de degradação que o sistema cimento-aço foi submetido e do tempo de exposição. A degradação da pasta de cimento envolveu a formação de duas zonas, zona carbonatada de alta densidade e zona bicarbonatada de alta porosidade, sendo que esta última é crítica uma vez que pode constituir um meio de fuga para o CO2. Os filmes de produto de corrosão formados no aço são compostos por carbonatos mistos de ferro e cálcio e nas condições testadas tendem a apresentar características protetoras ao tubo de aço de revestimento do poço.