La temperatura de curado, utilizada por la industria de fibrocemento como catalizador en la hidratación del cemento para lograr alta resistencia inicial en sus productos, genera la hipótesis de expansión causada por formación tardía de etringita. Para el planteamiento de dicha hipótesis, el siguiente estudio contempló dos grupos de muestras con el objetivo de estudiar aisladamente su comportamiento químico y físico: uno de los grupos conformado por pasta cementicia con 35% de sustitución de calcario, y el otro conformado por fibrocemento con incorporación de PVA y celulosa. Por calorimetría isotérmica se observó la cinética de reacción de dos pastas, una de ellas curada a 23 ºC y la otra a 85 ºC donde esta última experimentó un efecto catalizador en sus reacciones. Ensayos de DRX y DTG/TG mostraron la presencia de etringita a 23 °C durante todas las edades de hidratación exhibiendo una tendencia de aumento en la intensidad de los picos y en la cantidad, respectivamente, en función del tiempo; sin embargo, a 85 ºC la presencia de esta fase fue inconstante durante las primeras edades de hidratación, a partir de mes de hidratación mostró aumento en cada una de las siguientes medidas realizadas mensualmente; a 85 °C hubo una menor formación de portlandita en comparación con los resultados obtenidos a 23 °C. Utilizando el método Rietveld y análisis químico fueron determinadas las cantidades y las composiciones químicas, respectivamente, de las fases del cemento anhidro y del calcario para alimentar el programa GEMS y simular la hidratación de la pasta estudiada en laboratorio para un tiempo infinito bajo la influencia de la temperatura. Simulaciones de la hidratación de la pasta se aproximaron a los resultados reportados por la revisión bibliográfica permitiendo predecir la presencia de fases en función de la estabilidad termodinámica. Resultados de porosimetría por inyección de mercurio mostraron una mayor concentración de poros, asociados a defectos, en muestras curadas a 85°C con respecto a las de 23 °C. Finalmente, medidas de variación longitudinal para muestras de fibrocemento elaboradas en laboratorio y en fábrica presentaron dispersión en los resultados de expansión para cada uno de los escenarios sin poder correlacionar todos los datos con el aumento de masa exhibido por cada una de las muestras; no obstante, se resalta el riesgo de deterioro del fibrocemento por el aumento de defectos causado por la temperatura así como la creación de todas las condiciones necesarias que favorecen la formación tardía de etringita a partir del proceso de fabricación empleado para este producto. / The curing temperature using by the fibercement industry as a catalyst in the hydration of cement, hypothesizes expansion caused by delayed ettringite formation. To approach this hypothesis, this study looked at two groups of samples in order to study its chemical and physical behavior individually. One group was composed of cement paste with 35% substitution of limestone filler, and the other by fibercement with addition of PVA and cellulose. In the isothermal calorimetry test was observed the kinetics reaction of both pastes, one cured at 23 °C and the other at 85 °C, the latter showed a catalytic effect in his reactions. XRD and DTG/TG showed the presence of ettringite at 23 °C for all hydration ages exhibiting a trend of increase in the peak intensity and amount, respectively in function of time, however, at 85 °C the presence of this phase was unstable during early ages of hydration until completing one month hydration where showed an increase in each of the following measurements monthly performed. At 85 °C there was a lower formation of portlandite when it was compared with results obtained at 23 °C. Using the Rietveld quantitative method analysis and chemical analysis were determined amounts and chemical compositions, respectively, of the phases of cement anhydrous and limestone filler to feed the GEMS software and simulate the hydration of paste studied in the laboratory for an infinite time under the influence of temperature. Simulations of paste hydration approached the reported data in literature allowing predicting the presence of phases according to thermodynamic stability. Additionally, results of mercury intrusion porosimetry showed a higher concentration of pores associated with defects, in samples cured at 85 ° C compared to 23 °. Finally, were taken measures of length offset of fibercement samples produced in laboratory and factory which had incorporation of PVA fibers and cellulose; they presented dispersion in the results of expansion for each of the scenarios unable to correlate with the mass gain exhibited by each sample. However, the risk of deterioration of the fibercement is highlighted by the increase of defects caused by temperature and the creation of all necessary conditions to favor the late formation of ettringite from the manufacturing process used for this product.

Os investimentos iniciais em moldes na indústria de pré-moldados de concreto de cimento Portland, em geral, são altos, havendo a necessidade de utilizá-los o mais intensivamente possível entre uma e outra moldagem. A conseqüência é que a desforma pode ocorrer em instantes inadequados, comprometendo a durabilidade do produto. Isto contraria o conceito fundamental da pré-moldagem que está relacionado ao rigoroso controle de qualidade do produto. A cura térmica é uma alternativa, pois é utilizada para acelerar a resistência mecânica inicial do concreto. Esse beneficio imediato é acompanhado por uma redução na resistência final comparativamente à cura normal em câmara úmida. Esta redução é atribuída ao desenvolvimento de uma microestrutura modificada. Para investigar esse fenômeno, com base nos conhecimentos em ciência e engenharia dos materiais, desenvolve-se um estudo experimental, aplicado a pré-moldados com pequena espessura. O objetivo principal é analisar tais modificações e os compostos hidratados, formados ao longo do tempo após a cura térmica, considerando os materiais empregados e estabelecendo relações com a perda de resistência final. Leva-se em conta a influência das adições e da duração dos ciclos térmicos. A análise da microestrutura está baseada nos seguintes ensaios: porosimetria por intrusão de mercúrio, microscopia eletrônica de varredura, termogravimetria e difração de raio-X. Confirma-se com base nos resultados que a cura térmica favorece a maior formação de portlandita e também acelera a reação pozolânica. Para a composição entre cimento Portland, a escória de alto forno (30%) e a sílica ativa (10%), submetidas a ciclos térmicos longos (12 horas Tmax=61°C), observa-se a maior perda na resistência mecânica a longo prazo. Neste caso, há fortes indícios de que há formação de fases com menor desempenho mecânico. Através de micrografias, para essa amostra, sugere-se a formação da etringita secundária com maior prejuízo na interface pasta-agregado. As conclusões sugerem que para minimizar as interferências no processo de cura e garantir resistências mínimas nas desmoldagens rápidas, com poucas perdas a longo prazo, é interessante associar ciclos térmicos curtos, cimento de alta resistência inicial, sílica ativa e superplastificante. / The initial investments of molds in the industry which makes pre-cast of Portland cement concrete is usually very high, thus creating a necessity to maximize the utilization of each moldings. The consequence is that the forms can be removed at inadequate time, which compromise the durability of the product. This contradicts the fundamental concepts of the pre-castings, which is related to a severe quality control. Steam curing is an alternative treatment and is used to accelerate the initial mechanical resistance of the concrete. This immediate benefit is accompanied by the decrease on final resistance compared to normal curing in humid chamber. This reduction is attributed to the development of a modified microstructure. To investigate this phenomenon, based on knowleledge of materials science and engineering, an experimental study is developed which is applied in pre-cast wich small thichness. The main objective of this work is to analyze the microstructure modifications and the hydrated compounds formed, after a period of steam curing, taking in account the used materiaIs, also to establish a relations with the loss of final strength. The influence of additions and duration of steam cycles are considered. The analyses of microstructures are based on the following tests: mercury intrusion porosimetry, scanning electron microscope, thermogravimetry and X-ray diffraction. Based on the results it can be confirmed that steam curing favors a large formation of ponlandite and also accelerates pozzolanic reaction. For the composition of Portland cement, slag fumace blast (30%) and active silica (10%), submitted for long period of thermal cycles (12 hours, Tmax=61°C), a great loss strength was observed. In this case it is possible the formation of phases with poor mechanical performance. Through micrographs, for this sample, it is observed the formation of secondary ettringite with a large damage in the interface aggregate-paste. The conclusions suggest that to minimize the interference in the process of curing and to guarantee a minimum strength during the rapid separation of the concrete from the molds, with a minor loss in a long term, it is interesting to associate short steam cycles, high initial resistance cement, adive silica and superplasticizer.

The thesis is focused on the possibility of using secondary energy resources as an additive to concrete to improve some of its resulting properties. The theoretical part is devoted to the problems of shrinkage and prominence hydration process during hydration of the concrete. This section also contains the results of research work from domestic and foreign sources of high temperature fly ash and fluidized bed combustion fly ash use and their using in concrete. The practical part verifies the possibility of using these materials and their combination as an additive to concrete with impact on the physical and mechanical properties.

Secondary energy products are used in the construction industry for a long time. More strict environmental limits for emissions to air have created new technologies combustion of materials in thermal power plants. In this way combustion are produced a new secondary energy products. It is an attempt to find of suitable use for these products. Their use will have ecological impact on the environment and it will allow prepare of new compositions of higher utility properties. The aim of this study was to develop a new mixture, using the new secondary energy products, for production concrete with high utility properties.

La réaction sulfatique interne (RSI) est une pathologie conduisant au gonflement et à la dégradation du béton de certains ouvrages. En tant que gestionnaire d'ouvrages, VINCI doit assurer la sécurité des usagers et des biens. Pour cela, une évaluation de l'aptitude au service des ouvrages concernés est nécessaire. Ce travail a pour but d'améliorer la modélisation des phénomènes mécaniques induits par la formation d'ettringite différée, notamment sous contrainte. Une campagne expérimentale a été réalisée sur éprouvettes prismatiques en béton réactif libres de contraintes, armées uniaxialement, armées triaxialement et soumises à un chargement uniaxial de compression de 14,5 MPa. Les phénomènes expansifs sont relativement isotropes en l'absence de contraintes et atteignent 0,6 % en fin de réaction. Le bridage induit par la présence des armatures conduit à une diminution importante des déformations dans les directions concernées, sans impact majeur sur le gonflement dans les directions libres : les déformations du béton initiées par la RSI sont de fait anisotropes sous chargement anisotrope. Une fissuration préférentielle est observée parallèlement à la direction gênée. L'application d'un chargement uniaxial de compression à hauteur de 14,5 MPa entraine un raccourcissement du béton dans la direction chargée, les déformations de fluage masquant les éventuelles expansions. La décharge de ces corps d'épreuve après environ 420 jours d'immersion a provoqué une reprise des gonflements de l'ordre de 0,10 % en 3 jours dans la direction chargée, sans effet visible dans les autres directions. Au cours des 200 jours suivants, des gonflements longitudinaux et transversaux similaires en termes de cinétique et d'amplitude ont été observés. Ce phénomène a été attribué au renouvèlement de l'eau de conservation ayant eu lieu au moment de la décharge, en particulier à une réaccélération du lessivage des alcalins. L'endommagement induit par la RSI sur le béton a été caractérisé par le biais d'essais de compression, traction par fendage et mesures de module d'Young avant et après gonflement. [...] / Delayed ettringite formation is a pathology leading to swelling and degradation of the concrete of certain structures. As structure manager, VINCI must ensure the safety of users and goods. To do so, an assessment of the serviceability of affected structures is necessary. This work aims to improve the modeling of mechanical phenomena induced by delayed ettringite formation, especially under stress. An experimental campaign was carried out on prismatic reactive concrete specimens. Some were plain, uniaxially reinforced, triaxially reinforced and subjected to an uniaxial compressive loading of 14.5 MPa. Expansions appeared fairly isotropic in stress-free conditions and reached 0,6 %. Restraint due to reinforcements led to decreased strains in the restrained directions. Expansions were only slightly impacted in transversal free directions. Therefore, DEF expansion under uniaxial stress is anisotropic. Cracks were observed parallel to the restrained direction. For prestressed concrete, creep strains hid possible strains induced by DEF. These specimens were unload after 420 days of immersion in water. It led to a strain increase of about 0,10 % in 3 days in the loaded direction, without any effect on transversal directions. Similar kinetic and range of expansion was measured in both longitudinal and transversal throughout the 200 following days. This phenomenon was understood as the consequence of an alkali leaching acceleration after storage water renewal that occurred during specimens unloading. DEF induced damage on concrete was characterize through compressive tests, brazilian tensile tests and Young modulus measurements before and after expansions. DEF effect on steel-concrete bond behavior was also measured through pull-out tests. Maximal steel-concrete bond stress appears slightly impacted by longitudinal expansions of about 0.25 %, but the bond shear modulus decreases significantly after DEF. All collected experimental data were used to fit a poromechanical model of DEF taking into account all the phenomena involved in the of reinforced concrete behavior (plasticity, damage, creep, shrinkage, distributed reinforcements...). [...]

Abstract Millions of tons of mine tailings are generated worldwide annually. Since many valuable metals such as Ag, Cu, Pb, Zn, Au and Ni are usually incorporated into sulphidic minerals, a large proportion of the tailings generated contain high amounts of sulphates and heavy metals. Some of these tailings are used as paste backfill material at mining sites, but large amounts are still being deposited into the tailings dams under water coverage. Sulphidic minerals are stable underground but after mining of the ore and several processing steps these minerals can be oxidized when they come into contact with water and air. This oxidation generates acid and thus reduces the pH of the surrounding environment. Furthermore, the heavy metals present in the mine tailings can be leached into the environment. This phenomenon, called Acid Mine Drainage (AMD), is one of the most critical environmental issues related to the management of sulphidic-rich tailings. Since AMD generation can still occur hundreds of years after closure of the mine, the mine tailings need stable, sustainable and economically viable management methods in order to prevent AMD production in the long term. The aim of this PhD thesis was to study various solidification/stabilization (S/S) methods for the immobilization of sulphidic mine tailings. The main focus was to develop a suitable chemical environment for achieving effective heavy metal (mainly arsenic) and sulphate immobilization while simultaneously ensuring good mechanical properties. Three treatment methods were tested: alkali activation, stabilization using hydrated lime (Ca(OH)2) and blast furnace slag (GBFS), and calcium sulphoaluminate-belite (CSAB) cement stabilization. The mine tailings used in this study contained large amounts of sulphates and heavy metals such as Cr, Cu, Ni, Mn, Zn, V and As. The leaching of arsenic and sulphates from powdered tailings exceeded the legal limits for regular and inert waste. All treatment methods were found to generate a hardened matrix that was suitable for use as a backfilling or construction material, but the calcium-based binding system was the most suitable for effective immobilization of all the heavy metals (including arsenic) and the sulphates. Precipitation in the form of calcium sulphates/calcium arsenate and the formation of ettringite are the main stabilization methods employed in calcium-based stabilization/solidification (S/S) systems. Some evidence of physical encapsulation occurring simultaneously with chemical stabilization was noted. These results can be exploited further to develop more sustainable mine tailing management systems for use in the future. The tailings could be stored in a dry landfill area instead of in tailing dams, and in this way a long-term decrease in AMD generation could be achieved, together with a high potential for recycling. / Tiivistelmä Monet arvometallit kuten kulta, kupari ja nikkeli ovat sitoutuneena sulfidipitoisiin mineraaleihin. Louhittaessa ja rikastettaessa näitä sulfidimineraaleja syntyy miljoonia tonneja sulfidipitoisia rikastushiekkoja vuosittain. Rikastushiekat voivat sisältää myös runsaasti erilaisia raskasmetalleja. Osa rikastushiekoista hyödynnetään kaivostäytössä, mutta suurin osa rikastushiekoista läjitetään edelleen ympäristöön rikastushiekka-altaisiin veden alle. Kun sulfidipitoinen malmi kaivetaan ja käsitellään, sulfidiset mineraalit hapettuvat ollessaan kosketuksissa veden ja hapen kanssa. Hapettuessaan ne muodostavat rikkihappoa, laskien ympäristön pH:ta jolloin useimmat raskasmetallit liukenevat ympäristöön. Muodostuvia happamia kaivosvesiä voi syntyä vielä pitkään kaivoksen sulkemisen jälkeen ja ovat näin ollen yksi suurimmista kaivosteollisuuteen liittyvistä ympäristöongelmista. Lisäksi suuret rikastushiekka-altaat voivat aiheuttaa vaaraa myös ihmisille, mikäli altaan rakenteet pettävät. Rikastushiekkojen kestäviä ja ympäristöystävällisiä varastointimenetelmiä täytyy kehittää, jotta näitä ongelmia voidaan tulevaisuudessa ehkäistä. Tässä työssä tutkittiin menetelmiä, joilla kultakaivoksella syntyvät sulfidipitoiset vaaralliseksi jätteeksi luokitellut rikastushiekat saataisiin stabiloitua tehokkaasti. Työssä keskityttiin kolmeen erilaiseen menetelmään: alkali-aktivointiin, stabilointiin kalsiumhydroksidin ja masuunikuonan avulla ja stabilointiin CSAB sementin avulla. Valmistettujen materiaalien mekaanisia ja kemiallisia ominaisuuksia arvioitiin. Tavoitteena oli ymmärtää, miten eri menetelmät soveltuvat raskasmetallien (erityisesti arseenin) ja sulfaattien sitoutumiseen ja mikä on eri komponenttien rooli reaktioissa. Alkali-aktivoimalla rikastushiekkaa sopivan sidosaineen kanssa saavutettiin hyvät mekaaniset ominaisuudet ja useimmat haitta-aineet sitoutuivat materiaaliin. Ongelmia aiheuttivat edelleen sulfaatit ja arseeni. Kalsiumpohjaiset menetelmät sitoivat raskasmetallit (myös arseenin) ja sulfaatit tehokkaimmin. Sulfaatit ja arseeni saostuivat muodostaen niukkaliukoisia komponentteja kalsiumin kanssa. Samanaikaisesti rakenteeseen muodostui ettringiittiä, jolla on tutkitusti hyvä kyky sitoa erilaisia raskasmetalleja rakenteeseensa. Raskasmetallit myös kapseloituivat rakenteen sisään. Työn tuloksia voidaan hyödyntää, kehitettäessä rikastushiekkojen turvallista varastointia. Kun materiaalille saavutetaan riittävän hyvä lujuus ja kemiallinen stabiilius, rikastushiekat voitaisiin läjittää tulevaisuudessa kuivalle maalle altaan sijaan. Näin vältyttäisiin rikastushiekka-altaiden rakentamiselta ja voitaisiin vähentää happamien kaivosvesien muodostumista pitkällä ajanjaksolla. Saavutettujen tulosten perusteella rikastushiekkoja voidaan mahdollisesti tulevaisuudessa hyödyntää myös erilaisissa betonin tapaisissa rakennusmateriaaleissa.

Les espèces chimiques contenues dans les matrices solides sont susceptibles d'être transférées vers le milieu ambiant, notamment lors de leur contact avec l'eau. Les études précédentes du relargage des métaux lourds traces contenus par les matériaux de construction (en particulier ceux à base de ciment) lors d'essais de lixiviation, montrent une difficulté analytique importante. L'objectif de cette étude est de déterminer les cinétiques et les mécanismes de relargage de métaux traces (Cr, Cu, Ni, Pb, V et Zn) des pâtes de ciments industriels (présents à des teneurs de l'ordre de 20 à 300 ppm).<br /><br />Le développement du test de lixiviation dynamique CTG-LEACHCRETE (utilisé à pH=5, 20°C) permettant d'accéder aux cinétiques de relargage des métaux lourds traces est présenté dans une première partie. Ensuite, des techniques d'analyse du solide (ICP-MS-LA, DRX locale et en incidence rasante (GIXD)), novatrices quant à leur application aux matrices cimentaires, ont été employées pour caractériser les zones dégradées générées lors de la lixiviation. Ces techniques permettent de suivre les transformations minéralogiques et la répartition des métaux lourds traces dans ces zones. La confrontation de ces deux approches, cinétique et analyse du solide, couplée à l'exploitation approfondie des modélisations existantes a alors permis de proposer les mécanismes de relargage des métaux lourds traces étudiés.<br /><br />Dans toutes les pâtes de ciments de l'étude (CPA-CEM I, CPJ-CEM II/A et CLC-CEM V/A), on a démontré que le chrome est piégé dans l'ettringite par substitution SO42-ÛCrO42- et que son relargage est régi par la dissolution de cet hydrate. Le comportement du cuivre, du nickel et du zinc dans les phases solides et dans les lixiviats, est corrélé à celui de la silice des CSH, ce qui suppose que ces métaux s'y trouvent localisés. Enfin, le plomb n'est jamais détecté en phase liquide. Son comportement est également corrélé à la silice dans les zones dégradées.

Cette thèse s'inscrit dans un projet de recherche de solutions de bétons à impacts environnementaux réduits. Nous focalisons la présente étude sur le clinker sulfoalumineux en mélange avec du gypse. Son bilan environnemental est plus favorable que celui des clinkers Portland (plus faibles émissions de CO2 et consommation d'énergie, lors de la production). Nous présentons dans ce manuscrit une étude expérimentale du comportement physico-chimique des liants obtenus par mélange de clinker sulfoalumineux et de gypse, et décrivons les propriétés constructives de ces derniers. L'hydratation du clinker sulfoalumineux étant responsable de la formation d'ettringite, nous vérifions la stabilité en milieu humide de telles compositions. Dans un premier temps, nous avons identifié les proportions de gypse pour lesquelles le liant est stable en présence d'eau, i.e. sans apparition de fissures à l'échelle macroscopique. Ce domaine de stabilité est influencé favorablement par la maturité du matériau au moment du contact avec l'eau. Nous avons par ailleurs utilisé des plans d'expériences factoriels afin d'étudier l'influence de la teneur en alcalins ainsi que celle de la température : les résultats révèlent un bon comportement du matériau peu sensible à ces facteurs, dans un large domaine d'emploi. La caractérisation physique de mortiers et de bétons est complétée par une étude de l'hydratation de ces liants : le suivi du processus d'hydratation a montré que la fissuration des éprouvettes instables n'a pas pour origine la formation supplémentaire d'hydrates. Pour finir, nous présentons une étude de la rhéologie et de la résistance en compression ainsi qu'une évaluation du risque de corrosion qui permettent d'identifier des domaines d'emploi pour ce liant.

Civil engineers are at times required to stabilize sulfate bearing clay soils with calcium based stabilizers. Deleterious heaving in these stabilized soils may result over time. This dissertation addresses critical questions regarding the consequences of treating sulfate laden soils with calcium-based stabilizers. The use of a differential scanning calorimeter was introduced in this research as a tool to quantify the amount of ettringite formed in stabilized soils. The first part of this dissertation provides a case history analysis of the expansion history compared to the ettringite growth history of three controlled low strength mixtures containing fly ash with relatively high sulfate contents. Ettringite growth and measurable volume changes were monitored simultaneously for mixtures subjected to different environmental conditions. The observations verified the role of water in causing expansion when ettringite mineral is present. Sorption of water by the ettringite molecule was found to be a part of the reason for expansion. The second part of this dissertation evaluates the existence of threshold sulfate levels in soils as well as the role of soil mineralogy in defining the sensitivity of soils to sulfate-induced damage. A differential scanning calorimeter and thermodynamics based phase diagram approach are used to evaluate the role of soil minerals. The observations substantiated the difference in sensitivity of soils to ettringite formation, and also verified the existence of a threshold level of soluble sulfates in soils that can trigger substantial ettringite growth. The third part of this dissertation identifies alternative, probable mechanisms of swelling when sulfate laden soils are stabilized with lime. The swelling distress observed in stabilized soils is found to be due to one or a combination of three separate mechanisms: (1) volumetric expansion during ettringite formation, (2) water movement triggered by a high osmotic suction caused by sulfate salts, and (3) the ability of the ettringite mineral to absorb water and contribute to the swelling process.

Properly proportioned, placed and cured concrete can be durable under most conditions. However, deterioration of concrete does occur under certain environments. One of the problems that affect the durability of hardened concrete is delayed ettringite formation (DEF) which is an important problem encountered in precast concrete industry where high temperature curing is applied. Although there had been many researches on DEF, there are still many uncertainties about its chemistry and mechanism. In this study, the effects of partial cement replacement by different mineral admixtures (trass, blast furnace slag and fly ash), SO3/Al2O3 molar ratio and specific surface area of cement on DEF were investigated. For this purpose, 9 groups of control cements were prepared with 3 different specific surface areas and 3 different SO3/Al2O3 molar ratios. Different amounts of mineral admixtures were blended with the control cements. High temperature curing was applied to the cement pastes and the expansions of these pastes were measured periodically for 240 days. v The experimental results obtained were interpreted for a comparative analysis of the effects of the afore-mentioned parameters.