Early plastic shrinkage cracking of concrete is an important factor affecting the durability of modern concrete structures. Early cracking (within 24 hours after pouring) may become a problem for any concrete structure. It will promote the entry of harmful materials, destroy the beauty of concrete members, and reduce their durability and performance. In addition, due to long-term shrinkage and/or load, these cracks may gradually expand in the service life of components. Scientific research and engineering technicians often have to face the difficulties caused by early plastic shrinkage cracking of concrete. From the aspects of shrinkage mechanism, measurement method, prediction model and strength development, this paper reviews the scientific and technological status of plastic shrinkage and strength development of early-age concrete, and based on this, summarizes the important conclusions in existing research and establishes the relevant concrete strength prediction model.:1 Introduction 2. Shrinkage in concrete 2.1 Classification and mechanism of concrete shrinkage 2.2 Main factors causing concrete shrinkage 2.3 Concluding remarks 3. Plastic shrinkage in early age concrete 3.1 Method for determining the time of initial and final setting 3.2 Mechanism of plastic shrinkage 3.3 Evaporation 3.4 Capillary pressure 3.5 Main factors affecting plastic shrinkage cracking 3.6 Concluding remarks 4. Different methods for determining the resistance to plastic shrinkage cracking 4.1 Rectangular mould test setup 4.2 ASTM C 1579 4.3 Ring test method (NT BUILD 433) 4.4 Capillary pressure test 5. Development of early age strength of concrete 5.1 Mechanical properties 5.1.1 Compressive strength 5.1.2 Tensile strength 5.1.3 Early-age shrinkage of concrete 5.2 Test and prediction model evaluation 6. Test and quantitative model 6.1 pullout tests on early-age concrete 6.1.1 Tests principle 6.1.2 test result 6.2 Compilation of existing pullout capacity prediction models 6.2.1 Strength and pullout force model based on 𝒉𝒆𝒇 6.2.2 Strength and pullout force model based on 𝒉𝒆𝒇 and ∅𝒉 6.2.3 Tensile strength and pullout force model 6.3 Application of existing prediction model in early age concrete 7. Conclusions 8. Literature

Concrete curing has long been realized to be important to produce durable concrete. Curing compound is widely used to cure concrete in the field. The current curing membrane evaluation method ASTM C 156, however, is incapable of distinguishing the curing compound quality and guiding the curing practice in the field. A new laboratory curing membrane evaluation protocol is developed in this study. It has the ability to rank the quality of curing compound and guide curing practice in the field according to the field ambient weather conditions and the type of curing compound. A series of field tests were conducted to investigate the key factors that affect the curing effectiveness in the field conditions. A finite element program, temperature and moisture analysis for curing concrete (TMAC2), is updated to solve the coupled and nonlinear heat transfer and moisture transport problems in early-age concrete. Moisture capacity is induced into the TMAC2, which makes it unique to characterize the self-desiccation. A full scale concrete pavement test study was conducted at the FAA National Airport Pavement Test Facility (NAPTF) near Atlantic City, New Jersey. In this study, the material properties, i.e. thermal conductivity and moisture diffusivity, were backcalculated from field data. Thereafter, backcalculated material properties were used to forward-calculate the temperature and moisture histories of all other sections. High order shear deformable theory is used to model the concrete slab curling and warping behavior because of highly nonlinear temperature and moisture gradients. The maximum shear strain is obtained a couple of inches below the concrete slab. This might account for the occurrence of delamination.

This diploma thesis is conceived as theoretical and empirical. The theoretical part has two objectives. The first of these objectives is to explore options to help the surviving siblings in the family and society. The second objective is to describe the principles of educational work with traumatized children. This work introduces the specifics of early age and possible consequences of acting trauma in this life period. It outlines briefly the development of frequency of children's mortality and it considers whether death pertains among the taboos of the postmodern society. There are described manifestations of grief and mourning and factors, which determine the ability to accept a bereavement of a loved one. The findings are used to formulate the principles of education of the traumatized children. The practical part contains five case studies that provide information about factors which affected the lives of the surviving siblings. Keywords Early age, sorrow, trauma, mourning, death of a sibling

O estudo do comportamento do concreto nas primeiras idades está se tornando cada vez mais importante, pois os efeitos térmicos e de retração do concreto, neste período inicial, geram fissuras, aumentando a permeabilidade das estruturas e podendo induzir problemas de durabilidade e funcionalidade das mesmas. Um detalhado estudo da evolução das tensões durante as primeiras idades pode ser decisivo para manter baixos os níveis de fissuração. Neste trabalho foi implementado um modelo computacional, baseado no método dos elementos finitos, para a simulação do comportamento de peças de concreto nas primeiras idades, tendo, em especial, o propósito de avaliar o potencial risco de fissuração. A análise por elementos finitos abrange a modelagem computacional dos fenômenos químicos, térmicos, de difusão de umidade e mecânicos que ocorrem nos primeiros dias após o lançamento do concreto. Na análise química é determinado o calor gerado pelas reações exotérmicas de hidratação do cimento. Na análise térmica o programa considera ainda o fluxo de calor devido à diferença de temperatura entre o corpo e o ambiente. Em função das propriedades térmicas e geométricas do corpo em estudo são determinadas as temperaturas nodais. Na seqüência, realiza-se a análise de difusão de umidade. Aproveitando a semelhança entre as equações que regem os fenômenos de transferência de calor e difusão de umidade, empregam-se os mesmos procedimentos da análise térmica para a determinação do valor nodal da umidade relativa dos poros. Na análise mecânica, por sua vez, são calculados os estados de tensões decorrentes das variações de temperatura e umidade determinadas nas etapas anteriores e dos fenômenos de retração e fluência do concreto. Quando o estado de tensão de determinado ponto de integração atinge a superfície de ruptura, o ponto passa a ser considerado fissurado. O programa considera a fissuração através de um modelo de fissuras distribuídas com fisssura fixa. Os resultados desta modelagem computacional foram comparados com valores experimentais encontrados na literatura, demonstrando excelente aproximação em todas as etapas de solução implementadas. / The study of the early age properties of concrete is becoming more important, because the thermal effects and the shrinkage, even in the first hours, could generate cracks, increasing the permeability of the structure and being able to induce problems of durability and functionality. The detailed study of the stresses development during the construction process can be decisive to keep low the cracking levels. In this work a computational model, based on the finite element method was implemented, to simulate the early age concrete behavior, having as a special feature, the evaluation of the cracking risk. The finite element analysis encloses the computational modeling of the following phenomena: chemical, thermal, diffusion and mechanical which occur at the first days after the concrete cast. In the chemical analysis, the heat generated by the exothermic reactions of cement hydration is evaluated. In the thermal analysis the program still considers the heat flow due to differences in temperatures between the body and the environment. Considering the thermal and geometric properties of the body, the nodal temperatures are determined. The following analysis is the humidity diffusion. Using the similarity between the equations that describe the phenomena of heat transfer and humidity diffusion, the same thermal analysis procedures are used to evaluate the pore relative humiditys nodal values. In the last analysis, mechanical, the stress states due to temperature and humidity variations, evaluated in the previous steps, and also due to shrinkage and creep are calculated. When the stress state in a determined sample point reaches the rupture surface, the point is considered cracked. The program evaluates cracking through a smeared fixed crack model. The developed software results were compared with experimental values found in the literature, demonstrating an excellent agreement for all the implemented analysis.

Les structures en bétons sont souvent exposées dès le jeune âge du matériau à des milieux pouvant être agressifs pour leur durabilité. En effet, dans certains cas, ces structures sont directement au contact d’une eau de mer riche en ions chlorure et sulfate. L’attaque sulfatique affecte surtout la pâte de ciment par des mécanismes physico-chimiques complexes et couplées entrainant la ruine mécanique, souvent liée à l’expansion par la formation de produits expansifs tels que le l’ettringite et le gypse. Les ions chlorure peuvent engendrer une corrosion des armatures Ces deux pathologies sont largement étudiées dans la littérature. Cependant, l’ASE est encore sujette à controverses, ce qui peut expliquer l’absence d’un essai normé européen. La prédiction de la durée de vie des ouvrages dans des conditions couplant le jeune âge, la prise en compte des ions sulfate et chlorure ainsi que le pH du milieu peut être très complexe. Dans ce contexte, nous avons tout d’abord comme finalité avec cette étude de proposer un essai le plus représentatif possible des conditions d’exposition réelles, particulièrement dans le cas de l’ASE. L’attention est portée sur les effets de la cure dans les aspects physico-chimiques de l’ASE, du transfert et l’interaction de la matrice cimentaire avec les ions chlorure en conditions saturées et de de semi-immersion et l’effet d’un environnement couplant ces ions délétères sur les évolutions de la microstructure des pâtes de ciment jeune et mature à base de ciment Portland, de type CEM I et un ciment mélangé au laitier, de type CEM III/A. Le couplage de plusieurs techniques d’analyses expérimentales a permis la prise en compte de l’aspect physique du transport ionique, et l’aspect chimique par quantification de la microstructure avant et après la contamination par les éventuels ions. Cette quantification est réalisée en couplant plusieurs méthodes expérimentales comme les analyses thermiques ATG/ATD et la Résonance Magnétique Nucléaire (RMN de l’27Al et RMN du 29Si). Dans le cas de l’ASE, ces analyses ont montré à la fois l’effet neutre de la cure sur la propagation des ions sulfate dans la matrice et l’effet important sur les mécanismes de fixation chimique entre les ions sulfates apportées par la solution et les hydrates de la pâte de ciment. Ces essais ont aussi mis en évidence l’effet néfaste de l’exposition dès le jeune âge à la solution de sulfate de sodium dans le cas des pâtes de ciment au laitier. A l’inverse la cure saine longue dans l’eau a un effet négatif vis-à-vis de la résistance l’ASE des pâtes de ciment Portland. La compétition ionique dans le cas du couplage est mise en évidence. Cette compétition a un effet mitigé quant au transport et la fixation des ions chlorure. La capacité de fixation des ions est plus grande dans le cas du ciment CEM III/A, en présence ou non d’ions sulfate.Mots Clés: pâte de ciment, attaque sulfatique externe (ASE), jeune âge, chlorure, couplage ionique, RMN 29 Si et RMN 27Al, ATG/ATD, ICP / In industrial practice, concrete structural elements are exposed to various physical and chemical aggressions as soon as their formwork is removed. This early age exposure has an obvious influence on the element future transfer properties. Indeed, in some cases, these structures are directly immersed in sea water, rich in chloride and sulfate ions. Ingress of sulfate ions from the external environment and its consequences on the microstructure are known as External Sulfate Attack (ESA). Sulfate ion in seawater or underground can attack the cement paste leading to expansion and strength loss. This expansion is usually related to ettringite and gypsum precipitation. The chloride ions can cause corrosion of the reinforcements steel bars. This two pathologies are widely studied in the literature. However ESA is still controversial, which may explain the need of a European standardized test. Predicting the durability of concrete under conditions involving an early age exposure, the inclusion of chloride and sulfate ions and the pH of the external mixtures can be very complex. One of the aim of this work is to purpose a test as representative as possible of field conditions, particularly to study the ESA under controlled conditions (the pH and the external solution content). Tests are done in saturated and partially-immersed conditions. We focus on the initiation process of this degradation. The physicochemical aspects of ESA are studied. The impact of an early age exposure is highlighted in the case of ESA and chloride ingress. The microstructure changes are monitored by using several experimental techniques such as NMR (29Si and 27 Si), ICP, TGA, XRD and SEM. These analyses showed a neutral effect of an early age exposure on the sulfate ingress in both cement types (CEM I and CEM III/A). However, a negative effect of slag cement is observed after only 3 months of exposure the sulfate sodium solution at early age. Also, neither cracker when the slag cement paste are exposed after curing. Conversely, Portland cement paste resist very well and long to ASE, for an early age exposer and fail for the cured specimens. Ionic competition in the coupling case is highlighted. This competition has a mixed effect on the transport and attachment of chloride ions. The ion binding capacity is greater in the case of cement CEM III / A, in the presence or absence of sulfate ions.Key words: cement paste, External sulfate attack, ESA, early age, chloride and sulfate ingress, marine environment, RMN 29 Si and RMN 27Al, ATG/ATD, ICP

Cytochrome P450¡]CYP¡^2J2, the single member of human cytochromes P450 II J subfamily, plays an important role in the biosynthesis of biologically active cis-epoxyeicosatrienoic acids. An allelic variant named CYP 2J2*7, a relatively frequent G¡÷T substitution at position-50 relative to the transcription start site, which interrupts a critical Sp1 binding site, results in both decreased promoter activity in vitro and reduced circulating levels of CYP2J2 epoxygenase metabolites. Epoxyeicosatrienoic acid (EETs) are endogenously produced and incorporated into membrane phospholipids in the pancreas. Low concentrations of 5,6-EETs stimulate insulin secretion, whereas 8,9-, 11,12-, and 14,15-EETs stimulate glucagon secretion from the pancreas. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear hormone receptor superfamily. EETs increased PPAR-£\ and PPAR-£^ transcription activity. PPAR-£\ and PPAR-£^ play a key role in the regulation of adipogenesis, lipid metabolism, insulin sensitivity and inflammation. Thus, genetic abnormalities in the function or expression of CYP2J2, the pathogenetic of enzymes may play a role in diabetes. The present study investigates whether CYP 2J2*7 gene polymorphism can be associated with type 2 diabetes in a Chinese population. We studied 2,073 Chinese type 2 diabetes patients and 704 control subjects without. CYP 2J2*7 gene polymorphism was determined by PCR-RFLP and real-time PCR. In both study groups, the genotype frequency distributions of this polymorphism were in Hardy-Weinberg equilibrium. The CYP2J2*7 genotype distribution or allele frequencies were not different between type 2 diabetes and control subjects. Diabetics with young age of onset¡]¡Ø35 years old¡^ had a higher frequency of T variant than that of the age of onset of greater than 35 years old and controls ( GG / GT + TT = 84.2% / 15.8% vs. 90.3% / 9.7% vs. 91.3% / 8.7%¡Fp = 0.018¡Ap = 0.027 ). CYP2J2*7 genotype had a statistically significant association with age of onset ( p for trend = 0.042 ). The HOMA-IR and HOMA-£] values were significantly higher in diabetic patients with young age of onset compared to those of late onset diabetics and controls. CYP2J2*7 polymorphism was associated with HOMA-IR and HOMA-£] in diabetics with young age of onset and controls, subjects and T variants had significant higher value of HOMA-IR and HOMA-£]¡]early onset diabetics¡GGG / GT + TT = 8.9 ¡Ó 6.1 / 6.4 ¡Ó 3.8, p=0.045¡Fcontrols¡GGG / GT + TT = 2.6 ¡Ó 1.1 / 2.1 ¡Ó 0.8, p = 0.007¡^.These findings suggest that CYP 2J2*7 polymorphism may play a role in the pathogenesis of young onset type 2 diabetes and family diabetic history.

L’hydratation du ciment est une réaction exothermique. Ce phénomène est particulièrement surveillé lorsque des pièces massives sont construites étant donné l’élévation de la température, le développement de contraintes thermomécaniques et le risque de réaction sulfatique interne. Compte tenu de la grande variété des formules de béton, le choix d’un ciment ayant une basse chaleur d’hydratation à 41 h n’est plus exclusif. La chaleur totale dégagée dépend d’autres paramètres de formulation tels que le dosage en ciment et l’emploi d’addition. D’un point de vue mécanique, le risque de fissuration dépend aussi du développement des propriétés mécaniques. Dans le but de mieux connaître et contrôler ces risques, une étude de l’effet de la composition du ciment sur la cinétique d’hydratation et les propriétés du ciment, et notamment, sur le dégagement de chaleur est d’abord réalisée. A la suite de cela, la formulation du béton est étudiée afin de voir son effet sur les propriétés thermomécaniques de celui-ci. Enfin, un nouvel essai permettant d’évaluer le risque de fissuration du béton est développé. Le premier chapitre présente donc tout d’abord un condensé des connaissances sur l’hydratation du ciment et de ses propriétés, suivi du type d’essais réalisés et les différents ciments fabriqués, et enfin l’analyse des résultats puis les ciments sélectionnés pour la poursuite de l’étude au niveau béton. Dans le deuxième chapitre, après une étude bibliographique du béton, une trentaine de bétons sont formulés à partir des ciments précédemment sélectionnés et sont étudiés thermiquement par mesure de chaleur d’hydratation. Grâce aux résultats obtenus, un outil de formulation permettant de prendre en compte un cahier des charges est développé. Après sélection de 9 bétons – dont l’échauffement thermique et les résistances mécaniques varient, le troisième chapitre s’attache à les caractériser de manière plus poussée au jeune âge, avec un suivi de l’évolution du module d’Young statique et dynamique, des déformations endogènes ainsi que du fluage. Un nouvel essai à l’anneau mettant en jeu l’échauffement thermique durant l’hydratation et les déformations endogènes gênées du béton est développé. L’imposition de l’échauffement thermique mesuré d’une pièce massive dans l’anneau permet de tester le béton comme s’il était utilisé dans une structure. L’utilisation d’anneau en invar ayant un coefficient de dilatation thermique inférieur à celui du béton induit, lors de l’échauffement, des contraintes en compression dans le béton, et lors du refroidissement, des contraintes en traction. Lorsque les contraintes en traction générées sont supérieures à la résistance en traction du béton, il y a fissuration. Enfin, le dernier chapitre consiste à modéliser l’essai à l’anneau avec le logiciel de calcul CESAR en prenant en compte l’évolution de l’échauffement thermique, du module d’Young, des déformations endogènes et du fluage du béton et de confronter les résultats obtenus avec les essais expérimentaux / Hydration reactions of cement are exothermic. This phenomenon is especially tracked in large concrete structures because temperature gradients create mechanical stresses which can induce the development of cracks or of Delayed Ettringite Formation (DEF). Nowadays, because of the wide range of concrete formulations, low 41 h hydration heat cement need not to be used. Hydration heat depends on other formulation parameters such as quantity of cement and addition use. From a mechanical point of view, the risk of cracking also depends on the development of mechanical properties. In this study, screenings of constituents and characteristics of cement and concrete are performed to determine which ones have the most influence on the thermal activity and on the heat released in massive concrete structures. Then, the effect of concrete formulation on its thermo-mechanical properties is studied. Finally, a new experimental test is developed in order to evaluate the risk of cracking. In the first chapter, a summary of knowledge on the cement hydration and its properties is presented. Experimental tests, fabrication of cement and results are then explained. Nine cements are selected for pursuing the study at the concrete level. The second chapter presents state of the art on concrete and the results obtained for 30 formulated concretes. Hydration heat and compressive strengths are measured. A mix design tool is created according to the results in order to meet the required specifications. In the third chapter, the risk of cracking at early age is assessed for nine different concretes, including concretes with a low heat of hydration. Characteristics of concrete at early age such as the evolution of the mechanical properties (dynamic and static Young’s modulus, dynamic shear modulus and Poisson ratio) are measured dynamically, thanks to ultrasonic waves, and statically, by loading cycles. Autogenous shrinkage is evaluated since setting. Finally, the risk of cracking is monitored using dual concentric rings for evaluating stress development due to restrained volume change. In the fourth chapter, BT-Ring test is modeled with CESAR - an IFSTTAR software – and compared to the experimental results

O estudo do comportamento do concreto nas primeiras idades está se tornando cada vez mais importante, pois os efeitos térmicos e de retração do concreto, neste período inicial, geram fissuras, aumentando a permeabilidade das estruturas e podendo induzir problemas de durabilidade e funcionalidade das mesmas. Um detalhado estudo da evolução das tensões durante as primeiras idades pode ser decisivo para manter baixos os níveis de fissuração. Neste trabalho foi implementado um modelo computacional, baseado no método dos elementos finitos, para a simulação do comportamento de peças de concreto nas primeiras idades, tendo, em especial, o propósito de avaliar o potencial risco de fissuração. A análise por elementos finitos abrange a modelagem computacional dos fenômenos químicos, térmicos, de difusão de umidade e mecânicos que ocorrem nos primeiros dias após o lançamento do concreto. Na análise química é determinado o calor gerado pelas reações exotérmicas de hidratação do cimento. Na análise térmica o programa considera ainda o fluxo de calor devido à diferença de temperatura entre o corpo e o ambiente. Em função das propriedades térmicas e geométricas do corpo em estudo são determinadas as temperaturas nodais. Na seqüência, realiza-se a análise de difusão de umidade. Aproveitando a semelhança entre as equações que regem os fenômenos de transferência de calor e difusão de umidade, empregam-se os mesmos procedimentos da análise térmica para a determinação do valor nodal da umidade relativa dos poros. Na análise mecânica, por sua vez, são calculados os estados de tensões decorrentes das variações de temperatura e umidade determinadas nas etapas anteriores e dos fenômenos de retração e fluência do concreto. Quando o estado de tensão de determinado ponto de integração atinge a superfície de ruptura, o ponto passa a ser considerado fissurado. O programa considera a fissuração através de um modelo de fissuras distribuídas com fisssura fixa. Os resultados desta modelagem computacional foram comparados com valores experimentais encontrados na literatura, demonstrando excelente aproximação em todas as etapas de solução implementadas. / The study of the early age properties of concrete is becoming more important, because the thermal effects and the shrinkage, even in the first hours, could generate cracks, increasing the permeability of the structure and being able to induce problems of durability and functionality. The detailed study of the stresses development during the construction process can be decisive to keep low the cracking levels. In this work a computational model, based on the finite element method was implemented, to simulate the early age concrete behavior, having as a special feature, the evaluation of the cracking risk. The finite element analysis encloses the computational modeling of the following phenomena: chemical, thermal, diffusion and mechanical which occur at the first days after the concrete cast. In the chemical analysis, the heat generated by the exothermic reactions of cement hydration is evaluated. In the thermal analysis the program still considers the heat flow due to differences in temperatures between the body and the environment. Considering the thermal and geometric properties of the body, the nodal temperatures are determined. The following analysis is the humidity diffusion. Using the similarity between the equations that describe the phenomena of heat transfer and humidity diffusion, the same thermal analysis procedures are used to evaluate the pore relative humiditys nodal values. In the last analysis, mechanical, the stress states due to temperature and humidity variations, evaluated in the previous steps, and also due to shrinkage and creep are calculated. When the stress state in a determined sample point reaches the rupture surface, the point is considered cracked. The program evaluates cracking through a smeared fixed crack model. The developed software results were compared with experimental values found in the literature, demonstrating an excellent agreement for all the implemented analysis.

Lors de la construction de structure réalisée en plusieurs phases de bétonnage, les déformations du béton sont restreintes durant son durcissement. Quand le retrait est restreint, des contraintes de traction sont induites dans le matériau et un risque de fissuration est présent. Il est alors nécessaire de modéliser l’évolution des propriétés au jeune âge afin de prédire le comportement de la structure durant le jeune âge du béton. La difficulté réside dans le fait que la modélisation des propriétés du béton doit être basée sur des données expérimentales au jeune âge et que ces données doivent être obtenues automatiquement car le durcissement du béton se produit rapidement pendant les premières heures et les premiers jours. La thèse porte sur l’étude expérimentale et numérique des propriétés au jeune âge des matériaux à base de ciment et plus particulièrement sur le développement des déformations endogènes, le coefficient de dilatation thermique, le module d’élasticité et le fluage propre en compression et en traction. A cet effet, un travail complet a été réalisé à l'ULB et à l’Ifsttar impliquant le développement d'une nouvelle approche avec de nouvelles procédures d'essai et la conception de nouveaux dispositifs d'essai pour générer des données expérimentales depuis la prise du matériau. La méthodologie est basée sur deux méthodes d'essai répété. Pour la caractérisation du comportement viscoélastique d'un béton depuis sa prise, un essai de chargement permanent couplé à un essai avec des chargements répétés de plusieurs minutes est nécessaire. Les déformations endogènes, le coefficient de dilatation thermique et la prise sont caractérisés avec des variations thermiques répétées sur un échantillon de béton. Cette nouvelle approche a été définie sur un béton ordinaire et ensuite étendue sur l’étude de 4 paramètres pertinents : le rapport eau-ciment, l'effet de restriction de l'agrégat sur la pâte de ciment dans le développement des propriétés du béton au jeune âge, la substitution du ciment par des additions minérales et la différence de comportement en traction et en compression. Sur la base de ces résultats expérimentaux, de nouveaux modèles ont été développés pour la caractérisation des propriétés au jeune âge de matériaux cimentaires depuis le temps de prise. Une version adaptée de la modélisation du fluage propre dans le Code modèle 2010 est également proposée / For usual concrete structure built in several phases, concrete deformations are restrained during the hardening process. When shrinkage is restrained, tensile stresses are induced and a cracking risk occurs. Modelling the evolution of an early age set of parameters on concrete is necessary to predict the early age behaviour of concrete structures. The difficulty lies in the fact that the modelling of concrete properties must be based on experimental data at early age and this data must be obtained automatically because the hardening process of the concrete takes place rapidly during the first hours and also the first days. The thesis deals with experimental and numerical study of the early age properties of cement based materials and more specifically the development of the autogenous deformation, the coefficient of thermal expansion, the E-modulus and the basic creep in compression and tension. For this purpose, a comprehensive work was carried out at ULB and Ifsttar involving the development of a new approach with new test procedures and the design of new testing devices to generate experimental data since the setting of the material. The methodology is based on two repeated testing methods. For the characterization of the viscoelastic behaviour of a concrete since setting, a permanent loading coupled to a test with repeated minute-long loadings is needed. Whereas, the autogenous strain, the coefficient of thermal expansion and the setting are characterized with repeated thermal variations on a concrete sample. The new approach was defined on an ordinary concrete and then extended to the study of the following parameters: the water-cement ratio, the restrained effect of aggregate on the cement paste in the development of concrete properties at early age, the substitution of cement by mineral addition and the difference of behaviour in tension and in compression. Based on these experimental results, new models were developed for the characterization of the early age properties of cement based materials since setting time. An adapted version of the Model Code 2010 for the modelling of basic creep is also proposed

[pt] O presente trabalho tem como objetivo investigar o efeito da adição de fibras dispersas de polipropileno e de curauá na fluência básica a compressão e na retração autógena e por secagem de pastas de cimento nas primeiras idades. O comprimento das fibras de polipropileno e de curauá foi de 12 mm e a fração volumétrica variou de 0,03 a 0,30 por cento da massa do cimento. As pastas de cimento tinham relação água/cimento de 0,44. A retração autógena foi estudada pelo método do tubo corrugado, acompanhando a variação do comprimento desde as primeiras horas. A avaliação da retração por secagem livre se deu por meio da medição da variação de comprimento de primas durante os primeiros dias de idade. Utilizou-se o método do teste do anel para observação do comportamento das pastas sob retração restrita no intuito de se obter a idade de fissuração de cada pasta. A abertura dessas fissuras também foi acompanhada com auxílio de um microscópio. Testes de fluência a compressão foram realizados para determinar a deformação por fluência em idade jovem. Foi observada uma redução significativa da retração autógena nas pastas reforçadas com 0,30 por cento fibras de curauá. A adição de ambas as fibras reduziu ligeiramente a retração por secagem livre, não tendo diferença significativa entre os teores de fibras. Também foi observado atraso no desenvolvimento de fissuras e redução na abertura de fissuras para ambas as fibras independente do teor. As pastas com adição de fibras exibiram, no geral, uma ligeira melhora na deformação por fluência. / [en] The present research aims to investigate the effect of the addition of discrete polypropylene and curauá fibers on the early age autogenous and drying shrinkage and basic creep in compression in cement pastes. The length of the polypropylene and curauá fibers was 12 mm and the volume fraction varied from 0.03 to 0.30 percent of the mass content of cement. The cement pastes had water to cement ratio (w/c) of 0.44. Autogenous shrinkage tests were carried out following the Corrugated Tube Method, monitoring the length changes since casting. The evaluation of free drying shrinkage was given by measuring the length changes during the first days of age. The ring test method was used to determine the age when cracking occurred. The crack opening of the samples was also monitored by a microscope. Compressive creep tests were performed with cylindrical specimens to determine the early age creep strain. A significant reduction of the autogenous shrinkage was observed in the specimens with 0.30 perent of curauá fibers. The addition of both fibers slightly reduced the free drying shrinkage of the specimens and the fiber content did not appear to influence significantly the shrinkage behavior of the specimens. A delay in the development of cracks and a reduction in crack opening for specimens with both fibers were also observed. This behavior was similar for all fiber content. Pastes reinforced with fibers exhibited, overall, a slight improvement in creep strain. The addition of 0.30 percent of polypropylene fibers showed greater improvement in creep strain.