yes / There are very few, if any, available experimental investigations on aggregate interlock capacity along diagonal cracks in lightweight concrete deep beams. As a result, the shear design provisions including the modification factor of ACI 318-08 and EC 2 for lightweight concrete continuous deep beams are generally developed and validated using normal weight simple deep beam specimens. This paper presents the testing of 12 continuous beams made of all-lightweight, sand-lightweight and normal weight concrete having maximum aggregate sizes of 4, 8, 13 and 19 mm. The load capacities of beams tested are compared with the predictions of strut-and-tie models recommended in ACI 318-08 and EC 2 provisions including the modification factor for lightweight concrete. The beam load capacity increased with the increase of maximum aggregate size, though the aggregate interlock contribution to the load capacity of lightweight concrete deep beams was less than that of normal weight concrete deep beams. It was also shown that the lightweight concrete modification factor in EC 2 is generally unconservative, while that in ACI 318-08 is conservative for all-lightweight concrete but turns to be unconservative for sand-lightweight concrete with a maximum aggregate size above 13 mm. The conservatism of the strut-and-tie models specified in ACI 318-08 and EC 2 decreased with the decrease of maximum aggregate size, and was less in lightweight concrete deep beams than in normal weight concrete deep beams.

Le béton projeté est une méthode de mise en place consistant en la projection pneumatique de béton sur une surface à grande vitesse. Dans le cas de la méthode par voie sèche, le mélange granulats-ciment est introduit sec en machine, l'eau est ajoutée à la fin du transfert. Cette technique, très employée, est néanmoins génératrice de pertes importantes par rebond, pouvant s'élever jusqu'à 40% de la masse projetée. L'enjeu de la réduction des pertes est à la fois économique et environnemental. Les facteurs influents sur le rebond sont liés aux techniques de projection et à la formulation. Ce travail de thèse a pour objectif l'optimisation de la formulation du béton afin de réduire les pertes par rebond, mais également d'améliorer la durabilité. L'étude porte en particulier sur l'influence sur le rebond : du squelette granulaire, de la teneur en eau et de l'emploi d'additifs et/ou d'additions de substitution. Une approche modélisation du phénomène de rebond est également abordée. / Sprayed concrete is a concrete pneumatically projected onto a surface at high velocity. Dry-mix shotcrete is a process in which dry constituents are introduced into the machine and conveyed through a hose to the nozzle, where the water is added. This process is used in various civil engineering or construction projects; unfortunately, it can lead to high losses of concrete due to rebound (up to 40% of the total mass of material). Such losses induce overconsumption of material, which is damaging for the cost of the work and for the environment. Rebound depends on technicals parameters and mix design. The present work focuses on rebound reduction and also on durability enhancement by modification of the mix design. The influence of aggregate size distribution, water content and supplementary cimentitious material is studied. An analytical approach of rebound phenomenon is also implemented.

Modernization has brought about steady increase in the consumption of goods and services by human societies across the globe, which mostly driven by both population growth and the change of individual living standards. This, of course, leads to an ever-increasing waste production that ends up in landfills and very often as a source of pollution on natural ecosystems, especially in the low and middle-income countries where waste management is almost inexistent. The management of waste streams is a huge challenge for developed countries as well, where societal and environmental impacts are visible despite massive investments in waste management. One of the most problematic waste materials is plastic, which can remain in nature for over 100 years without degradation, leading to serious environmental concerns. As one of the most significant innovations of the 20th century, plastic is a widely used and cost-effective material for many applications. After their useful lifetimes, their management is problematic. Thus, robust and innovative approaches of managing such waste material are needed in order to mitigate the problem. One of the innovative approaches of tackling the menace cause by plastic waste is through its incorporation into the construction materials. This thesis seeks to address this problem by exploring the use of melted plastic wastes (High Density Poly Ethylene, HDPE and Low Density Poly Ethylene, LDPE) as binder in developing new construction materials (mortar with melted plastic as the only binder, MPB and Plastic Waste Crete, PWC) as an alternative to partially replace traditional concrete and mortar, or finding other engineering uses for this type of waste. Worldwide, about 190 m3 of concrete is poured every second, which translates to 6 billion m3 per year and making it, one of the most widely used manufactured materials. However, the production of concrete requires water and cement. Cement is expensive, and its production contributes to the emission of environmentally polluting gases. Replacing this binding element with recycled plastic derivatives would have significant economic and environmental benefits. In addition to the elimination of cement cost, this will result in water savings, which is especially important for areas without fresh water scarcity. Some researchers have used plastics in concrete and mortars as additives and/or replacement for fine and coarse aggregates. In addition, different types of plastics have been used in bitumen as an additive to reduce construction cost and improve sustainability by adding value to wastes materials. However, there is paucity of technical information about the use of the melted HDPE and LDPE plastic wastes as the only binding phase in concrete- or mortar-like materials. Moreover, many parameters such as preparation conditions, field variables, constituent elements, and final applications have impacts on the performance of construction materials Thus, the key objective of this PhD research is to develop the mortar with plastic binder (MPB) and PlasticWasteCrete (PWC) by using molten HDPE and LDPE plastic wastes as the only binder as well as to investigate the engineering properties of these new types of construction materials. The plastic contents of 45%, 50%, 60% and 65% and HDPE to LDPE ratios of 40/60, 50/50, and 60/40 were selected for the experimental tests. Clean river sand was used as the only aggregate for the MPB, while both sand and gravel were used for the PWC. Various tests were then performed on prepared MPB and PWC samples at different curing times from early to advanced ages to assess their engineering properties. These tests were conducted in accordance with the ASTM standards to evaluate the mechanical properties (compressive strength and splitting tensile strength), permeability and density of the MPB and PWC materials. Additional tests were carried out to analyze the products at the microstructural level (optical microscope, SEM, MIP and thermogravimetric analysis) to gain an insight into the microstructural properties of the developed materials and how that affect their engineering properties. The compressive strength tests revealed the optimal plastic content for the MPB and PWC with the best strength performance. The average compressive strength values for various optimal formulations after 28 days were found to be in the range of 9 to 18 MPa. The splitting tensile strength for the new materials from 1 to 28 days of curing time, were found to be between 1 and 5 MPa. The average hardened density of the MPB and PWC is about 2 g/cm3, which makes them lightweight material according to RILEM classification. In addition, various absorption tests (capillary and immersion) were performed on different MPB and PWC samples, and the obtained results showed that they are porous materials having lower rate of absorption than the traditional cementitious materials (mortar, concrete). This observation was supported by the results from both MIP and SEM analyses. Finally, thermogravimetric analysis provided interesting details on the thermal decomposition of the new materials, with significant changes or mass loss for these products being observed only at temperatures higher than 300°C. The findings from this study suggest MPB and PWC made with melted plastic waste as the only binder have a promising potentials for use in construction. The research conducted in this PhD study offers a good understanding of the engineering properties of the materials as well as the optimal formulations that yield best performance in terms of strength and durability. In summary, it provides useful technical information and tools on the MPB and PWC that will contribute in setting guidelines on the optimal applications of these products in the field of construction in order to have safe, durable and cost-effective structures. Résumé Avec la modernisation de nos sociétés, les habitudes ont considérablement changé, ainsi, on observe une forte consommation des biens et services, due à l’augmentation de la population et l’amélioration de leurs conditions de vie. Ce qui conduit à une augmentation considérable des quantités des déchets qui terminent leurs cycles au niveau des décharges ou dans les océans/fleuves devenant ainsi une source de source de pollution des écosystèmes naturels, surtout dans les pays à revenu faible et intermédiaire avec des systèmes défaillants ou moins performants de gestion des déchets. La gestion des flux de déchets est aussi un défi pour certains pays développés, où les impacts sociaux et environnementaux sont visibles en dépit des investissements massifs dans ce secteur. Parmi ces déchets, nous avons les plastiques, l’une des innovations du 20e siècle avec des qualités versatiles et coût faible, se trouve partout dans nos vies quotidiennes. Après leur utilisation, les plastiques deviennent des déchets qui peuvent rester dans la nature plus de 100 ans sans aucune dégradation, avec des conséquences néfastes sur l’Homme et l’environnement. Ainsi, une approche robuste et innovante de gestion de ces déchets est nécessaire afin d'atténuer leurs impacts. L'une des approches innovantes pour réduire l’impact causé par les déchets plastiques consiste à les incorporer dans les matériaux de construction. Ainsi, le problème est abordé dans cette thèse en développant des technologies permettant de recycler les plastiques fondus comme liant dans les nouveaux matériaux de construction (MPB et PWC), afin d’offrir une alternative pour remplacer partiellement le béton / mortier traditionnel. Le béton est l’un des matériaux les plus utilisés au monde, avec environ 190 m3 coulés chaque seconde, correspondant à 6 milliards de m3 par an. Cependant, la production de béton nécessite de l'eau et du ciment. Le ciment coûte cher et sa production contribue à l'émission de gaz polluants l'environnement. Le remplacement d'une partie du béton traditionnel par un matériau à base des déchets plastique aura des avantages économiques, sociaux et environnementaux importants. Allant dans ce sens, certains chercheurs ont utilisé les plastiques dans le béton et le mortier comme additifs et / ou substituts des matériaux granulaires tels que le sable et le gravier. Aussi, différents types de plastiques ont été utilisé dans le bitume comme additif pour réduire les coûts de construction et améliorer la durabilité, ainsi contribuer à donner de la valeur aux déchets. Cependant, jusqu'à présent, il existe peu d’informations techniques sur l'utilisation de déchets plastiques (HDPE et LDPE) fondus comme seuls liants pour développer de nouveaux types de matériaux de construction. En plus, plusieurs facteurs (les conditions de préparation, les éléments constitutifs, les applications finales, etc.) ont un impact sur les caractéristiques des matériaux de construction. Ainsi, l'objectif de cette recherche doctorale est de développer des nouveaux matériaux de construction (MPB et PWC) en utilisant les déchets plastiques fondus (HDPE et LDPE) comme seul liant, puis déterminer les propriétés caractéristiques de ces matériaux afin de trouver la formulation optimale conduisant à la meilleure résistance. En plus de l'élimination du coût du ciment, cette technologie permet aussi de faire des économies d'eau, bénéfique surtout pour les zones avec des difficultés d'accès à l’eau potable. Cela contribuera à la réduction des coûts de la construction en utilisant les produits innovants comme alternative au béton / mortier conventionnel. Un vaste programme expérimental, comprenant des tests à petite et grande échelle, a été développé afin d'atteindre les objectifs de cette étude de doctorat. La campagne expérimentale a comporté différentes étapes comprenant la sélection des matériaux, la détermination de la formulation optimale et les conditions appropriées pour la préparation des matériaux susmentionnés. Par la suite, pour une meilleure compréhension du comportement technique et des propriétés du produit final, divers tests ont été effectué sur les matériaux préparés à différents temps de durcissement. Ces tests ont été menés conformément aux normes ASTM pour évaluer les propriétés mécaniques (résistance à la compression et à la traction), la perméabilité et la densité des nouveaux matériaux. Les expériences ont été approfondies en analysant les produits au niveau microstructural (microscope optique, SEM, MIP et analyse thermique) pour avoir un aperçu des propriétés microstructurales des matériaux développés et essayer de comprendre les relations avec leur comportement mécanique. Les essais de compression ont permis de trouver la teneur en plastique optimale pour les matériaux (MPB et PWC) avec les meilleures valeurs de résistance. Les résistances moyennes à la compression à 28 jours pour diverses formulations étaient comprises entre 9 et 18 MPa. La résistance à la traction par fendage des nouveaux matériaux entre 1 et 28 jours se situait entre 1 et 5 MPa. La densité moyenne du béton et mortier écologique est proche de 2 g / cm3, ils peuvent donc être considérés comme des matériaux légers selon la classification RILEM. De plus, divers tests d'absorption (capillaire et par immersion) ont été réalisé sur différents échantillons de MPB et PWC, les résultats obtenus ont montré qu'il s'agit de matériaux poreux ayant un taux d'absorption plus faible que les matériaux traditionnels contenant du ciment. Plusieurs analyses microstructurales ont été réalisées sur différents échantillons des nouveaux produits (MPB et PWC) et les matériaux cimentaires traditionnels ont été utilisés pour renforcer notre compréhension. Enfin, l'analyse thermique a fourni des détails intéressants sur la décomposition thermique de ces nouveaux matériaux ; des changements significatifs avec une perte de masse considérable ont été observés seulement pour des températures supérieures à 300 ° C. Les résultats de ces essais permettent d'acquérir une bonne compréhension des propriétés techniques des nouveaux matériaux (MPB et PWC) ainsi que de déterminer les teneurs optimales en plastique conduisant aux meilleures performances en termes de résistance et de durabilité. Ainsi, les recherches menées dans cette étude de doctorat fournissent des informations techniques et des outils utiles sur le MPB et le PWC; et contribueront à installer des bases pour guider les applications optimales de ces nouveaux produits dans le domaine de la construction afin d'avoir des structures sûres, durables et rentables.

X-ray computed tomography is a technique that has been successfully utilized to characterize internal microstructure of asphalt mixtures. The city of Linköping (Sweden) developed an action plan to reduce noise; accordingly KTH and VTI developed a method to determine air void content in porous asphalt using x-ray computed tomography and an image processing software called ImageJ. The present study is a continuation of the previously mentioned work and focuses on the investigation of aggregate structure in porous asphalt by x-ray computed tomography. First the previously proposed method to estimate air void content was validated. Then, the assessment of aggregate structure including qualitative and quantitative analysis was completed. Qualitative evaluation was performed to determine the quality of slices in regard to establishing challenging areas, and the extent of beam hardening present in the X-ray images. This evaluation produced quality slices for each sample in Y-direction to work as a reference to establish general threshold ranges and image enhancement procedures, as well as identifying the interface between the top and bottom layer of the porous asphalt. The quantitative analysis consisted of analysing aggregate structures in the porous asphalt and developing a method to estimate the aggregate size distribution in porous asphalt layers. The gradation curves from the quantification of aggregate size distribution in all directions (X, Y, Z) were compared to the gradation curves from laboratory sieving tests previously performed on the drilled asphalt cores. To determine the accuracy of the method a perimeter analysis was performed to evaluate the suggested method to measure the aggregates. The results obtained indicate that to quantify the aggregates in porous asphalt, enhancement of the images is needed, as well as morphological operations to deal with beam hardening and overlapping stones due to unsuccessful separation of aggregates when thresholding. This further indicates that ImageJ Fiji is more suitable for complex cases, such as cases where aggregates and mastic are hard to distinguish from each other, rather than the original ImageJ software. This is due to the extended plugins available in ImageJ Fiji, where more options of for example filtering and enhancing of images are available. The results also suggest that the proposed method is a suitable method to determine the aggregate size distribution in porous asphalt pavements, as it allows to quantify the aggregate distribution and produces realistic results with slight inaccuracies due to the analysis being performed in 2D. Future development will be focused on automizing the determination of air void structure and aggregate size distribution, but also on the development of procedures to determine other relevant parameters such as mastic and binder content to establish a complete methodology to investigate the internal structure of a porous asphalt pavement, as well as 3D analysis to determine these parameters.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / No meio rodoviÃrio brasileiro, que detÃm 96,2% da matriz de transporte de passageiros e 61,8% da matriz de cargas, à flagrante a deterioraÃÃo dos revestimentos asfÃlticos provocada pelo crescente aumento do volume e do peso das cargas transportadas. Tal configuraÃÃo contribui sobremaneira para o surgimento de defeitos, destacando-se as deformaÃÃes permanentes e o trincamento por fadiga. Por outro lado, o estado do Cearà revela uma carÃncia por rodovias pavimentadas, onde apenas 16,0% da malha possuem algum tipo de revestimento asfÃltico. A mistura asfÃltica Stone Matrix Asphalt (SMA) surgiu hà alguns anos como soluÃÃo para combater defeitos em rodovias com elevadas solicitaÃÃes de carga. Alguns estudos, contudo, mostram que SMAs com granulometrias de tamanho mÃximo nominal (TMN) menores que os tradicionalmente utilizados oferecem desempenhos semelhantes aos SMAs com TMN usuais. O objetivo desta pesquisa foi dosar misturas SMA com granulometrias distintas para estudar algumas caracterÃsticas desse tipo de mistura, investigando a influÃncia (i) do TMN, (ii) do percentual de agregado passante na peneira N 4 (4,75mm) para SMAs com TMN de 12,5mm e (iii) do tipo de compactaÃÃo (Marshall à Superpave) no comportamento mecÃnico das mesmas por meio dos ensaios de (i) mÃdulo de resiliÃncia (MR), (ii) resistÃncia à traÃÃo (RT), (iii) fadiga à tensÃo controlada, (iv) resistÃncia à traÃÃo retida (RTR) por umidade induzida e (v) desgaste CÃntabro. Os resultados reforÃam a noÃÃo de que SMAs com pequeno TMN apresentam desempenhos comparÃveis a SMAs tradicionais, sendo o SMA com TMN de 4,75 um atrativo como potencial soluÃÃo para a pavimentaÃÃo cearense, considerando as caracterÃsticas de trÃfego da malha do estado. / In Brazilian roadways, which concentrate 96.2% of the passengers and 61.8% of the cargo, it is clear the deterioration of asphalt pavements caused by an increasing volume and weight of the vehicle loadings. This configuration strongly contributes to pavement distresses, specially rutting and fatigue cracking. On another hand, the state of Cearà shows a lack of paved roadways, with only 16.0% of paved roads. The Stone Matrix Asphalt (SMA) mixture appeared a few years ago as a solution for minimizing distresses on roadways with high traffic levels. Some researches, however, demonstrate that SMA mixtures with small Nominal Maximum Aggregate Sizes (NMAS) offer similar performances to SMA mixtures with usual NMAS. The objective of the present research was to design SMA mixtures with different gradations in order to study some characteristics of this type of mixture, investigating the effect (i) of the NMAS, (ii) of the percentage of aggregate passing in sieve N. 4 (4.75mm) for 12.5mm NMAS SMA mixtures and (iii) of the compaction type (Marshall à Superpave) on the mechanical behavior of the mixtures. The mixtures were evaluated by (i) resilient modulus, (ii) indirect tensile strength, (iii) fatigue life (stress controlled), (iv) resistance to moisture damage and (v) Cantabro abrasion. The results support the idea that SMA mixtures with small NMAS behave similar to those with usual NMAS. Furthermore, the 4.75mm NMAS SMA appears to be a potential solution for roadways in CearÃ, considering the traffic configuration of this state.

The goal of this research is to investigate the fundamentals of fracturing processes in heterogeneous materials such as concrete using geophysical methods and dynamic micromechanical models. This work describes how different aspects of fracture formation in concrete can be investigated using a combination of Acoustic Emission (AE) techniques, ultrasonic wave velocity imaging, and high resolution Computed Tomography (CT). Fracture formation and evolution were studied during shear failure of large reinforced concrete beams and compressive failure of concrete samples. AE analysis includes studying complex spatial and temporal fracture development that precedes shear failure. Predominant microcrack mechanisms were analyzed at different stages of fracture formation. CT images were used to investigate the influence of concrete microstructure on fracture topography. Combined AE and CT damage evaluation techniques revealed different aspects of fracture development, thus expanding our understanding of AE events and their mechanisms. These images show how aggregate particles influence fracture nucleation and development. An emphasis has been placed on the role of coarse aggregates during the interlocking of fracture surfaces at transferring shear stresses. Ultrasonic wave velocity and AE techniques have been applied to uniaxial compression tests of concrete with various aggregate sizes and strengths similar to that of the concrete beams. AE parameters, p-wave velocities, and stress-strain data have been analyzed concurrently to image damage evolution under compression. Influence of material composition on microcracking and material state changes during loading has been investigated in detail. The results of compressive tests were used as building blocks for developing realistic micromechanical numerical models of concrete. The models were designed using a distinct element code, where material is modelled through the combination of bonded particles. A number of procedures were developed to transfer the exact microstructure of material incorporating its visual representation into the model. The models’ behaviour has been verified against experimental data. It was shown that these models exhibit realistic micromechanical behaviour. The results of the experimental investigation of concrete fracturing were expanded by modelling more cases with aggregate size and strength variations. It was shown that geophysical imaging techniques, along with advanced micromechanical numerical modelling, can help us understand damage formation and evolution.

The goal of this research is to investigate the fundamentals of fracturing processes in heterogeneous materials such as concrete using geophysical methods and dynamic micromechanical models. This work describes how different aspects of fracture formation in concrete can be investigated using a combination of Acoustic Emission (AE) techniques, ultrasonic wave velocity imaging, and high resolution Computed Tomography (CT). Fracture formation and evolution were studied during shear failure of large reinforced concrete beams and compressive failure of concrete samples. AE analysis includes studying complex spatial and temporal fracture development that precedes shear failure. Predominant microcrack mechanisms were analyzed at different stages of fracture formation. CT images were used to investigate the influence of concrete microstructure on fracture topography. Combined AE and CT damage evaluation techniques revealed different aspects of fracture development, thus expanding our understanding of AE events and their mechanisms. These images show how aggregate particles influence fracture nucleation and development. An emphasis has been placed on the role of coarse aggregates during the interlocking of fracture surfaces at transferring shear stresses. Ultrasonic wave velocity and AE techniques have been applied to uniaxial compression tests of concrete with various aggregate sizes and strengths similar to that of the concrete beams. AE parameters, p-wave velocities, and stress-strain data have been analyzed concurrently to image damage evolution under compression. Influence of material composition on microcracking and material state changes during loading has been investigated in detail. The results of compressive tests were used as building blocks for developing realistic micromechanical numerical models of concrete. The models were designed using a distinct element code, where material is modelled through the combination of bonded particles. A number of procedures were developed to transfer the exact microstructure of material incorporating its visual representation into the model. The models’ behaviour has been verified against experimental data. It was shown that these models exhibit realistic micromechanical behaviour. The results of the experimental investigation of concrete fracturing were expanded by modelling more cases with aggregate size and strength variations. It was shown that geophysical imaging techniques, along with advanced micromechanical numerical modelling, can help us understand damage formation and evolution.

No description available.

No description available.

Il est de plus en plus admis que l’effet d’échelle doit être pris en compte dans la conception des structures de Génie Civil. Pour le béton, ce problème est complexe car celui-ci ne possède pas d’adoucissement plastique, et sa rupture est due à la fissuration caractérisée par une grande zone de microfissuration (fracture process zone) qui dépend de la taille du granulat max d .Cette fissuration passe par un adoucissement sous la forme de microfissures et de glissement interparticules. Expérimentalement, l’effet d’échelle sur le béton est très souvent étudié à l’aide des corps d’épreuves homothétiques entaillés où l’on cherche à relier la résistance nominale ( oN )estimée à partir de la charge de rupture en flexion à une dimension caractéristique D. Ceci conduit à une diminution du ratio dmax/D avec l’augmentation de la taille de la structure. Parmi les objectifs de cette thèse est d’étudier expérimentalement l’impact de l’hétérogénéité ( dmax/D)supposé comme facteur fondamental de l’effet d’échelle. Trois coupures granulaires ont été testées sur trois tailles de poutres différentes en suivant le processus de fissuration par émission acoustique et la technique de corrélation d’images. Celles-ci permettent de suivre l’ouverture des fissures et identifient assez clairement la FPZ. Les résultats mettent en évidence une grande influence de la taille du granulat sur le comportement à la rupture du béton. Il existe une relation directe entre les paramètres de l’effet d’échelle obtenus par la loi de Bazant et la taille du granulat( dmax ). Le traitement des résultats d’une même taille avec différents granulométries dans le même diagramme conduit à la même loi d’effet d’échelle structurelle classique avec une valeur de transition identique. La modélisation du comportement mécanique est effectuée par la méthode d’éléments discrets (DEM). Le modèle de contact linéaire ne s’avère pas adéquat pour le mortier et le béton où le rapport compression / traction est très élevé. De ce fait, Il a été modifié pour prendre en compte la contribution des moments inter-granulaires. Les paramètres micromécaniques sont déterminés par des essais classiques avec une analyse inverse en utilisant l’algorithme de Levenberg-Marquardt. Les résultats montrent que cette approche est capable de reproduire le comportement à la fissuration locale du béton et de reproduire l’effet d’échelle et celui des granulats. Ensuite, un modèle d'adoucissement est développé afin de mieux reproduire la réponse post pic et le processus de fissuration. / It is now commonly understood that in the design of civil engineering structures, size effect must be taken into consideration. For concrete, this problem is complex because it does not exhibit plastic softening. The failure of concrete is generally preceded by propagation of cracks, characterized by alarge microcracking zone (fracture process zone or FPZ) which is proportional to the maximum aggregate size ( dmax ). This fracture process is accompanied by strain-softening in the form of microcracking and fractional slip.Experimentally, size effect in concrete is commonly studied by using geometrically similar notched beams where thenominal strength ( oN ) obtained from the bending failure loadis related to the characteristic dimension (D). This leads to adecrease in the ratio of dmax/D with an increase in the size of the structure. One of the objective of this thesis is to study experimentally the effect of heterogeneity ( dmax/D) size. This ratio is recognized as a fundamental factor causing the size effect. Three aggregate grading segments were tested on three different sizes of beams and the cracking process was investigated by acoustic emission and the image correlation technique. These methods make it possible to trace the crack.openings and identify distinctively the FPZ. The results demonstrate a significant influence of the aggregate size on the fracture behaviour of concrete. There is a direct relationship between the size effect parameters obtained by Bazant's law and maximum aggregate size ( dmax ). The results obtained from the specimen having the same size but made of concretes with different aggregate sizes produced the same classical size effect with identical transitional between LEFM and strength based laws. The mechanical behaviour is modelled by the Discrete Element Method (DEM). However, the linear contact model inserted in DEM is not suitable to satisfy the materials like mortar and concrete with high unconfined compressive strength to tensile strength ratio. As a result, the model is modified to take into account the contribution of interparticle moments. The micromechanical parameters are determined by conventional tests with inverse analysis using the Levenberg-Marquardt algorithm. The results showed that this approach is able to reproduce the local cracking behaviour of concrete as well as classical size effect and aggregate size effect. Then, a softening model is developed to better reproduce the post-peak response and the cracking process.