Concrete is a brittle material prone to cracking due to its low tensile strength. Crack repairs are not only expensive and time-consuming but also increase the carbon footprint. Designing a novel concrete material possessing the ability to self-repair cracks would enhance its sustainability. Self-healing can be defined as a material’s ability to repair inner damage without any external intervention. In the case of concrete, the process can be autogenous, based on an optimized mix composition, or autonomous, when additional capsules containing some healing agent and/or bacteria spores are incorporated into the binder matrix. The first process uses unhydrated cement particles as the healing material while the other utilizes a synthetic material or bacteria precipitating calcite which are released into the crack from a broken capsule or activated by access to water and oxygen. The main disadvantages of the autonomous method are the loss of the fresh concrete workability, worsened mechanical properties, low efficiency, low survivability of the capsules and bacteria during mixing and the very high price. On the other hand, the autogenous self-healing was found to be more efficient, more cost effective, safer, and easier to implement in full-scale applications. Knowledge related to mechanisms and key factors controlling the autogenous self-healing is rather limited. Therefore, the aim of this research work was to better understand the autogenous self-healing process of concrete and to optimize the mix design and exposure conditions to maximize its efficiency. This licentiate thesis summarizes the main findings of the first 2.5 years of the PhD project. Several factors affecting autogenous self-healing were studied, including the amount of unhydrated cement, mix composition, age of material, self-healing duration and exposure conditions. The process was investigated both externally, at the surface, and deeper inside of the crack, by evaluating the crack closure and chemical composition of formed self-healing products. In addition, the flexural strength recovery was also studied. It was observed that a large amount of cement in the concrete mix does not ensure an efficient autogenous self-healing of cracks. A very dense and impermeable binder microstructure limited the transport of calcium and silicone ions to the crack and diminished the precipitation of the healing products. Addition fly ash increased the crack closure ratio close to the crack mouth, but its presence did not support the recovery of the flexural strength, presumably due to a very limited formation of load bearing phases inside the crack. Calcium carbonate was detected mainly at the crack mouth, whereas calcium silicate hydrate (C-S-H) and ettringite were found deeper inside the crack. The formation of C-S-H and ettringite presumably resulted in a regain of the flexural strength. On the other hand, calcite crystals formed close to the surface of the specimen controlled conditions inside the crack through its external closure. Healing exposure based on pure water appeared to be inefficient even despite the application of different temperature cycles and water volumes. The application of a phosphate-based retarding admixture in the curing water resulted in the highest self-healing efficiency. The admixture presumably inhibited the formation of a dense hydration shell on the surface of the unhydrated cement grains and promoted the precipitation of calcium phosphate compounds inside the crack. In addition, water mixed with microsilica particles caused a regain of the flexural strength through formation of C-S-H in the crack.

<p>Developing a reliable in-situ non-destructive testing method to determine the strength of in-place concrete is critical because a fast-paced construction schedule exposes concrete pavement and/or structures undergoing substantial loading conditions, even at their early ages. Conventional destructive testing methods, such as compressive and flexural tests, are very time-consuming, which may cause construction delays or cost overruns. Moreover, the curing conditions of the tested cylindrical samples and the in-place concrete pavement/structures are quite different, which may result in different strength values. An NDT method that could directly correlate the mechanical properties of cementitious materials with the sensing results, regardless of the curing conditions, mix design, and size effect is needed for the in-situ application.</p><p>The piezoelectric sensor-based electromechanical impedance (EMI) technique has shown promise in addressing this challenge as it has been used to both monitor properties and detect damages on the concrete structure. Due to the direct and inverse effects of piezoelectric, this material can act as a sensor, actuator, and transducer. This research serves as a comprehensive study to investigate the feasibility and efficiency of using piezoelectric sensor-based EMI to evaluate the strength of newly poured concrete. To understand the fundamentals of this method and enhance the durability of the sensor for in-situ monitoring, this work started with sensor fabrication. It has studied two types of polymer coating on the effect of the durability of the sensor to make it practical to be used in the field.</p><p>The mortar and concrete samples with various mix designs were prepared to ascertain whether the results of the proposed sensing technique were affected by the different mixtures. The EMI measurement and compressive strength testing methods (ASTM C39, ASTM C109) were conducted in the laboratory. The experimental results of mortar samples with different water-to-cement ratios (W/C) and two types of cement (I and III) showed that the correlation coefficient (R²) is higher than 0.93 for all mixes. In the concrete experiments, the correlation coefficient between the EMI sensing index and compressive strength of all mixes is higher than 0.90. The empirical estimation function was established through a concrete slab experiment. Moreover, several trial implementations on highway construction projects (I-70, I-74, and I-465) were conducted to monitor the real-time strength development of concrete. The data processing method and the reliable index of EMI sensing were developed to establish the regression model to correlate the sensing results with the compressive strength of concrete. It has been found that the EMI sensing method and its related statistical index can effectively reflect the compressive strength gain of in-place concrete at different ages.</p><p>To further investigate the in-situ compressive strength of concrete for large-scale structures, we conducted a series of large concrete slabs with the dimension of 8 feet × 12 feet × 8 inches in depth was conducted at outdoor experiments field to simulate real-world conditions. Different types of compressive strength samples, including cast-in-place (CIP) cylinder (4” × 6”) – (ASTM C873), field molded cylinder (4” × 8”) – (ASTM C39), and core drilled sample (4” × 8”) – (ASTM C42) were prepared to compare the compressive strength of concrete. The environmental conditions, such as ambient temperatures and relative humidity, were also recorded. The in-situ EMI monitoring of concrete strength was also conducted. The testing ages in this study were started from 6 hours after the concrete cast was put in place to investigate the early age results and continued up to 365 days (one year) later for long-term monitoring. The results indicate that the strength of the CIP sample is higher than the 4” x 8” molded cylinder , and that core drilled concrete is weaker than the two aforementioned. The EMI results obtained from the slab are close to those obtained from CIP due to similar curing conditions. The EMI results collected from 4 × 8-inch cylinder samples are lower than slab and CIP, which aligns with the mechanical testing results and indicates that EMI could capture the strength gain of concrete over time.</p><p>The consequent database collected from the large slab tests was used to build a prediction model for concrete strength. The Artificial Neuron Network (ANN) was investigated and experimented with to optimize the prediction of performances. Then, a sensitivity analysis was conducted to discuss and understand the critical parameters to predict the mechanical properties of concrete using the ML model. A framework using Generative Adversarial Network (GAN) based on algorithms was then proposed to overcome real data usage restrictions. Two types of GAN algorithms were selected for the data synthesis in the research: Tabular Generative Adversarial Networks (TGAN) and Conditional Tabular Generative Adversarial Networks (CTGAN). The testing results suggested that the CTGAN-NN model shows improved testing performances and higher computational efficiency than the TGAN model. In conclusion, the AI-guided concrete strength sensing and prediction approaches developed in this dissertation will be a steppingstone towards accomplishing the reliable and intelligent assessment of in-situ concrete structures.</p><br>

Zementklinker ist der Hauptbestandteil von Zement und verbraucht zu dessen Herstellung signifikante Mengen von natürlichen Ressourcen und trägt gleichzeitig zu seiner sehr ungünstigen Treibhausgasbilanz bei. In dieser Arbeit wird gezeigt, dass Zementersatzstoffe mit spezifischen Eigenschaften aus Abfallstoffen wie Kieswaschschlämmen, Strassenwaschschlämmen und Gipskartonplatten ohne Leistungseinbußen auf Produktseite, bei geringeren Temperaturen und geringerer CO2 Emission hergestellt werden können. Entsprechend den angestrebten Eigenschaften solcher zum Teil anthropogener Zementbestandteile wurden lokal verfügbare geeignete Abfallstoffe ausgewählt und thermisch aktiviert. Eine industriell anwendbare Methode zur Aktivierung solcher Stoffe bei Temperaturen von 700 °C – 850 °C wurde entwickelt und patentiert. Es basiert auf einem neu entwickelten Trocknungsverfahren und der Kombination von zwei Produktionslinien, um durch die Verknüpfung der Gasströme beider Systeme eine energieeffiziente thermische Behandlung von Abfallstoffen zu ermöglichen sowie auf umweltfreundliche Weise einen Zementersatzstoff herzustellen.:Table of Contents List of Tables List of Figures List of Abbreviations Glossary Chapter 1: Introduction 1.1 Motivation 1.2 Research hypotheses and objectives 1.3 Research methodology 1.4 Thesis outline Chapter 2: State of the art in SCM production 2.1 Supplementary cementitious materials 2.2 Classification of SCMs 2.2.1 Classification according to origin 2.2.2 Classification according to reaction behaviour 2.3 Chemical composition of SCMs 2.4 Formation of hydraulic or pozzolanic minerals in thermal processes 2.4.1 Cement clinker 2.4.2 Burnt oil shale 2.4.3 Fly ash 2.4.4 Calcined clay 2.5 Performance of composite cements 2.6 Calcining technologies 2.6.1 Flash calciner 2.6.2 Rotary calciner 2.7 Comparison of process technologies 2.8 Summary of Chapter 2 Chapter 3: Alternative SCMs and a new method for activation 3.1 Introduction 3.2 Target of alternative SCM 3.3 Waste materials 3.3.1 Aggregate washing sludge 3.3.2 Road cleaning sludge 3.3.3 Deconstruction gypsum 3.4 Producing alternative SCMs 3.5 Thermal activation of alternative SCMs 3.6 Limitations in current calcining technology 3.6.1 Difficult emission control 3.6.1.1 Particulate emission 3.6.1.2 Gaseous emission 3.6.2 Challenging material preparation 3.6.3 Demand for noble fuels 3.6.4 Difficult colour control 3.6.5 Strict temperature control 3.6.6 CO2 footprint of calciners 3.7 Proposed new method of calcination 3.7.1 Feed material handling 3.7.2 Thermal heat-exchange system 3.7.3 Clay calciner design 3.7.4 Grinding 3.8 Summary Chapter 3 Chapter 4: Theoretical Considerations 4.1 Material considerations 4.1.1 Composition of alternative SCM 4.1.2 Anticipated products and characteristics 4.2 Process considerations 4.2.1 System capacity 4.2.2 Material characteristics 4.2.3 Material receiving, crushing and handling 4.2.4 Thermodynamic modelling 4.2.4.1 Mass balance 4.2.4.2 Drying and cooling heat balance 4.2.4.3 Calcination heat balance 4.2.4.4 Gas balance 4.2.4.5 Impact on clinker kiln line 4.2.4.6 Impact of calcite on the gas balance 4.2.5 Calciner design 4.2.6 Colour control 4.2.7 Emission prediction 4.2.7.1 Emission during drying 4.2.7.2 Emission during calcination 4.2.8 CO2 footprint of produced material 4.2.9 Grinding requirements 4.3 Summary of Chapter 4 Chapter 5: Experimental tests and proof of concept 5.1 Introduction 5.2 Sampling and characterization 5.2.1 Kaolinitic AWS from France 5.2.2 Non-kaolinitic AWS from Switzerland 5.2.3 Road cleaning sludges from Switzerland 5.2.4 Deconstruction gypsum from Switzerland 5.2.5 Sample preparation and shipping 5.3 Drying screw conveyor testing 5.4 Calcination testing 5.4.1 Mineralogy of activated products 5.4.1.1 Non-kaolinitic SCM 5.4.1.2 Kaolinitic AWS from France 5.4.2 Colour 5.5 Crushing tests 5.6 Grinding tests 5.7 Mortar compressive strength testing 5.8 Water demand testing 5.9 Summary of Chapter 5 Chapter 6: Experimental results 6.1 Characteristics of activated materials 6.2 Concrete performance and colour 6.2.1 Thermally activated kaolinitic AWS from France 6.2.2 Thermally activated non-kaolinitic alternative SCM from Switzerland 6.3 Equipment dimensioning 6.3.1 Process mass flow 6.3.2 Heat-exchanging screws and thermal oil system 6.3.3 Rotary calciner dimensioning 6.3.4 Ball mill dimensioning 6.4 CO2 reduction 6.5 Summary of Chapter 6 Chapter 7: Conclusion and outlook 7.1 Conclusions 7.2 Outlook. Literature

Concrete, the second most consumed material on earth after water, is a source of environmental problems due to global urbanization. The production of this construction material requires a large amount of natural resources, and portland cement (PC) is responsible for around 8 % of planet-warming CO2 emissions. Producing 1 ton of PC will release roughly 1 ton of CO2 into the atmosphere. In 2021, around 92 million metric tons of PC were produced in the U.S., and a total of 4.4 billion tons were manufactured worldwide. While there was a yearly increase of around 1.5 % in the direct CO2 intensity of cement production from 2015 to 2021, urgent annual declines of 3 % until 2030 are necessary to be in line with the Net Zero Emissions by 2050 Scenario. This dissertation presents different approaches and technologies to offset the CO2 footprint of the production of cement clinker, concrete, and cementitious materials in general. First, this dissertation investigated the possibility of using end-of-life tire (ELT) rubber powder and its zinc-recovered residual (treated ELT rubber) to partially replace fine aggregates of different construction and infrastructure materials including stabilized soft soil (0 %, 10 %, 30 %, and 50 % ELT rubber added by clay volume), portland cement concrete (0 %, 10 %, 20 %, and 30 % ELT rubber added by sand volume), and asphalt concrete (20 % ELT rubber added by sand volume). This work was discussed through aspects of engineering properties and environmental impacts. The results reveal that the ELT rubber had both negative and positive effects on the engineering properties of the three materials while this waste posed a huge leachability of zinc and total organic carbon (TOC) content when being subjected to aqueous environments. However, the findings indicate that all three materials' matrices could effectively immobilize most leachable zinc from the ELT rubber by more than 90 %. Meanwhile, only stabilized soft soil and asphalt concrete could effectively deal with leachable TOC content from ELT rubber, and portland cement concrete needed the addition of silica fume to reduce TOC concentration in its leachate. Second, while previous studies have shown that steel furnace slag (SFS) can stabilize clay soils, the evidence is not clear if the stabilization mechanism is chemical and/or mechanical. This dissertation used isothermal calorimetry (IC) to quantify the heat of hydration of the mixture to assess the chemical aspects of the stabilization. Specifically, kaolin and bentonite clays were each blended with 40 % SFS by mass at water-to-binder ratios ranging from 1.0 to 1.5. The hydration properties of stabilized mixtures using lime or PC were also tested for comparison at the same experimental conditions. The obtained thermal power and total heat curves of stabilized mixtures confirmed that, for the specific SFS in this study, there is a hydration process taking place in clay stabilized by SFS. Relative to lime and PC, the SFS performed similarly in terms of heat of hydration behavior. When blended into clays, SFS provided a more significant heat of hydration behavior than cement, but that was much milder than lime. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were also employed to qualitatively analyze the mineralogy of the stabilized mixtures. Finally, this dissertation adopted a Digestion-Titration Method (DTM) for the determination of CO2 content in cementitious materials that has been mineralized in the form of calcium carbonate (CaCO3). This method was modified based on tests that were originally developed in the early 1900s. The method uses hydrochloric acid to digest CaCO3 under vacuum conditions. The CO2 released is captured by a barium hydroxide solution, which is then titrated to quantify the amount of CO2 absorbed. A design of experiments approach was used to optimize the experimental conditions. Samples of known CaCO3 content were first evaluated to establish the baseline test performance, and additional tests were performed on portland cement and various rock samples. The results were also compared to TGA, including a discussion to compare the two test methods. The data suggest that the new test method is feasibly applicable to chemically determine the CO2 captured in cementitious materials, and it can be an alternative method for TGA with lower experimental cost and easier access. Overall, it is evident that cement, concrete, and construction materials are essential to the functionality of civilization. Dealing with CO2 emissions and natural resource depletion induced by the production of these construction materials is urgent for sustainable development. Attempts toward construction materials with lower embodied CO2 by using low-carbon aggregates (e.g., waste aggregates, recycled aggregates) and alternative cementitious binders while controlling the environmental effects of the utilized waste materials are currently viable sustainable approaches. In addition, tools or new test methods that can support measuring the effectiveness of these reduced carbon cementitious materials are necessary. This dissertation investigates the feasibility of the use of ELT rubber waste in construction materials to reduce the exploitation of natural resources considering engineering properties and environmental impacts. It also provides a deeper understanding of the hydration behavior of stabilized soil using SFS which is expected to partially or fully replace PC in the material. Experimentally, it develops a chemical test model as an alternative method for TGA with lower experimental cost, less interference, and easier access to determine the CO2 captured in cementitious materials. / Doctor of Philosophy / Concrete, the second most consumed material on earth after water, is a source of environmental problems due to global urbanization. The production of this construction material requires a large amount of natural resources, and portland cement (PC) is responsible for around 8 % of planet-warming CO2 emissions. This dissertation presents different approaches and technologies to offset the CO2 footprint of the production of construction materials (i.e., cement clinker, concrete, and general cementitious materials). First, this dissertation investigated the possibility of using end-of-life tire (ELT) rubber powder in different construction materials including stabilized soft soil, portland cement concrete, and asphalt concrete. This work was discussed through aspects of engineering properties and environmental impacts. The results reveal that the ELT rubber had both negative and positive effects on the engineering properties of the three materials. In return, all three materials' matrices could effectively immobilize most leachable zinc and total organic carbon (TOC) from the ELT rubber, which are detrimental to aquatic animals, plants, and humans. Second, this dissertation used isothermal calorimetry (IC) for the first time to study the heat of hydration of soil stabilized by steel furnace slag (SFS) to assess the chemical aspects of the stabilization. The work compared the hydration behavior of SFS in clayey soil with traditional stabilizers such as lime or portland cement. The results demonstrated that there were chemical reactions taking place during the hydration of stabilized soil using SFS, explaining the improvement in engineering properties of the stabilized soil. Moreover, this dissertation adopted a Digestion-Titration Method (DTM) for the determination of mineralized CO2 content in cementitious materials. The method uses hydrochloric acid to digest CaCO3 under vacuum conditions. The CO2 released is captured by a barium hydroxide solution, which is then titrated to quantify the amount of CO2 absorbed. The data suggest that the new test method is feasibly applicable to chemically determine the CO2 mineralized in cementitious materials, and it can be an alternative method for thermogravimetric analysis with lower experimental cost and easier access. Overall, it is evident that cement, concrete, and construction materials are essential to the functionality of civilization. Dealing with CO2 emissions and natural resource depletion induced by the production of these construction materials is urgent for sustainable development. This dissertation is expected to fill the knowledge gap in carbon neutral construction materials research, including increasing the use of low-carbon aggregates (e.g., waste aggregates, recycled aggregates) and alternative cementitious binders as well as developing new test methods that can support measuring the effectiveness of these reduced carbon cementitious materials.

Concrete is the most widely used man-made material in the world. Its versatility, strength, and relative ease of construction allow it to be used in the majority of civil infrastructure. However, concrete production plays a significant role in greenhouse gas emissions, accounting for around 8% of CO2 emissions worldwide. This thesis aims to reduce the demand for cement in concrete construction, thus reducing the carbon footprint of the concrete, by focusing on classifying and determining the effectiveness of seven different quarry by-products as partial replacements of cement. Several methods were utilized in this study to characterize the quarry by-products: particle size distribution, helium pycnometry, X-Ray diffraction, X-Ray fluorescence, scanning electron microscopy, and a modified ASTM C1897 Method A that utilizes isothermal calorimetry and thermogravimetric analysis. These various methods allowed for the determination of the physical properties (e.g., gradation, specific gravity, and morphology) and the chemical properties (e.g., mineralogy and reactivity in a cementitious system). The quarry by-products were classified as four granites, two limestones, and one greenstone. These quarry by-products were found to be non-pozzolanic and non-hydraulic. However, there are indications that there may be reactions with the various clays and feldspars in the quarry by-products with calcium hydroxide, which suggests a degree of reactivity that is not necessarily pozzolanic or hydraulic. / Master of Science / Concrete is the most widely used man-made material in the world. Its versatility, strength, and relative ease of construction allow it to be used in the majority of civil infrastructure. However, concrete production plays a significant role in greenhouse gas emissions, accounting for around 8% of CO2 emissions worldwide. This thesis aims to reduce the demand for cement in concrete construction, thus reducing the carbon footprint of the concrete, by focusing on classifying and determining the effectiveness of seven different quarry by-products as partial replacements of cement. Several methods were utilized in this study to determine the physical properties (e.g., gradation, specific gravity, and morphology) and the chemical properties (e.g., mineralogy and reactivity in a cementitious solution) of the materials. The quarry by-products were classified as four granites, two limestones, and one greenstone. In general, these quarry by-products were not found to be reactive as a supplementary cementitious material, although the data may suggest some degree of reactivity between calcium hydroxide and the clays and/or feldspars in the quarry by-products.

<p>  </p> <p>Concrete is the second most consumed material in the world after water and is an essential element of constructed infrastructure. Over 14 billion m3 of concrete are being produced annually, resulting in a serious impact on the environment. The production of cement, which is the main component of concrete, is responsible for 5 – 8 % of global CO2 emissions. As a result, several global initiatives have been undertaken to achieve carbon neutrality by 2050. This carbon neutrality target coincides with the Paris Agreement's goal to limit global warming to 1.5 °C. A well-known, and successful strategy to reduce CO2 emissions in the concrete industry is to use supplementary cementitious materials (SCMs) as a partial replacement for cement. However, it is projected that in 2030 the demand for two of the most commonly used SCMs, fly ash and slag cement, will exceed their supply. Using nontraditional and natural pozzolans (NNPs) can help to close this supply gap, but there is a lack of knowledge regarding the reactivity and long-term performance of these materials.</p> <p>The purpose of this research was to perform experiments on several NNPs, some of which can be supplied in commercially viable quantities with the objective of evaluating their performance in cementitious systems (mortars and concretes) with the goal of accurately assessing their potential for use as alternative SCMs. The mortar study was performed using a total of 11 different NNPs, belonging to 4 distinctive groups and distributed as follows: 3 from the group of calcined clays (CCs) - CC1, CC2, and CC3, 3 from the group of natural pozzolans (NPs) - NP1, NP2 and NP3, 2 from the group of fluidized bed combustion (FBCs) ashes - FBC1 and FBC2, and 3 from the group of bottom ashes (GBAs) - GBA1, GBA2, and GBA3.</p> <p>The concrete study was performed on 4 different materials, one from each of the previously mentioned groups. The materials selected for concrete study were the worst-performing members of each group, as determined by the analysis of the test results obtained from mortars. These included CC2, NP3, FBC1, and GBA3 materials. This approach was adopted under the assumption that achieving adequate concrete characteristics with lowest-quality materials will all but assure satisfactory performance of concretes with higher-quality materials. </p> <p>The findings generated from this research indicate that several of the NNPs used in this study present a viable alternative to traditional SCMs. As an example, out of the 11 NNPS, 9 were found to conform to the requirements of the ASTM C618-19, the standard specification currently used to assess the suitability of coal fly ash and raw or calcined natural pozzolans for use in concrete. Results obtained from tests performed on mortars demonstrated that, when used at the replacement level of 25%, all 11 NNPs produced mixtures with characteristics similar to those obtained from the plain cement (OPC) mortar. For that reason, this level of replacement was selected to prepare concrete specimens. The results collected from concrete specimens showed that, when compared to plain concrete, mixtures with all 4 NNPs attained comparable (or improved) mechanical (compressive and flexural strength), durability (freeze-thaw resistance), and transport (formation factor and rate of water absorption) properties. As in the case of traditional SCMs, the mixtures with NNPs were found to require extended curing times to fully realize their property-enhancing potential associated with pozzolanic reactions. Overall, the best performing materials were those from the CCs group, followed by those belonging to, respectively, NPs, GBAs, and FBCs groups. </p>

Face à la finitude des ressources de la terre et de sa capacité d’absorption de la pollution, le développement d’écobétons pour un futur industrialisé durable représente un défi majeur de la science du béton moderne. En raison de sa nature hétérogène complexe, les propriétés macroscopiques du béton dépendent fortement des constituants de sa microstructure (ex. silicates de calcium hydratés [C–S–H], Portlandite, inclusions anhydres, porosité, agrégats, etc.). De plus, la nécessité d’une exploitation rapide et optimale des matériaux cimentaires émergents dans les applications industrielles demande de nos jours une meilleure compréhension de leurs particularités chimico-mécaniques à l’échelle micrométrique. Cette thèse vise à développer une méthode de pointe de couplage de la nanoindentation et de la spectroscopie quantitative aux rayons X à dispersion d'énergie (NI-QEDS), puis à fournir une caractérisation chimico-mécanique originale des phases microstructurales présentes dans les matrices réelles de ciments mélangés. La combinaison d’analyses NI-QEDS statistiques et déterministes a ainsi permis d’élargir la compréhension des systèmes avec ciment Portland et ajouts cimentaires (ACs) conventionnels ou alternatifs. Plus spécifiquement, l’étude des C–(A)–S–H (C–S–H incluant l’aluminium ou non) dans différents systèmes à base de ciments mélangés a montré des compositions différentes pour cet hydrate (variations dans les taux de Ca, Si, Al, S et Mg), mais ses propriétés mécaniques n’ont pas été significativement affectées par l’incorporation des ACs dans des dosages typiques. Les résultats présentés ont aussi démontré le rôle important des autres phases imbriquées dans la matrice de C–(A)–S–H, soit les inclusions anhydres dures (ex. le clinker et les ACs) et les autres hydrates tels que la Portlandite et les hydrates riches en aluminium (ex. les carboaluminates) avec des propriétés mécaniques plus élevées que celles des C–(A)–S–H. La thèse est basée sur cinq articles couvrant : (1) une analyse NI-EDS de systèmes incorporant des volumes élevés de pouzzolanes naturelles; (2) le développement de la méthode NI-QEDS; des analyses statistiques NI-QEDS (3) de systèmes avec cendres volantes et laitier, et (4) d’un système combinant ciment, calcaire et argile calcinée; et (5) une exploration déterministe NI-QEDS de systèmes conventionnels et alternatifs incorporant la poudre de verre, le métakaolin, le laitier ou la cendre volante. Finalement, en plus d’avancer les derniers modèles et méthodes micromécaniques, l’outil développé a fourni une perception chimico-mécanique originale des phases microstructurales et de leur arrangement. Le dévoilement de la signature chimico-mécanique de ces pâtes de ciments mélangés particulièrement complexes offre un savoir unique pour l’ingénierie des bétons de demain. / Abstract : Facing the limitedness of the earth’s resources and pollution absorption capacity, the development of eco-concrete for a sustainable industrialized future is one of the major challenges of modern concrete science. Due to its complex heterogeneous nature, the macro-scale properties of concrete strongly depend on the microstructure constituents (e.g., calcium-silicate-hydrates [C–S–H], Portlandite, anhydrous inclusions, porosity, aggregates, etc.). Moreover, the need for rapid and optimal exploitation of emerging binding materials in industrial applications urges today a better understanding of their chemo-mechanical features at the micrometer scale. This thesis aims at developing a state-of-the-art method coupling NanoIndentation and Quantitative Energy-Dispersive Spectroscopy (NI-QEDS), and providing an original chemo-mechanical characterization of the microstructure phases in highly heterogeneous matrices of real blended-cement pastes. The combination of statistical and deterministic NI-QEDS analysis approaches opened new research horizons in the understanding of Portland-cement systems incorporating conventional and alternative supplementary cementitious materials (SCMs). More specifically, the investigations of C–(A)–S–H (C–S–H including aluminum or not) in different blended-cement systems showed variable compositions for this hydrate (i.e., Ca, Si, Al, S and Mg contents), but the mechanical properties were not significantly affected by the incorporation of SCMs in typical dosages. The presented results also showed the important role of the other phases embedded in the C–(A)–S–H matrix, i.e., hard anhydrous inclusions (e.g., clinker and SCMs) and other hydrates such as Portlandite and Al-rich hydrates (e.g., carboaluminates) with mechanical properties higher than those of the C–(A)–S–H. The thesis is based on five articles focusing on: (1) the NI-EDS investigation of high-volume natural pozzolan systems; (2) the development of the NI-QEDS method; the statistical NI-QEDS analyses of (3) fly ash and slag blended-cement systems and of (4) a limestone-calcined-clay system; and (5) the deterministic NI-QEDS exploration of alternative and conventional systems incorporating glass powder, metakaolin, slag or fly ash. Finally, the developed tool not only advanced the latest micromechanical methods and models, but also provided original chemo-mechanical insights on the microstructure phases and their arrangement. Unveiling the chemo-mechanical signature of these highly-complex blended cement pastes further provided unique knowledge for engineering concretes for tomorrow.

Cette thèse porte sur la modélisation morphologique de matériaux cimentaires, et sur l'analyse de leurs propriétés linéaires élastiques. Dans cet objectif, des images 3D, obtenues par micro-tomographie, de matériaux cimentaires (mortier et béton) sont étudiées. Dans un premier temps, l'image de mortier est segmentée afin d'obtenir une image de microstructure réelle pour des calculs en élasticité linéaire. L'image de béton est utilisée, après traitement, pour la détermination des caractéristiques morphologiques du matériau. Un modèle aléatoire de béton est ensuite développé et validé par des données morphologiques. Ce modèle comporte trois phases qui correspondent à la matrice, les granulats et les pores. La phase des granulats est modélisée par implantation sans recouvrement de polyèdres de Poisson. Pour cela, un algorithme de génération vectorielle de polyèdres de Poisson est mis en place et validé par des mesures morphologiques. Enfin, les propriétés linéaires élastiques effectives de la microstructure de mortier et de microstructures simulées sont déterminées par méthode FFT (Fast-Fourier Transform), pour différents contrastes entre le module de Young des granulats et de la matrice. Cette étude des propriétés effectives est complétée par une analyse locale des champs dans la matrice, afin de déterminer l'arrangement spatial entre les zones de concentration de contraintes dans la matrice, et les différentes phases de la microstructure (granulats et pores). Une caractérisation statistique des champs est de plus réalisée, avec notamment le calcul du Volume Élémentaire Représentatif (VER). Une comparaison des propriétés élastiques effectives et locales obtenues d'une part sur une microstructure simulée contenant des polyèdres et d'autre part sur une microstructure contenant des sphères est de plus effectuée. / The goal of this thesis is to develop morphological models of cementitious materials and use these models to study their local and effective response. To this aim, 3D images of cementitious materials (mortar and concrete), obtained by micro-tomography, are studied. First, the mortar image is segmented in order to obtain an image of a real microstructure, to be used for linear elasticity computations. The image of concrete is used, after being processed, to determine various morphological characteristics of the material. A random model of concrete is then developed and validated by means of morphological data. This model is made up of three phases, corresponding to the matrix, aggregates and voids. The aggregates phase is modelled by implantation of Poisson polyhedra without overlap. For this purpose, an algorithm suited to the vector generation of Poisson polyhedra is introduced and validated with morphological measurements. Finally, the effective linear elastic properties of the mortar and other simulated microstructures are estimated with the FFT (Fast-Fourier Transform) method, for various contrasts between the aggregates and matrix' Young moduli. To complete this work, focused on effective properties, an analysis of the local elastic response in the matrix phase is undertaken, in order to determine the spatial arrangement between stress concentration zones in the matrix and the phases of the microstructure (aggregates and voids). Moreover, a statistical fields characterization, in the matrix, is achieved, including the determination of the Representative Volume Element (RVE) size. Furthermore, a comparison between effective and local elastic properties obtained from microstructures containing polyhedra and spheres is carried out.

The microstructure of concrete contains random features over a wide range of length scales in which each length scale possess a new random composite. The influence of individual material constituents at different scales and their mutual interactions are responsible for the formation of fracture process zone (FPZ). The presence of the FPZ and the various toughening mechanism occurring in it, influences the fatigue and fracture behavior of concrete which also gets influenced by the geometry, spacial distribution and material properties of individual material constituents and their mutual interactions. Hence, in order to study the influence of interfacial transition zone, microcrack and aggregate bridging on the fracture and fatigue behavior of concrete, a multiscale analysis becomes necessary. This study aims at developing a linearized model which helps in understanding the fracture and fatigue behavior of cementitious materials by considering the predominant fracture process zone (FPZ) mechanisms such as microcracking and aggregate bridging. This is achieved by quantifying the critical microcrack length and the bridging resistance offered by the aggregates. Further, the moment carrying capacity of a cracked concrete beam is determined by considering the effect of aggregate bridging. A modified stress intensity factor (SIF) is derived based on linear elastic fracture mechanics (LEFM) approach by considering the material behavior at different scales through a multiscale approach. The model predicts the entire crack growth curve for plain concrete by considering these process zone mechanisms. Furthermore, the fracture and fatigue response of concrete is studied through the development of analytical models which include the properties of the mix constituents using the multiscale based SIF. The effect of the interfacial transition zone, microcracks and resistance offered through aggregate bridging on the resistance to crack initiation and propagation are studied. A fatigue crack growth law is proposed using the concepts of dimensional analysis and self-similarity. Through sensitivity analyses, the influence of different parameters on the overall fracture and fatigue behavior are studied. In addition, studies related to concrete-concrete bi-material interfaces are conducted in order to understand the influence of repair materials on the service life of damaged concrete structures when subjected to fatigue loading. An analytical model is proposed in this study to predict the crack growth curve using the concepts of dimensional analysis and self-similarity in conjunction with the human population growth model. It is seen that a repair done with a patch having similar elastic properties as those of the parent concrete will have a larger fatigue life.

Cette thèse s’inscrit dans le cadre du projet SEPOLBE qui a pour ambition d’élaborer des adjuvants respectueux de l’environnement qui doivent se substituer à des produits soumis à autorisation REACH. Elle a pour but de mettre en évidence les propriétés de mortiers enrichis d’un adjuvant fabriqué à partir de produits extracellulaires issus de bactéries selon un protocole original. Ce travail consiste en l’étude des caractéristiques de mortiers bioadjuvantés dans le but de développer l’usage de bétons plus éco‐respectueux en améliorant leurs compositions chimiques et leur durabilité. L’action du produit biologique utilisé a été évaluée aussi bien sur sa capacité à modifier le réseau poreux des mortiers et pâtes cimentaires que sur ses effets sur la prise du ciment, la rhéologie à l’état frais et les caractéristiques mécaniques à l’état durci des mortiers permettant ainsi de qualifier ce produit comme bioadjuvant. Il a présenté un effet notable sur l’ouvrabilité de mortiers (de CEM I ou CEM V) avec une action plastifiante. De plus, quel que soit le temps de cure, un optimum de concentration en bioadjuvant de 1,5% a été déterminé pour obtenir des résistances mécaniques dumême ordre de grandeur que les échantillons non adjuvantés, et supérieures au minimum requis par la norme EN 196‐1. Le bioadjuvant n’influence pas la porosité totale accessible à l’eau des mortiers et des pâtes de ciment, toutefois, pour ces dernières, les mesures par porosimétrie par injection de mercure ont révélé l’existence d’un seuil (entre 0,5 et 0,75% de bioadjuvant) à partir duquel la structure poreuse des pâtes cimentaires est modifiée. Les effets de modification de surface de pâtes cimentaires – le liant du béton pouvant constituer un maillon faible en ce qui concerne les problèmes de durabilité de celui‐ci – ont été analysés. Pour des temps de cure élevés, la rugosité des surfaces des pâtes cimentaires diminue en présence du bioadjuvant. Ce travail a permis de lever des verrous techniques concernant l’emploi d’un produit biosourcé en tant qu’adjuvant, ainsi que d’apporter une contribution à la connaissance des interactions entre les micro‐organismes et les matériaux cimentaires. En effet, une approche originale, grâce à la PCR – technique peu utilisée avec les matériaux cimentaires – a permis de mettre en évidence qu’il y avait des bactéries au coeur du béton ayant une capacité à se développer dans des conditions de cures normalisés pour des temps de cure supérieurs à 120 jours. Le bioadjuvant est susceptible de modifier le développement bactérien et présente ainsi la possibilité de conférer aux bétons des capacités de résistances aux agressions environnementales plus importantes lui permettant d’être plus éco‐respectueux, aussi bien par sa composition que par sa meilleure durabilité. / This work is a part of the SEPOLBE project, which aims to develop eco‐friendly admixtures. The active principle of this admixture is made of extra‐cellular substances, secreted by microorganisms into their surroundings. It contributes to the effort in sustainable development that consists to limit the impact of buildings on environment and human health, with a guarantee of better quality concerning esthetical, durability and resistance criteria, according to the REACH regulation. The action of thisorganic product was evaluated on its setting time effects on cement as well as the mechanical behavior to the hardened state. The bioadmixture presents a significant effect on the workability of mortar (CEM I or CEM V) with a plasticizing action. Whatever the curing time, the compressive strength values of samples containing 1.5% of bioadmixture remain higher than the minimum data of standard strength according to the EN 196‐1 standard. The porosimetry by intrusion with mercury carried out with cement pastes showed the existence of a threshold (in the range 0.5‐0.75% of bioadmixture) from which the porous structure of cement pastes changes, while no modification were observed with the measurement of porosity accessible to water. For higher curing times, thesurface roughness of cement pastes, more heterogeneous, decreases with the presence of the bioadmixture. This work allowed to better control the use of a bio‐product assimilated as an admixture, as well as to contribute to the knowledge of the interactions between microorganisms and cementitious materials. An original approach, using the PCR ‐ not routinely used technique forthat purpose with cementitious materials ‐ helped to highlight that bacteria were present inside the mortar samples with a capacity to grow to higher curing time. The studied bioadmixture allows giving to the concrete the ability to resist against environmental stresses while being eco‐friendly, concerning both its chemical composition and its durability.