The incorporation of waste tyre rubber into thermoplastics to develop a class of polymer composites with both elastomeric and thermoplastic behaviour has gained a lot of attention and is becoming one of the most straightforward and preferred options to achieve the valorisation of waste tyres. In view of the unique properties rubber possesses and the rapid expansion and versatile application of wood plastic composites (WPC) materials, the inclusion of tyre rubber as raw material into WPC to develop an entirely new generation of WPC, namely rubber-wood-plastic composites (RubWPC), was presumed to be another highly promising solution to turn waste tyres into value-added materials. This research starts with the interfacial optimisation of Rubber-PE composites and WPC by the use of maleated and silane coupling agents, aiming at addressing their poor constituent compatibility and interfacial bonding, thus enabling the optimal design of RubWPC. Chemical, physical and mechanical bonding scenarios of both untreated and treated composites were revealed by conducting ATR-FTIR, NMR, SEM and FM analyses. The contribution of the optimised interface to the bulk mechanical property of the composites were assessed by carrying out DMA and tensile property analysis. The influence of the coupling agent treatments on the in situ mechanical property of WPC was first determined by nanoindentation analysis, which led to a thorough understanding of the interfacial characteristics and the correlation between in situ and bulk mechanical properties. This research focuses on the novel formulation of RubWPC and the understanding of bonding mechanism. Chemical bonding and interface structure studies revealed that interdiffusion, molecular attractions, chemical reactions, and mechanical interlocking were mutually responsible for the enhancement of the interfacial adhesion and bonding of the coupling agent treated RubWPC. The improved interface gave rise to the increase of bulk mechanical properties, while the continuous addition of rubber particle exerted an opposite influence on the property of RubWPC. The composite with optimised interface possessed superior nanomechanical properties due to the resin penetration into cell lumens and vessels and the reaction between cell walls and coupling agents.

Cement has been selected for wastes immobilization as a simple, low temperature and low cost process for decades. The mechanical and immobilization properties of cement are mainly decided by cement hydration process, especially in the first 24 hours. Previous methods for studying the cement hydration are those include isothermal calorimetry, continuous monitoring of chemical shrinkage, in situ quantitative X-ray diffraction, nuclear magnetic resonance spectroscopy (NMR), quasi-elastic neutron scattering (QENS) and small angle neutron scattering (SANS). Few available in-situ imaging methods were successfully used for net rate study of cement hydration. In this Ph.D. research, innovative imaging techniques such as X-ray computed tomography (XCT) combined with 2D SEM-BSD analysis were combined to study the microstructure and phase change of cement or cement & SrCl2 mixture during hydration. Digital Volume Correlation (DVC) and Digital Image Correlation (DIC) were applied to study the chemical volume shrinkageand drying shrinkage of cement samples during hydration. The effects of SrCl2 simulating the radioactive nuclide from nuclear waste on cement hydration were studied by XRD and ICP-AES techniques. These studies verified that the hydration net rate could be characterised by XCT imaging techniques and the volume shrinkage of cement or cement& SrCl2 mixture during hydration could be characterised by the DVC and DIC techniques.

Alkali-activated binders (AABs) are the third-generation class of binders after lime and Portland cement. These binders have the potential to be made from a variety of industrial waste sources, many of which have remained largely unexplored. Significant drawbacks of AABs are the requirement of highly alkaline solutions for its production and the lack of available data regarding its implementation in the field. To bridge this gap, this study aimed to research the recycling and valorization of tungsten mining waste (TMW) to produce AABs, using waste glass (WG) as a supplementary material for reducing the alkali activator demand. Finally, a connection was made between the fundamental research on AABs and a practical engineering application. A detailed approach was undertaken to determine the most appropriate TMW-WG AAB preparation methods and curing conditions, an understudied area, with a strong emphasis on the microstructural development during hardening. The alkali activator appeared to be sensitive to prolonged stirring, which appeared to induce a stripping effect of the water molecules from the alkali metal ions, leading to a less intense attack on the silicon-oxygen bonds in precursor material. The effects of WG (dissolution and chemical reaction) were investigated to understand its contribution to the AAB system. WG was observed to provide an additional source reactive silica, contributing to the formation of a calcium-containing N-A-S-H gel, and significantly improve the mechanical strength. PCM macro-encapsulated aggregates (ME-LWAs) were also researched and incorporated into the TMW-WG AAB for the development of an energy-saving building material. The ME-LWAs stood out to be leak proof, with excellent thermal stability and thermal conductivity, latent heat capacity and abrasion resistance. It was also found out it is feasible to produce foamed lightweight alkali-activated materials using tungsten mining waste (TMW-WG FAAB) and other precursor materials. FAAB can be used in several applications where low density and fire resistance is required. The TMW-WG FAAB was also designed to suit a wide range of densities and compressive strengths using chemical foaming, achieving very low thermal conductivity. Finally, the TMW-WG AAB proved itself to be convenient to prepare on-site, demonstrating in service its ease of preparation, rapid hardening and durability as a novel road repair mortar.

Foamed concrete has considerable potential as a material for use in the construction industry. However, although some researches have been conducted on the characteristics of foamed concrete, thus far, knowledge on the behaviour of foamed concrete has been limited. Hence, predictions of the stability of foamed concrete under different conditions and mix constituents have been uncertain. The aim of the presented study is to investigate causes of instability of foamed concrete by examining its rheological properties and microstructure. This study explores the complex causes of instability in foamed concrete by examining the rheological parameters, the yield stress and the plastic viscosity, since the rheological properties affect the hardened state. Using flowability as a guide, the relationships are examined between yield stress and viscosity, specifically with reference to their effect on density and w/c ratio. Other factors affecting the rheological properties related to the proportions and fineness of the mix constituents are also considered. Thereafter, the microstructure of foamed concrete is examined to establish links with the rheological values and the relationship with stability. The microstructure, best described by the bubble sizes, has been found to be a function of yield stress, plastic viscosity, material fineness and surfactant types. The bubble diameters have been shown to range between 0.1 to 0.5 mm. Bubbles less than 0.35 mm in diameter correspond to stable mix with a drop in level of less than 5% in height in densities of 1000 kg/m3 and higher. The big bubbles link to unstable mixes and have been found to be a source of instability. Other chemical additions were shown to result in disintegration of bubbles. As this study unfolds, a relationship is established between bubbles and the yield stress values. Bubble sizes reduced when the yield stress increased. For flowability out of Marsh cone test taken between 1 to 2 minutes, the corresponding yield stress was between 6.0 N/m2 to 8.5 N/m2. For this range, the empirical bubble sizes were found to be between 0.33 to 0.35 mm in diameter. In examining the possible causes of instability, it was found that stability improved markedly with increase in density and lesser effect by other factors such as w/c ratio, constituent materials and specimen height. However, the rate of hardening was a dominant factor in stability as evidenced by the use of Calcium Sulfoaluminate cement, CSA and CEM I 52.5R cement which increased the setting times. Stability was drastically achieved even at lower density 300 kg/m3. Blends of CSA with CEM I 52.5R and fine fly ash, FAf, demonstrated similar results. This research has implications for the development of foamed concrete as a material that could be more widely used in certain construction contexts where stability in lightweight density foamed concrete is crucial. It has contributed to better understanding of the rheological properties and the effect on the microstructure, even though the results are based on empirical values. Hence, it is anticipated that the prediction of stability can be made through a selection of materials and proportions to suit different contexts and their requirements.

Coral reefs are faced and will be faced with many challenges this century. One danger is the rapid decline of oceanic pH due to anthropogenic sources. The more acidic the environment becomes, the harder reefs and coral (order: scleractinia) in particular will be hit. Experiments to measure the effect on scleractinian coral were performed to glean a better understanding of the processes that will be affected by our acidifying oceans. Additionally, the search for and analysis of coral microstructure and micromorpholgy were carried out in an attempt to understand homology within an environmentally responsive taxa.

En réponse aux exigences de la réglementation REACH qui prévoit que les substances à base de chrome hexavalent devront être soumises à autorisation dès 2017, les industriels du secteur aéronautique mènent depuis plusieurs années des activités de recherche et développement de nouveaux procédés de traitement de surface moins néfastes pour l’environnement et la santé. Le travail prévu dans le programme de recherche NEPAL (NouvellEs Protections des ALuminiums) s’inscrit dans cette dynamique. Les traitements mettant en oeuvre des composés à base de Cr(VI) sont destinés à disparaître dans un proche avenir ; ainsi de nouvelles formulations ont été développées parmi lesquelles des procédés de conversion à base de chrome trivalent. Le projet de thèse vise à renforcer la robustesse de ces procédés en apportant des éléments de compréhension pour ce qui concerne la tenue à la corrosion des alliages d’aluminium revêtus de couches de conversion au chrome trivalent en relation avec leur état microstructural. Les travaux de thèse ont été développés sur une nuance d’alliage d’aluminium 2024, parmi celles les plus utilisées dans le secteur aéronautique. Plusieurs microstructures ont été considérées dans le but de modifier la distribution en éléments d’alliages majoritaires, le cuivre et le magnésium. La caractérisation fine de la microstructure et l’évaluation de la réactivité des échantillons dans les différents bains de traitement de conversion ont permis de mettre en évidence l’influence de la répartition du cuivre dans l’alliage, élément néfaste pour la croissance des couches de conversion lorsqu’il se trouve sous forme de précipités fins. Finalement, l’étude de deux tôles d’alliage d’aluminium d’épaisseurs différentes met en évidence l’influence de nouveaux paramètres microstructuraux tels que les joints de grains ou la précipitation grossière. Ce travail a été réalisé dans le cadre du projet FUI NEPAL. Le CIRIMAT a été financièrement soutenu par le Ministère de l’Économie et de l’Industrie français (BPI-France), la Région Occitanie Pyrénées-Méditerranée et l’Union Européenne (FEDER/ERDF).

A functionally-graded Al(subscript)2TiO(subscript)5/ZrO(subscript)2-Al(subscript)2O(subscript)3 (AT/zirconia-alumina) composite has been successfully synthesized by an infiltration process involving an alpha-Al(subscript)2O(subscript)3-ZrO(subscript)2 (90:10 by weight) green body and a solution containing titanium chloride. The mass gain after infiltration has been used to estimate the amount of new phase introduced into the system. The phase composition character of the functionally-graded material (FGM) has been determined by x-ray diffraction. The Rietveld "whole pattern" refinement method was applied to diffraction patterns of the sample which were collected from the surface and at several depths which were made by polishing away the material. Absolute weight fraction determination using the Rietveld external standard method showed that the concentration of AT reduces linearly from the surface to the core. In contrast, the alpha-alumina content increases with depth in a complementary manner. Low level amorphous phase was also observed. Other functionally-graded microstructural profiles examined were x-ray characteristic line intensity of Ti, Ti dot-mapping, and alpha-alumina grain size. The FGM also exhibits graded character in both thermal and mechanical properties, i.e. thermal expansion, microhardness, and Young's modulus. The thermal expansion coefficient (TEC) of the FGM increased with polishing-depth and approached that of the zirconia-alumina reference sample at a depth of 0.5 mm. / Relatively lower thermal expansion and softer surface layer in comparison to those of the core (TEC value of 5.9 x 10(subscript)-6 degrees celsius(subscript)-1 and microhardness of 6 GPa compared to 7.4 x 10(subscript)-6 degrees celsius(subscript)-1 and 12 GPa, respectively) render possibilities to implement the material to which thermal shock resistance surface but hard core, such as a metal melting crucible, are required. Load-dependent microhardness was obviously observed on the surface of the material but only slight dependence was observed in the core. This observation indicated that the material exhibit "quasi-ductile" surface but brittle core. In comparison to the reference specimen, the FGM displayed damage-tolerance and remarkable machinability.

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Equal channel angular pressing ECAP is a process whereby simple shear is applied to a billet during multiple passages through an angled channel of constant cross section. The process is capable of generating very large plastic strains that significantly refines the microstructure without altering the external dimensions of the billet. A number of properties are influenced by grain refinement with the generation of a submicron grain structure SMG by ECAP resulting in improved strength and hardness and enhanced superplasticity. In this thesis, both an AA7075 alloy and AA7075 Al-base metal matrix composite MMC reinforced with 5 wt. percent of 50 nm diameter SiC particles was produced by a powder metallurgy route followed by hot extrusion. The materials were subsequently deformed by ECAP at 350 C to a true effective strain of 4.6 in an attempt to refine the microstructure and further distribute the SiC reinforcement phase in the composite. The high temperature microstructural stability of both the as-deformed alloy and composite was investigated to elucidate the effect of the reinforcement phase on continuous and discontinuous grain coarsening. It was found that ECAP generated a fine equiaxed grain size of ~ 2.3 !m and ~1.8 !m in the alloy and composite, respectively. The composite was more refined after ECAP since the SiC particles allow the matrix to undergo more grain refinement during deformation. ECAP was found to be a reasonable method for further distributing SiC clusters in this composite which is important for optimizing the reinforcement phase in terms of ambient temperature strengthening and enhanced grain stability at elevated temperature. Both the alloy and composite were annealed at times up to 5h at 500 C to assess grain stability. During annealing, the grain structure of both materials evolved in a continuous manner unlike the discontinuous process of recrystallization. Such a process is similar to continuous recrystallization observed in a range of heavily deformed Al alloys. Substantial grain boundary interactions with MgZn2 precipitates and oxide particles were found in the alloy, with precipitate, oxide and SiC particles found in the composite. The strong pinning force exerted by these particles minimised grain growth in both materials with the composite exhibiting a finer less than 2.5 !m grain size than the alloy less than 3.5 !m after extended annealing. This enhanced grain stability was attributed to the high volume fraction SiC particles which resulted in a large value of the dispersion parameter f/d which results in significant boundary pinning during annealing. Grain stability was also analysed in terms of a recently-proposed mean field model of annealing where it was predicted that the composite should not undergo discontinuous coarsening, as observed experimentally.