Decreasing the pH value of a concentrated sodium silicate solution while maintaining its basic environment, largely affects solution stability. The charge modification induces by the presence of acidic species is expected to destabilize initial equilibrium, thus affecting original structure. Acidification along with dilution of a concentrated sodium silicate solution ([Si] = 7 mol/L, Si/Na = 1.71, pH = 11.56) was realized by slightly adding a 0.5-2 mol/L hydrochloric acid solution under stirring. Through small angle X-ray scattering (SAXS), Fourier Transform Infrared (FTIR) spectroscopy, specific surface area and elementary chemical analysis, chemical species involved in the gelation and maturation of a concentrated sodium silicate solution were characterized. Results show that the initial mother solution which is a high pH-sensitive solution, is composed of both neutral and charged species such as Si7O18H4Na4, Si7O18H5Na3, (Si7O18H3Na4)(-) and (Si7O18H4Na3)(-). These complex species are likely to dissociate, aggregate and/or condense as a function of both pH and silicon concentration. Accordingly, it is possible to master these solutions for appropriate usage.

Portland cement (PC) and Calcium sulfoaluminate cement (CSA) blends are used to produce binders with properties as rapid hardening. However, characteristics of calcium sulfoaluminate cements such as chemical and mineralogical composition, particle size distribution, among others, can have an enormous variation and affect the performance of the PC-CSA cement mixture. Therefore, current research focus on the mechanical properties and hydration of PC-CSA (75 wt%-25 wt%) blend cement using three different CSA cements in order to better understand the influence of property variations like ye’elimite quantity and ye’elimite/anhydrite ratio in CSA cements on PC-CSA systems. Compressive strength was determined on mortars and hydration was studied on paste using isothermal calorimetry, X-ray diffraction and thermal analysis. Results showed that ye’elimite quantity in CSA used into PC-CSA hybrid cements have a large influence in early hardening and hydration. But, beyond the quantity of ye’elimite, findings showed that there is a greater influence of the ye’elimite/anhydrite ratio on the heat release, mineralogy and compressive strength of PC-CSA blends. For example, it was found that it is necessary to adjust the sulfate content to avoid compressive strength stagnation. Higher ye’elimite/anhydrite yields to higher mechanical strengths independent on the type of CSA.

The development of silicon-core fibers have drawn strong interest over the last decade. Indeed, silicon is a material offering interesting properties such as mid-wave infrared transparency (1-7 μm), high refractive index (3.48 @ 1.55 μm) and large third order non linearity (≈ 1.5×10 -13 cm 2 /W). Until now, three fabrication processes have been developed to achieve glass-clad silicon-core fibers: the high-pressure microfluidic chemical deposition method [1], the molten core method from silicon rods [2] and the powder-in-tube method [3]. This last one shows a very high potential to achieve hybrid optical fibers as it allows not only to use a wide range of materials but it is also compatible with the stack-and-draw process; in this way, many different designs of fibers can be especially drawn. Unfortunately, fibers fabricated by this method are very short, only a few centimetres long because of the mechanical stresses accumulation at the interface between the two materials which have different thermal expansion coefficients (Si: 3×10 -6 K -1 ; SiO 2 : 5×10 -7 K -1 ), and because of the presence of air between the grains.

This chapter presents the work carried out to study the influence of recycled concrete aggregates on concrete durability properties. Numerous previous studies have highlighted that recycled concrete aggregates are more porous than natural aggregates (NAs) and can lead to a decrease in the durability properties. The durability properties investigated by the French national project RECYBÉTON and the ANR project ECOREB are the properties related to the corrosion risks of the reinforcement (carbonation, chloride migration, gas permeability, and porosity), the resistance to freeze/thaw cycles, the risks linked to alkali–silica reactions (ASRs), and the presence of sulfates (ettringite/thaumasite formation). The results obtained show that the porosity accessible to water is a durability indicator not relevant in itself to sufficiently predict the risks of corrosion. It is more rigorous to consider at least the chloride diffusion coefficient and the resistance of concrete against carbonation penetration. The recycled aggregates (RAs) predictably decrease the performances of the concrete relating to the transfer properties with an intensity which depends on the intrinsic characteristics of RAs (porosity), the substitution rate, and the compactness of the cement matrix of the new concrete. By optimizing concrete mix (reduction of the W/B ratio in particular), it is easy to produce concretes that are as resistant as concretes only constituted by NAs. The frost resistance of RA depends on the characteristics of the original concrete. RA concrete (RAC) can be resistant to freeze/thaw cycles with or without deicing the salts depending on the frost resistance of RA and the application of the rules of formulation (binder content, W/B ratio, entrained air content and so forth). Concerning the risks of ASRs, RA can release significant amount of water-soluble alkalis in particular for the fine aggregates that contain an important fraction of adherent cement paste (ACP). RA can also contain unstable silica phases provided by some specific NA and possible pollutants (broken tiles). The studies also show that the actual recommendations can be used. Meanwhile, the main tests currently used for NA have to be adapted (higher water absorption of RA), and nevertheless, some of them (microbar test) are not adapted to RA. The studies on ettringite and thaumasite formation due to the presence of sulfates lead to recommendations in order to avoid the risk of disorders: 0.3% and 0.2% for the maximum water-soluble sulfate content, in RA and total aggregate, respectively.

Ye’elimite is formed during the production of sulfoaluminate cement. In this article, the orthorhombic ye’elimite formation, the optimal synthesis conditions and the microstructural evolution during synthesis, by solid-state reaction from pure oxide raw materials, is investigated. The phase assemblage was substantially affected by temperature and duration of sintering. Making reference to Rietveld quantitative analysis results, optimal solid-state synthesis conditions of ye’elimite was 1300 °C for 3 h. During ye’elimite synthesis, significant gas releases were observed at different stages of firing using TGA coupled with mass-spectrometer. The gases are the product of carbonate decomposition, gypsum dehydration and sulfate decomposition from the unreacted anhydrite and the formed ye’elimite. Based on the present work, it emerges that a key strategy for forming ye’elimite with a high purity is to compensate sulfate decomposition by the addition of a slight excess of CaSO4 before repeating the firing cycle at optimal conditions. Finally, the porosity was investigated using Archimedes principle measurements compared to BSE-image analysis. It shows the difficulty to achieve dense sintered ye’elimite because of the high decomposition gas releases during the firing process.

AbstractThis paper presents a study carried out on concrete made with seven Tunisian cements with varying limestone filler content (binders) and manufactured on an industrial scale. The purpose of the study is to promote portland-limestone cement in countries where these cements are not usually used. The mechanical aspects of the concrete’s behavior were examined over a period of 3 days to 1 year. Permeability and accelerated and natural carbonation as a function of initial curing time were also studied over periods that were occasionally even longer. The results show that limestone filler does have a beneficial action on some properties, such as strength at early age, but is less beneficial for other properties, such as carbonation. However, the addition of limestone filler leads to concretes of entirely acceptable properties for current uses, certainly if filler content does not exceed 25%, and if optimized grinding of binders is conducted.

Concrete is one of the most abundant construction and demolition wastes. It can be crushed to produce Recycled Concrete Aggregates (RCA) that can eventually be recycled for the manufacture of new concrete. However, the presence of adherent cement paste leads to higher alkalis content in these aggregates that could increase the risk to observe Alkali Silica Reaction (ASR). Moreover, the origin of natural aggregates in the RCA is generally unknown and these aggregates can potentially be reactive concerning ASR. Among standards which qualify the risk of ASR for natural aggregates, two main tests are used in this paper to evaluate the risk of ASR of RCA: tests on mortars and tests on microbars. In these tests, the water absorption of aggregates is not taken into consideration for the effective water calculation. However, in the case of absorbing aggregates like RCA, absorption water cannot be neglected. It could change significantly the effective water to cement ratio, and then influence the measured expansion. The first aim of this paper is to study the influences of absorption water and initial saturation state of RCA on the expansion of mortars and microbars. The second objective is to propose a new simple method for the assessment of water absorption coefficient of the fine granular fraction 0.16/0.63mm used for the manufacture of microbars. It is shown that absorption water has a strong influence on the expansion of mortars and microbars made with RCA, and that it has to be taken into account in the composition of the mixes. The initial state of saturation of RCA is less influential. The proposed method for the water absorption coefficient determination of fraction 0.16/0.63mm is based on the correlation between water absorption and cement paste content. The estimation of the latter from the mass loss between 105 and 475°C for two fractions of RCA, allows for an accurate determination of the water absorption coefficient of the fine fraction.

Ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) cement are two chemically different hydraulic binders. OPC and CSA cement blends can be used to adjust the binder properties for specific applications. The first part of this article compares the compressive strength and hydration products of three blends (85–15, 70–30 and 40–60% of OPC–CSA cement) using two different OPC. CSA cement percentage modifies the hardening speed as well as the hydration mechanisms (hydrates nature and quantity). The composition of OPC has also a significant influence even for the lowest OPC proportion (40% of OPC). In the second part, investigations based on compressive strength and calorimetry analysis indicate that OPC free lime is a key parameter.

This paper presents a study of seven Tunisian cements with varying limestone filler content, manufactured on an industrial scale. The purpose of the study is to promote Portland-limestone cement in countries where these cements are not usually used. Materials characterization showed that the grinding quality of the seven cements was very different. This parameter was defined by the ratio of specific surface (Blaine) and residue at 40 mu m. Generally limestone fillers behave in a similar way to crushed clinker although they do accelerate the setting because they are finer. Monocarboaluminate appeared from a young age when filler content was high. At a young age (2 days), mechanical strengths are equivalent, at least if grinding quality is satisfactory. At a medium age (28 days), grinding quality influences performance. At a later age (1 year), only those cements with high limestone content underperform. Limestone fillers increase sorptivity and modify porosity but have little influence on dimensional stability. (C) 2013 Elsevier Ltd. All rights reserved.

Les laitiers d’aciérie de conversion (LAC) sont les résidus de la transformation de la fonte en acier. Ces produits abondants (plus de 2 millions de tonnes/an en France) sont peu valorisés en génie civil car ils contiennent de la chaux libre qui, en s’hydratant, cause des expansions souvent conséquentes. Un outil pour leur utilisation dans les mélanges granulaires routiers a été développé. Il est basé sur deux modèles paramétriques décrivant, l’un le taux de grains dégradés en milieu aqueux à température et à âge donnés en fonction de la teneur en chaux libre, de la taille et de la structure des grains, l’autre l’expansion volumique d’empilements granulaires, purs ou mélangés à des granulats inertes, soumis à un flux de vapeur. La combinaison de ces deux modèles avec le Modèle d’Empilement Compressible du LCPC permet alors de prédire la cinétique de l’expansion d’un mélange granulaire quelconque, et de désigner des mélanges optimisés en termes de granularité et de proportions, incorporant des LAC, pour un usage spécifié par une expansion tolérée à une échéance et dans un environnement donnés. BOF Slags are residues of the transformation of melting steel. These abundant products (more than 2 million tonnes per year in France) are little valued in civil engineering because they contain free lime which, by hydrating, cause often substantial expansions. A tool for use in road granular mixtures has been developed. It is based on two parametric models describing; i) the rate of grain degraded in water at temperature and age given, in function of the content of free lime, the size and the structure of the grain, ii) the expansion of the packing granular, pure or mixed with inert aggregates, exposed to a flow of steam. The combination of these two models with the Compressible Packing Model of LCPC allows then the prediction of the kinetics of expansion of a granular mixture, and the designation of mixtures optimized in terms of granularity and proportions, incorporating BOF Slag, for a use specified by an expansion to a given deadline and in a given environment.

BOF Slags are residues of the transformation of melting steel. These abundant products (more than 2 million tonnes per year in France) are little valued in civil engineering because they contain free lime which, by hydrating, cause often substantial expansions. A tool for use in road granular mixtures has been developed. It is based on two parametric models describing; i) the rate of grain degraded in water at temperature and age given, in function of the content of free lime, the size and the structure of the grain, ii) the expansion of the packing granular, pure or mixed with inert aggregates, exposed to a flow of steam. The combination of these two models with the Compressible Packing Model of LCPC allows then the prediction of the kinetics of expansion of a granular mixture, and the designation of mixtures optimized in terms of granularity and proportions, incorporating BOF Slag, for a use specified by an expansion to a given deadline and in a given environment.

Both concentrated and diluted sodium silicate solutions have been investigated by combining (29)Si NMR spectroscopy and SAXS experiments. The chemical nature of the entities responsible for the high siliceous species solubility observed in such alkaline concentrated sodium silicate solutions and their evolution according to dilution have been identified. For the most concentrated solution ([Si]=7 mol/l; pH=11.56; Si/Na atomic ratio=1.71), the results evidence the preponderant presence of neutral Si(7)O(18)H(4)Na(4) complexes, which behave like colloids of about 0.6-0.8 nm able to form very small aggregates with an average size lower than 3 nm. Addition of distilled water to this initial concentrated solution leads, on one hand, to a doubling of the colloid size, i.e. 1.2-1.5 nm, and, on the other hand, to a progressive decrease of the aggregate size until their total disappearance. Such a behavior could be explained by considering, first, the dissociation of the neutral Si(7)O(18)H(4)Na(4) complexes present in the concentrated solution into Na(+) ions and charged (Si(7)O(18)H(4)Na(4-n))(n-) complexes (with 1 ≤ n ≤ 4) and, second, the condensation of these siliceous charged species in order to form larger (Si(7y)O(18y-z)H(4y-2z)Na((4-n)y))(ny-) colloids. The mean size of these colloids suggests that the condensation occurs between 2 and 8 (Si(7)O(18)H(4)Na(4-n))(n-) groups.

Homogeneous, transparent, and mechanically rigid gels have been successfully synthesized in the tellurium isopropoxide-isopropanol-citric acid and water system. The sol to gel transition and the gels microstructure have been studied by using small angle X-ray scattering (SAXS) experiments. For any value of the two key synthesis parameters, which are the citric acid ratio and the alkoxide concentration, very small Te-rich elementary particles, about 1-1.5 nm in radius, form immediately when the water is added, leading to colloidal sols. During gelation, these elementary particles stick progressively together to build up fractal aggregates by a pure hierarchical aggregation process which has been identified as a reaction-limited cluster aggregation (RLCA) mechanism. The SAXS curve analysis, based on scaling concepts, shows that the gelling network exhibits a time and length scale invariant structure factor characterized by self-similarity. This self-similarity is also displayed for a wide range of chemical compositions and the gel microstructures only differ in their fractal aggregate size according to the tellurium isopropoxide concentration as well as the citric acid ratio.

A sol–gel process for TeO2 thin layers synthesis was developed, including the tailoring of the tellurium alkoxide reactivity, their preparation by dip-coating and the effects of heat treatments on their structure and microstructure. High quality thin films were made by dipping silica glass substrates in solutions prepared in the tellurium isopropoxide, isopropanol, citric acid and water system. The structure and microstructure of the films were characterized by X-ray reflectometry, X-ray diffraction, optical and scanning electron microscopies as a function of the chemical parameters of the sol, withdrawal speed, temperature and time of annealing. They were found to be highly dependent on the initial thickness and applied thermal treatment. Indeed, TeO2 thin films could be either quite fully dense and amorphous or made of randomly orientated γ-TeO2 or/and α-TeO2 crystals. Firing at the highest tested temperature (∼450–500°C) promotes grain growth and islanding, so producing a layer of textured but isolated grains.

Sol-gel processing of tellurium oxide has been investigated in the tellurium isopropoxide/citric acid/isopropanol/water system. As evidenced by Fourier transformed infrared spectroscopy (FTIR), citric acid has been found to be a relevant chemical modifier to control hydrolysis-condensation reactions of highly reactive tellurium isopropoxide Te(OCH(CH3)2)4. Thus, depending on the main synthesis chemical parameters such as alkoxide concentration, water and modifier ratios, colloidal sols and gels have been successfully synthesised. The thermal behaviour of the dried gels has been investigated by X-ray diffraction, differential scanning calorimetry coupled with thermogravimetry and also FTIR spectroscopy. On the one hand, the crystallisation of the non-centrosymmetric γ-TeO2 polymorph as well as the α-TeO2 phase which the crystallite size ranges from a few ten nanometers (∼50 nm) to a few microns as a function of heat treatment, and, on the other hand, the synthesis of homogeneous sols which can be handled in air and so particularly suitable for the elaboration of thin films provide new opportunities for making tellurite based materials and thin film devices for practical applications.

The La0.8Sr0.2MnO3 (LSM) cathode materials are widely used in solid oxide fuel cells (SOFCs) as electronic conductors. In such materials, the reduction of oxygen is located at the triple contact boundaries: air/cathode LSM/electrolyte which is generally Yttria Stabilised Zirconia (YSZ). In order to improve the chemical reactions at these air/cathode LSM/electrolyte interfaces, the triple phase boundary length has to be optimised. In this aim, we have first synthesised the La0.8Sr0.2MnO3 phase by a sol–gel route and, second, LSM thin films have been deposited on various polished substrates by using a dip-coating process. The structure and microstructure of the resulting LSM thin layers have been investigated by using well suited complementary techniques such as X-ray reflectometry, grazing incidence small angle X-ray scattering, X-ray diffraction and scanning electronic microscopy. The structural and microstructural parameters of LSM thin films have been managed and studied as a function of synthesis parameters such as initial metallic salt concentration, time and temperature of annealing. The higher the metallic salt concentration, the higher the thickness of the film, the smaller the film density. The as-prepared layers are amorphous and the single crystallised perovskite form is obtained for low temperature heat treatments. Therefore, the annealed coatings are constituted by randomly oriented LSM nanocrystals, which organise in a more or less dense close-packed microstructure according to the initial metallic salt concentration.

The development of original technologies to fabricate new kinds of fibres is presented here. First of all, the sol–gel process is developed to achieve fibres with original properties of waveguiding (new wavelength of emission of rare earths or transition metals, ultraviolet waveguiding): either a fibre composed of doped nanocrystals in a silica matrix or fibres composed of a one dimensional photonic bandgap structure. In this way, high refractive index dielectric oxides like ZrO 2 , TiO 2 are studied. Secondly, the core suction technique associated with the stack and draw process is developed to fabricate fibres with various glasses and then, original profiles of refractive index to achieve multiwavelength lasers.

A SiO2–ZrO2 nanostructured optical fiber developed using the chemical sol-gel method is fabricated and its waveguiding properties are studied. The refractive index difference between the core and the cladding is 0.021 for a (30%ZrO2–70%SiO2) molar core composition. Illumination of the fiber with a supercontinuum source (350–1750nm) shows that the light is guided over this entire range. The measured attenuation losses are 0.7dB∕m at a 1064nm wavelength and the calculated cutoff wavelength is 714nm.

X-ray reflectometry, X-ray diffraction and grazing incidence small angle X-ray scattering have been complementary used to fully characterize zirconia (ZrO2) thin films obtained by the sol–gel route. The films were synthesized on various sapphire (Al2O3), silicon (Si) and glass mirror-polished wafers by a dip-coating process in a zirconia precursor sol. Versus the synthesis parameters as alkoxide sol concentration, withdrawal speed and annealing temperature, the microstructure of the layer is managed and its different microstructural parameters such as thickness, mass density, crystalline phase, grain size and spatial arrangement have been determined. The as prepared layers are amorphous. During a thermal treatment at low temperature (<1000 °C), the layers thickness decreases while their mass density increases. Simultaneously the zirconia precursor crystallises in the zirconia tetragonal form and the coating is made of randomly oriented nanocrystals which self organise in a dense close-packed microstructure. At low temperature, this microstructural evolution is similar whatever the substrate. Moreover, the layer evolves as the corresponding bulk xerogel showing that the presence of the interface does not modify the thermal microstructure evolution of the layer which is controlled by a normal grain growth leading to relatively dense nanocrystalline thin films.