Super sulphated cement (SSC) is a very promising substitute for traditional construction materials (i.e. Portland cement), due to its enhanced durability and particularly low environmental impact. This paper explores the microstructure and certain properties of SSC, focusing on the particular complexities of its microstructure and the difficulties of microanalysis of its hydrates. To do so, SSC paste samples were first cast to identify hydration products using X-ray diffraction, then observed at early age using confocal laser scanning microscopy (CLSM) and at early and late age using scanning electron microscopy. In addition, concrete cores impregnated with fluorescein in order to highlight porosity, cracking and aggregates debonding were observed under UV light using optical microscopy (OM), showing a complete absence of cracking and aggregate debonding. Both microscopy techniques (CLSM and UV light OM) have been applied to this type of binder for the first time. The results show that SSC microstructure is characterised by a sophisticated intergrowth of various phases, including ettringite and amorphous calcium-(alumina)-silicate hydrate gels. Finally, Monte-Carlo simulation of electron-matter has been provided for a better understanding of EDS analysis. This work focuses on the study of a particular construction material known as super sulphated cement (SSC). SSC appears to be a promising alternative to traditional building materials as it offers improved durability reduced and environmental impact attributed to its composition comprising at least 75% of a by-product of the steel industry. This study investigates the microstructure and properties of this type of cement, focusing particularly on its complex microstructure and the challenges posed by the analysis of its hydration products. To do this, samples of SSC cement paste were first cast to identify hydration products using X-ray diffraction. They were then examined at early stages using confocal laser scanning microscopy (CLSM) and at early and late stages using scanning electron microscopy (SEM). In addition, fluorescein-impregnated SSC concrete cores were observed under ultraviolet (UV) light using optical microscopy (OM) to highlight porosity, cracking and delamination of aggregates, phenomena that may be present in such materials. These observations revealed the absence of these problems on this type of cement in this work. This research marks the first application of CLSM and OM under UV light to this type of cement. These microscopic techniques enabled us to understand the hydration phenomenon of this type of cement and its highly complex morphology. Finally, Monte-Carlo simulation was used in this study to model electron-matter interaction, enabling us to understand the elemental analyses obtained and to gain a better understanding of the microstructure of SSC samples.

The nucleation and growth of calcium-silicate-hydrate (C-S-H) is of fundamental importance for the strength development and durability of the concrete. However, the nucleation process of C-S-H is still not fully understood. The present work investigates how C-S-H nucleates by analyzing the aqueous phase of hydrating tricalcium silicate (C3S) by applying inductively coupled plasma-optical emission spectroscopy as well as analytical ultracentrifugation. The results show that the C-S-H formation follows non-classical nucleation pathways associated with the formation of prenucleation clusters (PNCs) of two types. Those PNCs are detected with high accuracy and reproducibility and are two species of the 10 in total, from which the ions (with associated water molecules) are the majority of the species. The evaluation of the density and molar mass of the species shows that the PNCs are much larger than ions, but the nucleation of C-S-H starts with the formation of liquid precursor C-S-H (droplets) with low density and high water content. The growth of these C-S-H droplets is associated with a release of water molecules and a reduction in size. The study gives experimental data on the size, density, molecular mass, and shape and outlines possible aggregation processes of the detected species.

Introduction: Metakaolin (MK) is used as supplementary cementitious material to reduce the CO2 footprint of Portland cements. However, the early hydration of Portland cement (OPC) is often retarded due to its use. The present work investigates the mechanisms of this retardation. Focus is laid on the interaction of MK with the main clinker phase C3S (Ca3SiO5, pure form of alite) that is known to govern the kinetics of early hydration of OPC.Methods: Hydration reactions of MK and C3S were analysed by optical emission spectroscopy, electron microscopy, thermal analysis, X-ray diffraction and reaction calorimetry.Results: Results on MK showed that compared to sodium ions the presence of calcium ions reduced the maximum amounts of silicate and aluminate ions released into solution by MK. For MK + C3S mixtures, C-A-S-H was formed at the surfaces of both C3S and MK within minutes with a composition of (CaO)(1.3)(SiO2)(0.8)(Al2O3)(0.2)(H2O)(2.7). The solubility constant of (CaO)(1.3)(SiO2)(0.8)(Al2O3)(0.2)(H2O)(2.7) was determined.Discussion: C-A-S-H appeared to be an unsuitable substrate for C-S-H nucleation. Therefore, its formation during early hydration is expected to play an important role in the retardation of C3S hydration. Indeed, when C-A-S-H seeds are formed, less C-S-H seeds are formed leading to lengthen the duration of the induction period. The presence of sulfate ions reduces the amount of C-A-S-H seeds as most aluminate ions are consumed to form ettringite. Consequently, sulfate ions induce an increase of the hydration kinetics such as observed in MK + C3S mixtures.

Die Verwendung von kalziniertem Ton als Zementersatzstoff ist ein vielversprechender Weg, um die künftige Zementproduktion umweltfreundlicher zu gestalten und den CO 2 -Fußabdruck von Beton zu verringern. Jedoch wird durch den Ersatz von kalziniertem Ton wird die Zementhydratation häufig verzögert. Obwohl die kombinierte Verwendung von Kalkstein und kalziniertem Ton mit Portlandzement die Verzögerung kompensieren kann, werden die Ursachen für diesen Effekt noch immer diskutiert. Insbesondere die Rolle der gebildeten C-A-S-H-Phasen in Kombination mit C-S-H-Phasen ist umstritten. Die vorliegende Studie untersucht die geschilderte Verzögerung in Modellsystem C3S und Metakaolin. Die Hydratationsreaktionen von Metakaolin und C 3 S wurden mittels optischer Emissionsspektroskopie, Rasterelektronenmikroskopie, Röntgenbeugung und Reaktionskalorimetrie analysiert. Die Ergebnisse zeigen, dass Calcium- und Sulfationen eine dominierende Rolle für die Reaktionsgeschwindigkeit von Metakaolin spielen, was sich wiederum auf die Hydratationsgeschwindigkeit von C 3 S auswirkt. Die Rolle der C-A-S-H- gegenüber der C-S-H-Bildung wird in diesem Zusammenhang hervorgehoben.

Changes in the diversity of indigenous calcifying bacterial communities were determined before and after 1 year of biorepair treatment applied on indoor micro-cracked concrete walls. The biotreatment was based on the formation of an organo-mineral coating generated by Alkalihalobacillus pseudofirmus cultured in the presence of calcium lactate. Before and after the biotreatment, the calcifying bacterial strains belonging to either Firmicutes or Actinobacteria phylum were dominant depending on the sampling area. Nevertheless, the proportion of the calcifying Bacillus, Brachybacterium, Microbacterium, and Rhodococcus genera changed. These bacterial strains were likely to participate in the effectiveness of the biotreatment. Isolated bacteria of Microbacterium and Rhodococcus genera reported interesting calcifying capacity associated to microbial growth rates greater than the one observed for Alkalihalobacillus pseudofirmus. A bacterial consortium containing Alkalihalobacillus pseudofirmus, Rhodococcus cercidiphylli, and Microbacterium schleiferi demonstrated an improved calcifying capacity. Consequently, using a bacterial consortium instead of a single strain is an efficient way to improve the robustness of the biorepair treatment. • Indigenous calcifying bacteria mainly belonged to Firmicutes and Actinobacteria • Microbacterium and Rhodococcus reported the quickest growth rate with calcium lactate • A bacterial consortium with improved calcifying capacity is proposed

Adherent hardened cement paste attached to recycled concrete aggregates (RCA) generally presents a higher porosity than natural aggregates, which induces a lower porosity in the properties of RCA. The characterization of the adherent hardened cement paste content (HCPC) in the fine RCA would promote better applications of RCA in concrete, but the determination of HCPC in fine RCA is not well established. A simple method based on salicylic acid dissolution was specifically developed to quantify the HCPC in RCA, especially for RCA containing limestone aggregates. The results demonstrated that the soluble fraction in salicylic acid (SFSA) was equal to the HCPC for white cement and slightly lower for grey Portland cement, which was also confirmed by a theoretical approach using modelling the hydration of cement paste with the chemical equations and the stoichiometric ratios. The physical and mechanical properties of RCA (e.g., water absorption) were strongly correlated to the SFSA. For industrial RCA, SFSA did not give the exact value of HCPC, but it was sufficient to correlate HCPC with the other properties of RCA. The water absorption could be estimated with good accuracy for very fine RCA (laboratory-manufactured RCA or industrial RCA) by extrapolating the relationship between water absorption and HCPC, which is very important for concrete formulation.

Drinking water pipes can be lined with a cement matrix based on CEM III, which can release aluminium into the water. However, the European Union limits the aluminium concentration in drinking water for public health reasons. In order to study the long-term leaching mechanism of aluminium, semi-dynamic leaching tests using an aggressive solution (demineralised water) or drinking water (mineralised water) were conducted on crushed CEM III pastes maintained at pH 7. They resulted in a very high leaching coefficient, approaching 50%. However, in spite of this strong leaching, the amount of Al leached remained very low, at less than 1.5% of the initial amount of Al in the material. Under these conditions, the leaching of Al from a CEM III paste is complex since it involves several steps, where slag (1st and last steps) or cement paste (2nd step) are the main contributors.

This study aimed at developing a bacteria-based method to repair cracks in concrete (crack opening < 1 mm) that would be suitable for full-scale operations and economically viable. CaCO3-producing bacteria were injected into calibrated cracks with bioavailable calcium and nutrients in a suspension thickened with a combination of Welan gum and Attagel (R) 50. These thickeners have synergistic effects, enhancing viscosity and shear-thinning behavior. These rheology characteristics made injection without drainage possible for crack widths ranging from 150 to 800 mu m. Bacterial growth and the associated CaCO3 biomineralization were enhanced in the presence of thickeners. (C) 2020 Elsevier Ltd. All rights reserved.

Highly swelling polymers, i.e. superabsorbent hydrogels, are hydrophilic, three dimensional networks that can easily absorb a significant amount water, fluid or drug. They are widely used in various applications such as foods, cosmetics, and medical devices. Bone cements are used in orthopaedics as a filling biomaterial or as a grout enhancing the embedding of a prosthesis into bone and fixation is achieved by mechanical interlock with metal or bone surfaces. Recently, hydrophilic bone cements have attracted the attention for bone tissue-engineering applications. Here a bone cement containing an acrylic hydrogel (HEMA) as a liquid phase and a blend of corn starch, cellulose acetate and bioceramic filler as a solid phase is investigated by means of a mixture design which is a special topic within statistical Design of Experiments (DoE). Output variables of interest, complex shear modulus, compressive modulus and swelling rate related to rheological, mechanical and swelling properties respectively, are measured for each cement formulation. Applying the mixture design strategy enables to assess the impact of the three powder components on each variable of interest and to determine the optimal formulation in order to achieve the required properties of this HEMA-based bone cement, especially the rheology adapted to the desired clinical application, but also appropriate mechanical and swelling properties.

Bioprecipitation of calcium carbonate - biofilm composite on the concrete surface by spraying a bacterial suspension can reduce the permeability of concrete especially in the presence of micro-cracks. This process was applied to a replica at 1/3 scale of a nuclear reactor enclosure that was then subjected to pressurization at 500 kPa. The effectiveness of bioprecipitation treatment was demonstrated in areas where deformations of the concrete during pressurization remained minimal. Additional laboratory tests confirmed that the calcium carbonate - biofilm composite bioprecipitated in a micro-crack can withstand an air flow with a pressure of 450 kPa. (C) 2019 Elsevier Ltd. All rights reserved.

La précipitation de carbonate de calcium par les bactéries constitue une méthode prometteuse pour la réparation des matériaux cimentaires fissurés. Une des applications potentielles de la biocicatrisation est la maintenance des enceintes nucléaires. Les objectifs de cette étude sont, dans un premier temps, de déterminer par des essais de laboratoire si le colmatage de fissures induit par la biocicatrisation persiste après une mise sous pression comparable à celle d’un essai décennal et, dans un deuxième temps, d’appliquer le traitement par bioprécipitation à une réplique à l’échelle 1/3 d’une enceinte de réacteur nucléaire (VERCoRs), qui a ensuite été soumise à une pressurisation à 500 kPa. Les résultats obtenus en laboratoire montrent que le cycle de pression ne modifie pas l’ouverture apparente des fissures, sur lesquelles a été appliqué le traitement par bioprécipitation, démontrant ainsi que le composite formé par le carbonate de calcium biogénéré et le biofilm n’est pas altéré par un flux d’air ayant une pression de l’ordre de 500 kPa. De même, le traitement par bioprécipitation réalisé sur la maquette VeRCoRs a montré son efficacité dans les zones où les déformations du béton au cours de la pressurisation sont restées minimes.

Bismuth(III) oxide is included as a radio-opacifier in dental materials, including hydraulic silicate cements, the material of choice for several endodontic procedures. It has been implicated in tooth discoloration after contact with endodontic irrigants, in particular NaOCl solution, To date, there has been no work on the chemistry: all reports have been of clinical findings only. The purpose now was to report the reactions leading to colour change from Bi2O3 in contact with solutions used in routine endodontic practice. Ten-gram portions of Bi2O3 were immersed in either water, NaOH, NaCl, NaOCl or HCl solution, either in the dark or exposed to visible light, and samples retrieved at 1, 4, 12 and 24 weeks. After washing, these were exposed to either added CO2 or not, for 1 week while drying, and under the same dark or light conditions. Changes in appearance were monitored by photography and colour measurement, and chemically by X-ray diffraction and Fourier-transform infrared spectroscopy. 24-week material was studied using electron paramagnetic resonance and Raman spectroscopy; NaOCl-treated material was also examined by scanning electron microscopy. With water, NaCl and NaOH, bismuth subcarbonate was formed. With or without added carbon dioxide, discoloration occurred from pale yellow to light brown when exposed to light, and to a lesser extent in the dark, intensifying with time. In contrast, exposure to NaOCl rapidly formed a dark brown-black sodium bismuthate. With HCl, white BiOCl was formed. Bi2O3 is not at all inert in this context as is commonly believed, denying its principle of use. Previously unreported solution-mediated reaction occurs readily even in water and NaCl solution, forming new compounds that discolour. In contact with NaOCl sodium bismuthate is formed; severe darkening occurs rapidly. The reactivity is such that Bi2O3 is not indicated for dental materials and should be withdrawn from use.

Precipitation of calcium carbonate by bacteria is a promising method for the repair of cracked cementitious materials. One of the potential applications of biohealing is the maintenance of nuclear enclosures. The objectives of this study were, firstly, to determine by laboratory tests whether the sealing of micro-cracks persists after a pressurization comparable to that of a 10-year test, and, in a second time, to apply the bioprecipitation treatment to a 1/3 scale replica of a nuclear reactor enclosure (VERCoRs), which was then pressurized to 500kPa. The results obtained in the laboratory showed that the applied pressure cycle did not modify the apparent opening of the micro-cracks on which the bioprecipitation treatment has been applied, demonstrating that the composite formed by the biogenerated calcium carbonate and biofilm was not altered by a flow of air having a pressure of 450kPa. Similarly, the bioprecipitation treatment applied to VeRCoRs proved effective in areas where the deformation of the concrete during pressurization remained minimal.

The knowledge of the aqueous phase composition during the hydration of tricalcium silicate (C3S) is a key issue for the understanding of cement hydration. A new in situ method of computing calcium ion concentration from the measurement of the electrical conductivity on paste was coupled to isothermal calorimetry and BET measurements to get new insights on the early hydration of C3S. Ion concentrations of the aqueous phase are mainly dependent on the degree of hydration and the water to C3S ratio. In the case of C3S paste, the calcium and silicon concentrations determined at low degrees of hydration can be related to the equilibrium curve of C-S-H having C/S = 1.27 and named C1.27SHy. It is expected that C1.27SHy thermodynamically controls the aqueous phase composition at this early stage. Indeed, the formation of C1.27SHy is quasi-immediate when C3S is in contact with water inducing a very rapid increase of the specific surface area that remains constant during the induction period. At higher degrees of hydration, the aqueous phase composition departs from the C1.27SHy equilibrium curve. C1.27SHy appears to be a metastable C-S-H that could be related to an intermediate phase previously reported. The quasi-immediate precipitation of C1.27SHy on C3S surface explains why calcium and silicon concentrations remain low during early hydration even though C3S is strongly undersaturated. This also agrees with the control of the end of the induction period by the nucleation and growth of more stable C-S-H.

The disposal of dredged marine sediments has become a major economic and environmental issue in the world. In this study, uncontaminated marine sediments dredged in the harbor of Dunkirk (France) were dried and ground and then used in partial substitution of cement in the manufacture of mortars and concretes. A given volume of cement has been replaced by the same volume of sediment for three substitution contents (10%, 20%, 30%) of a Portland cement CEM I 52.5. The flexural and compressive strengths of mortars decreased when the sediment replacement content increased. However, the mechanical properties of the mortar with 20% replacement of cement with sediments were better than those of a mortar made from cement CEM II/A-LL 32.5 containing a proportion of limestone similar to the sediment substitution. The total porosity measured by mercury intrusion porosimetry of different types of mortars showed that the porosity increased as the sediment substitution content increased but the pore size distribution was shifted toward smaller pores. Finally, it was demonstrated that concrete C30/37 could be designed with 20% cement replaced by sediment without the use of admixture. Additionally, this concrete fulfilled the standards with respect to the total chloride content required for unreinforced concrete. As a conclusion, dried and finely ground uncontaminated sediments appeared to be a very interesting constituent for partially substituting up to 20% of cement as its efficiency overpass limestone filler.

Large quantities of construction and demolition wastes are produced each year. In order to make good use of recycled concrete aggregates (RCA) in concrete, it is very important to study the influence of the granular fraction and the origin of RCA on their properties. In this study, RCA from industrial produced blocks (RCA_Blocks) and slabs (RCA_Slabs) were crushed and then separated into four granular fractions (0/2, 2/6.3, 6.3/14, 14/20 mm). Each granular fraction of RCA was physically characterised. Real RCA from recycling plant were also used for comparison. The results showed that recycled sands offered significantly higher cement paste content (higher bound water content) than coarse recycled aggregates. The fine RCA had therefore a higher water absorption coefficient compared to coarser fractions of RCA. The water absorption of finer fraction of RCA could be extrapolated precisely from the relationship between water absorption and cement paste content (or bound water content) of three coarse fractions of RCA. The values of hardened cement paste content obtained for the RCA_Blocks were lower than those measured on the RCA_Slabs, which was due to a smaller amount of initial cement paste content in blocks. The results showed that RCA_Slabs were more angular than RCA_Blocks.

Large amounts of construction and demolition wastes, especially concrete wastes, are generated annually. Until now, only a small fraction of concrete wastes has been reused as recycled concrete aggregates (RCA) in the manufacture of mortar and concrete. In order to optimise the use of RCA for new concrete, it is important to improve the properties of RCA. RCA are mainly composed of an intimate mix of natural aggregates and adherent hardened cement paste, which has a much larger porosity than natural aggregates. The influence of accelerated carbonation on the properties of RCA was studied in this work. Original concrete was manufactured and crushed by a jaw crusher in the laboratory. The different fractions of laboratory-produced RCA were stored in an accelerated carbonation room. The mass loss, density, porosity and water absorption of the RCA were tested before and after carbonation. Industrial RCA were also studied for comparison with the laboratory-produced RCA. The results clearly showed that, after accelerated carbonation, the density of the RCA increased due to the transformation of portlandite into calcite. The water absorption and porosity of the RCA decreased after carbonation.