Development and evaluation of methods to follow microstructural development of cementitious systems including slags

Production of cementitious materials causes the emission of CO2 gas, which has detrimental impact on the environment augmenting the global warming process. Using by-products such as slags is a possible strategy to limit the environmental impact of cementitious materials. Consequently, there is an increasing use of supplementary cementitious materials (SCMs), either pre-blended with ground clinker or added during fabrication of concrete. However, it is well known that these SCMs generally react slower than cement clinker so the levels of substitution are limited. However, substitution by SCMs should not compromise the development of mechanical properties especially at early ages. In order to better understand the factors affecting the degree of reaction of SCMs it is essential to have an accurate method to evaluate the actual rate of reaction of these materials independent from the degree of reaction of the clinker component. To this end, the contribution of slag in blended cements can be monitored and characterised as a function of time. In this thesis, methods of characterisation of anhydrous materials were initially improved and provided the starting point for the study of hydrated systems. Secondly, the effect of slag on clinker phases was identified. It was found that slag does not significantly affect the overall hydration of aluminate phase. Although, the slag favoured the hydration of the ferrite phases and significantly retarded the hydration of belite and, consequently, the degree of reaction of cement. It was also observed that the slag modified the composition of hydrates. Analyses of hydrated cements with and without slag have shown two major effects: a) no significant decrease in calcium hydroxide content (normalized to cement content) in blended systems, b) higher substitution of Al for Si and lower C/S ratio in outer C-S-H in blended systems. To measure the reactivity of slag in blended pastes at later ages, five methods were studied. As selective dissolution and differential scanning calorimetry have shown to be unreliable, even if SEM-IA-mapping is time consuming, it appeared to be the only accurate method to quantify the degree of reaction of slag. The computation of difference in cumulative calorimetry and chemical shrinkage curves of slag and its comparison to inert filler allowed the reaction of the slag to be isolated. Calibration of these techniques using the SEM-IA-mapping results proved to be a promising method to understand and quantify the reactivity of slag. Using the overall degree of reaction, it was established that increasing reaction in the slag corresponds to an increasing strength in blended mortars. Comparing the strength with calculated total porosity, it was concluded that the contribution of the slag seemed to be more than just filling the microstructural space by producing hydration products. Slag was observed to also enhance the strength by its interaction with other phases. The study will focus on differentiating the two effects to elicit the influence of slag on development of strength

Influence of limestone on the hydration of ternary slag cement

The hydration kinetics, microstructure and pore solution composition of ternary slag-limestone cements have been investigated. Commercial CEM I 52.5 R was blended with slag and limestone; maintaining a clinker to SCM ratio of 50:50 with up to 20% slag replaced by limestone. The sulphate content was maintained at 3% in all composite systems. Hydration was followed by a combination of isothermal calorimetry, chemical shrinkage, scanning electron microscopy, and thermogravimetric analysis. The hydration of slag was followed by the implementation of QXRD/PONKCS method. The accuracy of the calibrated PONKCS phase was assessed on slag and corundum mixes of varying ratios, at different w/s ratios. Thus, the method was used to analyse hydrated cements without dehydrating the specimens. The results show that the presence of limestone enhanced both clinker and slag hydration. The pore volume and pore solution chemistry were further examined to clarify to the synergistic effects. The nucleation effects account for enhanced clinker hydration while the space available for hydrate growth plus lowering of the aluminium concentration in the pore solution led to the improved slag hydration

Reactivity tests for supplementary cementitious materials: RILEM TC 267-TRM phase 1

A primary aim of RILEM TC 267-TRM: “Tests for Reactivity of Supplementary Cementitious Materials (SCMs)” is to compare and evaluate the performance of conventional and novel SCM reactivity test methods across a wide range of SCMs. To this purpose, a round robin campaign was organized to investigate 10 different tests for reactivity and 11 SCMs covering the main classes of materials in use, such as granulated blast furnace slag, fly ash, natural pozzolan and calcined clays. The methods were evaluated based on the correlation to the 28 days relative compressive strength of standard mortar bars containing 30% of SCM as cement replacement and the interlaboratory reproducibility of the test results. It was found that only a few test methods showed acceptable correlation to the 28 days relative strength over the whole range of SCMs. The methods that showed the best reproducibility and gave good correlations used the R3 model system of the SCM and Ca(OH)2, supplemented with alkali sulfate/carbonate. The use of this simplified model system isolates the reaction of the SCM and the reactivity can be easily quantified from the heat release or bound water content. Later age (90 days) strength results also correlated well with the results of the IS 1727 (Indian standard) reactivity test, an accelerated strength test using an SCM/Ca(OH)2-based model system. The current standardized tests did not show acceptable correlations across all SCMs, although they performed better when latently hydraulic materials (blast furnace slag) were excluded. However, the Frattini test, Chapelle and modified Chapelle test showed poor interlaboratory reproducibility, demonstrating experimental difficulties. The TC 267-TRM will pursue the development of test protocols based on the R3 model systems. Acceleration and improvement of the reproducibility of the IS 1727 test will be attempted as well

Tissue engineering for cornea reconstruction

En France, les dysfonctions endothéliales représentent environ la moitié des indications de greffes de cornée réalisées chaque année. Cependant, les problématiques liées à la pénurie de greffon, aux difficultés des techniques chirurgicales de greffes endothéliales ainsi qu’aux risques d’échec ou de rejet de greffe poussent les chercheurs à développer de nouvelles thérapies moins invasives et plus efficaces. La thérapie cellulaire cornéenne endothéliale est une des voies de recherche actuellement explorées dont le but est de s’affranchir des aléas de la greffe de cornée. La cornée humaine est un tissu idéal pour la thérapie cellulaire. Grâce à ses caractéristiques d’organe à la fois avasculaire et immunitairement privilégié, les cellules transplantées sont ainsi bien mieux tolérées par rapport aux autres tissus et organes vascularisés. Les avancées dans le domaine des cellules souches, de l'ingénierie, particulièrement avec l’arrivée des greffes de cellules souches épithéliales pour le traitement des pathologies sévères de la surface oculaire, ont suscité un intérêt massif afin d’adapter ces techniques aux cellules endothélialesIn France, around half of all corneal keratoplasties are performed to treat corneal endothelial dysfunction each year. However, the use of endothelial keratoplasty is limited by the technical difficulty of the procedure, a shortage of available grafts, and the potential for graft failure or rejection. These limitations are driving researchers to develop new, less invasive, and more effective therapies. Corneal endothelial cell therapy is being explored as a potential therapeutic measure, to avoid the uncertainty associated with grafting. The human cornea is an ideal tissue for cell therapy as owing to its avascular characteristics, transplanted cells are better tolerated compared with other vascularized tissues and organs. Advances in the field of stem-cell engineering, particularly the development of corneal epithelial stem cell therapy for the treatment of severe diseases of the ocular surface, have aroused a massive interest in adapting cell-therapy techniques to corneal endothelial cell