Characterization of supplementary cementitious materials by thermal analysis

Working Group 1 of RILEM TC 238-SCM ‘Hydration and microstructure of concrete with supplementary cementitious materials (SCMs)’ is defining best practices for the physical and chemical characterization of SCMs, and this paper focusses on their thermal analysis. Thermogravimetric analysis (TGA) can provide valuable data on the chemical and mineralogical composition of SCMs. Loss-on-ignition (LOI) testing is a commonly used, standardized, but less sophisticated version of TGA that measures mass at endpoints only, with heating generally in air. In this paper we describe the use of TGA and LOI to characterize Portland cement with limestone additions, coal combustion fly ashes, ground-granulated blast furnace slag, calcined clays, and natural pozzolans. This paper outlines the value and limitations of TGA and LOI (in the formats defined in different standards regimes) for material characterization, and describes testing methods and analysis. TGA testing parameters affect the mass loss recorded at temperatures relevant for LOI measurements (700–1000 °C) of slags and fly ashes, mainly associated with oxidation reactions taking place upon heating. TGA of clays and natural pozzolans is utilized to identify optimal calcination conditions leading to dehydroxylation and consequent structural amorphization, particularly for kaolinite. However, dehydroxylation and amorphization do not occur at similar temperatures for all clays, limiting the applicability of TGA for this purpose. Although TGA is widely utilized for characterization of SCMs, the testing parameters significantly affect the results obtained, and TGA results require careful interpretation. Therefore, standardization of TGA testing conditions, particularly for LOI determination of slags and fly ashes, is required

EMR modelling of a hydrogen-based electrical energy storage

This paper deals with multi-physics modelling of the stationary system. This modelling is the first step to reach the fuel cell system dimensioning aim pursued. Besides this modelling approach based on the stationary energetic system, the novelty in this paper is both the new approach of the photovoltaic EMR modelling and the EMR of the hydrogen storage process. The granular modelling approach is used to model each component of the system. Considering a stand alone PEM fuel cell system, hydrogen is expected to be produced and stored on the spot from renewable energy (photovoltaic) in order to satisfy the fuel availability. In fact, to develop a generic and modular model, energetic macroscopic representation (EMR) is used as graphical modelling tool. Allowing to be easily grasped by the experts even not necessarily gotten used to the modelling formalism, EMR is helpful to model the multi-domains energetic chain. The solar energy through solar module is converted in electrical energy; part of this energy is transformed in chemical energy (hydrogen) thanks to an electrolyser. Then the hydrogen is compressed into a tank across a storage system. The latter part of the solar module energy is stored as electrical energy within supercapacitor or lead-acid battery. Using the modularity feature of the EMR, the whole system is modelled entity by entity; afterwards by putting them together the overall system has been reconstructed. According to the scale effect of the system entities, some simulation and/or experimental results are given. Given to the different aims which are pursued in the sustainable energy framework like prediction, control and optimisation, EMR modelling approach is a reliable option for the energy management in real time of energetic system in macroscopic point of view

Experimental Test Plan and Data Analysis Based on the Design of Experiment Methodology

The development of fault diagnostics for fuel cell (FC) stacks and systems can increase their lifetime and therefore their overall efficiency. The development of such techniques often requires a reliable computational FC stack or system model. Given the complexity of such systems, endless time and effort has to be used to test the systems and identify the related models unless an adequate trade-off between available time and desired model accuracy is found. The Design of Experiment (DoE) methodology enables determining the best compromise between the number of experiments to conduct and the obtained information. In this work, the DoE approach is used to define a test plan that is carried out on a solid oxide fuel cell stack. The methodology is then further exploited to analyse the measured data and to determine the influence of the selected parameters (i.e. input variables) on the response extracted from the monitored variables. Specifically, a Full Factorial DoE analysis is performed and the relative results are compared. The results show which parameters have a direct effect and which affect indirectly, in coupling with other parameters, on the system response.</jats:p

Tunnel du Fréjus : les mesures géotechniques effectuées sur le chantier français et leur application pour la détermination et l'adaptation du soutènement provisoire

Le tunnel routier du Fréjus, long d'un peu plus de 13 km, relie la France à l'Italie de Modane à Bardonnèche en traversant sur la majeure partie de son tracé la nappe des schistes lustrés.A l'occasion du creusement de ce tunnel dans sa partie française, une importante campagne de mesures géotechniques a été réalisée sur les schistes lustrés et on en trouvera ici la synthèse. L'aspect le plus original de cette campagne est la prépondérance des mesures in situ et leur utilisation pour la conduite du chantier.L’implantation systématique à intervalles réguliers (tous les 30 m environ) de sections de mesure de convergence complétée par quelques sections de mesure d'expansion et des observations endoscopiques a permis de connaître précisément à tout moment la nature et l'ampleur des mouvements du terrain au voisinage de l'excavation.L'évolution logarithmique des convergences en fonction du temps a été mise en évidence, elle a permis de prévoir quantitativement l'évolution de chaque section dès les premières mesures et, si nécessaire, de modifier en conséquence les caractéristiques du soutènement provisoire : on indique les règles utilisées à cette fin qui ont donné satisfaction