Développement de nouveaux bétons ''accumulateurs d'énergie'' : investigations expérimentale, probabiliste et numérique du comportement thermique

The thermal policies have been kept to fit the new economic in a global context particularly in terms of buildings energy efficiency. To meet these challenges, different technologies have been used such as the Phase Change Materials (PCMs) which have the ability to store and release energy. PCMs are generally used with conventional building materials in order to improve their thermal inertia and provide better comfort to users. To enhance the properties of the final composite, the PCMs thermo-physical properties must be sufficiently controlled. In this context, this thesis is a contribution aimed to develop specific methodologies for better characterization of PCM and PCM-concrete. Different experimental approaches will be presented for the identification of PCMs thermophysical properties and to identify the effect of the incorporation and the damage of these materials on the thermal and mechanical properties of concrete. A multiscale modelling considering the average of experimental thermal properties was applied to predict the thermal behaviour of PCMs-concrete. A probabilistic study of experimental uncertainties will be also conducted to assess the level of confidence of the impact of PCM on the thermodynamic properties of PCM-concrete. A numerical study was conducted using experimental data to study the heat transfer through a PCM-concrete wallA l'heure actuelle, les nouvelles contraintes de la réglementation thermique en vigueur ne cessent de s'adapter au contexte économique global pour lequel la recherche d'une efficacité énergétique dans le bâtiment est devenue incontournable. Pour répondre à ces défis, des Matériaux intelligents à Changement de Phase (MCP) ont fait leur apparition sur le marché de la construction. Grâce à leur capacité de stockage de l'énergie, les MCP sont de plus en plus associés aux matériaux de construction classiques (béton, plâtre, etc.) afin d'améliorer leur inertie thermique et apporter un meilleur confort aux usagers. Pour ce faire, les propriétés thermophysiques intrinsèques aux MCP doivent être suffisamment maitrisées afin de pouvoir contrôler les propriétés du produit composite final. Dans ce contexte, cette thèse est une contribution ayant pour objectif de développer des méthodologies spécifiques pour une meilleure caractérisation des MCP et des béton-MCP. Une panoplie d'approches expérimentales a été présentée pour l'identification des propriétés thermophysiques des MCP et pour identifier l'effet d'incorporation et de l'endommagement de ces matériaux sur les propriétés thermiques et mécaniques de béton. Plusieurs modèles d'homogénéisation ont été utilisés afin de prédire le comportement thermique des bétons-MCP en utilisant les propriétés thermiques moyennées obtenues expérimentalement. Une étude probabiliste paramétrique a été menée afin de prendre en compte les incertitudes liées à la dispersion aléatoire des mesures expérimentales de propriétés thermiques du béton-MCP. Les résultats issus des essais expérimentaux ont été intégrés dans le cadre d'une étude numérique par la Méthode des Volumes finis (MVF) afin d'étudier le mécanisme de transfert de chaleur à travers une paroi en béton-MC

A review of microencapsulated and composite phase change materials: Alteration of strength and thermal properties of cement-based materials

Due to the population growth and the increased reliance on cooling and heating systems, buildings have become the largest energy consumer worldwide. The use of phase change material (PCM) has shown great potential to reduce the annual cooling and heating load by up to 50%. Nowadays, the direct incorporation of PCM in cement-based materials (CBM) is creating a considerable debate in the research community with regards to the proper selection and the beneficial utilization of PCM (microencapsulated or composite) in CBM. Therefore, this paper reviews the pros and cons of using microencapsulated and composite PCM in CBM by highlighting the mechanisms involved in the mechanical strength loss and thermal properties enhancement. Generally, a high thermal energy storage CBM was obtained. However, PCM exhibited a negative effect on the compressive strength of CBM. In view of the literature review, the compressive strength reduction varies considerably with no clear trend which is understandable in view of the differences in mix designs as well as the variety of materials used in each study. Finally, an up-to-date PCM case studies, gaps and future directions are also presented to provide a reliable basis and helpful reference for the future development of eco-friendly and energy-efficient building materials containing PCM

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

development of new concrete ''energy accumulator'' : experimental, probabilistic and numerical study of its thermal behavior

A l'heure actuelle, les nouvelles contraintes de la réglementation thermique en vigueur ne cessent de s'adapter au contexte économique global pour lequel la recherche d'une efficacité énergétique dans le bâtiment est devenue incontournable. Pour répondre à ces défis, des Matériaux intelligents à Changement de Phase (MCP) ont fait leur apparition sur le marché de la construction. Grâce à leur capacité de stockage de l'énergie, les MCP sont de plus en plus associés aux matériaux de construction classiques (béton, plâtre, etc.) afin d'améliorer leur inertie thermique et apporter un meilleur confort aux usagers. Pour ce faire, les propriétés thermophysiques intrinsèques aux MCP doivent être suffisamment maitrisées afin de pouvoir contrôler les propriétés du produit composite final. Dans ce contexte, cette thèse est une contribution ayant pour objectif de développer des méthodologies spécifiques pour une meilleure caractérisation des MCP et des béton-MCP. Une panoplie d'approches expérimentales a été présentée pour l'identification des propriétés thermophysiques des MCP et pour identifier l'effet d'incorporation et de l'endommagement de ces matériaux sur les propriétés thermiques et mécaniques de béton. Plusieurs modèles d'homogénéisation ont été utilisés afin de prédire le comportement thermique des bétons-MCP en utilisant les propriétés thermiques moyennées obtenues expérimentalement. Une étude probabiliste paramétrique a été menée afin de prendre en compte les incertitudes liées à la dispersion aléatoire des mesures expérimentales de propriétés thermiques du béton-MCP. Les résultats issus des essais expérimentaux ont été intégrés dans le cadre d'une étude numérique par la Méthode des Volumes finis (MVF) afin d'étudier le mécanisme de transfert de chaleur à travers une paroi en béton-MCPThe thermal policies have been kept to fit the new economic in a global context particularly in terms of buildings energy efficiency. To meet these challenges, different technologies have been used such as the Phase Change Materials (PCMs) which have the ability to store and release energy. PCMs are generally used with conventional building materials in order to improve their thermal inertia and provide better comfort to users. To enhance the properties of the final composite, the PCMs thermo-physical properties must be sufficiently controlled. In this context, this thesis is a contribution aimed to develop specific methodologies for better characterization of PCM and PCM-concrete. Different experimental approaches will be presented for the identification of PCMs thermophysical properties and to identify the effect of the incorporation and the damage of these materials on the thermal and mechanical properties of concrete. A multiscale modelling considering the average of experimental thermal properties was applied to predict the thermal behaviour of PCMs-concrete. A probabilistic study of experimental uncertainties will be also conducted to assess the level of confidence of the impact of PCM on the thermodynamic properties of PCM-concrete. A numerical study was conducted using experimental data to study the heat transfer through a PCM-concrete wal

Development of leak-free phase change material aggregates

This study aims to develop leak-free phase change material (PCM)-aggregates through a two-step pelletization process. Microencapsulated PCM (mPCM) was incorporated into the core of the aggregate during the granulation process and then coated with a PCM-free shell to overcome the PCM leakage. The thermal properties of pellets cured under CO2 and natural air, including their enthalpy and thermal conductivity as well as their thermal stability were measured and compared using differential scanning calorimeter, thermogravimetric analyses and transient plane source method. The effect of both mPCM content and CO2 curing on the strength of the aggregates was also analyzed. The results revealed that mPCM can be used to produce lightweight aggregates with a distinct core-shell structure having an oven-dry bulk density, water absorption and latent heat of about 788 kg/m3, 14% and 18 kJ/kg, respectively. In addition, the shell layer can effectively prevent the leakage of the PCM and can be further densified by CO2 curing. In addition, CO2 curing contributed to the improvement of the overall physical properties and early strength development of the aggregates. The developed leak-free PCM-aggregates would then allow adding PCM into the concrete mix as an inert material and hence suppress the degradation of mechanical strength and high-water demand caused by the direct use of mPCM in concrete. © 2019 Elsevier Lt

Effect of Phase Change Materials (PCMs) on the hydration reaction and kinetic of PCM-mortars

International audienceThe Phase Change Materials (PCMs) are considered as an attractive way to reduce energy consumption thanks to their heat storage capacity. Their incorporation in the construction materials (gypsum, concrete) contribute to the reduction of the energy consumption of the building structures.Even though PCMs have shown their reliability from a thermal point of view, some drawbacks linked to their use were emphasized such as the loss of the compressive strength of the cementitious material with the addition of PCMs.This paper attempts to provide a possible explanation by the investigation of the hydration kinetic of PCM-mortars. The conventional semi-adiabatic Langavant test was adapted for this purpose. The results showed a lower heat released by the PCM-mortars compared to a control mortar as well as a delay in the hydration process with the addition of PCMs which may contribute to the loss of the compressive strength

Effect of Phase Change Materials on the hydration reaction and kinetic of PCM-mortars

International audienceThe Phase Change Materials are considered an attractive way to reduce energy consumption thanks to their heat storage capacity. Their incorporation in the construction materials allows the energy to be an integral part of the building structure. Even though PCMs have shown their reliability from a thermal point of view, some drawbacks linked to their use were emphasized such as the loss of the compressive strength of the PCM-material. This paper attempts to provide an explanation by the investigation of the hydration kinetic of PCM-mortars. The semi-adiabatic Langavant test was adapted to this case. The numerical Diffuse Element Method was used for the computation of the heat flux which is a compulsory step for the determination of the hydration degree. The results showed a lower heat released by the PCM mortars compared to a control mortar as well as a delay in the hydration progress with the addition of PCMs

Investigation expérimentale et modélisation multi-échelle des propriétés thermiques des bétons incorporant des Matériaux à Changement de Phase (MCPs)

National audienceRÉSUMÉ. L'utilisation des matériaux à changement de phase (MCP) dans le domaine des bâtiments est une solution attractive contribuant à la réduction de la consommation d'énergie ainsi qu'à l'amélioration du confort thermique. Ce travail est consacré à l'étude des propriétés thermiques des MCP et des bétons modifiés (chaleur spécifique, conductivité thermique). Des techniques expérimentales ont été mises en jeu telles que la calorimétrie différentielle à balayage (DSC), le Hot Disk et le laser flash. Une modélisation micro-macro est aussi présentée afin de prédire la conductivité thermique des bétons-MCP en se basant sur quelques schémas d'homogénéisation classiques. ABSTRACT. The use of Phase Change Materials (PCMs) in the building sector is an attractive solution contributing to the reduction of energy consumption as well as the improvement of the thermal comfort. This research is devoted to the study of thermal properties of PCMs and modified concrete (specific heat, thermal conductivity). Experimental techniques were used such as the Differential Scanning Calorimetry (DSC), the Hot Dish and the Laser Flash. Also, a micro-macro modelling is presented in order to predict the thermal conductivity of PCM-concrete using some classic homogenization schemes

Experimental and multi-scale analysis of the thermal properties of Portland cement concretes embedded vith microencapsulated Phase Change Materials (PCMs)

International audienceThe present research deals with the investigation of a Portland cement concrete modified with organic microencapsulated Phase Change Materials (PCMs) named Micronal DS 5001 X, using experimental and homogenization approaches. First, a laboratory characterization of the PCM smart materials was performed using different experimental techniques. Second, different PCM-concrete mixtures were manufactured with different amounts of PCM. The specific heat capacity of PCM-concrete was analyzed by differential scanning calorimetry technique whereas the thermal conductivity was measured by hot disk. In addition, PCM-concrete mixes were subjected to artificial ageing then their thermal properties were analyzed. Besides, a homogenization approach was carried in order to predict the thermal conductivity of the PCM-concrete mixes. The results highlighted an improvement of the heat storage capacity of the PCM-concrete with the addition of PCMs. Moreover, a good correlation was noticed between the experience and the homogenization method for the thermal conductivity prediction