Experimental and numerical investigation of the hygrothermal behaviour of various building limestones

International audienceThis study investigates the hygrothermal behaviour of six French limestones commonly used in construction. An extensive experimental program was carried out to characterize their mineralogical, microstructural, thermal, and hydric properties. The results reveal clear relationships between pore structure and hygrothermal performance. The capillary absorption coefficient increases with the volume fraction of pores larger than 2 μm, confirming the key role of pore size in liquid transport. Water vapour permeability decreases exponentially with tortuosity, highlighting the combined effect of pore connectivity and pore size distribution. Thermal conductivity decreases with increasing total porosity following a geometric-mean relationship, as described by the Woodside and Messmer model, while volumetric heat capacity shows a linear correlation with dry apparent density. Despite compositional similarities, significant variability in performance is observed among the stones. Under transient climatic conditions, coupled heat and moisture simulations – based on the Künzel model – closely match experimental temperature measurements and reasonably capture humidity variations. Minor discrepancies are attributed to sorption hysteresis, not accounted for in the modelling. The quantified links between hygrothermal properties and pore structure provide valuable insights for the selection and simulation of natural stone in energy-efficient envelope design

Hydrological regime shifts in Sahelian watersheds: an investigation with a simple dynamical model driven by annual precipitation

International audienceAbstract. The Sahel, the semi-arid fringe south of the Sahara, experienced severe meteorological droughts in the 1970s–1980s. During and after these droughts, watersheds in the Central Sahel have experienced an increase in the annual runoff coefficient (annual runoff normalized by annual precipitation). We hypothesize that these increases correspond to regime shifts. To investigate the timing of these regime shifts, we introduce a lumped model that represents feedbacks between soil, water and vegetation at the watershed scale and the annual time step. This model relies on runoff coefficient as a constraint for the state variable and precipitation as unique external forcing. Four watersheds (Gorouol, Dargol, Nakanbé and Sirba), with pluri-decennial observations (1950s–2010s), are modeled. For each watershed, one million parameterizations of this model are sampled and run, and an ensemble of one thousand best parameterizations is selected based on observed runoff coefficients. Our results show that this model can reproduce the trend of runoff coefficients. For all watersheds, almost all selected parameterizations from the ensemble are bistable. We define two alternative runoff coefficient regimes (a low and a high regime) by splitting with a threshold the bifurcation diagram of bistable parameterizations. Most selected parameterizations undergo regime shifts: simulated runoff coefficients belong to the low regime in 1965 and to the high regime in 2014. Finally, we find that the year of the regime shift, defined as the year when the number of regime shifts is maximized, was 1971, 1972, 1973, 1983 for the Gorouol, Nakanbé, Dargol and Sirba watershed, respectively. These results were obtained with a parsimonious model which deliberately neglects fine-scale processes of Sahelian hydrology. It would therefore be wise to supplement this analysis with other models – with varying levels of complexity – that also allow regime shifting. Overall, this article proposes simple ideas toward improving the modelling and characterization of hydrological regime shifts

Evaluation and modeling of barrier layer efficiency for flame retardant PE-EVA systems containing low-melting phosphate glasses using a double layer setup

International audienceThe improvement of the flame-retardant properties of the outer sheath in optical cables is driven by the increasing packing density of cable architectures, the reduction in polymeric sheath thickness, and the demand for higher fire safety in densely installed environments. In this work, a dedicated methodology was established to evaluate the efficiency of barrier layers in flame-retardant cable sheath compounds. First, cone calorimetry and pyrolysis-combustion flow calorimetry (PCFC) data were combined to characterize the behavior of monolayer systems. These characterizations were then complemented by a bilayer configuration, where two key descriptors were defined: the slowdown factor (Sf) and the time-shift (δ), quantifying the ability of a barrier to attenuate and delay heat and mass transfer. Application of this methodology to polyethylene–ethylene vinyl acetate (PE–EVA) systems incorporating aluminum trihydrate (ATH) and low-melting phosphate glasses (LMGs) highlighted the superior performance of a potassium phosphate glass with a low glass transition temperature (∼165 °C) with Sf2 = 3.8 and δ = 565 s due to the strong expansion of the residue. Depth temperature analyses confirmed that the expanded mineral residue effectively limited heat penetration from the outer to the inner layer. The approach was further extended to ternary formulations, where 10 wt.% vermiculite reinforced the barrier, achieving Sf2 = 5 and δ = 572 s, while other synergists produced less efficient protection. These results demonstrate that the proposed methodology provides a reliable framework to quantify and compare barrier-layer efficiency, offering new insights into the condensed-phase mechanisms governing flame retardancy of cable sheath materials

Estimation of the surface tension and dispersive and polar components of polymers as a function of temperature for composite manufacturing applications

International audienceUnderstanding adhesion between fiber and matrix at elevated temperatures is essential for improving the mechanical performance of polymer-based composites, especially with thermoplastic matrices. However, detailed characterization of polymer surface tension and its polar and dispersive components as a function of temperature remains limited. In this work, reliable methods were set using the Wilhelmy plate and pendant drop approaches to investigate these properties against temperature. First, experimental procedures were developed, optimized, and validated through cross-comparison with reference liquids of known surface tension and components. Accurate and reproducible measurements were secondly achieved across a range of elevated temperatures for liquid polymers (polyethylene glycol, bio-based epoxy) and for molten thermoplastics (polypropylene, polylactic acid). The results reveal a linear decrease in surface tension with increasing temperature and contribute to a better understanding of fiber wetting phenomena. Additionally, a procedure was set to determine polymer dispersive and polar components as a function of temperature. Due to the volatility and thermal limitation of n-hexane used in interfacial tension measurements, alternative probe liquids were systematically evaluated. Silicone and paraffin oil were identified and validated as suitable replacements, enabling reliable measurements with polymers at high temperatures. These key findings demonstrate robust methodology for high-temperature surface characterization and provide essential data to understand fiber–matrix adhesion under realistic processing conditions

Equilibrium partition coefficients of semi-volatile organic compounds (SVOCs) between indoor surfaces and air assessed using two experimental methods

International audienceIndoor exposure to semi-volatile organic compounds (SVOCs) is affected by their sorption onto indoor surfaces such as clothes, toys, building materials and furniture. They are transferred from these contaminated surfaces to the body via various routes such as skin contact, inhalation or hand-to-mouth transfer. Knowledge of their sink surface/air partition coefficients KSurf are needed to apply indoor fate models and assess occupants’ exposure to SVOCs.Partition coefficients of triphenyl phosphate (TPP), 2-ethylhexyl diphenyl phosphate (EHDPP) and 1,2-cyclohexane-dicarboxylic acid, dinonyl ester (DINCH) on cotton, glass and stainless steel (SS) surfaces were experimentally determined using two different methods. In the Micro-Chamber/Thermal Extractor (M-CTE), Kcotton values were close to 104 m. For this method, improvements were proposed to investigate the sorption on surfaces having lower sorption capacities such as glass or SS. In the sandwich-like emission cell, Kglass and KSS values ranged from 20 to 465 m, and from 99 to 1570 m, respectively. In coherence with the literature, sorption on cotton was higher than on SS and glass. Moreover, based on literature data, the SVOC vapor pressure (VP) could be a good predictor of KSurf for non-porous surfaces such as SS and glass. For porous surfaces (cotton), additional parameters related to the surface (porosity or composition) should be used with VP. Strong sorption capacity of cotton reinforces the health risk posed by contaminated clothes. This study highlights the need for further research to understand the key parameters of SVOC sorption on textiles

Evidence of hydrological regime shifts associated with a major decades-long drought in West Africa

International audienceUsing ground-based meteorological, hydrological and land cover datasets from 1950 to 2015, we provide evidence that the increase in runoff observed in the semi-arid central Sahel (West Africa) since the 1970-1995 drought is a shift between alternative stable states of low and high runoff. We propose a conceptual model, governed by feedback loops between vegetation and surface runoff, which describes the stabilising mechanisms of each state and the basin-scale impact of local shifts. While the drought was likely the trigger for the shift, land clearing and rainfall intensification may have reinforced it. Due to wetter conditions and greater resilience, other basins further south did not shift. Our study suggests that the shift towards higher runoff is due to surface processes playing a dominant role in this region, with minimal contribution from subsurface processes. This regime shift framework offers a promising perspective on understanding long-term hydrological chan

Allocation dynamique de ressources : comparaison d'approches de recherche opérationnelle et d'apprentissage par renforcement

National audienceDe nombreux secteurs s'intéressent à la gestion de files d'attente physiques ou digitales. L'optimisation de ces files d'attente est par exemple particulièrement cruciale dans les hôpitaux, où la gestion des services d'urgence est un enjeu majeur. Nous exposons dans cette note le positionnement de nos travaux sur la gestion de files d'attente et l'allocation de ressources. Ceux-ci, résolument appliqués, sont réalisés en collaboration avec la société ESII, qui apporte ses données ainsi que son expertise en matière d'optimisation de files d'attente.Nous nous intéressons spécifiquement au problème d'allocation d'agents physiques à des usagers arrivant dynamiquement et stochastiquement sur un site. Nous nous appuyons pour cela sur des approches d'optimisation issues de la Recherche Opérationnelle (RO) et de l'Intelligence Artificielle (IA). L'objectif est de proposer la meilleure allocation - au sens de la minimisation du temps passé par les usagers dans le système - en un temps de calcul quasi-instantané

Spatiotemporal disruptions of reality perception in depersonalization

International audienceExperiences of time and space are core constituents of the sense of bodily self. Depersonalization (DP) is a condition characterized by distressing feelings of estrangement from the self, body and the external world. While previous studies showed that perception of the space close to the body (i.e., peri-personal space) remains intact in DP, time perception is disrupted. The origin of this asymmetry remains an open question. Addressing this gap, this online study (N = 1338) investigated the relation between DP traits measured by the Cambridge Depersonalization Scale (CDS) and altered subjective experiences of body, time, and space perception. The results demonstrated strong relationships between CDS facets and distorted experiences of time, bodily self and space. When considering the shared variance of CDS facets, different patterns emerge. The Anomalous Body Experiences facet is associated with time slowing down and represented a core aspect of DP contributing to spatiotemporal disruptions. In contrast, the Alienation from Surroundings facet is associated with time speeding up, leading to different patterns of spatiotemporal disruptions. Altogether, these results suggest that distinct DP facets related to body and world perception need to be disentangled to better understand the mechanisms underlying atypical space and time perception in this population

Feu couvant dans les matériaux biosourcés

National audienceDans le contexte actuel de transition environnementale du secteur du bâtiment, les matériaux biosourcés suscitent un intérêt croissant en raison de leur faible impact environnemental, de leur capacité de stockage du carbone et de leurs propriétés d’isolation. Parmi ces matériaux, les isolants biosourcés, tels que les fibres de bois ou les agro-bétons constitués d’un liant minéral associé à des granulats végétaux (paille, chènevotte ou autres fibres organiques), représentent une alternative prometteuse pour le développement de solutions constructives bas carbone.Cependant, l’utilisation de ces matières organiques soulève des interrogations importantes concernant leur comportement au feu, notamment vis-à-vis du développement du feu couvant. Ce mode de combustion, caractérisé par une propagation lente à basse température en l’absence de flamme visible, constitue un risque particulier pour les matériaux contenant de la biomasse. La compréhension de ce phénomène est donc essentielle afin de garantir la sécurité incendie et la durabilité des bâtiments réalisés à partir de matériaux biosourcés.L’étude menée vise à approfondir la compréhension du comportement des matériaux biosourcés vis-à-vis du développement du feu couvant. Plusieurs matériaux ont été investiguées afin d’évaluer leur susceptibilité à ce mode de combustion et d’en analyser les mécanismes de propagation. Les résultats mettent en évidence le rôle prépondérant de deux paramètres : la densité et la composition du matériau. Ces facteurs influencent directement les conditions de transfert thermique et d’apport en oxygène, déterminantes pour l’initiation et la progression du front de combustion. Par ailleurs, les observations expérimentales montrent qu’une production accrue de résidus charbonneux lors de la décomposition thermique favorise la persistance et la propagation du feu couvant, en fournissant un substrat réactif propice à l’oxydation hétérogène.Ces travaux apportent ainsi des éléments de compréhension essentiels des phénomènes mis en jeu dans les matériaux biosourcés soumis à ce type de sollicitation thermique. Ils permettent d’identifier les paramètres clés gouvernant leur sensibilité au feu couvant et constituent une base pour l’optimisation des formulations. À ce titre, ils contribuent à une meilleure prise en compte des enjeux de sécurité incendie dans le développement de matériaux de construction à faible impact environnemental, en conciliant performances d’usage et exigences réglementaires

A Round-Robin Study on Decomposition of Calcium Oxalate Monohydrate by Thermogravimetry

International audienceA round-robin study for thermogravimetric analysis (TGA) of carbon oxalate monohydrate was organised with thirteen participants. The main objectives were to provide best practice in the use of TGA and guidelines on uncertainties in the context of pyrolysis and fire modelling. The material studied, calcium oxalate monohydrate, is often used to evaluate the proper functioning of a given piece of equipment because its decomposition steps are well documented and known to be repeatable and reproducible. The experimental procedure was described in as much detail as possible, bearing in mind that it cannot be fully prescribed due to the different technologies of thermogravimetric analysers. All thermograms were evaluated for mass losses and onset, peak and end-set temperatures for the three decomposition steps using two outlier detection methods, the Grubbs method and an alternative two-step method inspired from Z-score technique, allowing an assessment of measurement deviation calculated throughout the duration of the experiment. This study allows a benchmarking of data scatter due to instrument and operator. It confirms that verification with calcium oxalate is a good screening method that can be used by laboratories. Within a laboratory, it can also help to identify problems with instrument accuracy that would otherwise be difficult to detect. This, together with the good practice outlined in the paper, should help the community to increase the validity of tests on other materials of interest to fire science