The fire spalling of concrete is a complex phenomenon, which can affect the integrity of the structures during a fire. This thermal instability is associated with a complex coupled ...chemo-thermo-hydro-mechanical mechanism and it can be influenced by many factors, related to material (e.g. per- meability, porosity and water content), geometry (e.g. shape and size) and environmental parameters (e.g. mechanical load and heating rate). Concrete made with recycled concrete aggregates presents higher porosity, higher water content and different interfaces between aggregates and mortar. All these aspects can lead to a different behaviour under fire exposure, including the spalling risk of these sustainable concretes. The main objective of this paper is to analyse the influence of the use of recycled concrete aggregates on the spalling risk of concrete. In this paper, concrete prisms with different replacement rates of recycled coarse aggregates (0 up to 100%) were exposed to a standard fire curve (ISO 834-1) with a constant uniaxial compression load. After heating, samples surfaces were evaluated by means of digital photogrammetry. Results showed that concrete with RCA is sensitive to explosive spalling. All replacement rates presented higher degree of spalling than concrete made with natural aggregates.
Experiments in which heated nitrogen/steam mixtures are passed through model cracks in concrete with thermocouples embedded along the inner surfaces of the cracks provide insights about the ...thermodynamic processes occurring within them. The thermal behaviour that is observed results from several interlinked processes that influence one another and the resulting transfer of nitrogen, steam, water and heat. By correlating the temperatures measured at different times and positions within cracks with different separations, one can observe how the flow is modified by the formation of condensation. When pure nitrogen is passed through the cracks, only a small amount of water evaporates from the concrete and partial obstruction of the cracks by condensed water only occurs in the cracks with small separations (∼30 µm). As the proportion of steam in the mixture is increased, the thermal fluctuations caused by the formation of condensation become more important and evolve over time as the concrete is heated.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Nous proposons d’apporter une contribution à la question de la place des émotions dans l’enseignement des textes littéraires. La méthode construite combine la sélection d’épisodes significatifs et le ...croisement de différentes traces, internes et externes aux séances de classe, pour comprendre le fonctionnement du système de relations ternaires enseignant/élèves/savoir. Les résultats montrent que l’émotion est utilisée pour interpréter le texte. L’enseignement de la lecture littéraire consiste à faire du sujet lecteur un sujet sensible. Exploiter les émotions en classe est certainement un chemin qui permet le passage de la lecture individuelle à la lecture collective.
The current paper aims to provide a critical review of the fire-induced spalling of concrete structures, its socio-economic and environmental impacts, and to establish a roadmap towards designing ...spalling-sustainable concrete structures utilizing synthetic and natural fibers. Spalling-induced damages of concrete structures during a fire are a serious threat to the fire performance of these structures. Such damages not only reduce the load-bearing capability of concrete members and deteriorate their mechanical properties but also could lead to the collapse of the entire structure. These damages are also a significant source of errors in fire-safety designs of structures if ignored. Among a handful of preventative measures to decrease the magnitude of spalling, the application of fibers is the most efficient alternative. Nevertheless, an in-depth understanding of the mechanism by which synthetic and natural fibers protect concrete members against spalling during a fire, influential parameters on their performance, and introducing new types of fibers with superior efficiency to combat fire-induced spalling still require further research.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
6.
Experimental analysis of concrete spalling due to fire exposure Mindeguia, Jean-Christophe; Pimienta, Pierre; Carré, Hélène ...
European journal of environmental and civil engineering,
06/2013, Volume:
17, Issue:
6
Journal Article, Conference Proceeding
Peer reviewed
Concrete thermal instability is observed when a concrete structure is totally, or partially, exposed to an accidental fire. This sudden phenomenon, which can appear in the first twenty minutes of a ...fire, is called "concrete spalling". Spalling can seriously jeopardise the stability of a concrete structure during a fire (loss of load-bearing cross section, exposure of the reinforcement to fire) as well as after a fire (decrease in the residual mechanical properties and weaker durability). Moreover, the costs of repairing the damages induced by spalling can be very high. Since the early 1980s, many studies (mainly theoretical) have tried to find the most probable causes for concrete spalling. However, we still do not exactly know the mechanisms of spalling, and this phenomenon still cannot be evaluated by calculations. We present in this paper the results from an experimental research dealing with the behaviour of concrete at high temperatures. The comparison of experimental results, from material characterisation at high temperature to fire tests on medium-sized concrete slabs, allows us to discuss the influence of different parameters of spalling risk. Some important conclusions are drawn on the most probable causes for spalling of concrete when exposed to fire. In particular, we show that pore gas pressure cannot be the only physical origin for concrete spalling.
Full text
Available for:
BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
The behaviour of concrete made with recycled concrete aggregates (RCA) at room temperature is well-studied. However, some points still need to be addressed, especially in extreme conditions such as ...durability and high temperature. This paper evaluates the effect of elevated temperatures on the durability of concrete made with RCA. Three concrete mixes were studied: concrete with NA (reference), 100% direct replacement (DR) mix (RCA-100-DR) and 100% strength-based replacement (SBR) mix (RCA-100-SBR). The latter was designed to achieve the same performance as concrete made with NA. Mixes were exposed to temperatures of 200∘C, 400∘C and 600∘C. After cooling, durability-loss due to thermal exposure was evaluated through water porosity, capillary water absorption, permeability, chloride diffusion and accelerated carbonation tests. At room temperature, the direct addition of RCA decreased all durability parameters. The SBR mix recovered some of the durability properties. Exposure to high temperatures decreases all the properties, but it varies depending on the property. The concrete made with NA and the SBR mix showed similar performance. The durability was also evaluated using a performance-based approach, both at room and high-temperature. The proposed approaches showed potential to evaluate durability indicators, but they should be considered with precaution. Overall, concrete made with RCA reduces the durability of concrete, with or without heat damage, but this decrease can be reduced with proper mix optimization. These evaluations contribute to the post-heating durability of concrete structures made with RCA, which is fundamental to the post-fire assessment of concrete structures.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•Mechanical properties of 11 self-compacting concretes studied up to 600°C.•Evolution of fc and E as a function of paste volume and water/binder ratio.•Modified and extended Eurocode 2 law proposed ...for E(fc).•Thermal strain, compressive strength and modulus of elasticity up to 600°C.
The composition of Self-compacting concretes (SCCs) differs significantly from that of vibrated concretes (VCs). In particular, SCCs generally contain higher paste volumes, larger contents of mineral admixtures and often lower binder to water ratios than VCs. These specific composition parameters allow fulfilling the hard-to-please fresh state requirements of SCCs. However they could also modify significantly their mechanical behavior when concrete is submitted to high temperatures. The main objective of this paper is to study the mechanical behavior of SCCs at room and high temperature. Compressive strength, modulus of elasticity and free thermal strain of 11 self-compacting concretes (SCCs) have been studied at room and high temperature (up to 600°C). Two series of SCCs are studied: a series in which the mixture proportions of a given concrete are changed in order to vary independently the water/binder ratio and the paste volume and a series with compositions similar to those employed in the precast industry. The variations of compressive strength and modulus of elasticity as a function of the two composition parameters studied are in good agreement with those obtained in the literature for vibrated and self compacting concretes. A relation is given to link the modulus of elasticity of SCC to its compressive strength, which is close to that proposed by ACI 363-2010. The free thermal strain of SCCs is then studied as a function of temperature. Below 300°C, the free thermal strain of SCCs is larger than that proposed by Eurocode 2 rules for vibrated concrete. Above 300°C, free thermal strain of SCCs lies between the values proposed by Eurocode 2 for siliceous and calcareous aggregates. The relative compressive strength determined at elevated temperature is generally lower than that proposed by Eurocode 2 for traditional vibrated concrete. The comparison of our results with those determined on several vibrated concretes shows that the obtained relative modulus of elasticity is in the same range. The influence of water to binder ratio and paste volume on these results is discussed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The current paper aims to provide a critical review of the fire-induced spalling of concrete structures, its socio-economic and environmental impacts, and to establish a roadmap towards designing ...spalling-sustainable concrete structures utilizing synthetic and natural fibers. Spalling-induced damages of concrete structures during a fire are a serious threat to the fire performance of these structures. Such damages not only reduce the load-bearing capability of concrete members and deteriorate their mechanical properties but also could lead to the collapse of the entire structure. These damages are also a significant source of errors in fire-safety designs of structures if ignored. Among a handful of preventative measures to decrease the magnitude of spalling, the application of fibers is the most efficient alternative. Nevertheless, an in-depth understanding of the mechanism by which synthetic and natural fibers protect concrete members against spalling during a fire, influential parameters on their performance, and introducing new types of fibers with superior efficiency to combat fire-induced spalling still require further research.
•Critical review of socio-economic impacts of fire-induced spalling of concrete.•Critical review of environmental footprints of fire-induced spalling of concrete.•Review of synthetic and natural fibers to tackle fire-induced spalling in concrete.•Establishing roadmap towards designing spalling-sustainable concrete structures.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Permeability is investigated on unloaded or preloaded during the heating process.•Axial permeability of concrete decreases with increasing radial confining pressure.•Axial permeability increases ...with increasing preheating under uniaxial loading.•Radial permeability of concrete decreases with increasing uniaxial compressive loading.•Permeability strongly depends on crack width and orientation, both influenced by axial compression or radial confinement.
Concrete permeability is related to pore connectivity and measures the flow rate of gases and liquids through the concrete under a pressure gradient. Information about concrete permeability - both in ordinary environmental conditions and after the exposure to high temperature - is, therefore, badly needed to better understand fluid transport in concrete, with specific reference to high temperature. In fact, permeability influences concrete spalling in fire by favoring pore-pressure build-ups during the heating process. In this research project, two different procedures are adopted to carry out permeability tests on concrete specimens either unloaded or preloaded during the heating process. The results show that concrete permeability strongly depends on crack width and orientation, both are affected by the axial compression or radial confinement.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
