•Fire spalling and pore pressure of concrete were investigated under different levels of biaxial compressive stress.•The specimens are more prone to spalling when externally loaded than the unloaded ...specimens.•Fire spalling of concrete occurs due to thermal stress and external biaxial compressive stress, and tensile stresses derived from the vapor pore pressure.•Pore pressure tends to increase with external biaxial compressive stress.•Fire spalling tests should be carried out in loaded conditions.
Explosive spalling of concrete exposed to fire consists in the expulsion of shards from the heated face during rapid heating. The phenomenon can seriously jeopardize the integrity of reinforced concrete structures due to the reduction of the cross-sectional area of the structural elements and even lead to the direct exposure of reinforcing bars to flames. The literature shows that various parameters influence the occurrence of fire spalling, such as heating rate, specimen geometry and boundary conditions, concrete grade, and external loads. In this regard, the present study aims at highlighting the role of external loading in combination with the effects of pore pressure and thermo-mechanical stresses in triggering spalling in normal-strength concrete (fc28days ≈ 45 MPa). Unreinforced concrete slabs (size: 800 × 800 × 100 mm3) were subjected to a standard (ISO 834–1) fire curve under seven different levels of external membrane biaxial compressive load. The experimental results clearly show that compressive loading significantly increases spalling propensity and severity.
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.
This article presents a work on optimization of choice of polypropylene fiber dosage and geometry to ensure thermal stability of high performance concrete subjected to fire. Three cementitious ...materials with different granular skeletons containing polypropylene fibers are studied. Experimental campaign of fire tests is conducted on uniaxially compressed concrete prisms via mobile gas furnace. Then, thermo-mechanical simulations are accomplished to validate experimental findings. Results show that an optimal PP fiber length should be selected in accordance with aggregate size. PP fiber diameter has shown to have no significant influence on spalling prevention.
Dynamic excitation of reservoir systems trapping hydrocar- bons is a potentially promising solution for increasing the production. At the laboratory scale, it was found that a vibration of the fluid ...pressure could induce an increase in permeability of fractures. We developed in a previous study experiments aimed at reproducing clogging in propped fractures and unclogging due to dynamic loads applied perpendicularly to the fracture Fawaz et al., 2021. This paper built on this experimental set-up and presents first a study of the major parameters governing the unclogging of propped fractures by dynamic stimulation. The influences of the quantity of fine particles clogging the fracture, amplitude and fre- quency of the signal are investigated at constant proppant density. Then, a prototype computational model based on coupled DEM and finite vol- ume method is developed. An original formulation of the evolution of apparent permeability of the fracture due to the presence and motion of solid particles in each finite volume cell is presented. Computations are consistent with experiments, although axial fluid flow is modelled instead of radial flow in the experiments. Results show that the increase of fracture conductivity is strongly related to the movement of proppant which helps at releasing and destabilizing fines clusters.
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.
Concrete made with recycled concrete aggregates (RCA) presents particular properties that may lead to a specific behaviour under fire conditions, including the spalling risk. The spalling sensitivity ...of concrete made with RCA was evaluated through a campaign conducted in three concrete series: reference, direct replacement, and strength-based replacement. The last was designed to have the same performance as concrete made with natural aggregates (NA). Samples with different replacement rates of recycled coarse aggregates (0%, 10%, 20%, 40%, and 100%) were exposed to the standard fire curve (ISO 834-1) with constant uniaxial loading (2.5 and 5MPa). During the tests, the furnace temperature and spalling events were recorded. After the tests, digital photogrammetry was used to observe the spalling damage (volume and depth). Fire tests indicated that concrete made with RCA exhibited a higher spalling degree than concrete made with NA. Results also show that the replacement rate acts in different ways: in concrete with RCA replacement rates up to 40%, the spalling damage increases, but a further increase does not lead to higher spalling. In addition, RCA changes the physical properties of concrete, which may trigger spalling, particularly water content.
•The spalling sensitivity of concrete made with RCA was investigated.•Digital photogrammetry was used to evaluate the damage degree of spalled specimens.•For the given conditions, concrete made with RCA showed more spalling damage than concrete made with NA.•The higher water content of concrete made with RCA was one of the triggering parameters for spalling.
In nuclear power plants, a severe accident in the containment building results in an increase in pressure, temperature and relative humidity that can reach respectively 5 bars, 140 °C and the ...saturation of water vapour. As well as the regulatory calculations, accurate knowledge of the thermal and mechanical behaviour of materials and more specifically of concrete is required to carry out more precise numerical simulations.
Our study aims to investigate the mechanical behaviour of concrete under homogeneous conditions of moisture and temperature. An experimental apparatus was designed in order to assess the evolutions of the fracture energy, modulus of elasticity and tensile strength of concrete. Different temperature levels up to a maximum of 90 °C and at different values of the controlled moisture content were investigated. The equipment was used to perform DCT (Disk-shape Compact Tension) tests at 30 °C and 90 °C. Five levels of degree of liquid water saturation (Sw) were investigated for each temperature level. Finite-element computations with the code Cast3m were carried out to determine the modulus of elasticity and the tensile strength from the results of DCT tests.
The fracture energy is the same at 30 and 90 °C and decreases with Sw between 36 and 100%. The modulus of elasticity decreases with temperature between 30 and 90 °C, decreases with Sw between 36 and 55% and increases between 72 and 100%. The tensile strength decreases with temperature between 30 and 90 °C and increases with Sw between 36 and 100%
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.
The excavation damage zone surrounding an underground tunnel/gallery, and in particular its evolution, is being studied for the performance assessment of a radioactive waste underground repository. ...This paper focuses on numerical analysis of the self-sealing of the damaged zone based on an in-situ CDZ experiment for exploring the self-sealing of excavation damage zone during a hydration process. A plastic damage model is employed to describe the mechanical behaviour of Callovo-Oxfordian claystone (COx), and an added deformation model coupled with the standard Biot’s model to simulate the significant deformation of COx claystone during the change of water content. Crack estimation and permeability evaluation of unsaturated fractured COx claystone are carried out through a post-processing method based on the fracture energy regularization and the cubic law, respectively. The validation of the proposed model is performed by numerical simulation of: (1) COx claystone swelling and triaxial compression tests, (2) self-sealing of fractured COx claystone samples during hydration process, (3) self-sealing of the damaged zone during a hydration process. Comparisons between the numerical and experimental results demonstrate the reliability of the proposed model to accurately describe the self-sealing of the fractured COx claystone, and the global water permeability reduction in hydration illustrates the accomplishment of the self-sealing of damaged zone.
This article discusses the influence of compressive shock waves on the permeability of cementitious materials. Shock waves are generated in water by Pulsed Arc Electrohydraulic Discharges (PAED). The ...practical aim is to increase the intrinsic permeability of the specimens. The maximum pressure amplitude of the shock wave is 250
MPa. It generates damage in the specimens and the evolution of damage is correlated with the intrinsic permeability of the mortar. A threshold of pressure is observed. From this threshold, the increase of permeability is linear in a semi-log plot. The influence of repeated shocks on permeability is also discussed. Qualitative X Ray Tomography illustrates the evolution of the microstructure of the material leading to the increase of permeability. Comparative results from mercury intrusion porosimetry (MIP) show that the micro-structural damage process starts at the sub-micrometric level and that the characteristic size of pores of growing volume increases.
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