The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Venkatesh Kodur - One of the best experts on this subject based on the ideXlab platform.
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modeling the fire response of reactive powder concrete beams with due consideration to explosive Spalling
Construction and Building Materials, 2021Co-Authors: Pengfei Ren, Xiaomeng Hou, Venkatesh Kodur, Yading Zhao, Wei ZhouAbstract:Abstract Reactive powder concrete (RPC) is susceptible to fire-induced Spalling because of its dense microstructure and lower permeability compared with normal-strength concrete and high-strength concrete, which may compromise the structural integrity and load-carrying capacity of RPC members significantly. A macroscopic finite-element model was therefore extended to track the fire behavior of RPC beams, especially fire-induced Spalling. New sorption isotherms were used to identify the mass of liquid water in RPC at elevated temperatures. Furthermore, an improved Spalling criterion was proposed, based on the biaxial strength theory of RPC, to judge if the Spalling occurs in RPC members. Additionally, the effect of the improved and previous Spalling criteria (based on the uniaxial strength theory) on the fire performance prediction of RPC beams was studied. It was found that the improved Spalling criterion can provide more-accurate Spalling and fire performance prediction for RPC beams since it considers the effect of both the stresses induced by pore pressure, thermal gradients and applied load and the change in concrete strength caused by the spatial stress superposition.
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Spalling behavior of metakaolin fly ash based geopolymer concrete under elevated temperature exposure
Cement & Concrete Composites, 2020Co-Authors: Hai Yan Zhang, Venkatesh Kodur, Guang Hong Qiu, Zhen Sheng YuanAbstract:Abstract Fire-induced Spalling is a serious risk to concrete structures, especially for high strength concrete structures. This paper presents results from high temperature Spalling tests on geopolymer concrete. The effect of moisture content, concrete strength, heating rate and temperature level on the Spalling behavior of geopolymer concrete is studied. The temperature-induced Spalling mechanism in geopolymer concrete is investigated through the measurement of residual compressive and splitting tensile strength, variation in permeability (by sorptivity test) and chemical composition (by X-ray diffraction test) of geopolymer concrete after elevated temperature exposure up to 700 °C. The test results indicate that geopolymer concrete exhibit a good Spalling resistance as compared to that of OPC concrete. The lower Spalling risk in geopolymer concrete under high temperature exposure is facilitated from the highly connected pore structures and lower strength degradation with temperatures. Further results indicate that the pore structure (permeability) of geopolymer concrete gets a significant evolution with the exposure temperature, especially above 500 °C range. This is related to the sintering reaction in geopolymer binders at high temperatures.
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Fire Induced Spalling in High Strength Concrete Beams
Fire Technology, 2009Co-Authors: M. B. Dwaikat, Venkatesh KodurAbstract:A macroscopic finite element model is extended to account for fire induced Spalling in high strength concrete (HSC) beams. The model is based on the principles of mechanics and thermodynamics and utilizes pore pressure calculations to predict fire induced Spalling in concrete. For validating the model, Spalling measurements were made by conducting fire resistance experiments on four normal strength and high strength concrete beams. Spalling predictions from the model are compared with the measured values of Spalling at various stages of fire exposure. The validated model is applied to investigate the influence of fire scenario, concrete strength (permeability) and axial restraint on the fire induced Spalling and fire response of RC beams. Results from the analysis show that fire scenario, and concrete permeability largely influence the extent of fire induced Spalling in concrete beams. Further, it is also shown that the extent of Spalling has significant influence on the fire resistance of RC beams.
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hydrothermal model for predicting fire induced Spalling in concrete structural systems
Fire Safety Journal, 2009Co-Authors: M. B. Dwaikat, Venkatesh KodurAbstract:A one-dimensional numerical model to predict fire-induced Spalling in concrete structures is presented. The model is based on pore pressure calculations in concrete, as a function of time. Principles of mechanics and thermodynamics are applied to predict pore pressure in concrete structures exposed to fire. An assessment of the possibility of tensile fracture is made by comparing the computed pore pressure with temperature-dependent tensile strength. The pore pressure calculations are coupled with heat transfer analysis to ensure that the loss of concrete section, resulting from Spalling, is accounted for in subsequent heat transfer analysis. The validity of the numerical model is established by comparing temperature, pore pressure, and concrete Spalling predictions with results from fire tests. The computer program is applied to conduct case studies to investigate the influence of concrete permeability, tensile strength of concrete, relative humidity in concrete, and heating rate on fire-induced Spalling in concrete members. Through these case studies, it is shown that permeability, tensile strength of concrete, and heating rate have a significant influence on fire-induced Spalling in concrete. It is also shown that relative humidity has a marginal influence on fire-induced Spalling in concrete.
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Spalling in high strength concrete exposed to fire concerns causes critical parameters and cures
Structures Congress 2000: Advanced Technology in Structural Engineering, 2000Co-Authors: Venkatesh KodurAbstract:The increased use of high strength concrete (HSC) in buildings has raised concerns regarding the behaviour of such concrete in fire. Spalling at elevated temperatures and the resulting reduction in fire resistance is of particular concern. In this paper, the various issues relating to Spalling and its impact on fire resistance are discussed. The Spalling phenomenon and its main causes in HSC are presented. This includes the critical parameters that influence Spalling in HSC under fire conditions. Design solutions (cures) to minimize Spalling in HSC structural members are presented.
Kang Hai Tan - One of the best experts on this subject based on the ideXlab platform.
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synergistic effects of hybrid polypropylene and steel fibers on explosive Spalling prevention of ultra high performance concrete at elevated temperature
Cement & Concrete Composites, 2019Co-Authors: Kang Hai Tan, Enhua YangAbstract:Abstract This study investigated synergetic effects of hybrid polypropylene (PP) and steel fibers on explosive Spalling prevention of ultra-high performance concrete (UHPC) at elevated temperature. Permeability of UHPC was measured and correlated to the extent of Spalling quantitatively. Microstructures of UHPC before and after elevated temperature exposure were examined to reveal potential mechanisms responsible for changes in permeability. Results showed that the use of hybrid PP and steel fibers completely prevented explosive Spalling even at low fiber dosage of both fibers due to significant increase of permeability. Microstructural analysis revealed that such synergistic effect on increased permeability of hybrid PP and steel fiber-reinforced UHPC was attributed to enhanced connectivity of empty PP fiber tunnels by multiple microcracks generated from the thermal expansion of both fibers.
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mechanism of pva fibers in mitigating explosive Spalling of engineered cementitious composite at elevated temperature
Cement & Concrete Composites, 2018Co-Authors: Jincheng Liu, Kang Hai TanAbstract:Abstract Polyvinyl alcohol (PVA) fibers have been found effective in preventing explosive Spalling of engineered cementitious composite (ECC) under fire loading. However, the fundamental mechanism of minimizing the Spalling risk by adding PVA fibers remains unclear. Thus, this paper addresses the mode of action of PVA fibers in combating explosive Spalling of ECC at high temperature. In this regard, hot permeability of ECC and mortar was measured. PVA fibers were found to increase hot permeability of ECC significantly before their melting. Microstructure and EDX analysis were conducted to achieve a better understanding of how PVA fibers actually function to increase hot permeability before melting. The enlarged empty zones around the PVA fibers were the reason for the significant increase in permeability. Residue from melted PVA fibers was observed on the channel walls and did not diffuse into the matrix. For the first time laser distance meter was used to record progressive Spalling history in heated samples. An in-depth discussion on the relationship between temperature, pore pressure, and Spalling was also provided.
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a new perspective on nature of fire induced Spalling in concrete
Construction and Building Materials, 2018Co-Authors: Jincheng Liu, Kang Hai Tan, Yao YaoAbstract:Abstract Spalling of concrete is a great potential threat to fire resistance of concrete structures. Understanding the underlying mechanism is important to predict and mitigate this unfavorable phenomenon. Currently, there are two main mechanisms to explain the fire-induced concrete Spalling: viz. Spalling due to (a) pore pressure buildup or (b) thermal stress. The relative importance of these two mechanisms has been a subject of intense debate in the research community over the past few decades. This paper presents a critical review of conflicting and concordant points on concrete Spalling at high temperature and proposes a unified and coherent fire-induced concrete Spalling theory. Therein, the authors propose three types of thermal Spalling depending on the governing mechanisms: thermo-hygral Spalling, thermo-mechanical Spalling and thermo-chemical Spalling. The criteria to forecast each type of Spalling are established and the Spalling temperature range for each of them is analysed. The Spalling pattern, influencing factors and preventive measures for each type of Spalling are also discussed in this paper.
Pietro Lura - One of the best experts on this subject based on the ideXlab platform.
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real time measurements of temperature pressure and moisture profiles in high performance concrete exposed to high temperatures during neutron radiography imaging
Cement and Concrete Research, 2015Co-Authors: Roberto Felicetti, Nikolajs Toropovs, Lo F Monte, Mateusz Wyrzykowski, Benedikt Weber, Genadijs Sahmenko, Peter Vontobel, Pietro LuraAbstract:High-Performance Concrete (HPC) is particularly prone to explosive Spalling when exposed to high temperature. Although the exact causes that lead to Spalling are still being debated, moisture transport during heating plays an important role in all proposed mechanisms. In this study, slabs made of high-performance, low water-to-binder ratio mortars with addition of superabsorbent polymers (SAP) and polypropylene fibers (PP) were heated from one side on a temperature-controlled plate up to 550 °C. A combination of measurements was performed simultaneously on the same sample: moisture profiles via neutron radiography, temperature profiles with embedded thermocouples and pore pressure evolution with embedded pressure sensors. Spalling occurred in the sample with SAP, where sharp profiles of moisture and temperature were observed. No Spalling occurred when PP-fibers were introduced in addition to SAP. The experimental procedure described here is essential for developing and verifying numerical models and studying measures against fire Spalling risk in HPC.
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reduction of fire Spalling in high performance concrete by means of superabsorbent polymers and polypropylene fibers small scale fire tests of carbon fiber reinforced plastic prestressed self compacting concrete
Cement & Concrete Composites, 2014Co-Authors: Pietro Lura, Giovanni P TerrasiAbstract:Abstract High-performance concrete (HPC) is prone to explosive Spalling when exposed to fire, which may lead to failure of the concrete elements. Polypropylene fibers (PP) are often added to HPC, as upon their melting they create channels through which water vapor is evacuated, preventing the build-up of high vapor pressures. In self-compacting HPC (HPSCC), the amount of PP fibers needs to be limited in order to keep the self-compacting properties, which may reduce the fire resistance. In this paper, a novel strategy to reduce fire Spalling in HPSCC is illustrated, based on adding small particles of superabsorbent polymers (SAP) during mixing. The SAP end up as empty macropores, similar to air voids, in the HPSCC matrix. The PP fibers-SAP voids system percolates at a lower fiber loading than the fibers alone, allowing maintenance of the self-compacting properties while reducing substantially the fire Spalling. In particular, in this paper it is shown how addition of SAP is able to reduce fire Spalling in thin-walled HPSCC slabs prestressed with carbon fibre reinforced plastic reinforcement.
Cheon-goo Han - One of the best experts on this subject based on the ideXlab platform.
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combining polypropylene and nylon fibers to optimize fiber addition for Spalling protection of high strength concrete
Construction and Building Materials, 2012Co-Authors: Guncheol Lee, Cheon-goo Han, Min-cheol Han, Dongyeop Han, Hojeong SonAbstract:This study investigates experimentally the synergistic effect of a polypropylene (PP) and a nylon (NY) fiber combination to provide improved Spalling protection of high-strength concrete subjected to fire. Optimum levels of fiber contents for Spalling protection with a less adverse effect on workability are provided based on the results of the fire test by varying the NY and PP fiber content. The combination of NY and PP fibers shows a synergistic effect on Spalling protection; that is, by using a combination of NY and PP fibers, the same level of Spalling protection is achieved using half as much fiber content as that when PP or NY fiber is used alone. The combined fibers show no explosion occurring even at 0.05% of NY (0.025% out of 0.05%) and PP (0.025% out of 0.05%) fiber content. By combining both the comparably low melting point of PP fiber, which is useful at the early stage of a fire, and the larger number of fibers that can be used due to the thinner diameter of NY fiber, which is useful at the later stage of fire, the combination of the two fibers can improve Spalling protection by providing connections between pores with low fiber content.
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Critical parameters of nylon and other fibres for Spalling protection of high strength concrete in fire
Materials and Structures, 2011Co-Authors: Young-sun Heo, Cheon-goo Han, Jay G Sanjayan, Min-cheol HanAbstract:This study investigated various types of fibre length, fibre diameter, fibre type and fibre content on the degree of Spalling of concrete in fire. Four types of fibres, namely, polypropylene, polyvinyl alcohol, cellulose and nylon with various lengths and diameters were studied. Fibre contents ranged from 0.05 to 0.15% by volume of concrete. Fire tests were conducted according to the ISO 834 standard heating curve. Results showed that when comparing all the fibres under the same fibre content levels (% volume of concrete), the nylon fibre was the most effective in protecting concrete from Spalling. This is because the diameter of the nylon fibres were significantly less than the other fibres, hence there were significantly more number of nylon fibres present for the same fibre content (% volume) in concrete. Analysis revealed, regardless of the amount of fibre, the type of fibre, diameter of and length of fibre, there is a strong relationship between the total number of fibres present per unit volume, length of fibres and the degree of Spalling observed. Based on this relationship, the authors established a critical minimum for total number of fibres per unit volume for Spalling protection in fire.
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Improvement of residual compressive strength and Spalling resistance of high-strength RC columns subjected to fire
Construction and Building Materials, 2009Co-Authors: Cheon-goo Han, Min-cheol Han, Young-sun HeoAbstract:Abstract This paper investigates the Spalling properties of high-strength concrete in order to improve the residual compressive strength and Spalling resistance in specimens subjected to 3 h of unloading fire conditions. This study consists of three series of experiments with eighteen different specimens varying in fiber type and content, finishing material and simultaneous fiber content and lateral confinement. They were fabricated to a 300 × 300 × 600 mm mock-up size. Results of the fire test showed that the control concrete was explosive, while the specimens that contained more than 0.1 vol% of polypropylene (PP) and polyvinylalcohol (PVA) fibers were prevented from Spalling. One specimen, finished by a fire endurance spray, exhibited even more severe Spalling than the control concrete. The specimen containing 0.1 vol% of PP fiber and using a confining metal fabric at the same time, showed the most effective Spalling resistance; in particular, the residual compressive strength ratio was even higher than that of the control concrete before the fire test. It was demonstrated that adding fibers in concrete prevented the Spalling occurrence and confining metal fabric around the main bars of concrete specimens can secure the strength of structures during the conditions of elevated temperature.
Young-sun Heo - One of the best experts on this subject based on the ideXlab platform.
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Critical parameters of nylon and other fibres for Spalling protection of high strength concrete in fire
Materials and Structures, 2011Co-Authors: Young-sun Heo, Cheon-goo Han, Jay G Sanjayan, Min-cheol HanAbstract:This study investigated various types of fibre length, fibre diameter, fibre type and fibre content on the degree of Spalling of concrete in fire. Four types of fibres, namely, polypropylene, polyvinyl alcohol, cellulose and nylon with various lengths and diameters were studied. Fibre contents ranged from 0.05 to 0.15% by volume of concrete. Fire tests were conducted according to the ISO 834 standard heating curve. Results showed that when comparing all the fibres under the same fibre content levels (% volume of concrete), the nylon fibre was the most effective in protecting concrete from Spalling. This is because the diameter of the nylon fibres were significantly less than the other fibres, hence there were significantly more number of nylon fibres present for the same fibre content (% volume) in concrete. Analysis revealed, regardless of the amount of fibre, the type of fibre, diameter of and length of fibre, there is a strong relationship between the total number of fibres present per unit volume, length of fibres and the degree of Spalling observed. Based on this relationship, the authors established a critical minimum for total number of fibres per unit volume for Spalling protection in fire.
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Improvement of residual compressive strength and Spalling resistance of high-strength RC columns subjected to fire
Construction and Building Materials, 2009Co-Authors: Cheon-goo Han, Min-cheol Han, Young-sun HeoAbstract:Abstract This paper investigates the Spalling properties of high-strength concrete in order to improve the residual compressive strength and Spalling resistance in specimens subjected to 3 h of unloading fire conditions. This study consists of three series of experiments with eighteen different specimens varying in fiber type and content, finishing material and simultaneous fiber content and lateral confinement. They were fabricated to a 300 × 300 × 600 mm mock-up size. Results of the fire test showed that the control concrete was explosive, while the specimens that contained more than 0.1 vol% of polypropylene (PP) and polyvinylalcohol (PVA) fibers were prevented from Spalling. One specimen, finished by a fire endurance spray, exhibited even more severe Spalling than the control concrete. The specimen containing 0.1 vol% of PP fiber and using a confining metal fabric at the same time, showed the most effective Spalling resistance; in particular, the residual compressive strength ratio was even higher than that of the control concrete before the fire test. It was demonstrated that adding fibers in concrete prevented the Spalling occurrence and confining metal fabric around the main bars of concrete specimens can secure the strength of structures during the conditions of elevated temperature.
