Molecular structure and orientation of gel‐spun polyethylene fibers

Characterization of molecular structure and orientation of six commercially available gel‐spun polyethylene fibers have been carried out using infra‐red and Raman spectroscopy, thermal and X‐ray diffraction analysis, together with optical microscopy techniques. Thermal and X‐ray diffraction analysis revealed the existence of highly oriented orthorhombic and monoclinic crystallites together with a highly oriented intermediate phase known as pseudohexagonal mesophase structure. The results suggest the existence of a three‐phase structure consisting, at room temperature, of orthorhombic and monoclinic polymorphic crystallites, oriented noncrystalline and un‐oriented noncrystalline (amorphous) phases, respectively. The crystallinity measurements have been carried out using density, thermal and X‐ray diffraction analysis together with infra‐red and Raman spectroscopy techniques whereas the molecular orientation measurements have been carried out using birefringence and polarized IR spectroscopy, respectively. The results obtained from density, thermal analysis, and Raman spectroscopy based on a simple two‐phase modeling approach lead to the overestimated amorphous fractions and appears to ignore the presence of an intermediate phase known as oriented noncrystalline structure. X‐ray analysis has also been used for the measurement of the apparent crystallite sizes. The birefringence values have been used to determine the overall orientation parameters whereas the dichroic measurements of IR bands have been used to determine the crystalline and oriented noncrystalline orientation parameters. The results show that the orthorhombic and monoclinic phases are more highly oriented than the oriented pseudohexagonally packed noncrystalline chains. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1317–1333, 2006     

Oxidation behavior of carbon steel in simulated kerosene combustion atmosphere: A valuable tool for fire investigations

Fire investigations aim to establish the origin and cause of fires by collecting and analyzing the comprehensive fire‐related evidences. Metallic materials exposed to the fire scene environments are usually subjected to melting and/or high‐temperature oxidation, and they have been considered vital parameters for temperature determination, as recommended in NFPA 921. The oxide characteristics obtained from the conventional fire investigations primarily rely on simple visual observations such as the variations in oxide color, the so‐called “oxidation patterns.” However, such information is not sufficiently convincing due to the complex nature of oxides formed in the fire scene. The oxide color is strongly affected by the type of oxide, the oxide thickness, the concentration of contaminant, and the interactions among different oxides. In this study, Q235 structural steel samples have been exposed to high‐temperature air and simulated kerosene combustion conditions at certain temperatures and for indicated periods. The oxidation rate was examined by thermogravimetric analysis. The morphologies and microstructures of the oxide scales were investigated by scanning electron microscopy, energy dispersive spectroscopy, and X‐ray diffractions. The results show that the oxide properties are strongly dependent on the oxidation temperature and oxidation atmospheres. These oxidation behaviors are expected to provide useful information on identifying fire characteristics.     

Postfire full stress–strain response of fire‐damaged concrete

This paper reports experimental data establishing the postfire full stress–strain response of fire‐affected concrete. Such data are useful in situations when redesign of fire‐damaged concrete elements is considered. Heating was carried out to various temperatures in the range 217–470°C. Cooling was carried out either by quenching or in air. The postfire strain at ultimate stress significantly increased after heating to temperatures higher than 320°C. Quenching seems to aggravate the loss in compressive strength and further increase the strain at ultimate stress. Quenching involved spraying the heated concrete with tap water for 5 min. It is evident that knowledge of maximum temperature of exposure alone is not sufficient for estimation of the postfire stress–strain relationship. Other characteristics of exposure such as method of cooling are also important in evaluating the modification in the structural behaviour of fire‐affected concrete. Copyright © 2005 John Wiley & Sons, Ltd.     

Behaviour of limecrete under fire conditions

Hydraulic lime concrete (limecrete) is a material that has a lower environmental impact than that of ordinary Portland cement (OPC) concrete and, consequently, may be increasingly used in some construction applications. Because of its reduced strength, pozzolanic materials, such as metakaolin, are commonly used to improve its strength and durability. Simultaneously, to the increased interest in more sustainable materials, the fire behaviour of materials has also deserved an increased attention during the last years because of some important disasters that occurred. In this study, the fire behaviour of limecrete has been investigated. To increase limecrete performance, hydraulic lime has been replaced by metakaolin in different percentages. Fire tests at different temperatures (200, 400, 600 and 830°C) and different durations (30 and 60 min) have been performed and the residual strength and chemical changes using X‐ray powder diffraction and thermogravimetric analysis techniques were investigated. It became apparent that a 20% replacement of hydraulic lime by metakaolin leads to an improved performance at room temperature and fire loading. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of insulation on the fire behaviour of steel floor trusses

This paper describes a study into the fire behaviour of open‐web steel trusses supporting concrete floor slabs, exposed to a range of realistic design fires. This study is intended to give some insight into the possible structural behaviour of the floor trusses in the World Trade Center (WTC) towers. The analysis was carried out using a non‐linear finite element program SAFIR. The trusses were analysed with and without protective insulation for several different fires, each with three types of connections; pinned at both ends, simply supported, and simply supported with an axial spring. This paper shows that the likely failure mode of the floor truss depends on the connection strength, and emphasizes the importance of ensuring that the insulation remains intact. Unlike the actual event in the WTC with multiple floors exposed to fire, this analysis only considers a single floor, hence the results from this analysis do not confirm the actual behaviour of the buildings while they collapsed. Copyright © 2004 John Wiley & Sons, Ltd.     

Charring rates and temperature profiles of wood sections

A research project was carried out at the Swiss Federal Institute of Technology (ETH) to study the fire behaviour of hollow core timber slabs and timber‐concrete composite slabs. This paper describes the main results of the basic fire behaviour of timber measured in the study. The first part of the analysis looks at the charring rate of timber. In the second part a new calculation model for the temperature development in wood members exposed to the standard ISO‐fire is presented and compared with the fire test results. Copyright © 2003 John Wiley & Sons, Ltd.     

Test method for concrete spalling using small electric furnace

Concrete spalling can cause severe damage to concrete structure when exposed to fire. The spalling mechanisms are not very well understood. For the testing of spalling, full‐scale structural members should be used, as spalling tests are sensitive to size effects. Full‐scale testing in large furnace is costly and is not suitable for testing large number of concrete mixture trials. The standard and hydrocarbon fire time–temperature curves have rapid temperature rise during the initial phase. This temperature rise requires a gas furnace with high heating capacity and cannot be generated by electric muffle furnace commonly available in many laboratories. This paper presents a method to carry out spalling test in small‐scale specimens with exposure to rapid temperature rise using a commonly available electric furnace in the laboratories. The tests are based on 150 mm diameter cylinders that are laterally confined to simulate full‐scale structural members. The cylinder surface is exposed to rapid temperature rise by exposing through vertical and/or horizontal holes in pre‐heated small electric furnace. Some unconfined 100 mm diameter cylinders were also exposed horizontally to test the performance of confinement. The paper shows that the hydrocarbon fire and standard fire exposure can be simulated by manipulating the exposure location of the surface of the concrete cylinder. Ordinary Portland cement concrete cylinders with different strengths were tested and different spalling patterns were observed. The spalling patterns matched the test results from a gas furnace fire test simulating the fire curves. The tests demonstrated that the method is an effective and convenient technique to predict the spalling risk of a concrete. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of cooling methods on residual compressive strength and cracking behavior of fly ash concretes exposed at elevated temperatures

This paper presents the effects of cooling methods on residual compressive strength and cracking behavior of concretes containing four different class F fly ash contents of 10%, 20%, 30% and 40% as partial replacement of cement at various elevated temperatures. The residual compressive strength of the aforementioned fly ash concretes is measured after being exposed to 200, 400, 600 and 800 °C temperatures and two different cooling methods, for example, slow cooling and rapid water cooling. Results show that the residual compressive strengths of all fly ash concretes decrease with increase in temperatures irrespective of cooling regimes, which is similar to that of ordinary concrete. Generally, control ordinary concrete and all fly ash concretes exhibited between 10% and 35% more reduction in residual compressive strength because of rapid cooling than slow cooling except few cases. Cracks are observed over concrete specimens after being exposed to temperatures ranging from 400 to 800 °C. Samples that are slowly cooled developed smaller cracks than those rapidly cooled. At 800 °C, all fly ash concretes that are exposed to rapid cooling showed the most severe cracking. X‐ray diffraction analysis shows reduction of Ca(OH)₂ peak and formation of new calcium silicate peak in concretes containing 20% and 40% fly ash when subjected to 800 °C in both cooling methods. Thermo gravimetric analysis and differential thermal analysis results show increase in thermal stability of concrete with increase in fly ash contents. The existing Eurocode also predicted the compressive strength of fly ash concretes with reasonable accuracy when subjected to the aforementioned elevated temperatures and cooling methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Polypropylene/Clay nanocomposites: Effect of compatibilizer on the thermal,crystallization and dynamic mechanical behavior

Polypropylene (PP)/clay nanocomposites are prepared using different grades of PP, compatibilizers, and organically modified clays. The melt intercalation of the PP is carried out in presence of a compatibilizer. The nanocomposites are characterized using various techniques for the structure and properties. X‐ray diffraction results indicate well‐defined structures. Thermogravimetric analysis indicates improved thermal stability of PP/clay nanocomposites. Isothermal crystallization studies carried out using differential scanning calorimeter illustrate enhanced crystallization of PP in all the nanocomposites. Optical microscopic study demonstrates that the nanocomposites can be crystallized at higher temperatures, exhibiting well‐defined birefringent structures. The dynamic mechanical analysis reveals higher storage moduli over a temperature range of ?40⁰C to 120⁰C for nanocomposites, and the extent of increase in the storage modulus is dependent on the type of compatibilizer used.     

A simplified model for predicting the ignition of FRP composites with validation using intermediate‐scale fire experiment data

This study presents a simplified theoretical model to predict the ignition of FRP composites of general thermal thickness (GTT) subjected to one‐sided heating. A simplified GTT heat transfer model to predict the surface temperature of GTT composite panels was developed, and the exposed surface temperature was used as ignition criterion. To validate the GTT model, intermediate scale calorimeter fire tests of E‐glass fiber reinforced polyester composite panels at three heat flux levels were performed to obtain intermediate‐scale fire testing data in a controlled condition with well‐defined thermal boundary conditions. The GTT model was also verified by using results from finite element modeling predictions. This model can be used to estimate the surface temperature increase, time‐to‐ignition, and mass loss of FRP composites for fire safety design and analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of specimen size and loading conditions on spalling of concrete

Different qualities of concrete have been fire tested using different geometries of the specimens as well as different load levels and load configurations. The main objective with the study was to examine a test methodology consisting of a full‐scale test and different small scale‐tests for determining the probability of spalling and the amount of spalling of fire exposed concrete structures. A reference specimen was defined as a one‐sided fire exposed slab with the dimensions 1800 × 1200 mm² giving an exposed area of 1500 × 1200 mm². A number of concrete qualities with different probabilities for spalling, were tested using the reference specimen. These tests showed that the reference specimens worked well giving the expected test results. Small specimens were manufactured in different shapes with the same concrete as the one used in the reference tests. These small specimens were tested either at the same time as the reference specimens in the large furnace or afterwards on a small‐scale furnace where the fire exposed surface was 450 × 360 mm². The test results clearly show the increased probability and the increased amount of spalling by using external compressive loading. The results also show that by using pre‐stress through bars or wires the load can be lost due to heating of the bars/wires which results in a decreased amount of spalling. The boundary of the specimen also affects the amount of spalling. The spalling around the edges was in all tests less than the spalling on the central parts of the exposed area. It could also be noted that the spalling did not pass completely through any of the specimens. The reason for this is probably that the water/vapour could migrate out from the unexposed surface of the specimen. Copyright © 2006 John Wiley & Sons, Ltd.     

Thermal,mineralogical, and microstructural characterizations of irradiated polymer blended cement mortar composites

In this study, the effects of styrene–acrylic ester (SAE), nanocalcined clay (NCC), and irradiation dose on the thermal, mineralogical, and microstructural characterizations of irradiated polymer‐blended cement mortar composites have been investigated. The composites were prepared by partial replacement of cement with 5 and 10% NCC and mixed with sand, SAE latex was added with different ratios (2, 4, 6, 8, 10, and 15%); the composites were subjected to various doses of γ‐irradiation ranged from 10 to 50 kGy. Physicomechanical properties, thermogravimetric analysis, X‐ray diffractometry, and scanning electron microscopy techniques were carried out. Mechanical investigation manifested that composites loaded with SAE up to 8% showed the best mechanical performance as compared with composites contains 10 and 15% SAE. POLYM. COMPOS., 36:1849–1858, 2015. © 2014 Society of Plastics Engineers     

Load ratio effects on the structural fire behaviour of glass fibre-reinforced polymer-reinforced concrete beams with mid-span bar lap splices – Experimental study

Fibre-reinforced polymer (FRP)-reinforced concrete members have been gaining attention as an alternative to conventional steel-reinforced concrete members due to their advantageous characteristics. A few to mention are excellent resistance to corrosion, high strength-to-weight ratio, and reduced maintenance cost in the long term. Nevertheless, FRPs are often limited in use mainly due to fire safety considerations since they can encounter significant deprivation of strength and bond with concrete in fire conditions. This paper presents the results of an experimental study aimed to investigate the effects of the applied load level on the structural behaviour of glass fibre-reinforced polymer (GFRP)-reinforced concrete beams having mid-span bar lap splices when exposed to standard fire. Two 2750-mm long beams with cross-sectional dimensions of 300 mm wide × 350 mm high were exposed to elevated temperatures that followed the CAN/ULC-S101 standard fire time–temperature curve while being subjected to a load level equivalent to 85% of the beam ultimate design load. The experimental results of the two beams were compared to those obtained for identical beams but subjected to a lower load level that is equivalent to only 40% of the beam's ultimate design load. Results show that the increased load level (slightly more than double the load ratio) unexpectedly did not impact the fire resistance time of the GFRP-reinforced concrete beams but affected other structural responses of the beam, such as its midspan deflections and cracking patterns.     

Residual response of fire‐damaged high‐strength concrete beams

This paper presents results from an experimental study on residual capacity of fire‐damaged high‐strength concrete (HSC) beams. Four reinforced concrete (RC) beams, fabricated with HSC, were first subject to structural loading and fire exposure with a distinct cooling phase and then loaded to failure upon cooldown to ambient conditions to evaluate residual capacity. Temperatures, deflections, and spalling in the beams were monitored during heating and cooling phases of fire exposure. Further, residual capacity, strains at critical section, and crack patterns (failure mode) of fire‐damaged beams were recorded during residual capacity tests. Results from experiments indicate that the load level during fire exposure, duration of heating phase, rate of cooling, extent (type) of spalling, and duration of postcooling storage influence residual deformations and also residual capacity of RC beams. Further, fire‐damaged HSC beams can recover 40% to 70% of their flexural capacity with respect to their room temperature design capacity provided they survive the entire duration of fire exposure.     

Structural and Theoretical Investigations of 3,4,5‐Triamino‐1,2,4‐Triazolium Salts

Reactions using the high nitrogen heterocycle 3,4,5‐triamino‐1,2,4‐triazole (guanazine) with strong acids (HNO₃, HClO₄, and “HN(NO₂)₂”) resulted in a family of highly stable salts. All of the salts were characterized using spectroscopic as well as single crystal X‐ray diffraction studies. The X‐ray structures were compared to that obtained from theoretical calculations (MP2/6‐311+G(d, p) level). Initial safety testing (impact, friction) was carried out on all of the new materials.     

C60高性能混凝土高温后红外检测及CT图像分析

对掺0%和0.2%聚丙烯纤维的C60高性能混凝土进行了模拟火灾高温试验,测试了高温前后混凝土的轴心抗压强度,采用红外热成像检测技术,研究了高温后混凝土的红外热像图谱.建立了高性能混凝土红外热像平均温升与受火温度和轴心抗压强度比的关系;对常温、300 ℃、400 ℃、500 ℃高温后高性能混凝土试件进行了CT图像扫描试验,分析纤维对混凝土内部裂纹产生和扩展的影响.     

Fire suppressing performance of superfine potassium bicarbonate powder

Fire suppression effectiveness of a new kind of dry powder based on potassium bicarbonate was studied in this paper. The powder consisted of superfine potassium bicarbonate and some organic and inorganic additives, which was denoted as ‘K‐powder’. The physical and chemical characteristics of the K‐powder were characterized by a series of techniques of X‐ray diffraction, scanning electron microscopy, Fourier transforms infrared (FTIR) and thermal gravity analysis, etc. Performance of the new potassium‐based powder in fire suppression was studied by laboratory‐scale experiments, which exhibited much superior fire suppression efficacy than that of the commercial bicarbonate powder. Such improvements could be reasonably ascribed to the special chemical composition, microstructure and radiation effect on the mechanisms. The preparation, fire suppression and possible fire‐extinguishing mechanisms were studied in detail. Copyright © 2010 John Wiley & Sons, Ltd.     

A study on fire behaviour of combustible components of two commonly used photovoltaic panels

Photovoltaic (PV) modules are installed in some modern buildings for generating renewable energy. When a building catches fire, burning PV panels can contribute to an already very hazardous environment. Two common polycrystalline silicon PV samples A and B were selected with their chemical composition analysed by the Fourier transform infrared spectroscopy with justification by X‐ray photoelectron spectroscopy results. Sample A was confirmed to be a silicate product with polyurethane adhesive, and sample B has epoxy resin and is likely to have flame retardant as claimed. Thermal analysis by heating the samples was carried out using thermogravimetric analysis and thermogravimetric analysis coupled with infrared spectroscopy. The fire behaviour was then studied by a cone calorimeter under radiative heat fluxes from 10 to 70 kWm^?2. Three key parameters representing flashover propensity, total heat release per unit area and smoke toxicity hazard were obtained from the cone calorimeter tests for ranking the thermal and smoke hazards. The thermal hazards of both PV samples are low, at least during the early stage of a fire without flame acting directly on the sample. However, vast quantities of smoke were emitted from burning PV panels under high heat fluxes. Copyright © 2016 John Wiley & Sons, Ltd.     

An empirical model for confined concrete after exposure to high temperature

In this study, constitutive relationships have been developed for confined concrete subjected to elevated temperature to specify the fire‐performance criteria for concrete structures after exposé to fire. This study extends over a total of 63 circular hoop confined concrete specimens that were casted and tested under concentric compression loading after exposure to high temperature. The test variables studied are the yield strength of transverse reinforcement, spacing of the hoop, and exposure to temperatures from ambient to 800°C. It is shown that all of these variables have significant influence on concrete behavior at different temperatures and further an improvement in the thermal resistance of concrete when confined using transverse steel reinforcement. On the basis of experimental results, a model for confined concrete after exposed to high temperature is proposed to predict the results of residual behavior after thermal cycles. The proposed empirical stress‐strain equations are suitable to predict the postfire behavior of confined normal strength concrete in compression. The predictions were found to be in good agreement and well fit with experimental results.     

Experimental and numerical study on the performance of hollow and concrete‐filled elliptical steel columns subjected to severe fire

This paper presents the results of an experimental and validated theoretical study to investigate the performance of steel columns with hollow and concrete‐filled elliptical sections subjected to hydrocarbon fire. The test programme involved 18 columns with 200 × 100 × 8‐mm, 300 × 150 × 8‐mm and 400 × 200 × 8‐mm elliptical sections representing slenderness of 50, 33 and 24, respectively. The 1800‐mm columns were subjected to the severe hydrocarbon fire curve and tested under loadings ratios of 20%, 40% and 60% of the EC3 ultimate strength. The paper presents the obtained experimental results including measured axial and lateral displacements, failure temperatures and failure time. A three‐dimensional model was built using the finite element method (FEM) and was validated using the obtained tests results. The finite element model showed an excellent agreement with tests results of failure temperatures, failure modes, and axial and lateral displacements. However, because of restrictions in the software capabilities, the mechanical–thermal behaviour of concrete including spalling was not considered in the model. The verified finite element model was used to conduct a parametric analysis involving a range of parameters of loading level and slenderness. The study has shown that the concrete‐filled sections have demonstrated an improved fire resistance when compared with the hollow sections under the low loading ratios. The FEM model has successfully predicted the unique thermal profile of elliptical section under fire, which was observed during the tests. Copyright © 2015 John Wiley & Sons, Ltd.