Fire and Materials最新文献

As the golden period for evacuation and rescue in road tunnel fires, the fire growth stage is indispensable for security. The key parameters of this stage must be clearly defined, including the maximum heat release rate (HRR), growth time, and growth coefficient. Based on the squared model, the correlations between the key parameters are investigated according to the existing fire tests of vehicle-related materials and actual vehicles or mock-ups. The maximum HRR and the growth coefficient of different types of vehicles are obtained. The results show that the maximum HRR is linearly related to the growth coefficient in the fire tests of vehicle-related materials. And it is logarithmically related in the fire tests of actual vehicles or mock-ups. The growth coefficient and growth time represent the possibility of a disaster. The larger the growth coefficient is or the shorter the growth time is, the greater the possibility is. The maximum HRR in a fire is 2 ~ 10 MW for a car, 10 ~ 50 MW for a bus, and 50 ~ 200 MW for a heavy goods vehicle. The growth coefficient in a fire is 0.003 ~ 0.013 kW/s² for a car, 0.05 ~ 0.15 kW/s² for a bus, and 0.2 ~ 0.3 kW/s² for a heavy goods vehicle. The corresponding fire growth types are slow and medium, fast, fast, and ultra-fast, respectively. This study is beneficial for the establishment of the fire growth model and the setting of emergency response time.

Pressure-sensitive adhesive tapes are used in several industrial applications such as construction, railway vehicles and the automotive sector, where the burning behavior is of crucial importance. Flame retarded adhesive tapes are developed and provided, however, often without considering the interaction of adhesive tapes and the bonded materials during burning nor the contribution of the tapes to fire protection goal of the bonded components in distinct fire tests. This publication delivers an empirical comprehensive knowledge how adhesive tapes and their flame retardancy effect the burning behavior of bonded materials. With a special focus on the interaction between the single components, one flame retarded tape and one tape without flame retardant are examined in scenarios of emerging and developing fires, along with their bonds with the common materials wood, zinc-plated steel, mineral wool, polycarbonate, and polymethylmethacrylate. The flame retardant significantly improved the flame retardancy of the tape as a free-standing object and yielded a V-2 rating in UL 94 vertical test and raised the Oxygen Index by 5 vol.%. In bonds, or rather laminates, the investigations prove that the choice of carrier and substrates are the factors with the greatest impact on the fire properties and can change the peak of heat release rate and the maximum average rate of heat emission up to 25%. This research yielded a good empirical overall understanding of the fire behavior of adhesive tapes and bonded materials. Thus, it serves as a guide for tape manufacturers and applicants to develop tapes and bonds more substrate specific.

High-strength steels can be used in civil structures that demand high strength/weight ratios, but their advantages may be weakened by fire. For this reason, this study has been concerned with the mechanical properties of a type of quenched-and-tempered high-strength steel at elevated temperatures up to 800°C, the steel grade is S690. A standard axial tensile test was conducted on plate specimens with a reduced section. The test results demonstrated that the stress–strain curves of S690 steel at elevated temperatures had no distinctive yield plateau but post-yield hardening, the effective yield strengths and elastic modulus deteriorated dramatically with the increasing temperature due to microstructure changes. Besides, this study also investigated the effects of steel plate thickness on said temperature-dependent mechanical properties. The plate thicknesses are 8 and 12 mm nominally. The comparisons showed that, different from the trend at room temperature where the thinner steel plates usually have higher strength than their thicker counterparts, the thinner plates exhibited lower strengths at elevated temperatures, this implies that with the same cross-sectional area, a steel member formed by thinner plates would have a lower cross-sectional load-carrying capacity under fire.

A portable lab scale test setup (1 × 1 × 0.72 m³) with apparatus and procedure has been illustrated to test the fire extinguishability of fire retardant materials (FRMs) as water additives on class A fires. The main objective was to use selected commercial, eco-friendly FRM powders such as hydroxides, carbonates, and clays as water additive-based fire extinguishing agents for suppressing solid fires. FRM powders, namely, Mg(OH)₂, Ca(OH)₂, CaCO_3, and MMT-Clay were added to water and were mist sprayed on a wooden fire (class A) to test their fire-suppressing ability. A comparison involving tests with only water (without any additives) was also recorded. The solutions made with FRM additives in water showed promising results in suppressing the fire in comparison to systems with only water as an extinguishing agent. Heat sink materials, such as hydroxides and clays depicted commendable performances in retarding the burning process and almost doubled the capability of fire suppression with low loading. Their heat-absorbing nature resisted the increase in temperature and slowed down the burning process causing an increase in the total burning time of the crib and avoiding reignition. Whereas, carbonates (CaCO₃) showed a faster flame out by the release of CO₂ gas, which diluted the oxygen content in the surroundings. The article concludes with a discussion of the requirements for the ideal water mist additive-based fire extinguishing agent and a recommendation that future work include validation of the laboratory-scale method based on a comparison with full-scale suppression data for the same additives.

This paper presents a study on the structural behaviour of stainless steel profiles under fire conditions. An experimental campaign of three-point bending tests on rectangular hollow section beams of the grade 1.4301 (also known as 304) were conducted, considering both steady-state and transient state conditions. Prior to those tests, the mechanical characterization of the stainless steel was investigated. The constitutive laws obtained by tensile tests at high temperatures are compared with those recommended in Eurocode 3, whose respective material models were recently proposed for modifications, still requiring complete validation. In addition, numerical modelling of the bending tests has been performed afterwards achieving close approximation to the observed experimental results. Finally, analytical methods to predict the load-deflection behaviour are also presented. Good agreement between the considered methodologies was attained validating their application on the prediction of the fire behaviour of stainless steel beams.

This research examines the residual mechanical properties of normal and recycled aggregate concrete when subjected to elevated temperatures. The concrete specimens containing recycled aggregate (0%, 50%, 75%, and 100%) were exposed to different temperatures (25, 200, 400, and 600°C) in a muffle furnace at a heating rate of 10°C/min. The variations in flexural strength, compressive strength, and density were then tested according to ASTM standards. Findings from this investigation indicate that the degradation in the mechanical strength of concrete does not seem to be significantly affected by the increase in the percentage of recycled aggregates. However, a significant and linear decrease in the density was observed at 400°C with an increase in the percentage of recycled aggregates. The degradation of the compressive and flexural strengths of recycled aggregate concrete with increasing temperatures obtained from the experimental analysis was compared with the analytical predictions provided by Eurocode 2. Moreover, simplified equations have been proposed to estimate the degradation of the mechanical properties of recycled aggregate concrete at higher temperatures. The incorporation of recycled aggregates into concrete resulted in satisfactory residual performance.

Bio-based aggregates can be seen as one of the promising alternatives to reduce the environmental impacts of buildings due to their lower carbon footprint and energy efficiency. They have great potential to be incorporated into inorganic matrices and produce insulating materials. However, there is a lack of information about the flammability of these materials. This work presents the results of an experimental investigation of the fire behaviour of bio-based materials. In this study, wastes of bamboo, wood shavings and rice husk were used and were evaluated for their fire performance in the natural state and after treatment in an alkaline solution. The fire reaction properties were determined by using a Mass Loss Cone Calorimeter in order to obtain the parameters of heat release rate (HRR), total heat released (THR), effective heat of combustion (EHC), total mass loss (TML), ignition time (IT) and time of combustion (TC). In addition, physical characterization and thermogravimetric tests were carried out as well as scanning electron microscopy analyses. The results show that the alkaline treatment of the bio-based aggregates is able to reduce the average HRR and the EHC of all bio-aggregates but does not delay the ignition of these materials. Among the residues studied, rice husk presented the lowest peaks and averages of HRR, THR, total mass loss, EHC and time to flameout; however, the ignition occurred faster.

This paper investigates the influence of gap size (openings/spaces between two structural members) and the presence of intumescent sealants on the development of temperature when timber connections are exposed to fire conditions. The experimental results of 21 samples representing a concealed steel-to-timber connection configuration that was exposed with a 0, 3, 6, and 10 mm gap to the ISO834 standard fire for 120 min are presented. Half of the samples in each sample group were protected with an intumescent fire protection sealant. The temperatures in the timber were measured at various locations around the gap and directly next to the steel component. The experimental results show that the presence of a gap increases the temperature of the timber more than predicted by the thermal penetration models available, with current code guidelines (e.g., Eurocode 5) possibly being non-conservative. The use of an intumescent fire protection sealant in the gap is shown to be an effective protection method, but that the application configuration is important to ensure effective protection, especially as the gap becomes smaller. The results also show that the use of an intumescent fire protection sealant in a gap increases the predictability of the temperatures in the timber in longer duration fires. Unprotected samples and 0 mm gap samples exhibited large variability in the thermal development outcomes over time.

Ammonium polyphosphate (APP), piperazine pyrophosphate (PAPP), and melamine cyanurate (MCA) were used as raw materials to develop an intumescent flame retardant system (IFRS) for polypropylene (PP). The synergistic flame retardancy among APP, PAPP, and MCA was explored. The effect of the proportion of APP, PAPP, and MCA on the IFRS flame-retardant performance was studied. For the range of samples tested, the IFRS with the proportion of PAPP, MCA, and APP at 4:1:7.5 showed the best flame retardancy. When the addition of PAPP/MCA/APP IFRS in PP was 20%, the prepared flame-retardant PP composite (PP-PMA-3) passed UL-94 V-0 rating. Moreover, the PP-PMA-3 total heat release (THR) decreased by 46.4% compared with PP-0. Meanwhile, PAPP/MCA/APP IFRS showed good smoke suppression performance because the total smoke production (TSP) of PP-PMA-3 decreased by 65.0% compared with PP-0. In addition, the high flame retardancy and the flame-retardant mechanism of the prepared IFRS was explained.

This study investigates the influence of fibre orientation and heat flux on the post-fire (residual) load-bearing properties of carbon fibre-reinforced polymer (CFRP) laminates. As a result, a deep insight into the post-fire load-bearing response is gained, which is necessary to fully understand and assess the advantages of CFRP laminates containing different fibre orientations for use in load-bearing structures. Specimens were produced from three CFRP laminates containing different fibre orientations, exposed to varying heat fluxes up to 40 $��\mathrm{kW}�/�m^2�$ and then loaded in either tension or three-point bending at ambient room temperature. The study's results have shown that the post-fire behaviour of CFRP specimens is sensitive to changes in fibre orientation and heat flux. For example, specimens with an anisotropic fibre orientation in tension had the highest tensile load-bearing capacity, whereas those with bidirectional and multi-directional fibre orientations demonstrated lower tensile load-bearing capacities. In bending, however, specimens containing bidirectional and multidirectional fibre orientations had higher load-bearing capacities than specimens with an anisotropic fibre orientation. Furthermore, the data also shows that exposure to a heat flux reduces the load-bearing capacity in both the bending and tensile specimens.