Fire and Materials最新文献

To promote the application of fly ash (FA) in UHPC at elevated temperatures and achieve green development in the construction industry. In this study, the effects of curing regimes and FA on the evolution of compressive properties, hydrates, and microstructure of ultra-high performance cementitious materials (UHPCM) at elevated temperatures were systematically investigated by macroscopic mechanical performance testing and microscopic analysis. The results indicated that the combination of steam curing and dry-hot air curing could accelerate the secondary hydration to significantly enhance the compressive strength of UHPCM. As the FA content increased from 0% to 15%, the residual compressive strength at elevated temperatures was improved, the specimen cracks reduced in size, and the mass loss rate decreased after elevated temperatures. The mechanism of FA improving the fire resistance of UHPCM is that the secondary hydration reaction of FA was intensified by thermal curing, especially the suitable dry-hot air curing, to generate more stable calcium silicate hydrates, which filled the internal defects. This process had been well verified by analyzing the samples through X-ray diffractometer (XRD) and scanning electron microscope (SEM). Furthermore, as the exposure temperature increased, the residual strength of UHPCM initially increased and then decreased, reaching a maximum of 217.4 MPa at 400°C. Finally, based on the analysis of the test results, a compressive strength model of UHPCM at elevated temperatures was established considering the influence of FA content.

Earthen construction materials offer environmental benefits and strong thermal, hygric, and mechanical properties, but their fire behavior is not well understood, limiting their use. This study examines how external load and water content affect, simultaneously, the fire behavior of compressed earth bricks. Three types of bricks were tested: unstabilized bricks compacted at 5 and 50 MPa, and cement-stabilized bricks with 3.5% cement compacted to Proctor level (the compaction necessary to achieve the material's maximum dry density at its optimum water content). These bricks were equalized at 0%, 75%, and 100% relative humidity, then exposed to the time–temperature curve defined in ISO 834-1 while subjected to loads from 0 to 2.5 MPa. Results showed that at 0% and 100% RH, all materials were thermally stable regardless of load. At 75% RH, SW50 and SWC3.5 became thermally unstable with increased load, at different intensities, while SW5 remained stable. Increased loading affected crack opening/closure, internal pore pressure, and vapor permeation in SW50 and SWC3.5. In contrast, SW5's stability was unaffected by load or crack behavior. Further load-bearing capacity tests conducted on the thermal stable samples confirmed prior hypotheses about the interrelated thermo-hydro-mechanical coupling in the behavior of earthen materials at high temperatures.

The primary purpose of student residential colleges is to serve as a secure and well-equipped place to reside while adhering to established safety standards and regulations. Fire safety ought to incorporate a comprehensive and harmonized array of measures, encompassing continuous fire safety education and awareness initiatives. This study aims to investigate the correlation between individuals' educational background and their perception of fire safety, encompassing their awareness and understanding of fire safety measures. The study focuses specifically on the residents of a college dormitory. The present study employed a quantitative methodology. Data collection is conducted using a closed-ended questionnaire. The quantitative methodology comprises four primary components: Section A pertains to demographic information, Section B focuses on educational background, Section C assesses the level of fire safety awareness, and Section D assesses the level of fire safety knowledge. The results of the hypothesis testing indicate a statistically significant inverse relationship between individuals' perception of fire safety and their participation in fire safety educational activities. The aggregate score regarding the perception of fire safety is relatively high. This study holds significance for professionals engaged in the field of fire safety engineering and regulations, as it will assist them in enhancing their preparedness for conducting effective fire hazard and risk assessments.

Tunnel fire is one of the major challenges that cannot be ignored in the safe operation of tunnels. Considering the structural characteristics of tunnel fires, it is feasible to use longitudinal ventilation coupled with multi-point centralized smoke exhaust in subway tunnel engineering. Combining common slope tunnels, it is of great significance to investigate the ceiling temperature characteristics of such tunnels. Experimental testing was conducted. The results indicate that there is a strong linear relationship between the ceiling maximum temperature and the tunnel slope. A prediction formula for the ceiling maximum temperature of a sloping subway ventilation tunnel with a multi-point centralized smoke exhaust mode has been proposed. Based on the double exponential addition temperature decay model, the decay trend upstream and downstream of the exhaust vent was discussed. The constant coefficient remains basically unchanged; the decay index coefficient is linearly related to the tunnel slope, and the reduction coefficient is linearly related to the smoke exhaust volume. A tunnel ceiling temperature decay model with a multi-point centralized smoke exhaust mode affected by tunnel slope was proposed.

Highway tunnel fires caused by traffic accidents can lead to multiple simultaneous fires, which are more destructive and difficult to control compared to single fires. This study conducts a series of experimental tests to examine the smoke backlayering length, maximum gas temperature rise beneath the tunnel ceiling, and other critical parameters of dual source fires. The experiments were carried out in a 1:10 reduced-scale model tunnel with longitudinal ventilation, varying burner separation distances and burner dimensions. The results indicate that the smoke backlayering length in dual source fires is influenced by the longitudinal ventilation speed, heat release rate, and burner separation distances, while the maximum temperature rise beneath the ceiling decreases with increasing burner separation distances. A function incorporating burner separation distance and burner dimensions was proposed to predict the smoke backlayering length, based on the prediction model for a single fire source and the experimental data for dual fire sources. Additionally, based on the single fire source theory, a prediction model for the maximum temperature rise beneath the ceiling with dual fire sources was established. These findings provide a theoretical basis for risk prevention in tunnel fires involving multiple fire sources.

To study the explosion suppression mechanism of nonpremixed inert gas, this paper uses CFD software Simtec to simulate the suppression process of methane explosion by nonpremixed nitrogen in a square tube. The closed square tube includes three sections: ignition section, suppression section, and combustible gas mixture section. The results show that the critical explosion suppression length increases first and then decreases with the increase of methane concentration. When the methane concentration is 11%, the critical explosion suppression length is the biggest, which is 1.6 m. With the increase of the length of the suppression section, the overpressure curve first changes from a high-pressure single peak to a double peak and finally to a low-pressure single peak. After ignition, the nitrogen in the suppression section moves to the right with the flame under the driving effect of thermal expansion of combustion products. When the flame propagates near the suppression section, the nitrogen section stops moving right. Then, under the disturbance of the explosion wave, the suppression section is stretched. When the length of the suppression section is less than the critical explosion suppression length, the flame passes through the suppression section to ignite the combustible mixture, causing a secondary explosion. If the suppression length is greater than the critical explosion suppression length, the flame will gradually extinguish in the suppression section. The feasibility of suppression explosion by nonpremixed inert gas was verified, and the suppression mechanism of nonpremixed inert gas is inertial isolation rather than dilution.

This paper investigates the inhibitory effects and mechanisms of different powder inhibitors on corn starch explosion flame propagation. The results indicate that ABC powder exhibits the strongest suppression effect, followed by Al(OH)₃ powder and dolomite powder. Increasing the inerting ratio progressively suppresses the flame acceleration characteristics of corn starch explosion. The addition of 25 wt.% ABC powder significantly inhibits flame propagation, reducing the average flame propagation velocity by 83.6% and the maximum propagation velocity by 91.7% compared to the uninhibited condition. Compared to Al(OH)₃ and dolomite powder, ABC powder has a lower initial thermal decomposition temperature, a broader pyrolysis temperature range, and greater endothermic efficiency. The thermophysical properties of the powder inhibitors show good consistency with their explosion suppression effectiveness. The inhibitors generate NH₃, H₂O, SO₂, and N₂, which effectively reduce both the laminar burning velocity and heat release rate of corn starch pyrolysis gases. The competition between H + O₂ = O + OH and H + CH₃(+M) = CH₄(+M) dominates the combustion reactions of pyrolytic gases from corn starch. The CO₂, H₂O, and NH₃ generated by the thermal decomposition of inhibitors do not alter the fundamental reactions governing combustion. However, the generated SO₂ introduces two additional key inhibitory elementary reactions: H + SO₂(+M) = HOSO(+M) and H + O₂(+M) = HO₂(+M).