Fire and Materials最新文献

Fire accidents directly threaten the tunnel operation target that are safe, comfortable, efficient. As a new type of tunnel, the pipes and joints of immersed tube tunnel are difficult to repair and replace, which makes post-fire damage assessment particularly important. In order to efficiently evaluate the damage range of concrete in immersed tube tunnel after fire, this paper establishes the stress calculation model of immersed tube tunnel structure under fire by theoretical analysis and numerical simulation. The stress variation rule of immersed tube structure under fire action is studied. This study found that the fire influence range on the structure can be considered as 60 cm, while the thickness was 25 cm subjected to high fire temperature, and there was a large increase in compressive stress which is in the thickness range of 0–10 cm, and the compressive stress was the largest in deep buried section. The relationship between the damage thickness and the ignition time was applied $�\; ��\; �y�\; �=�\; �a�\; �\ln �\; �x�\; �+�\; �b��$. The study bridges the gap of fire damage assessment of immersed tube tunnel in China and provides powerful scientific and technological support for fire damage assessment and damage maintenance. At the same time, it provides a comparative study for the fire prevention of tunnel structure.

Compartments with ceiling vents find application in commercial buildings, ship cabins and nuclear facilities. Fire development in such compartments is characterised by the accumulation of hot gases at the ceiling level. Flow through the vent is complex in nature, wherein the effects of both buoyancy and pressure-driven flow become important. In the present work, a set of dimensionless groups is developed by the systematic application of the Buckingham Pi theorem for analysing quasi-steady-state fire in a ceiling-vented compartment. The dimensionless groups are then used to develop a procedure for estimating heat release rate (HRR) and heat losses through the compartment boundaries and vent. A sample calculation is presented to show the application of the dimensionless groups. It is shown that heat losses through the compartment boundaries can be estimated without explicit knowledge of the convection and radiation heat transfer coefficients. The overall heat transfer coefficient for heat flow through the solid boundaries of the compartment is obtained as part of the calculation procedure. The estimated HRRs are compared with CFD predictions for heptane and ethanol pool fires in compartments of volume 0.75 and 17 m³ having ceiling vents of different sizes. The results are found to agree within ±20%.

In recent years, wildfires have escalated into a global crisis, with the United States witnessing a particularly alarming increase in both frequency and severity. Wildfires generate substantial amounts of smoke containing a wide range of toxic and carcinogenic substances, posing significant exposure risks to firefighters during suppression operations. While previous studies have explored individual aspects of smoke toxicity, firefighter exposure and the performance of wildland firefighters' personal protective clothing (PPC), comprehensive reviews integrating toxicological insights with PPC material-specific factors are notably lacking. This review critically examines the exposure risks of wildland firefighters to smoke particles and their toxic components, including polycyclic aromatic hydrocarbons (PAHs), which are generated from the incomplete combustion of biomass during wildfires. A significant public health concern arises from the elevated cancer risk among wildland firefighters, attributed to their recurrent exposure to these hazardous substances during fire suppression activities. An analysis of potential carcinogenic exposure pathways reveals that dermal absorption plays a predominant role, with PAHs and other substances accumulating on and penetrating protective gear. Furthermore, the factors affecting the efficacy of firefighter protective clothing in mitigating carcinogenic exposure are evaluated. The filtration efficiency of toxic particles correlates with the pore size of the fabric, while the accumulation of these particles is affected by the surface texture. The findings of this study underscore the critical need to optimize the properties of the materials and to develop advanced fabrics with self-cleaning or decontaminating surfaces to reduce exposure to hazardous substances during wildfire response efforts.

Concrete structures are inevitably exposed to fire, and the resulting waste is typically recycled in the same manner as ordinary concrete debris. Therefore, evaluating the performance of post-fire concrete waste and its derived materials is essential for promoting the broader use of recycled aggregates. In this study, intact concrete specimens were heated to 600°C, 800°C, and 1000°C to simulate the fire damage. The fire-exposed concrete was crushed into fine aggregates and incorporated into cement mortar to evaluate their effects on drying shrinkage and mechanical strength. The results indicated that the drying shrinkage of the mortar increased to different extents, depending on the replacement ratio and heating temperature of the recycled fine aggregates. Meanwhile, the loss of mechanical strength increased with higher replacement ratios and heating temperatures. Overall, this study provided evaluations of post-fire concrete waste for engineering applications, contributing to sustainable construction material management.

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.