Fire and Materials最新文献

Concrete spalling is a thermo-mechanical instability induced by fire exposure that needs to be investigated when the fire behavior of specific structures is to be assessed. In Europe, experimental fire behavior is commonly assessed by reference to EN 1363-1 “Fire resistance tests – Part 1: General requirements.” According to this standard, conditioning at 23°C, 50% RH for at least 3 months should be applied for concrete elements but it is also specified that at the time of the test the strength and the moisture content of the test specimen shall approximate to those expected in normal service and the test specimen shall preferably not be tested until it has reached an equilibrium moisture content resulting from storage in an ambient atmosphere of 50% relative humidity at 23°C. In this context, the main objective of this work is to study the impact of drying duration and conditions on (i) the spalling profiles of different concrete and (ii) the associated moisture profiles. An accelerated drying protocol is proposed based on an extensive experimental campaign and a numerical drying kinetics study on two high-performance concretes, and two ordinary concretes. The accelerated drying protocol aims (i) to propose a protocol allowing to reproduce of the hydric state of concrete structures in service condition (2 years) while ensuring the reproducibility of the spalling facies and secondarily (ii) to explore the possibility to reduce the conditioning time usually used in standard conditions (3 months) while maintaining acceptable representativity. The fire behavior of mechanically loaded and non-loaded slabs was evaluated at various times and conditioning modes. The important influence of the moisture gradient and the moisture content on spalling are highlighted. A good representativity of the proposed accelerated drying protocol is also observed.

Geopolymer concrete (GPC) is a novel and sustainable building material that tends to be more brittle than that of conventional concrete (CC). As such, exposure to fire makes the GPC even more brittle. Fortunately, this brittleness can be reduced by adding fibers, which improves its homogeneity and shear strength in the interfacial region. The present work investigates the influence of high temperatures on the interfacial shear strength of fiber-reinforced GPC (FGPC) and hybrid GPC (HGPC) using shear (push-off) samples exposed to the ISO 834 fire curve. The GPC is developed using two alkaline binders at a 10 M NaOH concentration. A total of six types of mix proportions were used: normal GPC mix without fibers, FGPC mix with basalt fiber (BF), crimped steel fiber (SF) and polypropylene fiber (PF), and HGPC mixes with a combination of SF and BF and with a combination of SF and PF. After 30 and 60 min of heating, the highest residual compressive strength (CS) and residual shear strength (SS) are observed for specimens with BF, and lower residual CS and SS are observed for GPC-PF and GPC mixes. After 90 and 120 min of heating, the BF and SF + BF exhibited almost similar residual CS and residual SS, whereas the PF had the least residual compressive and residual shear strengths.

The Brazilian Amazon Rainforest is home to a vast number of fauna and flora species and plays a crucial role in mitigating the effects of global climate change. Despite its importance, the biome has been severely impacted by wildfires for years. Fuels are the most critical element in wildfire management, and leaves are the combustible particles present in all potential layers of fire spread. This paper presents the flammability evaluation of oven-dried live leaves from 24 native tree species of the Brazilian Amazon Ombrophilous Dense Forest, using the mass-loss cone calorimeter (MLCC) at 50 kW/m². Additionally, through hierarchical clustering analysis, species were grouped into five flammability clusters. The interquartile range (IQR) of the cone calorimeter parameters—PHRR, THR, and TPHRR—was the difference between 67.90 and 61.03 kW/m²; 5.93 and 5.50 MJ/m²; and 33.67 and 29.58 s, respectively, showing a smaller variation than that reported in live leaf cone calorimeter test literature (both dry and fresh). A clear distinction was also observed between palms and other species with compound leaves. While palms—Leopoldinia piassaba, Oenocarpus bacaba, and Phytelephas macrocarpa—were classified into the flammable, highly flammable, and Extremely Flammable groups, respectively, other species with compound leaves were grouped into the low flammable (Pentaclethra macroloba) and very low flammable groups (Anadenanthera colubrina and Parkia pendula). Finally, the results have the potential to improve predictions of Brazilian Amazon wildfire behavior and inform the selection of less flammable species for green belts or reforestation projects.

The development of technology and newer requirements for materials leads to an increase in their production and storage. In the past, serious fires have occurred in public buildings, residential buildings, industrial halls, and warehouses where plastics were used or produced, resulting in disastrous consequences for the environment and human health. For this reason, it is important to examine the risks to people and the environment that arise during a fire in places where these materials are located and stored. Polyurethane foams (PUF) used in building insulation and the automotive industry have been analyzed to determine their flammability and smoke emission during combustion. The thermal stability of PUFs was assessed using simultaneous thermal analysis (STA). Released gases were identified using STA combined with FT-IR (STA/FT-IR). Fire resistance and smoke emission during combustion were evaluated using cone calorimetry and a smoke chamber. Differences in thermal decomposition and combustion characteristics, including smoke release, were observed. The combustion of semi-rigid foam was accompanied by the lowest total smoke release and the lowest total heat release. However, the combustion of flexible foam was characterized by the highest amount of smoke and a high rate of heat release, despite only a 5% weight loss at the highest temperature. In the case of rigid foam, a large residue in the form of a carbonized layer was observed.

For the safety of workers in the oil and gas field, flame-resistant clothing is recommended to reduce the risks of skin burns and fatalities resulting from heat and fire hazards. However, flame-resistant fabrics (FRFs) contaminated with flammable substances can compromise their flammability and heat transfer properties. Therefore, this study aims to evaluate the heat transfer performance (HTP) of the contaminated FRFs to improve workers' safety from burn injuries by understanding how contamination affects fabric thermal protection. The HTP in terms of second-degree burn time was evaluated and characterized by exposing the fabrics to 84 kW/m² mixed convective and radiant heat flux. The peak temperature and average heat release rate of the FRFs were also evaluated. Two levels of contamination, consisting of drilling mud and crude oil, were added to three FRFs: Meta-aramid/cotton, meta-aramid/para-aramid, and para-aramid/polybenzimidazole. The HTP of drilling mud-contaminated fabrics increased, while the HTP of crude oil-contaminated fabrics varied by fabric type and contamination level. This may be attributed to drilling mud's higher specific heat capacity and lower flammability than crude oil. Among the fabrics tested, meta-aramid/cotton fabric showed the best HTP with higher second-degree burn times of 9.63 s with drilling mud and 9.07 s with crude oil. The relationship among contamination level, fabric properties, and HTP was developed using a multiple linear regression statistical model. The fabric's properties, such as fabric weight and air permeability, significantly contributed to the HTP of the contaminated fabrics.