Fire and Materials最新文献

This study explores the forensic potential of thermal damage traces on clothing fibers to identify arsonist. Seven common fiber materials, including cotton, linen, wool, silk, PET, nylon, and/or their blended fabrics, were picked and their thermal properties were analyzed first. A cone calorimeter, the internationally recognized standard heat resource, was applied to simulate transient high-temperature conditions similar to those in arson cases. Thermogravimetric analysis revealed that silk (270°C), wool (280°C) and cotton (280°C) entered the thermal decomposition stage first, followed by cotton–linen blends (320°C), with the synthetic fibers PET and nylon decomposed from 370°C and 400°C, respectively. Up to 450°C, all fabrics have experienced a mass loss over 50%. Macroscopic and microscopic observations (scanning electron microscopy (SEM)) showed that distinct thermal damage characteristics formed on each kind of fabrics after heating. Cotton fabric began to discolor at around 280°C, with cotton fiber presenting rupture traces due to thermal decomposition observed at 320°C. Similarly, cotton–linen fabric exhibited discoloration at around 320°C, with fiber ruptured due to thermal decomposition at 340°C. Silk fabric began to discolor at around 225°C, with carbonization traces detected by both macroscopically and SEM after heating at 310°C. Wool fabric showed discoloration and shrinkage at about 320°C, with fiber curling, cracking, wrinkling, and expansion observed microscopically. Polyester and polyester–cotton fabrics exhibited wrinkling and shrinkage at around 175°C, with fiber melting at 225°C distinguished microscopically. Nylon fabric showed wrinkling and shrinkage at around 225°C, with fiber melting observed via SEM. This analysis on thermal damage traces offers crucial forensic evidence to determine suspects' proximity to fire, aiding in arson investigations.

Engineered wood structures are widely used in modern buildings, for example, glued laminated timber, cross-laminated timber, finger-jointed solid wood, laminated veneer lumber, and so forth. These products often contain bond lines between the lamellae and/or within the lamellae. The most common types of bond lines are face bonding, finger joints, and edge bonding. The type of bond line can impact the behaviour of engineered wood in fire. At ambient temperatures, the bond line integrity is usually maintained; however, at elevated temperatures or in fire, the bond lines can lose their integrity. The new Eurocode 5 for fire design of timber structures will contain different design scenarios and parameters depending on the behaviour of adhesives at elevated temperatures. This paper aims to support the development of the new Eurocode 5. The bond line integrity was tested with 10 adhesives using two cone heater test methods and furnace tests with glulam. All specimens were made with softwood. Loaded finger-jointed specimens and unloaded face-bonded specimens were tested under the cone heater. Unloaded glued laminated timber specimens were tested in a model-scale furnace. The results are analysed and compared. Generally, a good correlation between the different types of tests was seen. The same adhesives tested in various experiments showed similar performance levels. Adhesive families may have different performances depending on various factors. To assess the adhesives and choose the appropriate calculation method, test methods for assessing the adhesives with cone heater are analysed, compared to fire test results, and proposed in this paper.

Although concrete is non-combustible, it experiences a decline in mechanical properties when exposed to high temperatures. This study investigates the impact of varying temperatures (T) and constant exposure durations (H) on the mechanical performance degradation of coral aggregate concrete. Coral seawater sea sand concrete (CSSC) was produced using equal proportions of coral aggregates, seawater, sea sand, and P•O 42.5 cement. The compressive failure characteristics of CSSC were analyzed under different T and H conditions. To characterize the mechanical properties, compressive tests were conducted on 30 sets of 150 × 150 × 150 mm cubic specimens. The resulting stress–strain curves were used to determine the influence of T and H. The results indicate that the compressive strength (f _cu ^T ) and elastic modulus (E ₀) of CSSC decrease with increasing temperature. At T = 800°C, the f _cu ^T of CSSC is reduced to 27.8% of its original value at 25°C, while the E ₀ decreases to 9.7%. Additionally, the mass loss rate (I _w ) and volume expansion rate (R _s ) increase with rising temperature. At T = 800°C, the I _w reaches 12%, and the R _s reaches 7.1%. Finally, the stress–strain constitutive model of concrete after high temperature was fitted to the experimental data.

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.