Charring Rate Research Articles

Enhancing fire performance of glulam beams through thermal treatment, inorganic impregnation, and densification techniques

The present research investigates a novel, environmentally benign modification method for improving the fire performance of Chinese fir that grows quickly and at low density. This wood is known for its susceptibility to burning and rapid loss of load-bearing capacity in fires. After thermal treatment, inorganic impregnation, and densification, Chinese fir was utilized as the fire-exposure surface for glulam beams. Three sides of full-size members were subjected to fire tests lasting 60 and 90 minutes. Considering the gluelines' thermal conductivity, the improved glulam beams' fire performance was thoroughly evaluated using the finite element program ABAQUS. The study found that the composite modification approach enhanced the weight percentage and mass density of the wood laminates by 32.53 % and 67.87 %, respectively. After 60 min of fire exposure, the charring rates on the exposed surface of the members with the modified laminates were 13.5 % and 27.8 % lower than those of standard glulam beams, indicating a considerable improvement in fire resistance. Greater post-fire residual cross-sectional area and improved fire resistance performance were correlated with an increase in the quantity of modified laminates. The composite modified glulam beams showed a noticeable temperature gradient, which was explained by higher density and specific heat capacity and consequently improved overall fire resistance, according to finite element analysis. The corner effect on the glulam beam cross-section became more evident with prolonged heating, while the gluelines had minimal impact on overall heat transfer.

Experimental study to assess the impact of different connection types on the fire resistance of composite concrete-topped CLT slabs

This paper summarizes the results of an experimental study of fire resistance of composite concrete-topped cross-laminated timber (CT-CLT) slabs exposed to fire at their soffit. Six composite CT-CLT slabs and one untopped CLT slab were tested under ISO 834 standard fire exposure while subject to an applied load equal to 20 % of the slab ultimate capacity. Test variables included the type and configuration of shear connection between the topping and CLT. Large bending deflections were observed as the slabs reached their fire resistance. Although the untopped CLT slab exhibited a fire resistance of only 16 min, all CT-CLT exhibited fire resistance greater than 1 h. The improved behavior is attributed to the stiffer CT-CLT behavior. CT-CLT slabs exhibited delamination of the lowermost layer of the CLT following through-layer charring. Observed charring rates were approximately 46 mm/h. Observed charring depths were well-predicted by existing design standard-recommended equations. Importantly, the interface between the concrete topping and CLT remained close to 30 °C and never exceeded 65 °C in any test. This is a promising result for employing adhesive systems to affect composite behavior between the topping and CLT.

Two-Stage Global Biomass Pyrolysis Model for Combustion Applications: Predicting Product Composition with a Focus on Kinetics, Energy, and Mass Balances Consistency

This work presents a comprehensive model for lignocellulosic biomass pyrolysis, addressing kinetics, energy balances, and gas product composition with the aim of its application in wood combustion. The model consists of a two-stage global mechanism in which biomass initially reacts into tar, char, and light gases (non-condensable gases), which is followed by tar reacting into light gases and char. Experimental data from the literature are employed for determining Arrhenius kinetic parameters and key energy parameters, like tar and char heating values and the specific enthalpy of primary and secondary reactions. A methodology is introduced to derive correlations, allowing the model’s application to diverse biomass types. This work introduces several novel approaches. Firstly, a pyrolysis model that determines the composition of light gases by solving mass, species, and energy balances is developed, limiting the use of correlations from the literature only for tar and char elemental composition. The mass rate of light gases, tar, and char being produced is also determined. Secondly, kinetic parameters for primary and secondary reactions are determined following a Shafizadeh and Chin scheme but with a modified Arrhenius form dependent on Tn, significantly enhancing the accuracy of product composition prediction. Additionally, correlations for the enthalpies of reactions, both primary and secondary, are determined as a function of pyrolysis temperature. Primary reactions exhibit an overall endothermic behavior, while secondary reactions exhibit an overall exothermic behavior. Finally, the model is validated using cases reported in the literature, and results for light gases composition are presented.

Experimental investigation into the effect of transparent fireproof coatings on charring behavior of glued laminated timber exposed to fire

As timber structures evolve towards greater heights and longer spans for buildings, there is a pressing need to enhance the fire resistance of timber structures. Considering the charring behavior of timber is crucial to the fire resistance of timber structures, it is a promising way to retard the charring behavior of timber and further enhance the fire resistance by applying transparent fireproof coatings. In this study, a series of fire tests were conducted to investigate the effect of transparent fireproof coatings on the charring behavior of Douglas fir glued laminated timber (Glulam) under small-scale ISO 834 standard fire conditions. Different coating types, coating quantities, exposed time to fire and member sizes were considered in the experiments. The experimental results including temperature profiles, maximum temperature, and charring rates for uncoated and coated Glulam specimens were carefully recorded and analyzed. Then, the effect of transparent fireproof coatings was quantified by the proposed ratio of delayed charring. The main mechanism of the delayed charring in fire was finally discussed. This study demonstrated that two transparent fireproof coatings can both effectively lower the temperature at different depths and delay the charring behavior of timber. The reduction in charring rates increased with the increase of coating quantity and decreased as the fire exposure time progressed. The ratio of delayed charring for two coatings can be over 30% in the initial stage of fire and over 20% for one-hour standard fire exposure. This study can provide technical support for enhancing the fire resistance of timber structures using transparent coatings.

Correction: Predicting the Average Charring Rate of Mass Timber Using Data-Driven Methods for Structural Calculations

Correction: Predicting the Average Charring Rate of Mass Timber Using Data-Driven Methods for Structural Calculations

The Influence of the Heat Flux of the Infrared Heater on the Charring Rate of Spruce Wood.

The study investigates the determination of selected fire properties of spruce wood, specifically the charring rate, using a modified testing method described and registered at the Industrial Property Office of the Slovak Republic PUV 50121-2020, utility model no. 9373. The samples were exposed to a square ceramic infrared heater, FTE-750W, with a power output of 750 W, using which we determined the heat flux as a function of voltage (V). Spruce wood specimens with dimensions of 75 mm × 75 mm × 50 mm (l × w × h) were subjected to thermal exposure under heat fluxes of 10, 15, 20, and 25 kW∙m-2. The charring rate was evaluated using two distinct approaches: the first method measured the thickness of the char layer formed after a duration of 1800 s, while the second method was based on reaching a temperature threshold of 300 °C. The findings demonstrated a positive correlation between the thermal load and the charring rate. The charring rates obtained using the first method ranged from 0.2397 to 0.6933 mm∙min-1, whereas those derived from the second method varied from 0 to 1.0344 mm∙min-1. This suggests that the 300 °C temperature criterion may not be a reliable parameter for calculating the charring rate. The precision of the results was corroborated through numerical simulations.

Thermal behavior of adhesively bonded timber‐concrete composite slabs subjected to standard fire exposure

AbstractFire tests were performed for the first time on adhesively bonded timber‐concrete composite slabs. The two medium‐scale (1.8 × 1.25 m) slabs were produced by gluing an 80‐mm thick three‐layer cross‐laminated timber (CLT) board to a 50 mm thick prefabricated reinforced concrete (RC) slab with epoxy and polyurethane (PUR) adhesives, respectively. The behavior of the composite slabs under elevated temperature was monitored by (1) observing the burning behavior of the used CLT, for example, charring and delamination and (2) measuring the temperature development at different locations of the CLT slabs, in the adhesive bond between concrete and timber boards, and in RC slabs. It was found that employing a one‐dimensional charring model for pure softwood, as prescribed by Eurocode 5‐1‐2, underestimated the charring depth of CLT due to the delamination effects. Measurements revealed that the average charring rates in the middle layer of CLT panels were approximately 0.65 mm/min, suggesting that the presence of concrete does not significantly affect the thermal behavior of the CLT panel. Delamination within the CLT was observed when its adhesive temperature was around 230°C. It was followed by the free‐fall of delaminated wood plies, which progressed slowly and lasted until the end of the test. At 90 min into the test, the temperatures of epoxy at the nine locations ranged between 55°C and 130°, while that of PUR between 60°C and 100°. The adhesive between concrete and CLT could lose stiffness significantly along the rising of temperature after surpassing of glass transition temperature (58°C for epoxy and 23°C for PUR in this study). The results indicated a high risk of weakening the composite action between the concrete slab and timber board. The measured temperatures of steel rebar were lower than 50°C. However, the concrete temperature reached about 120°C and the concrete cracked due to the distinct thermal expansions between concrete and timber and the rigid constraint of adhesive bond.

Siloxane-containing epoxy resins derived from magnolol with low dielectric properties, excellent toughness, and flame retardancy

The entanglement disorder, highly polar groups and carbon-rich structure of conventional epoxy resins result in high dielectric constants and flammability, posing challenges to the development of high-frequency communications. Therefore, a silicone-containing active ester curing agent (FMAE) derived from magnolol was synthesized via a straightforward two-step process. And a thermosetting resin (FMAE/TGDDM) was then obtained by moisture self-cross-linking as well as curing epoxy N, N, N, N-tetraethoxypropyl-4, 4-diaminodiphenylmethane (TGDDM). The epoxy resin (MAE/TGDDM) cured by MAE that was not undergoing click chemistry was used for comparison. The results showed that the large volume of curing agents (31.86 Å × 14.98 Å × 9.03 Å for FMAE, 16.01 Å × 11.46 Å × 8.09 Å for MAE) and the absence of –OH enabled both resins to have excellent dielectric properties, especially FMAE/TGDDM, with a Dk of 2.78 and a Df of 0.0066 at 10 MHz. Additionally, FMAE/TGDDM demonstrated favorable impact resistance (43.9 kJ/m2) and lower hygroscopicity (0.56%) than MAE/TGDDM, which due to the introduction of siloxane chain (Si% = 7.08%) and the increase of the crosslinking density (2302 mol/cm3 vs 6751 mol/cm3). Furthermore, the charring rate of FMAE/TGDDM was 39.1%, almost twice that of MAE/TGDDM, and the PHHR and THR were 201.2 W/g and 22.6 kJ/g, 103.9% and 67.7% lower than MAE/TGDDM, respectively, proving that the intrinsic flame retardancy of FMAE/TGDDM. Hence, this paper provides a strategy to synergistically address the limitations of TGDDM and conventional epoxy resins for impact resistance, dielectric properties and flame retardancy through a simple structural design.

Experimental investigations on the behaviour of structural-sized wood-CFRP composite beams in local fire

AbstractThe study involved combustion of 24 structural-sized beams under three-point bending subjected to substantial loading prior to ignition, reaching 90% of characteristic load-carrying capacity. A localised fire exposure zone was established proximal to the region experiencing the highest bending moment. The specimens were categorised into two groups: the first consisted of tituted by glued-laminated timber (B), and the second comprised wood-CFRP (carbon fibre reinforced polymer) composite (BW). Initial measurements encompassed pre-ignition static deflection and load. Subsequently, the specimens underwent controlled combustion, during which parameters including burning duration and deflection up to failure, were documented. Following cooling with sand, two cross-sectional slices were extracted from each fractured beam, enabling to find vector-based contours of the remaining cross-section. The charring rate and the approximate heat flux density for each test were determined, enabling a direct comparison of the results. A statistically significant number of specimens was examined, facilitating a comparative analysis between reinforced and unreinforced beams concerning failure time and form. Incorporating CFRP tapes among wooden constituents was found to increase the fire resistance of the structure, however, the thickness of the wooden material enveloping the CFRP composite emerges as a pivotal determinant. This issue needs thorough testing under standard fire in the future. Nevertheless, the fact is that adding CFRP tapes engenders a distinct form of beam collapse, transitioning from instantaneous cracking in B-beams to ductile failure in BW-beams.

Effect of different boundary conditions on the combustion properties and fire characteristics of typical woods

To provide guidance on the bioenergy potential of wood and its fire spread numerical simulation, insights into the combustion properties and fire characteristics of one hardwood (sassafras) and two softwoods (pine and fir) were investigated. The effect of different boundary conditions are focused. The condensed phase decomposition in thermogravimetric analysis indicated that the main degradation processes for all wood combustion could be divided into two stages, and the corresponding demarcation point of conversion rate is 0.4 and 0.35 for hardwood and softwood, respectively. Three specific regions could further be established based on the activation energies variations in Stage Ⅰ. The governing reaction mechanism of sassafras wood is determined to be the diffusion model connect with order-based model, while the reaction mechanism of softwoods (pine and fir) can be considered as the reaction order (1st to three-halves) type followed by diffusion model. The gas phase flaming in FPA combustion experiments suggest that fir and pine wood have a faster charring rate and produce less CO and CO2 during pyrolysis and combustion. Sassafras requires more time to be ignited owing to its high density, which causes higher thermal inertia therefore decelerating the temperature increase on the sample surface. In addition, the dense structure of sassafras leads to an early appearance of the second HRR and MLR peaks. As hardwood has a higher density than softwood, the thermal insulation in hardwood delays char cracking on sassafras wood surface and enhances the duration between ignition and flameout. Such findings should provide guidance for wood combustion modeling and flame spread simulation in future works.

Predicting the Average Charring Rate of Mass Timber Using Data-Driven Methods for Structural Calculations

Predicting the Average Charring Rate of Mass Timber Using Data-Driven Methods for Structural Calculations

Charring of and Chemical Changes in Historical Wood under Thermal Loading

Research in historical timber assessment is hindered by the limited availability of samples, yet understanding the fire resistance of historic wood is crucial for preservation efforts. There is an opinion that historic wood behaves similarly to contemporary wood in terms of fire resistance. The aim of this paper is to observe the rate of charring of historical pine wood during the experiment, the color changes in the sample that occurred due to thermal loading, and the changes in the chemical composition of pine wood. Test samples made from historic pine wood were loaded with a 50 kW∙m−2 radiation panel for 60 min. The charring process was faster at the beginning of the charred layer formation. The charring rate at the beginning of the test at a depth of 10 mm from the exposed side reached values from 1.28 mm∙min−1 to 3.16 mm∙min−1. At a depth of 30 mm from the exposed side, the individual charring rates approached a value of 1 mm∙min−1 (0.99 mm∙min−1 to 1.08 mm∙min−1). Observations during medium-scale testing revealed distinct layers forming on the exposed side: a charred layer, charring base, pyrolysis layer, and intact wood. The chemical composition of the wood changed under the influence of the thermal load. The relative contents of extractives and holocellulose decreased with the increasing temperature while the lignin content increased. The highest value of combustion heat was measured in the charred layer of the sample. Correlation analysis demonstrated a negative relationship between the combustion heat and holocellulose, while a positive correlation was found with the lignin content. Chemical changes were also monitored using the FTIR method. These findings provide valuable insights into the behavior of historic pine wood under thermal loading, which is essential for understanding and preserving historical structures.

Large-scale fire experiments in a cross-laminated timber compartment with an adjacent corridor – Partly and fully protected with a water sprinkler system

Two fire experiments have been conducted to study sprinkler system extinguishing performance in a compartment (13 m2) with an adjacent corridor (12 m2), both with exposed cross-laminated timber (CLT). Four nozzles were installed in the corridor and two in the compartment. In Experiment 1, the sprinkler system was fully functional and successfully controlled a concealed fire. In Experiment 2, nozzles in the compartment were disconnected, while the corridor nozzles were operative, giving flashover after 5 min with large flames emerging into the corridor, rapidly worsening evacuation conditions. Despite four activated nozzles in the corridor, the temperatures remained high, and flames spread through the corridor along the CLT ceiling and the upper parts of the wall, an area that was not effectively protected by the nozzles. After flashover, the compartment temperatures remained stable at ∼1000 °C until experiment termination at 96 min. This continued fire in the compartment can be explained by water from the corridor sprinklers not reaching this area, extensive radiative feedback by the CLT surfaces and delamination of CLT elements of the 20 mm layers. The charring rate was ≥1.1 mm/min for large parts of the exposed CLT wall and ceiling in the compartment during the fire.

Theoretical model of the three - Stage parameter fire curve considering the contribution of combustible materials

Fire resistance is a critical factor constraining structural safety performance, specifically for Cross Laminated Timber (CLT) structures. Due to wood being a combustible material, the exposed wood will participate in combustion, increasing the fire load density and char rates, thereby causing more severe fire risks. In order to investigate the effect of exposed wood on fire temperature, this paper summarized 32 char rate data from 11 CLT room fire tests and fitted the relationship between wood exposure area and char rate, establishes a theoretical formula for the proportion of fire load burned outside the room to the total fire load, and it also establishes a theoretical formula for the three-stage parameter fire curve, which considers the contribution of combustible materials to fire load and char rate, as well as the transition from ventilation controlled to fuel controlled during the cooling stage of the fire. The accuracy of the three-stage parameter fire curve was verified through comparison with test results. Sensitivity analysis was conducted on the main parameters that affect the three-stage parameter fire curve. The results showed that the degree of influence of each factor on the maximum temperature of the fire and the time to reach the maximum temperature was as follows: fire load density > vent height > vent width > wood exposure area.

Preparation of ablation-resistant ethylene propylene trioxide/polyimide staple fiber composite insulation layer by solution wet mixing process

This research developed a solution wet mixing process for creating Ethylene propylene diene monomer/polyimide staple fiber composites (EPDM/PISF), overcoming the uneven fiber distribution seen in traditional dry mixing techniques. By uniformly dispersing PISF within the EPDM matrix, the wet mixing process improves the composite's performance. This is evidenced by an 18.08 % reduction in ΔG′, a 14.29 % lower linear ablation rate (0.042 mm/s), enhanced thermal stability, a higher charring rate, and a denser carbonized layer. Optimal overall performance was achieved using a PISF content of 10phr in the wet mixing process. This advancement significantly enhances the ablation resistance of EPDM/PIS, making them a promising choice for high-performance and durable insulation in solid rocket motors.

An Analysis of the Fire Performance of Small-Scale Canadian Heritage Hardwood and Softwood

A common consideration in the rehabilitation of historic timber structures is addressing the concerns for fire safety. Heritage structures can have softwoods but depending on the time they were built they may also have hardwoods present. Currently, there is a lack of knowledge on the char rate of heritage hardwood and softwood. This study presents initial findings into the charring of these historic materials as they would be encountered in practice through samples taken from pre-existing aged timber structures in Canada that are greater than 100 years old. The materials were tested in a cone calorimeter following a modified ASTM 1354 procedure. Hardwood samples typically exhibited a faster charring rate than the softwoods but the charring rates converged at 1.05 mm/min when exposed to higher fluxes of 50 kW/m2. As rehabilitation and readaptation may require performance-based approaches such as structural fire modelling, a provisional framework for a numerical model using LS DYNA for historic timber members is presented. The objective is to identify future research and testing areas to develop a higher certainty model. In the a-priori model presented, results showed conservative charring rate results with charring trends seen in the experiment generally being followed.

Decoupling the Ca release characteristics induced by O-containing functional groups during volatile-char interaction based on model compounds

Alkali metals and alkaline earth metals (AAEM) are important factors to be considered in coal gasification process, and understanding the release behavior of AAEM under the interaction of volatile-char is the key to realize efficient thermal conversion of coal. In this study, four typical O-containing functional groups (—COOH,—OH, CO,—OCH3) were used to react with coal char in a fixed-bed reactor, the reaction temperature was set up at 750，800，850，900 ℃ to survey the release characteristics of Ca by different oxygen functional groups during the interaction of volatile-char at different temperatures from a quantitative point of view. The result show that the Ca release rate of coal char is not high in the whole reaction temperature range, and the interaction of O-containing compounds-coal char at lower temperature will increase the O content (C—O and CO) of coal char, the content of Ca in interactive coal chars was higher than that of the coal char. At lower temperature, the order of compounds inhibiting Ca release ability is: C6H5CHO≈C6H5COOH > C10H8O2 > C6H5OCH3. In addition, it also seems that O-containing compounds (except C6H5COOH) can obviously promote the conversion of ammonium acetate-soluble Ca to water-soluble Ca during the interaction with char. As the temperature increases, the change trend of O-containing functional groups on the surface of sample after interaction is completely opposite to that at lower temperature, the O-containing model compounds undergo de-oxidation, cracking and polymerization in the effect of coal char and AAEM, causing the formation of polycyclic aromatic hydrocarbon on the surface of the char, which hinders the diffusion of Ca from the char to the gas phase. This work is good for enriching and developing the study on the release characteristics of alkali earth metals during the interaction of volatile-char, and provides a theoretical basis for the development of related industries.

Enhancing fire resistance of glulam columns with modified laminas via resin impregnation and compression

Wood's vulnerability to combustion compromises its structural integrity during fire incidents, primarily due to a decrease in effective cross-section area. This study investigates the efficacy of impregnation Chinese fir lumbers with a 30 % concentration of borate-containing phenol–formaldehyde resin, coupled with a 30 % compression treatment, employed as exposed side laminas for glulam columns. Full-scale glulam columns underwent one-sided fire exposure to assess the impact of the modified laminas. Results reveal a significant increase in column ignition time by 55–195 s, due to the combined treatment. The charring rate of columns containing a single modified lamina in the fire-side zone decreased from 0.733 to 0.552 mm/min after 60 min of fire exposure and further reduced from 0.503 to 0.351 mm/min after 120 min fire exposure for double modified laminas. Compared to the control, glulam columns containing a single modified lamina showcased a 31 % increase in residual bearing capacity at 60 min fire exposure duration and a 62.1 % increase at 120 min with double modified laminas. ABAQUS simulation results corroborated experimental findings, highlighting substantial enhancement in fire resistance achieved due to the modified laminas in the fire-side zone.

Full-Scale Fire Experiments on Cross-Laminated Timber Residential Enclosures Featuring Different Lining Protection Configurations

AbstractThe adoption of timber, specifically cross-laminated timber (CLT), as a primary construction material is gaining traction due to its carbon sequestration capabilities, environmental advantages, and potential for precision manufacturing. However, the combustibility of wood raises legitimate concerns about fire safety in timber-based residential buildings. This paper investigates the fire performance of timber in a residential context, attempting to fill knowledge gaps and outline strategies for improving fire robustness in timber-built dwellings. Through comprehensive experimental studies on residential-type enclosures constructed with CLT panels, this research explores different configurations and the effects of varying degrees of non-combustible protective lining. The findings underscore the significance of considering timber surface exposure and adopting effective encapsulation strategies in CLT buildings. It has been estimated that the exposure of timber walls leads to a proportional increase in heat release rate, corresponding to the area of exposed timber surfaces and their charring rates. Consequently, the external flame has a larger projection, resulting in a much greater heat flux to the façade. Furthermore, threshold conditions for initial flaming self-extinguishment of timber defined in literature of 44.5 ± 1.2 kW/m2 have been found to be applicable to the experiments conducted in this research. Finally, it has been observed that partial encapsulation, where the protective lining will likely fall off during a fire, may hinder rather than increase the likelihood of self-extinguishment. This work contributes towards a nuanced understanding of fire dynamics in timber structures, offering insights for safer and more effective design strategies for CLT-based construction.

Experimental determination of the charring rate of cross-laminated timber panels

Recent design guides include charring models for cross-laminated plane timber (CLT) members. When the bond line integrity is not maintained, charring is illustrated as a combination of sequenced phases. Significant research has been conducted on the charring behaviour of CLT panels, and the criterion of 300 °C has been an accepted definition for the char front line. The charring rate of a solid wood-based panel is determined by the char depth divided by the time to reach the char depth. In the CLT structure, this method can be applied to the first lamella layer. However, due to the char fall-off, it cannot be directly applied to the lamella layers behind the first layer. In this research, eight fire tests were conducted to investigate how charring rates of different lamella layers can be determined from measured temperatures. An assessment method based on the mean char depth development determined from experimental temperature distributions of CLT panels is introduced. Also, the effects of thermocouple positioning and specimen orientation on the assessment results were analysed. The charring rates determined for both horizontal and vertical specimens align well with the results calculated using the European Charring Model and a post-protection factor k3 of 2.