Fire Resistance Research Articles

Foam Stabilization Process for Nano-Al2O3 and Its Effect on Mechanical Properties of Foamed Concrete.

Foamed concrete is increasingly utilized in engineering due to its light weight, excellent thermal insulation, fire resistance, etc. However, its low strength has always been the most crucial factor limiting its large-scale application. This study introduced an innovative method to enhance the strength of foamed concrete by using nano-Al2O3 (NA) as a foam stabilizer. NA was introduced into a foaming agent containing sodium dodecyl sulfate (SDS) and hydroxypropyl methylcellulose (HPMC) to prepare a highly stable foam. This approach significantly improved the foam stability and the strength of foamed concrete. Its drainage volume, settlement distance, microstructure, and stabilizing action were investigated, along with the strength, microstructure, and hydration products of foamed concrete. The presence of NA effectively reduced the drainage volume and settlement distance of the foam. NA is distributed at the gas-liquid interface and within the liquid film to play a hindering role, increasing the thickness of the liquid film, delaying the liquid discharge rate from the liquid film, and hindering bubble aggregation, thereby enhancing foam stability. Additionally, due to the stabilizing effect of NA on the foam, the precast foam forms a fine and uniform pore structure in the hardened foamed concrete. At 28 d, the compressive strength of FC0 (0% NAs in foam) is 2.18 MPa, while that of FC3 (0.18% NAs in foam) is 3.90 MPa, increased by 79%. The reason for this is that NA promotes the formation of AFt, and its secondary hydration leads to the continuous consumption of Ca(OH)2, resulting in a more complete hydration reaction. This study presents a novel method for significantly improving the performance of foamed concrete by incorporating NA.

Safety research of textile materials with flame retardant properties

This article discusses the findings of a study that explored the use of new compositions containing tetraethoxysilane, sodium dihydrogen phosphate, and hexamethylenediamine to improve the flame retardancy of cellulose fiber materials. The impact of different components and temperatures on the fire-resistant properties of the fabric was examined. In an untreated sample measuring 17*22 cm, ignition occurred in 15 seconds and the fabric burned completely within 60 seconds, whereas a treated sample showed signs of retardation. Increasing the concentration of flame retardant impregnation at a temperature of 150 degrees had minimal effects on the material's strength, air permeability, and appearance. With the help of electron scanning device it was found that on the surface of the fibers of the treated sample morphological changes were observed in the form of film, which in turn contain particles of Si (25.48%), P (17.61%), Na (1.70%). The optimum conditions of fabric processing are determined, the influence of concentration of working solution, impregnation and thermofixation temperature on flame retardant properties of fabrics investigated, also processing can be carried out on standard equipment of finishing enterprises and laboratories. Cotton materials treated with a compound based on tetraethoxysilane, sodium dihydrophosphate and hexamethylenediamine provides adequate fire resistance.

A new strategy for developing a Nb microalloyed fire-resistant steel: Effects of boron and cooling rate

This study investigates the correlation among cooling rates, boron addition, and their subsequent effects on the microstructure and mechanical properties of niobium microalloyed steels, specifically with an intent to develop new fire-resistant steels. Slower cooling rates enhanced the ferrite transformation and (Nb,Ti)C precipitation, promoting a shift toward an equilibrium-phase microstructure. A boron addition of 30 ppm was sufficient to increase the fire resistance of niobium microalloyed steels when slowly cooled after thermocontrolled rolling. At rapid cooling rate boron induced the formation of upper bainite. Boron is mainly segregated at the interface of (Nb,Ti)C precipitates, possibly hindering the coarsening kinetics of nanosized carbides and contributing to the maintenance of a high yield strength during fire exposure simulations. The boron addition promoted a ratio between yield strength at 600 °C and room temperature greater than 66%., boron also shifted the strain-temperature curve to higher temperatures in transient tensile tests. These findings contribute to the potential use of boron additions in advancing cost-effective, high-performance, fire-resistant steel development, highlighting the central role of microstructural control and optimized thermomechanical treatment.

Synthesis and optimization of GO/TiO2@n-octadecane microcapsules for thermal management of smartphone charging

To reduce the charging temperature of smartphones effectively, the GO/TiO2@n-octadecane microcapsules were prepared in this study. Various testing methods were used to analyze the thermal performance of microcapsules. To achieve maximum enthalpy of phase change, various preparation conditions for the preparation process were optimized. The GO was doped into the optimized microencapsulated phase change materials for further analysis. Moreover, the GO/TiO2@n-octadecane microcapsules were used for the thermal management of smartphone charging. GO was attached to the surface of microcapsules, enhancing the thermal conductivity. Microcapsules were physically encapsulated without any chemical reactions. The enthalpies of microcapsules decreased with the proportion of GO, while the thermal conductivity increased. The prepared GO/TiO2@n-octadecane microcapsules had excellent thermal cycling stability and fire resistance. The GO could reduce the mass loss of microcapsules in high temperatures. Microencapsulated phase change materials containing 0 wt%, 1 wt%, 2 wt%, and 3 wt% GO had an excellent ability to reduce the charging temperature of smartphones, which could reduce the peak charging temperature of smartphones by 2.9, 3.1, 2.7, and 2.5 ℃, respectively. Microcapsules containing 1 wt% GO had a large enthalpy of phase transition and high thermal conductivity, which could most effectively reduce the peak charging temperature of the smartphone. Therefore, microcapsules with 1 wt% GO were the optimal microcapsules for the thermal management of smartphone charging.

The Uses of Lightweight Material in Civil Engineering : A Review

A lightweight aggregate (LWA) is a group of aggregates with a relative density lower than normal density aggregates (natural sand, gravel, and crushed stone), sometimes referred to as low density aggregate. It is utilized for its reduced weight and exceptional qualities in sound reduction, fire resistance, insulation, and geotechnical applications LWA, or lightweight aggregate, is a cutting-edge construction material that is employed to decrease the overall weight of tall structures. Despite being lighter, it possesses a strength that is comparable to that of regular concrete. In recent times, there has been a significant surge in the use of lightweight aggregate in the field of building, mostly because of its exceptional performance in seismic situations. In addition, substituting natural aggregate with other industrial by-products and trash enables us to minimize the adverse environmental consequences. Laser wavelength ablation (LWA) has also been employed to address a wide range of geotechnical engineering challenges, including the transformation of soft and unstable soil into a suitable and usable property. Lightweight fillings have a weight that is around 50% less than fills made using typical materials. The load reduction, along with the high internal friction angle of the lightweight aggregate, can decrease vertical and lateral pressures by almost 50%, potentially resulting in less settling. This literature study examines the use of lightweight materials, including LECA, Bonza, and Thermostone, in geotechnical engineering applications. The results demonstrate a significant emphasis on improving slope stability and minimizing stresses on susceptible soils. Nevertheless, several knowledge gaps exist regarding the efficacy of these materials under challenging conditions and when subjected to dynamic loads. A growing inclination towards using these lightweight aggregates is observed because of their advantageous environmental and mechanical properties. Further investigation is needed to examine the extended-term performance and interactions of these materials with different soil types in order to enhance their performance in diverse geotechnical situations.

Protein-tannin interactions towards fabricating flame-retardant, UV-resistance, antibacterial and mechanical-reinforced PA66 fabric

The “Protein-polyphenol interactions” is a hot research topic in the field of interaction between biological macromolecules. Strong interactions between biomass polyphenolic tannins and proteins can be generated through covalent and non-covalent bonds. Inspired by this, keratin (Ker) and oxidized tannin (TA) was co-deposited on polyamide 66 (PA66) fabric to fabricate OTA/Ker coated PA66 fabric (PA66@OTA/Ker), which was then chelated with Fe3+ to prepare fire resistance and anti-dripping PA66 fabric (PA66@OTA/Ker@Fe). The results showed that the total heat release rate (THR), peak heat release rate (pHRR) and total smoke production (TSP) of PA66@OTA/Ker@Fe were reduced by 51 %, 57 % and 52 %, respectively. PA66@OTA/Ker@Fe had a residue char of 21.6 % at 800 °C under N2 atmosphere. In addition, the LOI of PA66@OTA/Ker@Fe increased from 20.5 % of the control sample to 28.5 % and reached a UL-94 V-0 rating. Besides, PA66@OTA/Ker@Fe exhibited excellent UV resistance, good mechanical and anti-bacterial properties. This work provides an eco-friendly strategy for developing multifunctional PA66 fabrics.

Tri-source integrated adenosine triphosphate complexed copper ions anchored to boron nitride surfaces for enhancing flame protection of waterborne epoxy coatings

The abundant C, P, and N elements in the structure of adenosine triphosphate (ATP) can act as carbon, acid, and gas sources, and thus can be used as an efficient intumescent flame retardant. Here, a layer of polydopamine (PDA) with polyhydroxyl groups was firstly loaded on the surface of BN to provide a bridging effect for the surface modification of BN. Then, ATP-Cu was immobilized on the BN surface by complexation of ATP with Cu2+, resulting in an efficient inorganic-organic-metal composite flame retardant (BNP@ATP-Cu). This composite flame retardant effectively combined the high barrier effect of BN, the high swelling property of ATP and the catalytic carbon formation activity of Cu2+. The experimental results revealed that the EP loaded with BNP@ATP-Cu showed the lowest backside temperature (171.2 °C), indicating the highest thermal barrier effect. Moreover, BNP@ATP-Cu/EP exhibited the most significant swelling characteristics (22.7 mm, 17.46) and smoke suppression effect (42.8 %). In contrast, the carbon residue of BNP@ATP-Cu/EP (30.8 %) was significantly higher than that of the other coated samples, which was related to the combined effect of BN and ATP-Cu. The above relevant results fully demonstrated the effectiveness of the composite flame retardants in improving the fire resistance of epoxy coatings.

Experimental study on combustion characteristics of engineered bamboo considering smoldering and self-extinction

Bamboo and wood materials have the characteristics of low carbon and high strength, making them the best building material for building green buildings. Compared to traditional building materials, the easy to burn characteristic has become an obstacle to the promotion and widespread application of bamboo and wood materials, so it is urgent to study their combustion characteristics. This article investigated the combustion characteristics of engineered bamboo at different heat fluxes, taking into account the smoldering and self-extinction characteristics through cone calorimeter experiments. The combustion performance, mass loss rate, heat release rate, etc. were studied, and the self-extinction phenomenon of the specimens was explored. The results indicated that the direction of heating had a certain impact on the combustion characteristics of glued laminated bamboo (LBL), and the fire resistance of parallel strand bamboo (PSB) was better than that of LBL. When the heat flux exceeded 50 kW/m2, the color of the flame on the surface of the specimen would change from bright yellow to strong orange, which is an important sign that the flame will self-extinguish. The self-extinction of flames at different heat fluxes was caused by insufficient supply of combustible gas generated by bamboo pyrolysis, with slightly different specific reasons. The multi-layer structure of glued laminated bamboo also makes it more difficult to self-extinguish than PSB, cross-laminated timber (CLT), and solid wood is the most prone to self-extinguish. The impact of adhesive layer delamination was not considered in this experiment, and further research is needed.

A comparative study between ultra-high-performance concrete structures and normal strength concrete structures exposed to fire

The use of ultra-high-performance concrete (UHPC) in civil infrastructure is increasing due to its numerous advantages compared to normal strength concrete (NSC). In this research, thermal analysis of NSC and UHPC beams and columns was developed to understand and compare the fire performance of these structures. A numerical analysis was performed using finite element (FE) modeling with ABAQUS software. Compared to NSC, UHPC structures in some cases have lower fire resistance due to their slender cross-sections and unfavorable thermal properties and mechanical capacity degradation due to temperature effect. The results show that UHPC structures experience significantly higher cross-sectional temperatures when exposed to fire compared to NSC. The results are particularly relevant for high-rise buildings, where fire safety requirements are more stringent and the use of UHPC is attractive, leading to an unprecedented contradiction. Alternative strategies for the application of UHPC, such as the contradictory increases in cross-section or the use of fire protection coatings, must be considered. In some cases, NSC may be more attractive as a structural material than UHPC if structural fire design requirements are taken into account.

Fire Resistance Performance of Constrained H-Shaped Steel Columns with Uneven Vertical Temperature Distributions

Steel columns, which are widely used in building frameworks and spatial structures, are susceptible to capacity degradation during fires, potentially leading to the overall collapse of buildings. Existing research on the fire resistance of steel columns assumes that the temperature loads encountered by steel columns are evenly distributed vertically. However, real-world fire scenarios often feature significant vertical temperature differences. Therefore, this study comprehensively investigated these variations to derive a temperature curve that accurately represents real fire conditions. Subsequently, the fire resistance limits of steel columns were studied using this temperature curve, leading to a revised calculation formula for the critical fire resistance temperatures of steel columns. The following conclusions were drawn: (1) Nonuniform longitudinal temperature distributions are influenced by parameters such as the fire source distance, the heights of ventilation openings, and the distance between a vent and the temperature measurement point. Among them, the fire source distance has the greatest impact, with the maximum longitudinal temperature difference reaching over 500 °C. (2) Variations in the load ratio and longitudinal temperature differences alter the failure positions of steel columns, reducing their critical temperatures by up to 200 °C. (3) The revised critical fire resistance temperature formula is more accurate and safer compared with that outlined in the “Technical Code for Fire Protection of Steel Structures” (GB51249-2017). These findings offer valuable insights for the fire designs of steel columns.

Optimal design of a post-demolition autoclaved aerated concrete (AAC) recycling network using a capacitated, multi-period, and multi-stage warehouse location problem

Autoclaved aerated concrete is a popular building material in constructing one- and two-family houses because of its low thermal conductivity and fire resistance. Since autoclaved aerated concrete production rose significantly in the 1960s and 1970s, increasing post-demolition volumes can be expected in the following decades. However, these are currently landfilled as high-quality recycling options are still to be established.This study develops a new capacitated, multi-period, and multi-stage network model for optimising a Germany autoclaved aerated concrete recycling network. The multi-period character of the model enables the precise consideration of increasing post-demolition volumes by constantly allowing the move of recycling plants or opening new ones throughout the planning horizon. Additionally, the multi-stage formulation facilitates incorporating an optional second recycling step, which involves additional effort and higher revenues. The model aims to find a cost-minimised recycling network and identify optimal network transformations until 2050. Results show that recycling is preferred over landfilling. The optimised recycling network uses large recycling plants for economies of scale and opens new plants in the future to handle the expected increase in post-demolition autoclaved aerated concrete. Transport costs account for the largest share of total costs (50%), while fixed costs reach around 40%, and revenues offset approximately 20% of all costs. The total costs of the network reach about 2200 M€ until 2050, which is 4600 M€ (68%) less than without establishing recycling. The results offer new insights into cost-minimal network structures and their future development to encourage decision-makers to promote autoclaved aerated concrete recycling.

Perceptions, Tensions, and Contradictions in Timber Construction: Insights from End-Users in a Chilean Forest City

The study addresses the underutilisation of wood in construction in Chile, particularly given the country’s robust forestry sector. The research investigates perceptions, tensions, and contradictions among end-users regarding timber construction in Valdivia, a city with a mixed forestry industry. Methods included a comprehensive survey of 96 households across various socioeconomic clusters, utilising descriptive and exploratory statistical analyses. Key findings reveal persistent negative perceptions about wood’s durability, fire resistance, and maintenance costs. However, positive aspects, such as lower construction costs and adequate thermal comfort, were also noted. Surprisingly, concerns were raised about wood’s environmental impact, including deforestation and its role in combating climate change, contrasting with the material’s known ecological benefits. The study concludes that these perceptions are deeply influenced by ideological and sociopolitical factors, suggesting that mere marketing strategies may not suffice to alter public opinion. Instead, a collaborative effort involving public policy, industry advancements, and transparent scientific communication is essential to promote the benefits of timber construction and address the entrenched biases.

RESEARCH OF THE DESTRUCTION CONDITIONS OF GLAZING OF ENCLOSING STRUCTURES UNDER THE CONDITIONS OF THERMAL INFLUENCE OF FIRE

The article presents the main results of mathematical modelling of the destruction of glazing of enclosing building structures with translucent elements under fire conditions. The authors analyse literature data on calculating the fire resistance of enclosing building structures with glazing. The results show that improving methods for predicting the fire resistance of glazing is relevant. Mathematical models for the numerical study of the behaviour of glazing under the thermal influence of the standard fire temperature regime are substantiated. Mathematical models of the heat transfer process involve using a non-stationary differential equation of heat conduction with boundary conditions of the third kind, accounting for the convective and radiant heat exchange between the air in the room with the fire and the glazing. As a criterion for the destruction of glazing under the influence of fire, the authors establish the temperature resistance parameter, which is determined based on the mechanical characteristics of the glass. The article highlights the relevant data on the study of temperature indicators and the mechanism of glazing failure, using mathematical modelling with well-founded mathematical models. It obtains the results of the thermal calculation by applying the finite difference method for solving the non-stationary differential equation of thermal conductivity. The methodology for determining the time of glazing failure under the influence of the standard temperature regime of a fire using the calculation parameters obtained based on well-founded mathematical models is substantiated. An analysis of the adequacy of the obtained calculation data was carried out by comparing them with the results of experimental studies using statistical criteria. As a result of the analysis, the authors confirmed the validity of the calculation data. A complete factorial experiment was conducted based on well-founded mathematical models, which revealed the regularities of the dependence of the parameters of thermomechanical processes in single-layer glass on its structural characteristics. The revealed regularities have the form of linear regression dependences of the destruction time on the thickness of the glazing and the maximum length of the glass panel without bars. Using the regularities of the dependence of the parameters of thermomechanical processes in single-layer glazing on its structural characteristics, the authors constructed reference tables for evaluating the fire resistance of enclosing structures with glazing. The research obtained new scientific data on the study of the behaviour of glazing of enclosing building structures under the thermal influence of fire through mathematical modelling, which is the basis for improving the methods of calculating the fire resistance of enclosing structures with translucent elements. Keywords: enclosing building structures, glazing, fire resistance limit, calculation method, glass heat resistance.

Fire-Resistant and Thermal Stability Properties of Fluorosilicone Adhesives by Incorporation of Surface-Modified Aluminum Trihydrate.

Fluorosilicone was combined with aluminum trihydrate (ATH) to induce synergistic flame-retardant and thermal-resistant properties. The surface of ATH was modified with four different silane coupling agents. The flammability and mechanical properties of the fluorosilicone/ATH composites were assessed using an UL94 vertical test and a die shear strength test. The change in shear strength was investigated under aging for 1000 h at -55 °C and 150 °C. Pure fluorosilicone had inherent fire resistance and thus achieved a V-0 rating even at 20 wt.% ATH loading. Upon addition of ATH treated with 3-glycidoxypropyl trimethoxysilane, the composites exhibited the highest shear strength of 3.9 MPa at 23 °C because of the additional crosslinking reaction of fluorosilicone resin with the epoxide functional group of the coupling agent. Regardless of the types of coupling agents, the composites exhibited similar flame retardancy at the same ATH content, with a slight reduction in shear strength at 180 °C and 250 °C. The shear strength of the adhesives gradually decreased with aging time at -55 °C, but increased noticeably from 3.9 MPa to 11.5 MPa when aged at 150 °C due to the occurrence of the additional crosslinking reaction of fluorosilicone.

Sustainable Fire Protection: Reducing Carbon Footprint with Advanced Coating Technologies

Metallum Fire-Resistant paint, denoted as MFR henceforth, represents a cutting-edge insulating material with dual functionality as a fireproof solution, presenting substantial advantages in the realm of construction applications. This exposition derives its primary insights from the scholarly contributions documented in publications. The focal point of these investigations includes the assessment of fire hazards associated with polyethylene materials in building structures and the enhancement of mortars in high-temperature environments in tunnels. The purpose of this study is to evaluate the effectiveness of a modified cork-based coating (MFR) compared to traditional coatings in terms of corrosion protection, fire resistance, and thermal insulation properties in construction applications. This evaluation focuses on quantifying the efficacy of MFR by examining key properties, such as adhesion, the reduced thickness required for fire protection, thermal conductivity reduction, and corrosion resistance under extreme environmental conditions. MFR is highly effective in fire prevention for buildings and tunnels, withstanding temperatures over 1000 °C while maintaining structural integrity. A unique aspect of MFR is its use of cork shavings, a typically underutilized byproduct from wine-bottle-stopper production. This innovative not only amplifies MFR’s fire-resistant attributes, but also introduces sustainability and judicious resource utilization into its manufacturing processes.

ОБЕСПЕЧЕНИЕ ПОЖАРНОЙ БЕЗОПАСНОСТИ МНОГОЭТАЖНЫХ ЗДАНИЙ ИЗ ДЕРЕВЯННЫХ КОНСТРУКЦИЙ

Проведен обзор современного деревянного домостроения в России и за рубежом. Проанализированы результаты испытаний строительных материалов из древесины на пожарную опасность, а также деревянных строительных конструкций различных типов на огнестойкость и пожарную опасность как без огнезащиты, так и с огнезащитой различных видов. Разработаны предложения в нормативные документы. Намечены направления дополнительных исследований пожарной опасности зданий из деревянных конструкций. The paper considers the issues of ensuring fire safety of multi-storey buildings made of timber frame construction. At present, wooden houses in Russia are built mainly in the individual housing sector and account for 22% of the total construction volume, while industrial wooden houses account for no more than 3% of the wooden houses built annually. Abroad, wood is also widely used in the construction of buildings of various functional purposes: hotels, sports facilities, public and administrative buildings, low-rise and multi-storey buildings. The achievements of science, technology and engineering in the field of timber construction make it possible to design and build buildings of any type and purpose. Modern technology makes it possible to build high-rise timber houses. For example, high-strength composite materials based on wood are used for the construction of multi-storey buildings, in particular LVL beams and CLT panels. Numerous tests carried out at VNIIPO on load-bearing elements made of solid wood (frames, beams) and load-bearing structures made of CLT panels (walls, ceilings) have shown that they provide a significant limit of fire resistance in terms of load-bearing capacity. It is well known that wood is a highly flammable material (G4). This circumstance significantly complicates the use of various building structures in construction from the point of view of ensuring fire safety requirements, including in multi-storey buildings. A set of necessary engineering, technical and organisational measures to ensure fire safety has been developed for buildings with wooden structures up to 4 storeys. Based on the results of these tests, there have been developed proposals to include fire technical parameters in the regulatory requirements for buildings of classes I–III of fire resistance and structural fire hazard class C3. Further research is necessary to develop proposals for inclusion in the regulatory documents for fire safety of multi-storey residential and public buildings made of timber structures up to 28 metres in height.

Prospects for the use of Foam Glass Products in the Foundation of Buildings and Structures on Long Term Frozen Soils

The degradation of permafrost is the reason for the increase in deformability of the foundations of buildings and structures built on long term frozen soils. It is necessary to develop geotechnical solutions that guarantee their operational reliability in a warming climate. The introduction of foam glass for use in the cryolithozone as thermal insulation solutions making it possible to preserve the frozen state of the soils of the bases is relevant. This will make it possible to limit the use of materials with lower durability. The existing scope of application of foam glass in Russia and the prospects for the use of foam glass products in the permafrost zone are considered. The high prospects of using foam glass at the base of buildings and structures on permafrost soils are determined by its physico-mechanical and thermos-physical characteristics such as durability, low water absorption and environmental safety. These properties of foam glass make it a promising material for use in the long term frozen soils zone. The main advantages of foam glass in comparison with its analogues are also low sorption capacity and capillary absorbency, high strength, fire resistance and resistance against aggressive media. In the production of foam glass for use in the cryolithozone, it is possible to use alternative local sources of raw materials: aluminosilicate and siliceous rocks. This will reduce the cost of the material, make it more affordable and increase sales volumes.

The Influence of the Addition of Melamine/Boric Acid Salt on the Fire Resistance and Physicomechanical Properties of Polypropylene

The Influence of the Addition of Melamine/Boric Acid Salt on the Fire Resistance and Physicomechanical Properties of Polypropylene

Transient temperature analysis and engineering application of steel shell immersed tunnel protected by fireproof board

Based on the Shenzhen-Zhongshan Link, the transient analytical solution of the steel shell immersed tunnel under the protection of fireproof board was deduced and verified through fire test. Then, the variation of the maximum temperature of the bottom steel shell with the thickness and thermal conductivity of the fireproof board was analyzed and suggestions on the selection of fireproof boards were given. Finally, a fitting formula for the maximum temperature of bottom steel shell was proposed. The results show that: (1) When the thermal contact resistance of the steel-concrete interface and the thermal resistance of cavity are 0.01 m2 °C/W and 0.02 m2 °C/W respectively under the case of 25 mm thick fireproof board, the variation of the analytical solution is consistent with test results, and the peak value is similar. (2) Based on the three-dimensional diagram of d -λ-T, with 300 °C as the fire resistance limit of structure, the range of the fireproof board parameters is obtained: when λ reaches 0.14 and 0.4 respectively, d shall not be less than 10 mm and 28.38 mm (3) The scatter points obtained from analysis were fitted using quadratic polynomials and linear functions respectively. Considering the accuracy and simplicity, the linear fitting formula is given as T = 275.66–7.41*d+644.6*λ.

Redox reaction models for carbonation of hardened cement under elevated temperature up to 1000°C

Concrete structures are exposed to various temperature environments and often come into contact with CO2 under these conditions. With the recent surge in interest in carbonation, there is a growing demand for a numerical model that can more comprehensively and flexibly account for the reactions of hydration, carbonation, decomposition, and recovery of cement hydrates. A comprehensive framework for concrete carbonation is proposed from a wide perspective of temperature with thermo-chemical modeling including de-carbonation and re-carbonation. By overlaying rates of bidirectional redox reactions, the dominant reaction at any temperature can be determined. The model framework, encompassing cement hydration, carbonation, de-hydration, de-carbonation, re-hydration, and re-carbonation, was experimentally validated by previous measurements of changes in weight and porosity under different CO2 concentrations and repeated exposure to high temperatures followed by post-fire-curing. These validations demonstrate a strong connection between the micro- and macroscopic properties of concrete in the proposed model. With this scheme, fire resistance of concrete composite under unexpected cases was explored computationally. Significant weight loss and strength reduction of cement paste are predicted after the first heating cycle, followed by gradual decline in subsequent repetitions of temperature. In the cases with water post-fire-curing, it is observed that the strength tends to restore even with repeated heating. In the cases with RH-60 % vapor post-fire-curing, the strength recovery is significantly increased by re-carbonation, but is still smaller than that of the cases with water post-fire-cuing.