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Article

Mechanism Study on the Influence of High-Temperature Exposure on the Thermal Transfer Characteristics of Explosion-Proof Concrete

by
Qiusha Wang
1,*,
Zhenmin Luo
1,
Wei He
1,* and
Zhixuan Hou
2
1
School of Safety Science and Engineering, Xi’an University of Science and Technology, 58, Yanta Middle Road, Xi’an 710054, China
2
School of Architecture and Civil Engineering, Xi’an University of Science and Technology, 58, Yanta Middle Road, Xi’an 710054, China
*
Authors to whom correspondence should be addressed.
Processes 2025, 13(9), 2712; https://doi.org/10.3390/pr13092712
Submission received: 27 July 2025 / Revised: 20 August 2025 / Accepted: 24 August 2025 / Published: 26 August 2025
(This article belongs to the Section Chemical Processes and Systems)
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Abstract

Concrete used in high-risk infrastructures must withstand elevated temperatures and thermal shocks. This study investigated the thermal transfer behavior of explosion-proof concrete exposed to 100–400 °C through a combined experimental and numerical approach. X-ray diffraction (XRD) revealed that the dominant crystalline phases remained identifiable across this range, but peak broadening and intensity reduction indicated partial decomposition of hydration products and microstructural disorder. Thermal conductivity reached its maximum of 1.48 W/(m·K) at 100 °C and decreased at higher temperatures due to porosity growth and microcracking, reflecting detrimental alterations in heat conduction pathways. In contrast, the specific heat capacity increased from 963.89 J/(kg·K) at 100 °C to 1122.22 J/(kg·K) at 400 °C, enhancing the material’s heat absorption. Density initially decreased with temperature but showed a temporary rebound at 300 °C due to secondary hydration, before dropping sharply to 1830 kg/m3 at 400 °C. Numerical simulations confirmed that high temperatures reduce surface–core temperature gradients, leading to more uniform but structurally weakened heat transfer. These findings highlight that explosion-proof concrete retains acceptable thermal stability below 200 °C, while significant degradation occurs beyond 300 °C. The novelty of this work lies in integrating experimental thermophysical tests with finite element simulations to link microstructural changes with macroscopic thermal behavior. Practically, the results provide guidance for optimizing concrete formulations and protective strategies in fire- and explosion-prone facilities such as LNG storage units and petrochemical infrastructures.

1. Introduction

Concrete is widely recognized as a core material in structural engineering, valued for its high compressive strength, durability, and cost-effectiveness [1,2]. However, in high-risk environments such as petrochemical facilities, liquefied natural gas (LNG) storage units, and industrial infrastructures, structural components are frequently exposed to extreme thermal conditions caused by fire or localized explosions [3]. Under such scenarios, conventional concrete often experiences thermal degradation, explosive spalling, and rapid loss of mechanical integrity, leading to structural failure and significant safety hazards [4,5].
Although numerous studies have investigated the thermal and mechanical behavior of ordinary and fiber-reinforced concretes under elevated temperatures, systematic investigations targeting explosion-proof concrete remain limited [6]. In this study, the term “explosion-proof concrete” specifically refers to a thermally resistant cementitious material designed to withstand rapid heating and fire-induced thermal shocks rather than resistance to mechanical blast pressures. Recent works further emphasize the complex relationship between pore evolution, thermal transfer, and structural degradation [7,8]. Building on these insights, our research integrates experimental thermophysical tests with numerical simulations, aiming to clarify the link between microstructural transformations and macroscopic heat transfer in explosion-proof concrete [9,10,11].
Numerous studies have evaluated the thermal performance of ordinary and fiber-reinforced concretes, often focusing on single parameters such as thermal conductivity, specific heat, or residual strength after high-temperature exposure [12]. Recent studies have further highlighted the complex relationship between pore evolution, heat transfer, and mechanical degradation in concretes subjected to elevated temperatures [13]. Lucio et al. reported a 40% reduction in thermal conductivity in ordinary concrete between 20 °C and 800 °C, mainly due to moisture loss and microcracking [14]. Sun et al. examined fire resistance in cementitious coatings and cable insulation systems, emphasizing ignition prevention rather than the thermal transport behavior of the composite itself [15]. However, only limited research has examined explosion-proof concrete as a distinct category, especially using integrated experimental–numerical methods to explore the coupled evolution of microstructure, thermal transport properties, and density under controlled high-temperature conditions [16].
The present work addresses this gap by investigating the thermal transfer characteristics of explosion-proof concrete in the 100–400 °C range through a coupled methodology combining laboratory testing and finite element simulation [17]. This approach enables the correlation of X-ray diffraction (XRD)-identified mineralogical changes with variations in thermal conductivity, specific heat, and density. Unlike previous studies, this work quantifies the property changes in detail and directly links them to underlying microstructural transformations [18].
Understanding these thermal transfer mechanisms is essential for the engineering design of fire barriers, containment structures, and thermal insulation layers in hazardous industrial environments. The results provide practical data for selecting explosion-proof concretes that optimize thermal protection, structural reliability, and durability under severe thermal exposure.

2. Materials and Experimental Methods

2.1. Materials

The raw materials used in this study for the preparation of explosion-proof concrete were divided into three categories: cementitious binders, aggregates, and functional additives. The primary binder was 42.5R-grade Ordinary Portland Cement (OPC) supplied by Huaxin Cement Co. (Wuhan, China). This cement complies with the national standard GB 175-2007 [19]. This cement exhibits a guaranteed 28-day compressive strength of ≥42.5 MPa, flexural strength of ≥6.5 MPa, initial setting time of >45 min, and final setting time of ≤600 min [20]. Its chemical composition was analyzed using X-ray fluorescence spectroscopy (XRF, PANalytical AxiosMAX, Eindhoven, The Netherlands), and the results are summarized in Table 1. The analysis showed CaO and SiO2 as the dominant oxides, with minor amounts of Al2O3, Fe2O3, MgO, and SO3, along with a loss on ignition (LOI) of 2.35% [21,22]. These features reflect the high calcium content of OPC, which provides the fundamental basis for hydration reactions and strength development in the concrete matrix [23].
To improve the composite performance, two supplementary cementitious materials were incorporated. The first was Class II fly ash obtained from Shandong Puxin Hardware & Mould Co., Ltd. (Jining, China), with a fineness of ≤20% and a LOI of ≤5%. The second was S95-grade ground granulated blast furnace slag (GGBS), supplied by Shanxi Taisheng Chemical Co. (Xixian New Area, China), with a specific surface area of ≥400 m2/kg and a 28-day activity index of no less than 95%. Additionally, steel slag powder and phosphorus slag powder were included as mineral fillers. The chemical compositions of all Supplementary Materials were determined via XRF and are listed in Table 1.
The aggregates consisted of both coarse and fine fractions. The coarse aggregate was continuously graded basalt gravel with a particle size range of 5–20 mm, crushing value of ≤12%, and silt content of ≤0.5%. The fine aggregate was natural river sand with a fineness modulus of 2.6–2.9 and silt content of ≤1.0%. The particle size distribution of both coarse and fine aggregates was measured using a laser particle size analyzer (Mastersizer 2000, Malvern Instruments, Malvern, UK), as shown in Figure 1 [24].
To enhance high-temperature resistance and explosion-proof performance, three types of functional additives were employed. The flame retardant used in this study was hexabromobiphenyl ether (DBDPE), with a bromine content of ≥82% and a decomposition temperature above 320 °C. While DBDPE is more commonly applied in polymer-based systems, its inclusion here is exploratory, aiming to preliminarily evaluate its potential contribution to enhancing fire resistance in cementitious composites [25]. We recognize that the use of DBDPE in concrete raises important concerns regarding long-term compatibility, leaching, and environmental persistence, and therefore, its application should be regarded as experimental. Further studies are required before practical implementation can be recommended.
An ettringite-based expansion agent was added at a dosage of 8–10%, providing a restricted expansion ratio of no less than 0.030% after 7 days of water curing, thus ensuring dimensional stability under thermal exposure. Mineral fillers included limestone powder, steel slag powder, and phosphorus slag powder [26]. The limestone powder had a specific surface area of 450 m2/kg and a CaCO3 content above 90%; the steel slag powder contained free-CaO ≤3% and had an activity index of at least 65%; the phosphorus slag powder contained ≤1.2% P2O5.
These additives had distinct but complementary roles. Steel slag powder acted as a reactive cementitious material that participated in hydration reactions, thereby contributing to long-term strength development. The mineral fillers, by contrast, primarily enhanced particle packing density and reduced porosity through micro-filling effects. The synergy between chemical reactivity and physical modification thus optimized the thermal and mechanical performance of explosion-proof concrete. The macroscopic appearance and microscopic morphology of the raw materials are presented in Figure 1.

2.2. Specimen Preparation and Experimental Design

In accordance with standard specifications for concrete preparation and application, explosion-proof concrete specimens were fabricated using standard molds. The fire- and explosion-resistance of the concrete was regulated by adjusting the dosages of flame retardants and mineral admixtures [27,28,29]. The detailed fabrication process is illustrated in Figure 2.
The mix proportion was designed with a binder-to-aggregate ratio of 1:3, a water-to-binder ratio of 0.32, and partial replacement of cement with 20% fly ash and 15% ground granulated blast furnace slag (by mass). The expansion agent was incorporated at a dosage of 8–10% of the binder mass. Aggregates consisted of 65% coarse basalt gravel (5–20 mm) and 35% natural river sand, ensuring proper grading.
The detailed fabrication process was as follows. First, limestone powder and water were mixed at a mass ratio of 10:3, while water and expansive agent were mixed at a ratio of 15:1 to prepare the limestone suspension and expansion solution, respectively [30]. In a plastic mixing bucket, the dry components (cement, slag powder, fly ash, and aggregates) were blended for 2 min. The expansion solution and approximately two-thirds of the mixing water were then added and mixed for 3 min. Finally, flame retardant and the remaining water were introduced, followed by an additional 2 min of mixing to ensure homogeneity [31,32,33,34].
The resulting slurry was poured into molds in two equal layers, each aligned with the height of the mold wall. During casting, 30–35 g of mineral admixture was accurately weighed and added to the mold. The mixture was compacted using a spiral tamping method with a steel rod, followed by mechanical vibration to ensure proper consolidation. The surface was then leveled, and the specimens were cured in a standard curing chamber (20 ± 2 °C, RH ≥ 95%) for 15 days. A 15-day curing period was chosen to balance the need for adequate hydration with the practical constraints of the testing program. At this curing age, the specimens had already achieved sufficient strength and stability for reliable high-temperature testing while avoiding unnecessary delays associated with extended curing periods. After curing, the molds were removed to obtain finished explosion-proof concrete specimens [35,36]. The molding process and specimen geometry are shown in Figure 3.
A total of 12 specimens were prepared and divided equally into four groups. Each group was subjected to one of four target temperature levels: 100 °C, 200 °C, 300 °C, and 400 °C. These specimens were used to investigate the thermal transfer behavior of explosion-proof concrete under different high-temperature exposures. The experimental setup and specimen grouping are illustrated in Figure 4.

2.3. Test Methods

Two temperature-controlled furnaces were employed in this study to simulate high-temperature environments and conduct the thermal conditioning of explosion-proof concrete specimens. The first, an SX2-12-10 box-type resistance furnace manufactured by Guangzhou Ruifeng Experimental Equipment Co., Ltd. (Guangzhou, China), offers a maximum operating temperature of 1000 °C and ensures a temperature uniformity error within ±1 °C, making it suitable for both preheating and constant-temperature thermal treatments. The second, an STQ-8-12 atmosphere-controlled box furnace produced by Henan Sante Furnace Technology Co., Ltd. (Luoyang, Henan, China), allows for controlled heating in specific atmospheric conditions, with a maximum operating temperature of 1200 °C and a temperature control precision of ±1 °C. Its internal chamber dimensions accommodate standard concrete specimens, making it ideal for high-temperature exposure experiments.
To evaluate thermophysical properties under different thermal conditions, four groups of specimens were prepared. Prior to heating, all specimens were oven-dried at 105 °C until a constant mass was achieved (mass change <0.1% between two consecutive 2-h intervals), ensuring comparable moisture conditions. Each group was then independently heated to its designated target temperature (100 °C, 200 °C, 300 °C, or 400 °C) at a controlled rate of 5 °C/min and held isothermally for 2 h to ensure uniform internal heating. After conditioning, the specimens were cooled naturally to room temperature before subsequent testing. This static heating protocol enabled controlled comparisons between groups; however, it does not replicate progressive multi-stage heating as may occur in real fire scenarios. This limitation and its implications for practical applicability are addressed in the Discussion section.
The experimental procedures encompassed four core test methods:
  • X-ray Diffraction (XRD) Analysis
X-ray diffraction (XRD) analysis was conducted to investigate mineralogical changes in the concrete after exposure to 100 °C, 200 °C, 300 °C, and 400 °C. Powdered samples were prepared by grinding the specimens, then uniformly spread in the sample holder groove. The surface was leveled with a glass slide to ensure consistent contact with the sample stage and perpendicular alignment to the incident X-ray beam. The analysis was performed using a D8 Advance diffractometer, with operating parameters and scan settings provided in Table 2 and Table 3. Real-time data acquisition was conducted using a digital data recording system, enabling the phase composition and diffraction intensity variations to be identified [37,38].
2.
Thermal Conductivity Testing
Thermal conductivity testing was performed using a preheated thermal probe method. Concrete specimens were dried at 105 °C for 24 h to eliminate residual moisture and then exposed in the STQ-8-12 furnace to the target temperatures (100–400 °C) according to the independent heating protocol. A thermal probe, stabilized in the SX2-12-10 furnace, was brought into direct contact with the specimen surface. A K-type thermocouple embedded in the probe recorded the transient temperature response, which was logged by an Agilent 34970A data acquisition system. The thermal decay curves were analyzed using established models to determine thermal conductivity [39,40,41,42].
For each test condition (100 °C, 200 °C, 300 °C, and 400 °C), three replicate specimens were tested to ensure repeatability. The reported values represent the mean and standard deviation of these replicates.
3.
Specific Heat Capacity Measurement
Specific heat capacity was measured using a calorimetric method. After high-temperature exposure in the STQ-8-12 furnace following the independent heating protocol, specimens were cooled to 20 ± 2 °C. They were then immersed in calorimeter buckets containing distilled water to a depth of 15 mm above the specimen surface. Following a 3-h equilibration, controlled heating was initiated, and the rise in water temperature (10–15 °C) was continuously recorded. The specific heat capacity of the specimens was calculated using the principle of energy conservation, accounting for both specimen and water heat absorption [43,44,45,46].
4.
Density and Porosity Testing
Density and porosity were measured using Archimedes’ principle. After high-temperature exposure following the independent heating protocol, specimens were weighed in a dry state and then vacuum-saturated in water for 48 h until mass stabilization. The saturated surface-dry mass and mass of displaced water during immersion were measured to calculate apparent density and porosity [47,48]
Together, these experimental methods provided a comprehensive understanding of the changes in the thermophysical parameters—namely thermal conductivity, specific heat capacity, density, and porosity—of explosion-proof concrete under varying high-temperature exposures.

3. Results and Discussion

3.1. XRD Analysis of Explosion-Proof Concrete Specimens Under High-Temperature Exposure

X-ray diffraction (XRD) was conducted on concrete specimens exposed to 100 °C, 200 °C, 300 °C, and 400 °C. The corresponding diffraction patterns are presented in Figure 5. The XRD spectra show clear diffraction peaks in the 2θ range of 10–50°, with the major crystalline phases including ettringite, quartz, and larnite consistently present across all temperatures. As temperature increased, a general decrease in peak intensity was observed, particularly beyond 200 °C. The three major marked peaks (labeled 1, 2, and 3 in Figure 5)—attributed to ettringite, quartz, and larnite, respectively—exhibit notable thermal responses: Peak 1 shows a clear reduction in intensity starting at 300 °C, suggesting initial decomposition; Peak 2 remains stable in position but broadens at 400 °C, indicating loss of crystallinity; and Peak 3 displays a gradual intensity decrease with rising temperature, reflecting progressive structural disordering. At 300 °C and 400 °C, significant peak broadening and reduced intensity across these key peaks indicate progressive decomposition of crystalline hydrates and increased amorphous material formation. Minor peaks between 40° and 50° 2θ correspond to secondary phases from fly ash and ettringite-derived gels, associated with pozzolanic and thermal degradation processes
The XRD patterns indicate that the dominant crystalline phases—quartz, larnite, and residual ettringite—remained detectable across all temperature conditions, with no major shifts in peak positions. However, noticeable variations in peak intensity and peak broadening were observed, particularly at 300–400 °C. These changes suggest partial decomposition of hydration products such as ettringite and portlandite, accompanied by localized amorphization and microstructural disorder. Therefore, the term “structural stability” in this context refers to the persistence of major crystalline phases rather than the complete absence of mineralogical transformations. This interpretation is consistent with reports that cementitious hydrates begin to decompose beyond 200 °C, even though the crystalline skeleton remains identifiable. It should also be noted that XRD is less sensitive to amorphous phase evolution; hence, complementary analyses (e.g., TGA/DSC, SEM-EDS) would be required to fully capture the thermal degradation mechanisms of the matrix.
These observations imply that while the main mineral phases do not undergo phase transitions within this temperature range, localized structural degradation and amorphization occur, which may affect subsequent thermal and mechanical performance.

3.2. Effect of High-Temperature Exposure on the Thermal Conductivity of Concrete

Figure 6 presents the measured thermal conductivity values of the specimens under different thermal exposures. The results show a progressive decline in thermal conductivity with increasing temperature. The highest value, 1.48 W/(m·K), was recorded at 100 °C, indicating efficient heat transfer at moderate temperatures. This can be explained by the evaporation of free water, which initially does not significantly disrupt conduction pathways.
At higher temperatures (200–400 °C), thermal conductivity decreased notably. This reduction is attributed to the decomposition of cement hydration products, microcracking in the interfacial transition zone (ITZ), and increased porosity, all of which disrupt continuous heat conduction paths. Fluctuations observed at elevated temperatures may also be linked to changes in interfacial resistance between aggregates and cement paste.
It should be noted that the probe-based measurement method primarily reflects near-surface thermal properties and may be influenced by contact resistance and lateral dissipation. Therefore, the reported values should be interpreted with caution, acknowledging the methodological limitations.

3.3. Effect of High-Temperature Exposure on the Specific Heat Capacity of Concrete

The results of the specific heat capacity tests are summarized in Table 3. Specific heat capacity increased consistently with rising temperature, from 963.89 J/(kg·K) at 100 °C to 1122.22 J/(kg·K) at 400 °C. This trend indicates that the ability of the material to absorb and store heat improves under elevated temperatures.
Table 3. Test results of the influence of temperature on the specific heat capacity of concrete (mean ± SD).
Table 3. Test results of the influence of temperature on the specific heat capacity of concrete (mean ± SD).
Temperature (°C)Initial Temperature (°C)Termination Temperature (°C)Specific Heat Capacity [J/(kg·k)]
10025.3 ± 0.235.8 ± 0.3963.89 ± 15.2
20024.8 ± 0.336.2 ± 0.21022.2 ± 18.5
30025.1 ± 0.236.5 ± 0.21075 ± 20.1
40024.6 ± 0.336.7 ± 0.21122.22 ± 22.7
The primary mechanism underlying this increase is the evaporation of free water and the release of chemically bound water, both of which require significant energy absorption. In addition, the progressive development of pores enhances the concrete’s capacity to store heat, even though this simultaneously weakens its structural integrity.
These results demonstrate that high-temperature exposure enhances the apparent heat storage capacity of concrete due to moisture-related phase changes, but this improvement comes at the expense of microstructural stability.

3.4. Effect of High-Temperature Exposure on the Density of Concrete

Through experimental testing, the mass of the specimens was measured after saturating them with an identical volume of water at different temperatures, as illustrated in Figure 7. Based on the observed changes in mass, the density of each specimen was subsequently calculated. The resulting density values, along with the corresponding porosities, are summarized in Table 4. At 100 °C, the density reached a maximum value of 2400 kg m−3, with an associated porosity of 5.0%. When the temperature was increased to 200 °C, the density decreased to 2280 kg m−3, which corresponded to a statistically significant increase in porosity.
Interestingly, at 300 °C, a partial rebound in density (2350 kg/m3) was observed despite a rise in porosity. This phenomenon is attributed to steam-curing-like effects, where retained water vapor may promote further hydration of unreacted cement particles, temporarily densifying the microstructure. However, this effect is transient and should be interpreted with caution, as prolonged heating typically results in irreversible mass loss and microcracking.
At 400 °C, the density dropped sharply to 1830 kg/m3, while the porosity increased to 20.0%. This reflects significant cracking, water loss, and void formation, which markedly reduce the material’s thermal and mechanical stability.

3.5. Simulation Analysis of the Temperature Field

Numerical simulations were performed to analyze transient heat transfer in the specimens under exposure to nominal boundary temperatures of 100 °C, 200 °C, 300 °C, and 400 °C (Figure 8). The initial specimen temperature was 20 °C, and each case was maintained for 30 min.
At the early stage of heating, steep surface-to-core gradients developed. For instance, under the nominal 100 °C condition, the surface temperature transiently reached approximately 120 °C, while the core remained near 30–40 °C. This apparent overshoot does not reflect physical thermodynamic equilibrium but arises from the applied boundary condition, where a constant external heat flux was imposed rather than a true isothermal bath. We have revised the description accordingly to avoid misinterpretation.
At higher exposures, the internal temperature rise accelerated: at 200 °C, the core reached 90–110 °C; at 300 °C, it reached 150–170 °C; and at 400 °C, equilibrium was nearly achieved within 30 min, with a surface-to-core difference below 20 °C.
These findings highlight the strong influence of the heating rate and boundary definition on thermal gradients in concrete. They also underscore the limitations of simplified simulation assumptions, which may not fully capture real fire scenarios but nonetheless provide useful insights into the transient heat transfer behavior of explosion-proof concrete.

3.6. Mechanistic and Microstructural Insights

The observed macroscopic changes are strongly linked to microstructural evolution. Interactions between aggregates and the cement paste are critical, where the thermal expansion mismatch initiates microcracks within the interfacial transition zone (ITZ). These microcracks propagate and coalesce at temperatures of 300 °C or higher, reducing conduction pathways and significantly weakening the structural integrity. Simultaneously, the pore structure evolves due to progressive water loss, transforming fine pores into coarser, interconnected networks. Above 400 °C, porosity increases sharply because of extensive microcrack coalescence.
Chemical transformations also play a key role. Compounds such as ettringite and portlandite decompose at temperatures above 200 °C. Around 300 °C, secondary hydration reactions occur, leading to a temporary increase in material density. However, above 400 °C, irreversible dehydration becomes the dominant process, severely weakening the cementitious matrix.
These microstructural alterations directly impact thermophysical properties. Thermal conductivity decreases due to cracking in the ITZ and the resulting disruption to heat conduction continuity. Specific heat capacity increases as moisture evaporates, and bound water is released. Density follows a non-linear trend, exhibiting a temporary rebound at approximately 300 °C due to secondary hydration before collapsing at 400 °C under the influence of severe dehydration and pore structure coarsening [49].

3.7. Comparison with Previous Studies and Novelty of This Work

Our findings are consistent with those of Zheng), who reported that the thermal conductivity of fiber-reinforced concrete decreases with temperature due to microcracking and pore coarsening [49]. However, the explosion-proof concrete studied here exhibits an additional densification effect at 300 °C, likely from delayed crack development and continued hydration, which was not reported in ordinary or fiber-reinforced concrete.
More recent studies, such as those of Wang and Guo, have primarily examined ignition resistance, cable insulation, or fire-protective coatings [43]. These works did not quantify thermophysical parameters such as thermal conductivity, specific heat, or density. In contrast, our study directly links microstructural changes (via XRD) with thermal transfer performance, filling a critical research gap in the evaluation of explosion-proof composites.
The integration of experimental data with numerical simulation represents another novelty of this work. Unlike single-parameter studies, this multi-parametric approach provides a holistic understanding of how thermal, structural, and microstructural changes interact under elevated temperatures.
Therefore, this study not only validates general thermal degradation trends observed in conventional concrete research but also advances the field by quantifying the unique thermal behavior of explosion-proof concrete, making it highly relevant for applications in fire- and explosion-prone environments.

4. Conclusions

This study combined experimental testing and numerical simulation to investigate the thermal transfer behavior of explosion-proof concrete under high-temperature exposure ranging from 100 to 400 °C. The results highlight several key trends regarding thermophysical properties. Thermal conductivity reached its maximum value of 1.48 W/(m·K) at 100 °C, after which it progressively decreased with increasing temperature due to microstructural disruption from dehydration and microcrack formation, which reduced the continuity of thermal conduction pathways. The specific heat capacity increased from 963.89 J/(kg·K) at 100 °C to 1122.22 J/(kg·K) at 400 °C, indicating enhanced heat absorption and storage capacity at elevated temperatures; this behavior is attributed to moisture evaporation, pore evolution, and the release of bound water from hydration products. The density was highest at 2400 kg/m3 at 100 °C but decreased with rising temperature due to porosity growth and water loss, culminating in a sharp reduction to 1830 kg/m3 at 400 °C, consistent with extensive cracking and void formation. Numerical simulations revealed that high-temperature exposure reduced the surface–core temperature gradient, resulting in more uniform internal heat distribution—beneficial for short-term thermal buffering but detrimental to long-term structural integrity.
Building on these observations, the findings provide concrete recommendations for engineering practice. Explosion-proof concrete maintains acceptable stability below 200 °C, while partial densification occurring at 300 °C may offer temporary performance benefits. However, above 400 °C, severe microstructural degradation renders the material unsuitable without additional protective measures. Engineers should consequently adopt conservative design margins for fire safety applications, assuming irreversible degradation beyond 300 °C. For critical facilities such as LNG storage units, petrochemical plants, and tunnels, explosion-proof concrete should be supplemented with protective coatings, insulation layers, or fiber reinforcement to effectively mitigate cracking and porosity. The material is most effective for scenarios involving short- to medium-term thermal exposure rather than prolonged high-temperature service.
It should be acknowledged that this study primarily focused on the thermal transfer properties of explosion-proof concrete and did not include mechanical strength tests (e.g., compressive or flexural strength) after high-temperature exposure. This represents a limitation in fully evaluating structural reliability. Future research will integrate thermo-mechanical experiments with strength testing to more comprehensively assess both thermal stability and structural integrity under fire and explosion conditions.

Author Contributions

Conceptualization, Q.W. and Z.L.; methodology, W.H. and Z.H.; validation, Q.W., Z.L. and Z.H.; formal analysis, W.H.; investigation, Z.H.; resources, Z.L.; data curation, Q.W. and Z.H.; writing—original draft preparation, Q.W.; writing—review and editing, Z.L., W.H. and Z.H.; visualization, Z.H.; supervision, Z.L.; project administration, Z.L.; funding acquisition, Q.W. and W.H. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (Grant No. 52174200).

Data Availability Statement

The original contributions presented in this study are included in the article.

Conflicts of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest.

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Processes 13 02712 g001
Figure 1. Physical and microscopic morphology of fly ash and slag.
Figure 1. Physical and microscopic morphology of fly ash and slag.
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Figure 2. Flowchart for the preparation of explosion-proof concrete specimens.
Figure 2. Flowchart for the preparation of explosion-proof concrete specimens.
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Figure 3. The specimen-forming process and its geometric parameters.
Figure 3. The specimen-forming process and its geometric parameters.
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Figure 4. Experimental design showing the grouping of concrete specimens subjected to high-temperature exposures at 100 °C, 200 °C, 300 °C, and 400 °C.
Figure 4. Experimental design showing the grouping of concrete specimens subjected to high-temperature exposures at 100 °C, 200 °C, 300 °C, and 400 °C.
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Figure 5. XRD test results of concrete specimens.
Figure 5. XRD test results of concrete specimens.
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Figure 6. Influence of temperature on the thermal conductivity coefficient of concrete.
Figure 6. Influence of temperature on the thermal conductivity coefficient of concrete.
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Figure 7. Mass and density variations in explosion-proof concrete specimens after water injection at different exposure temperatures.
Figure 7. Mass and density variations in explosion-proof concrete specimens after water injection at different exposure temperatures.
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Figure 8. Stress cloud diagram of the temperature field at the concrete interface.
Figure 8. Stress cloud diagram of the temperature field at the concrete interface.
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Table 1. Chemical compositions of OPC, fly ash, and slag (wt%).
Table 1. Chemical compositions of OPC, fly ash, and slag (wt%).
ComponentOPCFly AshSteel Slag PowderPhosphorous Slag Powder
SiO220.652.316.532.8
Al2O35.327.17.813.2
Fe2O33.27.618.92.5
CaO62.14.644.742.1
MgO2.11.26.84.5
SO32.90.61.51.1
P2O5--0.53.8
LOI3.86.42.12.7
Table 2. Test parameter settings of diffractometer.
Table 2. Test parameter settings of diffractometer.
ProjectParameter
Scanning range (2θ)10°~60°
Step length0.02°
Scanning speed3°/min
Detector opening angle3.3°
Voltage40 kV
Current40 mA
Rotation range−10°~168°
Angle reproducibility0.0001°
Detection area4 mm × 16 mm
Single detector pixel75 μm
Power9 kW
Minimum step0.0001°
X-Y-Z range of the sample150 × 150 mm/9 mm
Resolution5 μm
2θ angle measurement range0~145°
Table 4. Test results of the influence of temperature on the density of concrete (mean ± SD).
Table 4. Test results of the influence of temperature on the density of concrete (mean ± SD).
Temperature (°C)Porosity (%)Density (kg/m3)
1005.02400
2007.52280
30012.02350
40020.01830
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MDPI and ACS Style

Wang, Q.; Luo, Z.; He, W.; Hou, Z. Mechanism Study on the Influence of High-Temperature Exposure on the Thermal Transfer Characteristics of Explosion-Proof Concrete. Processes 2025, 13, 2712. https://doi.org/10.3390/pr13092712

AMA Style

Wang Q, Luo Z, He W, Hou Z. Mechanism Study on the Influence of High-Temperature Exposure on the Thermal Transfer Characteristics of Explosion-Proof Concrete. Processes. 2025; 13(9):2712. https://doi.org/10.3390/pr13092712

Chicago/Turabian Style

Wang, Qiusha, Zhenmin Luo, Wei He, and Zhixuan Hou. 2025. "Mechanism Study on the Influence of High-Temperature Exposure on the Thermal Transfer Characteristics of Explosion-Proof Concrete" Processes 13, no. 9: 2712. https://doi.org/10.3390/pr13092712

APA Style

Wang, Q., Luo, Z., He, W., & Hou, Z. (2025). Mechanism Study on the Influence of High-Temperature Exposure on the Thermal Transfer Characteristics of Explosion-Proof Concrete. Processes, 13(9), 2712. https://doi.org/10.3390/pr13092712

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