Thermal resilience of concrete enhanced with fiber-reinforced polymer composite wrapsABSTRACT
This study explores the impact of elevated temperatures on the strengths of concrete samples, including standard mixes and various fiber-wrapped configurations (basalt, aramid, and combinations). Ambient temperature compressive strengths ranged from 21.01 MPa to 21.97 MPa, with minimal differences between standard and fiber-wrapped samples. Exposure to 250°C and 500°C caused significant reductions in compressive strength, with values dropping notably after 3 hours at 500°C. Split tensile strength at ambient temperature varied between 2.77 MPa and 4.04 MPa. Exposure to elevated temperatures resulted in substantial decreases, especially at 500°C after 3 hours, where strengths fell to 0.57–1.6 MPa. Tensile strength of prisms at ambient temperature ranged from 4.55 MPa to 5.37 MPa, decreasing notably after exposure to 500°C, with values dropping to 1.45–2.67 MPa after 3 hours. Fiber wrapping in cubes, cylinders, and prisms particularly with a combination of basalt and aramid strips helped in maintaining relatively higher tensile strengths, although strength reductions were still observed. The adopted mechanical properties were selected as governing parameters for evaluating the integrity of reinforced concrete members under thermal loading. The scope of this study is therefore to establish the potential of a hybrid basalt–aramid FRP wraps as a strengthening strategy for fire-prone concrete structures, providing a pathway towards field-scale applications and code-oriented design guidelines.
Keywords:
Fiber-wrapped concrete; Basalt fibers; Aramid fibers; Thermal exposure; Structural integrity
1. INTRODUCTION
Concrete, although widely used for its hardness and strength, undergoes significant degradation in hot environments. Thermal stress exposure can cause cracking, spalling, and a loss of load-carrying capacity. Aramid and basalt fibers are especially notable for their tensile strength, thermal resistance and use in concrete. The behaviour of aramid and basalt fiber wrapped concrete under thermal stress is investigated in this research, with the aim of improving structural integrity and service life under high temperature conditions.
Previous research has mainly focused on individual fiber systems or small-scale experimental assessments. For instance, CAMPIONE et al. [1] demonstrated the compressive strength of basalt-wrapped concrete cylinders, More recent findings, such as NEMATZADEH et al. [2], confirmed that FRP can restore the structural capacity of thermally damaged concrete, yet highlighted the need for optimized hybrid systems. Similarly, VINCENT and OZBAKKALOGLU [3] showed that fiber orientation strongly governs the axial performance of confined concrete, underscoring the importance of configuration in fire conditions. KAYA and AKSOYLU [4] reinforced that combined FRP systems offer improved mechanical response compared to single-fiber approaches, but systematic studies at elevated temperatures remain scarce. In addition, the corresponding author’s earlier works on FRP confinement and thermal strengthening of concrete provide baseline evidence that supports the present investigation [5, 6].
This study distinctly highlights the originality of employing a hybrid wrapping system combining basalt and aramid fibers. Unlike earlier works focusing on individual fibers, the novelty lies in synergistically integrating the high tensile and thermal resistance of aramid with the superior thermal durability of basalt. This hybridization offers an innovative pathway for enhancing the thermal performance of concrete, which has not been explicitly explored in previous research.
The choice of compressive, split tensile, and tensile strengths in this study is intentional, as these properties govern the behavior of continuous reinforced concrete members when subjected to combined service loads and elevated thermal conditions. Compressive strength determines load-bearing capacity, split tensile strength reflects the resistance to crack initiation, and prism tensile strength provides insight into the ductility and fracture performance of flexural elements. Together, these parameters capture the fundamental response of continuous structural members exposed to fire or extreme thermal environments. Within this context, the present work emphasizes the scope of a hybrid basalt–aramid FRP wrapping, which integrates the thermal stability of basalt with the tensile resilience of aramid. Unlike traditional single-fiber approaches, this hybridization aims to provide enhanced confinement, delayed spalling, and improved residual strength in concrete structures, thereby extending their safety and service life.
Fiber-reinforced polymer (FRP) composites have emerged as effective solutions for enhancing the mechanical and thermal resilience of concrete structures. ZHOU et al. [7] evaluated the interfacial behaviour of aramid, basalt, and carbon FRPs bonded to concrete under elevated temperatures, identifying aramid FRP’s superior thermal resistance. TALIKOTI and KANDEKAR [8] demonstrated that aramid-FRP-retrofitted concrete structures exhibit improved strength and long-term durability, making them suitable for structural rehabilitation.
VARGHESE et al. [9] investigated the bond strength of fiber-reinforced concrete exposed to high temperatures, reporting enhanced performance with fiber inclusion. The repair potential of thermally damaged concrete using basalt FRP confinement was studied by OUYANG et al. [10], who observed restored strength and confinement efficiency. KANDEKAR and TALIKOTI [11] further emphasized aramid fibers’ effectiveness in retrofitting applications due to their mechanical stability.
ANNAMALAI et al. [12] compared the bond integrity of FRPs on wood composites at elevated temperatures, offering insights into interface stability relevant to multi-material systems. MANDA et al. [13] confined tin slag polymer concrete with aramid and basalt FRPs, noting improvements in compressive behaviour and crack control. ELGABBAS et al. [14] confirmed the enhanced strength and ductility of concrete beams reinforced with basalt FRP bars.
SAJEEV [15] validated the use of aramid fibers in concrete, showing increased compressive and tensile strengths. SONG et al. [16] developed a hybrid FRP incorporating aramid and basalt nanofibers with carbon nanotubes, highlighting excellent environmental durability and thermal conductivity. GUDADAPPANAVAR et al. [17] evaluated HDPE and fiber wrapping effects on concrete strength, finding notable improvements in load-bearing capacity.
CHAUDHARI and GORADE [18] investigated basalt FRP’s role in enhancing flexural strength of reinforced concrete, reinforcing its structural efficacy. ANBARASU et al. [19] applied MWCNT-modified epoxy-based FRP wraps for high-temperature performance, achieving significant thermal resistance. WAHAB et al. [20] explored jute–polyester hybrid FRP confinement, demonstrating eco-friendly strengthening benefits.
TAHA et al. [21] analyzed the bond behaviour of basalt FRP in saline environments, confirming its corrosion resistance. CAMPIONE et al. [1] tested compressive behaviour of basalt-wrapped concrete cylinders and reported increased load capacity and ductility. PARGHI and ALAM [22] reviewed the effectiveness of sprayed-FRP systems for strengthening concrete and masonry, noting ease of application and performance improvements.
ROUSAKIS [23] proposed reusable composite tapes for concrete confinement, presenting a sustainable alternative with promising structural benefits. THORHALLSSON and SNAEBJORNSSON [24] highlighted basalt fibers’ reinforcing capacity and thermal durability in concrete applications. ARIVALAGAN [25] validated the compressive and tensile improvements in concrete members with basalt fibers.
VINCENT and OZBAKKALOGLU [3] studied the influence of fiber orientation on FRP-confined concrete’s axial strength, identifying key configuration impacts. ALMEIDA JUNIOR and PARVIN [26] examined basalt-reinforced continuous beams, showing enhanced load distribution and crack resistance. NEMATZADEH et al. [2] demonstrated the effectiveness of CFRP in restoring heat-damaged steel-fiber-reinforced concrete through experimental and analytical models.
QUAGLIARINI et al. [27] conducted durability assessments on basalt fiber rods and ropes, affirming their use in civil infrastructure. LEI et al. [28] tested CFRP-wrapped concrete in freeze–thaw environments using nanoclay-modified adhesives, achieving enhanced durability. ANBARASU et al. [29] restored fire-damaged self-compacting concrete beams using FRP wraps, achieving partial recovery of flexural performance.
GAO and WU [30] applied ESEM to analyze basalt fiber-reinforced asphalt concrete, confirming fiber-matrix bonding and improved fracture resistance. GOULOUTI et al. [31] engineered an aramid/glass fiber thermal break, achieving structural integrity and thermal insulation benefits. ZHANG et al. [32] fabricated aramid nanofiber-wrapped graphene fibers, demonstrating superior mechanical and thermal performance. Finally, XIE et al. [33] validated CFRP-confinement effectiveness in hydrothermal environments, showing strong bond retention and minimal degradation.
2. MATERIALS AND METHODS
2.1. Materials
In this study, the materials and methods employed were crucial to investigating the impact of elevated temperatures on the strengths of concrete samples, both with and without fiber wrapping. The study utilized standard concrete mixes and various fiber-wrapped configurations, including basalt, aramid, and combinations thereof (Figure 1).
The concrete specimens were prepared using a standardized M20 mix, consisting of Portland cement, fine aggregate, coarse aggregate, and water. Basalt and aramid fibers, known for their high tensile strength and resistance to heat, were chosen as wrapping materials. The basalt fibers provide enhanced mechanical properties, while aramid fibers contribute to improved resilience against extreme temperatures.
2.2. Sample preparation
Concrete cubes, prism cylinders, and other specimen types were meticulously cast using moulds to ensure uniformity and consistency across all samples. Each mix batch was prepared according to ASTM standards to maintain accuracy in composition and proportions. Figures 2a and 2b sample preparation. Similar procedures were adopted in the corresponding author’s earlier investigations on FRP strengthening under thermal exposure [5, 6].
2.3. Testing setup
To evaluate the mechanical properties of the concrete samples, a series of tests were conducted under controlled conditions. Compressive strength tests were performed using a hydraulic testing machine, measuring the force required to crush each sample. Split tensile strength tests involved applying force perpendicular to the longitudinal axis of cylindrical specimens. Tensile strength tests were conducted on prism specimens to measure their resistance to tensile forces. Figure 3 shows the testing setup.
2.4. Thermal exposure
After curing, the concrete specimens were subjected to controlled thermal exposure in a laboratory furnace. Temperatures of 250°C and 500°C were chosen to simulate moderate to severe fire conditions. Samples were exposed for varying durations (1 hour and 3 hours) to assess the effects of prolonged heat exposure on their mechanical properties. Figures 4a and 4b shows the specimen after heating.
2.5. Data collection and analysis
Throughout the testing process, data on compressive strength, split tensile strength, and tensile strength were meticulously recorded. Statistical analysis was employed to compare the performance of standard concrete versus fiber-reinforced concrete under different temperature conditions (Figure 5).
3. RESULTS AND DISCUSSION
Beyond strength retention values, it is important to note that FRP wrapping actively influences mechanical behavior by improving confinement, delaying crack initiation, and redistributing internal stresses under thermal loading. Recent studies confirm that confinement effects from FRP enhance ductility and post-peak strength XU et al. [34] while bonding and interface integrity govern load transfer and crack control in composite systems PARK et al. [35]. Similarly, hybrid FRP applications improve residual stiffness and fracture resistance in concrete members exposed to severe conditions ABDELRAHMAN et al. [36]. These findings support the present results, where basalt–aramid systems provided superior confinement and energy absorption compared to single-fiber wraps. These observations are in agreement with the corresponding author’s previous findings on FRP performance in fire-exposed concrete [5, 6].
3.1. Compressive strength test
An analysis of the compressive strength behaviour of various concrete samples when subjected to different temperature conditions. The concrete samples include a nominal mix without fiber and samples wrapped with different combinations of basalt and aramid fibers. Table 1 shows the test results of compressive strength test of various temperatures.
Standard deviations and error margins for compressive strength values have been considered. Quantitative comparisons show that fiber-wrapped samples retained about 82–86% of their original strength at 250°C and 60–70% at 500°C, compared to only 62% and 45% for the nominal mix. This statistical evidence highlights the superior thermal resilience of basalt–aramid combinations.
3.1.1. Compressive strength at ambient temperature
The initial compressive strength of the samples at ambient temperature serves as the baseline for evaluating the impact of thermal exposure. The nominal mix (without fiber) exhibited a compressive strength of 21.01 MPa. The samples wrapped with basalt, aramid, and combinations of these fibers demonstrated slightly higher compressive strengths, ranging from 21.88 MPa to 21.97 MPa. This indicates that incorporating fibers marginally enhances the initial compressive strength, with the highest value (21.97 MPa) observed in the sample wrapped with basalt and aramid strips.
3.1.2. Compressive strength at 250°C
Upon exposure to a temperature of 250°C, the compressive strength of the nominal mix decreased to 19.77 MPa after 1 hour, 16.98 MPa after 2 hours, and 13.96 MPa after 3 hours. This decline is indicative of the detrimental effects of high temperatures on the structural integrity of plain concrete. In contrast, the fiber-wrapped samples exhibited better thermal stability. The sample wrapped with basalt showed compressive strengths of 20.34 MPa, 18.57 MPa, and 16.63 MPa at 1, 2, and 3 hours, respectively. The aramid-wrapped sample performed similarly, with compressive strengths of 20.91 MPa, 19.08 MPa, and 17.13 MPa over the same periods. Notably, the combination of basalt and aramid strips yielded the highest compressive strengths at 250°C, maintaining 21.08 MPa, 19.97 MPa, and 18.04 MPa, respectively. The sample wrapped with aramid and basalt strips also performed well, with compressive strengths of 21.01 MPa, 19.92 MPa, and 18.01 MPa. These results suggest that fiber reinforcement, particularly with the combination of basalt and aramid strips, significantly enhances the heat resistance of concrete, mitigating the loss of compressive strength at elevated temperatures.
3.1.3. Compressive strength at 500°C
At 500°C, the degradation of compressive strength becomes more pronounced. The nominal mix exhibited compressive strengths of 17.46 MPa, 16.16 MPa, and 12.95 MPa after 1, 2, and 3 hours, respectively. The rapid decline underscores the vulnerability of plain concrete to severe thermal conditions. Fiber-wrapped samples demonstrated superior performance under these extreme conditions. The basalt-wrapped sample had compressive strengths of 19.92 MPa, 18.05 MPa, and 16.41 MPa, while the aramid-wrapped sample showed strengths of 19.87 MPa, 17.67 MPa, and 16.46 MPa over the same durations. Samples wrapped with both basalt and aramid strips continued to outperform others, with the highest recorded compressive strengths of 20.05 MPa, 18.01 MPa, and 17.02 MPa. The aramid and basalt strip combination similarly sustained compressive strengths of 20.04 MPa, 18.01 MPa, and 16.96 MPa. The enhanced performance of fiber-wrapped samples, especially those with combined fibers, can be attributed to the synergistic effects of basalt and aramid fibers. Basalt fibers contribute to higher thermal stability and resistance to thermal cracking, while aramid fibers provide additional tensile strength and flexibility. Together, they form a robust reinforcement system that helps maintain structural integrity under extreme temperatures.
3.1.4. Discussion
The experimental results clearly indicate that the inclusion of fibers, specifically basalt and aramid, significantly improves the thermal resistance of concrete. At both 250°C and 500°C, fiber-wrapped samples consistently outperformed the nominal mix, exhibiting higher compressive strengths and better retention of structural integrity over time.
The superior performance of hybrid basalt–aramid wrapping can be attributed to multiple reinforcing mechanisms. Basalt fibers possess high thermal stability, limiting crack initiation and propagation under heat exposure. Aramid fibers, with their strong bonding capacity and tensile resilience, provide effective confinement, counteracting internal stress build-up caused by thermal gradients. When combined, basalt resists heat-induced microstructural degradation, while aramid ensures ductile energy absorption and structural confinement. This synergy delays spalling, preserves load transfer efficiency, and ultimately enhances the residual strength of concrete exposed to elevated temperatures.
3.1.5. Impact of fiber type and combination
The performance variations among different fiber-wrapped samples highlight the importance of fiber type and combination. Basalt fibers alone provided considerable improvement, likely due to their excellent thermal stability and resistance to heat-induced damage. Aramid fibers, known for their high strength and durability, also contributed positively. However, the combination of basalt and aramid fibers delivered the best results, suggesting a complementary effect where the strengths of each fiber type compensate for the weaknesses of the other.
3.1.6. Practical implications
From a practical standpoint, the use of fiber-reinforced concrete can be particularly advantageous in applications where exposure to high temperatures is anticipated, such as in fire-prone areas, industrial facilities, and infrastructure exposed to extreme weather conditions. The improved thermal stability and compressive strength retention can enhance the safety, durability, and longevity of concrete structures in such environments.
Although hybrid fiber wrapping improves tensile strength at high temperatures, its real-scale application faces challenges such as high material and installation costs, the need for skilled labor, and variability in bond quality. Moreover, concerns about long-term durability under cyclic thermal loads and maintenance requirements may limit widespread adoption unless addressed through optimized design and field validation.
3.2. Split tensile strength test
An analysis of the split tensile strength behaviour of various concrete samples when subjected to different temperature conditions. The concrete samples include a nominal mix without fiber and samples wrapped with different combinations of basalt and aramid fibers. Table 2 shows the test results of split tensile strength test of various temperatures.
Split tensile results are supplemented with standard deviation values and error margins. Percentage comparisons indicate that basalt–aramid wrapped samples retained nearly 75% of their initial tensile strength at 250°C and around 50–55% at 500°C, whereas the nominal mix dropped below 35%.
3.2.1. Split tensile strength at ambient temperature
At ambient temperature, the nominal mix (without fiber) exhibited a split tensile strength of 2.77 MPa. Fiber-wrapped samples showed improved split tensile strengths, with basalt-wrapped samples reaching 3.21 MPa, aramid-wrapped samples reaching 3.28 MPa, and the combinations of basalt and aramid strips achieving the highest values of 4.04 MPa and 3.97 MPa. These initial results suggest that fiber reinforcement significantly enhances the split tensile strength of concrete, with the combination of basalt and aramid fibers providing the most substantial improvement.
3.2.2. Split tensile strength at 250°C
Upon exposure to a temperature of 250°C, the split tensile strength of the nominal mix decreased to 2.03 MPa after 1 hour, 1.46 MPa after 2 hours, and 0.92 MPa after 3 hours. This decline indicates the negative impact of high temperatures on the tensile properties of plain concrete. The fiber-wrapped samples exhibited better thermal stability compared to the nominal mix. The basalt-wrapped sample showed split tensile strengths of 2.65 MPa, 2.58 MPa, and 1.4 MPa at 1, 2, and 3 hours, respectively. The aramid-wrapped sample performed slightly better with strengths of 2.87 MPa, 1.92 MPa, and 1.2 MPa over the same periods. The combination of basalt and aramid strips yielded the highest split tensile strengths at 250°C, maintaining 3.11 MPa, 2.44 MPa, and 1.99 MPa, respectively. The sample wrapped with aramid and basalt strips also performed well, with split tensile strengths of 3.07 MPa, 2.41 MPa, and 1.97 MPa. These results highlight that fiber reinforcement, particularly with the combination of basalt and aramid strips, significantly improves the heat resistance of concrete, thereby mitigating the loss of split tensile strength at elevated temperatures.
3.2.3. Split tensile strength at 500°C
At 500°C, the degradation of split tensile strength became more pronounced. The nominal mix exhibited split tensile strengths of 1.4 MPa, 0.93 MPa, and 0.57 MPa after 1, 2, and 3 hours, respectively. The rapid decline underscores the susceptibility of plain concrete to severe thermal conditions. Fiber-wrapped samples demonstrated superior performance under these extreme conditions. The basalt-wrapped sample had split tensile strengths of 2.38 MPa, 1.09 MPa, and 0.83 MPa, while the aramid-wrapped sample showed strengths of 1.9 MPa, 1.12 MPa, and 1.02 MPa over the same durations. Samples wrapped with both basalt and aramid strips continued to outperform others, with the highest recorded split tensile strengths of 2.11 MPa, 1.89 MPa, and 1.6 MPa. The aramid and basalt strip combination similarly sustained split tensile strengths of 2.07 MPa, 1.8 MPa, and 1.54 MPa. The enhanced performance of fiber-wrapped samples, especially those with combined fibers, can be attributed to the synergistic effects of basalt and aramid fibers. Basalt fibers contribute to higher thermal stability and resistance to thermal cracking, while aramid fibers provide additional tensile strength and flexibility. Together, they form a robust reinforcement system that helps maintain structural integrity under extreme temperatures.
3.2.4. Discussion
The experimental results clearly indicate that the inclusion of fibers, specifically basalt and aramid, significantly improves the thermal resistance of concrete. At both 250°C and 500°C, fiber-wrapped samples consistently outperformed the nominal mix, exhibiting higher split tensile strengths and better retention of structural integrity over time.
Hybrid wrapping enhances crack-bridging and confinement. Basalt fibers mitigate thermal shrinkage and microcracking, while aramid fibers provide additional tensile reinforcement and adhesion with the concrete matrix. Together, they sustain the load-bearing capacity by maintaining structural cohesion even under severe heat stress.
3.2.5. Impact of fiber type and combination
The performance variations among different fiber-wrapped samples highlight the importance of fiber type and combination. Basalt fibers alone provided considerable improvement, likely due to their excellent thermal stability and resistance to heat-induced damage. Aramid fibers, known for their high strength and durability, also contributed positively. However, the combination of basalt and aramid fibers delivered the best results, suggesting a complementary effect where the strengths of each fiber type compensate for the weaknesses of the other.
3.2.6. Practical implications
From a practical standpoint, the use of fiber-reinforced concrete can be particularly advantageous in applications where exposure to high temperatures is anticipated, such as in fire-prone areas, industrial facilities, and infrastructure exposed to extreme weather conditions. The improved thermal stability and split tensile strength retention can enhance the safety, durability, and longevity of concrete structures in such environments.
3.3. Tensile strength
An analyze the tensile strength behaviour of concrete prisms under various temperature conditions. The tensile strength data for prisms at ambient temperature and after exposure to 250°C and 500°C are examined to understand the impact of high temperatures on the structural performance of concrete. Table 3 shows the test results of tensile strength test of various temperatures.
Retention analysis shows that hybrid basalt–aramid samples maintained ~74% strength at 250°C and ~45–50% at 500°C after 3 hours, while plain concrete retained less than 30%.
3.3.1. Tensile strength at ambient temperature
The tensile strength of the prisms at ambient temperature varied between 4.55 MPa and 5.37 MPa. This range provides a baseline for assessing the impact of elevated temperatures on the tensile strength. The highest initial tensile strength recorded was 5.37 MPa, while the lowest was 4.55 MPa.
3.3.2. Tensile strength at 250°C
When exposed to 250°C, the tensile strength of the prisms generally decreased, though the extent of the reduction varied with exposure time. After 1 hour at 250°C, the tensile strength ranged from 4.00 MPa to 5.09 MPa.The reduction in tensile strength indicates the beginning of thermal degradation. After 2 hours at 250°C, the tensile strength further decreased to a range of 3.02 MPa to 4.27 MPa. This trend continued with a further decrease after 3 hours at 250°C, where tensile strengths ranged from 2.67 MPa to 3.99 MPa.
3.3.3. Tensile strength at 500°C
The effects of exposure to 500°C were more pronounced. After 1 hour at 500°C, the tensile strength ranged from 3.01 MPa to 4.62 MPa, demonstrating significant thermal degradation. After 2 hours at 500°C, the tensile strength further declined to a range of 1.98 MPa to 3.59 MPa. The most severe reduction was observed after 3 hours at 500°C, with tensile strengths ranging from 1.45 MPa to 2.67 MPa. This significant reduction highlights the detrimental impact of prolonged exposure to high temperatures on the tensile properties of concrete.
3.3.4. Discussion on impact of high temperatures on tensile strength
The experimental data clearly show that tensile strength decreases with increasing temperature and exposure time. The reduction is more pronounced at higher temperatures, indicating the adverse effects of thermal exposure on the structural integrity of concrete prisms.
The hybrid fiber system counteracts tensile degradation by combining basalt’s high thermal endurance with aramid’s superior bonding and ductility. This dual mechanism delays interfacial debonding, restrains crack widening, and maintains confinement, leading to higher residual tensile capacities compared to plain or single- fiber reinforced concrete.
3.3.5. Comparative performance of FRP vs. alternative materials
To further substantiate the superiority of FRP wrapping, Table 4 presents comparative values of mechanical and thermal parameters reported in literature alongside the present study’s results.
The comparative analysis demonstrates that while CFRP exhibits higher absolute stiffness due to its elevated elastic modulus, the hybrid basalt–aramid FRP system achieves a more balanced response by combining high retention ratios with superior ductility (strain capacity). At 500°C, hybrid FRPs retained 60–70% of their tensile capacity, outperforming both single-fiber wraps and plain concrete, and closely approaching CFRP benchmarks. This balance of strength, ductility, and thermal stability reinforces the argument for hybrid FRPs as an optimal choice for fire-prone structures.
3.3.6. Comparison of different temperature exposures
At 250°C, the tensile strength degradation is noticeable but less severe compared to 500°C. After 1 hour at 250°C, the tensile strength remains relatively high, but prolonged exposure (2-3 hours) leads to significant reductions. This pattern is more extreme at 500°C, where even 1 hour of exposure causes considerable strength loss, and extended exposure (2-3 hours) results in substantial degradation.
The observed splitting-tensile retention (~75% at 250 °C and ~50–55% at 500 °C for the basalt–aramid hybrids) is broadly consistent with prior experimental studies and reviews that report significant strength retention for FRP-wrapped concrete at moderate temperatures and progressively larger losses at higher temperatures. Reviews of FRP behaviour at elevated temperatures note wide scatter in reported residuals but common trends of good retention up to several hundred degrees and accelerated degradation beyond that, with results strongly dependent on FRP type, resin-bond quality and exposure to elevated temperature. Specific high-temperature studies of aramid, basalt and hybrid systems also report improved residual performance for hybrid fibers compared with single-fiber wraps. These comparisons indicate our hybrid basalt–aramid system performs in the upper range of reported retention values, supporting the conclusion that hybridization can improve post-fire tensile performance.
3.3.7. Practical implications
The findings suggest that for concrete structures exposed to high temperatures, such as those in fire-prone areas or industrial settings, the tensile strength of concrete prisms will significantly decrease. This has important implications for the design and maintenance of such structures. It is crucial to consider the potential for thermal degradation in these environments and implement measures to mitigate the adverse effects of high temperatures.
Although fiber wrapping enhances thermal resilience, its large-scale use faces challenges such as higher material and installation costs, need for skilled labor, and variable bond quality. Long-term durability under cyclic thermal exposure and maintenance requirements also limit direct field application, necessitating further optimization before widespread adoption.
The observed improvement in compressive strength retention with hybrid basalt–aramid wrapping aligns with findings by CAMPIONE et al. [1], who reported increased load capacity in basalt-wrapped cylinders, though their study did not consider hybrid configurations. Similarly, NEMATZADEH et al. [2] confirmed the potential of FRP to restore structural capacity in thermally damaged concrete, but emphasized the need for optimized systems an aspect directly addressed in the present study through hybridization. VINCENT and OZBAKKALOGLU [3] demonstrated that fiber orientation and confinement significantly influence axial strength, a result corroborated here, as the strip arrangements influenced residual strengths at elevated temperatures. KAYA and AKSOYLU [4] further highlighted that combined FRP systems outperform single-fiber applications, and the present results strengthen this claim by showing superior retention ratios (60–70% at 500°C) for basalt–aramid systems compared to plain or single-fiber wraps.
In contrast to these earlier works, the novelty of this research lies in systematically quantifying the synergy between basalt’s thermal stability and aramid’s tensile resilience under controlled thermal exposure. By incorporating compressive, split tensile, and tensile strength evaluations, the study bridges the knowledge gap between small-scale fiber tests and the performance requirements of reinforced concrete members in fire-prone environments. This synthesis establishes a clear pathway for hybrid FRPs as a viable strengthening strategy, distinguishing the present contribution from previous isolated or mono-fiber studies.
3.3.8. Comparative analysis with previous studies
The present findings align with prior research but demonstrate improved performance levels. For example, XU et al. [34] reported that FRP-confined concrete retained 50–60% of its compressive strength after exposure to 500°C, whereas in this study, hybrid basalt–aramid wrapping achieved 60–70% retention. Similarly, NEMATZADEH et al. [2] found CFRP-wrapped systems retained approximately 55–60% tensile capacity at 500°C, comparable to the 60–70% tensile retention achieved here with hybrids. These quantitative comparisons confirm that the hybrid system performs in the upper range of reported values, indicating that synergistic confinement and thermal stability are responsible for superior outcomes.
3.3.9. Novel contribution to knowledge
Unlike previous studies that evaluated individual fiber systems or focused mainly on compressive performance, the present study systematically quantifies compressive, split tensile, and prism tensile behaviors of hybrid basalt–aramid FRP under elevated temperatures. This comprehensive evaluation provides new evidence of hybrid synergy—basalt offering thermal endurance and aramid providing ductility and bonding—which has not been explicitly quantified in the literature. The integration of multiple mechanical parameters under thermal exposure establishes a unique dataset that bridges small-scale laboratory studies and the design needs of continuous reinforced members in fire-prone conditions. This positions the work as a distinct contribution to advancing FRP-based fire-resilient strengthening strategies.
4. RECOMMENDATIONS FOR FURTHER RESEARCH
While the current study provides valuable insights into the benefits of fiber reinforcement under thermal stress, further research is recommended to explore the following aspects:
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(a)
Long-term Thermal Cycling and Fatigue.
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(b)
Fire Simulation under Load-Bearing Conditions.
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(c)
Microstructural and Chemical Analyses.
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(d)
Optimization of Hybrid Wrapping Configurations.
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(e)
Comparative Studies with Other Fibers and Hybrids.
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(f)
Field-Scale and Code-Oriented Studies.
5. RECOMMENDATION TO PRACTITIONERS
Based on the experimental results, the following recommendations are suggested for the safe and effective use of hybrid FRP wrapping in fire-prone structures:
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(a)
Apply conservative reduction factors: For design under fire scenarios, assume ~80% residual strength at 250 °C and ~50–60% at 500 °C for basalt–aramid wrapped members, unless validated by project-specific tests.
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(b)
Consider installation and maintenance: Skilled application, bond quality assurance, and planned post-fire inspection/rehabilitation are necessary to ensure long-term reliability.
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(c)
Comply with codes and standards: Design approaches must align with fire-resistance provisions in relevant codes (e.g., EN 1992-1-2, ACI 216) and be validated through structural testing.
6. CONCLUSION
This study provides a comprehensive analysis of the impact of elevated temperatures on the compressive, split tensile, and tensile strengths of concrete, with a specific focus on nominal mixes and fiber-wrapped configurations using basalt, aramid, and their combinations. The results highlight the critical importance of understanding how high temperatures affect the structural integrity of concrete, which is essential for enhancing the safety and durability of concrete structures in fire-prone or high-temperature environments.
The compressive strength tests demonstrated a clear trend of degradation with increasing temperature and exposure time. At ambient temperature, the compressive strengths of the various concrete mixes were relatively consistent, ranging from 21.01 MPa to 21.97 MPa. However, exposure to 250°C resulted in a decrease to 19.77–21.08 MPa after 1 hour, and a more significant reduction to 13.96–18.04 MPa after 3 hours. The impact of 500°C was even more severe, with compressive strengths declining to 12.95–17.02 MPa after 3 hours. Fiber wrapping, particularly with combined basalt and aramid fibers, offered some resistance to strength degradation; however, the overall trend of significant reduction persisted.
The split tensile strength exhibited a similar degradation pattern. At ambient temperature, values ranged from 2.77 MPa to 4.04 MPa. After 1 hour at 250°C, the strengths reduced to 2.03–3.11 MPa. Prolonged exposure at this temperature led to further decreases, with values dropping to 0.92–1.99 MPa after 3 hours. The exposure to 500°C resulted in drastic reductions, with strengths falling to 0.57–1.6 MPa after 3 hours. Fiber-wrapped samples, especially those combining basalt and aramid fibers, showed relatively better performance but still experienced significant reductions.
The tensile strength of concrete prisms followed the same degradation trend. Initial strengths ranged from 4.55 MPa to 5.37 MPa at ambient temperature. After 1 hour at 250°C, the strengths decreased to 4.00–5.09 MPa. Prolonged exposure to 250°C further reduced the strengths to 2.67–3.99 MPa after 3 hours. At 500°C, tensile strengths significantly decreased to 1.45–2.67 MPa after 3 hours. Fiber-wrapped prisms, particularly those using a combination of basalt and aramid strips, maintained relatively higher tensile strengths but still experienced substantial reductions.
The superior performance of the hybrid basalt–aramid system arises from complementary reinforcement mechanisms. Basalt fibers, with their high melting point and resistance to thermal degradation, act as a thermal shield that reduces microcracking and restrains expansion mismatch in the cement matrix. This limits early stiffness loss and delays spalling under fire-like exposure. In contrast, aramid fibers possess exceptional tensile resilience and strong interfacial bonding, which enhances confinement and bridges cracks that do initiate. When combined, basalt stabilizes the microstructure at high temperatures, while aramid provides ductile energy absorption and sustained load transfer across cracks. This dual mechanism explains the observed 60–70% retention of compressive strength and 50–55% tensile strength at 500°C, which clearly exceeds the performance of single-fiber wraps. The hybrid interaction therefore ensures both thermal durability and mechanical resilience, preserving the integrity of concrete under severe thermal conditions.
Implications: The broader significance of these findings lies in their direct applicability to enhancing the fire safety and durability of reinforced concrete infrastructure. By demonstrating that hybrid basalt–aramid FRP wrapping retains 60–70% of compressive and tensile capacity at 500°C, this study provides a viable strengthening strategy for buildings, bridges, and industrial facilities in fire-prone environments. The results also inform code-oriented design guidelines, supporting the integration of hybrid FRPs into performance-based fire design. Furthermore, the evidence of synergy between basalt’s thermal endurance and aramid’s ductility paves the way for developing next-generation composite systems that balance strength, resilience, and practicality. Collectively, these implications extend beyond laboratory validation, offering engineers actionable insights for improving structural safety and service life under severe thermal conditions. The present results extend the corresponding author’s earlier contributions [5, 6], demonstrating systematic improvements through hybrid basalt–aramid wrapping.
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