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Articles • Matéria (Rio J.) 31 • 2026 • https://doi.org/10.1590/1517-7076-RMAT-2025-0777 linkcopy

Open-access Assessment of polymer fibers on mechanical behavior and high-temperature performance of GFRP-reinforced beams

AuthorshipSCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

This study evaluates the influence of polyvinyl alcohol (PVA) fibers on the mechanical behavior and high-temperature performance of concrete beams reinforced with glass fiber-reinforced polymer (GFRP) bars. The experimental variables included fiber addition levels (0.00%, 0.10% and 0.15% by volume) and exposure to thermal cycling at 300°C, 500°C, or no heating. For unheated specimens, fiber addition reduced void ratio, water absorption, bulk density, ultrasonic pulse velocity, dynamic modulus of elasticity, and compressive strength, while enhancing flexural strength with increasing fiber content. For beams exposed to thermal cycling, the 0.10% fiber content showed least loss in flexural strength after heating, with an increase of 2.72% and a decrease of 15.68% in strength at 300 °C and 500 °C, respectively. Exposure to 500 °C significantly reduced flexural strength for all mixtures, with a maximum reduction of 41.71% for the 0.15% fiber content. Nevertheless, fiber-reinforced beams consistently exhibited higher ultimate loads than reference beams. No clear improvement in ductility was observed at elevated temperatures. Engineering analysis demonstrates that fiber effectiveness is non-linear, with 0.10% identified as optimal content for maximizing thermal-mechanical performance. These findings highlight importance of dosage control in GFRP-reinforced beams as a practical strategy to enhance structural resilience and safety under high-temperature conditions.

Keywords:
GFRP bars; PVA fiber; Concrete; Elevated temperature; Flexural behavior

1. INTRODUTION

The use of fiber-reinforced polymer (FRP) bars has become established as a more durable alternative, providing longer service life for concrete structures exposed to aggressive environments, such as those with chloride ingress and carbonation, when compared with conventional steel reinforcement. Among the different types of FRP, glass fiber-reinforced polymer (GFRP) bars offer relevant advantages, including relatively low cost, high tensile strength, low self-weight, and high corrosion resistance [1, 2].

Despite these advantages, a challenging aspect associated with the use of these bars is their behavior at elevated temperatures. Generally, above 100 °C, a reduction in the mechanical strength of the bars occurs. At the glass transition temperature (Tg), the polymeric matrix loses rigidity and its ability to transfer stresses between the fibers. At higher temperatures, between 250 °C and 400 °C, known as the decomposition temperature (Td), the polymeric matrix may undergo degradation or decomposition [3]. Consequently, GFRP bars may exhibit unfavorable behavior when exposed to fire and elevated temperatures, both during and after fire events.

In addition to the degradation of polymeric bars, concrete also undergoes significant deterioration when subjected to high temperatures. When exposed for prolonged periods to temperatures above 300 °C, concrete exhibits various physical and chemical changes in its constituents [4]. In terms of mechanical properties, compressive strength decreases drastically between 300 °C and 800 °C, leaving only a minimal residual strength. Similar behavior is observed for properties such as flexural strength, tensile strength, and elastic modulus [5].

The main changes responsible for alterations in the mechanical properties of concrete include: (1) evaporation of free water, physically adsorbed water, chemically bound water, and capillary water; (2) decomposition of hydration products, such as AFt, AFm, calcium hydroxide, and C-S-H; (3) changes in pore structure, with an increase in pore size and porosity; (4) microstructural alterations involving the formation of microcracks in the hardened cement matrix and the interfacial transition zone starting at approximately 400 °C; and (5) phase transformations and possible disintegration of aggregates [5]. In addition, thermal properties of concrete, such as thermal conductivity, specific heat, thermal diffusivity, and mass loss, significantly influence heat transfer within structural elements [6]. Therefore, it is essential to evaluate the behavior of concrete and polymeric reinforcement jointly when subjected to elevated temperatures.

Another relevant phenomenon associated with concrete exposure to fire is explosive spalling. LIU et al. [7] observed that this phenomenon can occur due to three main mechanisms: thermo-hygral, thermo-mechanical, and thermo-chemical. Thermo-hygral spalling is associated with the buildup of vapor pressure in concrete pores due to the obstruction of moisture migration. Thermo-mechanical spalling results from the combination of applied stresses and thermal stresses induced by restraints. Thermo-chemical spalling occurs due to the decomposition of hydration products and calcite, as well as the rehydration of calcium oxide [7].

Spalling can manifest in various forms, ranging from surface spalling to violent explosive dislodgement. Thermo-hygral spalling is commonly reported in the 220–320 °C range, thermo-mechanical spalling is linked to thermal stresses between 430 and 660 °C, and thermo-chemical spalling becomes critical above 700 °C [7]. The consequences of this phenomenon include rapid loss of cross-sectional area, exposure of reinforcement, and premature collapse during fire events [8]. Recent studies indicate that FRP confinement techniques can partially restore the strength of heat-damaged concrete up to about 400 °C, though efficiency diminishes significantly beyond 600 °C [9, 10]. Tests on reinforced concrete frames subjected to high temperatures also revealed substantial reductions in structural ductility and stiffness [11].

To mitigate spalling, various thermal protection systems have been developed, including coatings such as FIRECOAT and REALROCK, as well as advanced insulation systems capable of delaying heat penetration and enhancing the fire resistance of FRP-reinforced concrete elements [12, 13]. However, another effective strategy involves incorporating polymeric fibers into the concrete matrix, particularly polyvinyl alcohol (PVA) fibers, which can reduce explosive spalling by creating vapor relief channels upon melting at high temperatures.

From a structural perspective, GFRP bars exhibit linear stress-strain behavior up to rupture, lack of yielding, and lower modulus of elasticity compared to steel bars, resulting in more brittle structural performance [14, 15]. To compensate for this limitation, GFRP-reinforced concrete beams are typically designed with higher safety factors than those used for steel-reinforced structures [16]. Due to the lower modulus of elasticity, these beams also tend to show wider and more frequent cracks, as well as greater deflections, compared to conventional reinforced concrete elements [17].

One effective strategy to enhance concrete cracking resistance and ductility involves fiber incorporation, as recommended in the ACI 544.4R-18 guide [18]. In addition to improving concrete’s mechanical performance, fibers also contribute to better high-temperature behavior, depending on fiber type and dosage. Among various fiber types, polyvinyl alcohol (PVA) fibers exhibit particularly favorable characteristics, such as high adhesion to the cementitious matrix, elastic modulus close to that of concrete, and ability to form strong chemical bonds between their hydroxyl groups and the C-S-H formed during hydration reactions. These properties increase flexural strength and control cracking, with recommended volume additions below 1.0% [19].

Polymeric fibers with low melting points, such as polyvinyl alcohol (PVA) and polypropylene (PP), melt when concrete is exposed to high temperatures. This process creates new pathways for water vapor release, reducing internal pore pressure and thermal gradient-related damage, thereby enhancing spalling resistance [20].

Several design codes and guidelines have been developed for reinforced concrete structures using FRP bars, notably the “Guide for the Design and Construction of Structural Concrete Reinforced with Fiber-Reinforced Polymer (FRP) Bars” (ACI 440.1R-15), “Design and Construction of Building Structures with Fibre-Reinforced Polymers” (CSA S806-12 (R2021)), and the “Building Code Requirements for Structural Concrete Reinforced with Glass Fiber-Reinforced Polymer (GFRP) Bars - Code and Commentary” (ACI CODE-440.11-22) [21].

In the design of flexural structural elements, these guidelines generally adapt principles originally developed for steel-reinforced concrete structures [22]. While steel-reinforced elements are designed to exhibit tension-controlled behavior, characterized by steel yielding prior to concrete crushing, GFRP bar-reinforced beams display different behavior due to the linear-elastic and brittle nature of these bars [22]. Recent studies have also employed fire protocols and finite element simulations to analyze the residual performance of GFRP-reinforced concrete elements following fire exposure [23, 24].

According to the American Concrete Institute ACI 440.1R-15 guide [16], two failure modes are considered in the design of GFRP bar-reinforced elements: sudden failure by concrete crushing and sudden failure by tensile rupture of the bar fibers. The former mode is deemed slightly more desirable, as it allows some inelastic behavior prior to failure. In this context, the enhanced post-peak deformation of fiber-reinforced concrete can contribute to improving the ductility and ultimate flexural strength of polymeric bar-reinforced beams [25].

Studies have investigated the use of synthetic fibers in concrete beams reinforced with GFRP bars. Experimental results showed that adding polypropylene fibers at dosages of 0.55% and 1.10% led to significant reductions in instantaneous deflection and an increase in average cracking load [17]. ISSA et al. [26] also observed that incorporating 0.5% polypropylene fibers in GFRP-reinforced beams resulted in a 66.70% increase in the deformability factor.

Studies on the effect of temperature on GFRP bars indicate significant reductions in mechanical strength following thermal exposure. HOSSEINI et al. [27] observed a 23% reduction in the tensile strength of bars exposed to 80 °C for one month. Additionally, concrete beams reinforced with GFRP and exposed to 400 °C exhibited greater crack widths, increased deflections, and reduced load-carrying capacity [28].

Specific studies on PVA fibers also indicate strong thermal degradation of these fibers at elevated temperatures. MAGALHÃES et al. [29] observed significant reductions in the elastic modulus and tensile strength with increasing temperature. However, the melting of these fibers may contribute to alleviating internal vapor pressure in concrete [30]. Tests conducted by CAO et al. [31] showed that concretes containing PVA fibers exhibited failure without spalling. Similar results were observed by ÇAVDAR [32], who verified improved flexural strength performance at high temperatures for composites containing PVA fibers.

1.1. Novelty and significance of the research

Despite advances in research on the fire resistance of FRP-reinforced structural elements and the substantial number of studies on fiber-reinforced concrete, significant gaps persist in the scientific literature. Most experimental studies on the fire resistance of fiber-reinforced concretes primarily focus on steel and polypropylene fibers, with a very limited number of investigations involving other polymeric fibers, such as polyvinyl alcohol (PVA) fibers [20].

Additionally, numerous studies have separately investigated the behavior of GFRP bars under high temperatures or the performance of fiber-reinforced concretes under severe thermal conditions. However, these investigations typically do not simultaneously address the combined effects of GFRP reinforcement and polymeric fibers incorporated into the concrete matrix. Consequently, discussions on the structural behavior of concrete beams reinforced with GFRP bars and supplemented with PVA fibers under high-temperature exposure remain scarce.

Consequently, a significant knowledge gap exists regarding the behavior of structural elements combining fiber-reinforced concrete and GFRP reinforcement when subjected to thermal cycles. Understanding this behavior is particularly relevant for structures at risk of fire, such as buildings, storage facilities, tunnels, bridges, and other critical infrastructure.

In this context, the main contribution of this research lies in the experimental evaluation of the combined effect of PVA fibers and GFRP bars on concrete beams subjected to thermal cycles. Unlike previous studies, which analyzed these materials separately, this work investigates in an integrated manner the mechanical performance and structural behavior of GFRP-reinforced beams containing different PVA fiber contents after exposure to elevated temperatures.

Thus, this study aims to assess whether the incorporation of these fibers can mitigate the structural brittleness and loss of mechanical strength commonly observed in GFRP-reinforced beams after heating, thereby advancing the understanding of hybrid structural systems comprising polymer fiber-reinforced concrete and GFRP reinforcement.

Accordingly, the main objective of this research is to experimentally evaluate the influence of different PVA fiber contents on the mechanical behavior and high-temperature performance of GFRP-reinforced concrete beams. To this end, concrete beams were reinforced with 12 mm diameter GFRP bars and PVA fibers at three volume contents (0%, 0.10%, and 0.15%), exposed to thermal cycles at 300 °C and 500 °C, and subsequently tested to four-point bending failure.

2. MATERIALS AND METHODS

2.1. Experimental program stages

In this study, the influence of polymeric fibers at three volumetric contents (0%, 0.10%, and 0.15% by volume) was investigated in concrete beams reinforced with GFRP bars after exposure to elevated temperatures. For each fiber content, 11 specimens were produced, as illustrated in Figure 1, resulting in a total of 33 specimens across the three addition levels. Among the specimens for each content, six were cylindrical with dimensions of 20 × 10 cm for testing void index (per ABNT NBR 9778 [33]), compressive strength (per ABNT NBR 5739 [34]), and dynamic modulus of elasticity (per ABNT NBR 15630 [35]).

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Figure 1
Experimental program flowchart.

The remaining five specimens for each fiber content, referred to as beams, were prismatic with dimensions of 35 × 10 × 10 cm. Of these beams, one was heated in a furnace to 300 ºC and another to 500 ºC, while the remaining three were kept at room temperature. After exposure to elevated temperatures, all beams were subjected to ultrasonic pulse velocity (UPV) testing (per ABNT NBR 8802 [36]) and flexural tensile strength testing (per ABNT NBR 12142 [37]). The ages at which each test was performed are presented in Figure 1.

The beams and cylinders were cast and cured according to ABNT NBR 5738 [38]. The beams were cast in two layers, each compacted manually with 25 strokes per layer, in addition to five strokes applied to the sides of the mold. The GFRP bars were positioned after ensuring a concrete cover of 2 cm. After demolding, both cylindrical and prismatic specimens were stored in a humid chamber at a temperature of 23 ± 2 ºC and relative humidity above 95%. No top longitudinal reinforcement or transverse reinforcement (stirrups) was used in the beams. The geometric configuration of the beams is shown in Figure 2.

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Figure 2
Dimensions and reinforcement details of the tested beams.

2.2. Material properties

The materials used in the concrete included CPV Portland cement, natural riverbed sand, crushed stone, superplasticizer admixture, PVA fibers, and water. The physical properties of the cement and aggregates are shown in Table 1.

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Table 1
Physical properties of aggregates.

The superplasticizer additive used is based on polycarboxylates and has the following properties, according to the supplier: a specific gravity of 1.19 g/mL, a pH range of 6 to 9, a brown appearance/color, and a recommended dosage between 0.2% and 1.5%.

The polymeric fibers used in this study are polyvinyl alcohol (PVA) fibers. They have a smooth surface without end anchoring, and their main physical and mechanical properties, according to the manufacturer, are presented in Table 2.

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Table 2
Fiber properties.

The glass fiber reinforced polymer (GFRP) bars used in the construction of the beams were produced by the pultrusion process. They have a diameter of 8 mm and a helical surface finish around the bar to enhance adhesion. The values of the main properties of these bars, according to the manufacturer, are presented in Table 3.

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Table 3
Mechanical properties of the bar.

The concrete used in all the specimens was mixed in an automatic vertical-axis concrete mixer. Initially, the dry materials (cement and sand) were homogenized. Subsequently, approximately 75% of the mixing water was added, followed by further homogenization. The superplasticizer was then introduced together with the remaining water.

Finally, the polymeric fibers were added manually in small portions layered atop the mix and were dispersed with the mixer running. All the fibers were incorporated into the mix within 1 minute during this procedure. Prior to incorporating the fibers into the concrete mixture, the fibers were pre-dispersed to separate them from one another. This pre-dispersion step entailed placing the fibers in a plastic bag and using an air blower at ambient temperature to disperse them effectively. The procedure was implemented specifically to minimize fiber clumping and thereby facilitate homogeneous distribution throughout the cementitious matrix.

Although no quantitative assessment of fiber dispersion, such as image analysis or statistical sampling, was performed, visual examination of the fresh concrete mixture revealed no significant agglomeration. This observation supports the consistency and reliability of the produced specimens across all fiber contents. The concrete mix design used for each fiber content is presented in Table 4. The concrete mix consumption in kg/m3 was 295: 878: 1040: 162 (cement: sand: crushed stone: water).

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Table 4
Mix proportions of concrete.

2.3. Test procedure

2.3.1. Exposure to thermal cycle

For each fiber content, two were subjected to thermal cycling tests at 300°C and 500°C. The heating was performed in a muffle furnace starting from room temperature (23 ± 2 °C), with a controlled heating rate of 5 °C/min until reaching the target temperature. This required approximately 55 min and 95 min to reach 300 °C and 500 °C, respectively.

Heating was monitored by the furnace’s internal thermocouple and digital controller (closed-loop control; ±5 °C tolerance). No embedded thermocouples were employed, so reported temperatures reflect chamber air conditions. Once the target temperature was achieved, the specimens were maintained at this level for 3 h, followed by an additional 30 min to stabilize the thermal field.

After the heating cycle, the beams were allowed to cool naturally in still air under laboratory conditions, without forced ventilation, until reaching room temperature. According to the adopted heating ramp (5 °C/min), the time to reach the glass transition temperature (Tg) of the GFRP bars can be estimated by tTg ≈ (TTg−23)/5 minutes. For typical resin systems with Tg between 80°C and 120°C, this corresponds to approximately 11-19 minutes from the start of heating, which is indicated in Figure 3.

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Figure 3
Temperature-time curves of thermal cycles.

The selection of 300 °C and 500 °C as the maximum exposure temperatures was justified by: (i) the onset of significant degradation in concrete and hydrated cement products above ~300 °C, with strength reduction and microcracking intensification; (ii) the typical decomposition range of GFRP polymer matrices (~250 - 400 °C); and (iii) prior studies employing analogous thresholds to simulate moderate and severe post-fire exposures. Additionally, PVA fibers exhibit pronounced mass loss between ~300 °C and 410 °C, creating vapor-relief pathways. Therefore, the exposure at 300 °C captures this transition, while 500 °C represents a severe condition where both concrete and GFRP deterioration impairs flexural response. The adopted temperature-time history is illustrated in Figure 3, showing the heating ramp, plateau, and cooling stage.

2.3.2. Physical tests

Water absorption, void index, and specific gravity were determined according to ABNT NBR 9778 [33], using cylindrical specimens tested in triplicate. Ultrasonic wave propagation velocity tests were performed on all molded beams in accordance with ABNT NBR 8802 [36]. The equipment used was the Pundit Lab+ with a 150 kHz frequency transducer, a wavelength of 24.7 mm, and a diameter of 2.8 cm. The transmission method adopted was indirect. With the transmitter transducer fixed 2.5 cm from the end, marked in red in Figure 4, two sets of readings were performed, with the receiver transducer positioned at distances of 10 cm and 20 cm, and then at 15 cm and 30 cm from the emitter, all aligned in a straight line. This totalled 4 propagation time readings for each beam.

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Figure 4
Methodology used for indirect ultrasonic measurement.

The dynamic modulus of elasticity of these beams was calculated in accordance with ABNT NBR 15630 [35]. Considering that the presence of internal reinforcement bars may influence ultrasonic wave propagation, the results obtained from specimens with different geometries (cylindrical and prismatic) were not directly compared in this study.

UPV and Ed measurements on cylindrical specimens were performed only at room temperature. This decision was based on two main considerations: (i) the cylindrical specimens were primarily intended for the characterization of the reference mechanical and physical properties of the concrete; and (ii) after the thermal cycle, their reduced size and geometry made them more susceptible to non-uniform heating, edge effects, and excessive surface cracking. Therefore, only prismatic beams were evaluated after heating, as they provide more representative data of the structural behavior.

2.3.3. Mechanical tests

Prior to the compressive strength test, the specimens were rectified to obtain parallel and plane loading surfaces. No capping materials such as sulfur mortar or neoprene pads were employed. Surface grinding was the only method used to prepare the specimen ends, in accordance with ABNT NBR 5739 [34]. The compressive strength test was performed on a universal machine EMIC DL-30000 with a loading rate of (0.25 ± 0.05) MPa/s, following ABNT NBR 7215 [39]. Dynamic modulus of elasticity of cylinders was determined via ABNT NBR 15630 [35]. The equipment used was the Pundit Lab+ with a 150 kHz frequency transducer, a wavelength of 24.7 mm, and a diameter of 2.8 cm.

The beams were tested in flexural tension under a four-point bending test according to ABNT NBR 12142 [37]. However, the flexural tensile strength was not calculated strictly according to the standard, since failure occurred outside the middle third of the span, at a distance greater than 5% of the beam length (l). The loading device was coupled to the EMIC DL-30000 testing machine, ensuring that the applied load was perpendicular to the upper and lower faces of the specimen, without eccentricities. The instrumentation follows the configuration described in Figure 5(a), while the test setup adopted in this study is illustrated in Figure 5(b).

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Figure 5
Four-point bending test setup: (a) isometric schematic from ABNT NBR 12142 [37]; (b) experimental laboratory setup.

After failure, each beam was photographed. The images were then processed by converting them to black and white, removing identification marks, and highlighting the cracks in red to facilitate visualization. The beams were identified according to fiber content and thermal exposure. Beams without fibers and tested at reference temperature (no heating) were designated V000-RT, divided into three specimens, and those heated to 300 ºC and 500 ºC were designated V000-300 and V000-500, respectively. The same nomenclature was adopted for the other fiber contents, for example: V010-RT-1, V010-RT-2, V010-RT-3, V010-300, V010-500, V015-RT-1, V015-RT-2, V015-RT-3, V015-300, and V015-500.

2.4. Data analysis

Statistical analyses were applied to tests with three replicates per group using one-way analysis of variance (ANOVA), followed by Tukey’s post-hoc test for multiple comparisons. All ANOVA results reported herein satisfied prerequisite assumptions: data normality (Shapiro-Wilk test) and variance homogeneity (Levene’s test), with p > 0.05 in both cases.

3. RESULTS AND DISCUSSION

3.1. Dynamic modulus of elasticity and ultrasonic pulse velocity

Ultrasonic pulse velocity (UPV) and dynamic elastic modulus (Ed) results for cylindrical specimens are presented in Table 5. These indicate that fiber addition reduced both UPV and Ed. ANOVA (Table 6) and Tukey’s test (Table 7) confirm statistically significant Eddifferences between control and fiber-reinforced groups. However, the difference between the 0.10% and 0.15% fiber contents was not statistically significant.

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Table 5
Ultrasonic pulse velocity and dynamic modulus of elasticity for cylindrical specimens (direct transmission).
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Table 6
One-way ANOVA results for the dynamic modulus of elasticity (Ed) of cylindrical specimens.
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Table 7
Tukey’s post-hoc test – Dynamic modulus of elasticity of cylindrical specimens.

UPV and Ed results for beams are shown in Table 8. For unheated beams, significant Edreductions occurred only between the 0.10% and 0.15% fiber groups (Table 9 and 10). In other words, the addition of 0.10% fibers did not significantly affect the dynamic modulus of elasticity of the beams. Among the specimens exposed to 300 °C, a reduction in UPV and Ed was observed only for the beam containing 0.15% fibers, when compared with its respective reference condition. On the other hand, when the specimens subjected to the 500 °C thermal cycle were compared with their respective reference conditions, a significant reduction in UPV and Ed was observed for all fiber contents.

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Table 8
Ultrasonic pulse velocity and dynamic modulus of elasticity for beams specimens (indirect transmission).
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Table 9
One-way ANOVA results for the dynamic modulus of elasticity (Ed) of beams specimens.
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Table 10
Tukey’s post-hoc test – Dynamic modulus of elasticity of beams specimens.

NOUSHINI et al. [40] observed that reinforced concrete beams with the addition of PVA fibers at volume fractions of 0.50% and 0.25%, without exposure to a thermal cycle, exhibited a reduction in both the modulus of elasticity and compressive strength at the higher fiber content. Similarly, SI et al. [41] analyzed mortar samples containing PVA fibers with different fiber reinforcing index (RI) and found that the UPV in fiber-reinforced matrices was consistently lower than in matrices without fibers. Since UPV reflects the density, uniformity, and homogeneity of the matrix, the authors emphasized that PVA fibers introduce defects into the cementitious matrix. However, within an intermediate range of RI, the fibers adequately mitigate these defects, resulting in a compact matrix with UPV values close to those of a fiber-free matrix [41].

The behavior of UPV and dynamic modulus of elasticity observed at elevated temperatures is expected due to the degradation of concrete, which becomes more pronounced at temperatures above 300 °C [4], as well as the decomposition of PVA fibers, which generally begins at temperatures below 300 °C. In the study by MAGALHÃES et al. [29], the thermal degradation of PVA fibers began at approximately 239 °C, with a mass loss of about 4% up to 300 °C, followed by a 71% mass loss between 300 °C and 410 °C. In concrete samples reinforced with polyethylene terephthalate (PET) fibers and heated up to 700 °C, a reduction in UPV was observed for specimens with higher fiber contents, which was attributed to structural modifications caused by increased porosity resulting from the incorporation of PET fibers [42]. Considering the characteristics of PVA fibers and the UPV test, at high temperatures the fibers melt and create voids within the concrete beam, which interrupt the propagation of ultrasonic waves and consequently reduce UPV.

UPV measured by indirect transmission is consistently lower than that obtained by direct transmission in the same specimen, with differences typically ranging from 5.0% to 20.0%, depending also on the quality of the concrete [43]. When comparing the cylindrical specimens and beams at the reference temperature, measured using direct and indirect transmission methods, reductions in UPV of 21.38%, 16.16%, and 28.33% were observed for fiber contents of 0%, 0.10%, and 0.15%, respectively.

3.2. Determination of void index and bulk density

The results of the physical tests are presented in Table 11. It can be observed that the addition of fibers reduces the concrete density, proportionally to the increase in fiber content. The analysis of variance (ANOVA) (Table 12) and Tukey’s test (Table 13) indicate a statistically significant difference among all evaluated groups. This ­reduction can be attributed to the lower density of the fibers (1.30 g/cm3) compared with that of the reference concrete (2.28 g/cm3).

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Table 11
Void index, absorption, and bulk density of concrete.
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Table 12
One-way ANOVA results for the bulk density of concrete (real sample).
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Table 13
Tukey’s post-hoc test – Bulk density of concrete.

Despite the lower density, the average values of the void index and water absorption were lower in the samples containing fibers, indicating a smaller amount of permeable pores in the matrix. Similarly, JIANG et al. [44] observed that mortars reinforced with polypropylene (PP) fibers exhibited a lower water penetration depth in permeability tests. The reduction in void index and water absorption may be related to the ability of fibers to reduce crack formation and disconnect pore networks.

Among the evaluated fiber contents, the concrete with 0.10% fibers presented a lower void index compared with the 0.15% fiber content. This behavior may be attributed to poorer fiber dispersion at higher fiber contents, which favors fiber agglomeration and creates regions with higher porosity in the cementitious matrix.

3.3. Compressive strength

The compressive strength results of the cylindrical specimens are presented in Table 14. The analysis of variance (ANOVA) (Table 15) and Tukey’s test (Table 16) indicated that there was no statistically significant difference between the reference concrete and the concrete containing 0.10% fibers. However, a significant reduction in compressive strength was observed for the 0.15% fiber content compared with the other groups.

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Table 14
Compressive strength of the specimens.
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Table 15
One-way ANOVA results for the compressive strength.
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Table 16
Tukey’s post-hoc test – Compressive strength.

The reduction in compressive strength at higher fiber contents has also been reported by ÇAVDAR [32] in mortars reinforced with PVA fibers, and by CAO et al. [31] in high-strength concretes. One factor associated with this reduction is that fibers exhibit a more ductile behavior compared with the cement and aggregate matrix, which may introduce discontinuities within the cementitious matrix [32]. Higher fiber contents may also lead to dispersion difficulties within the matrix, contributing to the formation of fiber agglomerates. This phenomenon impairs the compaction and homogeneity of the concrete, resulting in a reduction in compressive strength.

3.4. Flexural tensile strength of the beams

3.4.1. Failure patterns

The cracking patterns of the beams after failure in the flexural tensile test are presented in Figures 6 and 7. Beam V010-500 is shown in its original condition (Figure 6) and after image processing (Figure 7h). For the beams not exposed to the thermal cycle, including the six additional beams not represented in Figure 7, variability in cracking patterns was observed among specimens with the same fiber content. This variability prevented a clear assessment of the influence of fiber content on the cracking pattern.

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Figure 6
Failure of beam V010-500 after the flexural test.
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Figure 7
Cracking patterns for the reference temperature with fiber contents of (a) 0.00%, (b) 0.10%, (c) 0.15%; after heating to 300°C with fiber contents of (d) 0.00%, (e) 0.10%, (f) 0.15%; after heating to 500°C with fiber contents of (g) 0.00%, (h) 0.10%, (i) 0.15%.

For the specimens exposed to 300 °C, the cracking patterns were similar between the beams without fibers and those containing 0.10% fibers. Among the specimens exposed to 500 °C, the beam with 0.10% fiber content exhibited a greater number of cracks. All beams failed by shear in a region close to the supports, outside the middle third extended by 1.5 cm. As a result, neither tensile rupture of the polymer bars nor crushing of the concrete in the upper face was observed.

3.4.2. Failure load

From the test, the ultimate load values were obtained for each beam, together with the variation in failure load (ΔF) after exposure to high temperatures compared with the non-heated specimens, as presented in Table 17. The results show that exposure to 500 °C had a negative influence on the flexural tensile strength for all evaluated fiber contents. This behavior may be attributed to the decomposition of the polymeric fibers, resulting in the loss of their contribution to the mechanical resistance of the concrete. In addition, even for the specimen without fiber addition, exposure to 500 °C also resulted in a reduction in strength. This reduction can be attributed to the deterioration of the polymeric reinforcement and the thermal degradation of the concrete matrix.

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Table 17
Flexural tensile strength.

The graph in Figure 8 illustrates the increase in flexural tensile strength resulting from fiber addition. For the specimens not exposed to high temperatures, the addition of 0.15% fibers resulted in a 48.64% increase in the supported load compared with the reference mixture.

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Figure 8
Graph of flexural tensile strength vs. temperature.

The increase in flexural strength provided by the addition of PVA fibers has also been observed by other authors. In mortar specimens at room temperature (21 °C), the addition of 1.5% PVA fibers by volume increased flexural strength by approximately 43% [32]. In unheated high-strength concrete specimens, the addition of 0.4% PVA fibers increased flexural strength by about 32% [25]. In concrete beams reinforced with a combination of steel and GFRP bars at room temperature (25 °C), the addition of 1.0% PVA fibers by volume increased the load-carrying capacity by approximately 16% [44].

In concrete beams with PVA fiber addition and hybrid reinforcement using GFRP and steel bars, the ultimate load capacity increased by 19.3% and 20.6% for PVA fiber contents of 4.5 and 7.5 kg/m3, respectively, compared with the fiber-free beam [45]. SUN et al. [46] reported that concrete beams reinforced with GFRP bars and containing 1% and 2% PVA fibers by volume, tested under four-point bending, exhibited increases of 15.4% and 34.6%, respectively, in limit load compared with beams without fibers. An increase in ultimate capacity of 12% and 27% for PVA fiber contents of 0.75% and 1.0% in hybrid beams reinforced with GFRP and steel bars was also reported by SAID et al. [47].

Heating the beams to 300 °C had minimal influence on the tensile strength for fiber contents of 0.00% and 0.10%. Regarding the effect of thermal treatment on specimens with different fiber contents, the mixture with 0.10% fibers showed the smallest loss of strength when heated. The mixture without fibers (0.00%) presented a reduction in ultimate load relative to the reference temperature (ΔF) of 2.18% and 23.45% at 300 °C and 500 °C, respectively. For the 0.15% fiber content, the reductions were 42.41% and 41.71% at 300 °C and 500 °C, respectively. In contrast, for the 0.10% fiber content, there was an increase in strength of 2.72% and a reduction of 15.68% at 300 °C and 500 °C, respectively.

Furthermore, although the beams with 0.15% fiber content showed a greater reduction in ΔF compared with those without fibers, the ultimate load at 500 °C remained higher. Similar results have been reported by other researchers. Therefore, Figure 8 suggests that the incorporation of PVA fibers at contents of 0.10% and 0.15% by volume improves the residual flexural tensile strength of concrete exposed to 500 °C.

A higher residual flexural strength in specimens with PVA fiber addition after exposure to a thermal cycle was also observed by ÇAVDAR [32] in mortar specimens and by EL-SAYED et al. [48] in concrete beams reinforced with GFRP and steel bars. The flexural strength of mortar without fibers decreased by about 76% at 450 °C and approximately 87% at 650 °C, whereas for mortars with 2.0% PVA fibers the reductions were about 53% at 450 °C and 77% at 650 °C [28]. The load-carrying capacity of beams without fibers decreased by about 12% at 300 °C and 32.2% at 600 °C, while for PVA fiber contents of 0.50% and 1.0% the reductions were approximately 9.7% and 7.4% at 300 °C, and 31.0% and 38.5% at 600 °C, respectively [48].

3.4.3. Statistical analysis

The statistical analysis of the unheated (RT) specimens using ANOVA (Table 18) and the Tukey test (Table 19) indicated that there was no statistically significant difference between the reference group and the 0.10% fiber content. However, significant differences were observed for the group with 0.15% fiber addition compared with the 0.00% and 0.10% groups. Therefore, the addition of the higher fiber content significantly contributed to the increase in flexural tensile strength under ambient conditions (without heating).

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Table 18
One-way ANOVA results for the flexural tensile strength.
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Table 19
Tukey’s post-hoc test – flexural tensile strength.
3.4.4. Load-deflection behavior

The load vs. deflection curves, presented in Figures 9 and 10, highlight the influence of elevated temperatures on the flexural behavior of the beams, corroborating the discussion presented previously.

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Figure 9
Load vs. deflection curve of the beams for each fiber content under different temperatures: (a) 0% fiber content; (b) 0.10% fiber content; (c) 0.15% fiber content.
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Figure 10
Load vs. deflection curve of the beams for each temperature with different fiber contents.

The thermal cycle with exposure to 500 °C generally showed the greatest impact on the flexural strength of the beams, except for the 0.15% fiber content, for which the ultimate load observed at 300 °C was slightly lower than that at 500 °C. The average deflection at failure of the unheated beams (three specimens) and those exposed to heating (300 °C and 500 °C) showed similar values for the 0.00% and 0.10% fiber contents. In contrast, although the beams with 0.15% fibers exhibited a higher average deflection at failure under unheated conditions compared with the other fiber contents, a decrease in deformation was observed after the heating process.

Similar behavior has been reported by other authors in concrete beams reinforced with GFRP bars without fiber reinforcement. Beams heated to 100 °C, 200 °C, 300 °C, and 500 °C showed an increase of 5.6% in ultimate load capacity at 100 °C, followed by reductions of 1.2%, 8.5%, and 93.8%, respectively. In addition, a 69.5% reduction in deflection at failure was observed at 500 °C compared with unheated beams [49]. Beams subjected to thermal cycles at 200 °C, 400 °C, and 600 °C showed reductions in ultimate load capacity of 2.7%, 10.7%, and 76.0%, respectively, relative to room temperature [28]. These results highlight the critical role of GFRP bar deterioration in the reduction of tensile resistance, particularly in the absence of fiber reinforcement.

Figure 10 illustrates the load vs. deflection response of beams with different fiber contents after heating. At 300 °C, the 0.10% fiber content showed the highest ultimate load and deflection, whereas the beam with the highest fiber content exhibited the lowest ultimate load and deformation. At 500 °C, the 0.10% fiber content continued to exhibit the highest ultimate load, although its maximum deflection was lower than that of the reference beam. It is important to note that the effects of fiber content in concretes exposed to high temperatures may be inconsistent and may not follow a clear trend [50].

No significant improvement in ductile behavior was observed with increasing fiber content at any of the heating temperatures. This may be attributed to the failure mechanisms governing the behavior of these beams under elevated temperatures. A similar trend was observed by HASSANLI et al. [51], in which fibers did not significantly improve the ductility of GFRP-reinforced concrete slabs, while steel-reinforced slabs exhibited superior ductile behavior in comparison.

3.4.5. Toughness

In addition to the ultimate load, the energy absorption capacity (toughness) is also a relevant parameter. The toughness of a reinforced concrete beam is defined as the amount of energy absorbed by the beam during loading. The area under the load vs. deflection curve is used to calculate the beam toughness [52]. Table 20 and Figure 11 summarize the toughness values of the beams.

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Table 20
Toughness.
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Figure 11
Toughness of the tested beams.

The results of the analysis of variance (Table 21) for the unheated beams indicate significant differences among the groups. The Tukey test (Table 22) reveals that a statistically significant difference occurred only for the beams with 0.15% fiber addition compared to the 0.00% and 0.10% contents. These results indicate that the higher fiber content significantly increases the energy absorption capacity of the beams under ambient temperature conditions. PVA fibers bridge cracks, distribute stress, and prevent crack widening, thereby enhancing toughness and ductility [53].

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Table 21
One-way ANOVA results for the toughness.
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Table 22
Tukey’s post-hoc test – toughness.

Regarding thermal exposure, Figure 11 illustrates that beams with 0.10% fiber content exhibited higher toughness at both 300 °C and 500 °C. Conversely, the 0.15% fiber dosage did not produce the expected improvement in toughness after heating at 300 °C and 500 °C.

4. CONCLUSIONS

This study explored the use of PVA-type polymeric fibers in concrete beams reinforced with polymeric bars to enhance mechanical behavior, particularly under exposure to high temperatures. The main variables of the study were fiber contents of 0.00%, 0.10%, and 0.15% by volume, and exposure of the specimens to thermal cycles, divided into unheated, 300°C, and 500°C conditions. The main conclusions drawn from the study are presented below:

  • The addition of fibers reduced the ultrasonic pulse velocity and the dynamic elastic modulus in samples without exposure to the thermal cycle.

  • The addition of PVA fibers to concrete, at contents of 0.10% and 0.15%, reduces the dynamic modulus of elasticity (Ed).

  • In beams reinforced with GFRP bars, the addition of PVA fibers at contents of 0.10% and 0.15% had no significant effect on the dynamic modulus of elasticity (Ed) compared with the reference beam.

  • In the samples subjected to the thermal cycle, only at 500°C did all fiber contents show a significant reduction in UPV. This reduction is attributed to the fiber melting temperature, which creates larger voids in the samples.

  • The addition of PVA fibers to concrete, at contents of 0.10% and 0.15%, reduces the bulk density proportionally with increasing fiber content. Specimens with 0.10% fiber content showed a lower void index and lower water absorption compared with the other groups.

  • The 0.10% fiber content in the concrete did not significantly affect the compressive strength, whereas the 0.15% fiber content resulted in a reduction in compressive strength. This behavior may be related to the dispersion of fibers within the cementitious matrix.

  • The failure mode in the flexural tensile test of all beams occurred by shear near the supports. For the unheated beams, no clear cracking pattern was identified among the groups.

  • Regarding the cracking pattern of beams exposed to 300°C, similar crack distributions were observed between the fiberless beams and those containing 0.10% fibers. However, for beams heated to 500°C, the 0.10% fiber content exhibited a greater number of cracks.

  • In unheated beams reinforced with GFRP bars, the addition of 0.15% PVA fibers significantly increased the flexural tensile strength. In contrast, the 0.10% fiber content did not produce a significant difference in flexural tensile strength.

  • When evaluating thermal impacts on the beams, the 0.10% fiber addition was identified as the optimal content for minimizing strength degradation. This was evidenced by a slight strength gain of 2.72% at 300 °C and a moderate loss of 15.68% at 500 °C. These results correlate with the toughness analysis, where the 0.10% group achieved the highest energy absorption at both temperature thresholds.

  • Exposure to a temperature of 500°C had a strong negative impact on the tensile strength of all tested fiber contents. Nevertheless, at this temperature, the beams with fiber addition exhibited a higher final rupture load compared to those without fiber addition.

  • Regarding ductility, no clear improvement in ductile behavior was observed with the addition of fibers at the tested heating temperatures.

From an engineering perspective, these findings suggest that while PVA fibers may enhance flexural capacity and residual strength, they cannot be solely relied upon to guarantee satisfactory structural performance under high-temperature conditions. Further research should therefore focus on optimizing fiber dosage, evaluating scale effects, and exploring complementary reinforcement strategies. In this context, OUKAILI et al. [54] observed the impact of shear reinforcement configuration on the load-carrying capacity and cracking pattern of GFRP-reinforced beams. Moreover, it should be emphasized that other degradation mechanisms also play a critical role. For example, MOURA et al. [55] observed significant reductions in tensile strength of GFRP bars depending on the polymeric matrix, with epoxy matrices providing superior residual performance. Similarly, AKBULUT et al. [10] confirmed that FRP confinement effectiveness decreases significantly at 600 °C and above. Furthermore, AKBULUT et al. [9] demonstrated that the cooling regime after fire exposure critically affects residual performance, where rapid water cooling induced severe cracking due to thermal shock. In particular, future investigations should also consider the influence of different polymer matrices in GFRP bars [55], the hybrid use of multiple fiber types in the concrete matrix [53], the effect of cooling regimes after heating [9], and the use of innovative insulation coatings [12]. These aspects are essential to advance the engineering applicability of FRP-reinforced elements under fire scenarios.

The observations reported here are limited to the type and dosage of the fibers used in this study, as well as the type and characteristics of the polymeric bar adopted. Considering that the beams are very short (35 x 10 x 10 cm), the results cannot be extrapolated to slender or even deep beams. That is, the results cannot be directly extrapolated to larger or more slender structural elements, such as full-scale bridge or tunnel structures. Further studies are needed to investigate the effect of PVA fiber dosage on the flexural behavior of beams reinforced with GFRP exposed to high temperatures.

Finally, this study was purely experimental, with no Finite Element (FE) analysis conducted to simulate thermal gradients or structural response. Future research should further investigate the influence of PVA fibers and develop numerical models to validate the experimental findings and predict the structural behavior under fire scenarios.

In conclusion, this study evidence that fiber addition is not a linear factor for thermal resilience. Therefore, dosage must be carefully controlled to ensure the balance between structural behavior and fire safety.

5. ACKNOWLEDGMENTS

The authors would like to thank the Laboratory of Materials and Technology of the Built Environment – Lamtac at the Federal University of Rio Grande do Sul – UFRGS for its support in conducting this research.

6. BIBLIOGRAPHY

  • [1] ARCZEWSKA, P., POLAK, M.A., PENLIDIS, A., “Degradation of glass fiber reinforced polymer (GFRP) bars in concrete environment”, Construction & Building Materials, v. 293, pp. 123451, Jul. 2021. doi: https://doi.org/10.1016/j.conbuildmat.2021.123451.
    » https://doi.org/10.1016/j.conbuildmat.2021.123451
  • [2] WU, W., HE, X., YANG, W., et al, “Degradation factors and microstructure degradation characteristics of B/GFRP bars in harsh environment: A review”, Construction & Building Materials, v. 366, pp. 130246, Feb. 2023. doi: https://doi.org/10.1016/j.conbuildmat.2022.130246.
    » https://doi.org/10.1016/j.conbuildmat.2022.130246
  • [3] ROSA, I.C., FIRMO, J.P., CORREIA, J.R., “Experimental study of the tensile behaviour of GFRP reinforcing bars at elevated temperatures”, Construction & Building Materials, v. 324, pp. 126676, Mar. 2022. doi: https://doi.org/10.1016/j.conbuildmat.2022.126676.
    » https://doi.org/10.1016/j.conbuildmat.2022.126676
  • [4] MALIK, M., BHATTACHARYYA, S.K., BARAI, S.V., “Thermal and mechanical properties of concrete and its constituents at elevated temperatures: A review”, Construction & Building Materials, v. 270, pp. 121398, Feb. 2021. doi: https://doi.org/10.1016/j.conbuildmat.2020.121398.
    » https://doi.org/10.1016/j.conbuildmat.2020.121398
  • [5] MA, Q., GUO, R., ZHAO, Z., et al, “Mechanical properties of concrete at high temperature—A review”, Construction & Building Materials, v. 93, pp. 371–383, Sep. 2015. doi: https://doi.org/10.1016/j.conbuildmat.2015.05.131.
    » https://doi.org/10.1016/j.conbuildmat.2015.05.131
  • [6] KODUR, V., “Properties of concrete at elevated temperatures”, ISRN Civil Engineering, v. 2014, pp. 68510, Mar. 2014. doi: https://doi.org/10.1155/2014/468510.
    » https://doi.org/10.1155/2014/468510
  • [7] LIU, J.-C., TAN, K.H., YAO, Y., “A new perspective on nature of fire-induced spalling in concrete”, Construction & Building Materials, v. 184, pp. 581–590, Sep. 2018. doi: https://doi.org/10.1016/j.conbuildmat.2018.06.204.
    » https://doi.org/10.1016/j.conbuildmat.2018.06.204
  • [8] AMRAN, M., HUANG, S.S., ONAIZI, A.M., et al, “Fire spalling behavior of high-strength concrete: A critical review”, Construction & Building Materials, v. 341, pp. 127902, May. 2022. doi: https://doi.org/10.1016/j.conbuildmat.2022.127902.
    » https://doi.org/10.1016/j.conbuildmat.2022.127902
  • [9] AKBULUT, Y.E., NAYIR, S., ALTUNIŞIK, A.C., et al, “Effectiveness of FRP wrapping of heat-damaged concrete in compression for different cooling procedures”, Materials and Structures, v. 58, n. 4, pp. 156, May. 2025. doi: https://doi.org/10.1617/s11527-025-02683-0.
    » https://doi.org/10.1617/s11527-025-02683-0
  • [10] AKBULUT, Y.E., NAYIR, S., ALTUNIŞIK, A.C., et al, “Experimental assessment of FRP repairing in concrete cylinders exposed high temperatures”, Case Studies in Construction Materials, v. 21, pp. e03656, Aug. 2024. doi: https://doi.org/10.1016/j.cscm.2024.e03656.
    » https://doi.org/10.1016/j.cscm.2024.e03656
  • [11] ÇOLAKOĞLU, H.E., HÜSEM, M., DEMIR, S., et al, “The behavior of reinforced concrete frames exposed to high temperature under cyclic load effect”, Structures, v. 63, pp. 106446, May. 2024. doi: https://doi.org/10.1016/j.istruc.2024.106446.
    » https://doi.org/10.1016/j.istruc.2024.106446
  • [12] ALTUNIŞIK, A.C., AKBULUT, Y.E., ADANUR, S., et al, “Experimental study of the effect of different insulation schemes on fire performance of FRP strengthened concrete: FIRECOAT and REALROCK”, International Journal of Concrete Structures and Materials, v. 17, n. 1, pp. 55, Nov. 2023. doi: https://doi.org/10.1186/s40069-023-00604-5.
    » https://doi.org/10.1186/s40069-023-00604-5
  • [13] ALTUNIŞIK, A.C., AKBULUT, Y.E., ADANUR, S., et al, “Evaluating the high-temperature endurance of FRP-strengthened concrete using an innovative insulation system: Experimental investigation”, Journal of Building Engineering, v. 73, pp. 106444, Apr. 2023. doi: https://doi.org/10.1016/j.jobe.2023.106444.
    » https://doi.org/10.1016/j.jobe.2023.106444
  • [14] KINJAWADEKAR, T.A., PATIL, S., NAYAK, G., “A critical review on glass fiber-reinforced polymer bars as reinforcement in flexural members”, Journal of The Institution of Engineers, v. 104, n. 2, pp. 501–516, 2023. doi: https://doi.org/10.1007/s40030-023-00729-6.
    » https://doi.org/10.1007/s40030-023-00729-6
  • [15] FERNANDES, T.V., PALIGA, A.R., PALIGA, C.M., “Bending reinforced concrete beams with glass fiber reinforced polymer bars: an experimental analysis”, Revista IBRACON de Estruturas e Materiais, v. 14, n. 3, pp. e14306, 2021. doi: https://doi.org/10.1590/s1983-41952021000300006.
    » https://doi.org/10.1590/s1983-41952021000300006
  • [16] AMERICAN CONCRETE INSTITUTE, Guide for the design and construction of structural concrete reinforced with fiber-reinforced polymer (FRP) bars, ACI 440.1R-15, Farmington Hills, ACI, 2015.
  • [17] AL MARAHLA, R.H., SHEHZAD, M.K., GARCIA-TAENGUA, E., “Flexural and deflection behaviour of synthetic fibre reinforced concrete beams reinforced with glass fibre reinforced polymers bars under sustained service load”, Structures, v. 54, pp. 946–955, Aug. 2023. doi: https://doi.org/10.1016/j.istruc.2023.05.134.
    » https://doi.org/10.1016/j.istruc.2023.05.134
  • [18] AMERICAN CONCRETE INSTITUTE, Guide to design with fiber-reinforced concrete, ACI 544.4R-18, Farmington Hills, ACI, 2018.
  • [19] ZHAO, C., WANG, Z., ZHU, Z., et al, “Research on different types of fiber reinforced concrete in recent years: An overview”, Construction & Building Materials, v. 365, pp. 130075, Feb. 2023. doi: https://doi.org/10.1016/j.conbuildmat.2022.130075.
    » https://doi.org/10.1016/j.conbuildmat.2022.130075
  • [20] WU, H., LIN, X., ZHOU, A., “A review of mechanical properties of fibre reinforced concrete at elevated temperatures”, Cement and Concrete Research, v. 135, pp. 106117, Sep. 2020. doi: https://doi.org/10.1016/j.cemconres.2020.106117.
    » https://doi.org/10.1016/j.cemconres.2020.106117
  • [21] ISSA, A.M., ALLAWI, A.A., OUKAILI, N., “Performance of doubly reinforced concrete beams with GFRP bars”, Journal of the Mechanical Behavior of Materials, v. 33, n. 1, pp. 20220308, 2024. doi: https://doi.org/10.1515/jmbm-2022-0308.
    » https://doi.org/10.1515/jmbm-2022-0308
  • [22] ISSA, M.A., ALLAWI, A.A., OUKAILI, N., “Effects of GFRP stirrup spacing on the behavior of doubly GFRP-reinforced concrete beams”, Civil Engineering Journal, v. 10, n. 2, pp. 502–520, Feb. 2024. doi: https://doi.org/10.28991/CEJ-2024-010-02-011.
    » https://doi.org/10.28991/CEJ-2024-010-02-011
  • [23] MAHMOOD, E.M., ALLAWI, A.A., EL-ZOHAIRY, A., “Analysis and residual behavior of encased pultruded GFRP I-Beam under fire loading”, Sustainability, v. 14, n. 20, pp. 13337, Oct. 2022. doi: https://doi.org/10.3390/su142013337.
    » https://doi.org/10.3390/su142013337
  • [24] MAHMOOD, E.M., ALLAWI, A.A., “Experimental and numerical behavior of encased pultruded GFRP beams under elevated and ambient temperatures”, Fire, v. 6, n. 212, pp. 212, May. 2023. doi: https://doi.org/10.3390/fire6050212.
    » https://doi.org/10.3390/fire6050212
  • [25] YANG, J.-M., MIN, K.-H., SHIN, H.-O., et al, “Effect of steel and synthetic fibers on flexural behavior of high-strength concrete beams reinforced with FRP bars”, Composites. Part B, Engineering, v. 43, n. 3, pp. 1077–1086, Apr. 2012. doi: https://doi.org/10.1016/j.compositesb.2012.01.044.
    » https://doi.org/10.1016/j.compositesb.2012.01.044
  • [26] ISSA, M.S., METWALLY, I.M., ELZEINY, S.M., “Influence of fibers on flexural behavior and ductility of concrete beams reinforced with GFRP rebars”, Engineering Structures, v. 33, n. 5, pp. 1754–1763, May. 2011. doi: https://doi.org/10.1016/j.engstruct.2011.02.014.
    » https://doi.org/10.1016/j.engstruct.2011.02.014
  • [27] HOSSEINI, S.M., SHAKIBA, M., BAZLI, M., et al, “Using four-point flexure test to investigate effects of temperature and bar size on the tensile properties of GFRP bars”, Polymer Testing, v. 112, pp. 107627, Aug. 2022. doi: https://doi.org/10.1016/j.polymertesting.2022.107627.
    » https://doi.org/10.1016/j.polymertesting.2022.107627
  • [28] ZHAO, J., PAN, H., WANG, Z., et al, “Experimental and theoretical study on flexural behavior of GFRP- and CFRP-Reinforced concrete beams after high-temperature exposure”, Polymers, v. 14, n. 19, pp. 4002, Sep. 2022. doi: https://doi.org/10.3390/polym14194002. PubMed PMID: 36235949.
    » https://doi.org/10.3390/polym14194002
  • [29] MAGALHÃES, M.S., TOLEDO FILHO, R.D., FAIRBAIRN, E.M.R., “Durability under thermal loads of polyvinyl alcohol fibers”, Matéria, v. 18, n. 4, pp. 1587–1595, Dec. 2013. doi: https://doi.org/10.1590/S1517-70762013000400018.
    » https://doi.org/10.1590/S1517-70762013000400018
  • [30] ABADEL, A.A., KHAN, M.I., MASMOUDI, R., “Influence of elevated temperature on the engineering properties of ultra-high-performance fiber-reinforced concrete”, Materials Science Poland, v. 41, n. 1, pp. 140–160, Mar. 2023. doi: https://doi.org/10.2478/msp-2023-0010.
    » https://doi.org/10.2478/msp-2023-0010
  • [31] CAO, R., YANG, H., LU, G., “Effects of high temperature on the burst process of carbon fiber/PVA fiber high-strength concretes”, Materials, v. 12, n. 6, pp. 973, Mar. 2019. doi: https://doi.org/10.3390/ma12060973. PubMed PMID: 30909627.
    » https://doi.org/10.3390/ma12060973
  • [32] ÇAVDAR, A., “A study on the effects of high temperature on mechanical properties of fiber reinforced cementitious composites”, Composites. Part B, Engineering, v. 43, n. 5, pp. 2452–2463, Jul. 2012. doi: https://doi.org/10.1016/j.compositesb.2011.10.005.
    » https://doi.org/10.1016/j.compositesb.2011.10.005
  • [33] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, Argamassa e concreto endurecidos – Determinação da absorção de água, índice de vazios e massa específica, NBR 9778, Rio de Janeiro, ABNT, 2009.
  • [34] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, Concreto – Ensaio de compressão de corpos de prova cilíndricos, NBR 5739, Rio de Janeiro, ABNT, 2018.
  • [35] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, Argamassa para assentamento e revestimento de paredes e tetos – Determinação do módulo de elasticidade dinâmico através da propagação de onda ultrassônica, NBR 15630, Rio de Janeiro, ABNT, 2009.
  • [36] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, Concreto endurecido – Determinação da velocidade de propagação de onda ultrassônica, NBR 8802, Rio de Janeiro, ABNT, 2019.
  • [37] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, Concreto – Determinação da resistência à tração na flexão de corpos de prova prismáticos, NBR 12142, Rio de Janeiro, ABNT, 2010.
  • [38] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, Concreto – Procedimento para moldagem e cura de corpos de prova, NBR 5738, Rio de Janeiro, ABNT, 2016.
  • [39] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, Cimento Portland – Determinação da resistência à compressão de corpos de prova cilíndricos, NBR 7215, Rio de Janeiro, ABNT, 2019.
  • [40] NOUSHINI, A., SAMALI, B., VESSALAS, K., “Ductility and damping characteristics of PVA-FRC beam elements”, Advances in Structural Engineering, v. 18, n. 11, pp. 1763–1787, Nov. 2015. doi: https://doi.org/10.1260/1369-4332.18.11.1763.
    » https://doi.org/10.1260/1369-4332.18.11.1763
  • [41] SI, W., CAO, M., LI, L., “Establishment of fiber factor for rheological and mechanical performance of polyvinyl alcohol (PVA) fiber reinforced mortar”, Construction & Building Materials, v. 265, pp. 120347, Dec. 2020. doi: https://doi.org/10.1016/j.conbuildmat.2020.120347.
    » https://doi.org/10.1016/j.conbuildmat.2020.120347
  • [42] BISKRI, Y., BABOURI, L., BENZERARA, M., et al, “Mitigating high-temperature vulnerabilities in concrete: utilizing waste plastic fibers for enhanced mechanical resilience and environmental sustainability”, Innovative Infrastructure Solutions, v. 9, n. 7, pp. 252, Jul. 2024. doi: https://doi.org/10.1007/s41062-024-01571-w.
    » https://doi.org/10.1007/s41062-024-01571-w
  • [43] BRITISH STANDARD, Testing concrete – Part 203. Recommendations for measurement of velocity of ultrasonic pulses in concrete, BS 1881: Part 203, London, BS, 1986.
  • [44] JIANG, C., HUANG, S., ZHU, Y., et al, “Effect of polypropylene and basalt fiber on the behavior of mortars for repair applications”, Advances in Materials Science and Engineering, v. 2016, pp. 1–11, 2016. doi: https://doi.org/10.1155/2016/5927609.
    » https://doi.org/10.1155/2016/5927609
  • [45] WANG, B., LIU, G., WANG, Z., “Flexural behavior of polyvinyl alcohol (PVA) fiber concrete beam reinforced with hybrid glass fiber reinforced polymer (GFRP) bars and steel bars”, Structural Concrete, pp. suco.70410, 2025. doi: https://doi.org/10.1002/suco.70410.
  • [46] SUN, Q., JIN, Q., GAO, Y., et al, “Flexural behavior of PVA‐FRC GFRP reinforced concrete beams”, Polymer Composites, v. 42, n. 7, pp. 3331–3348, Jul. 2021. doi: https://doi.org/10.1002/pc.26062.
    » https://doi.org/10.1002/pc.26062
  • [47] SAID, M., MUSTAFA, T.S., SHANOUR, A.S., et al, “Experimental and analytical investigation of high performance concrete beams reinforced with hybrid bars and polyvinyl alcohol fibers”, Construction & Building Materials, v. 259, pp. 120395, Oct. 2020. doi: https://doi.org/10.1016/j.conbuildmat.2020.120395.
    » https://doi.org/10.1016/j.conbuildmat.2020.120395
  • [48] EL-SAYED, A.A., HAMDY, H., KHALIL, M.M., et al, “Structural performance of hybrid reinforced concrete beams containing polyvinyl alcohol fibers under thermal loads”, Journal of Building Engineering, v. 96, pp. 110666, Nov. 2024. doi: https://doi.org/10.1016/j.jobe.2024.110666.
    » https://doi.org/10.1016/j.jobe.2024.110666
  • [49] IRSHIDAT, M.R., HADDAD, R.H., ALMAHMOUD, H., “Post-heating behavior of concrete beams reinforced with fiber reinforced polymer bars”, Structural Engineering and Mechanics, v. 53, n. 6, pp. 1253–1269, Mar. 2015. doi: https://doi.org/10.12989/sem.2015.53.6.1253.
    » https://doi.org/10.12989/sem.2015.53.6.1253
  • [50] YAO, X., HAN, Y., SHEN, L., et al, “Experimental study on the effect of polypropylene fiber on compressive strength and fracture properties of high-strength concrete after elevated temperatures”, Journal of Building Engineering, v. 86, pp. 108860, Jun. 2024. doi: https://doi.org/10.1016/j.jobe.2024.108860.
    » https://doi.org/10.1016/j.jobe.2024.108860
  • [51] HASSANLI, R., MANALO, A., VAFAEI, D., et al, “Cyclic behavior of GFRP-reinforced concrete one-way slabs with synthetic fibers”, Journal of Building Engineering, v. 65, pp. 105741, Apr. 2023. doi: https://doi.org/10.1016/j.jobe.2022.105741.
    » https://doi.org/10.1016/j.jobe.2022.105741
  • [52] ALLAWI, A.A., SHUBBER, N., GHARAWI, M.A., et al, “Enhancement of RC T-beams toughness using laced stirrups reinforcement for blast response predictions”, Structural Concrete, v. 24, n. 3, pp. 3839–3856, Dec. 2022. doi: https://doi.org/10.1002/suco.202200894.
    » https://doi.org/10.1002/suco.202200894
  • [53] MASHAYEKHI, A., HASSANLI, R., ZHUGE, Y., et al, “Cyclic performance of GFRP-reinforced seawater sea-sand concrete culverts reinforced with synthetic fibers”, Structures, v. 72, pp. 108262, Feb. 2025. doi: https://doi.org/10.1016/j.istruc.2025.108262.
    » https://doi.org/10.1016/j.istruc.2025.108262
  • [54] OUKAILI, N., ALLAWI, A.A., ISSA, M.A., et al, “On the effectiveness of shear reinforcement type in GFRP-reinforced concrete beams: Experimental study”, Structural Concrete, v. 26, n. 5, pp. 6547–6575, Apr. 2025. doi: https://doi.org/10.1002/suco.70114.
    » https://doi.org/10.1002/suco.70114
  • [55] MOURA, R.C.A., LIMA, P.R.L., RIBEIRO, D.V., “Effect of temperature on mechanical behaviour of concrete reinforced with different types of GFRP bar”, Polymers, v. 14, n. 17, pp. 3437, Aug. 2022. doi: https://doi.org/10.3390/polym14173437. PubMed PMID: 36080516.
    » https://doi.org/10.3390/polym14173437

Publication Dates

  • Publication in this collection
    25 May 2026
  • Date of issue
    2026

History

  • Received
    14 Sept 2025
  • Accepted
    31 Mar 2026
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