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Article

Study on the Basic Mechanical Properties of Waste Steel Fiber Reinforced Concrete After High-Temperature Exposure

by
Dan Yang
1,
Xiaopeng Ren
1,
Yongtao Gao
2,*,
Tao Fan
2,
Mingshuai Li
2 and
Hui Lv
3
1
Department of Transportation and Municipal Engineering, Sichuan College of Architectural Technology, Deyang 618000, China
2
State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu 610059, China
3
College of Civil Environment and Architecture, Nanchang Hangkong University, Nanchang 330063, China
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(7), 1025; https://doi.org/10.3390/buildings15071025
Submission received: 18 February 2025 / Revised: 16 March 2025 / Accepted: 19 March 2025 / Published: 23 March 2025
(This article belongs to the Special Issue Advances in Green, Low-Carbon, High-Performance, and Intelligent Building Materials and Structures)
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Versions Notes

Abstract

The increasing incidence of urban fires poses significant threats to structural integrity, underscoring the urgent need for concrete materials with enhanced mechanical properties post-fire. Incorporating recycled waste steel fibers (WSF) from industrial byproducts into concrete not only bolsters its crack resistance but also advances circular economy principles by transforming industrial waste into valuable resources. Although a large amount of research has focused on native steel fiber-reinforced concrete, there is still a lack of systematic exploration on the optimal dosage and effectiveness of waste steel fibers in slowing down the strength degradation of concrete after high-temperature action. In this study, two grades of concrete (C40 and C60) containing 0%, 1%, and 2% WSF by volume were subjected to heating cycles ranging from 200 °C to 800 °C. Post-cooling evaluations encompassed mass loss quantification, cube compressive strength testing (using 100 mm3 specimens), and splitting tensile tests conducted at a loading rate of 0.1 MPa/s. Results indicated that mass loss escalated to 11% at 800 °C, with C60 experiencing a 12% higher loss compared to C40. Compressive strength decreased by 15% for every 200 °C increment; however, the inclusion of 1% WSF significantly minimized this degradation, preserving 44.5% (for C40) and 37.8% (for C60) of the original strength at 800 °C. Notably, the splitting tensile strength of 1% WSF-reinforced C60 concrete exceeded that of plain concrete by 39.4% after exposure to 800 °C, demonstrating its superior crack-bridging capabilities.

1. Introduction

In recent years, with the dynamic and vigorous growth of the social economy, the tempo of urbanization construction has been picking up pace at an unprecedented rate. The influx and congregation of a substantial number of people in urban areas have concomitantly augmented the likelihood of fire incidents [1,2]. Statistical data reveal that annually, fires claim more than 100,000 lives across the globe, thereby triggering far-reaching social and political ramifications [3,4]. As urbanization marches forward and the construction industry experiences a meteoric rise, research centered around building fires has garnered extensive and widespread attention. The quintessential objective of probing into the fire resistance capabilities of building structures lies in guaranteeing that edifices can uphold adequate stability when confronted with a fire emergency [5,6,7]. Among the various factors, the performance of concrete materials subsequent to a fire is of paramount importance. Concrete must possess the capacity to endure high-temperature challenges in the aftermath of an accident so as to safeguard the structural integrity and stability of the building [8,9,10].
The deterioration of concrete performance at high temperatures is critical for structural safety, as it directly impacts the load-bearing capacity and integrity of buildings during and after fire events. Understanding these degradation mechanisms is essential for designing fire-resistant structures and developing effective rehabilitation strategies for fire-damaged concrete. The high temperature generated by the fire causes changes in the concrete structure, which will seriously affect the mechanical properties and durability of the concrete structure under high temperature [11,12,13]. Adding steel fibers to concrete can prevent the occurrence and development of cracks, improve the compressive and tensile strength of concrete, enhance its ductility and toughness, and improve its durability. A large number of experimental studies have found that adding appropriate fibers to concrete can improve the structure’s resistance to high-temperature cracking, with steel fibers showing the most significant performance [14]. It is generally believed that when the volume fraction is 2%, steel fibers can play a good reinforcing role and effectively suppress the cracking of concrete [15,16,17], and the compressive strength of the specimen is optimal. Through the splitting tensile test, it was found that the splitting tensile strength was best when the volume fraction of steel fibers was 1.5%. The development of internal cracks in concrete was detected using acoustic emission technology, and the results showed that the energy released by steel fiber reinforced concrete was greater than that of ordinary concrete [18,19,20].
The enhancement in the compressive strength of concrete after exposure to high temperatures, brought about by steel fibers, primarily takes place when the temperature exceeds 500 °C. Moreover, the higher the content of steel fibers within the concrete, the more pronounced the improvement effect becomes [21,22,23,24,25].
When it comes to the impact resistance of steel fiber self-compacting concrete following high-temperature exposure, the optimal impact resistance is attained when the steel fiber content is set at 2% [25,26,27,28]. Recycled steel fibers, which are obtained through the treatment of waste tires, were incorporated into concrete, and subsequent high-temperature cube compressive strength tests were carried out on this concrete. It was discovered that these waste steel fibers (WSF) significantly enhanced the mechanical properties of concrete after it had endured high temperatures [29,30,31,32].
Concrete mixtures containing both steel fibers and PVA fibers maintain a relatively strong residual strength during the process of high-temperature cracking [33,34]. Additionally, for mixed steel-polypropylene fiber concrete, there is a downward trend in its compressive strength, tensile strength, and dynamic modulus of elasticity as the temperature increases at different levels such as 20 °C, 450 °C, 650 °C, and 825 °C [35,36,37,38].
Steel fibers also play a strengthening role in improving the high-temperature strength of recycled concrete. Through experiments on steel fiber-reinforced concrete with single and mixed additives under different cooling methods, it was observed that the compressive strength, splitting tensile strength, and flexural strength all witnessed an increase [39,40,41,42].
Regarding the variation law of the mechanical properties of steel fiber-reinforced concrete after high-temperature exposure under different cooling methods, it has been found that the mechanical strength of concrete under water cooling conditions is lower than that under natural cooling. However, steel fibers exhibit a favorable improvement effect on the cracking phenomenon of concrete during the water cooling process [43,44,45].
There are also studies indicating that steel fibers can enhance the residual strength of concrete after high temperatures. Nevertheless, the degree of deterioration of steel fiber-reinforced concrete is greater than that of ordinary concrete [46,47]. The principal reason for this lies in the fact that steel fibers tend to restrict the development of concrete cracks at high temperatures, which in turn prevents the internal steam pressure of the concrete from being discharged effectively, ultimately resulting in the occurrence of concrete cracking [3,48,49,50].
The waste steel fibers (WSF) obtained through the mechanical processing of residual materials are incorporated into waste steel fiber concrete. Owing to the distinctive spiral morphology of WSF, a three-dimensional composite structure is generated within the concrete [51,52,53], which exerts a remarkable restraining influence on the cracks present in the concrete. Consequently, its fundamental mechanical properties do not deviate significantly from those of the original steel fiber concrete. Hence, the utilization of WSF to fabricate recycled steel fiber-reinforced concrete composite materials proves to be more economically viable and environmentally friendly. In light of the principles underlying green building materials and sustainable development, three volume ratios and two strength grades of waste steel fiber concrete (WSFC) were prepared. Subsequently, mechanical tests were carried out after subjecting the specimens to heating, with the aim of probing into the strengthening and toughening mechanisms of WSF in concrete under high-temperature conditions. This endeavor lays a solid foundation for future research and practical application of this particular type of material.

2. Materials and Methods

2.1. Test Materials

2.1.1. Cement

Cement is PO 42.5 ordinary Portland cement and is characterized by high early strength. Cement is produced by Jinghu cement plant in Deyang city, China. Moderate setting time, stable hardening process, and good durability and impermeability. The chemical composition is stable, and the quality stability is reliable. The specific properties of cement are shown in Table 1, where % represents the mass percentage.

2.1.2. Fly Ash

The experimental fly ash is produced by xinneng fly ash building materials factory in Houma city, China. The main components of fly ash are silicon dioxide and aluminum oxide. The hydrated calcium silicate and other substances generated during the cement hydration process can fill the pores inside the concrete and reduce its solubility. The XRD pattern of hydrated calcium silicate is shown in Figure 1a. This not only improves the strength and impermeability of concrete but also enhances its frost resistance and durability, reducing the risk of drying shrinkage and cracking.
Grade I fly ash was used in the experiment; the fineness is 45 μm and the sieve residue is 11%, which has high quality and stable performance. The XRD pattern of fly ash is shown in Figure 1b. The various indicators and chemical composition are shown in Table 2.

2.1.3. Aggregates

The coarse aggregate is selected as continuously graded crushed stone with a particle size of 15–20 mm, and the fine aggregate is selected as medium sand with a particle size of 2.3–3.0 mm; the sand is artificial. The moderate particle size of coarse and fine aggregates ensures that the concrete has good workability and reduces the occurrence of segregation and water seepage during the molding process. The appearance of coarse and fine aggregates is shown in Figure 2 and Figure 3.

2.1.4. Waste Steel Fibers

The WSF used in the experiment are residual materials processed by Chengdu Machinery, made of SUS304 stainless steel with a tensile strength of 386 MPa and a spiral shape, as shown in Figure 4. The length range of processed WSF is 4–8 cm, the width range is 0.5–0.7 cm, and the average aspect ratio is about 11.6. The processed shape is shown in Figure 5. The chemical composition of WSF is shown in Table 3.

2.2. Mix Proportion Design

In this experiment, referring to the provisions of the “Technical Specification for Application of Fiber Reinforced Concrete” (JGJ/T221-2010) and the “Code for Design of Ordinary Concrete Mix Proportion” (JGJ55-2011) [54,55], the design concrete strength grades are C40 and C60, and the volume fraction of WSF is 0%, 1%, and 2%. The concrete mix after calculation and trial adjustment is shown in Table 4.

2.3. Heating Equipment

This experiment uses a muffle furnace as a high-temperature box-type resistance furnace, and its appearance is shown in Figure 6. Its rated power is 12 KW, its rated voltage is 330 V, and the maximum heating temperature is up to 1200 °C.
After the curing period of the sample reaches 28 days, the sample is taken out of the curing box and naturally dried in the air. After the surface water stains are completely removed, it is weighed, and the humidity of the sample is measured. The humidity of the sample is approximately 91%. The working size is 800 × 500 × 400 mm, which fully meets the testing requirements. The temperature inside the furnace can be adjusted through the heating button, and when the set temperature is reached, it automatically maintains a constant temperature heating state.
In order to better simulate the changes of concrete in building fires, refer to international standards ASTM E119 [56] and ISO 834 [57], the sample heating process adopted is to heat the sample to the specified temperature (200 °C, 400 °C, 600 °C, 800 °C) at a heating rate of 10 °C/min. The heating process of the test block is shown in Figure 7. Refer to the instructions of international standards ASTM E119 and EN 1363-1 [58]. After reaching the specified temperature, the sample is heated at a constant temperature for 1.5 h. Then, the sample is cooled to around 100 °C using natural cooling and take it out. Then, it is placed in an open outdoor area to cool to ordinary temperature. After cooling, it is placed on the test block for 3 days for mechanical testing.

3. Experimental Process and Result Analysis

3.1. Testing Process

In light of the varying strength levels, fiber content proportions, and heating temperatures of the concrete specimens, a systematic grouping and numbering scheme was implemented. The specific details of this grouping are presented in Table 5. The grouping codes follow the A-B-C format, wherein A denotes the strength grade of the concrete, B signifies the volume fraction of waste steel fibers (WSF), and C indicates the heating temperature of the concrete. To illustrate, the code A4B1C2 corresponds to a concrete sample with a strength grade of C40, a waste steel fiber volume fraction of 1%, and a heating temperature of 200 °C. This coding convention allows for clear identification and differentiation of each test block configuration within the experimental setup.
During the heating process of the samples, several notable phenomena were observed. When the temperature climbed to 250 °C, evaporation led to the formation of a white mist on the sample surfaces. As the temperature further advanced to 310 °C, a copious amount of water vapor was forcefully discharged, persisting until it ceased around 400 °C. At 425 °C, the concrete test blocks situated within the furnace emitted a dull, muffled sound. Subsequently, when the temperature ascended continuously to 500 °C, a profusion of smoke was generated, accompanied by a sharp and pungent odor. Notably, when the temperature ranged from 500 °C to 600 °C, the concrete underwent high-temperature cracking, giving rise to conspicuous explosive sounds reverberating within the furnace.
The underlying cause behind the aforementioned phenomena can be analyzed as follows. The free water, which accounts for the highest proportion within the concrete matrix, undergoes evaporation under high-temperature conditions, giving rise to the generation of white water vapor. This vapor accumulates and creates pressure within the confined pores of the concrete. As the temperature continues to climb, the pressurized water vapor induces a micro-explosion-like effect, causing the concrete to rupture and emit a sound. Concurrently, the admixture of water vapor and entrained dust is expelled, manifesting as white smoke. When the furnace heating temperature reaches 200 °C, the concrete enters a state of physical dehydration, wherein the free water molecules within its structure commence evaporation. Subsequently, with a further increment in the heating temperature, the evaporation rate of these water molecules accelerates proportionately.
Simultaneously, within the concrete, the calcium silicate gel, ettringite, and hydrated lime generated by the hydration heat reaction undergo dehydration and decomposition processes. The free water molecules start to evaporate under high-temperature conditions, with the evaporation rate reaching its maximum when the temperature ascends to 400 °C. Thereafter, the evaporation intensity gradually diminishes. By the time the temperature reaches 500 °C, the water vapor present inside the concrete has been largely depleted, approaching complete evaporation.
After cooling the sample and observing its surface, it was found that the appearance of the concrete test block did not change significantly after heating at 200 °C, and the appearance characteristics were similar to those at ordinary temperature, as shown in Figure 8a. After heating at 400 °C, local black spots appeared on the surface of the test block, and the color changed to bluish gray. The appearance was intact with no missing corners around, and there were very few small cracks distributed on the surface, as shown in Figure 8b. After heating at 600 °C, there were missing edges and corners around the test block, and the sound was dull when tapping the sample, as shown in Figure 8c. When tapping the sample, the dullness of the sound is further enhanced, and it is obvious that the weight of the sample is lighter.
The reason for the change in the surface of the sample is that after being exposed to high temperatures, the surface moisture of the concrete will rapidly evaporate. After the evaporation of free water at high temperatures, the surface of concrete may become dry and crack. As water continues to evaporate, the escape of water molecules can lead to the formation of relatively dry areas inside the concrete, resulting in the concrete structure becoming loose and detached.
At the same time, under high temperature, some water molecules inside the concrete may be in a closed pore environment and cannot evaporate due to the lack of escape channels. As the temperature increases, water molecules in a closed cell environment expand. When the expansion pressure exceeds the bearing capacity of the pore wall, the pore wall will be broken, causing damage to the internal structure of the concrete, leading to cracking and peeling.

3.2. Quality Loss of WSFC After High Temperature

The curve changes in Figure 9 and Figure 10 indicate that under the same conditions of concrete strength grade and waste steel fiber content, the mass loss rate of concrete samples increases with the increase of heating temperature.
As shown in Figure 9, when the temperature rises from ordinary temperature to 200 °C, the quality loss rate of C40 concrete is relatively low, with a range of approximately 1.2% to 1.3%. The difference in quality loss under different dosages of WSF is not significant.
When the temperature reaches 400 °C, the mass loss rate of plain concrete specimens is 2.7%, while the mass loss rate of concrete with 1% steel fiber content is 2.2%, and the mass loss rate of concrete with 2% steel fiber content is 2.1%. Compared with 200 °C, the difference in quality loss rate between WSFC and plain concrete is significantly increased at 400 °C.
When the temperature further increases to 600 °C, the growth rate of the mass loss rate of concrete samples with different steel fiber dosages accelerates, while the loss rate of plain concrete specimens is slightly higher than the other two dosages, but the growth rate is slightly slower than the other two.
When the temperature reaches 800 °C, the mass loss rate of the test block reaches over 10%. Among them, the lowest mass loss rate of concrete is 10.5% when the steel fiber content is 2%. The loss rate values of plain concrete and concrete with a steel fiber content of 1% are close.
As shown in Figure 10, when the temperature rises from ordinary temperature to 200 °C, the mass loss range of WSFC with a strength of C60 is 1.6~2.2%. The quality loss rate of plain concrete is 2.2%, significantly exceeding the quality loss rates of concrete with steel fiber content of 1% and 2%.
When the temperature reached 400 °C, the mass loss of C60 plain concrete specimens reached 3%, higher than the 2.5% and 2.4% of the two types of WSFC with different dosages.
When the heating temperature reaches 600 °C, the growth rate of the mass loss rate of plain concrete specimens is significantly faster than that of WSFC specimens. The quality loss rate of plain concrete is 7.3%, while the quality loss rate of concrete with 1% steel fiber content is 5.4%, and the quality loss rate of concrete with 2% steel fiber content is 5.6%.
After the temperature exceeds 800 °C, there is a significant difference in the quality loss rate between plain concrete and WSFC. The quality loss rate of plain concrete is 12.0%, the quality loss rate of concrete with 1% steel fiber content is 11.2%, and the quality loss rate of concrete with 2% steel fiber content is 10.88%.

3.3. Compressive Strength Test

After being heated at high temperature, the concrete test block is allowed to cool naturally for 3 days before conducting a cube compressive strength test. The size of the test block used for the cube compressive strength test is a cube of 100 × 100 × 100 mm. Before loading, the outer surface of the sample is checked for cracks caused by high temperature, and the crack free test block is wiped and tested.
At ordinary temperature, the surface cracks of the plain concrete specimen extend longitudinally with the increase of load, and the concrete peels off and becomes dense on the side. After that, the specimen fails, and the failure process is brittle. With the increase of steel fiber content, the failure mode of the test block tends to be ductile.
This is due to the disordered distribution of WSF in the test block, which disperses energy and alleviates the peeling phenomenon of the test block shell. The structure is relatively intact after the final damage. The failure phenomena of each sample at ordinary temperature are shown in Figure 11.
The failure mode of the sample after being subjected to a high temperature of 200 °C is similar to that at ordinary temperature, as shown in Figure 12.
The overall integrity of the specimen after being subjected to high-temperature treatment at 400 °C is more brittle when it fails compared to ordinary temperature. After loading, microcracks appeared earlier than at ordinary temperature and rapidly developed. The failure modes of the samples with steel fiber content of 1% and 2% were more complete than those with 0% content, and the test loading duration was longer. The failure phenomenon is shown in Figure 13.
After being heated at high temperatures ranging from 600 °C to 800 °C, many fine cracks appeared on the surface of the specimen during the loading process. Under the action of axial load, the cracks extended and expanded, and fragments continuously fell off the corners of the specimen. The failure showed obvious brittleness, and aggregate failure occurred inside the specimen. The failure phenomenon is shown in Figure 14 and Figure 15.
Analysis of the above cube compression test phenomenon shows that WSF improves the brittle properties of concrete. Due to its spiral distribution structure and good extensibility and tensile performance, it enhances the mechanical biting force with the concrete matrix, improves the bonding force with the material, and better plays a bridging role.
The disorderly distribution of WSF acts like steel bars, significantly improving the material’s resistance to deformation and limiting the lateral deformation of concrete under load. When the steel fibers inside the test block are pulled or pulled out, the energy generated by external forces is consumed, which improves the integrity of the test block after failure and enhances the toughness of the concrete.
In terms of temperature impact, due to the high temperature, the internal materials of concrete undergo carbonization and oxidation, resulting in a decrease in aggregate strength. The connection between aggregates and cementitious materials is more prone to cracking, leading to the formation of a failure surface. Secondly, the expansion coefficients of WSF and concrete materials are different at high temperatures. The different expansion coefficients cause subtle cracks at the interface between steel fibers and concrete materials, which provide escape channels for water vapor and reduce the damage of air pressure to the internal microstructure, thus protecting the structural integrity of concrete to some extent.
Figure 16 shows the correlation between compressive strength and temperature of concrete under different steel fiber contents and strength grades. From the curve changes in the graph, it can be seen that with the increase of temperature, the compressive strength of both plain concrete and WSFC gradually decreases. At the same temperature, the strength of WSFC is greater than that of plain concrete.
Figure 17 shows the effect of steel fiber content on the compressive strength of specimens with a strength grade of C40 at different temperatures. At ordinary temperature, the compressive strength of C40 concrete with a steel fiber content of 1% increased by 10% compared to plain concrete, while the increase was 4.9% when the content was 2%. When the temperature rises to 200 °C, the compressive strength of the sample with 1% steel fiber content increases by 12.8% compared to plain concrete, while the compressive strength increases by 6.1% when the content is 2%. The main reason for the improvement of mechanical properties of concrete after high-temperature action of WSF is that they form a composite three-dimensional structure with concrete, which significantly slows down the trend of compressive strength attenuation of concrete. Compared with it, the compressive strength attenuation of plain concrete is more rapid at the same temperature.
From an overall analysis, it can be seen that as the temperature increases, the compressive strength of concrete shows a decreasing trend, but within the same temperature range, the compressive strength of WSFC is greater than that of plain concrete. At the same time, with the increase of steel fiber content, the decreasing trend of strength also slows down. When the temperature increases from ordinary temperature to 200 °C, there is no significant change in the amplification effect of steel fibers on concrete specimens after high temperature compared to ordinary temperature. The main change occurs after the temperature reaches 400 °C, and the improvement effect of WSF on the performance of concrete materials after high temperature is reflected. When the temperature exceeds 600 °C, the difference in the ratio of compressive strength between WSF and plain concrete increases. The effect is most significant when the steel fiber content is 1%, gradually increasing from 10% at ordinary temperature to 12.8%, 14.6%, 22.5%, and 44.5% at high temperature. When the steel fiber content is 2%, the reinforcement effect changes by 4.9%, 6.1%, 7.5%, 9.6%, and 34.6%. The results show that when the temperature reaches a higher temperature, especially 800 °C, the mechanical properties of the sample change significantly with the addition of steel and no fibers.
Figure 18 shows the effect of steel fiber content on the compressive strength of specimens with strength grade C60 at different temperatures. From the graph, it can be seen that in the experiment, the compressive strength of C60 concrete decreased by more than 20% after being subjected to a temperature of 400 °C. At 600 °C, the decrease reached 35~50%, and at 800 °C, the compressive strength was only 30~25% of that at ordinary temperature. The compressive strength of C60 concrete with 1% steel fiber content increased by 9.5%, 17.2%, 18.5%, 37.8%, and 31.1% at different temperatures, while the compressive strength increased by 8.0%, 9.5%, 10.3%, 21.2%, and 20.9% at 2% steel fiber content.
Therefore, it can be inferred that WSF can effectively alleviate the compressive strength attenuation trend of concrete after high-temperature action. When the content of WSF is 1%, both C40 and C60 have the optimal compressive strength.

3.4. Splitting Tensile Strength

The splitting tensile test adopts force control mode for loading, with a loading rate of 0.1 MPa/s. The cube specimen size used in the test is 100 × 100 × 100 mm (Figure 19). The fixture for concrete splitting and tensile strength is shown in Figure 19.
Figure 20 shows the failure of various types of concrete in the splitting tensile test at ordinary temperature. In the splitting tensile test, as the load increases, a small crack appears at the center of the vertical edge of the specimen, and the crack gradually expands, forming a peeling phenomenon on the surface of the specimen. As the load further increases, cracks gradually expand and eventually penetrate the entire specimen, causing vertical failure. When the specimen cracks and fails, a loud sound is emitted.
At ordinary temperature, for plain concrete, as the main cracks develop, the concrete specimen continuously emits a cracking sound. When the specimen ultimately fails, a loud bang will be heard, which is relatively crisp. The specimen is divided into two parts, and the failure characteristic is brittleness. The overall load-bearing time of the test is relatively short.
The crack width of the WSFC sample is significantly smaller than that of plain concrete. The cracks are mainly composed of penetrating main cracks and a small number of fine cracks, and the sound of destruction is relatively dull. The overall integrity of the test block is intact when it is ultimately destroyed. The reinforcing effect of WSF effectively improves the tensile performance and integrity of concrete. Compared with plain concrete, WSFC specimens exhibit more ductile characteristics during failure. During the failure of the test block, it was observed that the fibers were pulled out and yielded, and the overall test time was longer than that of plain concrete.
Figure 21 shows the failure of the test block after being subjected to high temperatures ranging from 200 °C to 400 °C. It can be seen that the failure mode of the sample under high temperature is similar to that of the sample with the same steel fiber content at ordinary temperature. When the sample is subjected to high-temperature heating from 600 °C to 800 °C, small fragments will fall off during the splitting tensile test, as shown in Figure 22.
By analyzing the failure modes of diverse specimens presented in Figure 20, Figure 21 and Figure 22, it was discerned that the predominant failure mode witnessed in the splitting tensile test of waste steel fiber concrete (WSFC) was vertical crack penetration failure. Owing to the incorporation of steel fibers, the failure mode of the concrete manifested more conspicuous ductility traits. Throughout the experiment, it was noted that the fibers were being pulled out and yielded, which implies that the fibers played a crucial part in absorbing and dissipating the energy generated by the externally applied load.
The high-temperature environment has a certain impact on the mechanical properties and failure modes of concrete. Due to the effects of water decomposition and chemical reactions, the integrity of the test block is reduced, but WSF can still play a certain reinforcing role.
Figure 23 shows the relationship between the splitting tensile strength of WSFC and temperature at different temperatures. The figure shows that the splitting tensile strength of both plain concrete and WSFC decreases with increasing temperature. But overall, the splitting tensile strength of plain concrete is lower than that of WSFC, and WSF effectively enhances the splitting tensile strength of concrete.
Figure 24 illustrates the impact of steel fiber content on the splitting tensile strength of C40 waste steel fiber concrete (WSFC) under diverse temperature regimes. Under normal ambient temperature conditions, it can be observed that the splitting tensile strength of the specimen containing 1% waste steel fibers is 1.2-fold that of the plain concrete. In contrast, for the sample with a 2% waste steel fiber content, its splitting tensile strength reaches 1.1 times that of the plain concrete.
When the heating temperature of the sample is raised from ordinary temperature to 200 °C, the splitting tensile strength slightly decreases, but the overall reduction is not significant. The trend of splitting tensile strength changes between WSFC and plain concrete in the range of ordinary temperature to 200 °C is similar.
When the temperature was elevated to 400 °C, a pronounced decline in the splitting tensile strength of the sample was witnessed. At this juncture, in comparison to plain concrete, the splitting tensile strength of the sample with a 1% steel fiber content exhibited an increment of 19%, whereas for the sample with a 2% steel fiber content, the increase was 8%. Under the same heating temperature, the splitting tensile strength of waste steel fiber concrete (WSFC) was found to be relatively higher. Moreover, when the steel fiber content remained constant, it was evident that the higher the operating temperature, the more pronounced the brittleness of the sample became.
When the temperature reaches 600 °C, the ratio of splitting tensile strength between WSFC and plain concrete increases. The effect is most significant when the steel fiber content is 1%, and the increase increases from 15.9% at ordinary temperature to 15.7%, 19.4%, 25.0%, and 28.6% at high temperature. The increase rates when the steel fiber content is 2% are 5.0%, 5.1%, 6.1%, 7.4%, and 9.8%, respectively. This indicates that when the temperature reaches a higher level, especially 600 °C, the tensile strength of the sample with steel fiber addition is significantly enhanced. But when the temperature reaches 800 °C, the normal tensile properties of WSFC and plain concrete are basically lost, but WSFC still has a strengthening effect compared to plain concrete. Indicating that the optimal blending rate for steel fibers is 1%.
The effect of different fiber contents on the tensile strength of WSFC with strength grade C60 is shown in Figure 25. The splitting tensile strength of C60 concrete shows a similar trend to the cube compressive strength. When heated from ordinary temperature to 200 °C, the splitting tensile strength of the sample decreases by more than 10%, but the decrease in the splitting tensile strength of WSFC is lower than that of plain concrete. Compared to plain concrete, under the same temperature conditions (ordinary temperature, 200 °C, 400 °C, 600 °C, 800 °C), its splitting tensile strength has increased by 13.3%, 16.3%, 29.2%, 24.3%, and 39.4%, respectively. When the content of WSF is 2%, the improvement rates are 4.0%, 4.3%, 16.3%, 14.0%, and 22.8%.

4. Conclusions

By heating and cooling samples with three different dosages of WSF and two different strength grades of concrete and then conducting cube compression and splitting tensile tests, the following conclusions were drawn:
(1)
Upon examination, it was revealed that the influence of steel fiber content on the apparent characteristics of the samples subsequent to exposure to high temperatures was not particularly pronounced. As the temperature progressively rose, the visual appearance of the samples underwent a transformation, shifting from a dark gray hue initially to a white-gray shade and further evolving into a light yellow color. Concurrently, the surface cracks on the samples became more numerous and pronounced. Moreover, an upward trend was observed in the mass loss rate of the samples in tandem with the increase in temperature, indicating a direct correlation between the two variables.
(2)
The comprehensive analysis of mechanical test phenomena and the underlying data mechanisms, both before and after high-temperature exposure in concrete, demonstrates that waste steel fibers (WSF) play a significant and effective role. They notably augment the compressive and splitting tensile strength of concrete cubes, leading to an improvement in the ultimate failure mode of test blocks and bolstering the overall structural integrity of the specimens. Notably, the optimal enhancement in the mechanical strength of concrete is attained when the fiber content reaches 1%. At this concentration, WSF are most efficacious in counteracting the detrimental effects of high temperature on concrete properties, thereby ensuring that the concrete retains greater strength and durability even under extreme thermal conditions. This finding not only highlights the importance of WSF in concrete applications but also provides a practical guideline for engineers and researchers when designing concrete mixes for high-temperature environments.
(3)
An in-depth examination of the mechanical strength data of concrete with varying strength grades under high-temperature circumstances reveals a rather intriguing finding. When subjected to elevated temperatures, C60 concrete demonstrates comparatively less favorable mechanical properties in contrast to C40 concrete. Specifically, at an identical temperature level, the mass loss rate and strength attenuation rate of C60 concrete are both noticeably greater than those of C40 concrete. This disparity can likely be attributed to the differences in the internal microstructure and composition of the two types of concrete. The denser microstructure of C60 concrete, which is engineered to achieve higher strength under normal conditions, may impede the release of internal vapor pressure during heating, thereby exacerbating the damage caused by high temperatures and leading to more pronounced mass and strength losses. In contrast, C40 concrete, with its relatively more porous structure, allows for better dissipation of vapor pressure, resulting in relatively milder degradation. These insights not only deepen our understanding of the behavior of different strength grades of concrete under high temperatures but also offer valuable guidance for the selection and design of concrete in applications where high-temperature exposure is anticipated.
Recycling WSF reduces industrial waste and promotes circular economy principles, while the substitution of WSF for virgin steel fibers can lower CO₂ emissions by reducing energy consumption in steel production. Economically, WSF are typically cheaper than conventional steel fibers, offering material cost savings for large-scale construction projects. Future studies will focus on quantifying these benefits to provide a more comprehensive evaluation of WSF’s role in sustainable construction.

5. Research Prospect—Advancements in Non-Destructive Evaluation of Fire-Damaged Concrete

In recent years, non-destructive evaluation (NDE) methods have emerged as powerful tools for assessing the internal damage and residual mechanical properties of fire-damaged concrete. Techniques such as acoustic emission (AE) and ultrasonic pulse velocity (UPV) have been widely used to quantify microcracking, porosity changes, and overall structural integrity in thermally damaged steel fiber-reinforced concrete (SFRC) [59].
For instance, AE monitoring has been employed to detect the initiation and propagation of cracks in SFRC under high-temperature conditions, providing real-time insights into damage mechanisms. Similarly, UPV measurements have been correlated with compressive strength loss and porosity changes, offering a non-invasive approach to evaluate the extent of fire-induced deterioration [60]. These NDE methods not only complement traditional destructive testing but also provide valuable data for developing rehabilitation strategies for fire-affected structures.
In the context of waste steel fiber-reinforced concrete (WSFC), the unique spiral shape and distribution of WSF may influence crack propagation and energy dissipation under high temperatures. While the current study focuses on mechanical testing, future work could integrate NDE techniques to further elucidate the role of WSF in mitigating fire-induced damage and to validate the findings of this study.

Author Contributions

Conceptualization, M.L.; methodology, Y.G.; software, T.F.; validation, H.L.; formal analysis, T.F.; investigation, D.Y.; resources, H.L.; data curation, X.R.; writing—original draft preparation, D.Y.; writing—review and editing, D.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Jiangxi Province Intelligent Building Engineering Research Center Open Fund Project (No. HK20231009), the National Natural Science Foundation of China (51978088), and the State Key Laboratory of Geological Disaster Prevention and Geological Environmental Protection of Chengdu University of Technology, grant numbers 2015BAK09B01, 41877273, and SKLGP2019K019.

Data Availability Statement

Data will be made available upon request.

Acknowledgments

The author of the paper would like to thank the editors and reviewers for their guidance and feedback on the paper.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

  1. Shen, X.G.; Li, X.; Liu, L.; Chen, X.Z.; Du, J. Research on Mechanical Properties of Steel-Polypropylene Fiber-Reinforced Concrete after High-Temperature Treatments. Appl. Sci. 2024, 14, 3861. [Google Scholar] [CrossRef]
  2. Abid, S.R.; Abbass, A.A.; Murali, G.; Al-Sarray, M.L.J.; Nader, I.A.; Ali, S.H. Post-High-Temperature Exposure Repeated Impact Response of Steel-Fiber-Reinforced Concrete. Buildings 2022, 12, 1364. [Google Scholar] [CrossRef]
  3. Janga, S.; Raut, A.N.; Adamu, M.; Ibrahim, Y.E. Thermo-mechanical performance assessment of geopolymer synthesized with steel slag and glass powder at elevated temperatures. Powder Technol. 2024, 444, 120047. [Google Scholar]
  4. Li, X.D.; Lu, C.D.; Cui, Y.F.; Zhou, L.C. Study on the bond properties between steel bar and fiber reinforced concrete after high temperatures. Structures 2023, 49, 889–902. [Google Scholar]
  5. Khan, A.A.; Usmani, A.; Torero, J.L. Evolution of fire models for estimating structural fire-resistance. Fire Saf. J. 2021, 124, 103367. [Google Scholar]
  6. Kordosky, A.N.; Drury, M.M.; Quiel, S.E. Structural fire resistance of partially restrained, partially composite floor beams, I: Experiments. J. Constr. Steel Res. 2020, 167, 105945. [Google Scholar]
  7. Pang, S.J.; Ahn, K.S.; Oh, J.W.; Lee, H.S.; Kang, S.G.; Oh, J.K. Fire Resistance of Structural Wooden Walls Covered by Gypsum and Diatomite Board. Bioresources 2023, 18, 991–1007. [Google Scholar]
  8. Ogrin, A.; Hozjan, T. Fire resistance of timber-concrete composite slabs A simplified method. Mater. Struct. 2020, 53, 106. [Google Scholar]
  9. Gedam, B.A. Fire resistance design method for reinforced concrete beams to evaluate fire-resistance rating. Structures 2021, 33, 855–877. [Google Scholar]
  10. Choi, J.H.; Yang, D.H.; Choi, S.J.; Yi, S.T.; Kim, J.H.J. Fire resistance of bi-directionally prestressed concrete under extreme fire loading. Proc. Inst. Civ. Eng.-Struct. Build. 2021, 174, 749–764. [Google Scholar]
  11. Luhar, S.; Nicolaides, D.; Luhar, I. Fire Resistance Behaviour of Geopolymer Concrete: An Overview. Buildings 2021, 11, 82. [Google Scholar] [CrossRef]
  12. Wen, B.; Zhang, L.; Wu, B.; Niu, D.T.; Wang, L.Z.; Zhang, Y.L. Fire resistance of earthquake damaged reinforced concrete columns. Struct. Infrastruct. Eng. 2022, 18, 789–806. [Google Scholar]
  13. Grubega, I.N.; Markovic, B.; Gojevic, A.; Brdaric, J. Effect of hemp fibers on fire resistance of concrete. Constr. Build. Mater. 2018, 184, 473–484. [Google Scholar]
  14. Pekgökgöz, R.K.; Avcil, F. Effect of steel fibres on reinforced concrete beam-column joints under reversed cyclic loading. Gradevinar 2021, 73, 1185–1194. [Google Scholar]
  15. Yun, H.D.; Jeong, G.Y.; Choi, W.C. Shear Strengthening of High Strength Concrete Beams That Contain Hooked-End Steel Fiber. Materials 2022, 151, 17. [Google Scholar]
  16. Ibrahim, S.K.; Hadi, N.A.; Rad, M.M. Experimental and Numerical Analysis of Steel-Polypropylene Hybrid Fibre Reinforced Concrete Deep Beams. Polymers 2023, 15, 2340. [Google Scholar] [CrossRef]
  17. Shen, W.; Chen, S.P.; Zhang, J.B. Calculation of Cracks in Partially Steel Fiber Reinforced Concrete Beams with BFRP Bars. Adv. Mater. Sci. Eng. 2022, 2022, 9158379. [Google Scholar]
  18. Kim, D.J.; Kim, S.H.; Choi, W.C. Characteristics of Restrained Drying Shrinkage on Arched Steel Fiber-Reinforced Concrete. Appl. Sci. 2021, 11, 7537. [Google Scholar] [CrossRef]
  19. Domski, J.; Zakrzewski, M. Deflection of Steel Fiber Reinforced Concrete Beams Based on Waste Sand. Materials 2020, 13, 392. [Google Scholar] [CrossRef]
  20. Di Carlo, F.; Spagnuolo, S. Cracking behavior of steel fiber-reinforced concrete members subjected to pure tension. Struct. Concr. 2019, 20, 2069–2080. [Google Scholar]
  21. He, F.Z.; Biolzi, L.; Carvelli, V.; Feng, X.W. A review on the mechanical characteristics of thermally damaged steel and polypropylene hybrid fiber-reinforced concretes. Arch. Civ. Mech. Eng. 2024, 24, 69. [Google Scholar]
  22. Al-Attar, A.A.; Abdulrahman, M.B.; Hamada, H.M.; Tayeh, B.A. Investigating the behaviour of hybrid fibre-reinforced reactive powder concrete beams after exposure to elevated temperatures. J. Mater. Res. Technol.-JMR&T 2020, 9, 1966–1977. [Google Scholar]
  23. Jiang, J.; Wu, M.; Ye, M. Prediction of fire spalling behaviour of fiber reinforced concrete. Mag. Concr. Res. 2023, 76, 229–244. [Google Scholar]
  24. Wu, H.Y.; Lin, X.S.; Zhou, A.N. A review of mechanical properties of fibre reinforced concrete at elevated temperatures. Cem. Concr. Res. 2020, 135, 106117. [Google Scholar]
  25. Tretyakov, A.; Tkalenko, I.; Wald, F. Fire response model of the steel fibre reinforced concrete filled tubular column. J. Constr. Steel Res. 2021, 186, 106884. [Google Scholar]
  26. Ponikiewski, T.; Katzer, J.; Kilijanek, A.; Kuzminska, E. Mechanical behaviour of steel fibre reinforced SCC after being exposed to fire. Adv. Concr. Constr. 2018, 6, 631–643. [Google Scholar]
  27. Zhang, C.; Li, Z.H.; Ding, Y.N. Post-fire flexural performance of hybrid-fibre-reinforced SCC symmetric inclination beams. Mag. Concr. Res. 2019, 71, 1025–1042. [Google Scholar]
  28. Li, H.Y.; Chen, B.G.; Zhu, K.C.; Gong, X.L. Flexural Toughness Test and Inversion Research on a Thermal Conductivity Formula on Steel Fiber-Reinforced Concrete Components Post-Fire. Materials 2022, 15, 5103. [Google Scholar] [CrossRef]
  29. Figueiredo, F.P.; Huang, S.S.; Angelakopoulos, H.; Pilakoutas, K.; Burgess, I. Effects of Recycled Steel and Polymer Fibres on Explosive Fire Spalling of Concrete. Fire Technol. 2019, 55, 1495–1516. [Google Scholar]
  30. Rashid, K.; Balouch, N. Influence of steel fibers extracted from waste tires on shear behavior of reinforced concrete beams. Struct. Concr. 2017, 18, 589–596. [Google Scholar]
  31. Qin, X.; Huang, X.; Kaewunruen, S. Sustainable design and carbon-credited application framework of recycled steel fibre reinforced concrete. Dev. Built Environ. 2024, 18, 100404. [Google Scholar]
  32. Fakoor, M.; Nematzadeh, M. Evaluation of post-fire pull-out behavior of steel rebars in high-strength concrete containing waste PET and steel fibers: Experimental and theoretical study. Constr. Build. Mater. 2021, 299, 123917. [Google Scholar] [CrossRef]
  33. Khaliq, W.; Kodur, V. Effectiveness of Polypropylene and Steel Fibers in Enhancing Fire Resistance of High-Strength Concrete Columns. J. Struct. Eng. 2018, 144, 04017224. [Google Scholar]
  34. Zhang, C.; Liu, J.C.; Han, S.C.; Hua, Y. Pore pressure and spalling in fire-exposed high-strength self-consolidating concrete reinforced with hybrid fibres. Eur. J. Environ. Civ. Eng. 2021, 25, 337–367. [Google Scholar]
  35. Santos, P.R.; Stochero, N.P.; Marangon, E.; Tier, M.D. Mechanical and thermal behavior of kaolin/rice-husk ash matrix composites reinforced with corrugated steel fibers. Ceram. Int. 2018, 44, 14291–14296. [Google Scholar]
  36. Dogruyol, M.; Ayhan, E.; Karasin, A. Effect of waste steel fiber use on concrete behavior at high temperature. Case Stud. Constr. Mater. 2024, 20, e03051. [Google Scholar]
  37. Wang, J.J.; Xie, J.H.; He, J.H.; Sun, M.W.; Yang, J.; Li, L.J. Combined use of silica fume and steel fibre to improve fracture properties of recycled aggregate concrete exposed to elevated temperature. J. Mater. Cycles Waste Manag. 2020, 22, 862–877. [Google Scholar]
  38. Simalti, A.; Singh, A.P. Comparative study on performance of manufactured steel fiber and shredded tire recycled steel fiber reinforced self-consolidating concrete. Constr. Build. Mater. 2021, 266, 121102. [Google Scholar]
  39. Chen, G.M.; Yang, H.; Lin, C.; Chen, J.F.; He, Y.H.; Zhang, H.Z. Fracture behaviour of steel fibre reinforced recycled aggregate concrete after exposure to elevated temperatures. Constr. Build. Mater. 2016, 128, 272–286. [Google Scholar] [CrossRef]
  40. Ahmad, J.; Zhou, Z.G. Waste marble based self compacting concrete reinforced with steel fiber exposed to aggressive environment. J. Build. Eng. 2024, 81, 108142. [Google Scholar]
  41. Chen, G.M.; He, Y.H.; Yang, H.; Chen, J.F.; Guo, Y.C. Compressive behavior of steel fiber reinforced recycled aggregate concrete after exposure to elevated temperatures. Constr. Build. Mater. 2014, 71, 1–15. [Google Scholar] [CrossRef]
  42. Ahmed, W.; Lim, C.W.; Akbar, A. Influence of Elevated Temperatures on the Mechanical Performance of Sustainable-Fiber-Reinforced Recycled Aggregate Concrete: A Review. Buildings 2022, 12, 487. [Google Scholar] [CrossRef]
  43. Wang, T.; Yu, M.; Shan, W.T.; Xu, L.H.; Cheng, S.S.; Li, L.Y. Post-fire compressive stress-strain behaviour of steel fibre reinforced recycled aggregate concrete. Compos. Struct. 2023, 309, 116735. [Google Scholar] [CrossRef]
  44. Pachideh, G.; Gholhaki, M.; Moshtagh, A. Performance of concrete containing recycled springs in post-fire conditions. Proc. Inst. Civ. Eng.-Struct. Build. 2020, 173, 3–16. [Google Scholar] [CrossRef]
  45. Tayebi, M.; Nematzadeh, M. Effect of hot-compacted waste nylon fine aggregate on compressive stress-strain behavior of steel fiber-reinforced concrete after exposure to fire: Experiments and optimization. Constr. Build. Mater. 2021, 284, 122742. [Google Scholar] [CrossRef]
  46. Caverzan, A.; Colombo, M.; di Prisco, M.; Rivolta, B. High performance steel fibre reinforced concrete: Residual behaviour at high temperature. Mater. Struct. 2015, 48, 3317–3329. [Google Scholar] [CrossRef]
  47. Nematzadeh, M.; Karimi, A.; Fallah-Valukolaee, S. Compressive performance of steel fiber-reinforced rubberized concrete core detached from heated CFST. Constr. Build. Mater. 2020, 239, 117832. [Google Scholar] [CrossRef]
  48. Netinger, I.; Kesegic, I.; Guljas, I. The effect of high temperatures on the mechanical properties of concrete made with different types of aggregates. Fire Saf. J. 2011, 46, 425–430. [Google Scholar] [CrossRef]
  49. Nematzadeh, M.; Mousavi, R. Post-fire flexural behavior of functionally graded fiber-reinforced concrete containing rubber. Comput. Concr. 2021, 27, 417–435. [Google Scholar]
  50. Nematzadeh, M.; Nazari, A.; Tayebi, M. Post-fire impact behavior and durability of steel fiber-reinforced concrete containing blended cement-zeolite and recycled nylon granules as partial aggregate replacement. Arch. Civ. Mech. Eng. 2021, 22, 5. [Google Scholar] [CrossRef]
  51. Gao, Y.T.; Wang, B.; Liu, C.J.; Hui, D.; Xu, Q.; Zhao, Q.H.; Wei, J.C.; Hong, X.Y. Experimental study on basic mechanical properties of recycled steel fiber reinforced concrete. Rev. Adv. Mater. Sci. 2022, 611, 417–429. [Google Scholar]
  52. Yan, J.Q.; Gao, Y.T.; Tang, M.G.; Ding, N.S.; Xu, Q.; Peng, M.; Zhao, H. Experimental study on the mechanical properties of recycled spiral steel fiber-reinforced rubber concrete. Buildings 2024, 14, 897. [Google Scholar] [CrossRef]
  53. Yan, J.Q.; Gao, Y.T.; Fan, T.; Xu, Q.; Yuan, W.G.; Zhao, X. Experimental Study on Flexural Performance of Recycled Steel Fiber Concrete Beams. Buildings 2023, 13, 3046. [Google Scholar] [CrossRef]
  54. JGJ/T221-2010; Industry Standards of the People’s Republic of China. Technical Specification for Application of Fiber Reinforced Concrete. China Architecture & Building Press: Beijing, China, 2010.
  55. JGJ55-2011; Industry Standards of the People’s Republic of China. Code for Design of Ordinary Concrete Mix Proportion. China Architecture & Building Press: Beijing, China, 2011.
  56. ASTM E119-23; American Society for Testing and Materials. Standard Test Methods for Fire Tests of Building Construction and Materials. ASTM International: West Conshohocken, PA, USA, 2023.
  57. ISO 834-1:1999; International Organization for Standardization. Fire-Resistance Tests—Elements of Building Construction—Part 1: General Requirements. ISO: Geneva, Switzerland, 1999.
  58. EN 1363-1:2020; European Committee for Standardization. Fire Resistance Tests—Part 1: General Requirements. CEN: Brussels, Belgium, 2020.
  59. Mpalaskas, A.C.; Kytinou, V.K.; Zapris, A.G.; Matikas, T.E. Optimizing Building Rehabilitation through Nondestructive Evaluation of Fire-Damaged Steel-Fiber-Reinforced Concrete. Sensors 2024, 24, 5668. [Google Scholar] [CrossRef]
  60. Petr, M.; Josef, N.; Jakub, H. Destructive and non-destructive experimental investigation of polypropylene fibre reinforced concrete subjected to high temperature. J. Build. Eng. 2019, 26, 100906. [Google Scholar]
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Figure 1. The XRD pattern of hydrated calcium silicate and fly ash.
Figure 1. The XRD pattern of hydrated calcium silicate and fly ash.
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Figure 2. Coarse aggregate.
Figure 2. Coarse aggregate.
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Figure 3. Fine aggregate.
Figure 3. Fine aggregate.
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Figure 4. Waste steel fibers.
Figure 4. Waste steel fibers.
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Figure 5. Cut waste steel fibers.
Figure 5. Cut waste steel fibers.
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Figure 6. Muffle furnace.
Figure 6. Muffle furnace.
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Figure 7. High-temperature heating of the sample.
Figure 7. High-temperature heating of the sample.
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Figure 8. WSFC test blocks subjected to different temperatures. (a) Untreated concrete test block; (b) concrete test block after high temperature of 200 °C; (c) concrete test block after high temperature of 400 °C; (d) concrete test block after high temperature of 600 °C; (e) concrete test block after high temperature of 800 °C.
Figure 8. WSFC test blocks subjected to different temperatures. (a) Untreated concrete test block; (b) concrete test block after high temperature of 200 °C; (c) concrete test block after high temperature of 400 °C; (d) concrete test block after high temperature of 600 °C; (e) concrete test block after high temperature of 800 °C.
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Figure 9. Quality changes of C40 concrete with different fiber contents before and after heating up; (a) quality change of C40 plain concrete; (b) quality change of concrete with 1% C40 steel fiber content; (c) quality change of concrete with 2% C40 steel fiber content.
Figure 9. Quality changes of C40 concrete with different fiber contents before and after heating up; (a) quality change of C40 plain concrete; (b) quality change of concrete with 1% C40 steel fiber content; (c) quality change of concrete with 2% C40 steel fiber content.
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Figure 10. Quality changes of C60 concrete with different fiber contents before and after heating up; (a) quality change of C60 plain concrete; (b) quality change of concrete with 1% C60 steel fiber content; (c) quality change of concrete with 2% C60 steel fiber content.
Figure 10. Quality changes of C60 concrete with different fiber contents before and after heating up; (a) quality change of C60 plain concrete; (b) quality change of concrete with 1% C60 steel fiber content; (c) quality change of concrete with 2% C60 steel fiber content.
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Figure 11. Cube compressive damage phenomenon of concrete at ordinary temperature; (a) plain concrete; (b) waste steel fiber 1% content concrete.
Figure 11. Cube compressive damage phenomenon of concrete at ordinary temperature; (a) plain concrete; (b) waste steel fiber 1% content concrete.
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Figure 12. Damage phenomenon of concrete after heating at 200 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
Figure 12. Damage phenomenon of concrete after heating at 200 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
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Figure 13. Damage phenomenon of concrete after 400 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
Figure 13. Damage phenomenon of concrete after 400 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
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Figure 14. Damage phenomenon of concrete after 600 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
Figure 14. Damage phenomenon of concrete after 600 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
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Figure 15. Damage phenomenon of concrete after 800 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
Figure 15. Damage phenomenon of concrete after 800 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
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Figure 16. Relationship between temperature, waste steel fiber content, and compressive strength.
Figure 16. Relationship between temperature, waste steel fiber content, and compressive strength.
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Figure 17. The effect of waste steel fiber content on C40 compressive strength under different temperature conditions.
Figure 17. The effect of waste steel fiber content on C40 compressive strength under different temperature conditions.
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Figure 18. The effect of waste steel fiber content on C60 compressive strength under different temperature conditions.
Figure 18. The effect of waste steel fiber content on C60 compressive strength under different temperature conditions.
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Figure 19. Splitting tensile mold.
Figure 19. Splitting tensile mold.
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Figure 20. Damage phenomenon of concrete at ordinary temperature; (a) plain concrete; (b) waste steel fiber 1% content concrete.
Figure 20. Damage phenomenon of concrete at ordinary temperature; (a) plain concrete; (b) waste steel fiber 1% content concrete.
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Figure 21. Damage phenomenon of concrete after 200~400 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
Figure 21. Damage phenomenon of concrete after 200~400 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
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Figure 22. Damage phenomenon of concrete after 600 °C~800 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
Figure 22. Damage phenomenon of concrete after 600 °C~800 °C; (a) plain concrete; (b) waste steel fiber 1% content concrete.
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Figure 23. Relationship between splitting tensile strength and temperature of WSFC.
Figure 23. Relationship between splitting tensile strength and temperature of WSFC.
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Figure 24. The effect of waste steel fiber content on the tensile strength of C40 at different temperatures.
Figure 24. The effect of waste steel fiber content on the tensile strength of C40 at different temperatures.
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Figure 25. The effect of waste steel fiber content on the tensile strength of C60 at different temperatures.
Figure 25. The effect of waste steel fiber content on the tensile strength of C60 at different temperatures.
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Table 1. Cement properties.
Table 1. Cement properties.
Loss on Ignition
/%		SO3
/%		MgO
/%		Cl−
/%		Set Time
/min		Final Setting Time
/min
2.961.933.130.019259318
Table 2. Various indicators and composition of fly ash.
Table 2. Various indicators and composition of fly ash.
Composition of Fly AshIndicator Requirements/%Test Result/%
Al2O3≤3027.7
SiO2≤5042.4
Cl−≤0.020.012
SO3≤31.7
CaO≤107.1
f-CaO≤10.78
HO−≤1.50.9
Fe3+0.8~1.00.89
Water content≤10.75
Table 3. The chemical composition of WSF.
Table 3. The chemical composition of WSF.
CompositionFe/%C/%Si/%Mn/%P/%S/%Cd/%Ni/%Mo/%
Proportion930.090.080.210.0240.0210.497.91.8
Table 4. Concrete mix proportion.
Table 4. Concrete mix proportion.
Strength GradeWater
/kg/m3		Cement
/kg/m3		Fly Ash
/kg/m3		Stones
/kg/m3		Sand
/kg/m3		WSF/kg/m3
1%2%
C40190411.2541.131161.65547.1479.3158.6
C60249870.9187.0978640579.3158.6
Table 5. Grouping codes for concrete sample tests.
Table 5. Grouping codes for concrete sample tests.
Serial NumberSample CodeNumberStrength GradeHeating Temperature/℃WSF Content/%
1A4B0C08C40Ordinary temperature0
2A4B0C28C402000
3A4B0C48C404000
4A4B0C68C406000
5A4B0C88C408000
6A4B1C08C40Ordinary temperature1
7A4B1C28C402001
8A4B1C48C404001
9A4B1C68C406001
10A4B1C88C408001
11A4B2C08C40Ordinary temperature2
12A4B2C28C402002
13A4B2C48C404002
14A4B2C68C406002
15A4B2C88C408002
16A6B0C08C60Ordinary temperature0
17A6B0C28C602000
18A6B0C48C604000
19A6B0C68C606000
20A6B0C88C608000
21A6B1C08C60Ordinary temperature1
22A6B1C28C602001
23A6B1C48C604001
24A6B1C68C606001
25A6B1C88C608001
26A6B2C08C60Ordinary temperature2
27A6B2C28C602002
28A6B2C48C604002
29A6B2C68C606002
30A6B2C88C608002
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Yang, D.; Ren, X.; Gao, Y.; Fan, T.; Li, M.; Lv, H. Study on the Basic Mechanical Properties of Waste Steel Fiber Reinforced Concrete After High-Temperature Exposure. Buildings 2025, 15, 1025. https://doi.org/10.3390/buildings15071025

AMA Style

Yang D, Ren X, Gao Y, Fan T, Li M, Lv H. Study on the Basic Mechanical Properties of Waste Steel Fiber Reinforced Concrete After High-Temperature Exposure. Buildings. 2025; 15(7):1025. https://doi.org/10.3390/buildings15071025

Chicago/Turabian Style

Yang, Dan, Xiaopeng Ren, Yongtao Gao, Tao Fan, Mingshuai Li, and Hui Lv. 2025. "Study on the Basic Mechanical Properties of Waste Steel Fiber Reinforced Concrete After High-Temperature Exposure" Buildings 15, no. 7: 1025. https://doi.org/10.3390/buildings15071025

APA Style

Yang, D., Ren, X., Gao, Y., Fan, T., Li, M., & Lv, H. (2025). Study on the Basic Mechanical Properties of Waste Steel Fiber Reinforced Concrete After High-Temperature Exposure. Buildings, 15(7), 1025. https://doi.org/10.3390/buildings15071025

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