Hooked-end Steel Fibers Research Articles

Experimental investigation on axial compressive and splitting tensile behaviour of reinforced concrete with a low content of hybrid steel fibres

This study intends to explore how the hybrid steel fibre reinforcement with a low content affects the mechanical characteristics of concrete. The axial compression properties of hybrid steel fibre-reinforced concrete (HSRC) were systematically investigated regarding stress-strain curves, failure modes, elastic modulus, and toughness. The crack propagation and fracture process of HSRC were analyzed based on the cumulative crack width and horizontal strain field. The results showed that the micro-straight steel fibre (mSF) demonstrated a more pronounced influence on post-peak stress retention in the axial compression test, whereas macro hooked-end steel fibre (MHF) positively affected the peak strain enhancement. The average peak stress of the HSRC increased by 8.6 % higher than that of H40 and 16.4 % higher than that of S40. It is noteworthy that the mixing of steel fibres at a low fibre content was detrimental to the compressive toughness. The splitting tensile test showed a transitional stage before the HSRC reached its peak load, during which the load steadily increased and crack propagation slowly occurred. Moreover, the digital image correlation (DIC) measurement results suggested that mSF can enhance the internal quality of concrete. The study contributes to a deep understanding of the synergistic reinforcement mechanism and the fracture processes in HSRC.

Experimental exploration of fracture behavior (pure mode III) in eco-friendly steel fiber-reinforced self-compacting concrete with waste tempered glass as coarse aggregates

To aid in the creation of sustainable structures, scientists have utilized waste materials found in the environment to serve as alternatives for traditional resources in the construction sector. They have undertaken extensive investigations pertaining to this matter. In this particular study, tempered glass as waste glass coarse aggregate (WGCA) was substituted for natural coarse aggregate (NCA) at varying proportions of 15%, 30%, and 45% in the formulation of eco-friendly self-compacting concrete (SCC), combined with hooked-end steel fibers (SFs) at various volumes. The study assessed concrete’s flowability, permeability, compressive strength, and fracture parameters at 28 and 56 days. A total of 240 edge-notched disc bending samples (ENDB) and 60 cubic samples (150 × 150 mm) were tested to assess fracture resilience and compressive strength, respectively. The results showed that increasing SF and WGCA content reduced slump flow diameter and blockage ratio, particularly at higher levels. The solidified characteristics of all specimens incorporating SF and WGCA displayed heightened attributes when contrasted with the reference sample. Among the entire array of specimens, WG15SF0.5 and WG30SF0.5 exhibited the most superior performance, demonstrating an average percentage elevation of 20.29 and 27.63 in both compressive strength and fracture toughness assessments across the different curing periods. SF had the most significant impact on post-cracking behavior by enhancing load-bearing capacity through a bridging fiber mechanism. Through a comparison of the influence of SFs and WGCA on the fracture toughness of pure mode III, it was observed that the inclusion of SF in samples with a 30% replacement of WGCA resulted in an average increase of approximately 15.48% and 11.1% in this mode at the ages of 28 and 56 days, respectively, compared to the control sample.

The investigation and estimation of flexural strength in shear-critically designed RC beams considering the steel fiber content

Despite numerous studies investigating the effectiveness of steel fibers in RC members subjected to various loading conditions, the majority ignored the impact of the interaction between the tensile reinforcement ratio, compressive strength of fibrous concrete, and steel fiber dosage. This paper aimed to inspect and quantify the effects of hooked-end steel fiber dosage on the bending behavior of RC beams considering the interaction arising from various longitudinal reinforcement ratios. For this purpose, an extensive and hybrid investigation involving both experimental and numerical techniques was conducted. In the experimental part, an investigation was carried out to evaluate the contribution of a specific amount of fiber ratio and various aspect ratios to the behavior of large-scale RC beams having a shear-deficient design. Three beams with a 0.5% hooked-end steel fiber ratio and one without fibers but with a minimum amount of stirrups were produced, and three-point bending tests were conducted. All beams having fibers utilized full flexural strength as in the beam with stirrups. Once the experimental studies were completed, the numerical models were then developed and validated with those of experimental three-point bending tests using the non-linear finite element code VecTor2 to establish a basis for the comprehensive parametric study. The parametric study consisted of 33 analyses. Rebar and volumetric fiber ratios were selected to be variables, and the ratios adopted were within the typical range used in structural engineering applications. Based on the regression analysis a linear and a quadratic model were proposed for estimating the yield and peak strength depending on the steel fiber content. Finally, the obtained models were verified using work from the literature and found to be effective in forecasting the strength of shear-deficient RC beams with 0.8%, 1.0%, and 1.2% tensile reinforcement ratios and hooked end steel fibers (0.5 to 1.5%).

Failure mechanism of steel fiber pullout in UHPC affected by alternating cryogenic and elevated variation

This paper investigates the pullout response of straight and hooked-end steel fiber embedded in Ultra-high Performance Concrete (UHPC) subjected to alternating cryogenic (−170 °C) and elevated (200 °C) temperature variation. The temporal evolution of Acoustic Emission (AE) parameters and failure behavior during the pullout process were monitored in situ using the AE test. Additionally, changes in the UHPC microstructure were also evaluated. Results showed that in addition to the UHPC matrices exposed to elevated temperature, the compressive and flexural strength of UHPC matrices subjected to single or multiple cycles were generally higher than those at ambient temperature. Whereas the bond strength/pullout energy of straight fiber increased with a single cycling exposure of UHPC specimens to either cryogenic or elevated temperature, the improvement in the pullout performance of the hooked-end fiber was obtained only after the post-cryogenic thawing of specimens. Moreover, the exposure to an increased number of temperature-variation cycles caused the pullout strength and energy of both fiber groups to gradually decrease. Nonetheless, the pullout performance of the hooked-end fiber was significantly and consistently superior to that of the straight fiber, regardless of the exposure temperature or cycles. The AE test confirmed that the pullout process of both fibers was mainly characterized by tensile failure, with a marginal occurrence of shear failure for the hooked-end fiber. When the UHPC was exposed to various temperatures, the fiber pullout behavior was predominantly influenced by the physical structure of the fibers, thermal deformation proclivity of the matrix, and the competition between mechanisms such as pore moisture phase change, secondary hydration, and the composition of hydrates.

Numerical Analysis of Hybrid Fibre-Reinforced Concrete Beam-Column Joint

Beam-column joint is the most vulnerable location of a moment-resisting reinforced concrete frame structure. The joint region experiences the maximum shear stress both in vertically and horizontally which is generated due to the shear transfer mechanism from the adjoining beams and columns. The shear capacity and bond stress capacity are the two major factors affecting the strength of a joint core in RC structure. An important discovery recently is the ductile behaviour of the whole structure under repeated loading. The behaviour of the concrete beyond elastic limit which is in the concrete hardening zone can drastically influence the ductility of the concrete. The non-linear stress-strain behaviour after the onset of the initial crack and up to ultimate compressive strength plays an important role in improving ductility. Beyond the ultimate compressive strength, concrete will undergo softening which is neglected in this study as once concrete reaches ultimate stress it is unsafe for service. This material ductility can be fulfilled with the application of high-strength fibres with ductile behaviour. However, the hybridization of two or more fibres can incorporate two different characteristics of the fibre used. The use of ordinary-grade of concrete moreover reduces the shear-resisting capacity of the joint. A hybrid mix of hooked-end steel fibre with basalt fibre and crimpled steel fibre with polypropylene fibre are used with a volume fraction of 1% to 1.4% of the concrete. In this study, ordinary M25 grade concrete and fibre mixed M25 grade concrete is employed under static and cyclic loading. The laboratory tests are also conducted to evaluate the compressive strength, split-tensile strength, and flexural strength of the hybrid mix fibre-reinforced concrete at the age of 28th days. Five full-scale models of the beam-column joint are designed as per the Bureau of Indian Standards. Numerical models of concrete and steel reinforcement are developed. Numerical analysis is carried out using finite element software ANSYS-v21. The behaviours of the beam-column joint are observed under static as well as cyclic loading. Crack patterns, first crack load, initial displacement, ultimate load, and ultimate displacement are observed under static conditions. And under cyclic loading, hysteresis load vs displacement, energy dissipation, and stiffness degradation are observed. The hybridization of hooked steel with basalt fibre gives better results in mechanical strengths and the hybrid effect of crimpled steel with polypropylene fibre gives better results in mechanical strengths. And also under numerical study, the above specimens show an improvement in energy dissipation capacity. Keywords beam-column joint, hybrid fibre reinforced concrete, numerical concrete model, ANSYS, static, reverse cyclic, energy dissipation, stiffness, crack

Self-healing evaluation of bacteria grouted light weight aggregate concrete containing rice husk ash and steel fibers

Utilization of microbiologically induced calcite precipitation along with fiber composite have great influence on improving strength and durable properties of concrete. The concept of mechanical properties of grouted concrete added with bacteria, steel fibers (SF), rice husk ash (RHA) and light weight aggregate (LWA) has been focused on this work. In the fabrication of concrete specimens, concentration of bacteria, combination of steel fibers and LWA was placed in the formwork, and to fill the voids flowable grout was injected. The variables studied in this work are two different sizes of LWA viz., 10 mm and 12.5 mm with constant dosage of 2% hooked end steel fibers by volume of concrete, 10% RHA was used as cement replacement for preparation of grout and bacteria was incorporated in cement grout by direct application. The properties such as compressive strength (CS), compressive strength regain (CSR), crack width healing, impact strength for first crack and final failure, rate of healing was studied for pre-cracked specimens using visual and microscopic observation. In addition, microstructure was studied for grouted concrete without bacteria and with bacteria under immersed curing conditions. From the experimental results, performance of bacteria added grouted concrete properties such as CS, CSR, cracking healing capacity, and impact strength has improved with the addition of fibers.Utilization of microbiologically induced calcite precipitation along with fiber composite have great influence on improving strength and durable properties of concrete. The concept of mechanical properties of grouted concrete added with bacteria, steel fibers (SF), rice husk ash (RHA) and light weight aggregate (LWA) has been focused on this work. In the fabrication of concrete specimens, concentration of bacteria, combination of steel fibers and LWA was placed in the formwork, and to fill the voids flowable grout was injected. The variables studied in this work are two different sizes of LWA viz., 10 mm and 12.5 mm with constant dosage of 2% hooked end steel fibers by volume of concrete, 10% RHA was used as cement replacement for preparation of grout and bacteria was incorporated in cement grout by direct application. The properties such as compressive strength (CS), compressive strength regain (CSR), crack width healing, impact strength for first crack and final failure, rate of healing was studied for pre-cracked specimens using visual and microscopic observation. In addition, microstructure was studied for grouted concrete without bacteria and with bacteria under immersed curing conditions. From the experimental results, performance of bacteria added grouted concrete properties such as CS, CSR, cracking healing capacity, and impact strength has improved with the addition of fibers.

Shear response and fracture processes of hybrid steel fiber reinforced concrete

Ten hybrid steel fiber reinforced concrete mixtures are designed to analyze the influence of the hybridization of three different steel fibers (long hooked-end, medium hooked-end, short wave) on the shear performance by Z push-off shear tests. The presence of steel fibers improves the shear strength and toughness of the concrete, which increase with the volume fraction of hybrid fibers. The hybrid steel fiber reinforcement affects the fracture processes. Micro cracks propagation, cracks onset, cracks propagation and cracks post-peak propagation are the four main fracture stages. The volume fraction above 1.0% changes the evolution trend of fracture process zone length. The hybridization of the long hooked-end steel fiber with the other steel fibers produces a synergistic effect on inhibiting the propagation of the fracture process zone (FPZ) compared with the long hooked-end steel fiber reinforced concrete. The hooked-end steel fiber produces a better effect on slowing down the damage degree factor than short wave shaped steel fiber. The damage degree factor at the same loading level is reduced with the increase of the volume fraction of hybrid steel fiber.

Impact strength and weight loss of fiber-reinforced concrete exposed to elevated temperatures

The article presents experimental results that were directed to explore the effect of weight loss on the residual repeated impact strength of concrete exposed to high temperatures. The experimental program included the testing of shallow cylindrical specimens under repeated impact loading following the ACI 544-2R test setup recommendations. Five concrete mixtures were prepared for this purpose to evaluate the influence of two major parameters, which are the concrete design compressive strength and the volumetric content of fiber. Three plain mixtures with three levels of design strength including normal-strength and high-strength concrete were prepared in addition to two fibrous mixtures that have the same constituents of the normal-strength mixture. Hooked-end steel fibers were used in the fibrous mixtures at two volumetric contents of 0.5 and 1.0 %. In addition to the repeated impact strength, the compressive strength was also tested using 100 mm cubes. A group of six shallow cylinders and three cubes was tested at room temperature without heating as a reference group from each mixture, while three similar groups were subjected to 200, 400 and 600 °C then tested after natural cooling. The weight loss was recorded for all heated specimens. The results showed that both the specimen weigh and the repeated impact exhibited a trend of continuous decrease with the increase of temperature. However, the repeated impact suffered serious damages after exposure to 200 °C and almost faded after exposure to the higher temperatures, while reasonable decreasing weight losses were recorded at all temperatures.

Investigating the fracture toughness of the self compacting concrete using ENDB samples by changing the aggregate size and percent of steel fiber

In reality, concrete structures are normally under various loadings, and results of different studies have shown that cracks in these structures and their materials, due to their nature as well as the loading type, do not develop along the crack plane (pure mode I); rather, they expand under mixed modes, making the crack growth studies under these modes a very important issue. In the crack growth phenomenon, the fracture toughness is a very effective parameter usually calculated by ENDB samples because they are easy to handle. In this study, several samples were made by changing the maximum aggregates size (dmax = 9.5, 12.5 & 19 mm) and the amount of hooked-end steel fibers (SF = 0.1, 0.3 & 0.5%), and tested under different loading modes (pure/mixed modes I and III) using the strain control jack device. According to the results, the lowest fracture toughness belonged to pure mode III, aggregates with dmax = 12.5 mm performed better in the self-compacting concrete reinforced with steel fiber, Also, the results show that the increasing trend of steel fibers does not have a positive effect on the fracture toughness performance.

Optimization of the Shape of Hooked-End Steel Fiber Based on Pulling Out and Reinforcing Cementitious Composites.

Efficient steel fiber-reinforced cementitious composites (SFRCC) should improve not only the ultimate tensile strength but also the residual tensile strength (post-cracking tensile strength) of the SFRCC matrix. The degradation of the post-cracking tensile strength of SFRCC depends on the pullout properties of the steel fibers from the cementitious matrix. When the straight steel fiber was pulled out from the matrix, the pullout resistance was affected by the actions of bonding and friction. After debonding, the load was transferred only by friction, and the pullout resistance decreased rapidly, resulting in a weak reinforcing effect. In addition, changing the fiber shape can effectively slow down the decreasing rate of the pullout resistance of the steel fibers, thus improving their reinforcing effects. In this study, the shape of the steel fibers was optimized to slow down the decrease in the pullout resistance of the steel fibers from the cementitious matrix, thus achieving better tensile properties of SFRCC. First, a calculation model for the steel fiber pullout resistance was established. On this basis, a method to optimize the shape of the steel fibers was proposed. Finally, the pulling out behavior of steel fibers with different end hook shapes was tested, and the influence of the steel fiber shape on the decreasing rate of the residual pullout resistance was analyzed. The results showed that the optimized hooked-end steel fibers had better pullout resistance than ordinary hooked end steel fibers of the same diameter, tensile strength, and matrix.

Mechanical and Durability Evaluation of Hooked End Steel Fibers Reinforced Concrete

Steel fibres reinforced concrete has recently been good alternative to normal concrete.This research seeks to explore the characteristic strength of high-performance concrete through the incorporation of hooked-end steel fibers, simultaneously evaluation their mechanical and durability attributes. In the experimental setting, multiple concrete mixes were meticulously prepared and examined, each containing different percentages of steel fibers varying from 0.5 to 2.0 percent. The percentages of fibres were used with the respect by volume of concrete. The primary objective was to ascertain the saturation point at which maximum strength is achieved and to identify any other pertinent factors. Five mixes were formulated, with one mix serving as the normal group, containing no fibers whatsoever. M30 grade concrete was employed in this investigation, incorporating steel fiber content ranging from 0.5% to 2.0%. Test specimens in the form of cubes, cylinders, and prisms were meticulously prepared and subjected to controlled laboratory testing following 28 days of water curing. Various mechanical properties, such as compressive strength, split tensile strength, and modulus of rupture, were assessed for all fiber percentages. Additionally, a durability assessment was conducted for period of 30 days to specimens containing 0% and 1.5% steel fibers, evaluating their resistance to acid, sulfate, and saltwater. Non-destructive tests, including rebound hammer and ultrasonic pulse velocity, were performed both before and after immersion to study the effects. The study’s findings revealed that high-strength concrete specimens containing fibers demonstrated a decreased occurrence of cracks, suggesting an improvement in ductility attributed to the inclusion of fibers in the concrete matrix.

Flexural Toughening of Hooked-End Steel Fibers Reinforced Mortars

This paper investigated the effect of hooked-end steel fiber at varying fiber content on the flexural toughening of fiber reinforced cement mortars (FRCM) by using three-point bending tests. In particular, to preserve the mortar workability, three low weight fractions (0.3%, 0.5% and 0.7%) and two cement matrices (M10 and M15) were investigated. The results showed that the mechanical bending behavior of the FRCM increases significantly at increasing fiber content and cement plaster matrix. An important aspect that has been addressed is how the flexural toughening is varied at varying fiber content and the type of matrix. Especially, all composite mortars exhibited a toughness index (TI) in the range of 10–45, indicating a suitable strengthening and toughening effect supplied by the hooked-end fiber addition. The best TI value, equal to 44, was experienced for the M10-D7 batch characterized by 0.7 wt.% of hooked-end steel fibers and an M10 cement matrix. Furthermore, unlike unreinforced concrete where brittle and unexpected failure occurs dominated by a sudden and catastrophic propagation of tensile cracks, the FRCM samples exhibited a ductile behavior with a marked residual post-crack resistance even for composites mortars with low metal fiber content.

High-strength high-performance concrete incorporating different macro fiber types and contents: Engineering and durability performance

ABSTRACT Generating a synergistic response by combining the advantages of different fiber types in concrete is of current scholarly interest. This study investigated the effects of different hooked-end steel fiber (SF) volume fractions up to 1.6% and three macro fiber types including polypropylene (PP), SF, and typical hybrid fibers (HF: 50% SF + 50% PP) at a fixed dosage of 1.6% on properties of high-strength high-performance concrete (HSHPC). A novel densified mixture design algorithm was used to incorporate a high quantity of fly ash and rice husk ash as an eco-binder. Results showed the specimens with added macro SF exhibited improved mechanical strength, dynamic modulus of elasticity and rigidity, and lower drying shrinkage while the ones with added PP exhibited reductions in compressive strength and dynamic modulus. Interestingly, the incorporation of macro fibers, regardless of fiber type and content, reduced electrical resistivity, ultrasonic pulse velocity and increased the total charge passed in the chloride ion penetration test, resulting in likely underestimation of the reinforcement corrosion resistance, especially for SF specimens. The findings also confirm that HF demonstrating synergistic response may be effective and creative in improving most of the concrete characteristics, contributing to the efficient use of HSHPC in real-world structures.

Prediction of the complete flexural load–deflection curve of self-compacting concrete reinforced with hook-end steel fiber

The flexural performance is vital for evaluating the characteristics of steel fiber reinforced self-compacting concrete (SFR-SCC). Although the tested load–deflection curve is commonly used to predict the flexural performance, little research has been done on the tested curve prediction. In this study, the complete flexural load–deflection curves of SFR-SCC beam specimens were obtained by a four-point bending test. The hook-end steel fiber with a length about 25 mm, 30 mm or 35 mm was respectively added for SFR-SCC at volume fraction of 0.4 %, 0.8 %, 1.2 % or 1.4 %. The characteristic points of tested curves are statistically analyzed to build the prediction formulas for the initial cracking strength, the flexural strength, and the first and second residual flexural strengths. The formulas for predicting the complete flexural load–deflection curve of SFR-SCC are proposed, and verified by comparing with the test curves. Meanwhile, the distribution of steel fiber in concrete matrix of beam specimen was measured to explain the mechanisms of flexural performance of SFR-SCC.

Long-term performance of concrete reinforced with scrap tire steel fibers in hybrid and non-hybrid forms: Experimental behavior and practical applications

This study examines the potential impact of scrap tire steel fibers (SSFs) on concrete properties, focusing on long-term performance. The reuse of discarded tires in construction addresses the environmental challenge of tire disposal. While previous research has explored SSFs in concrete, long-term properties and practical implementation pathways of SSF-reinforced concrete are lacking. To address these gaps, this study assesses the influence of locally available SSFs from Bratislava, Slovakia, on concrete properties, specifically targeting the 120-day hardened properties. Locally sourced C20/25 concrete is used, incorporating SSFs in non-hybrid (single type of fibers) and hybrid forms (30% industrial hook end steel fibers “ISF”). SSF dosages range from 0.3% to 1.75% for non-hybrid fibers and 0.50% to 0.70% for hybrid fibers. Experimental properties, including elastic modulus (EM), compressive strength (CS), tensile splitting strength (SS), flexure strength (FS), residual flexure strength (RFS), linear shrinkage (LS), and water absorption (WA), are evaluated. The toughness and energy absorption capacity are demonstrated for SS and FS. The results indicate that the inclusion of SSFs enhances the EM and SS of SSF-reinforced concrete (SSFRC). Additionally, SSFRC exhibits reduced linear shrinkage compared to concrete without SSFs. Notably, the hybrid fiber concrete (HSFRC) shows superior performance, outperforming both ISF concrete and SSFRC in enhancing the considered properties. HSFRC exhibits promising potential for replacing ISF concrete in various civil engineering applications. However, further investigation is needed to evaluate the performance of HSFRC under extreme environmental conditions.

Mechanical performance evaluation of steel fiber-reinforced concrete (FRC) based on multi-mechanical indicators from split hopkinson pressure bar (SHPB) test

Fiber-reinforced concrete (FRC) is a new composite material composed of various fibers and a cement matrix that has been widely used and developed in the construction engineering field. In this paper, split Hopkinson pressure bar (SHPB) tests are carried out with the aim of investigating the mechanical properties and failure characteristics of FRC containing different types and dosages of steel fibers. The main findings are as follows: At a fiber content of 0 %–3.5 %, the strength of FRC shows two trends: continuously increasing and then decreasing. The ductility of hooked-end steel fiber-reinforced concrete (HFRC) is better than that of hybrid steel fiber-reinforced concrete (HSFRC) and straight steel fiber-reinforced concrete (SFRC) under static loads, whereas the ductility of HSFRC is better than that of SFRC and HFRC under dynamic loads. Straight steel fibers (SF) are better than hooked-end steel fibers (HF) in improving tensile toughness but worse than HF in improving compressive toughness. In terms of the degree of failure, NFRC and HFRC were the most severely fragmented, whereas SFRC and HSFRC exhibited better integrity. Finally, based on the multi-mechanical indicators of the FRC, a comprehensive performance evaluation method and optimization suggestions for the FRC are proposed. This provides theoretical support for the application of FRC as seismic-resistant materials in reinforced structures (i.e., anti-slide piles, retaining walls, and beam structures) of rocky landslides in strong seismic areas, which have important engineering significance.

Effect of fibre diameter and tensile strength on the mechanical, fracture, and fibre distribution properties of eco-friendly high-strength self-compacting concrete

The development of Steel Fibre-Reinforced Self-Compacting Concrete (SFR-SCC) is a complex task with significant practical implications for the construction industry. However, the absence of established design guidelines and recommendations, and the limited availability of design methodologies, present a significant challenge. Achieving the targeted rheological and mechanical properties while simultaneously minimising production costs requires a comprehensive understanding of the optimal blend of fibre type and quantity and the coarse aggregate content. This paper addresses the impact of steel fibre properties on the rheological and fundamental mechanical properties of eco-friendly high-strength self-compacting concrete (HSSCC), using 40% ground granulated blast furnace slag (GGBS) as a cement replacement. The research focused on 30 mm long hooked-end steel fibres with tensile strengths of 1345 MPa and 3070 MPa, and diameters of 0.55 mm and 0.38 mm, respectively. In addition, the study investigated the combined effect of coarse aggregate content and steel fibre type on the performance of eco-friendly HSSCC. The fresh properties of eco-friendly HSSCC were assessed using the slump flow and J-ring tests. Furthermore, mechanical and fracture properties such as compressive strength, splitting tensile strength, elastic modulus, four-point flexural strength, and three-point flexural strength on notched prisms were also evaluated. The distribution and alignment of steel fibres in the HSSCC were assessed using image analysis techniques, which showed that the steel fibre diameters were a crucial factor in the fibre dispersion. The results demonstrated that using steel fibres with higher tensile strength and smaller diameter significantly enhanced the splitting tensile strength, flexural strength, and fracture energy, compared to steel fibres with larger diameters and lower tensile strengths. Additionally, the study indicated that the elastic modulus and fracture energy of eco-friendly HSSCC reinforced with both types of steel fibre are highly dependent on the content of coarse aggregate used. The study highlighted that the coarse aggregate proportion and the steel fibre characteristics were two vital factors that influenced the rheological and mechanical properties of HSSCC and must be considered during the mix design process to optimise the desired properties while also minimising production costs.

Mechanical performance of fiber-reinforced concrete and functionally graded concrete with natural and recycled aggregates

This study aims to assess the mechanical performance of functionally graded concrete (FGC) in comparison to conventional plain cement concrete (PCC) and fibre-reinforced concrete (FRC). For this purpose, five concrete mixes were prepared, defined in eleven patterns, including PCC as a control mix, two FRC mixes, and eight combinations for FGC mixes. The hooked-end steel fibres and recycled thin polyethylene terephthalate (PET) strips from used bottles were utilized as fibres in 0.75 % of the volume of the mix in the FRC and FGC mixes. The natural aggregates were replaced by 15 % by weight with recycled plastic aggregates (RPA) and recycled concrete aggregates (RCA) in the FGC mixes. The mechanical performance of all specimens was assessed by compressive, split tensile and flexural strength tests, whereas the concrete quality was evaluated by the ultrasonic pulse velocity (UPV) test. The results revealed that the FRC mix containing steel fibres has 50.6 % higher compressive strength, while PET-FRC exhibited 42.4 % lower strength than the PCC. The best combination of the FGC mix is RCA + SFRC (H), which showed 27.6 % more compressive strength than PCC. The steel fibre-reinforced concrete (SFRC) mix has the highest split tensile strength, which is 47.5 % higher than the PCC. The best combination of FGC mixes is SFRC + PET-FRC (J), yielding 29.3 % higher tensile strength than PCC. On the other hand, both fibres contribute to the flexural strength enhancement of FRC. The FGC mix (K) yielded the highest flexural strength, with PET-FRC and SFRC in the upper and bottom layers, respectively, giving 40 % more flexural strength than the PCC specimen. The UPV values depicted that fibres and recycled aggregates in FGC specimens enhanced the quality of concrete. The highest value of UPV was recorded in the mix PCC + SFRC (G) containing PCC and steel fibres, which almost reached the upper limit of the recommended UPV values.

Mechanical properties of slurry-infiltrated fiber concrete (SIFCON) as sustainable material with variable fiber content

For any member, sustainability is very important, which refers to the capacity to endure. Normal concrete has low tensile strength and could not exhibit significant tensile strain margins. Accordingly, it is essential to implement strategies that can enhance the behavior of conventional concrete before using it as structural concrete. Therefore, using Slurry-Infiltrated Fiber Concrete (SIFCON) composites is a current innovation in the field of civil engineering that has a considerable influence. This study presented an experimental study to improve the mechanical efficiency of a SIFCON mix with varying fiber content. To satisfy this objective, several SIFCON mixes, incorporating hook-end steel fiber with three different volume fractions (6, 7, and 8.5%) were prepared. The prepared mixtures performed compressive strength tests at 7 and 28 days, splitting tensile strength tests, and flexural strength tests both in the fresh and hardened states. The results pointed out that the fresh state mortar had proper filling and flow ability properties, satisfying the spread diameter requirement (between 240 and 260 mm) for SIFCON mortar, which is equal to 249 mm. For mechanical performance, the maximum compressive strength increased by 53% after 28 days for the mix’s SF of 8.5%. Furthermore, when compared to the reference mix, splitting, and flexural enhancement increased by 44% and 91%, respectively. On the other hand, the failure shape of SIFCON for all tested mixes has an impact on strengthening, that’s assigned to the high vast area of SF.

Effect of Contents, Tensile Strengths and Aspect Ratios of Hooked-End Steel Fibers (SFs) on Compressive and Flexural Performance of Normal Strength Concrete

This study is a part of the study to simplify the reinforcing details of reinforced concrete (RC) structural members by substituting the conventional reinforcement with hooked-end steel fibers (SFs). This paper investigates the effects of SF strength, dosage and aspect (l/d) ratio on the compressive and flexural behaviors of normal strength concrete with specified compressive strength of 30 MPa. In this study, hooked-end SFs of high strength (2000–2400 MPa) and normal strength (1100–1200 MPa) were used with three l/d ratios of 64, 67 and 80. Hooked-end SFs were incorporated with three dosages of 20 kg/m3 (0.25 vol.%), 40 kg/m3 (0.50 vol.%) and 60 kg/m3 (0.75 vol.%). Eighteen steel fiber reinforced concrete (SFRC) mixes were mixed. To evaluate the compressive and flexural performance of each SFRC mixture, three SFRC cylindrical and prismatic specimens for each mixture were manufactured and tested, respectively. The test results that the inclusion of hooked-end SFs had little effect on the compressive strength, while it improved the toughness of concrete. Hooked-end SFs were also found to be effective in enhancing the flexural performance of concrete. The dosage and properties (strength and l/d ratio) of SFs significantly affect the residual flexural tensile strength (fR1 and fR3) at serviceability (SLS) and ultimate limit state (ULS) defined in fib Model Code 2010 (MC2010).