Hooked-end Steel Fibers Research Articles

Performance of hybrid steel fiber-reinforced self-compacting concrete RC beam under flexure

Hybrid steel fiber-reinforced self-compacting concrete (HSFRSCC) has desirable properties for improving the performance of structures. But the literature is sparse on the flexural performance of the reinforced concrete (RC) beam reinforced with hybrid fibers. The impact of the combined action of micro- and hooked-end steel fibers on the flexural performance of the SCC beam to which mineral admixtures and superplasticisers have been added to improve their workability is investigated in this study. In the experiment, beam specimens, reinforced with micro-steel and hooked-end fibers, with a compressive strength of 60 and 80 MPa and of size 150×230×3000 mm were prepared. The results clearly demonstrate that the flexural performance of the SCC beam significantly improved with the addition of hybrid steel fibers. The combination of 0.5% of hooked-end steel fibers and 0.25% of micro-steel fibers offers a better flexural performance than the addition of hybrid fibers in other proportions. Adding hybrid steel fibers in RCSCC beam increases the beam’s load- and moment-carrying capacities by 40.64% and 40%, respectively, compared to the RCSCC beam without hybrid steel fibers. The crack spacing and crack width are also reduced by 16–45% and 25–75%.

Experimental investigation of steel fiber reinforced concrete slabs subjected to underwater contact explosions

Fiber reinforced concrete has gained significant attention due to its higher ductility and flexural behavior, making it a promising material for resisting extreme loads such as those caused by blast and impact. In this study, we present experimental results from static tests conducted on steel fiber reinforced concrete with different content of hooked end steel fibers and concrete strength. Underwater contact explosion tests were performed for 6 pieces of 50 cm × 50 cm x 6 cm steel fiber reinforced concrete slabs. The damage patterns observed in the slabs were analyzed, and shock pressure data was measured and compared with empirical formula calculations. Test results demonstrate that the addition of steel fiber effectively enhances the compressive and tensile strength of concrete while also significantly improving its anti-explosion capacity. In contrast, the plain concrete slab (control group) displayed an overall state of failure during underwater contact explosions. Steel fiber reinforced concrete slabs primarily experienced bending failure and “Y" crack damage, accompanied by local collapse failure on the back surface. Overall, these findings suggest that steel fiber reinforced concrete holds great promise as a superior material for resisting extreme loads, particularly in marine environments.

Effect of hooked end steel fibers on strength and durability properties of ambient cured geopolymer concrete

Growing carbon emissions in the construction industry have warranted the use of alternative materials such as geopolymer concrete. At the same time exposure of concrete material to harsh environmental conditions has compelled to design of durable geopolymer concrete. The use of hooked-end steel fibers in conventional fiber-reinforced concrete has proven to improve its crack resistance, and thus, positively influence the durability properties of concrete structures. Nevertheless, limited studies explore the effect of hooked-end steel fibers on the strength and durability properties of ambient cured geopolymer concrete with a low NaOH content (i.e., 8 M concentration). In this study, ambient cured geopolymer concrete was prepared by fly ash, ground granulated blast furnace slag (GGBS), NaOH, Na2SiO3, manufactured sand, and natural coarse aggregates. Additionally, hooked-end steel fibers with an aspect ratio of 67 were added to the mix by volume fraction in dosages of 0 %, 0.5 %, 1 %, 1.5 %, and 2 %. The experimental results showed that the addition of fibers reduced the workability with a minimum slump of 70 mm and a maximum Vee Bee time of 8 s for mixes with 2 % steel fibers. The addition of fibers improved the compressive strength, split tensile strength, and flexural strength of geopolymer concrete, with a maximum strength of 41.44 MPa, 4.28 MPa, and 5.23 MPa at an optimum fiber dose of 1 %, respectively. Above the optimum dose, the strength of the steel fiber-reinforced geopolymer concrete (SFRGPC) was reduced. The depth of water penetration reduced in SFRGPC when compared to GPC. Moreover, the resistance to chloride ion penetration was not significantly affected by addition of steel fibers till optimum dose of 1 %. The scanning electron microscopic results revealed the positive effect of steel fibers in restricting the progression of cracks. This has resulted in smaller crack width in the SFRGPC when compared to GPC. Overall, steel fibers in optimum dose have improved the performance of geopolymer concrete and this will contribute towards low carbon material.

Investigations on mechanical and durability properties for pavement quality concrete using hybrid fibres

Hybrid fiber reinforced concrete was used to develop pavement quality concrete (PQC) to overcome the disadvantages associated with rigid pavements prepared with plain cement concrete. Hooked-end steel (ST) fiber of 60 mm in length and polypropylene (PP) fiber with a length of 36 mm were used as reinforcement for the hybrid fiber concrete mix. The proportion of ST and PP fibers used was upto 1% with which PP fibers varied from 0 to 0.45% at a 0.15% increment in the total mix. This study aims to assess the various strength workability and durability issues of the concrete mixes. Significant improvement in the properties of mechanical and durability characteristics was observed in the results with the addition of these fibers as compared to control cement concrete. Among all the mix proportions, the overall performance of the mixture by adding steel fiber at 0.85% and polypropylene fiber at 0.15% contents was found to be the best. However, a slight increase in water absorption value was observed by the incorporation of fibers into concrete due to increased thickness in the transition zone and porosity.

The Effect of Type of Fiber in Density and Splitting Tensile Strength of SIFCON

SIFCON is characterized as a construction material of high ductility and very high strength. It is suitable for concrete structures used for special applications. However, the density of SIFCON is much higher than that of Fiber Reinforced Concrete (FRC) due to the need for a large amount of high-density steel fibers. This work examines the split tensile behavior of modified weight slurry infiltrated fiber concrete utilizing a mixture of two types of fibers, steel fiber, and polyolefin fiber. For the investigation, 30 cylinders and 15 cubes were poured. The used volume fraction (V.F) is (6 %) and the use of five series once as each type separately and once a hybrid in proportions of 2/3 polyolefin with 1/3 steel fiber and vice versa. The splitting tensile strength and the unit weight of SIFCON resulting from tests were studied. The results indicate that SIFCON produced from a mixture of 1/3 hook-end steel fibers with 2/3 polyolefin fibers achieved good results in reducing density while maintaining a high split tensile strength. It significantly decreased density by 140 kg per cubic meter and improved splitting tensile strength by 494%.

2,000 MPa급 고강도 후크형 강섬유로 보강된 60 MPa급 콘크리트의 잔류 휨 인장강도

본 연구는 고강도 강섬유를 이용하여 전통적인 철근이나 망사를 대체하여 콘크리트구조를 단순화하려고 강섬유 보강콘크리트의 기계적 특성을 기반으로 하는 구성 모델을 연구하려고 한다. 특히, 휨 분석과 설계에 필요한 휨 인장응력 모델은 잔류 휨 인장강도의 영향을 크게 받는다. 본 논문에서는 2,000 MPa 고강도 후크형 강섬유로 보강된 27개의 노치 고강도 콘크리트 보에 대한 3점 휨 실험을 진행하고 논의하였다. 본 실험에선, 고강도 콘크리트에 형상비(lSUBf/SUB/dSUBf/SUB)가 64 및 67, 80의 섬유 세 타입을 사용하였으며, 변수로는 체적비 0.25 %(20 kg/㎥), 및 0.5 %(40 kg/㎥), 0.75 %(60 kg/㎥) 를 선정하였다. 본 실험 결과와 타 연구자들 문헌을 통해서 수집한 결과를 분석하여 사용 한계 상태(SLS) 및 극한 한계 상태(ULS)에서 HSFRC의 잔류 휨 인장강도에 대한 콘크리트 및 강섬유의 특성의 영향을 조사하였다.

The impact of specimen size and alteration of fiber configuration on the flexural performance of high-performance concrete

This study examines the impact of fiber configuration and specimen size on the flexural performance and thus the energy absorption capacity of moderate and high-performance fiber reinforced concrete (FRC). A total of 180 specimens were produced using hooked-end steel fibers in lengths of 30-mm and 60-mm, and 54-mm long macro synthetic fibers. The specimens, in the form of small beams (75 × 75 × 320 mm3), large beams (150 × 150 × 750 mm3), and square panel specimens (600 × 600 × 100 mm3), were tested in accordance with EN14488-5 and ASTM C1609 standards. The results showed that as the amount of fibers increased, the flexural performance of FRC improved significantly, provided that precautions were taken to avoid mixing and placement issues when using higher amounts of fibers. 60-mm hooked-end steel fibers had the best performance among all the fibers tested with higher ultimate and post-cracking flexural strengths. 54-mm synthetic fibers seemed to be a cost-effective alternative with comparable energy absorption performance when compared to 30-mm hooked-end steel fibers. Small beams had a slightly higher ultimate (∼15% more) and post-cracking (∼35% more) flexural strengths than large beams, but the equivalent flexural strength ratio was not significantly affected by the specimen size. No clear relationship between fiber dosage and ultimate flexural strength was observed, but a relationship was observed between the fiber dosage and the equivalent flexural strength ratio, with R2 values ranging from 65% to 93% depending on the concrete matrix and the fiber type. The study also showed strong correlations (R2>91%) between the energy absorption capacity of plate specimens and beam specimens, suggesting that plate specimens can be used to reduce the time and effort required in testing during trial batches and product development. Finally, the use of high-performance concrete does not seem to be necessary, when the target is to improve the energy absorption capacity of FRC, particularly at low fiber volumes.

Effects of elevated temperature and water re-curing on the compression behavior of hybrid fiber reinforced concrete

Over the past decades, the effect of elevated temperatures on the mechanical properties of concrete has received significant attention because of the importance for fireproof design, safety evaluation and repair of fire damaged constructions. However, very few researches have been dedicated to the consequences of water re-curing of a thermally damaged concrete. In this paper, the effect of elevated temperatures and water re-curing on the mechanical response of two hybrid fiber reinforced concretes was investigated. For the first hybrid reinforced mix, long hooked-end and medium hooked-end steel fibers were adopted, as well as high strength short wave shaped steel fibers. In the second mix, polypropylene fibers substituted the short-wave shaped steel fibers. The mechanical behavior in compression was studied by measuring the stress-strain response. The elevated temperatures above 200 °C decreased: Young's modulus, compressive strength and toughness of the hybrid fiber reinforced concretes. The stable crack growth stage was reduced with the increase of the temperature above 200 °C, with an extension of the unstable crack growth stage for both kinds of hybrid fiber reinforced concrete. Water re-curing partially recovered Young's modulus, compressive strength, toughness, and extended the stable crack growth. An existing model was modified for predicting the stress-strain response of thermally damaged hybrid fiber reinforced concrete.

Effect of fiber synergy on strength & durability of high-performance concrete

The distinct fiber addition to concrete can improve weak performance in tension. Due to its higher performance, fiber hybridization is becoming more and more competitive. In this study, the hardened and durability characteristics of performance-based concrete reinforced with polypropylene, basalt and hooked end steel fibers are investigated. Total 12 mixes are prepared to evaluate the different characteristics of performance-based concrete. The influence of basalt fibers (0.2, 0.25, 0.5, 0.75 & 1%), polypropylene fibers ( 0.025, 0.03, 0.035, 0.05 & 1%), hooked end steel fibers (0.225, 0.475, 0.65, 0.75, 0.80 & 1%) to explore the impact of fiber synergy, various hybrid fibers with maximum volume fraction of 1% were used out of total concrete volume with and without copper slag (20% & 40%) replacement with fine aggregate are investigated on the hardened characteristics including; compressive strength, flexural strength, splitting tensile strength. Moreover, durability properties including; water absorption, electrical Resistivity, for performance-based concrete are also conducted. Out of the 12 mixes considered for this study, PP0.05B0.2S0.75CS40 performs better and exhibit excellent performance in terms of strength and durability.

Comprehensive experimental and numerical modeling of strength parameters of eco-friendly steel fiber reinforced SCC containing coarse copper slag aggregates

The copper slag waste (CSW) is an industrial by-product, the annual production of which is huge and its disposal and management are a big challenge for environmentalists. This research has comprehensively studied, experimentally and numerically, the possibility of substituting 20–60% copper slag (CS) for natural coarse aggregates in self-compacting concretes (SCCs) reinforced with 0.1, 0.3 and 0.5% hooked-end steel fibers. According to the results, increasing the CS volume improves the characteristics of the fresh concrete, but there is an obvious drop in its flowability, fillability and passability at the highest steel fiber (SF) volume. Although increasing CS reduces the compressive strength of concretes containing low SF volumes, positive CS effects on the concrete strength are evident at the highest SF volume. Based on the scanning electron microscope (SEM) images, in concretes containing 0.1% SF, an increase in CS increases the tensile strength, and increasing this volume up to 30% makes the concrete microstructure homogeneous and integrated. To check the statistical importance of the results of the tensile and compressive strengths, use was made of the analysis of variance (ANOVA) method. To reduce costs (and human errors) and avoid time wastage, artificial neural network (ANN) prediction models and robust multiple regression analyses (MRA) methods were used to predict the compressive and tensile strengths. Results of this research confirm that using CS in producing steel fiber reinforced self-compacting concrete (SFRSCC) has technical, environmental and economic advantages.

Investigation of Mechanical Properties of M-sand concrete with Polypropylene and Steel fibers

This study looks into the impact of the adding of polypropylene(pp) and Hooked-end steel (HES) fibre on the mechanical characteristics of M-sand concrete (MSC). HES fibres with a 30-mm length were used at 1% to the weight of the cement for every mix and Polypropylene(pp) fibers with length 12-mm were used at the content of 0.25%, 0.50%, and 0.75% and 1%. All the mixes were produced with the mixing of HES and pp fibers. All the mixes with fiber-reinforced concretes (FRC) contained 60% M-sand as fine aggregate (FA) replacement. For increment of workability, the super plasticizer is also added. The compressive strength, splitting tensile strength, flexural strength of the concrete mixes was examined for M30 Concrete. Results of this work indicated that the adding of the M-sand improves compression characteristics of plain concrete mix. The outcomes also show that the mechanical characteristics of MSC were amplified by the addition of steel (HES) and polypropylene (pp) fibers at each weight fraction taken into account in this investigation. Additionally, it was found that adding 1% steel fiber considerably increased the concrete’s split tensile test values and also flexural test values. The blend with the highest performance out of all the varied steel and polypropylene(pp) fibre combinations tested had 1% HES and 0.5% pp fiber. Finally, the findings demonstrated that adding fibres to concrete led to reduction in compressive strength and increase in the value of split tensile strength and also flexural strength.

The Combined Impact of Imposed Loads and Elevated Temperature on Steel Fiber Reinforced Concrete Samples

Reinforced concrete buildings and structures are exposed to fire, and the concrete's qualities can vary in the case of an uncontrolled fire. It is essential to know how concrete's properties may change as a result of exposure to high temperatures and loading for normal concrete with or without fiber reinforcement. Understanding the strength characteristics of concrete structures exposed to high temperatures is important in order to be able to predict how these structures will perform after exposure to this condition. This study investigates the combined impact of loading and high temperature on the properties of concrete samples by testing the compressive, flexural strength, and ultrasonic pulse velocity (UPV) of normal-strength concrete (NSC) with or without steel fiber. The type of steel fiber employed in this investigation is hooked-end steel fiber with a 1% volume fraction of concrete. The concrete samples were subjected to four sustained load cases (0, 20, 40, and 60% of ultimate load) and exposed to elevated temperatures (25, 300, and 500°C) for about 2 hours. In addition, using an unrestrictive test before and after loading and heating, the results indicated the maximum deference of compressive strength decreasing is 4% for the steel fiber (SF1) mixture compared with NSC mixture at 300°C for all load cases. While at 60% sustained load and 500°C, the maximum deference of compressive strength decreasing is 12% for the NSC mixture as compared with the SF1 mixture. The maximum difference in flexural strength is 20% for mixtures with steel fiber (SF1) compared to NSC mixtures at 500°C for all load cases. In addition, the UPV test was used to investigate the microstructure and quality of concrete. This test indicated no difference or approximately equal values for SF1 and NSC mixtures at 25 and 300°C for all load cases, while at 500°C, the UPV test for NSC had a higher value than the UPV value of the SF1 mixture.

Experimental Study on the Behavior of Axially Loaded Reinforced Concrete Square Columns Strengthened with SIFCON Shell

Slurry infiltrated fiber concrete (SIFCON) is an advanced generation of fiber-reinforced concrete (FRC) with higher fiber content. SIFCON offers excellent potential for use in areas that require high ductility and impact resistance, particularly when designing seismic retrofits and repairing or strengthening structural reinforced concrete members. This study investigated the behavior of square normal strength concrete (NSC) columns of grade M35 strengthened with SIFCON shell and compared them with unstrengthen NSC. The effect of different SIFCON shell thicknesses (2 and 3) cm, fiber type and volume fraction (4 and 6%), and tie spacing (8 and 16) cm were studied. The fiber types employed were polypropylene and hooked-end steel fiber. Eleven columns were cast and tested for the current investigation in two groups, where the first group (control specimens) consists of two unstrengthen NSC columns and one square NSC column strengthened with a 2 cm SIFCON shell with a 6% steel fiber ratio. The second group comprises eight NSC columns strengthened with a hybrid fiber SIFCON shell. The NSC square columns had dimensions of (8x8x80) cm. 3 cm SIFCON shell thickness was observed to evolve the strengthen columns' load-carrying capacity and energy absorption. The maximum load achieved is about 223% as compared with unstrengthened NSC columns. The energy absorption was about 16 times that of the control. At the same time, the stiffness of strengthened columns is less than that of NSC columns.

An Experimental and Numerical Investigation on the Bending Behavior of Fiber Reinforced Concrete Beams

The effects of hooked end steel and polypropylene (PP) fibers on the behavior of large-scale doubly reinforced concrete beams under flexure were investigated using experimental and numeric methods. For this purpose, a total of eight beam specimens consisting in two groups were produced in the laboratory and three-point bending tests were conducted under monotonically increasing load. The beams in the groups were designed to have 0.86 and 1.30% tensile reinforcement ratios leading to either flexural or shear critical sections. Three out of eight were produced to be control samples and did not have any fiber additive while remaining five had 0, 0.5 and 1.0% steel or PP fibers by volume. Experimental results showed that the existence of 0.5% either type of fiber in densely reinforced specimens contributed to shear strength and allowed flexural capacities to be fully used instead of an improvement in the capacity. However, when the steel fiber ratio increased to 1.0% flexural capacity was enhanced by 10% for both type of beams. After the experimental study, the beams numerically modeled using nonlinear finite element method and flexural stiffness before yielding as well as yield strength with load carrying capacities were found to be consistent with that of experiments specifically for the beams having stirrup and steel fibers.

Comparison Between the Effects of Straight And Hook Steel Fibers on Fresh and Hardened Characteristics of Concrete

This research looked into how steel fiber type and concentration influence Steel Fiber Reinforced Concrete (SFRC) mechanical properties. According to tests, the percentage of steel fibers in SFRC is directly related to compressive, flexural, splitting tensile, and direct tensile strength. Straight and hooked steel fibers with the same aspect ratio, 13 mm in length and 0.2 mm in width of straight steel fibers, and 35 mm long and 0.55 mm wide hook-end steel fibers were utilized. Three different percentages of fiber were used: 0.5, 1, and 1.5% by volume. Seven variants of concrete with different types and different percentages of steel fiber were created and evaluated. At 0.5, 1.0, and 1.5% fiber content, the compressive strength of a cube reinforced with hook steel fibers increased by 1.41, 11.52, and 20.81%, respectively, while the compressive strength of a cube reinforced with straight steel fibers increased by 7.27 and 20%, and 21.4% for the same percentages of steel hooked fiber. This indicates that the straight steel fibers are more effective than the hook steel fibers when increasing the compressive strength of the (SFRC). This means that (pressure force increases, albeit gradually). The concrete's splitting tensile strength may be significantly increased by introducing straight and hook steel fiber into the mixture. The tensile strength is improved by (52.78, 69.44, 122.22%) and (44.44, 62.8, 94.44%) when compared to the control concrete sample. Straight steel fibers increased flexural strength by (44.23, 61.54, 86.54%) compared to the control sample, and hook steel fibers increased flexural strength by (11.54, 28.85, 55.77%). When straight fibers are introduced to the control concrete sample, the direct tensile strength increases by about (54.17, 87.5, 162.5) %, and when hook fibers are added, the direct tensile strength increases by (45.83, 75, and 150%).

Influence of steel slag and steel fibers on mechanical properties of normal concrete

Cement, water, and both fine and coarse aggregate make up the composite material known as concrete. It is more versatile than the other building materials and has a variety of uses. However, it is brittle in nature and weak in tensile strength. Concrete also has low impact strength and poor energy absorption. Steel slag and steel fibres are added to the concrete to strengthen the weak spots and create a sustainable mix, and green concrete is created. In this study, concrete is mixed with hook-end steel fibres at concentrations of 0.25%, 0.50%, 0.75%, and 1% by volume, and its mechanical properties are assessed and compared with conventional concrete having 20 % replacement with slag. It was observed that adding hooked-end steel fibres to concrete enhanced its mechanical properties. The required number of cubes were cast, and the M40-grade concrete was then put through compressive, split tensile, and shear tests. The mechanical characteristics of concrete that have changed as a result of the addition of steel fibres were then compared.

Experimental and Statistical Study of the Effect of Steel Fibers and Design Strength on the Variability in Repeated Impact Test Results

The ACI 544-2R repeated impact test is known as a low-cost and simple qualitative test to evaluate the impact strength of concrete. However, the test’s main deficiency is the high variability in its results. The effect of steel fibers and the compressive strength of concrete on the variability in repeated impact test results was investigated experimentally and statically in this study. Two batches from four mixtures were prepared and tested for this purpose. Hooked-end steel fibers were utilized in the fibrous mixtures. The mixtures NC, NC-SF0.5 and NC-SF1.0 were normal strength mixtures with 0, 0.5 and 1.0% of steel fibers, respectively, while HC was a plain high-strength mixture. The impact tests were conducted using an automatic testing machine following the setup of the ACI 544-2R repeated impact test. The impact numbers at cracking (N1) and at failure (N2) were recorded for both batches of the four mixtures. The results were also analyzed using the normal probability and Weibull distribution tests. The test results showed that the fibers increased the impact results at the cracking stage and significantly increased the failure impact resistance. Adding 0.5 and 1.0% of steel fibers increased the N1 by up to 66 and 111%, respectively, and increased the N2 by 114 and 374%, respectively. The test results also showed that duplicating the design compressive strength from 40 to 80 MPa increased the impact resistance by up to approximately 190%. The test results revealed no clear trend of an effect of steel fibers and compressive strength on the variability in the test results.

Shear strength of steel fiber reinforced lightweight self-consolidating concrete joints under monotonic and cyclic loading

The shear behavior of precast concrete segmental bridges depends on the type of joints between the segments. However, there are few studies evaluating the shear strength of steel fiber reinforced lightweight self-consolidating concrete for application to precast concrete bridges. The purpose of this study is to compare the shear behavior of joints made of general concrete with developed concrete that includes lightweight aggregate and steel fiber under monotonic and cyclic loading. In this study, the push-off shear test was performed in accordance with experimental parameters of different concrete mixtures, key type, confining stress, and application of epoxy between the segments. The tests were carried out to assess the shear strength, shear behavior, crack propagation and failure mode of joints. The test results represented shear capacity of joints decreased 15.2% by replacing normal coarse aggregates with lightweight aggregates but could be enhanced through the incorporation of hooked-end steel fibers. The shear capacities of joints fabricated using developed mixture tended to be underestimated compared to analytically calculated strengths. Furthermore, the normalized stiffness of the joint was decreased with an increased number of load cycles under high-amplitude low-cycle load. The shear resistance through aggregate interlock may gradually decrease with increasing number of cycles resulting in failure at 85% of the failure load of the monotonically tested specimen. An appropriate level of confining stress and application of epoxy shall be considered to prevent sudden failure of joints at high amplitude cyclical loading conditions.

Pure and mixed-mode (I/III) fracture toughness of preplaced aggregate fibrous concrete and slurry infiltrated fibre concrete and hybrid combination comprising nano carbon tubes

Concrete is the most widely used and inexpensive material in the construction sector. However, due to its weakness in tension, the cracking and brittle fracturing of concrete is considered a major deficiency. Advancements in fibrous concretes have recently been emerged to mitigate this issue. Preplaced Aggregate Fibrous Concrete (PAFC) and Slurry Infiltrated Fibrous Concrete (SIFCON) are unique cement composites made of fibres with surpassing mechanical properties and exceptional toughness values. The production of PAFC and SIFCON involves packing of aggregates and fibres in the mould and filling the gaps between the aggregates with the high flowability injected cement grout. Nevertheless, the mono and hybrid layered effect of PAFC and SIFCON on fracture toughness is still unexplored and needs special attention to bridge this research gap. This research examined the pure (I and III) and mixed (I/III) modes of fracture toughness of PAFC, SIFCON and hybrid two-layered PAFC-SIFCON samples. For this purpose, many notched specimens of circular disc shapes were prepared using single and double-layer concepts. To investigate the effect of fibres, three different fibre types were used; hooked-end steel fibre, macro polypropylene fibre and hybrid shape of crimped-hooked end steel fibre with dosages of 2.4% and 8% by volume to produce PAFC and SIFCON, respectively. Additionally, multi-walled nano-carbon tubes (MWCNT) were added to the composites with a dosage of 0.1% by cement weight. The compressive strength, stress intensity factors, effective stress intensity factors, mixity parameter, failure pattern, range of fracture toughness and scanning electron microscope were examined, discussed, and compared. Results indicated that pure mode III has a greater cracking risk than both mode I and mixed-mode I/III. The mixed-mode fracture toughness of PAFC specimens improved by 33.07 to 67.94%. Similarly, this improvement ranged from 59.77 to 210.70% for SIFCON and from 51.0 to 131.55% for PAFC-SIFCON. In addition, the fracture toughness of SIFCON is considerably higher than the PAFC and hybrid combination. In all three composite types, the hybrid shape steel fibre outperformed the hooked-end steel and polypropylene fibre under all three modes.

Experimental and numerical investigation on the resistance of steel fiber-reinforced heavyweight concrete slabs against rigid projectile impact

This study presents an inclusive experimental and numerical investigation of the resistance of steel fiber-reinforced heavyweight concrete under the impact of a high-velocity rigid projectile. Thus, concrete specimens were made using hooked-end steel fibers at 0%, 0.5%, 1%, 1.5%, 2%, and 2.5% volume fractions to assess the physicomechanical specifications of heavyweight concrete containing iron ore as fine and coarse aggregates. Also, the compressive and splitting tensile strengths, modulus of elasticity, stress–strain relationship, bulk density, and water absorption capacity of heavyweight concrete specimens were compared to those of the equivalent normal-weight concrete. The penetration tests were conducted on concrete slabs fabricated with normal weight and heavyweight concrete mixes to examine the specimens’ failure mode, penetration depth, and spalling volume. The results revealed that normal-weight concrete's compressive and splitting tensile strengths were more susceptible to adding steel fibers. It was also shown that increasing the density and fiber content significantly affected the impact resistance and residual velocity of fiber-reinforced concrete elements. Heavyweight concrete provided better life safety measures against the impact load than normal weight specimens, while the repair and reuse of heavyweight concrete components were feasible. Moreover, numerical modeling was performed using LS-DYNA finite element software, and the predictions were compared to the proposed experimental results and the analytical relations in the literature. There was good agreement between the results.