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Concrete is a constantly evolving building material whose demand is increasing due to population growth and urban development. This calls for more research on this composite material to improve its performance. However, concrete has some disadvantages, including that it is a brittle material and cannot withstand tensile stress. Therefore, rebars and fibers are incorporated into concrete to improve this property. Although previous works investigated the properties of concrete containing steel fibers, most of them were concerned with mechanical properties, while the durability properties still require further investigation to understand them. Thus, the purpose of this study is to ascertain how adding steel fibers to concrete in varying proportions (0.5, 1.0 and 1.5%) affects its mechanical and durability properties, including compressive strength, flexural strength, tensile strength, bulk density, water absorption, mode of failure, ultrasonic pulse velocity, dynamic modulus of elasticity and electrical resistance. Statistical relationships between the compressive strength and other characteristics were also established. The results indicated that all mechanical and durability characteristics significantly improved after adding steel fibers for all addition ratios, except for electrical resistivity, which showed lower values than the reference mixture for the 0.5 and 1% steel fiber proportions. Moreover, it was found that the best addition rate of steel fibers was 1.5%. At this percentage, the recorded increasing rates over the control sample were 29.3% in compressive strength, 83.7% in tensile strength, 27.9% in flexural strength, 50.1 in water absorption resistance, and 11.2% in electrical resistivity. [ABSTRACT FROM AUTHOR]

There is a growing trend toward employing sustainable materials to address the drawbacks of traditional construction materials. This experimental study explores the utilization of basalt and steel fibers, both independently and in combination, alongside fly ash and desert sand. The findings reveal that the introduction of further basalt fibers led to a reduction in concrete workability, density, and compressive strength. The optimal compressive strength for concrete made from desert sand was achieved in the mixed concrete incorporating 1% steel fibers, measuring at 50.6 MPa. Meanwhile, the highest flexural and tensile strengths were observed in a concrete mixture of 0.3% basalt fiber and 1% steel fiber, measuring 7.35 MPa and 4.6 MPa. Scanning Electron Microscopy, Energy Dispersive Spectroscopy, and X-ray Diffraction tests were conducted to examine the concrete microstructure. The results demonstrate that including a low content of hybrid steel and basalt fibers significantly improved the concrete microstructure. This study recommends conducting further studies to investigate the durability of concrete mixtures containing desert sand and basalt fibers and enhance sustainability in the construction industry. [ABSTRACT FROM AUTHOR]

This study investigates the behavior of the shear strength of fibrous concrete I-beams made from normal and lightweight concrete that have the same compression strength, of about 30 MPa. Lightweight aggregate concrete was made by replacing 75% of the coarse aggregate with lightweight aggregate (Bonza stone). Fourteen concrete I-beams with dimensions of 1000x210x175 mm were divided into two groups. In the first group, the web area was reinforced with steel fiber added in 0.5%, 1%, and 1.5% of the mix volume. The second group was reinforced with glass fiber added in the same percentage as the steel fiber. The results showed that the shear strength of a Normal Concrete Beam with Steel Fibers (NCSF) is increased by 3.5%, 13.5%, and 13.3% for the addition ratios of 0.5%, 1%, and 1.5%, respectively, compared to the Normal Concrete Beam without Fibers (NC). Webs with glass fibers gain an increase of about 3.7% and 14.05% for the addition ratios of 0.5% and 1%, respectively, while the shear strength decreased by 6.21% for the addition ratio of 1.5%. On the other hand, the Lightweight Concrete Beam with Steel Fibers (LWCBSF) achieved greater shear strength than the Lightweight Concrete Beams without Fibers (LWCB) by 4.8%, 13.5%, and 10.9%; for the three additional percentages, respectively. The shear strength increased by 8.4% and 11.04% for the Lightweight Concrete Beam with Glass Fibers (LWCBGF) at 0.5% and 1% ratios, while the shear strength decreased by 11.9% for the 1.5% glass fibers ratio compared to the Lightweight concrete Beam without Glass Fibers (LWCB). The best performance, according to the ultimate load, was achieved when fibers were added at a ratio of 1% in normal and lightweight concrete compared to other ratios. [ABSTRACT FROM AUTHOR]

Construction using eco-friendly materials reduces environmental impact and promotes sustainable practices. This research uses sawdust and steel fibers to design sustainable concrete. The main goal is to improve mechanical properties and reduce embodied carbon emissions. This study examines the mechanical properties of concrete with different sawdust and steel fiber combinations to fill a gap in the literature. In this research synergistic effect of saw dust and steel fiber on concrete characteristics have been studied. The research also examines these pairings' environmental benefits. This study used a response surface methodology (RSM) to design an experimental program and assess the effects of input variables (sawdust and steel fiber percentages) on output responses like compressive strength (CS), split tensile strength (STS), flexural strength (FS), modulus of elasticity (MOE), embodied carbon (EC), and eco-strength efficiency (ESE). Established testing methodologies and RSM provided an optimum prediction model based on specimen mechanical properties. Sawdust and steel fibers enhances concrete's mechanical properties. Varying proportions of both materials were added in mix; sawdust (0%-12%) and steel fiber (0%-2%). The experimental findings suggest that the optimized composition achieved the following mechanical properties: 13.85 MPa compressive strength, 1.4 MPa split tensile strength, 3.67 MPa flexural strength, 18.027 GPa modulus of elasticity, 211.272 kg CO2e/m3 embodied carbon, and 0.065487 eco-strength efficiency. This research showed that the aims of improving mechanical properties and reducing embodied carbon were achieved. As per multi-objective optimization, optimal percentages of saw dust and steel fibers in concrete are 11.81% and 0.063% respectively. The investigation yielded many suggestions. To test the optimal blend composition of ecologically friendly concrete in real-world building projects, start with realistic projects. Finally, life cycle evaluations and cost studies are needed to determine the environmental and economic impacts of eco-friendly concrete compared to standard options. [ABSTRACT FROM AUTHOR]

Concrete is a constantly evolving building material whose demand is increasing due to population growth and urban development. This calls for more research on this composite material to improve its performance. However, concrete has some disadvantages, including that it is a brittle material and cannot withstand tensile stress. Therefore, rebars and fibers are incorporated into concrete to improve this property. Although previous works investigated the properties of concrete containing steel fibers, most of them were concerned with mechanical properties, while the durability properties still require further investigation to understand them. Thus, the purpose of this study is to ascertain how adding steel fibers to concrete in varying proportions (0.5, 1 and 1.5%) affects its mechanical and durability properties, including compressive strength, flexural strength, tensile strength, bulk density, water absorption, mode of failure, ultrasonic pulse velocity, dynamic modulus of elasticity and electrical resistance. Statistical relationships between the compressive strength and other characteristics were also established. The results indicated that all mechanical and durability characteristics significantly improved after adding steel fibers for all addition ratios, except for electrical resistivity, which showed lower values than the reference mixture for the 0.5 and 1% steel fiber proportions. Moreover, it was found that the best addition rate of steel fibers was 1.5%. At this percentage, the recorded increasing rates over the control sample were 29.3% in compressive strength, 83.7% in tensile strength, 27.9% in flexural strength, 50.1 in water absorption resistance, and 11.2% in electrical resistivity.

This study focuses on the development and evaluation of a novel cement-free gamma-ray-resistant ultrahigh-performance concrete (UHPC), known as UHPC-CAS. UHPC-CAS is composed of calcium oxide–activated slag, iron and barite powders, and steel fibers, making it a type of ultrahigh-performance geopolymer concrete (UHPGC). In this study, the effects of replacing silica sand with varying percentages of iron and barite powders on the mechanical and radiation properties of UHPC-CAS were investigated. The optimal replacement ratio of iron powder was found to be 50%, resulting in the highest compressive, tensile, and bending strengths among all mixtures without fibers. Furthermore, the UHPC-CAS samples reinforced with steel fibers and containing barite powder exhibited a more pronounced softening zone than those containing iron powder. With 100% iron powder and 3% steel fibers, UHPC-CAS achieved superior resistance to gamma rays, as evidenced by the highest attenuation coefficient of 0.234 cm and the lowest half-value layer of 2.96 cm. This research demonstrates the potential for developing sustainable cement-free UHPC for use in nuclear facilities and other applications requiring high radiation shielding. [ABSTRACT FROM AUTHOR]

This study investigated the behavior of reinforced concrete columns using high-performance concrete (HPC) filled in prefabricated steel tubes to serve as reinforcement. The experimental setup involved HPC with a compressive strength of 1,515 kg/cm², filled into steel tubes with diameters of ¾, 1, and 1¼ inches, replacing the reinforcement in concrete columns sized 150x150x600 mm. The concrete used for casting the sample columns had a compressive strength of 257 kg/cm². The columns were tested for axial and eccentric loading at displacements of 20, 40, and 60 mm to determine the maximum compressive strength, bending moment, interaction diagrams, and failure patterns of the steel-reinforced concrete columns. The experimental results showed that the axial compressive strength of columns using HPC in steel tubes as reinforcement was higher than that of the control concrete columns. The compressive strength at various eccentricities showed a slight increase compared to the control columns. The comparison between experimental compressive strengths and bending moments with calculated values indicated a consistent trend. Furthermore, the failure patterns of the concrete columns revealed both compression and tension failures.

Deep beams are crucial for construction projects due to their load-carrying capacity, shear resistance, and architectural adaptability. Ultra-high strength concrete and ultra-high-performance concrete (UHPC) are used in their production. Basalt fiber is used as an alternative due to its corrosion resistance, tensile strength, and thermal stability. This study investigates the behavior of UHPC deep beams reinforced with basalt fibers. Three sets of 11 specimens were constructed without transverse reinforcement and reinforced with either fibers or steel fibers. The study also analyzes the impact of parameters like shear strength capacity, crack development, and load-deflection behavior on UHPC deep beams. The study discovered that the inclusion of basalt fibers in UHPC deep beam can effectively postpone the onset of diagonal cracks. Incorporating basalt fiber at concentrations of 0.5, 0.75, and 1.0% led to respective increases of 48.17, 70.07, and 86.66% in the diagonal fracture force, as compared to the inclusion of steel fibers which resulted in increases of 18.24, 56.93, and 98.54% in diagonal fracture loads. The ideal ratio for enhancing the maximum shear capacity was found to be 0.75% of basalt. This specific percent resulted in the highest measured force out of the three percentages that were examined. The addition of basalt fibers at concentrations of 0.5, 0.75, and 1.0% resulted in respective improvements of 11.62, 30.08, and 28.69% in the ultimate shear capacities. During that period, steel fibers significantly enhanced the ultimate shear capacity, resulting in an increase of 19.83, 34.49, and 55.24% compared to specimens without fiber reinforcement. Regarding the second parameter of this investigation, a drop in the shear span ratio is linked to an augmentation in shear capacity and a reduction in mid-span deflection to varying extents for both the utilization of basalt and steel fibers.

Abstract This study investigates the influence of LDHs (Layered Double Hydroxides) microparticles and steel fibers on the mechanical properties of lightweight concrete. Through a combination of experimental analysis and finite element modeling, the effects of LDHs and steel fibers on flexural strength and crack resistance were evaluated. The experimental results demonstrate a significant increase in flexural strength and toughness with the incorporation of LDHs microparticles and steel fibers. The finite element model corroborates these findings, highlighting the synergistic enhancement of mechanical properties due to LDHs and steel fibers. Additionally, the study discusses the frontier applications of LDHs in improving fracture characteristics and highlights the potential of hybrid reinforcement strategies in lightweight concrete. The findings reveal that both the quantity of microparticles and steel fibers significantly impact the concrete's residual strength. In scenarios without steel fibers, an optimal weight fraction of approximately 1 wt.% LDHs demonstrate a 39% increase in bearing capacity. Notably, under comparable conditions, the influence of LDHs microparticles on enhancing concrete mechanical characteristics appears to surpass the effects induced by steel fibers. However, at 2 wt.% LDHs usage, a decrease in load capacity by 3.3% is observed compared to the 1 wt.% LDHs configuration. This research provides valuable insights into optimizing concrete properties through novel material combinations and paves the way for future advancements in structural engineering.

Steel fiber reinforced high-strength concrete (SFRHSC) is a composite material composed of cement, coarse aggregate, and randomly distributed short steel fibers. The excellent tensile strength of steel fiber can significantly improve the crack resistance and ductility of high-strength concrete (HSC). In this study, experimental and numerical investigations were performed to study the cyclic behavior of the HSC beam-column joint. Three SFRHSC and one HSC beam-column joint were prepared and tested under cyclic load. Two different volume ratios of steel fibers and three stirrups ratios in the joint core area were experimentally studied. After verification of the experimental results, numerical simulations were further carried out to investigate the influence of steel fibers volume ratio and stirrups ratio in the joint core area on the seismic performance. Evaluation of the hysteretic response, ductility, energy dissipation, stiffness, and strength degradation were the main aims of this study. Results indicate that the optimal volume fraction of steel fibers is 1.5%, and the optimal stirrups ratio in the joint core area is 0.9% in terms of the enhancement of the seismic performance of the SFRHSC beam-column joint. [ABSTRACT FROM AUTHOR]

The presence of toxic elements in manganese slag (MSG) poses a threat to the environment due to potential pollution. Utilizing CO curing on MS offers a promising approach to immobilize toxic substances within this material, thereby mitigating their release into the natural surroundings. This study investigates the impact of CO cured MS on various rheological parameters, including slump flow, plastic viscosity (η), and yield shear stress (τ). Additionally, it assesses flexural and compressive strengths (f and f), drying shrinkage rates (DSR), durability indicators (chloride ion migration coefficient (CMC), carbonization depth (CD)), and the leaching behavior of heavy metal elements. Microscopic examination via scanning electron microscopy (SEM) is employed to elucidate the underlying mechanisms. The results indicate that CO curing significantly enhances the slump flow of ultra-high performance concrete (UHPC) by up to 51.2%. Moreover, it reduces UHPC's η and τ by rates ranging from 0% to 52.7% and 0% to 40.2%, respectively. The DSR exhibits a linear increase corresponding to the mass ratio of CO cured MS. Furthermore, CO curing enhances both f and f of UHPC by up to 28.7% and 17.6%, respectively. The electrical resistance is also improved, showing an increase of up to 53.7%. The relationship between mechanical strengths and electrical resistance follows a cubic relationship. The CO cured MS demonstrates a notable decrease in the CMC and CD by rates ranging from 0% to 52.6% and 0% to 26.1%, respectively. The reductions of leached chromium (Cr) and manganese (Mn) are up to 576.3% and 1312.7%, respectively. Overall, CO curing also enhances the compactness of UHPC, thereby demonstrating its potential to improve both mechanical and durability properties. [ABSTRACT FROM AUTHOR]

The utilization of recycled materials in concrete technology has gained significant attention in recent years, promoting sustainability and resource conservation. This paper investigates the behavior of lightweight self-compacting concrete (LWSCC) with recycled tire steel fibers (RTSFs). The effects of RTSFs on the flowability of the composite material and its density were assessed. The mechanical properties of the developed material were examined and beam tests were performed, aiming to assess its feasibility for structural applications. The compressive and tensile strengths were determined to evaluate the mechanical properties of the developed concrete mixtures. The beam tests were conducted to assess the flexural behavior of the beam specimens. Three different steel fiber contents of 0, 0.5, and 1% volumetric fractions of concrete were used in this study. The test results indicate that incorporating the fibers did not negatively impact the flowability and density of the LWSCC mixtures. In addition, the use of RTSFs enhanced the tensile strength of the developed concrete mixtures, where fibrous concrete showed increases in the splitting tensile strength in the range of 38 to 76% over that of non-fibrous concrete. On the other hand, the compressive strength of the mixtures was not affected. The test beams with RTSFs exhibited improved flexural performance in terms of delaying and controlling cracking, enhancing ultimate load, and increasing ductility. Compared with the control non-fibrous beam, the increases in the cracking load, ultimate load, and ductility index were up to 63.8, 9.3, and 16%, respectively. The test results of the beams were compared with theoretical predictions, and good agreement was found. [ABSTRACT FROM AUTHOR]

This study investigates the influence of steel fiber content (0%, 0.3%, 0.6%, 0.9%) on the axial compressive performance of ceramsite concrete. Four types of ceramsite concrete specimens were prepared and the cube compressive strength of each type of ceramsite concrete was tested. Four sets of uniaxial compression tests on prismatic specimens of ceramsite concrete were conducted. The failure process and characteristics of the specimens were analyzed, and the uniaxial compressive performance of each group of specimens was systematically studied. Additionally, the stress-strain curves equations were proposed. The research indicates that, after the addition of steel fibers, the strength and ductility of ceramsite concrete are significantly enhanced. The compressive strength of cubic specimens can increase by up to 42.6%, axial compressive strength can increase by up to 25.6%, and residual stress can increase by more than 300%. Ceramsite concrete with a steel fiber volume fraction of 0.9% demonstrates clear advantages. Its energy dissipation coefficient has increased by 17%, ductility coefficient has improved by 33%, toughness coefficient has enhanced by 68%, and stiffness degradation has noticeably become more gradual. The stress-strain curve model proposed in this study aligns well with the experimental results, accurately describing the stress-deformation characteristics of steel fiber ceramsite concrete under uniaxial compression. It demonstrates good applicability. The research findings of this study can provide a theoretical foundation for the structural analysis and design of such concrete, which is of significant importance for the utilization of ceramsite concrete as both a structural material and as a component in prefabricated lightweight wall panels. [ABSTRACT FROM AUTHOR]

Geogrids, first developed in the late 20th century, revolutionized soil reinforcement using polymer materials in grid-like structures to enhance soil stability, reduce erosion, and strengthen infrastructure, marking a pivotal advancement in geotechnical engineering. However, geogrids typically find limited application in structural engineering, especially reinforced concrete (RC) columns. The present research explores the feasibility of geogrids in concrete columns, thus optimizing construction practices by exploring innovative reinforcement methods beyond conventional steel, aiming to bolster durability and performance in diverse structural scenarios. The traditional method of using steel stirrups to confine circular columns was substituted with a new approach; i.e., geogrids were introduced partially as confining material alongside steel stirrups. Furthermore, the research examines the performance of concrete columns confined partially with geogrid, both with and without the inclusion of steel fibers, in comparison to traditional columns reinforced with steel. Columns, 16 in number, with different steel stirrup spacing, concrete types, and geogrid configurations, were cast and put under axial load. Load-deflection curves were obtained, and parameters including ultimate load, maximum axial displacement, ductility, secant stiffness, and energy dissipation were assessed and compared. The findings indicated that incorporating geogrids with greater tensile strength alongside steel fibers could uphold a peak load value 10.16% higher than the control column, improved stiffness, and enhanced energy dissipation, indicating a promising approach for reinforcing columns in conjunction with steel fibers. [ABSTRACT FROM AUTHOR]

With the addition of electrically conductive steel or carbon fibers, Ultra-High-Performance Concrete (UHPC) possesses an intrinsic self-sensing capability. This opens up the possibility of combining the resilience and sustainability of UHPC with the development of self-sensing solutions for structural applications. In this study, the self-sensing behaviour of a proprietary nano-engineered UHPC material subjected to tension was investigated. To assess the self-sensing performance of the material, bulk resistivity measurements were used on direct tension and pure flexure tests, while a novel wireless approach that operates on was used on out-of-plane bending tests. The wireless approach used alternate current (AC) measurements while the bulk resistivity methods were performed through direct current (DC) and the four-probe method. In both methods, the fractional change in resistance was correlated to the state of deformation. The disposition of the actual strain field was evaluated using Digital Image Correlation (DIC). It was found that in the case of direct tension and pure flexure, the fractional change of resistance was initially decreased up to the onset of strain localization, while it gradually increased in the post-peak range, where the separation of the localized crack gradually increased. In the case of the wireless approach using AC, the onset of cracking was successfully predicted with an abrupt increase in resistivity. The wireless strain-sensing approach also captured the Poisson's effect due to the loading. [ABSTRACT FROM AUTHOR]

In this study, the properties of steel strand-reinforced reactive powder concrete (RPC) with mixed steel fibers and basalt fibers were investigated. The volume ratios of steel fibers and basalt fibers ranged from 0% to 2%. The reinforcement ratio of steel strands was 1%. The flexural strength and toughness were measured. Moreover, the impact toughness was determined. The studies were carried out under an erosion environment with chlorides and sulfates. The electrical resistance and the ultrasonic velocity were obtained to assess the salt corrosion resistance performance of steel strand-reinforced RPC. The results show that the addition of basalt fibers and steel fibers can improve the mechanical strength, ultrasonic velocity, flexural toughness, and impact toughness and decrease the performance degradation of the steel strand-reinforced RPC under the conditions of dry–wet alternations of NaCl and Na2SO4 solutions. Basalt fibers and steel fibers can improve the steel strand-reinforced RPC's flexural strength by rates of up to 13.1% and 28.7%, respectively. Moreover, the corresponding compressive strength increases by 10.3% and 18.3%. The flexural strength decreases by 11.2%~33.6% and 7.3%~22.7% after exposure to the NaCl and Na2SO4 dry–wet alternations. Meanwhile, the corresponding compressive strength decreases by 22.1%~38.9% and 14.6%~41.3%. The electrical resistance increases with the addition of basalt fibers and decreases with the increasing dosages of steel fibers. The steel strand-reinforced RPC with the assembly units of 1% steel fibers and 1% basalt fibers shows the optimal mechanical properties and salt resistance considering its wet–dry alternation performance. The properties of steel strand-reinforced RPC decrease more rapidly after undergoing NaCl erosion than Na2SO4 erosion. [ABSTRACT FROM AUTHOR]

This study investigates the influence of LDHs (Layered Double Hydroxides) microparticles and steel fibers on the mechanical properties of lightweight concrete. Through a combination of experimental analysis and finite element modeling, the effects of LDHs and steel fibers on flexural strength and crack resistance were evaluated. The experimental results demonstrate a significant increase in flexural strength and toughness with the incorporation of LDHs microparticles and steel fibers. The finite element model corroborates these findings, highlighting the synergistic enhancement of mechanical properties due to LDHs and steel fibers. Additionally, the study discusses the frontier applications of LDHs in improving fracture characteristics and highlights the potential of hybrid reinforcement strategies in lightweight concrete. The findings reveal that both the quantity of microparticles and steel fibers significantly impact the concrete's residual strength. In scenarios without steel fibers, an optimal weight fraction of approximately 1 wt.% LDHs demonstrate a 39% increase in bearing capacity. Notably, under comparable conditions, the influence of LDHs microparticles on enhancing concrete mechanical characteristics appears to surpass the effects induced by steel fibers. However, at 2 wt.% LDHs usage, a decrease in load capacity by 3.3% is observed compared to the 1 wt.% LDHs configuration. This research provides valuable insights into optimizing concrete properties through novel material combinations and paves the way for future advancements in structural engineering. [ABSTRACT FROM AUTHOR]

AbstractThis study explores the use of cutting-edge materials to improve the strength and longevity of concrete constructions, with a particular emphasis on the design and functionality of light gauge steel hollow sections (LGSHS) that are filled with concrete reinforced with steel fibers (SFRC) under flexural stress scenarios. Because of its remarkable fire resistance, SFRC enhances the capabilities of Ordinary Portland cement (OPC). Examining member shape, fire being exposed, both concrete and steel buildings, and structural response, the study examines the mechanical qualities and reaction of LGSHS filled with SFRC. A curved trend in force against the midpoint of the displacement and a continuous 12% rise in maximum load capacity is revealed by a comparative comparison between practical and numerical results, demonstrating the synergy of composite components. Infilling LGSHS with SFRC enhances load-bearing capacity, ductility, and toughness. Characterization techniques such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and Fourier Transform Infrared Spectroscopy (FTIR) are utilized at temperatures up to 1050 °C. The objective of the investigation is to determine the load-carrying capacity, strain, deformation capacity, ductility, and failure characteristics of specimens at both ambient and elevated temperatures. Experimental and analytical findings are juxtaposed with theoretical values proposed by various code provisions. [ABSTRACT FROM AUTHOR]

The use of alkali‐activated concrete (AAC) as an alternative construction material to Portland cement‐based concrete (PCC) has been widely encouraged by its enhanced mechanical and durability performance and environmental benefits. However, AAC exhibits low flexural and tensile strength, limiting its application in areas where high post‐cracking flexural and tensile load‐bearing capacity are needed. Steel fibers can be added to improve the composite ductility and toughness. Steel fiber‐reinforced alkali‐activated concrete (SFRAAC) is a new emerging technology with research studies evaluating the effect of fiber addition on its mechanical properties still in the early stages. To promote the application of SFRAAC, analytical models predicting their mechanical performance are needed. This study evaluates the applicability to SFRAAC of previously published analytical models developed for steel fiber‐reinforced cement‐based concrete (SFRPCC). Experimental data available in the literature have been collected to create an extensive database to validate and then calibrate these currently available correlations between mechanical properties for SFRAAC. The prediction models considered in this study correlate the mechanical performance of SFRAAC, that is, compressive strength, modulus of elasticity, splitting tensile strength, flexural and residual flexural strength, to the compressive strength of the reference concrete without fibers, the fiber volume fraction and the fiber reinforcing index. Thus, by knowing the performance of the AAC matrix and the fiber properties and dosage, it is possible to predict the overall mechanical behavior of the steel fiber‐reinforced composite. [ABSTRACT FROM AUTHOR]

This research aims to develop sustainable high-strength concrete (SHSC) by replacing 100% fine and/or coarse aggregates with fine recycled aggregate (RA) and/or coarse RA. Due to the high surface water absorption of coarse RA, a surface treatment method was adopted, consisting of immersing it in a cement and silica fume slurry. Moreover, to improve the performance of the produced SHSC, steel fibers were employed at a relatively low volume fraction (0.5%). Eleven blends were cast and tested in this experimental study. A control SHSC mix (without RA) and ten other mixtures, including fine natural and RA, treated and untreated coarse RA, with and without steel fibers, were prepared. Compressive, splitting, and flexural strengths, water absorption, density, and ultrasonic pulse velocity (UPV) of the resulting SHSC were conducted. The results indicated that the use of RA in SHSC resulted in an average drop of 25% in its mechanical properties and an increase of about 30% in water absorption. However, using treated RA compensated the compressive and tensile strength reductions in SHSC by 9% and 7%, respectively, compared to mixes containing untreated RA. On the other hand, adding fibers helped improve compressive, flexural, and splitting tensile strengths by about 8%, 23%, and 31%, respectively, compared to the corresponding control mix. Consequently, the results showed that it is possible to produce durable SHSC made from 100% RA and 0.5% steel fibers with a reduced density and improved mechanical performance to a comparable level or even superior to high-strength concrete (HSC) with only natural aggregates (NAs). [ABSTRACT FROM AUTHOR]

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Construction using eco-friendly materials reduces environmental impact and promotes sustainable practices. This research uses sawdust and steel fibers to design sustainable concrete. The main goal is to improve mechanical properties and reduce embodied carbon emissions. This study examines the mechanical properties of concrete with different sawdust and steel fiber combinations to fill a gap in the literature. In this research synergistic effect of saw dust and steel fiber on concrete characteristics have been studied. The research also examines these pairings’ environmental benefits. This study used a response surface methodology (RSM) to design an experimental program and assess the effects of input variables (sawdust and steel fiber percentages) on output responses like compressive strength (CS), split tensile strength (STS), flexural strength (FS), modulus of elasticity (MOE), embodied carbon (EC), and eco-strength efficiency (ESE). Established testing methodologies and RSM provided an optimum prediction model based on specimen mechanical properties. Sawdust and steel fibers enhances concrete’s mechanical properties. Varying proportions of both materials were added in mix; sawdust (0%–12%) and steel fiber (0%–2%). The experimental findings suggest that the optimized composition achieved the following mechanical properties: 13.85 MPa compressive strength, 1.4 MPa split tensile strength, 3.67 MPa flexural strength, 18.027 GPa modulus of elasticity, 211.272 kg CO2e/m3 embodied carbon, and 0.065487 eco-strength efficiency. This research showed that the aims of improving mechanical properties and reducing embodied carbon were achieved. As per multi-objective optimization, optimal percentages of saw dust and steel fibers in concrete are 11.81% and 0.063% respectively. The investigation yielded many suggestions. To test the optimal blend composition of ecologically friendly concrete in real-world building projects, start with realistic projects. Finally, life cycle evaluations and cost studies are needed to determine the environmental and economic impacts of eco-friendly concrete compared to standard options.

Abstract 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.

Due to its inherent properties, concrete exhibits brittle failure once it attains its peak compressive and tensile strengths. As concrete is weak in tension, it is usually reinforced with steel bars to resist tensile stresses produced by the applied loading in its superstructure and infrastructure. However, over the last few decades, steel fibers have also been used in preparing concrete for the construction of structural components. Based on some published studies, it has been observed that the use of steel fibers significantly decreases the brittleness associated with concrete and causes an increase in peak compressive and tensile strengths. Furthermore, it was also observed that its behavior significantly differs under increasing compressive loading rates when compared under static loads. However, these studies have been unable to identify the causes of this change in behavior under increasing loading rates; therefore, in this study, a detailed numerical investigation has been carried out using non-linear finite-element analysis software, ABAQUS. It was found that the behavior exhibited by steel fiber reinforced concrete specimens under high rates of compressive loading represents a structural response rather than material behavior.

This paper investigates the effects of silica fume (SF) and metakaolin (MK) as cement substitutes on the mechanical properties, shrinkage, and toughness performances of steel fiber reinforced concrete (SFRC). Initially, a reference concrete mix with a water-to-binder ratio of 0.4 is blended with different volume fractions of steel fibers with varying geometries (crimped steel and straight steel), both individually and in combination, to examine their mechanical properties. Also, the possible influence of pozzolans on the variation of drying shrinkage and flexural toughness of hybrid steel fiber reinforced concrete (Hy-SFRC) was evaluated. An increase in workability was observed as a result of hybridization of steel fibers. Pozzolanic steel fiber reinforced concrete (SFRC) exhibited a more significant enhancement in compressive strength and flexural strength compared to non-pozzolanic SFRC. The hybrid combination of CS 1.5 % and SS 0.5 % was found to be the best in terms of mechanical properties. The addition of SF and MK reduced the shrinkage strain by up to 50 % compared to the reference mix. The flexural toughness values for both binary and ternary pozzolanic Hy-SFRC were notably higher than those for non-pozzolanic Hy-SFRC, indicating a stronger bond between the fibers and the matrix. Hy-SFRC containing a ternary pozzolanic mix of SF 10 % and MK 10 % gave the best results in flexural toughness. The results were consistent with morphology analysis, which revealed an increase in hydration products at the interface between the aggregate and concrete matrix, as well as between the steel fiber and concrete matrix, due to the ternary blending of SF and MK.

The use of fossil fuel and wood for cooking poses health, environmental, and economic challenges, especially with the growing population. This has led to an increase in the trend towards the use of clean and sustainable cooking sources, including solar cookers. This experimental study aims to contribute by enhancing the performance of a solar box cooker (SBC) according to the concept of porous media via adding steel fibers inside the box as a modified SBC and comparing it with a conventional SBC. The stagnation test to determine the first figure of merit and the load test to determine the second figure of merit, standard boiling time, and cooker optothermal ratio were conducted under the outdoor conditions of Baghdad city. Also, an energy and exergy efficiency analysis, and calculating the rate of heat loss by three water loads heating and cooling tests. The results revealed that the modified SBC has a higher thermal performance than the conventional SBC. [ABSTRACT FROM AUTHOR]

In light of the effort for decarbonization of the energy sector, it is believed that common geopolymer binding materials such as fly ash may eventually become scarce and new geological aluminosilicate materials should be explored as alternative binders in geopolymer concrete. A novel, tension-hardening geopolymer concrete (THGC) that incorporates high amounts of semi-reactive quarry wastes (metagabbro) as a precursor, and coarse quarry sand (granite) was developed in this study using geopolymer formulations. The material was optimized based on the particle packing theory and was characterized in terms of mechanical, physical, and durability properties (that is, compressive, tensile, and flexural resistance; Young's modulus; Poisson's ratio; absorption; drying shrinkage; abrasion; coefficient of thermal expansion; and chloride-ion penetration, sulfate, and salt-scaling resistance). The developed THGC, with an air-dry density of 1940 kg/m³ (121 lb/ft³), incorporates short steel fibers at a volume ratio of 2%, and is highly ductile in both uniaxial tension and compression (uniaxial tensile strain capacity of 0.6% at an 80% post-peak residual tensile strength). Using digital image correlation (DIC), multiple crack formation was observed in the strain-hardening phase of the tension response. In compression, the material maintained its integrity beyond the peak load, having attained 1.8% compressive strain at 80% post-peak residual strength, whereas upon further reduction to 50% residual strength, the sustained axial and lateral strains were 2.5% and 3.5%, respectively. The material exhibited low permeability to chloride ions and significant abrasion resistance due to the high contents of metagabbro powder and granite sand. The enhanced properties of the material, combined with the complete elimination of ordinary portland cement from the mixture, hold promise for the development of sustainable and resilient structural materials with low CO2 emissions, while also enabling the innovative disposal of wastes as active binding components. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

High-strength concrete is extensively used in the construction industry due to its higher stiffness and modulus, but it is inherently brittle. In order to reduce its brittle behavior, steel fibers are being used to increase their application in the construction industry. In this experimental study, a fixed volume fraction (Vf = 1.5%) of steel fiber was used in the concrete, whereas the type of confinement (steel tube and carbon fiber-reinforced polymer CFRP strip) was varied. Five high-strength concrete beams with and without steel fibers strengthened with different confinements (steel sheet and CFRP) were cast and evaluated for flexural performance. (Four-point loading tests were done here.) Conventional steel was used for reinforcing concrete as it has the same lateral and longitudinal strengths. The high initial cost of steel tubes is compensated by eliminating the cost of formwork required for casting regular concrete members. For conventional reinforcement, a balanced steel ratio was used. All specimens were tested under monotonic loading. The tested structural elements showed good plasticity and increased flexural capacity. The improved ductility and energy absorption capacity of the members indicate their promising use in building structures. [ABSTRACT FROM AUTHOR]

The rehabilitation of concrete structures has been a subject of extensive investigation, exploring various facets. One such avenue involves the incorporation of fiber additives into concrete materials. In parallel, the construction of reinforced concrete structures inevitably encounters construction errors, necessitating constant efforts from researchers to devise solutions for mitigating their impact. In the context of this research, a series of experiments was conducted involving the construction and testing of five reinforced concrete moment-resisting frames. The initial sample served as the control, while two additional samples were integrated with polypropylene and metal fibers. The subsequent two samples deliberately introduced a manufacturing error through the application of air-entraining admixture materials at the beam-to-column connection. This deliberate error aimed to assess the influence of additive fibers on frames affected by manufacturing errors. Several critical parameters were subjected to evaluation, including ultimate strength, stiffness, ductility, energy dissipation capacity, and strength reduction factor. The results of these assessments demonstrated that the utilization of additive fibers contributes to an enhanced overall performance of the frames, as inferred from the aforementioned seismic parameters. Furthermore, it was established that the incorporation of these additive fibers substantially alleviates the impact of manufacturing errors on moment-resisting reinforced concrete frames. Although a significant reduction in energy dissipation capacity was observed in samples with manufacturing errors, the other seismic parameters remained relatively unaffected. Subsequently, numerical models were generated in ABAQUS software to validate the experimental findings, and their outcomes were compared with the results derived from the physical experiments. [ABSTRACT FROM AUTHOR]

Several efficient applications of ultrahigh‐performance fiber‐reinforced concrete (UHPFRC). Among them are UHPFRC jackets utilized for strengthening or permanent formworks of the steel reinforcing normal strength concrete (NSC) columns since UHPFRC jackets could enhance the compressive strength and other properties of the NSC column. However, the efficiency of a UHPFRC jacket simultaneously depends on its thickness and the added steel fiber volume fraction. The paper aims to explore the interaction effect of UHPFRC jacket thickness and steel fiber volume fraction on the behavior of UHPFRC jackets confining the NSC core under compressive load. The circular ultrahigh performance concrete jacket filled inside with the normal strength concrete, named NSC‐UHPFRC column specimen, is tested under loading on the NSC core. UHPFRC jacket thickness of 18‐49 mm with three adding steel fiber volume fractions was conducted for the experimental study. The investigation and analysis of the effect of the UHPFRC jacket and the steel fiber volume fraction on compression behaviors of NSC‐UHPFRC columns proceeded after the compressive strength test results were validated using Richart's model. This comprised a review of various parameters such as specimen failure pattern, stress–strain relationship, and ductile indices. The Weibull distribution was employed to explain the interaction effect on the variation in the experimental results. Finally, an interaction model was proposed and used to discuss the interaction effect of UHPFRC jacket thickness and steel fiber volume fraction and the optimum condition of the compressive strength of the NSC‐UHPFRC columns. [ABSTRACT FROM AUTHOR]

In today's world, concrete structures are exposed to various influences, including explosive actions. With the increasing use of fiber-reinforced concrete (FRC), it is essential to investigate its response to blast effects. As there are few studies on this topic worldwide, this research is dedicated to the question of how blast effects affect the damage and properties of six different types of reinforced concrete (RC) slabs. These samples differ in concrete classes (C30/37 and C50/60) and in the type of fibers added (steel and polypropylene). Visual inspections and non-destructive measurements are carried out before and after blasting. The damaged area of the concrete surface is determined by visual inspection, while non-destructive measurements evaluate parameters such as the rebound value of the Schmidt hammer, the electrical resistivity of the concrete, the velocity of the ultrasonic wave, and the dynamic modulus of elasticity. Equal amounts of explosives are applied to five of the RC slabs to enable a comparative analysis of the resulting damage. Based on the comparison of the measured data from these five RC slabs, conclusions are drawn regarding the effects of the explosive impacts on conventionally reinforced concrete slabs compared to those with added fibers. In addition, one of the RC slabs with steel fibers is exposed to approximately three times the amount of explosives to assess the extent of increased damage and to evaluate the suitability of military standards in the calculation of explosive charges for blasting RC elements with fibers. [ABSTRACT FROM AUTHOR]

Due to its inherent properties, concrete exhibits brittle failure once it attains its peak compressive and tensile strengths. As concrete is weak in tension, it is usually reinforced with steel bars to resist tensile stresses produced by the applied loading in its superstructure and infrastructure. However, over the last few decades, steel fibers have also been used in preparing concrete for the construction of structural components. Based on some published studies, it has been observed that the use of steel fibers significantly decreases the brittleness associated with concrete and causes an increase in peak compressive and tensile strengths. Furthermore, it was also observed that its behavior significantly differs under increasing compressive loading rates when compared under static loads. However, these studies have been unable to identify the causes of this change in behavior under increasing loading rates; therefore, in this study, a detailed numerical investigation has been carried out using non-linear finite-element analysis software, ABAQUS. It was found that the behavior exhibited by steel fiber reinforced concrete specimens under high rates of compressive loading represents a structural response rather than material behavior. [ABSTRACT FROM AUTHOR]

In recent years, the alarming number of terrorist attacks has highlighted the critical need for extensive research aimed at fortifying structures against explosion-induced loads. However, the insufficient energy absorption and brittleness of conventional concrete make it ineffective in withstanding blast loading, encouraging researchers to explore innovative strategies for augmenting the energy dissipation capabilities of construction materials. This study specifically delves into the incorporation of recycled rubber, a sustainable and environmentally friendly solution to the pressing issue of scrap tire disposal. The primary focus of this research revolves around the integration of rubber recycling and steel fibers into concrete, with the ultimate goal of enhancing the dynamic response of reinforced concrete (RC) beams. This novel approach not only contributes to the structural resilience required for resisting blast impacts, but also aligns with eco-friendly practices by reusing recycled rubber. A meticulous numerical investigation was undertaken to comprehensively assess the static and blast response of these augmented beams. The numerical study involved developing finite element (FE) models using ABAQUS version 6.14 for static implicit analysis and LS-DYNA R11 for blast explicit simulations. The ABAQUS model was validated against previous experimental testing for load–displacement and failure patterns. Similarly, the LS-DYNA model was validated for blast pressure in accordance with UFC-3-340 standards and for material response under blast loading, utilizing existing experimental data. The numerical models were designed to accommodate varying weight percentages of rubber, ranging from 5% to 20%, and a consistent 1.0% incorporation of steel fibers. This comprehensive analysis aims to provide valuable insights into the efficacy of these materials in improving the structural integrity and blast resistance of RC beams, thereby contributing to the development of more secure and sustainable construction practices. By reducing the reinforcement ratio in order to meet the minimum code requirements, it became evident that the failures of the rubberized RC beams tended to exhibit ductility on the tension side under static loading. In addition, the increase in the reinforcement ratio correlated with a higher failure load and decreased deflection. Furthermore, the findings indicated an optimal concrete mixture characterized by improved ductility, energy absorption, and blast load capacity, achieved by combining 5–10% rubber with steel fibers. [ABSTRACT FROM AUTHOR]

Experimental research was carried out on the flexural behavior of full-scale external beam–column concrete joints cast with plain and steel fibrous reinforced concrete (SFRC) with hooked steel fibers, subjected to cyclic reversal loading. Four beam–column sub-assemblages were cast. Two of them, denoted as control specimens, were made of plain concrete (RC) and were reinforced with longitudinal bars and transverse stirrups, and two were made of hooked steel fiber-reinforced concrete (SFRC) with same longitudinal steel reinforcements of control specimens but with higher spacing of stirrups in the beam. The experimental results show that it is possible to avoid brittle failure of external beam to column joint assigning, as it is well-known, high percentage of transverse steel in joint region or utilizing less stirrups in all critical regions and replacing plain concrete with SFRC. In this case, it is possible also a more efficient control in the opening of the cracks. From the analytical point of view, experimental results were reproduced numerically by using a non-linear finite-element program (ABAQUS). With ABAQUS constitutive laws in compression and in tension able to include post-cracking resistance of material were adopted. In addition, utilizing a simplified closed-form softened strut-and-tie macro-model, it was possible reproduce the load-deflection curves of beam to column sub-assemblages. Analytical results were in a good agreement with monotonic response observed experimentally. Finally, design guides for ductile behavior of SFRC beam to column joints are given. [ABSTRACT FROM AUTHOR]

With the continuous upgrading of infrastructure construction and the gradual development of theoretical research about engineering construction, higher performance requirements have been put forward for concrete materials. Therefore, to meet the engineering quality requirements of various concrete structures, the research direction of engineering materials has shifted towards developing new concrete with high strength, high ductility, high toughness, and other multifunctional properties. Mixing two or more types of fibers with conductive properties with the cement matrix material allows various fibers to leverage their strengths and weaknesses, thereby utilizing their respective characteristics. This results in the formation of a complex-phase conductive fiber cementitious material (CFCM), which enhances the safety, durability, and toughness of the structure. It enables the engineering structure to exhibit intelligence and resourcefulness, thereby improving its service life and reducing the full life cycle cost of the cementitious material structure. Additionally, this approach relatively eases the demand for concrete materials and reduces material consumption. This method represents one of the research directions for new concrete. Complex-phase CFCMs are essentially smart materials capable of sensing not only compressive or tensile stresses but also temperature. The emergence of CFCM represents a significant step forward in enhancing the mechanics, functionality, and sustainability of modern infrastructure. In this experiment, an orthogonal test involving 16 working conditions with three factors and four levels was designed, with steel fiber (SF) type, SF content, and carbon fiber (CF) content as the factors. The study focused on the physical and mechanical properties of composite conductive fiber cement-based materials containing both SF and CF. Performance indicators such as flexural strength, volume resistivity, and energized temperature rise of the composite conductive fiber cement-based materials were tested. The analysis of orthogonal tests produced the following results regarding the degree of influence of each factor on the mechanical and physical properties: the order of influence on flexural strength was SF doping > SF type > CF doping. Further analysis revealed that the best combination was A4B4C4. The relationship between the effect of each factor on resistivity is as follows: carbon fiber doping > SF doping > SF type. Comparing the weights between the levels, it can be observed that the optimal combination of conductivity schemes is also A3B4C4. SF and CFs, respectively, enhanced the mechanical and physical properties of complex-phase conductive fiber cementitious materials. The results of the temperature rise test on cementitious materials concluded that there is a certain relationship between the temperature rise and electrical conductivity. Specifically, the higher the electrical conductivity, the greater the temperature rise observed. Through orthogonal analysis of electrical conductivity, disregarding the effect of the non-significant influence factor SF type on the conductive heating test, the impact of two factors, CF doping and SF doping, on the heating test was investigated under 16 sets of conditions, and the data were analyzed visually. The optimal mix ratio for the test is A3B4C4, determined through comprehensive optimization of orthogonal and intuitive analyses. This means that the optimal physico-mechanical properties are achieved when using copper-plated SFs, with a SF dosage of 1.25% and a CF dosage of 0.48%. As a preceding study in the field of intelligent concrete, this experiment explores the research path of intelligent concrete, which holds positive significance for subsequent, more intricate research endeavors.

Self-healing concrete presents an innovative and eco-friendly solution with the potential to reduce maintenance costs through self-activated crack repair. This study examined the effect of varying bacterial content across different environmental conditions. Additionally, the coupling effect between bacteria and steel fiber to enhance the mechanical and physical properties at different ages has been investigated. Bacillus Sphaericus (B. Sphaericus) was incorporated into the concrete at concentrations of 2 × 109 (CFU/ml), and different bacterial percentages selected utilizing calcium lactate as a nutrient source. Bacterial content of 0.0 %, 0.25 %, 1.0 %, and 2.5 %, cured in both fresh water and magnesium sulfate water solution, were tested to examine concrete behavior in harsh environments. Additionally, steel fibers at volume fraction percentages (Vf%) of 1.0 % and 1.5 %, along with 1.0 % bacterial content, were tested to highlight their combined effect. Tests were conducted at different ages to measure compressive, tensile, and flexural strengths. In addition, SEM and EDS analyses for cracked and uncracked specimens were performed. The results showed a significant increase in the long-term compressive, tensile, and flexural strengths at 180 days by 47 %, 80 %, and 50 %, respectively, with a bacterial content of 2.5 %. Moreover, the incorporation of steel fibers, 1.0 % and 1.5 % content, in the bacterial concrete resulted in a long-term compressive strength increase at 180 days by 45 % and 55 %, respectively with 1.0 % bacterial content, compared to 15 % and 27 % for 0 % bacteria. Curing in sulfate-rich water, concrete specimens exhibited increasing compressive strength at 180 days from 47 MPa for 0 % bacteria to 77 MPa with 2.5 % bacteria content. Despite lower initial strength of 29 MPa at 7 days, bacterial incorporation led to significant strength improvements, highlighting effective self-healing even in aggressive curing environments.

The conventional rebar-reinforced concrete (RRC) segmented lining of the Chamshir water conveyance tunnel (CWCT) in Bushehr Province, Iran, has experienced significant damage issues. This paper presents a comprehensive study involving laboratory experiments, numerical simulations and statistical site-survey analysis aimed at evaluating the mechanical behaviors and structural integrity of steel fiber-reinforced concrete (FRC) and fiber-rebar-reinforced concrete (FRRC) segment types, as compared to the traditional RRC segments. Laboratory compressive, tensile and flexural strength testing provided insights into the impacts of the fiber diameter and content on the ultimate strength capacities of the FRC test specimens. Numerical simulations scrutinized beam and segment models reinforced by the explicit inclusion of traditional rebar and/or randomly orientated and evenly distributed steel fiber reinforcements. The segment simulations were directed at investigating concentrated loading, representative of the jack thrust force applied in installing the segments during the tunnel boring machine (TBM) installation phase. Additionally, a field-monitoring program of the CWCT lining quantified common damage patterns among 545 RRC and 416 FRC segments that had experienced damage during their installation and in-service phases. For FRC beams, increased fiber content correlated with enhanced strength capacity, although the use of larger diameter fibers produced diminishing returns. Compared to the considerable damage expected near the applied TBM jack thrust force for the RRC segments, significantly reduced damage was predicted for both the FRC and FRRC segment types. However, even modest jack force misalignment (of 5–7.5°) led to cracking damage across the segment width for all models, although with the fibers included, the chipping damage was reduced substantially. The findings underscore the potential of FRC and FRRC segment types to achieve better structural integrity compared to traditional RRC segments.

Extensive research is being conducted globally on incorporating fibres into concrete to enhance its mechanical properties. This study aims to evaluate the strength characteristics of fibre-reinforced concrete (FRC) with varying mix proportions. 18 concrete samples of M-25 grade were prepared, incorporating different percentages of steel and glass fibers. Six samples contained glass fibres (GF) at 5%, 10%, and 15% by weight of cement, and six contained steel fibres (SF) at the same percentages. Additionally, two samples were prepared with a combination of 5% glass fibres and 10% steel fibres and two samples with 10% glass fibres and 5% steel fibres. These were compared to a control sample without fibre reinforcement. The compressive strength of the FRC was assessed at 7 and 28 days. The findings indicate that higher percentages of glass fibers had a notably negative impact on compressive strength, while the inclusion of steel fibers had a comparatively lesser effect. The maximum compressive strength was observed by including 5% steel fibres at 28 days. However, increasing the fiber content beyond this percentage resulted in a reduction in compressive strength. The lowest compressive strength was recorded in samples containing 15% glass fibers at 28 days.

This study aims to evaluate experimentally the mechanical characteristics of Self-Compacting Concrete (SCC) comprising expanded polystyrene beads (EPS) to produce flowable lightweight concrete reinforced with steel fibers. In this paper, the effect of steel fibers and EPS content on the fresh and hardened mechanical properties of SCC specimens, using two percentages for Polystyrene aggregate replacement (25% and 50%) and three values for volume fraction of steel fiber content (0%, 0.75%, and 1.5%), were examined. Fresh mixture properties were determined using slump flow, L-box, and V-funnel tests. Mechanical properties for hardened samples were obtained using standard specimens for compressive strength, density, split, and flexural strength. The study showed that EPS content has no adverse effect on the rheological features of the SCC. However, workability falls below specification limits when adding steel fibers to SCC. Results revealed that using 25% of EPS content resulted in lightweight structural concrete, while lightweight moderate-strength concrete was produced using 50% of EPS content. Furthermore, the study has shown that the split and flexural tensile strength were reduced substantially by 53% and 60% due to EPS addition. However, adding steel fibers remarkably improved the indirect tensile strength and Modulus of rupture by 46% and 80%, respectively. The mode of failure of the concrete specimens containing EPS beads and steel fibers did not show brittle failure behavior generally encountered in normal-weight concrete, indicating a more ductile behavior.

Grouted rock bolts subject to axial loading in the field exhibit various failure modes, among which the most predominant one is the bolt-grout interface failure. Thus, mechanical characterization of the grout is essential for understanding its performance in ground support. To date, few studies have been conducted to characterize the mechanical behaviour of fiber-reinforced grout (FRG) in rock bolt reinforcement. Here we experimentally studied the mechanical behaviour of FRG under uniaxial compression, indirect tension, and direct shear loading conditions. We also conducted a series of pullout tests of rebar bolt encapsulated with different grouts including conventional cementitious grout and FRG. FRG was developed using 15% silica fume (SF) replacement of cement (by weight) and steel fiber to achieve high-strength and crack-resistance to overcome drawbacks of the conventional grout. Two types of steel fibers including straight and wavy steel fibers were further added to enhance the grout quality. The effect of fiber shape and fiber volume proportion on the grout mechanical properties were examined. Our experimental results showed that the addition of SF and steel fiber by 1.5% fiber volume proportion could lead to the highest compressive, tensile, and shear strengths of the grout. The minimum volume of fiber that could improve the mechanical properties of grout was found at 0.5%. The scanning electron microscopy (SEM) analysis demonstrated that steel fibers act as an excellent bridge to prevent the cracks from propagating at the interfacial region and hence to aid in maintaining the integrity of the cementitious grout. Our laboratory pullout tests further confirmed that FRG could prevent the cylindrical grout annulus from radial crack and hence improve the rebar's load carrying capacity. Therefore, FRG has a potential to be utilized in civil and mining applications where high-strength and crack-resistance support is required.

This paper presents the experimental study and finite element modeling of the flexural behavior of concrete beams reinforced with reused steel bars as longitudinal reinforcements. The experimental program and results of eight reinforced concrete (RC) beams constructed with and without reused steel bars are described in detail. The replacement percentages of brand‐new bars with reused steel bars in the tested beams were 50% and 100%. The reused steel bars were coated with and without epoxy. Steel fibers with fractions of 0.5% and 1.0% of the concrete volume were added to the concrete mixes. The load‐deflection relationship, ductility index, toughness, and failure modes of the tested beams are presented and discussed. It is shown that utilizing reused steel bars decreases the ultimate load of RC beams but increases their deflection at the ultimate load compared with the control beam. Increasing the steel fiber ratio increases the ultimate load and the deflection at the ultimate load of RC beams incorporating reused steel bars. However, the zinc‐rich epoxy used to coat the reused steel bars does not affect the behavior of the beams. Three‐dimensional nonlinear finite element (FE) models of the tested beams were developed using ABAQUS and validated against the test results. The developed FE models are capable of accurately simulating the experimentally observed behavior of RC beams with reused steel bars. [ABSTRACT FROM AUTHOR]

Shear stress is one of the main design parameters for structures subjected to seismic demands. Steel fibers are a viable option for the shear reinforcement of concrete elements because they tend to increase the tensile strength and post-cracking performance of concrete. This study evaluated the direct shear strength of steel fiber-reinforced concrete (SFRC) using standardized specimens. The experimental program included direct shear tests of 14 column- and beam-type specimens using three test methods: FIP, JSCE-SF6, and Z-type. The steel fibers had double hooks at the ends and an aspect ratio of 65. The nominal fiber dosages (FD) were 30 and 60 kg/m3 , which correspond to fiber contents of 0.38% and 0.76%, respectively. The analysis of 887 data points measured during direct shear tests of the 14 specimens from this study and 69 specimens reported in the literature was performed by analyzing the trends of the shear strength parameters at the first cracking, maximum strength, and residual shear as a function of the reinforcement index. The measured results showed that the shear strength of SFRC at the limit states of cracking, maximum, and residual with FD of 60 kg/m3 was between 3% and 52%, 5% and 50%, and 29% and 63%, respectively, greater than the values associated with FD of 30 kg/m3. The study also proposed models to estimate the toughness, and the maximum and the residual shear strengths associated with specific displacements. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]