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Recently, addition of various natural fibers to high strength concrete has aroused great interest in the field of building materials. This is because natural fibers are much cheaper and locally available, as compare to synthetic fibers. Keeping in view, this current research conducted mainly focuses on the static properties of hybridized (sisal/coir), sisal and coir fiber-reinforced concrete. Two types of natural fibers sisal and coir were used in the experiment with different lengths of 10, 20 and 30 mm and various natural fiber concentrations of 0.5%, 1.0%, and 1.5% by mass of cement, to investigate the static properties of sisal fiber reinforced concrete (SFRC), coir fiber reinforced concrete (CFRC) and hybrid fiber reinforced concrete (HFRC). The results indicate that HFRC has increased the compressive strength up to 35.98% with the length of 20 mm and with 0.5% concentration, while the CFRC and SFRC with the length of 10 mm and with 1% concentration have increased the compressive strength up to 33.94% and 24.86%, respectively. On another hand, the split tensile strength was increased by HFRC with the length of 20 mm and with 1% concentration, CFRC with the length of 10 mm and with 1.5% concentration, and SFRC with the length of 30 mm and with 1% concentration have increased up to 25.48%, 24.56% and 11.80%, respectively, while the HFRC with the length of 20 mm and with 0.5% concentration has increased the compressive strength of concrete but has decreased the split tensile strength up to 2.28% compared to PC. Overall, using the HFRC with the length of 20 mm and with 1% concentration provide the maximum output in terms of split tensile strength. Graphical Abstract Experimental Investigation on the Mechanical Properties of Natural Fiber Reinforced Concrete

The inherent brittleness of glass-fiber-reinforced polymer (GFRP) bars limits their structural applicability despite their corrosion resistance and lightweight properties. This study addresses the critical challenge of enhancing the ductility and crack resistance of GFRP-reinforced systems while maintaining their environmental resilience. Through experimental evaluation, GFRC slabs reinforced with GFRP bars are systematically compared to steel-reinforced GFRC slabs and non-bar-reinforced SFRC slabs under bending loads. Eight slabs were subjected to four-edge-supported loading following standardized procedures based on prior strength assessments. The results demonstrate that GFRP-reinforced GFRC slabs achieve an ultimate load capacity of 83.7 kN, comparable to their steel-reinforced counterparts (96.3 kN), while exhibiting progressive crack propagation and 17% higher energy absorption than non-fiber-reinforced systems. The load capacity similarities between GFRP-bar-reinforced GFRC slabs and steel-reinforced slabs are 69% for crack loading and 86% for ultimate capacity. Furthermore, this study demonstrates that the reduction factor in flexural strength design of the novel slab should be comprehensively considered, incorporating the recommended value of 0.5. The findings confirm that GFRP-bar-reinforced GFRC slabs meet key structural performance criteria, including enhanced bending capacity, energy absorption, crack resistance, and ductility. This study underscores the potential of GFRP as an effective alternative to steel reinforcement, contributing to the development of resilient and durable concrete structures in demanding environments.

This study investigates the behavior of recycled steel fibers (RSFs) recovered from waste tires and industrial hooked-end steel fibers (ISF) in two single and hybrid reinforcement types with different volume content, incorporating microstructural and macrostructural analyses. Scanning electron microscopy (SEIM) is used to study the microstructure and fractures, focusing on crack initiation in the fiber interface transition zone (FITZ). The macrostructural analysis involves using digital image correlation (DIC) software, Ncorr, to analyze the split tensile behavior of plain and fiber-reinforced concrete (FRC) specimens, calculating strain distribution and investigating crack initiation and propagation. The SEM study reveals that, due to the presence of hooked ends, industrial fibers promoted improved mechanical interlocking; created anchors within the matrix; added frictional resistance during crack propagation; significantly improved load transfer; and had better bonding, crack bridging, and crack deflection than recycled fibers. RSFs significantly delay crack initiation and enhance strength in the pre-peak zone. The study suggests hybridizing recycled fibers from automobile tires with industrial fibers as an optimum strategy for improving tensile performance and using environmentally friendly materials in FRC. Keywords: digital image correlation (DIC); fiber interface transition zone (FITZ); recycled steel fibers (RSFs); scanning electron microscopy (SEM); split tensile behavior; sustainable fiber-reinforced concrete (FRC).

This paper determines the effect of discrete fibers on the elastic modulus of concrete and cement composites. Five types of discrete fibers consisting of steel, polypropylene, macro-polyolefin, polyvinyl alcohol (PIA), and basalt fibers were investigated Results show that discrete fibers had little effect on elastic modulus for fiber-reinforced concrete (FRC) with coarse-to-fine aggregate ratio (C/S) greater than 1. However, for FRC with C/S smaller than 1 and fiber-reinforced cement composites (FRCCs), discrete fibers reduced the elastic modulus. Accordingly, a new elastic modulus equation is proposed to better estimate the elastic modulus of FRC with a maximum fiber volume fraction of 10%. The proposed equation was compared with existing equations from other codes, including American, Japanese, Korean, Norwegian, and European codes, as well as equations proposed by other researchers. These equations were evaluated using more than 400 data points taken from the experimental program and other literatures. The proposed equation provides the most accurate prediction for the elastic modulus of FRC and FRCC with a coefficient of variation of 15% as compared to 32% using ACI 318 equation for C/S [less than or equal to] I. Keywords: basalt fibers; elastic modulus; fiber-reinforced cement composites; fiber-reinforced concrete; polypropylene; polyvinyl alcohol; strain hardening; strain softening; steel fibers.

This paper investigates the tensile behavior of green ultra-high-performance fiber-reinforced concrete (UHPFRC) using commercially available steelfibers. An ecofriendly ultra-high-performance concrete (UHPC) with a low carbon footprint was developed, aiming for a compressive strength of 150 MMPa (22 ksi) and a high packing density (0.81) while using recycled glass powder and micro-limestone powder as partial substitution of silica fume and ordinary portland cement. Besides the commercially available normal-strength deformed steel fibers, high-strength smooth steel fibers were used to establish a comparison. The study showed that, with appropriate hooked normal-strength and smooth high-strength steel fibers, 1% of fiber is enough to achieve strain hardening behavior. Moreover, the smooth fibers achieved the maximum tensile strength ([[sigma].sub.pc] = 11.04 MPa) when 2% of volume was used. However, despite having less tensile strength, only the hooked-end fibers achieved a maximum post-cracking strain ([[epsilon].sub.pc]) of over 0.3% using 2% of volume. Keywords: commercially available fibers; composite; direct tensile behavior; supplementary cementitious materials (SCM); ultra-high-performance fiber-reinforced concrete (UHPFRC).

Fiber-reinforced concrete has a wide application in practice, and many fields of research are devoted to it. In most cases, this is a specific problem, i.e., the determination of the mechanical properties or the test method. However, wider knowledge of the effect of fiber in concrete is unavailable or insufficient for selected test series that cannot be compared. This article deals with the processing of a comprehensive test study and the impact of two types of fibers on the quantitative and qualitative parameters of concrete. Testing was performed for fiber dosages of 0, 40, 75, and 110 kg/m3. The fibers were hooked and straight. The influence of the fibers on the mechanical properties in fiber-reinforced concrete was analyzed by functional dependence. The selected mechanical properties were compressive strength, splitting tensile strength, bending tensile strength, and fracture energy. The results also include the resulting load–displacement diagrams and summary recommendations for the structural use and design of fiber-reinforced concrete structures. The shear resistance of reinforced concrete beams with hooked fibers was also verified by tests.

An experimental study was conducted to identify the shear-enhancement and failure mechanisms behind the ultimate shear strength of steel fiber-reinforced concrete (SFRC) slender beams by using the full field-deformation-measuring capability of digital image correlation (DIC) technology. A total of 12 large-scale simply supported SFRC and RC beams with an overall height from 12 to 48 in. (305 to 1220 mm) were tested under monotonic point load up to failure. The greater shear strength in SFRC beams originates from the ability of the fiber bridging effect that delays the propagation of the cracks into the compression zone, whose shear strength is enhanced by the compressive stresses induced by the higher load. The slow progression of the cracks keeps the compression zone depth large, thereby enabling it to contribute to a higher shear resistance. In contrast with the traditional assumption for either plain concrete or SFRC beams, where the shear contribution resulting from dowel action is completely neglected, this research clearly shows that the dowel action has an appreciable effect on the ultimate shear strength. Its contribution varies from 10 to 30% when the beam depth increases from 12 to 48 in. (305 to 1220 mm). On the other hand, the compression zone s contribution decreases from 69 to 36% with the increase in beam depth. In addition, the shear contribution from the fiber bridging effect along the critical shear crack stays approximately unchanged at 20%, irrespective of the beam depth. In this study, the minimum shear strength obtained was in the range of [??] psi (0.42[??] MPa) for the beams with the greatest depth. This indicates thatthe maximum allowed shear stress limit of 1.5[??] psi (0.125[??] MPa) specified inACI 318-14 is on the very conservative side. Keywords: dowel action; hooked-end steel fiber; shear strength; steel fiber-reinforced concrete.

The main objective of this study is to better understand the performance changes of naturally aged glass fiber-reinforced concrete (GFRC) and polypropylene fiber-reinforced concrete (PPFRC), especially the degradation of fibers, which is of great significance for evaluating the durability of structures using these two types of composite materials. The mechanical properties, water absorption, and microstructures of GFRC and PPFRC at a curing age of three years, including their compressive strength, full curves of water absorption, fiber-matrix interaction, and fiber degradation, were systematically studied, and the related properties were compared with those at the curing age of 28 days. The degradation of fibers after freeze-thaw cycles was also studied. The results revealed the following. The water/binder ratio (w/b) affects the rate of increase of the long-term compressive strength of naturally aged concrete. In general, the water absorption of fiber-reinforced concrete (FRC) at the curing age of three years was found to be significantly reduced, but with the increases of w/b and the fiber content to the maximum values, the water absorption of the specimens cured for three years was higher than that of the specimens cured for 28 days. Moreover, with the increase of the curing age, the optimal glass fiber (GF) contents for reducing the water absorption decreased from 1.35% to 0.90% (w/b = 0.30), and from 0.90% to 0.45% (w/b = 0.35), respectively. The GF surface was degraded into continuous pits with diameters of about 200 to 600 nm, and the surface of the pits was attached with spherical granular C-S-H gel products with diameters of about 30 to 44 nm. The freeze-thaw cycles were found to have no significant effect on the pits on the GF surface and the granular C-S-H gel products attached to the pits, but caused a portion of the cement matrix covering the GF to fall off. The interfacial bonding between the polypropylene fiber (PPF) and the cement matrix exhibited almost no change in the PPFRC after three years of curing as compared with that after 28 days of curing. Furthermore, the cement hydration gel on the PPF surface was not significantly damaged by 150 freeze-thaw cycles.

Enhancing the damping capacity of concrete structures is crucial for improving their resilience under dynamic loading conditions such as earthquakes, vehicular impacts, and industrial vibrations. This study presents a comprehensive review of how material properties—specifically fiber reinforcement, ductility, and toughness—affect the damping behavior of concrete. Various types of fiber reinforcements, including steel, polypropylene, and glass fibers, are analyzed in terms of their contribution to energy dissipation mechanisms such as crack bridging, fiber pullout, and frictional sliding. The role of the ductility index and toughness in augmenting the damping ratio is also discussed, demonstrating that higher ductility and toughness directly correlate with enhanced energy dissipation. Furthermore, the interrelationships between material properties and structural performance under cyclic loading are critically evaluated. The findings highlight that optimizing fiber content and improving the mechanical properties of concrete can significantly increase its damping capacity, thereby offering strategic pathways for designing safer and more durable infrastructure, especially in seismic-prone regions. This review aims to consolidate the current understanding and provide recommendations for future research focused on developing high-damping concrete composites.

Fiber-reinforced concrete (FRC) is increasingly used in structural applications owing to its benefits in terms of toughness, durability, ductility, construction cost and time. However, research on the creep behavior of FRC has not kept pace with other areas such as short-term properties. Therefore, this study aims to present a comprehensive and critical review of literature on the creep properties and behavior of FRC with recommendations for future research. A transparent literature search and filtering methodology were used to identify studies regarding creep on the single fiber level, FRC material level, and level of structural behavior of FRC members. Both experimental and theoretical research are analyzed. The results of the review show that, at the single fiber level, pull-out creep should be considered for steel fiber-reinforced concrete, whereas fiber creep can be a governing design parameter in the case of polymeric fiber reinforced concrete subjected to permanent tensile stresses incompatible with the mechanical time-dependent performance of the fiber. On the material level of FRC, a wide variety of test parameters still hinders the formulation of comprehensive constitutive models that allow proper consideration of the creep in the design of FRC elements. Although significant research remains to be carried out, the experience gained so far confirms that both steel and polymeric fibers can be used as concrete reinforcement provided certain limitations in terms of structural applications are imposed. Finally, by providing recommendations for future research, this study aims to contribute to code development and industry uptake of structural FRC applications.