Synthetic Fiber-reinforced Concrete Research Articles

Mechanical Properties and Microstructure of Cellulose Fiber- and Synthetic Fiber-Reinforced High-Strength Concrete

Mechanical Properties and Microstructure of Cellulose Fiber- and Synthetic Fiber-Reinforced High-Strength Concrete

Machine learning-based models for predicting the shear strength of synthetic fiber reinforced concrete beams without stirrups

Stirrups can be added to reinforced concrete (RC) beams made of plain concrete to increase the shear strength providing better performance against embrittlement. If the need for shear stress is less than the strength of RC beams, reinforced with the minimum number of stirrups, then this choice might not be the most cost-effective. Synthetic Fiber Reinforced Concrete (SyFRC) in Reinforced Concrete (RC) structures is limited due to the lack of predicting models for this emerging material in current literature. However, recent advances in concrete technology have revealed more significant benefits of SyFRC, including high deformation capacity and less corrosive concrete. This study predicts shear strength of SyFRC beams without stirrups using the ACI 318-19 equation in addition to Machine Learning (ML) methods such as LightGBM, XGBoost, and Gene Expression (GEP). A database of 102 tested SyFRC specimens were compiled, processed, and evaluated. With R2 values of 98.91% and 97.22%, respectively, the LightGBM and XGBoost outperformed the other examined algorithms by having the least predictions discrepancy and highest accuracy values. As the ACI 318-19 equation does not account for the fibers volume ratio and shear span-to-depth ratio effects on the shear strength contribution, it projected shear strength with the lowest degree of accuracy, with R2 = 75.5%. The feature importance analysis revealed that these two factors, in addition to the effective beam depth, beam width, longitudinal steel reinforcement ratio, and concrete compressive strength should not be negligible in shear strength prediction. For forecasting the shear strength, a closed-form GEP-based model was suggested. The proposed GEP model has a little lower prediction accuracy with R2 = 88.4%. The performance of the four examined models was evaluated from various perspectives. The analysis shows that, apart from the ACI equation, all considered models effectively predict the effects of shear span-to-depth ratio. This is critical for investigating deep and slender beams, and size effect, which are critical for beams with high effective depths. The current study's findings should give practitioners a solid platform for making precise and straightforward assessments of shear strength.

Attenuation and Frequency Characteristics of Acoustic Waves in Steel and Synthetic Fiber-Reinforced Concrete: 3D-PCT and Unsupervised Pattern Recognition

In heterogeneous materials such as concrete, deterioration of the elastic wave—which acoustic emission technique (AET) is based on—is one of the research objects in the field. While many studies reveal that the wave is deteriorated due to the concrete content and deterioration of AE signals causes erroneous data interpretation, a limited number of them have suggested eliminating the effects of this problem. For this reason, contributing to the existing literature, this paper proposes to correct AE signals for fiber-reinforced concrete, which is a highly heterogeneous material, by 3D-PCT (Parameter Correction Technique) developed with new approaches in the authors’ previous study for concrete. First, the attenuation properties of concrete samples, including different types and amounts of fibers, were revealed within this scope. Contour maps showed that the type and amount of fiber are effective on elastic wave attenuation. Then, the samples were tested under flexure, and AE results were compared with mechanical findings after parameter correction. The effectiveness of the proposed correction method was verified by separating fiber activities from concrete cracking activities for the first time in the literature with weighted peak frequency and partial power. In this way, by successfully matching the fiber activities, which were revealed after the correction, with the crack development times obtained from frequency-based unsupervised pattern recognition, it was seen that a more accurate AE interpretation could be made with parameter correction. Moreover, corrected AE parameters also provided to propose a new inference for identifying a relationship between the amplitude and energy loss of the AE signals and the type of damage.

Influence of natural fiber in the mechanical and durability behaviour of hybrid fiber-reinforced concrete

ABSTRACT Cracks developed due to drying and shrinkage in plain cement concrete can be overcome by introducing discreet and randomly oriented fibrous material as a reinforcing agent. Researchers focused only on synthetic fiber-reinforced concrete (FRC) most of the time while neglecting natural FRC. Previously, researchers focused on double hybrid FRC, whereas triple hybrid FRC required a further behavioral study on FRC’s mechanical characteristics. The primary objective of this study is to enhance mechanical properties of matrix due to the effect of short fiber in randomly oriented without changing their individual identity. Here, sisal fiber (SF), banana fiber (BF), and human hair fiber (HH) are used as reinforcing agents with varying volume fractions ( from 0.5% to 2% and a hybrid of 1% with concrete matrix. This investigation found that BF 0.5%, SF 1.5%, HH 1%, and H6 (SF0.25BF0.5HH0.25) % showed the optimum volume fraction, which improved mechanical properties and resisted sulfate and alkaline attack on the concrete matrix. Product from individual and combined natural FRC could be a sustainable building material that is economical, eco-friendly, and durable.

Influence of fibers distribution on direct shear and flexural behavior of synthetic fiber-reinforced self-compacting concrete

The influence of fiber distribution on the direct shear and flexural behavior of Fiber-Reinforced Self-Compacting Concrete (FR-SCC) is investigated. This study characterizes FR-SCC reinforced with monofilament polypropylene fiber (P) and kinked multifilament polypropylene/polyethylene fiber (PP) at volumes of 0.6, 0.8, and 1.0%. The loss of workability in the FR-SCC mixtures increased the variation in the distribution of the fibers. The residual flexural strength and direct shear toughness increased linearly with the total number of fibers exposed on fracture cross-sections. In general, the P fiber provided better mechanical performance than the PP fiber due to its anchorage effectiveness, which improved the transfer of stress from the matrix to the fiber.

Influence of synthetic fibers on the seismic behavior of reinforced-concrete circular columns

The addition of discrete fibers to the concrete mixture to enhance its toughness and tensile strength is well acknowledged. Studies have also shown that fiber-reinforced concrete (FRC) can be favorable for its enhanced behavior in compression. This behavior, which is attributed to the confinement action of the fibers, is, in general, superior in terms of strength and ductility, compared to plain concrete. Reversed cyclic loading in flexure under constant axial load of large scale synthetic fiber-reinforced concrete columns is scarce as opposed to steel fiber-reinforced concrete columns. This paper presents an experimental study on the behavior of large-scale synthetic fiber-reinforced concrete columns with hoops transverse steel reinforcement under constant axial load and reversed flexure simulating seismic loading. The results from this study show slightly improved cyclic behavior compared to results obtained on similar columns reinforced with spiral transverse reinforcement. Enhanced behavior of synthetic fiber-reinforced concrete is achieved for practical transverse steel reinforcement spacings (⩾75 mm). In this case, similar ductile behavior of a reinforced-concrete column can be reached with a reduced amount of transverse steel reinforcement and the inclusion of synthetic fibers with an aspect ratio of 50–100 to the concrete mixture. Difficulty in placing synthetic fiber-reinforced concrete in very congested columns precludes its use in columns with hoops or spiral spacing less than 75mm until self leveling concrete with large amount of synthetic fibers is developed.

The influence of natural and synthetic fibers on mixed mode I/II fracture behavior of cement concrete materials

This paper evaluated mixed mode I/II fracture toughness of fiber-reinforced concrete using cracked semi-circular bend (SCB) specimens subjected to three-point bending test. Additionally, a comparison was made between the experimental results and the estimations made by different theoretical criteria. Natural and synthetic fibers at various concentrations were used in this study. After producing cracks in SCB specimens at different inclination angles to induce different mixed mode loading conditions (from pure mode I to II), the fracture toughness of SCB specimens was determined. Furthermore, the compressive, splitting tensile, and flexural strength of natural and synthetic fiber-reinforced concrete were measured after 7 and 28 days of curing. While there is an increase in the aforementioned strengths with fiber content increase, 0.3% was found to be the optimum percentage regarding fracture toughness for both fibers. Also, the comparison between the experimental and theoretical results showed that generalized maximum tangential stress criterion estimated the experimental data satisfactorily.

A study on the efficiency of steel vs. synthetic vs. hybrid fibers on fracture behavior of concrete in flexure using acoustic emission

Synergistic effect of different fibers on the improvement of fracture behavior of concrete is a widely accepted phenomenon. However, the fracture mechanisms behind their improvement need to be clearly understood for optimizing the fiber dosage. In this work, the fracture behavior of synthetic fiber-reinforced concrete (SynFRC), steel fiber reinforced concrete (SFRC) and hybrid fiber reinforced concrete (HFRC) under flexural loading is studied using acoustic emission (AE) technique. Three different fiber dosages, by volume of concrete, of 0.50%, 0.75% and 1.0% and their hybrid combinations were considered as study parameters. Test results show that it is possible to retain sufficient workability in the fresh state and obtain good fracture resistance through a hybrid combination of hooked end steel fibers and macro- synthetic polyolefin fibers. AE parameters were investigated to acknowledge the efficiency of the fibers in improving the fracture behavior and toughness of SynFRC, SFRC, and HFRC. AE parameters such as hits, events, AE energy, and 3D-crack source locations were presented to illustrate the role of different fiber dosages on the Mode-I fracture response. The source locations of AE event above the artificial notches created at the mid-span of specimens were investigated and classified into tensile or shear cracks. AE and fracture energy increased with fiber dosage. SFRC demonstrated higher energy dissipation capacity followed by HFRC and SynFRC.

Experimental study for determining applicable models of compressive stress–strain behavior of hybrid synthetic fiber-reinforced high-strength concrete

In order to be able to perform non-linear analysis and design of structures made of fiber-reinforced concrete members, the knowledge of their stress–strain behaviour under axial compression is required. In this study, an extensive experimental programme was conducted to investigate the compressive stress–strain behaviour of synthetic fiber-reinforced high-strength concrete. To accomplish this, 22 mixtures including different percentages of macropolymeric fibers and polypropylene fibers as well as different hybridisations of the two fiber types with or without the presence of nano-silica and silica fume pozzolans were prepared. Then, the effect of adding fibers and pozzolans on the properties of fiber-reinforced high-strength concrete including the shape of the stress–strain curve, compressive strength, strain at peak stress, ultimate strain and toughness index was investigated. Furthermore, based on the obtained experimental results, empirical relationships were proposed for the relevant parameters of the stress–strain curve of synthetic fiber-reinforced concrete. Finally, two simple yet accurate models were proposed to predict the compressive stress–strain curve of synthetic fiber-reinforced concrete based on the empirical relationships proposed for the maximum stress and the corresponding strain. The results suggest that the presented models are capable of predicting the experimental results with a very good accuracy.

Shear Behavior of Synthetic Fiber Reinforced Concrete

This paper presented a comprehensive experimental study on the shear capacity of zero-slump, dry-cast synthetic fiber-reinforced concrete (SYN-FRC) by using Japan Society of Civil Engineers (JSCE) G-553 test method. In adjacent with shear test, flexural and compression behavior of concrete determined based on ASTM C1609/C1609M-12 and ASTM C39/C39M-16b, respectively. In order to investigate the effect of different concrete compressive strengths on material properties of synthetic fiber-reinforced concrete, two different compressive strengths, 28 MPa (4000 psi) and 34 MPa (5000 psi), were selected. The test results demonstrated that the application of synthetic fibers in concrete yielded to significant improvements in material properties of concrete such as shear strength, shear toughness, flexural strength and flexural toughness. These enhancements were greater at higher synthetic fiber dosage rates.

Mechanical and durability evaluation of fiber-reinforced self-compacting concrete

In this paper, an investigation of the mechanical properties and durability aspects of steel, synthetic, and hybrid fiber-reinforced self-compacting concrete exposed to early wet/dry cycles are presented and discussed. The experimental program consisted of two phases. Phase I involved tests on specimens for workability, mechanical properties, Rapid Chloride Penetration (RCP), and Scanning Electron Microscopy (SEM). The evaluation of mechanical properties included compressive, flexural and splitting tensile strengths, and modulus of elasticity. In Phase II, specimens were exposed to wet/dry cycles, and the effect of moisture on mechanical properties was investigated. All mixes in Phase I achieved a cube compressive strength of 70±5MPa. Furthermore, it was observed that exposure of Fiber-Reinforced Self-Compacting Concrete (FRSCC) to early wet/dry cycles improved the mechanical properties of all mixes; an increase in compressive strength of 10MPa compared to non-exposed specimens was observed. The microstructure of Synthetic Fiber-Reinforced Self-Compacting Concrete (SyFRSCC) and Steel Fiber-Reinforced Self-Compacting Concrete (SFRSCC) was different, which explains the difference in their respective crack-resistance mechanisms.

Strength Prediction Models for PVA Fiber-Reinforced High-Strength Concrete

AbstractDuring the last decade, synthetic fibers have been used widely in the structure application; however, the strength models of synthetic fiber-reinforced concrete are not available, as most of the models have been proposed for steel fiber–reinforced concrete only. Extensive experimental investigation has been conducted on poly-vinyl alcohol (PVA) fiber-reinforced high-strength concrete to develop the strength model based on multiple linear regressions analysis through least square error. Regression models have been obtained for the different responses of concrete as a function of process variables, i.e., compressive strength of concrete, fiber matrix interface, and fraction of metakaolin (MK) as cement-replacing material. A total of 50 mixes of concrete have been examined using metakaolin of 0, 5, 10, 15, and 20% by weight of cement and PVA fibers of aspect ratio 45, 60, 90, and 120 with volume fraction of 0, 1, 2, and 3%. Five mixes without PVA fiber have been used as control mixes. For each mix, t...

Behaviour of Macro Synthetic Fiber Reinforced Concrete Columns Under Concentric Axial Compression

Previous studies have shown that fiber reinforced concretes can improve post-peak behaviour, ductility and energy-dissipation ability of concrete elements under flexure, shear and axial load. Ductile behaviour is one of the essential characteristics that have to be possessed by structures located in moderate to high seismic regions. This paper presents an experimental investigation of a series of nine macro synthetic fiber-reinforced concrete (MSNFRC) circular columns. The objective of the studies was to investigate the effects of the macro synthetic fibers on strength and ductility of the columns. The test parameters were the spacing of the spiral reinforcement and the volume fraction of the macro synthetic fibers. In two-thirds of the specimens, when macro synthetic fibers were added to the specimens, spiral reinforcement was reduced. The remaining specimens were detailed in accordance with the code minimum requirement for spiral reinforcement in order to examine the influence of the fibers on strength and ductility. A concentric axial compression load was applied monotically on the column specimens. The results show that the addition of macro synthetic fibers leads to improved ductility and strength. Furthermore, based on this study, the code required spiral reinforcement can be reduced whenever MSNFRC is used.

Performance of Synthetic Fiber-Reinforced Concrete Pipes

This study presents the production and full-scale testing of specific synthetic fiber-reinforced concrete pipes in a dry cast environment. Production and testing were conducted to identify the structural behavior of concrete pipes with synthetic fibers for the first time in the United States. Three production sites were selected to utilize different pipe manufacturing equipment. Each plant’s mix design was kept to be the same as those used in the production of the conventional reinforced concrete pipes (RCP), except for replacing the steel cage with synthetic fibers and adjusting the amount of water in the composite mix of concrete and fibers. Synthetic fiber-reinforced concrete pipes (SY-FRCP) were tested based on industry standard specifications for strength requirements for pipe diameters ranging from 375 mm to 600 mm (15 in. to 36 in.). Full-scale structural strength and stiffness tests were conducted based on industry standard test methods, three-edge bearing tests, for obtaining the load deformation characteristics of SY-FRCP. Control test pipes were also produced and tested for comparison purposes by using the conventional industry standard specifications for reinforced concrete pipes with steel cage. The load deformation plots along with the crack pattern formation for both SY-FRCP and RCP were compared. The results of this study indicated the BASF MasterFiber MAC Matric synthetic fibers could be used as an alternative reinforcement of concrete pipes.

Seismic Behavior of Synthetic Fiber-Reinforced Circular Columns

Ductile behavior and high energy-dissipation ability are two essential properties for a reinforced concrete column part of a structure in a moderate to high seismic region. Concrete design codes ensure ductile behavior of columns by setting a requirement for a minimum amount of transverse steel reinforcement. Studies have shown, however, that use of fiber-reinforced concrete (FRC) can enhance the post-peak behavior and hence, the ductility and energy dissipation ability of concrete columns subjected to axial force and bending moment. Therefore, the inclusion of macro fibers in the concrete mixture, combined with a reduced amount of lateral reinforcement, can be an alternative to the conventional lateral reinforcement required by the codes. Moreover, the higher resistance to crack growth and the excellent durability of FRC over nonfibrous concrete can result in a higher cost-effective value. In this regard, tests on large-scale circular synthetic fiber-reinforced concrete (SNFRC) columns subjected to a combined constant axial load and reversed cyclic flexure simulating earthquake loading were carried out. The aim of this test program was to examine the influence of adding synthetic fibers to the concrete mixture on the behavior of normal-strength concrete (NSC) columns. The results show that, in terms of ductility and energy dissipation, SNFRC columns outperformed NSC columns. The results also show that the larger the amount of lateral reinforcement the smaller the influence of the fibers on the column's behavior. Based on the test results, the amount of confinement steel required by concrete design codes could be reduced when SNFRC is used.

Synthetic Fiber-Reinforced Concrete Bridge Decks: Redefining Bridge Deck Design and Behavior

Researchers at the Technical University of Nova Scotia have pioneered the development of concrete slab on girder bridge decks totally devoid of all internal steel reinforcement. The decks are constructed of synthetic fiber-reinforced concrete on composite steel girders restrained by external steel straps. The discrete reinforcing fiber used is a collated fibrillated polypropylene fiber. The major benefit of this approach is the reduction of long-term maintenance costs and the increase in bridge deck lifespan. An overview of the concepts behind this technology, theoretical and experimental work that has been undertaken, and some the practical aspects of designing a fiber-reinforced concrete mix with high volume fractions of synthetic fiber are presented.

Synthetic Fiber-Reinforced Concrete Bridge Decks: Redefining Bridge Deck Design and Behavior

Researchers at the Technical University of Nova Scotia have pioneered the development of concrete slab on girder bridge decks totally devoid of all internal steel reinforcement. The decks are constructed of synthetic fiber-reinforced concrete on composite steel girders restrained by external steel straps. The discrete reinforcing fiber used is a collated fibrillated polypropylene fiber. The major benefit of this approach is the reduction of long-term maintenance costs and the increase in bridge deck lifespan. An overview of the concepts behind this technology, theoretical and experimental work that has been undertaken, and some the practical aspects of designing a fiber-reinforced concrete mix with high volume fractions of synthetic fiber are presented.