Fibers

17 pages, 2902 KiB

Open AccessArticle

Influence of Fiber Dimensions on Bridging Performance of Polyvinyl Alcohol Fiber-Reinforced Cementitious Composite (PVA-FRCC)

by Helen Negash Shiferaw, Selamawit Fthanegest Abrha, Toshiyuki Kanakubo, Madappa V. R. Sivasubramanian and Shamsher Bahadur Singh

Fibers 2024, 12(8), 70; https://doi.org/10.3390/fib12080070 - 22 Aug 2024

Viewed by 748

Abstract

This study investigates the influence of fiber dimensions on the bridging performance of polyvinyl alcohol fiber-reinforced cementitious composite (PVA-FRCC) through an experimental and analytical program. Bending tests, bridging law calculations, and section analysis are conducted. Bending tests of notched specimens of PVA-FRCC with [...] Read more.

This study investigates the influence of fiber dimensions on the bridging performance of polyvinyl alcohol fiber-reinforced cementitious composite (PVA-FRCC) through an experimental and analytical program. Bending tests, bridging law calculations, and section analysis are conducted. Bending tests of notched specimens of PVA-FRCC with six different PVA fiber dimensions are performed to determine the load–deflection (LPD) and bending moment–crack mouth opening displacement (CMOD) relationships. The fiber volume fraction for all PVA-FRCCs is set to 2%. It is found that the load capacity of PVA-FRCC with a 27 μm diameter fiber is much higher than that of the other fibers, and the load capacity decreases as the fiber diameter increases. The study proposes parameters for the characteristic points of the tri-linear model for the single-fiber pullout model as functions of diameter, bond fracture energy, elastic modulus, cross-sectional area, and perimeter of the fiber. These findings provide valuable insights into the behavior of PVA-FRCC under different fiber dimensions. Bridging law calculations are conducted to obtain tensile stress–crack width relationships using the developed single-fiber pullout models. The Popovics model for the complete tensile stress–crack width relationship is adopted to obtain a better fit with the bridging law calculation, and then section analysis is conducted. The bridging law calculation results show that the maximum tensile stress decreases as the fiber diameter increases. It is also determined that most of the smaller-diameter fibers ruptured, whereas the larger fiber diameters pulled out from the matrix. The section analysis results show good agreement with the maximum bending moments obtained from the bending test. Full article

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12 pages, 4092 KiB

Open AccessArticle

Identification of Effects of Parylene-C Coating on Electrospun Fibers

by Tae-Ha Song, Jeong Hwa Kim, Dong-Guk Kim, Jihyoung Roh and Young Hun Jeong

Fibers 2024, 12(8), 69; https://doi.org/10.3390/fib12080069 - 22 Aug 2024

Viewed by 656

Abstract

As various healthcare technologies such as regenerative medicine, precision medicine, and alternative approaches to animal testing develop, the interest in the use and application of nano- and microfibers is steadily increasing. In this study, the effect of parylene-C coating on electrospun fibers was [...] Read more.

As various healthcare technologies such as regenerative medicine, precision medicine, and alternative approaches to animal testing develop, the interest in the use and application of nano- and microfibers is steadily increasing. In this study, the effect of parylene-C coating on electrospun fibers was investigated, and a pattern coating method was developed to expand the potential utilization of parylene-C-coated electrospun fibers. An SEM analysis demonstrated that parylene-C was successfully deposited on the electrospun fibers without any failure such as pinholes or air bubbles. Biocompatibility was investigated through cell tests, which indicated that the coated fibers were non-toxic and supported cell growth well. Tensile tests demonstrated a significant increase in the elastic modulus of the parylene-C-coated fibers, with it nearly quadrupling compared to the original PCL fibers, and the fracture strength almost doubled. At the same time, hydrophobicity was well maintained without any statistically significant changes. In particular, a non-adhesive magnet–metal masking was proposed in order to selectively coat the electrospun fibers with parylene-C with a specific pattern. Furthermore, it was presented that the magnet–metal mask-based coating electrospun nanofibers with parylene-C could be used in the fabrication of hybrid fibers composed of different diameters and materials. Full article

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24 pages, 14446 KiB

Open AccessArticle

Thermal Recycling Process of Carbon Fibers from Composite Scrap—Characterization of Pyrolysis Conditions and Determination of the Quality of Recovered Fibers

by Piotr Szatkowski and Rafał Twaróg

Fibers 2024, 12(8), 68; https://doi.org/10.3390/fib12080068 - 21 Aug 2024

Viewed by 1454

Abstract

In this study, we took a closer look at the thermal recyclability of CFRP composites used in the manufacture of high-pressure cylinders. Thermal analysis was used to determine the minimum temperature at which stable resin decomposition begins. The aim was to find temperature [...] Read more.

In this study, we took a closer look at the thermal recyclability of CFRP composites used in the manufacture of high-pressure cylinders. Thermal analysis was used to determine the minimum temperature at which stable resin decomposition begins. The aim was to find temperature parameters and retention times with which the pyrolysis process is as economically viable as possible, and the recovered fibers retain optimum mechanical properties. The surface morphology of fibers annealed in both inert and oxidizing atmospheres was examined. In addition, the mechanical strengths under static as well as dynamic conditions of the newly manufactured laminates containing the recovered fibers were investigated. During research, it was found that reusing fibers is very difficult. The recycled carbon fibers were successfully compressed in an epoxy matrix in the form of a pre-impregnated carbon mat with the presence of air. The presence of oxygen during the thermal degradation of the composite severely damaged the surface and structure of the carbon fiber, causing composites made from these fibers to be mechanically weaker by more than 247%. Full article

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23 pages, 16215 KiB

Open AccessArticle

Structural Health Monitoring of Partially Replaced Carbon Fabric-Reinforced Concrete Beam

by Ramalingam Malathy, Jenifar Monica James, Mayakrishnan Prabakaran and Ick Soo Kim

Fibers 2024, 12(8), 67; https://doi.org/10.3390/fib12080067 - 21 Aug 2024

Viewed by 927

Abstract

Textile-reinforced concrete (TRC) is a composite concrete material that utilizes textile reinforcement in place of steel reinforcement. In this paper, the efficacy of the partial replacement of steel reinforcement with textile reinforcement as a technique to boost the flexural strength of reinforced concrete [...] Read more.

Textile-reinforced concrete (TRC) is a composite concrete material that utilizes textile reinforcement in place of steel reinforcement. In this paper, the efficacy of the partial replacement of steel reinforcement with textile reinforcement as a technique to boost the flexural strength of reinforced concrete (RC) beams was experimentally investigated. To increase the tensile strength of concrete, epoxy-coated carbon textile fabric was used as a reinforcing material alongside steel reinforcement. Beams were cast by partially replacing the steel reinforcement with carbon fabric. Partially replaced carbon fabric-reinforced concrete beams of size 1000 × 100 × 150 mm³ were cast by placing the fabrics in different layers. A four-point bending test was used to test cast beams as simply supported until failure. Then, 120 ohm strain gauges were used to study the stress–strain behavior of the control and TRC beams. Based on this experimental study, it was observed that 50% and 25% of the steel replaced with carbon fabric beams performed better than the conventional beam. ABAQUS software was used for numerical investigation. For the load deflection characteristics, a good agreement was found between the experimental and numerical results. Based on the experimental analysis carried out, a prediction model to determine the ultimate load-carrying capacity of TRC beams was created using an Artificial Neural Network (ANN). Full article

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35 pages, 37177 KiB

Open AccessArticle

Performance Prediction of GFRP-Reinforced Concrete Deep Beams Containing a Web Opening in the Shear Span

by Amena Sheikh-Sobeh, Nancy Kachouh and Tamer El-Maaddawy

Fibers 2024, 12(8), 66; https://doi.org/10.3390/fib12080066 - 6 Aug 2024

Cited by 1 | Viewed by 1146

Abstract

This study aimed to investigate the nonlinear structural behavior of concrete deep beams internally reinforced with glass fiber-reinforced polymer (GFRP) reinforcing bars and containing a web opening of various sizes and locations within the shear span. Three-dimensional (3D) numerical simulation models were developed [...] Read more.

This study aimed to investigate the nonlinear structural behavior of concrete deep beams internally reinforced with glass fiber-reinforced polymer (GFRP) reinforcing bars and containing a web opening of various sizes and locations within the shear span. Three-dimensional (3D) numerical simulation models were developed for large-scale GFRP-reinforced concrete deep beams (300 mm × 1200 mm × 5000 mm) with a shear span-to-depth ratio (a/h) of 1.04. Predictions of the numerical models were validated against published experimental data. A parametric study was conducted to examine the effect of varying the opening size and location on the shear response. Results of the numerical analysis indicated that the strength of the deep beam models with an opening in the middle of the shear span decreased with an increase in either the opening width or height. The rate of the strength reduction caused by increasing the opening height was, however, more significant than that produced by increasing the opening width. Placing a web opening in the compression zone close to the load plate was very detrimental to the beam strength. Conversely, a negligible strength reduction was recorded when the web opening was placed in the tension side above the flexural reinforcement and away from the natural load path. Data of the parametric study were utilized to introduce simplified analytical formulas capable of predicting the shear capacity of GFRP-reinforced concrete deep beams with a web opening in the shear span. Full article

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17 pages, 4149 KiB

Open AccessArticle

Upper and Lower Bounds to Pull-Out Loading of Inclined Hooked End Steel Fibres Embedded in Concrete

by David W. A. Rees and Sadoon Abdallah

Fibers 2024, 12(8), 65; https://doi.org/10.3390/fib12080065 - 5 Aug 2024

Viewed by 993

Abstract

Steel fibre-reinforced concrete (SFRC) consists of short, hooked steel fibres that are randomly distributed and oriented within the cementitious matrix. This paper presents a new analytical load-bounding approach that captures the tensile response of misaligned fibres embedded in the matrix. The contribution of [...] Read more.

Steel fibre-reinforced concrete (SFRC) consists of short, hooked steel fibres that are randomly distributed and oriented within the cementitious matrix. This paper presents a new analytical load-bounding approach that captures the tensile response of misaligned fibres embedded in the matrix. The contribution of fibres in bridging cracks to provide the required stress transfer relies on the orientation of the fibres in the concrete. Bridging fibres aligned with a crack are less effective than those inclined to it. Therefore, understanding the pull-out behaviour of misaligned fibres is a key factor in quantifying and optimising the design of SFRC in structural applications. In the laboratory, a single-oriented fibre embedded in a solid cylinder of concrete was subjected to a pull-out test, where the axis of the tensile force is aligned with the axis of the cylinder. Based on the observed behaviour, this paper presents a new analytical bounding approach to capture the pull-out response of misaligned hooked-end steel fibres embedded in a concrete matrix. The analysis was based on a transversely isotropic failure criterion assumed for the plasticity that occurs in the cold-drawn fibre. Lower and upper bounds to the loading failure were derived from fibre pull-out and fibre fracture, respectively. The division between bounds depended upon the fibre orientation, fibre diameter and the combined strengths of the steel and concrete. Bounding predictions were drawn from ratios between a fibre’s shear strength and its transverse and axial uniaxial strengths, as found from a novel testing proposal. The two bounds were compared with new data and other experimental results published in the literature. The results showed that the region between the bounds captured the failure loads of embedded fibres with effective load-bearing orientations. A critical orientation was observed at maximum strength. The present interpretation of the plasticity occurring within off-axis, hooked-end steel fibres suggests that it is possible to optimise the strength of concrete using this method of reinforcement. Full article

(This article belongs to the Special Issue Fracture Behavior of Fiber-Reinforced Building Materials)

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35 pages, 1755 KiB

Open AccessReview

Production of Nanofibers by Electrospinning as Carriers of Agrochemical

by Julia Colín-Orozco, Elena Colín-Orozco and Ricardo Valdivia-Barrientos

Fibers 2024, 12(8), 64; https://doi.org/10.3390/fib12080064 - 5 Aug 2024

Cited by 1 | Viewed by 1715

Abstract

Agrochemicals can now be protected from harsh environments like pH, light, temperature, and more with the help of a drug-loading system. This has allowed the creation of targeted and continuous release functions for pesticides and fertilizers, as well as the precise application, reduction, [...] Read more.

Agrochemicals can now be protected from harsh environments like pH, light, temperature, and more with the help of a drug-loading system. This has allowed the creation of targeted and continuous release functions for pesticides and fertilizers, as well as the precise application, reduction, and efficiency of agrochemicals. All of these benefits have been made possible by the recent advancements in the field of nanomaterials. A simple procedure known as electrospinning can be used to create nanofibers from natural and synthetic polymers. Nanofibers have come to be recognized as one of the sustainable routes with enormous applicability in different fields. In agriculture, a promising strategy may entail plant protection and growth through the encapsulating of numerous bio-active molecules as pesticides and fertilizers for intelligent administration at the desired places. Owing to their permeability, tiny dimensions, and large surface area, nanofibers can regulate the rate at which agrochemicals are released. This slows down the rate at which the fertilizer dissolves and permits the release of coated fertilizer gradually over time, which is more effectively absorbed by plant roots, as well as the efficiency of pesticides. Thus, modern agriculture requires products and formulations that are more efficient and environmentally friendly than traditional agrochemicals. In addition to highlighting the significance and originality of using nanofibers and offering a brief explanation of the electrospinning technology, the review article’s main goal is to provide a thorough summary of the research leading to breakthroughs in the nanoencapsulation of fertilizers and pesticides. Full article

(This article belongs to the Collection Review Papers of Fibers)

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20 pages, 6538 KiB

Open AccessArticle

Experimental and Numerical Study of Carbon Fibre-Reinforced Polymer-Strengthened Reinforced Concrete Beams under Static and Impact Loads

by Mohamed H. Mussa, Azrul A. Mutalib and Hong Hao

Fibers 2024, 12(8), 63; https://doi.org/10.3390/fib12080063 - 31 Jul 2024

Cited by 1 | Viewed by 1187

Abstract

This study aims to investigate the behaviour of reinforced concrete (RC) beams strengthened by Carbon Fibre-Reinforced Polymer (CFRP) under static and impact loads. A series of RC beams were tested and categorized into four groups, namely, unstrengthened RC beams (B1), RC beams strengthened [...] Read more.

This study aims to investigate the behaviour of reinforced concrete (RC) beams strengthened by Carbon Fibre-Reinforced Polymer (CFRP) under static and impact loads. A series of RC beams were tested and categorized into four groups, namely, unstrengthened RC beams (B1), RC beams strengthened with a CFRP longitudinal strip in the tension zone (B2), RC beams wrapped with CFRP fabric (B3), and RC beams strengthened with a combination of both CFRP longitudinal strips and wraps (B4). The results show that the average load–displacement capacity of RC beam group (B4) was improved by 84.88% as compared with the unstrengthened beam (B1) under static loads. The dynamic test results demonstrated an increase in the deflection resistance of RC beam group (B4) by −57.89% as compared with unstrengthened RC beam group (B1) under identical drop weights of 1 m. In addition, a collapse failure mode was noticed in the unstrengthened beams, while minor damage was recorded mainly in the case of RC beam group (B4). Furthermore, the numerical analysis conducted using LS-DYNA software (V 971 R6.0.0) proved that the adopted numerical models can efficiently predict the behaviour of RC beams under dynamic loads, with maximum differences reaching up to −12.5% compared with the experimental test results. Full article

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20 pages, 20552 KiB

Open AccessArticle

The Effect of Carbon Nanotubes and Carbon Microfibers on the Piezoresistive and Mechanical Properties of Mortar

by Irene Kanellopoulou, Ioannis A. Kartsonakis, Athanasia I. Chrysanthopoulou and Costas A. Charitidis

Fibers 2024, 12(8), 62; https://doi.org/10.3390/fib12080062 - 31 Jul 2024

Viewed by 1434

Abstract

Sustainability, safety and service life expansion in the construction sector have gained a lot of scientific and technological interest during the last few decades. In this direction, the synthesis and characterization of smart cementitious composites with tailored properties combining mechanical integrity and self-sensing [...] Read more.

Sustainability, safety and service life expansion in the construction sector have gained a lot of scientific and technological interest during the last few decades. In this direction, the synthesis and characterization of smart cementitious composites with tailored properties combining mechanical integrity and self-sensing capabilities have been in the spotlight for quite some time now. The key property for the determination of self-sensing behavior is the electrical resistivity and, more specifically, the determination of reversible changes in the electrical resistivity with applied stress, which is known as piezoresistivity. In this study, the mechanical and piezoresistive properties of mortars reinforced with carbon nanotubes (CNTs) and carbon micro-fibers (CMFs) are determined. Silica fume and a polymer with polyalkylene glycol graft chains were used as dispersant agents for the incorporation of the CNTs and CMFs into the cement paste. The mechanical properties of the mortar composites were investigated with respect to their flexural and compressive strength. A four-probe method was used for the estimation of their piezoresistive response. The test outcomes revealed that the combination of the dispersant agents along with a low content of CNTs and CMFs by weight of cement (bwoc) results in the production of a stronger mortar with enhanced mechanical performance and durability. More specifically, there was an increase in flexural and compressive strength of up to 38% and 88%, respectively. Moreover, mortar composites loaded with 0.4% CMF bwoc and 0.05% CNTs bwoc revealed a smooth and reversible change in electrical resistivity vs. compression loading—with unloading comprising a strong indication of self-sensing behavior. This work aims to accelerate progress in the field of material development with structural sensing and electrical actuation via providing a deeper insight into the correlation among cementitious composite preparation, admixture dispersion quality, cementitious composite microstructure and mechanical and self-sensing properties. Full article

(This article belongs to the Collection Feature Papers in Fibers)

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11 pages, 1317 KiB

Open AccessArticle

Polybenzoxazine/Epoxy Copolymer Reinforced with Phosphorylated Microcrystalline Cellulose: Curing Behavior, Thermal, and Flame Retardancy Properties

by Wissam Bessa, Djalal Trache, Sid-Ali Moulai, Ahmed Fouzi Tarchoun, Amir Abdelaziz, Tuan Sherwyn Hamidon and Mohd Hazwan Hussin

Fibers 2024, 12(8), 61; https://doi.org/10.3390/fib12080061 - 31 Jul 2024

Cited by 1 | Viewed by 1247

Abstract

This study aims to explore new flame-retardant composites based on a phosphorus-functionalized cellulose derivative and epoxy/benzoxazine thermosetting resins in order to broaden the use of natural fibers in advanced applications. The study involved the phosphorylation of microcrystalline cellulose followed by its characterization through [...] Read more.

This study aims to explore new flame-retardant composites based on a phosphorus-functionalized cellulose derivative and epoxy/benzoxazine thermosetting resins in order to broaden the use of natural fibers in advanced applications. The study involved the phosphorylation of microcrystalline cellulose followed by its characterization through employing various analytical methods to corroborate the accomplishment of its functionalization. The curing behavior of composites based on the polybenzoxazine/epoxy copolymer reinforced with (1 and 5 wt.%) modified microcrystalline cellulose was hereafter considered. The thermal behavior of these composites was correspondingly investigated using thermogravimetric analysis, where improved thermal stability and the limiting oxygen index were stressed. Flame retardancy tests using the vertical burning test UL 94 and heat of combustion analysis utilizing an oxygen bomb calorimeter were also carried out to deeply examine the possible flame retardancy ability of the considered composites. Full article

(This article belongs to the Special Issue Natural Fibers for Advanced Materials: Addressing Challenges)

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21 pages, 11315 KiB

Open AccessArticle

Tension Lap Splices in Recycled-Aggregate Concrete Strengthened with Steel–Polyolefin Fibers

by Abdullah Al-Hussein, Fareed H. Majeed and Kadhim Z. Naser

Fibers 2024, 12(8), 60; https://doi.org/10.3390/fib12080060 - 24 Jul 2024

Viewed by 929

Abstract

The bond strength of tension lap splices in recycled-coarse-aggregate-reinforced concrete strengthened with hybrid (steel–polyolefin) fibers was experimentally investigated. This study was conducted with the help of twelve lap-spliced beam specimens. The replacement level of coarse natural aggregates with recycled concrete aggregate (RCA) was [...] Read more.

The bond strength of tension lap splices in recycled-coarse-aggregate-reinforced concrete strengthened with hybrid (steel–polyolefin) fibers was experimentally investigated. This study was conducted with the help of twelve lap-spliced beam specimens. The replacement level of coarse natural aggregates with recycled concrete aggregate (RCA) was 100%. The following variables were investigated: various ranges of steel–polyolefin fibers—100–0%, 75–25%, 50–50%, 25–75%, and 0–100%—in which the total volume fraction of fibers (

V_{f}

) remains constant at 1%; and two lengths of lap splices for rebars of 16 mm diameter (

d_{b}

): 10

d_{b}

and 15

d_{b}

. The test results showed that the best range of steel–polyolefin fibers that gave the highest bond strength was 50–50%. The ductility of the fiber-reinforced recycled-aggregate (FR-RA) concrete was significantly improved for all the cases of various relative ratios of steel and polyolefin fibers. The bond strength was also predicted using three empirical equations proposed by Orangun et al., Darwin et al., and Harajli. This study showed that the Harajli equation gave a more accurate estimation of the bond strength of reinforcing bars embedded in FR-RA concrete than those proposed by Orangun et al. and Darwin et al. Full article

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Fibers, Volume 12, Issue 8 (August 2024) – 11 articles

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