Use of Fibers in Organic and Inorganic Composite Solutions for Structural Strengthening: Advances, Applications, and Challenges

A special issue of Fibers (ISSN 2079-6439).

Deadline for manuscript submissions: 15 June 2025 | Viewed by 8874

Special Issue Editor


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Guest Editor
Department of Civil Engineering, University of Calabria, Via P. Bucci, 87036 Arcavacata di Rende, CS, Italy
Interests: cementitious; geopolymer; mortar; concrete; construction engineering; civil engineering materials; building materials
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Special Issue Information

Dear Colleagues,

This Special Issue aims to provide a platform for researchers, engineers, and practitioners to share their latest findings, experiences, and challenges in using composites to strengthen existing structures. Composites, as an innovative solution, have gained increasing attention due to their high strength, light weight, and corrosion resistance.

Fibre-reinforced polymer (FRP) composites have been used for many years in the field of structural strengthening. FRP composites consist of high-strength fibres, such as carbon, glass, or aramid fibres, embedded in a polymer matrix. They are a popular choice for structural strengthening due to their high strength, light weight, and durability. One of the main advantages of FRP composites is their excellent resistance to corrosion. They are also highly durable and can withstand exposure to harsh environments, making them an ideal solution for strengthening structures that are exposed to chemicals, moisture, or saltwater. FRP composites are also easy to install and require minimal disruption to the existing structure. They can be bonded to the surface of the structure using adhesives or mechanical fasteners, which can be installed quickly and easily, minimizing downtime and inconvenience. FRP composites have been successfully used in a variety of structural strengthening applications, including the reinforcement of concrete and masonry walls, beams, columns, and slabs. They can also be used to increase the seismic performance of structures, as they have high ductility and energy dissipation capacity. However, the design and implementation of FRP composites require careful consideration of various factors, including the type of fibre used, the properties of the polymer matrix, and the bonding between the composite and the existing structure. Therefore, it is important to follow established design guidelines and standards to ensure the effective and safe use of FRP composites in structural strengthening. In summary, FRP composites are a proven and reliable solution for the strengthening of existing structures, offering many advantages over traditional materials. With ongoing research and development, FRP composites are expected to continue to play a critical role in the field of structural strengthening.

At present, fibre-reinforced cementitious matrix (FRCM) composites are a relatively new type of composite material that is gaining popularity in the field of structural strengthening. FRCM composites consist of a cement-based matrix reinforced with high-strength fibres such as carbon, glass, or basalt fibres. The use of FRCM composites has several advantages over other, traditional strengthening materials such as steel or FRP composites. One of the main advantages of FRCM composites is their high resistance to corrosion, which makes them an ideal solution for strengthening concrete and masonry structures in harsh environments. They are also highly durable and can withstand extreme temperatures, making them suitable for use in areas prone to high heat or cold. FRCM composites are also more environmentally friendly than traditional strengthening materials. They can be made from sustainable materials, such as basalt fibres, which are extracted from volcanic rock. Additionally, FRCM composites are easily recycled and reused. FRCM composites have been successfully used in a variety of structural strengthening applications, including the reinforcement of walls, beams, columns, and slabs. They can also be used to increase the seismic performance of structures, as they have high ductility and energy dissipation capacity. However, the design and implementation of FRCM composites require careful consideration of various factors, including the type of fibre used, the properties of the cement matrix, and the bonding between the composite and the existing structure. Therefore, further research and development are needed to establish design guidelines and standards for the use of FRCM composites in structural strengthening. Overall, FRCM composites represent a promising solution for the strengthening of existing structures and are expected to gain more attention and be adopted more in the future.

This Special Issue aims to cover a wide range of topics related to the use of composites, including but not limited to: material properties, design criteria, modelling and simulation, experimental studies, case studies, and implementation strategies. The goal is to encourage authors to contribute high-quality original research papers, reviews, and perspectives that will advance the knowledge, innovation, and practical application of composites in structural strengthening.

Dr. Alessio Cascardi
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fibers is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • composite materials
  • structural strengthening
  • existing structures
  • FRCM composites
  • FRP composites
  • high-strength fibers
  • durability
  • corrosion resistance
  • design criteria
  • implementation strategies
  • seismic retrofitting
  • performance evaluation
  • modeling and simulation
  • experimental studies
  • sustainable materials

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Published Papers (4 papers)

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Research

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14 pages, 18487 KiB  
Article
Synthesis of Carbon Nanofibers from Lignin Using Nickel for Supercapacitor Applications
by Meruyert Nazhipkyzy, Anar B. Maltay and Tulegen M. Seilkhanov
Fibers 2024, 12(10), 87; https://doi.org/10.3390/fib12100087 - 9 Oct 2024
Viewed by 876
Abstract
Carbon fiber is known for being lightweight and adaptable, making it useful for various current and future applications. However, to broaden the use of carbon fibers beyond niche applications, production costs must be lowered. A potential approach to achieving this is by using [...] Read more.
Carbon fiber is known for being lightweight and adaptable, making it useful for various current and future applications. However, to broaden the use of carbon fibers beyond niche applications, production costs must be lowered. A potential approach to achieving this is by using more affordable raw materials, such as lignin, which is renewable, cost-effective, and widely available compared with the materials commonly used in industry today. This study explores the impact of metal ions on the quality of carbon fiber derived from lignin, focusing on its mechanical and electrochemical properties and morphology. The effect of a specific metal ion (Ni(NO3)2·6H2O) was examined by incorporating it into the spinning solution. The carbonization stage of the fiber was conducted at temperatures of 800, 900, and 1000 °C in an inert atmosphere. Scanning electron microscopy (SEM) analysis showed no defects or damage in any of the fibers. Therefore, it was concluded that moderate concentrations of Ni2+ ions in the fibers do not influence the stabilization or carbonization processes, thus leaving the mechanical properties of the final carbon fiber unchanged. These carbon nanofibers were also tested as a sustainable alternative to the non-renewable materials used in electrodes for energy storage and conversion devices, such as supercapacitors. Electrochemical performance was assessed in a 6 M KOH solution using a two-electrode cell configuration. Galvanostatic charge–discharge tests were performed at different current densities (0.1, 0.25, 0.5, 1.0, and 2.0 A g−1). The specific capacitance of the carbon nanofibers was determined from CVA data at various scan rates: 5, 10, 20, 40, 80, and 160 mV s−1. The results indicated that at 0.1 A g−1, the capacitance reached 108 F g−1, and at a scan rate of 5 mV s−1, it was 91 F g−1. The innovation of this work lies in its use of lignin, a renewable and widely available material, to produce carbon fibers, reducing costs compared with traditional methods. Additionally, the incorporation of nickel ions enhances the electrochemical properties of the fibers for supercapacitor applications without compromising their mechanical performance. Full article
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17 pages, 5089 KiB  
Article
Experimental Study on Shear Performance of Concrete Beams Reinforced with Externally Unbonded Prestressed CFRP Tendons
by Hetao Qi, Haozhe Jiang, Bing Wang and Ping Zhuge
Fibers 2024, 12(3), 23; https://doi.org/10.3390/fib12030023 - 29 Feb 2024
Viewed by 1736
Abstract
To investigate the reinforcing effect of externally prestressed carbon-fiber-reinforced polymer (CFRP) tendons on the shear performance of reinforced concrete beams, a set of model tests was designed. Static load comparative tests were conducted on one original beam and four reinforced beams to experimentally [...] Read more.
To investigate the reinforcing effect of externally prestressed carbon-fiber-reinforced polymer (CFRP) tendons on the shear performance of reinforced concrete beams, a set of model tests was designed. Static load comparative tests were conducted on one original beam and four reinforced beams to experimentally investigate the impacts of the prestress level and damage in the shear zone on the shear reinforcement effect and analyze the reinforcement mechanism of CFRP tendons. The results show that in the beams reinforced with CFRP, the CFRP tendons could work collaboratively with the stirrups to reduce the strain on the stirrups; the increasing rate in the yield load was 28–70%. After the stirrups yielded, the CFRP tendons did not yet reach their ultimate tensile strength and could still withstand increased shear forces, resulting in an increasing rate of the ultimate load for the reinforced beams with a CFRP content of 56–78%. The enhancements in both the yield load and the ultimate load were positively correlated with the level of prestress in the CFRP tendons. This reinforcement technique efficiently restricts the growth and delays the first appearance of diagonal cracks. The prestress can close the pre-existing diagonal cracks and provide a reserve of shear capacity for the beams. The initial damage in the shear zone decreases the initial shear stiffness and increases the width of the initial diagonal cracks. However, this effect gradually diminishes as the load increases and does not significantly impact the shear capacity. Prestressing can significantly improve the strength utilization rate of the CFRP reinforcement when the reinforced beams fail. The deformation of the CFRP tendon is directly related to the shear deformation. By combining this relationship with the truss–arch model, the shear capacity for the reinforced beam can be predicted. The predicted results exhibit an error of less than 10% when compared to the test results, offering valuable design guidance for reinforced engineering composites. Full article
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17 pages, 4220 KiB  
Article
Innovative and Sustainable Composite Material for the Seismic and Energetic Upgrade of Historic Masonry Buildings
by Dora Pugliese, Valerio Alecci, Rosa Romano, Gianfranco Stipo, Mario De Stefano and Antonio Nanni
Fibers 2023, 11(9), 76; https://doi.org/10.3390/fib11090076 - 14 Sep 2023
Cited by 3 | Viewed by 1975
Abstract
Usually, energy and structural improvements for historic masonry buildings are addressed separately using distinct methods and protocols. This paper covers an integrated assessment of new composite materials to reduce the seismic vulnerability of historic masonry buildings while complying with sustainable conservation requirements, emissions’ [...] Read more.
Usually, energy and structural improvements for historic masonry buildings are addressed separately using distinct methods and protocols. This paper covers an integrated assessment of new composite materials to reduce the seismic vulnerability of historic masonry buildings while complying with sustainable conservation requirements, emissions’ reduction, and energy savings. Firstly, this study focused on selecting suitable thermal mortars that could serve as the base material for the innovative composite. Subsequently, the mechanical characteristics of these mortars were examined by subjecting them to compressive and three-point bending tests. Dynamic thermo-hygrometric simulations were conducted using commercially available software to check the energy performance of the composite material when used on walls of existing masonry buildings. The thermal mortar that exhibited the most favorable mechanical and thermal properties was subsequently reinforced with a basalt fabric. A composite sample was assembled and subjected to direct tensile testing to determine its stress–strain behavior. Full article
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Review

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25 pages, 3449 KiB  
Review
Characterization Specifications for FRP Pultruded Materials: From Constituents to Pultruded Profiles
by Ehsan Harati Khalilabad, Alvaro Ruiz Emparanza, Francisco De Caso, Hossein Roghani, Nima Khodadadi and Antonio Nanni
Fibers 2023, 11(11), 93; https://doi.org/10.3390/fib11110093 - 2 Nov 2023
Cited by 5 | Viewed by 3295
Abstract
Pultruded FRP composites have emerged as a promising alternative to traditional materials like concrete, steel, and timber, especially in corrosive environmental conditions. However, the unique properties of these composites necessitate careful consideration during their implementation, as they differ significantly from conventional materials. Proper [...] Read more.
Pultruded FRP composites have emerged as a promising alternative to traditional materials like concrete, steel, and timber, especially in corrosive environmental conditions. However, the unique properties of these composites necessitate careful consideration during their implementation, as they differ significantly from conventional materials. Proper testing and characterization of FRP pultruded materials is key for their efficient and safe implementation. However, the existing specifications are not unified, resulting in ambiguity among stakeholders. This paper aims to bridge this gap by thoroughly reviewing current destructive and non-destructive test methods for FRP pultruded materials, specifications, quality control, and health monitoring of FRP structures. Each subsection is further divided into subtopics, providing a comprehensive overview of the subject. By shedding light on these crucial aspects, this article aims to accelerate the adoption and utilization of these innovative materials in practical applications. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Restoration of Continuous RC Beams Pre-Damaged by Corrosion Using FRCM Composites
Authors: Youssef Elmezayen; Tamer El-Maaddawy
Affiliation: Department of Civil and Environmental Engineering, College of Engineering, United Arab Emirates University

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