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Fiber Reinforced Polymers Applications as Reinforcement of Concrete Structures—Design Aspects, Tests and Analysis, 2nd Edition

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A Special Issue of Polymers (ISSN 2073-4360) belonging to the section "Polymer Applications".

Deadline for manuscript submissions: closed (30 April 2026) | Viewed by 11338

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Editors

Dr. Violetta Kytinou

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Guest Editor

Laboratory of Reinforced Concrete and Seismic Design of Structures, Civil Engineering Department, School of Engineering, Democritus University of Thrace, 67100 Xanthi, Greece
Interests: FRP; RC; reinforced concrete; SFRC; fiber reinforced concrete; beam; shear; flexure; FEM; finite elements; columns; joints; repair; strengthening; rehabilitation; RC jacket
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Prof. Dr. Constantin Chalioris

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Guest Editor

Laboratory of Reinforced Concrete and Seismic Design of Structures, Civil Engineering Department, School of Engineering, Democritus University of Thrace, 67100 Xanthi, Greece
Interests: FRP; reinforced concrete; shear; tentioned concrete; steel fiber reinforced concrete; repair; tortion; structural health monitoring; strengthening and structural rehabilitation
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Dr. Adamantis Zapris

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Guest Editor

Laboratory of Reinforced Concrete and Seismic Design of Structures, Civil Engineering Department, School of Engineering, Democritus University of Thrace, 67100 Xanthi, Greece
Interests: reinforced concrete; FRP; shear; torsion; strengthening; rehabilitation; anchors; externally bonded; NSM; NDT
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The investigation of Fiber-Reinforced Polymers (FRPs) as a main, supplementary and strengthening reinforcement in concrete structures has received significant attention in recent years. The growing need for non-corrosive and durable reinforcement has resulted in a rise in the number of FRP reinforcement manufacturers worldwide, and these have produced a wide range of materials with a variety of properties including textile composite reinforcement and FRP bars. The successful application of FRPs as a reinforcement in concrete structures is becoming more frequent as different national and international provisions and recommendations regarding the performance of construction and design with FRP have been established in recent decades. Researchers have focused on the investigation of FRP composites to create novel and efficient solutions to address the ever-increasing challenges associated with aging in infrastructure. Innovative FRP reinforcement solutions are being presented more often, and the benefits of these implementations over traditional steel reinforcing methods are being proven.

This Special Issue will highlight current developments and innovations regarding the use of FRP as a reinforcement in existing or newly constructed concrete structures. Studies involving the integration of FRPs in concrete structural members and structures, including traditional and modern experimental, numerical and analytical investigations, are welcome. The scope of this Special Issue includes, but is not limited to, the following topics: the use of FRP systems in reinforced concrete structural members, as well as the performance of FRPs (including bond performance) under monotonic and cyclic loadings and various environmental exposures.

Dr. Violetta Kytinou
Prof. Dr. Constantin Chalioris
Dr. Adamantis Zapris
Guest Editors

Manuscript Submission Information

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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-anonymized peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly 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 2700 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

fiber reinforced polymers (FRPs)
fiber-reinforced bars
concrete
reinforced concrete (RC)
repair
strengthening
mechanical properties
experimental study
bond behavior
numerical modeling
structural behavior
field applications

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Published Papers (6 papers)

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Research

26 pages, 7250 KB

Open AccessArticle

Effect of Cooling Methods on CFRP–Concrete Bond Behavior After High-Temperature Exposure: An Experimental Study

by Bu Wang, Abdulmalik Al-barawi, Zhenxun Dai, Kehang Liu, Mostafa M. A. Mostafa and Mu Ma

Polymers 2026, 18(8), 939; https://doi.org/10.3390/polym18080939 - 11 Apr 2026

Cited by 1 | Viewed by 814

Abstract

Concrete structures are highly vulnerable to fire exposure, which accelerates the degradation of mechanical properties and may lead to partial or total structural failure. Externally bonded carbon fiber-reinforced polymer (CFRP) systems are widely used for post-fire strengthening; however, the bond behavior at the interfaces between CFRP and fire-damaged concrete, particularly under different cooling conditions, is not yet fully understood. In this study, the bond behavior was investigated experimentally and theoretically. Double-lap joint tests of thirty-nine specimens were conducted, including three unheated control specimens and thirty-six specimens exposed to temperatures of 200 °C, 400 °C, and 600 °C for durations of one and two hours. Two cooling methods, natural air cooling and water cooling, were applied prior to CFRP bonding. The results indicated that bond strength increased under exposure conditions of no more than 400 °C, whereas a significant reduction was observed at 600 °C. Water cooling resulted in lower bond strength compared with air cooling, while longer exposure durations improved bond performance under certain thermal conditions. The reasons behind the phenomena were analyzed in detail. Based on the experimental results, an analytical model for predicting the bond strength at the interfaces between fire-damaged concrete and CFRP sheets was developed. The model can account for the effects of peak temperatures, exposure durations, and cooling methods, and demonstrated high predictive accuracy (R² = 0.94). The findings provide valuable insight into CFRP–concrete interaction after fire exposure and offer practical guidance for the assessment and rehabilitation of fire-damaged concrete structures. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymers Applications as Reinforcement of Concrete Structures—Design Aspects, Tests and Analysis, 2nd Edition)

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24 pages, 2985 KB

Open AccessArticle

Explainable AI-Based Analysis of Deflection in RC Beams with Longitudinal GFRP Bars in Tension Zone

by Muhammet Karabulut

Polymers 2026, 18(6), 728; https://doi.org/10.3390/polym18060728 - 17 Mar 2026

Viewed by 678

Abstract

The research gap addressed in this study is the lack of a transparent and quantitative evaluation of the governing parameters influencing deflection behavior in reinforced concrete (RC) beams reinforced with glass fiber-reinforced polymer (GFRP) bars. The objective of this study is to identify and quantify the relative importance of the key parameters controlling deflection in GFRP-reinforced RC beams, which exhibit fundamentally different behavior compared to steel-reinforced beams due to the linear-elastic response of GFRP bars until rupture. To achieve this objective, the method integrates explainable artificial intelligence (XAI) techniques, including SHapley Additive exPlanations (SHAP), Pearson correlation heatmap, scatter plot analysis, and sensitivity analysis—with experimental structural data obtained from beams with three different concrete strength classes. The main contribution of this study is the quantitative ranking and interpretation of the governing parameters affecting deflection behavior through a transparent and data-driven framework. Key parameters—including elastic modulus (Ec), compressive strength (fck), creep coefficient (φ), failure moment (Mexp), effective moment of inertia (Ieff), and applied load (P)—were evaluated. The results consistently indicate that stiffness- and capacity-related parameters dominate the deflection response. Sensitivity analysis reveals that the failure moment (Mexp) is the most influential parameter, contributing approximately 23% of the total relative influence on deflection, followed by compressive strength (fck) and cracking-related parameters. Pearson correlation heatmap and scatter plot analyses further confirm strong relationships between deflection and Ec, fck, φ, and Ieff. The proposed framework improves the interpretability of deflection prediction in GFRP-reinforced RC beams and provides a transparent basis for serviceability-based structural design and performance-oriented assessment. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymers Applications as Reinforcement of Concrete Structures—Design Aspects, Tests and Analysis, 2nd Edition)

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40 pages, 16366 KB

Open AccessArticle

Assessment of Seismic Performance and Structural Health Monitoring of a Retrofitted Reinforced Concrete Structure with Polyurethane-Based Interventions and Vertical Greenery Systems

by Theodoros Rousakis, Vachan Vanian, Martha Lappa, Adamantis G. Zapris, Ioannis P. Xynopoulos, Maristella E. Voutetaki, Stefanos Kellis, George M. Sapidis, Maria C. Naoum, Nikos A. Papadopoulos, Violetta K. Kytinou, Martha Karabini, Athanasia Thomoglou and Constantin E. Chalioris

Polymers 2025, 17(23), 3104; https://doi.org/10.3390/polym17233104 - 22 Nov 2025

Cited by 4 | Viewed by 1065

Abstract

This study examines Phase B of the GREENERGY project focusing on the seismic performance and structural health monitoring of a renovated single-story RC frame with brick masonry infills that received significant strategic structural interventions. The columns were confined with basalt fiber ropes (FR, 4 mm thickness, two layers) in critical regions, the vertical interfaces between infill and concrete were filled with polyurethane PM forming PUFJ (PolyUrethane Flexible Joints), and glass fiber mesh embedded in polyurethane PS was applied as FRPU (Fiber Reinforced PolyUrethane) jacket on the infills. Further, greenery renovations included the attachment of five double-stack concrete planters (each weighing 153 kg) with different support-anchoring configurations and of eight steel frame constructions (40 kg/m²) simulating vertical living walls (VLW) with eight different connection methods. The specimen was subjected to progressively increasing earthquake excitation based on the Thessaloniki 1978 earthquake record with peak ground acceleration ranging from EQ0.07 g to EQ1.40 g. Comprehensive instrumentation included twelve accelerometers, eight draw wire sensors, twenty-two strain gauges, and a network of sixty-one PZTs utilizing the EMI (Electromechanical Impedance) technique. Results demonstrated that the structure sustained extremely high displacement drift levels of 2.62% at EQ1.40 g while maintaining structural integrity and avoiding collapse. The PUFJ and FRPU systems maintained their integrity throughout all excitations, with limited FRPU fracture only locally at extreme crushing zones of two opposite bottom bricks. Columns’ longitudinal reinforcement entered yielding and strain hardening at top and bottom critical regions provided the FR confinement. VLW frames exhibited equally remarkably resilient performance, avoiding collapse despite local anchor degradation in some investigated cases. The planter performance varied significantly, yet avoiding overturning in all cases. Steel rod anchored planter demonstrated superior performance while simply supported configurations on polyurethane pads exhibited significant rocking and base sliding displacement of ±4 cm at maximum intensity. PZT structural health monitoring (SHM) sensors successfully tracked damage progression. RMSD indices of PZT recordings provided quantifiable damage assessment. Elevated RMSD values corresponded well to visually observed local damages while lower RMSD values in columns 1 and 2 compared with columns 3 and 4 suggested that basalt rope wrapping together with PUFJ and FRPU jacketed infills in two directions could restrict concrete core disintegration more effectively. The experiments validate the advanced structural interventions and vertical forest renovations, ensuring human life protection during successive extreme EQ excitations of deficient existing building stock. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymers Applications as Reinforcement of Concrete Structures—Design Aspects, Tests and Analysis, 2nd Edition)

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24 pages, 49414 KB

Open AccessArticle

Geopolymer Concrete Physical and Mechanical Properties on a Combined Binder Reinforced with Dispersed Polypropylene Fiber

by Sergei A. Stel’makh, Alexey N. Beskopylny, Evgenii M. Shcherban, Diana Elshaeva, Andrei Chernilnik, Denis Kuimov, Alexandr Evtushenko and Samson Oganesyan

Polymers 2025, 17(12), 1710; https://doi.org/10.3390/polym17121710 - 19 Jun 2025

Cited by 11 | Viewed by 3643

Abstract

Geopolymer concrete is a promising construction material that acts as an alternative to cement concrete. Unlike traditional cement concrete, geopolymers are environmentally friendly materials, the production of which does not involve significant carbon dioxide emissions. However, the structure formation and properties of geopolymers significantly depend on raw materials and are insufficiently studied. The aim of the study is to select the optimal combination of ground granulated blast furnace slag (GGBS) and fly ash (FA) as a binder and the optimal content of polypropylene fiber to create a sustainable, environmentally friendly and effective geopolymer concrete. To study various compositions of geopolymer binders selected by combining GGBS and FA, experimental geopolymer concrete mixtures and samples from them were manufactured. The density and slump of fresh concrete and the density and compressive strength of hardened composites were studied as mechanical characteristics. The microstructure of the geopolymer matrix was analyzed using optical and scanning electron microscopes. The most rational combination of GGBS 80% and FA 20% was determined, which allows obtaining a composite with the highest compressive strength of up to 31.5 MPa. A dispersion reinforcement study revealed that 0.8% polypropylene fiber (PF) is optimal. This allowed us to increase the compressive strength by 7.3% and the flexural strength by 48.7%. The geopolymer fiber concrete obtained in this study is a sustainable and environmentally friendly alternative composite material and has sufficient performance properties for its use as an alternative to cement concrete. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymers Applications as Reinforcement of Concrete Structures—Design Aspects, Tests and Analysis, 2nd Edition)

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27 pages, 5828 KB

Open AccessArticle

Flexural Behavior of Thin Concrete Slabs Reinforced with Surface Embossed Grid-Type Carbon-Fiber Composites

by Kyung-Min Kim, Sung-Woo Park and Kyung-Jae Min

Polymers 2025, 17(3), 411; https://doi.org/10.3390/polym17030411 - 4 Feb 2025

Cited by 4 | Viewed by 1816

Abstract

Fiber-reinforced polymers (FRPs) are being increasingly used to replace rebars as reinforcements for concrete. In this study, the flexural behavior of one-way concrete slabs reinforced with a grid-type carbon FRP (CFRP) (carbon grid), in the form of strands with embossed surfaces, was experimentally investigated. The experimental variables included the effective depth, number of carbon grid layers, and concrete compressive strength. The results exhibit that the surface embossing of the CFRP strands effectively improves their bonding with concrete based on the crack formation pattern. Concrete specimens reinforced with carbon grids exhibited an increased maximum load and stiffness as the effective depth, number of carbon grid layers, and concrete compressive strength increased. Among the experimental variables, the effective depth exhibited the greatest influence on the flexural behavior of the carbon-grid-reinforced concrete specimen. Furthermore, the ratios of the experimental to calculated flexural strength values for all carbon-grid-reinforced concrete specimens ranged from 0.74 to 1.22. Based on the results, a trilinear load–deflection curve was proposed to simulate the flexural behavior of carbon-grid-reinforced concrete members, considering the bond property between the concrete and the carbon grid. The proposed trilinear load–deflection curve reasonably simulated the flexural behavior of the specimens reinforced with carbon grids. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymers Applications as Reinforcement of Concrete Structures—Design Aspects, Tests and Analysis, 2nd Edition)

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13 pages, 5830 KB

Open AccessArticle

Shear Capacity of Hollow High-Performance Concrete Beams with Cross-Wound Carbon Fiber-Reinforced Polymer Reinforcement

by Tomáš Vlach, Jakub Řepka, Jakub Hájek, Jan Pošta, Richard Fürst and Petr Hájek

Polymers 2025, 17(1), 75; https://doi.org/10.3390/polym17010075 - 30 Dec 2024

Viewed by 2201

Abstract

This paper introduces cross-wound CFRP shear reinforcement of hollow HPC beams. The CFRP reinforcement was manufactured in the form of a square tubular mesh from carbon rovings oriented at ±45° from the longitudinal axis. The shear reinforcement was made in two variants from carbon yarns with linear densities of 1600 and 3700 tex. Tensile reinforcement made of BFRP bars was positioned directly around the hollow core and was used as a platform for manual winding of the shear reinforcement. The hollow beams were subjected to a three-point bending test with four configurations of the tensile BFRP reinforcement for better evaluation of the effect of the shear reinforcement under different conditions. The 1600 tex shear reinforcement increased the ultimate flexural strength by at least 89% compared to specimens without any shear reinforcement. The 3700 tex shear reinforcement yielded slightly better results in most cases but was not utilized to its full shear capacity as these specimens always failed in shear due to the delamination of the concrete matrix from the shear reinforcement. There was too much reinforcement in the beam cross-section. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymers Applications as Reinforcement of Concrete Structures—Design Aspects, Tests and Analysis, 2nd Edition)

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