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Masonry and Concrete Members Strengthened with Fibre-Reinforced Composite Materials: Research Advances

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Construction and Building Materials".

Deadline for manuscript submissions: 10 January 2025 | Viewed by 11426

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Special Issue Editor

Dr. Annalisa Napoli

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Guest Editor

Department of Civil Engineering, University of Salerno, Via Giovanni Paolo II, 132, 84084 Fisciano, SA, Italy
Interests: reinforced concrete structures; masonry structures; seismic performance assessment; seismic retrofit; repairing and strengthening with FRP; sustainable materials; laboratory testing; modelling

Special Issue Information

Dear Colleagues,

The use of fiber reinforced polymer (FRP) is being an increasingly attractive solution for the repair and external strengthening of reinforced concrete (RC) and masonry structures thanks to several benefits, such as: high strength-to-weight ratio, good durability, and possibility of being ad hoc engineered to meet the targeted structural requirements. Since the first applications dated from the 1990s, the number of theoretical and experimental studies has significantly worldwide increased through years to lead to the publication of well-established international guidelines, such as ACI 440.2R and CNR-DT 200.

Recently, the fabric reinforced cementitious matrix (FRCM) has been applied as a “green” alternative solution to FRP materials; it is particularly useful to overcome some drawbacks related to the use of epoxy matrices, such as: the poor composite-substrate compatibility, the low permeability of the strengthened surface, and the difficulties in removing the FRP sheets without damaging the substrate. This last aspect represents an application limit for buildings recognized as culturally important, for which conservation and preservation are mandatory criteria and, therefore, structural engineers look for retrofitting techniques that reduce the invasiveness and, at the same time, assure a satisfactory level of reversibility (or at least removability). Despite the reduced amount of data and information available for the development of reliable design formulae, preliminary international guidelines for the strengthening of structural members with FRCMs are also now available, such as ACI 549.4R (for concrete applications), ACI 549.6R (for masonry applications), and CNR-DT 215.

In terms of advancing knowledge on repairing and strengthening of masonry and RC structures with FRP and FRCM materials, this Special Issue aims at providing the scientific community with a collection of high-quality and peer-reviewed papers addressing different aspects of the structural behavior, spanning from the material mechanical characterization to the analysis of material efficiency in several applications, such as (but not limited to): flexural and/or shear strengthening, confinement and RC beam-column joints’ strengthening. Both experimental and theoretical investigations are welcome.

Dr. Annalisa Napoli
Guest Editor

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Keywords

fiber reinforced polymer (FRP)
fabric-reinforced cementitious matrix (FRCM)
sustainable materials
concrete structures
masonry structures
repairing
external strengthening
seismic retrofitting
material characterization
experimental investigation
modeling

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Published Papers (7 papers)

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Research

19 pages, 7422 KiB

Open AccessArticle

Shear Performance of RC Beams Strengthened with High-Performance Fibre-Reinforced Concrete (HPFRC) Under Static and Fatigue Loading

by Xiangsheng Liu and Georgia E. Thermou

Materials 2024, 17(21), 5227; https://doi.org/10.3390/ma17215227 - 27 Oct 2024

Viewed by 704

Abstract

This study experimentally assessed the shear performance of reinforced concrete (RC) beams strengthened with U-shaped High-Performance Fibre-Reinforced Concrete (HPFRC) under static and fatigue loading. Key parameters included HPFRC jacket thickness and beam shear span–depth (a/d) ratio. Five beams were tested under static loads to determine ultimate shear strengths, followed by fatigue tests on identical beams at 30–70% of ultimate shear strengths at 4 Hz. In static loading experiments, all the HPFRC jacketing proved effective, increasing the shear strength of RC beams by 95% to 130%. Although the strengthening system did not change the failure mode of the beams, the strengthened beams exhibited pseudo-ductile behaviour. As the a/d increased, the shear enhancement capability of the HPFRC jackets decreased. In fatigue loading experiments, all the HPFRC systems improved the fatigue life of RC beams. Specifically, in beams with an a/d ratio of 2.0, the fatigue life was extended from 75 cycles to a maximum of 951 cycles, while in beams with an a/d ratio of 3.5, it increased from 12,525 cycles to 48,786 cycles. In addition, a predictive model has been developed for the fatigue life of HPFRC/UHPFRC shear-strengthened beams, utilising the maximum fatigue load and the design’s ultimate shear strength under static loading conditions. Full article

(This article belongs to the Special Issue Masonry and Concrete Members Strengthened with Fibre-Reinforced Composite Materials: Research Advances)

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17 pages, 9526 KiB

Open AccessArticle

Effect of Basalt/Steel Individual and Hybrid Fiber on Mechanical Properties and Microstructure of UHPC

by Yongfan Gong, Qian Hua, Zhengguang Wu, Yahui Yu, Aihong Kang, Xiao Chen and Hu Dong

Materials 2024, 17(13), 3299; https://doi.org/10.3390/ma17133299 - 4 Jul 2024

Cited by 2 | Viewed by 921

Abstract

Ultra High-Performance Concrete (UHPC) is a cement-based composite material with great strength and durability. Fibers can effectively increase the ductility, strength, and fracture energy of UHPC. This work describes the impacts of individual or hybrid doping of basalt fiber (BF) and steel fiber (SF) on the mechanical properties and microstructure of UHPC. We found that under individual doping, the effect of BF on fluidity was stronger than that of SF. Moreover, the compressive, flexural, and splitting tensile strength of UHPC first increased and then decreased with increasing BF dosage. The optimal dosage of BF was 1%. At a low content of fiber, UHPC reinforced by BF demonstrated greater flexural strength than that reinforced by SF. SF significantly improved the toughness of UHPC. However, a high SF dosage did not increase the strength of UHPC and reduced the splitting tensile strength. Secondly, under hybrid doping, BF was partially substituted for SF to improve the mechanical properties of hybrid fiber UHPC. Consequently, when the BF replacement rate increased, the compressive strength of UHPC gradually decreased; on the other hand, there was an initial increase in the fracture energy, splitting tensile strength, and flexural strength. The ideal mixture was 0.5% BF + 1.5% SF. The fluidity of UHPC with 1.5% BF + 0.5% SF became the lowest with a constant total volume of 2%. The microstructure of hydration products in the hybrid fiber UHPC became denser, whereas the interface of the fiber matrix improved. Full article

(This article belongs to the Special Issue Masonry and Concrete Members Strengthened with Fibre-Reinforced Composite Materials: Research Advances)

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28 pages, 4718 KiB

Open AccessArticle

FRCM Confinement of Masonry: Strain Model Assessment and New Proposals

by Annalisa Napoli and Roberto Realfonzo

Materials 2024, 17(5), 1159; https://doi.org/10.3390/ma17051159 - 1 Mar 2024

Viewed by 874

Abstract

One of the main limitations to the use of fabric-reinforced cementitious matrix (FRCM) composites for the external confinement of masonry is the lack of accurate formulas for estimating the compressive strength and ultimate strain of confined members. With the aim of providing a contribution on the topic, the authors have been carrying out studies on the FRCM-confined masonry for some time and, in a recent study, they proposed some formulations for the prediction of compressive strength. In continuity to that work, an analytical study on the ultimate strain of FRCM-confined masonry is presented in this paper, and preliminary models were derived by considering a wide experimental database compiled from the technical literature. The accuracy of the found relationships was examined based on a comparison with the few formulas published in the literature or reported in international guidelines. To this purpose, it is worth highlighting that the current Italian Guidelines CNR-DT 215/2018 do not provide indications about the estimation of the ultimate strain of FRCM-confined masonry, and the study proposed here attempts to provide a contribution to the mentioned document. Full article

(This article belongs to the Special Issue Masonry and Concrete Members Strengthened with Fibre-Reinforced Composite Materials: Research Advances)

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19 pages, 6502 KiB

Open AccessArticle

Experimental Analysis of the Mechanical Response of Masonry Columns Partially Confined with PBO FRCM (Fabric Reinforced Cementitious Mortar) Composites

by Luciano Ombres, Francesco Campolongo, Marielda Guglielmi and Salvatore Verre

Materials 2023, 16(13), 4812; https://doi.org/10.3390/ma16134812 - 4 Jul 2023

Cited by 1 | Viewed by 1024

Abstract

An experimental investigation on partially PBO (short of Polyparaphenylenebenzobisthiazole) FRCM (Fiber Reinforced Cementitious Mortar) confined clay brick masonry columns has been conducted. Ten small-scale specimens measuring 445 mm high with a square cross-section of the 250 mm side have been tested under monotonic axial loading until collapse. Two columns were unconfined, while the remaining ones were confined with single-layer PBO FRCM jackets varying the geometric configuration along their height. The vertical spacing ratio sf’/sf, being sf’ and sf the center-to-center and the net spacings between two consecutive jackets, respectively, was considered as the key parameter of the confinement configuration. The failure modes, stress–strain curves and peak axial stress and strain values are reported. The experimental results have been compared to the predictions of models found in the Italian guidelines CNR DT 215/2018 and the American ACI 549-R20 standards. The main aspects analyzed involved (i) the evaluation of the effectiveness of partial confinement on the mechanical response of columns, (ii) the definition of the mechanical and geometrical parameters that influence the structural response of partially confined columns, and (iii) the development of appropriate analytical models for the prediction of the resisting capacity of masonry columns partially confined with PBO FRCM. Full article

(This article belongs to the Special Issue Masonry and Concrete Members Strengthened with Fibre-Reinforced Composite Materials: Research Advances)

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18 pages, 18659 KiB

Open AccessArticle

Seismic Tests of Full Scale Reinforced Concrete T Joints with Light External Continuous Composite Rope Strengthening—Joint Deterioration and Failure Assessment

by Martha Karabini, Theodoros Rousakis, Emmanouil Golias and Chris Karayannis

Materials 2023, 16(7), 2718; https://doi.org/10.3390/ma16072718 - 29 Mar 2023

Cited by 9 | Viewed by 1627

Abstract

Beam–column connections (joints) are one of the most critical elements which govern the overall seismic behavior of reinforced concrete (RC) structures. Especially in buildings designed according to previous generation codes, joints are often encountered with insufficient transverse reinforcement detailing, or even with no stirrups, leading to brittle failure. Therefore, externally bonded composite materials may be applied, due to the ease of application, low specific weight and corrosion-free properties. The present work assesses the seismic performance of insufficiently reinforced large-scale T beam–column connections with large and heavily reinforced beams. The joints receive externally bonded NSM X-shaped composite ropes with improved versatile continuous detailing. The columns are subjected to low normalized axial load, while the free end of the beam is subjected to transverse displacement reversals. Different failure criteria are investigated, based on the beam free-end transverse load, as well as on the joint region shear deformations, to critically assess the structural performance of the subsystem. The experimental investigation concludes that cyclic loading has a detrimental effect on the performance of the joint. Absence of an internal steel stirrup leads to earlier deterioration of the joint. The unstrengthened specimens disintegrate at 2% drift, which corresponds to 34 mm beam-end displacement, and shear deformation of the joint equal to 30 × 10⁻⁴ rad. The composite strengthening, increases the structural performance of the joint up to 4% drift which corresponds to 68 mm of beam-end displacement and shear deformation of the joint equal to 10 × 10⁻⁴ rad. The investigated cases of inadequate existing transverse reinforcement in the joint and light external FRP strengthening provide a unique insight into the required retrofits to achieve different levels of post-yielding displacement ductility under seismic loading at 2%, 3% and 4% drift. It allows for future analytical refinements toward reliable redesign analytical models. Full article

(This article belongs to the Special Issue Masonry and Concrete Members Strengthened with Fibre-Reinforced Composite Materials: Research Advances)

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20 pages, 9325 KiB

Open AccessArticle

Behavior Under Repeated Loading of RC Beams Externally Strengthened in Flexure with SRG Systems

by Francesco Bencardino and Mattia Nisticò

Materials 2023, 16(4), 1510; https://doi.org/10.3390/ma16041510 - 10 Feb 2023

Cited by 1 | Viewed by 2125

Abstract

Steel-reinforced grout (SRG) systems are effective methods for the flexural strengthening of reinforced concrete (RC) beams. In this study, the effect of a limited number of repeated loads on the structural response and debonding evolution of strengthened beams was experimentally investigated. The number of available research concerning the cyclic behavior of SRG-strengthened members is quite limited and this research attempts to cover this knowledge. A total of ten full-scale RC beam specimens were tested under a four-point bending scheme. The effectiveness of the traditional externally bonded (EB) strengthening technique was compared with a promising innovative technique referred to as inhibiting/repairing/strengthening (IRS). The test variables included the use of two SRG configurations using high and low steel strip density. The experimental results revealed that the performance of the beams was largely dependent on the spacing of the steel strands within the reinforcing strip. Under repeated loading, the debonding of the external system takes place when steel fiber with high mass per unit of area was used. By increasing the matrix impregnation of the steel strip, the composite system was not affected by debonding. Further, the efficiency in terms of flexure enhancement, local and global ductility performance and energy dissipation of the beams are also discussed. Full article

(This article belongs to the Special Issue Masonry and Concrete Members Strengthened with Fibre-Reinforced Composite Materials: Research Advances)

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32 pages, 3409 KiB

Open AccessArticle

Optimisation of Embodied Carbon and Compressive Strength in Low Carbon Concrete

by Promise D. Nukah, Samuel J. Abbey, Colin A. Booth and Ghassan Nounu

Materials 2022, 15(23), 8673; https://doi.org/10.3390/ma15238673 - 5 Dec 2022

Cited by 4 | Viewed by 3016

Abstract

To improve the prediction of compressive strength and embodied carbon of low carbon concrete using a program algorithm developed in MATLAB, 84 datasets of concrete mix raw materials were used. The influence of water, silica fume and ground granular base slag was found to have a significant impact on the extent of low carbon concrete behaviour in terms of compressive strength and embodied carbon. While the concrete compressive strength for normal concrete increases with reducing water content, it is observed that the low carbon concrete using lightweight aggregate material increases in compressive strength with an increase in embodied carbon. From the result of the analysis, a function was developed that was able to predict the associated embodied carbon of a concrete mix for a given water-to-cement ratio. The use of an alkaline solution is observed to increase the compressive strength of low carbon concrete when used in combination with ground granular base slag and silica fume. It is further shown that ground granular base slag contributes significantly to an increase in the compressive strength of Low carbon concrete when compared with pulverised fly ash. The optimised mix design program resulted in a 26% reduction in embodied carbon and an R² value of 0.9 between the measured compressive strength and the optimised compressive strength. Full article

(This article belongs to the Special Issue Masonry and Concrete Members Strengthened with Fibre-Reinforced Composite Materials: Research Advances)

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