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This paper presents the pull-out bonding behaviour and mechanical performance of recycled carbon fibre (rCF) reinforced concrete based on the recent investigation of fibre reinforced concrete (FRC) with rCF recovered from pyrolysis. Single fibre pull-out tests have been carried out to identify the apparent interfacial shear strength of different types of rCF and virgin carbon fibre (vCF) to identify the fibre matrix connection. Furthermore, a series of tests have been carried out to identify the workability, compressive strength and tensile strength of FRC. Besides rCF, also vCF and steel fibre were used for fabrication of FRC test specimens. rCF have shown the same adhesion behaviour and strength like vCF. Furthermore, the use of unsized or acrylate-based sized rCF creates an adhesion between fibre and matrix material. During the pull-out tests, the failure does not occur as an adhesive crack between fibre and cement matrix, but as a cohesive crack in the cement matrix. The mechanical performance of FRC with rCF was compared with mortar and FRC with vCF and steel fibres. The results of compressive test conducted for FRC with vCF and rCF indicated that the influence of vCF and rCF on the compressive strength of FRC was insignificant. On the other hand, the results of tensile test conducted for FRC with vCF and rCF indicated that the tensile strength of FRC with rCF was at least 14.9% greater than that of FRC with vCF. [ABSTRACT FROM AUTHOR]

Abstract This study explores the mechanical and durability properties of Plastic-Fibre Reinforced Concrete, incorporating hand-shredded plastic fibers sourced from polyethylene bags and PET bottles. Evaluations, including compressive and split tensile strength tests, were conducted on M40 grade mixes containing plastic fibers and 100% treated Construction and Demolition Waste (CDW), comparing them with conventional concrete. The results demonstrate a significant enhancement in strength properties with the addition of 0.25%, 0.5%, 0.75%, and 1% plastic-fibres, alongside the complete replacement of coarse aggregate with CDW, particularly noticeable at both 7 and 28-day curing ages. Although higher fiber dosages led to a slight reduction in compressive by 7% at the optimum percentage of 0.25% of PE and 0.5% of PET, the flexural strengths and split tensile strength exhibited a proportional increase of 11.7% and 18%. Surface analysis via Scanning Electron Microscopy (SEM) and elemental composition determination using Energy Dispersive Spectroscopy (EDS) revealed minimal fiber damage post-exposure, confirming its efficiency and contribution to higher strength and reduced weight loss in optimum mix. This novel approach combines manually recycled plastic waste as fibers with treated CDW, enhancing concrete properties while promoting sustainability. Sustainability analysis indicates that utilizing 100% CDW and plastic fiber contributes to reduced energy consumption, lower carbon emissions, and economic benefits. These findings underscore the potential of integrating non-degradable plastics into concrete mixtures, combined with treated CDW, offering both environmental sustainability and enhanced performance advantages in construction materials.

The influence evaluation of the additive fibre on concrete structures is a concerned problem especially in strengthening and repairing engineering. Current theoretical studies on the damage mechanisms of tunnel lining are generally based on the tensile and compressive characteristics of the ordinary concrete. Little attention is paid to the toughness and damage development of the fibre reinforced concrete, as well as the influences of high-speed train dynamic loading. In this paper, both tensile and compressive experiments of fibre reinforced concrete with different lengths and volume contents are carried out considering three types of the glass, PVA (polyvinyl alcohol) and hybrid fibres. Afterwards, the damage evolution of fibre reinforced concrete is explored by application of the digital image correlation (DIC) technique. The hypothesis of strain equivalence and damage theory of Najar are employed to determine the damage parameters of the fibre reinforced concrete so as to establish three-dimensional finite element model of surrounding rock-tunnel. Finally, the parameters that affect damage development of concrete tunnel lining incorporated fibre under train loading, including the vehicle speed, fibre type, fibre length, and volume content, are performed. The results show that adding fibre into concrete can effectively enhance the damage resistance capacity of concrete and significantly improve the developing trend of multistep damage of ordinary concrete under train excitation loading. Moreover, fibre reinforced concrete can reduce the final damage values of tunnel lining subjected train loading. The paper contributes to the understanding of damage behaviours of fibre reinforced concrete lining for high-speed trains loading as a potential risk in the course of the operation. [ABSTRACT FROM AUTHOR]

This work explores the dynamic fracture characteristics of recycled tyre polymer (RTP) fibre reinforced concrete after exposure to 20, 105, 250, 400 and 600 °C. Split Hopkinson pressure bar tests were performed to characterize the dynamic compressive properties under strain rates of 40–120 s−1, in terms of the failure mode, strain-stress response, dynamic strength, dynamic increase factor (DIF), peak strain and energy absorption capacity. Results indicate that the failure pattern varies from splitting failure to core failure, and finally to pulverization failure due to strain rate effect, regardless of exposure temperatures. The dynamic strength and DIF are enhanced by strain rate effect but drop by 56.1% and 23.9% at 600 °C, respectively, while no explosive spalling occurs because of the thermal expansion of RTP fibres. The temperature-dependent dynamic fracture mechanism is closely related to the physicochemical reactions in the concrete matrix, bridging or rupture of RTP fibres and breaking of coarse aggregates. [ABSTRACT FROM AUTHOR]

Recently, new constitutive tensile models for describing the post-cracking behaviour of fibre reinforced concrete for different performance classes were developed by the author(s). The models are based on test data on notched beams with macro fibres, including one type of glass fibres and two polypropylene fibres. Nowadays, a wide range of macro fibres for reinforcing concrete mixtures is available. The objective of this paper is thus to examine whether the newly developed models are applicable for other FRC mixtures. For this purpose, the experimental results of 236 three-point bending tests on notched beams, obtained from Vrijdaghs et al. and the international company Bekaert, are compared with the model predictions. The results indicate that the proposed model for performance class a & b and class c exhibit a higher accuracy at CMOD1 than the model in MC10 and EC2 (next version). However, further optimization is required at CMOD3 for the model of performance class a & b and class d. A strong correlation is also found between the experimental fR1-values, as well as the fR3-values, and the predicted compression zone height of the beam cross-section at midspan by use of those new constitutive models. Moreover, this paper also proposes a modification to the model of Oettel et al. for better estimating the residual flexural tensile strength of FRC mixtures with 4D Dramix fibres. [ABSTRACT FROM AUTHOR]

This research was aimed to find the structural behaviour of Calotropis procera fibres added concrete and the effect of Azadirachta indica leaf slurry blended to concrete and exposed to seawater. Conventional and fibre reinforced concrete samples fabricated keeping the curing time as 7, 14 and 28 dayswere subjected to compression, split tensile, rebound hammer and ultrasonic pulse velocity test. Increase in curing time increased the structural properties and Calotropis procerafibres added samples produced respectively 19.5%, 15%, 10.3 and 14.5% improvement in the compression, tensile, rebound hammer and ultrasonic pulse velocity values. These fibres reduced the brittleness of the specimen and avoided unprecedented failures. Accelerated corrosion and gravimetric mass loss test conducted to estimate the anti-corrosive property of Azadirachta indica leaf slurry showed decrease in corrosion rate. The corrosion rate of concrete samples without and with inhibitors was 0.0654 ± 0.008 and 0.056 ± 0.011 mm/year respectively evincing the anti-corrosive effects of Azadirachta indica leaves. Thus green materials are compatible with concrete and can be used in making sustainable concrete structures. [ABSTRACT FROM AUTHOR]

Waste tires pose significant environmental, health, and fire risks. Creative waste management solutions, including reuse, recycle and repurpose, are necessary to mitigate those impacts while enriching their valorisation. An innovative solution is the upcycling of recycled steel fibre (RSF) from waste tires to enhance strength and durability of concrete. This study thus experimentally examines dynamic and mechanical behaviours of high-strength concrete with varying proportions of RSF, from 0% to 1.2% by volume. The results reveal that high-strength concrete with 1.2% RSF exhibits the best improvement in strengths. In addition, the damping ratio, dynamic modulus of RSF concrete and SEM images confirm valorisation potentials of waste fibres. Via a robust critical lifecycle analysis, the new insights form a new sustainable design and carbon credited application framework for RSF. Our results portray that innovative recycling practices for end-of-life tires yield substantial environmental benefits, including a significant carbon emission reduction.

The size effect is a well-known characteristic of concrete structures. However, in the case of fibre-reinforced concrete (FRC), this issue is not thoroughly explored. Most design recommendations of FRC neglect the size effect or handle the behaviour of FRC structures in case of different structural sizes similar to plain concrete structures (assuming FRC is a homogeneous material). The aim of this paper is to show that the size effect of FRC can be divided, the share of the concrete matrix and the fibres in the size-dependent properties is separable. For the size effect research fifteen synthetic macro fibre reinforced concrete and six plain concrete beam specimens were prepared and tested in three different sizes and then evaluated with the semi-discrete analytical (SDA) model. The analysis of the experimental specimens has shown that the size effect significantly influences the concrete material in the case of FRC with softening material behaviour, but the residual loadbearing capacity which mainly arise from the local bridging effect of fibres is essentially independent of the structural size. It is also shown in this paper that the two defining parameters of the SDA model is independent of the structural size, so the model provides an excellent tool in case of the design of real-sized FRC structures.

Ultra‐high performance concrete (UHPC) is characterised by a high compressive strength, high durability, and a dense microstructure. The latter causes UHPC to fail in a brittle and sometimes explosive manner. For this reason, UHPC is reinforced with microfibre reinforcement. On the one hand, these lead to increased tensile and bending loads being able to be absorbed, but above all to ductile post‐fracture behaviour. The fibres used are mostly steel fibres. An essential aspect of the fibre reinforcement is the bond strength between UHPC and metallic fibre. The bond is divided into chemical‐adhesive bond, form bond and friction bond. Depending on the shape, material and surface condition of the fibre, the individual types of bond have different effects on the concrete. To quantify these effects, fibre pull‐out tests are often carried out. These provide information about the bond strength between the fibre and the concrete. However, results of various studies show that the bond strength does not automatically correlate with the actual influence on the resulting tensile and flexural strengths of concrete components. [ABSTRACT FROM AUTHOR]

Faserverstärkte (Ultra‐)Hochleistungsbetone ((U)HPC) werden bereits seit den 1970er Jahren in großen Mengen für die Herstellung von Betonfertigteilen verwendet. Fasern werden eingesetzt, um die Zugfestigkeit zu erhöhen und sprödes Versagen in duktiles Nachbruchverhalten umzuwandeln. Funktionale Formgedächtnislegierungen (FGL) als Bewehrung haben das Potenzial, in Form von Vorspannelementen im erhärteten Beton zu wirken und die Frischbetoneigenschaften zu verbessern. FGL haben die Eigenschaft, sich an eine eingeprägte Form zu "erinnern". Durch thermische oder mechanische Aktivierung geht die zuvor verformte Legierung in eine eingeprägte Form zurück. Dieser Prozess beruht auf einer vollständig reversiblen Umwandlung der Tieftemperaturphase Martensit in die Hochtemperaturphase Austenit. Dadurch können zwei Effekte ausgenutzt werden: Superelastizität und Einweg‐Effekt. Die Superelastizität ist im Bauwesen wegen der vorhandenen Dämpfungsfähigkeit gut bekannt und wird bereits bei dämpfenden und selbstzentrierenden Elementen eingesetzt. Der Einweg‐Effekt wurde bisher weniger genutzt, bietet aber ein enormes Potenzial für das Bauwesen. Diese Arbeit zeigt, dass der Effekt zur Vorspannung von UHPC sowie zur Verbesserung der Verarbeitbarkeit von Frischbeton genutzt werden kann. [ABSTRACT FROM AUTHOR]

This paper presents a systematic experimental study on the effect of shape memory alloy (SMA) fibres (0.25–1% by volume) on microstructure and engineering properties, in particular mechanical properties of polyvinyl alcohol (PVA) fibre (2% by volume) reinforced engineered cementitious composites (ECC). A series of tests were performed to characterise the flowability, compressive properties and flexural and uniaxial tensile behaviour in terms of strain/deflection-hardening and multiple microcracking performance and flexural and tensile strengths, as well as the 3D fractal crack analysis and microstructural evolution of ECC. Results indicate that the presence of more SMA fibres diminished the flowability of ECC, which can be ascribed to the higher surface roughness of SMA fibres as confirmed by the atomic force microscopy analysis but did not result in any change in the self-compacting characteristics of ECC. The highest compressive strength was achieved at the ECC mix with 0.5% SMA inclusion as 62.5 and 72.1 MPa for ambient curing of 28 and 56 days. Although the presence of 1% SMA fibre reduced the compressive strength of ECC due to the increased interfacial porosity and fibre cluster, the residual flexural crack width of ECC containing 1% SMA fibre was effectively reduced by about 54.3% as compared with the reference ECC mix, consistent with its best tensile performance. Accordingly, the failure patterns of ECC changed from the tensile failure with more uniformly distributed cracks and the highest dissipated fractal fracture energy (Ws/Gf=167.7) to the tensile failure along with less tortuous crack path and fractal fracture energy (Ws/Gf=80.2).

Recent research has shown that the incorporation of fibres, such as steel and polypropylene fibres, in concrete can significantly improve its resistance to spalling under high-temperature conditions. However, the reported outcomes of studies on the spalling performance of Fibre Reinforced Concrete (FRC) vary significantly due to differences in cementitious matrix and fibre types, mix design, and testing techniques. Existing review studies have struggled to systematically and precisely consolidate the diverse aspects of the literature. To address these limitations, this paper adopts the latest approach for mining, processing, and analyzing data to interpret bibliographic data on the fire resistance of FRC. The primary objective of this study is to comprehensively explore the viability of FRC as a fire-resistant and refractory material. In pursuit of this goal, the paper thoroughly reviews various aspects of FRC behavior at elevated temperatures, including pore pressure behaviors. Moreover, this review also discusses spalling behaviors, mechanisms, and residual mechanical properties under high temperatures. The microstructural analysis of FRC is also discussed comprehensively to gain an in-depth understanding of its behavior under elevated temperatures. By analyzing available data, this study aims to shed light on the potential of FRC as a suitable material for resisting spalling in high-temperature scenarios. Additionally, the research delves into prospects and challenges in achieving sustainable FRC with enhanced spalling resistance, considering both material and structural levels.