Fiber-reinforced Concrete Research Articles

Investigation of the dynamic mechanical response of corroded ultra-high performance fiber reinforced concrete (UHPFRC) with initial defects

This study addresses the dynamic mechanical response of the corroded ultra-high-performance fiber-reinforced concrete (UHPFRC) with initial defects, considering the possibility of corrosion deterioration induced by various pre-existing cracks during the long-term service life. For this purpose, an integrated accelerated corrosion method and Split Hopkinson Pressure Bar (SHPB)/high-speed camera etc. techniques are employed. Results show that increasing pre-impacting damage promotes the crack density and maximum width by 32.4%–62.3 % and 1.11–1.8 times, respectively. In terms of mechanical properties, coupling damages of initial defects and corrosion have adverse effects on the dynamic mechanical response. Typical fib Model Code 2010 applies to predict the DIF evolution of the corroded UHPFRC with initial defects. Numerous shear cracks are created at an angle along the weak interface as the corroded specimens with initial defects are again subjected to axial loading, revealing the associated failure mechanism. These results shed light on the dynamic response of corroded UHPFRC containing various initial defects and the failure mechanism gives some reference to service status evaluation.

A detailed investigation on assessing the introduction of hybrid fibres in Geopolymer composites for pavement application

ABSTRACT Geopolymer concrete (GPC) has been widely researched as an emerging sustainable construction material. As GPC possesses excellent mechanical and durability properties, it is highly recommended for the construction of rigid pavements. However, the brittle nature of GPC limits its utilisation in heavy traffic roads, reducing its fatigue life. This study aims to minimise the brittleness of Pavement quality GPC (PQGPC) by adding hybrid fibres (steel fibre + polypropylene fibre). Fresh, hardened and durability properties of hybrid fibre-reinforced pavement quality geopolymer concrete (HGPC) under ambient curing have been analysed. In addition, the experimental study also compared the flexural fatigue life of PQGPC with that of the best HGPC mix. Both fibres were added in the same % (by volume) up to a maximum dosage of 1.25% each. Results show that workability decreases with increased fibre addition, but compressive and flexural strength increases with an increment in the quantity of fibres up to 1%. It was observed that the abrasion resistance and shrinkage resistance also increase with the inclusion of hybrid fibres in HGPC. Fatigue results prove that the fatigue life of HGPC-3 (with 2% hybrid fibres addition) mix under medium and heavy loads is 40% and 28%, higher than PQGPC.

Mechanical behavior and microscopic damage mechanism of hybrid fiber-reinforced geopolymer concrete at elevated temperature

Geopolymer concrete (GPC) that is prepared from eco-friendly materials exhibits much more excellent resistance on high temperature compared with ordinary Portland cement concrete. In this study, hybrid fibers containing varying proportions of steel fiber (0.5%–2.0 %) and polyvinyl alcohol (PVA) fiber (0.2%–0.8 %) were incorporated in GPC. The hybrid fiber-reinforced geopolymer concrete (HFRGC) was subjected to temperatures ranging from 200 °C to 800 °C. The physical properties tests, mechanical properties tests, and microstructure tests of HFRGC were carried out at elevated temperatures, while the environmental impact and cost-effectiveness of HFRGC were assessed. The results of physical properties tests showed that the appearance and mass loss of the HFRGC were mainly affected by temperature, while hybrid fibers had a negligible effect on both. The appearance of HFRGC gradually transformed from gray to brick red with increasing temperature, and the mass loss of HFRGC at 800 °C was as high as 9.4 %. The mechanical performance test results indicated that the mechanical strength of HFRGC increased at 200 °C and then decreased with elevated temperature. At 200 °C, the compressive strength, splitting tensile strength, and flexural strength of HFRGC containing 1.5 % steel fibers and 0.6 % PVA fibers were respectively increased by 13.1 %, 14.7 %, and 4.4 % as compared with ambient conditions. The microstructure test results showed that further geopolymerization at 200 °C promoted the densification of the matrix. The matrix was damaged at higher temperatures violently while the porosity of HFRGC was dramatically increased from 13.35 % at 25 °C to 27.83 % at 800 °C. Based on the thermal behavior, environmental impact, and cost-effectiveness of HFRGC, a reference for future research in the fire prevention of GPC was provided.

A fine-segmentation algorithm for XCT images of multiphase composite building materials based on deep learning

In response to the challenges presented by the variable internal structures and complex components of multiphase composite building materials, this study introduces a novel image segmentation network named UT-FusionNet. Building on the U-Net model, UT-FusionNet integrates Transformer module and tensor concatenation and fusion mechanism to overcome the limitations of convolutional networks in relation to the receptive field. UT-FusionNet is employed to segment CT images of conventional concrete, grout consolidation bodies, and fiber-reinforced concrete. The results demonstrate that UT-FusionNet achieves superior segmentation accuracy and robustness, with Accuracy (ACC), Intersection over Union (IoU) and Dice scores exceeding 90 % across all subtasks. The mean accuracy metrics are 99.44 %, 96.70 %, and 98.31 %, respectively. This innovative end-to-end network offers robust support for detailed structural analysis, damage detection, and digital modeling of multiphase composite building materials through deep learning.

Compressive strength study of fibre reinforced concrete

Abstract Materials play a vital role in the development of human life. Environmental and sustainable development concerns have seriously affected the development and applications of materials. Due to the advancement of rapid growth, it leads to the utilization of more materials, which leads to the depletion of natural materials. So, this leads the researchers to focus on the materials that have less impact on the environment. This study focuses on the compressive strength-based study of M30-grade fiber-reinforced concrete, partially replacing cement with flyash, fine aggregate with cocopeat, and adding coir fiber as a fiber. In recent times, there has been a tremendous increase in the usage of several natural fibers because of their low cost, ease of processing, and environmental friendliness. Due to their availability and eco friendliness, they are used in the development of fiber-reinforced concrete to improve its strength. The experiment entails casting and curing of different concrete mixtures for 3, 7, and 28 days with varying percentages of coconut fiber and cocopeat, 30% replacement of cement with flyash, and performing compressive strength tests in accordance with IS standards. Test results show adding 1% of coir fiber attains more strength in comparison with normal concrete and concrete with partial replacement of cement with fly ash and fine aggregate with cocopeat.

Advancements in Characterizing Fiber Distribution in Fiber-Reinforced Concrete Using X-ray Computed Tomography

Abstract The distribution of fibers within fiber-reinforced concrete significantly impacts its mechanical properties. X-ray computed tomography (CT) provides a distinctive and technically proficient method for examining fiber dispersion. This paper presents an exhaustive review of the methodologies used to characterize fiber distribution in concrete. It delves into the fundamental principles of X-ray CT and its application in studying fiber distribution, highlighting the current state of research. Additionally, the study explores the influence of fiber distribution and orientation on the failure mechanisms of concrete, offering insights that could guide future investigations in this domain. The paper concludes with a discussion on the potential of X-ray CT in evaluating fiber distribution and its implications for the mechanical properties of concrete, thereby setting the stage for further advancements in the field.

Study on the mechanical properties of non-calcined coal gangue geopolymer concrete reinforced by basalt fibers

Abstract Fiber-reinforced non-calcined coal gangue-based polymer concrete (BFCGGC) was synthesized utilizing gangue, slag, an alkali exciter solution, and coarse and fine aggregates, alongside basalt fibers as primary constituents. Mechanical characteristics of BFCGGC were investigated by varying the mass fractions of basalt fibers, while its micro-mechanism was examined using scanning electron microscopy. The findings indicated a trend in the compressive strength of BFCGGC, initially ascending and subsequently descending with fiber incorporation. Nevertheless, both tensile and flexural strengths exhibited continuous augmentation with the inclusion of fibers. Notably, basalt fibers demonstrated a pronounced improvement in the split tensile strength of BFCGGC, with a peak enhancement rate reaching 41.3%.

Experimental and numerical simulation study on the dynamic behavior of basalt-polypropylene fibers reinforced coral aggregate concrete

This study investigates the failure mode, dynamic compressive strength, strain rate effect and critical strain of basalt-polypropylene fiber-reinforced coral concrete (BPRCAC) under impact load using a 75 mm diameter split Hopkinson pressure bar (SHPB). The Holmquist-Johnson-Cook (HJC) model is modified to obtain parameters such as strain rate effect and strength based on the test results, utilizing LS-DYNA for numerical simulation analysis. The results indicated that the dynamic compressive strength and critical strain of BPRCAC significantly respond to the strain rate, increasing with the strain rate. A relationship between the dynamic increase factor (DIF) and the strain rate of BPRCAC is developed, showing that the DIF increases linearly with the decimal logarithm of the strain rate. However, the critical strain of BPRCAC increases linearly with the strain rate. The addition of basalt fiber (BF) and polypropylene fiber (PF) improves the strain rate sensitivity of the dynamic compressive strength, with increases of 19.21 %, 7.37 %, 22.60 %, and 11.37 % observed for BCAC-0.1, PCAC-0.1, BPCAC-0.1, and BPCAC-0.2, respectively, compared to CAC at a strain rate of 133 −143 s−1. The combined content of BF and PF has a more significant effect on the strain rate sensitivity of the critical strain, with BPCAC-0.2 exhibiting a critical strain 50.79 %−74.42 % higher than that of the other groups compared to CAC. The stress-strain curves and failure modes of the specimens simulated by LS-DYNA agree with the experimental results, verifying the applicability of the improved HJC model to BPRCAC.

Experimental and numerical study on polypropylene fibers reinforced concrete slabs with corroded reinforcement under monotonic loading

The degradation of structural performance due to reinforcement corrosion in reinforced concrete (RC) structures and the subsequent measures to improve the mechanical properties of corroded RC structures have garnered significant interest. This study investigates the structural performance of corroded polypropylene fiber RC slabs through both experimental and numerical approaches. Specimens were subjected to accelerated corrosion via electrochemical methods to simulate rebar corrosion. Key experimental parameters include polypropylene fiber volume fractions of 0% and 3%, design corrosion levels of 0%, 5%, and 10%, and both one-way and two-way constraints. The Digital Image Correlation (DIC) technique was employed for data acquisition. Load, deflection, strain, and crack morphology data were collected during loading. Results indicate that reinforcement corrosion increases the maximum crack width during loading, while a 3% polypropylene fiber volume fraction reduces this width by 20% to 48% at the same load level. Polypropylene fibers also enhance the peak loads and corresponding deflections of unidirectional and bidirectional specimens, with a more pronounced increase in unidirectional specimens of 11.3% and 15.4%, respectively. Although corrosion reduces the load-carrying capacity of the specimens, the inclusion of 3% polypropylene fibers significantly mitigates this reduction. A numerical model, incorporating rebar corrosion and polypropylene fibers through appropriate material constitutive models, was developed and validated against experimental results. The model accurately simulates the mechanical behavior of polypropylene fiber RC slabs with corroded reinforcement.

Study on the deterioration mechanism of hybrid basalt-polypropylene fiber-reinforced concrete under sulfate freeze-thaw cycles

This paper focuses on the deterioration mechanism of hybrid basalt-polypropylene fiber-reinforced concrete (HBPRC) under the coupling of sulfate freeze-thaw cycles. The changes in the macroscopic properties of HBPRC under the influence of different volume contents of basalt fiber (BF), polypropylene fiber (PF) and hybrid BF-BF were investigated. The microstructure of HBPRC was characterized using the nuclear magnetic resonance (NMR) technique, X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the deterioration models of the BF- matrix interfacial transition zone (BF-ITZ) and the PF- matrix interfacial transition zone (PF-ITZ) in HBPRC were developed. The results showed that the fibers effectively reduced the cracking and macroscopic property damage induced by sulfate freeze-thaw cycles as the number of freeze-thaw cycles increased. When both BF and PF volume contents are mixed at 0.05 %, they can produce complementary effects, and their formation of a uniformly distributed three-dimensional mesh structure is more conducive to reducing the damage to the concrete, and their relative dynamic modulus of elasticity and compressive strength after 300 times of sulfate freeze-thaw cycles were increased by 67.10 % and 46.92 % compared with control concrete. At the same time, the addition of fibers resulted in a more stable evolution of the pore structure of the concrete, and the porosity of the specimens with fibers added at a volume admixture of 0.05 % and 0.1 % was reduced by 13.69–21.35 % after 300 cycles of sulfate freeze-thaw cycling, compared with control concrete. From the BF-ITZ and PF-ITZ deterioration models, it was concluded that the differences in the bonding performance of BF and PF to the concrete matrix affected the degree of frost damage to which they were subjected to coupling and the efficiency of salt solution replenishment, which in turn led to differences in the damage of each group of HBPRC. The reliability of the model was further verified by SEM observation of the morphological changes of different fiber-matrix ITZs before and after sulfate freeze-thaw cycles.

Development and properties of cost-effective self-sensing Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) incorporating steel slags

This study examined the electrical and self-sensing capacities of ultra-high performance fiber-reinforced concrete （UHPFRC） with and without steel slag powder. The inclusion of steel slags provides a reliable way to enhance the electrically conductive and self-sensing capabilities of UHPFRC, which is composed of cement, silica fume, and steel fiber. The conductibility of UHPFRC and its response to external loading were investigated. Additionally, through 3D analysis of fiber structure and pore distribution, the conductive mechanisms were revealed. The results show that the addition of steel slags powder (SSP) can improve both mechanical properties and flowability. The maximum fractional change in electrical resistivity under compressive and flexural loads reached 37.6 % and 54.1 %, respectively. However, the conductive model under compressive loading differs from that under flexural loading. Furthermore, an analysis of carbon emissions and material costs revealed that using SSP reduced carbon emissions by 45.2–96.4 % and lowered costs by 41.8–88.8 %, making this approach both economically and environmentally advantageous.

Flexural behaviour and post-cracking performance of polypropylene fibre-reinforced waste cardboard blended concrete

The requalification of recycled materials has become of significance owing to a global shift towards net zero emissions and the severe environmental impact of misused recyclable waste. Cardboard and polypropylene have evolved into significant waste products, and the purpose of the study was to focus on the repurposing of both waste materials in determining the structural behaviour of an eco-efficient fibre-reinforced waste concrete. The study extended upon the findings of a precursor study in the development of an eco-efficient fibre-reinforced waste concrete mix. Finely processed municipally collected waste cardboard and recycled polypropylene macro-fibres were incorporated into a concrete mix design for which an experimental program was realised. To achieve this, uniaxial compressive strength, modulus of rupture, modulus of elasticity, and indirect tensile strength of the waste and reference mixtures were determined for 7- and 28-day intervals. Crack mouth open displacement testing was achieved to assess the post-cracking response, and retaining wall beams were prepared and loaded to determine the efficacy of the concrete mixture for low load-bearing structures. Mechanical and post-cracking properties of the hybrid waste concrete underscored excellent performance in comparison to other waste fibre-reinforced concrete mixtures, and superior to those blended with similar kraft fibre volume fractions. Moreover, the structural performance of beams cast from the hybrid mixture closely matched those of the reference mixture, emphasising the viability of the mixture and the role waste materials have in the construction and building industry.

Microbial acidification by N, S, Fe and Mn oxidation as a key mechanism for deterioration of subsea tunnel sprayed concrete

The deterioration of fibre-reinforced sprayed concrete was studied in the Oslofjord subsea tunnel (Norway). At sites with intrusion of saline groundwater resulting in biofilm growth, the concrete exhibited significant concrete deterioration and steel fibre corrosion. Using amplicon sequencing and shotgun metagenomics, the microbial taxa and surveyed potential microbial mechanisms of concrete degradation at two sites over five years were identified. The concrete beneath the biofilm was investigated with polarised light microscopy, scanning electron microscopy and X-ray diffraction. The oxic environment in the tunnel favoured aerobic oxidation processes in nitrogen, sulfur and metal biogeochemical cycling as evidenced by large abundances of metagenome-assembled genomes (MAGs) with potential for oxidation of nitrogen, sulfur, manganese and iron, observed mild acidification of the concrete, and the presence of manganese- and iron oxides. These results suggest that autotrophic microbial populations involved in the cycling of several elements contributed to the corrosion of steel fibres and acidification causing concrete deterioration.

A study of the effect of coconut fiber on reinforced concrete beams subjected to combined bending and shear

This review paper examines the impact of coconut fiber reinforcement on the behavior of reinforced concrete beams subjected to combined bending and shear. Coconut fibers, also known as coir fibers, are a sustainable and cost-effective alternative to traditional steel reinforcement. The use of coconut fibers in concrete has shown promise in enhancing the ductility, energy absorption capacity, fracture resistance, and durability of concrete structures. The study highlights the mechanical properties and applications of coconut fiber reinforced concrete (CFRC) and investigates the effects of varying fiber content on concrete performance. Factors affecting the properties of fiber-reinforced concrete, such as the relative fiber matrix index, volume of fibers, aspect ratio of fibers, fiber orientation, workability, compaction, size of coarse aggregate, and mixing techniques, are also discussed. Understanding these factors is crucial for designing and constructing durable and sustainable concrete structures.

Mechanical properties and dynamic compression behaviour of basalt/polypropylene fibre-reinforced high-strength concrete

Concrete is a typical brittle material. Although it has excellent compressive performance, it can be damaged by dynamic loads such as explosions and impacts due to its poor tensile strength and cracking susceptibility. In an attempt to improve the impact resistance of concrete, a ∅100 × 50 split Hopkinson pressure bar was used to carry out impact tests on high-strength concrete (HSC) specimens with different volume contents (0.1%, 0.3% and 0.5%) of basalt fibre (BF) or polypropylene fibre (PPF) under three different impact pressures. The compressive strength, splitting tensile strength, flexural strength and dynamic compression performance of BF/PPF-reinforced HSC (C60) were studied. With an increase in impact pressure, increasing the volume content of fibre significantly improved the impact resistance of the concrete, due to the crack resistance and bridging effects of the fibre. The BF and PPF were found to be sensitive to the strain rate. Within a certain range of strain rate, the relationship between peak stress and strain rate was positively correlated. Dynamic stress–strain curves of concretes with optimal dosages of BF and PPF were obtained through dynamic compression tests.

Study of Acoustic Emission Signal Noise Attenuation Based on Unsupervised Skip Neural Network.

Acoustic emission (AE) technology, as a non-destructive testing methodology, is extensively utilized to monitor various materials' structural integrity. However, AE signals captured during experimental processes are often tainted with assorted noise factors that degrade the signal clarity and integrity, complicating precise analytical evaluations of the experimental outcomes. In response to these challenges, this paper introduces an unsupervised deep learning-based denoising model tailored for AE signals. It juxtaposes its efficacy against established methods, such as wavelet packet denoising, Hilbert transform denoising, and complete ensemble empirical mode decomposition with adaptive noise denoising. The results demonstrate that the unsupervised skip autoencoder model exhibits substantial potential in noise reduction, marking a significant advancement in AE signal processing. Subsequently, the paper focuses on applying this advanced denoising technique to AE signals collected during the tensile testing of steel fiber-reinforced concrete (SFRC), the tensile testing of steel, and flexural experiments of reinforced concrete beam, and it meticulously discusses the variations in the waveform and the spectrogram of the original signal and the signal after noise reduction. The results show that the model can also remove the noise of AE signals.

Influence of Foam Content and Concentration on the Physical and Mechanical Properties of Foam Concrete

Foam concrete has been used in various real-life applications for decades. Simple manufacturing methods, lightweight, high flowability, easy transportability, and low cost make it a useful construction material. This study aims to develop foam concrete mixtures for various civil and geotechnical engineering applications, such as in-fill, wall backfill and soil replacement work. A blended binder mix containing cement, fly ash and silica fume was produced for this study. Its compressive strength performance was compared against conventional general purpose (GP) cement-based foam concrete. Polypropylene (PP) fibre was used for both mixtures and the effect of various percentages of foam content on the compressive strength was thoroughly investigated. Additionally, two types of foaming agents were used to examine their impact on density, strength and setting time. One foaming agent was conventional, whereas the second foaming agent type can be used to manufacture permeable foam concrete. Results indicate that an increase in foam content significantly decreases the strength; however, this reduction is higher in GP mixes than in blended mixes. Nevertheless, the GP mixes attained two times higher compressive strength than the blended mix’s compressive strengths at any foam content. It was also found that the foaming agent associated with creating permeable foam concrete lost its strength (reduced by more than half), even though the density is comparable. The compressive stress–deformation behaviour showed that densification occurs in foam concrete due to its low density, and fibres contributed significantly to crack bridging. These two effects resulted in a long plateau in the compressive stress–strain behaviour of the fibre-reinforced foam concrete.

Investigation of pull-out and mechanical performance of fibre reinforced concrete with recycled carbon fibres

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.

Fiber orientation and orientation factors in steel fiber‐reinforced concrete beams with hybrid fibers:Acritical review

AbstractFiber orientation is of paramount importance for the design of fiber‐reinforced concrete (FRC) structural elements, because it markedly influences the postcracking properties of such material. For this reason, structural codes introduce orientation factors which aim to correlate the real mechanical properties of the structural element with the ones determined from standard beams. Although the need of considering fiber orientation in design codes is commonly accepted, the orientation factors are still based on a limited number of research studies, raising the need to better determine fiber orientation to improve the current standards and support the design process of FRC elements. In this research, a steel fiber‐reinforced concrete (SFRC) with a hybrid system of macro and microfibers is steered into a broad range of fiber orientations and cast into standard beams. Besides measuring the mechanical performance of these SFRC beams, three different methods for assessing fiber orientation are employed, namely electromagnetic induction, image analysis, and micro‐computed tomography. The comparison between the outcomes of the different methods provides detailed information about the accuracy and suitability of each method, considering the corresponding domain of applicability at structural level. Finally, a critical review of the most common 2D and 3D orientation parameters found in literature is performed, and the equations are adapted to account for the hybrid system of fibers.

Hybrid rehabilitation of 3D RC beam-column joints using UHP-HFRC and FRP wrapping: Experimental evaluation and theoretical analysis

Beam-column joints are crucial elements in reinforced concrete (RC) structures subjected to seismic loading, as they are vulnerable elements prone to significant damage during earthquakes. Due to extensive structural damage, various methods have been developed to strengthen beam-column joints. However, research on rehabilitation and repair methods has been limited, with most studies focusing on 2-D joints and overlooking the confinement effect of corner beams on the joint core. This study aims to investigate novel hybrid rehabilitation systems, including ultra-high performance hybrid fiber-reinforced concrete (UHP-HFRC) and fiber-reinforced polymer (FRP) systems, alongside embedding reinforcement into heavily damaged 3-D beam-column joints subjected to pre-cyclic loading and subsequent cyclic loading. Parameters related to hysteresis response were obtained and discussed, such as ductility, lateral stiffness, dissipated energy, equivalent hysteresis damping, and pinching ratio of the tested specimens. The experimental findings revealed that utilizing an FRP and UHP-HFRC hybrid rehabilitation system enhanced ductility, dissipated energy, and lateral stiffness of heavily damaged joints by 25 %, 73 %, and 81 %, respectively, compared to the undamaged reference specimen. Additionally, a simplified design model was developed to predict the shear resistance of beam-column joints, incorporating principles of strut-and-tie. The theoretical design model was also validated against the experimental database, demonstrating a good accuracy with MV and COV of 0.97 and 13 %, respectively.