High Performance Fibre Reinforced Concrete Research Articles

A granular micromechanic-based model for Ultra High Performance Fiber-Reinforced Concrete (UHP FRC)

There is a growing interest in the application of UHP FRC (Ultra-High Performance Fiber-Reinforced Concrete) which has been under vigorous development since its inception over two decades ago. The advantages of these advanced materials is that they overcome the problems that plague conventional concrete, these include among others low residual strength and low tensile strength, poor crack control and resistance to crack propagation, which leads corrosion of the rebars and spalling. The aim of this paper is to provide a granular micromechanics-based model to describe the deformation behavior of UHP FRC material as it gives a robust method to link the micro-scale mechanisms with the macro-scale performance of materials with granular textures. In this model, the micro-scale is described by damage-elasto-plastic spring elements that represent the effective grain pair interactions decomposed into the so-called normal and tangential directions. Since the grain-pairs are variously oriented, the macro-scale response is obtained by integrating these interactions over the orientational space. Here we specialize the granular micromechanic model for UHP FRC by introducing a novel expression for the parameterized dissipation energy at the micro or the grain-pair scale. The newly introduced constitutive parameters are identified using experimental results for uniaxial extension and compression tests. The model is then applied to simulate the case of homogeneous compression, extension and shear to show the directional evolution of damage and plasticity and the consequent emergent anisotropy.

Microstructure and radiation shielding properties of lead-fiber reinforced high-performance concrete

The increasing application of nuclear technology in medical fields has amplified the demand for radiation shielding materials. Traditional large-volume concrete cannot simultaneously exhibit excellent neutron and gamma-ray shielding capabilities while ensuring superior mechanical properties. This study tailored a novel lead fiber-reinforced high-performance concrete (LFRHPC) with lead fibers and magnetite aggregates, focusing on radiation attenuation. The effect of lead fibers on the mechanical performance, microstructure and radiation attenuation characteristics for LFRHPC was comprehensively evaluated. The results indicate a significant improvement in the mechanical performance of LFRHPC compared to traditional radiation shielding concrete (RSC), due to the scientific skeleton design. Additionally, the pore structure in LFRHPC is refined by incorporating lead fibers. Moreover, the interfacial transition zone (ITZ) between the cementitious matrix and magnetite is improved because of the very low water-to-binder ratio. To assess the radiation attenuation ability of LFRHPC, both direct measurements and simulation models were utilized. The data reveals that the porosity of LFRHPC plays a crucial role in its shielding effectiveness against neutron and gamma radiation. Furthermore, the addition of lead fibers considerably boosts its neutron and gamma-ray shielding attenuation capabilities. In summation, LFRHPC combines excellent mechanical properties and radiation shielding capabilities, making it suitable for construction applications in medical settings.

High Performance and Ultra-High Performace Fibre Reinforced Concrete with Stabilized Homogeneity

This paper describes the segregation of fibres in high performance and high strength concretes. It focuses on both laboratory and practical conditions. It compares different mixtures produced and processed in the laboratory and in the precast concrete company. Two methods are chosen in the paper to avoid fibre segregation. The first method is a suitable mix design considering the water/cement ratio and the amount of superplasticizer. The second method is the addition of synthetic fibres to the mixture while maintaining sufficient workability. The paper examines the consistence of each mixture according to the concrete placement location, segregation of fibres in the fresh mixture and hardened composite. Both methods under laboratory and practical conditions have shown a positive impact on the reduction of segregation of steel fibres in the mixture. Simultaneously, the strength properties of all mixtures were compared, which depended mainly on the type of synthetic fibres used.

Experimental Study of Cast in Anchors Embedded in UHPFRC

This paper describes an experimental investigation of the behaviour of anchors precast in Ultra High-Performance Fiber-Reinforced Concrete (UHPFRC) under static loading. Initially, the current state of the art and related experimental studies are briefly mentioned. The next part of the paper is devoted to an experimental program aimed at describing the anchorage in cement composite UHPFRC in more detail. A total of 45 pull-out tests were performed. The tests investigated the effect of the fiber quantity in volume in the UHPFRC matrix (vf), the effective embedment depth of the anchor (hef) and the position of the anchor in the mould during concreting. Finally, the results are documented, the failure mode and the shape of the concrete cone, load-displacement curves and summary tables are presented. The paper concludes with a discussion of the results and further directions for solving the problem.

Effect of Bonding Type on the Failure of Reinforced Concrete Beam Strengthened with In-Situ High Performance Fibre Reinforced Concrete Layer

High performance fibre reinforced concrete (HPFRC) materials with tensile hardening behaviour can effectively be used for strengthening reinforced concrete beams. A perfect bond between the original and the reinforcing layer cannot be formed, the load-bearing capacity and ductility of the strengthened beam can significantly be affected by the interfacial bond strength between the contacting surfaces. In this paper, beam retrofitting with cast in-situ strengthening type is examined. The purpose of this experimental study is to investigate the impact of the different bond types on the load-bearing capacity, ductility, and failure mode of the strengthened beams in the case of cast in-situ strengthening. Twenty-four beam tests were performed with untreated and rough surfaced beams, with or without connecting elements. The effect of the bond type proved to be significant regarding the failure mode in the case of compression side strengthening, stronger bond resulted in higher load bearing capacity and ductility, too. When tensile side reinforcement was investigated no average increment was experienced in the maximal force and ductility due to the stronger bond. Based on the results, it can be concluded that the generally applied analytical models that assume perfect connection may lead to exaggerated results in the case of a compressed side HPC-strengthened beam. Therefore, it is necessary to develop a model that considers the effect of the imperfect bond.

Shear resistance of prestressed HPFRC beams without stirrups: A mechanical analysis of shear-transfer actions based on detailed experimental measurements

The use of High Performance Fibre-Reinforced Concrete (HPFRC with compressive strength up to 100 MPa) has shown to be a competitive alternative to conventional solutions for precast beams. This is justified by its affordable cost, high mechanical performance and enhanced durability. However, the shear response of such elements is still under scientific discussion and most design models provide scattered and highly conservative predictions, discouraging the use of HPFRC. In order to make a step forward in the understanding of such key aspect, this paper presents the results of an experimental investigation on eight full-scale HPFRC beams. The beams were tested with different levels of prestressing and were instrumented with refined optical DIC measurements. Using the experimental data, crack development and kinematics are investigated in detail, as well as the associated contributions of potential shear-transfer actions. The results confirm a significant contribution of the fibres in tension, as well as of the inclination of the compression chord for high levels of prestressing. The outcomes and failure modes of the different specimens are eventually compared and discussed, with the aim of setting the bases for more comprehensive and mechanically-based approaches for shear design of HPFRC.

Investigation of the Workability, Strength, and Durability of Fiber-Reinforced High-Performance Concrete with Full Aeolian Sand

Investigation of the Workability, Strength, and Durability of Fiber-Reinforced High-Performance Concrete with Full Aeolian Sand

Flexural behavior of beams strengthened with GFRP bars and high‐performance fiber‐reinforced concrete

AbstractThe flexural behavior of beams strengthened with GFRP bars and high‐performance fiber‐reinforced concrete (HPFRC) was investigated in this paper. The four‐point flexural response of one reference beam and four beams strengthened with high‐performance fiber‐reinforced concrete was investigated by experimental research and theoretical calculation. The experimental and theoretical data (strain, load, etc.) are discussed. Parameters varied included the strengthening scheme (bottom‐side strengthening and three‐side strengthening) and the type of high‐performance fiber‐reinforced concrete (engineered cementitious composite [ECC] and ultra‐high‐performance concrete [UHPC]). The results showed that the cracking load and ultimate load of beams strengthened with UPFRC material were 31.3%–170% and 9.6%–20.7% higher, respectively, relative to the reference beam. Beams with three‐side strengthening (without interfacial debonding) had higher ultimate load, smaller crack width, and better durability relative to beams with bottom‐side strengthening. The UHPC layer was more effective in increasing the ultimate bearing capacity, and ECC strengthening layer was more effective in inhibiting cracking development of beams. Based on the experimental results, a model was proposed to predict the ultimate bearing capacity of beams strengthened with high‐performance fiber‐reinforced concrete, which could provide good agreement between the experimental and predicted results.

Experimental characterization of a cost‐competitive tailor‐made HPFRC mix design for wide application in precast girder of roadway bridges

AbstractThis paper presents a comprehensive study on the development of a cost‐effective, high‐performance fiber reinforced concrete (HPFRC) for the construction of a 60 m‐span U‐girder roadway bridge without stirrups in the webs, meeting the design requirements of fck ≥ 100 MPa and the post‐cracking flexural strength fR3k ≈ 8–10 MPa. The main objective of this research is to develop a F5 workability class HPFRC that meets the specified design criteria without exceeding 2.5–3.0 times the cost of a C70/85. To achieve this goal, the concrete mix was obtained using 500 kg/m3 of cement and 50 kg/m3 of silica fume. This mix was investigated with nine different combinations of fibers and fiber contents, resulting that 80 kg/m3 of 4D‐fibers (lf = 60 mm) provided the optimal fR3k without compromising workability and cost. Subsequently, an extensive experimental campaign was conducted to cast the U‐girder following the conventional casting techniques involving casting prismatic samples, L‐shaped and rectangular‐shaped panels to represent different parts of the U‐girder. Innovative techniques were used to study the effect of different waiting times between concrete pours. Results from the testing of the prismatic specimens evidenced the need of stitching by means of a poker vibrator planes between successive concrete layers. Furthermore, the study of the panels evidenced that a waiting time of 90 min allows the HPFRC to achieve enough bending and compressive strength to bear internal vibration of the element without liquefying and, at the same time, avoiding cold joints. The results confirm the applicability of the developed HPFRC for the structural element under study following conventional casting techniques.

The Effect of Cross Sectional Properties of Concrete Column on the Repair Material: A Review

The utilization of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) as a material for repairing concrete structures holds immense promise and potential. UHPFRC usage in concrete has been a significant rise in the interest surrounding the enhancement and renovation of concrete structures, particularly focusing on columns. UHPFRC has showcased remarkable bonding potency with concrete, along with an impressive capacity to renew the load-bearing capability of compromised reinforced concrete columns. However, the limited application of UHPRFC as a repair material for concrete columns is primarily attributable to a lack of comprehension regarding the influence of shape and size effects, particularly as they pertain to square and rectangular columns. In this paper, the factors behind the impact of cross-sectional properties on the effectiveness of UHPFRC as a repair material is presented. Therefore, it can be adopted by researchers to explore the UHPFRC potential in structural rehabilitation applications especially for concrete columns. It is believed that the relationship between the cross-sectional area, aspect ratio, and corner radius ratio of the column and repair material is a vital parameter affecting the performance of repaired columns.

Fracture behaviour assessment of high-performance fibre-reinforced concrete at high strain rates using interpretable modelling approaches

High-performance fibre-reinforced concrete (HPFRC), a type of cementitious composite material known for its exceptional mechanical performance, has widespread applications in structures exposed to severe dynamic loading conditions. However, understanding nonlinear HPFRC fracture behaviour, particularly under high strain rates, remains challenging given the complexities of assessment procedures and cost-intensive nature of experiments. This study presents an interpretable framework for modelling and analysing HPFRC fracture strength at high strain rates. A wide range of machine learning methods, including ensemble techniques, were employed to capture multivariate effects of eight essential input features (e.g., mortar compressive strength, fibre physical and mechanical properties, cross-sectional area, and strain rate) on fracture strength response. To assess the derived models, a novel evaluation procedure was proposed involving a data-based analysis, employing established metrics (i.e., coefficient of determination, root mean squared error, and mean absolute error via K-fold cross-validation) and a domain experts-involved evaluation utilising global sensitivity analysis to discern first-order and higher-order interactions among input factors. The proposed approach efficiently yielded both quantitative and qualitative insights into crucial input factors governing HPFRC fracture strength with limited experimental data. The obtained findings highlight the significance of multivariate effects, such as the interaction between strain rate and fibre tensile strength, and between fibre volume and fibre diameter, on fracture behaviour. The proposed interpretable framework aims to provide a powerful tool for proactive material failure analysis by understanding fracture behaviour and identifying potential weak and strong interactions among input factors of HPFRC-based samples. Moreover, the utilisation of the proposed approach enables researchers and civil engineers to efficiently focus on the most critical input parameters during the early design stage and ensuring the structural integrity and safety of HPFRC-based constructions.

Effect of Slag on the Porosity and Microstructure of HPC Reinforced with Hybrid Steel Fiber

Due to their structural and economic performance, high performance metal fiber concretes are increasingly used in construction, but with the addition of metal fibers, workability decreases as the amount of fibers added increases. In order to improve workability, a larger quantity of fines should be used than for ordinary concrete. The use of granulated slag reduces the amount of clinker needed to make cement. It is considered that granulated slag improves the workability of concrete. According to Manai, this is due to the very low rates of water adsorption by the granulated slag grains at the start of mixing. Also, the addition of granulated slag has a positive effect on the porosity, but also on the microstructure of the hydrates. These two characteristics are factors determining the compressive strength and durability of the cement paste. The aim of this study is to define the effect of blast furnace slag on the porosity and microstructure of high performance fibre-reinforced concrete. The results of SEM and DRX observation of the microstructure of the concrete samples show that the addition of ultra-fine granulated slag resulted in a relative improvement in porosity and microstructure.

Explainable machine learning model for predicting punching shear strength of FRC flat slabs

Reinforced concrete slabs are vulnerable to punching shear failure at the slab-column joint, which can initiate catastrophic progressive collapse. The addition of steel fibers in the concrete matrix has emerged as an effective strategy to mitigate such progressive failure. However, the effects of the diverse mixture proportions of the concrete matrix with different types and dosages of fibers have made the accurate prediction of the punching shear strength (PSS) of the fiber-reinforced concrete (FRC) flat slabs a complex task, where the existing mechanical models have several limitations. Therefore, this study proposes an explainable XGBoost model for predicting PSS of flat slabs made with different types of FRC based on a newly established comprehensive database of 251 flat slabs including normal strength FRC slabs, high-performance FRC slabs, and ultra-high-performance FRC slabs. A customized procedure was proposed to establish the XGBoost model considering data preparation, feature selection, hyperparameter tuning and model validation. The performance of the XGBoost model was then compared with that of existing mechanical models. Finally, sensitivity analysis and SHapley Additive exPlanations (SHAP) analysis were applied to identify the most influential parameters on the prediction of PSS. Results show that the proposed feature selection method is effective in identifying six influential parameters from the eleven parameters related to the PSS of FRC flat slabs. The developed XGBoost model yielded highest prediction accuracy and lowest variation, which outperformed the other mechanical models. Sensitivity analysis also indicated similar trends of parameters in both the XGBoost model and the mechanical models. The PSS of FRC flat slabs can be improved by increasing the concrete compressive strength, reinforcement ratio, and fiber volume, and by decreasing the column width-to-depth ratio, water-to-binder ratio, and aggregate size ratio. The proposed XGBoost model could enhance the understanding of PSS of FRC flat slabs and guide future pertinent design code provisions.

Research on a Multi-Objective Optimization Design for the Durability of High-Performance Fiber-Reinforced Concrete Based on a Hybrid Algorithm

To achieve durable high-performance fiber-reinforced concrete that meets economic requirements, this paper introduces a hybrid intelligent framework based on the Latin hypercube experimental design, response surface methodology (RSM), and the NSGA-III algorithm for optimizing the mix design of high-performance fiber-reinforced concrete. The developed framework allows for the prediction of concrete performance and obtains a series of Pareto optimal solutions through multi-objective optimization, ultimately identifying the best mix proportion. The decision variables in this optimization are the proportions of various materials in the concrete mix, with concrete’s frost resistance, chloride ion permeability resistance, and cost as the objectives. The feasibility of this framework was subsequently validated. The results indicate the following: (1) The RSM model exhibits a high level of predictive accuracy, with coefficient of determination (R-squared) values of 0.9657 for concrete frost resistance and 0.9803 for chloride ion permeability resistance. The RSM model can be employed to construct the fitness function for the optimization algorithm, enhancing the efficiency of multi-objective optimization. (2) The NSGA-III algorithm effectively balances durability and cost considerations to determine the optimal mix proportion for the concrete. After multi-objective optimization, the chloride ion permeability resistance and frost resistance of the high-performance fiber-reinforced concrete improved by 38.1% and 6.45%, respectively, compared to the experimental averages, while the cost decreased by 2.53%. The multi-objective optimization method proposed in this paper can be applied to mix design for practical engineering projects, improving the efficiency of concrete mix design.

Fiber fraction-dependent flexural behavior of high-performance fiber-reinforced concrete under static and repeated loading

The effect of the fiber volume fraction on the flexural behavior of high-performance fiber-reinforced concrete (HPFRC) under both static and repeated loading is highlighted through a series of experiments. All rectangular prism-shaped flexural specimens were 40 × 40 × 160 mm3 and subjected to a three-point bending (3 PB) fixture with a span length of 120 mm. Macro-hooked and micro-smooth steel fibers with volume contents of 0.0%, 0.5%, 1.0%, and 1.5% were investigated. The flexural strength and deflection capacity of the HPFRCs under static loading generally increased with increasing fiber volume content. The micro-smooth fiber mostly produced a higher flexural strength and a lower deflection capacity compared to the macro-hooked fiber. Under repeated loading, a larger fiber volume fraction generally resulted in higher HPFRC endurance limits, which exceeded 40,000 cycles with a fatigue stress ratio of <0.5, at a fiber volume fraction of 1.5 vol%. The flexural fatigue equations of the HPFRCs of various fiber contents were calculated with the fatigue stress amplitude as well as the fatigue stress ratio, based on the experimental data. The HPFRCs’ sensitivity to endurance limits generally decreased with increasing fiber content; this finding was greater when using the micro-smooth fiber than when using the macro-hooked fiber.

Durability and fire resistance of high-performance fiber reinforced concrete with fly ash

ABSTRACT High-performance concrete (HPC) is currently widely utilised in the civil engineering and construction industry. The rising use of HPC in structural applications, as well as the necessity to justify fire resistance, has prompted numerous laboratories to research high-temperature characteristics. The relevant properties of HPC with polypropylene fiber (PPF) and fly ash (FA) were determined through an experimental study. This paper presents some key aspects related to compressive strength for High-Performance Fiber Reinforced Concrete (HPFRC) with and without FA at high temperatures ranging from 100°C to 800°C for use in fire resistance calculations. Visual investigation revealed a change in colour as the temperature rose. It may be used as a guide for maintaining, designing, and predicting the life of HPC structures, such as high-rise buildings that are exposed to high temperatures. Detailed research on the mechanical and durability characteristics like the workability of fresh concrete, as well as compressive strength, modulus of elasticity, drying shrinkage, water permeability, and sorptivity coefficient of hardened concrete containing PPF and FA is also reported in this paper. FA concentration in concrete mixtures was 0%, 10%, 20%, 30%, and 40% on a mass basis, with fibre volume fraction ranging from 0% to 0.3% on a volume basis.

An Extended Special Issue on Advances in High-Performance Fiber-Reinforced Concrete

Adding fiber to cement concrete can improve the shortcomings of concrete, such as low tensile properties and low ductility, and improve its resistance to permeability and impact [...]

Effect of temperature on electrical resistivity of high-performance fiber-reinforced concretes

The effect of temperature on the electrical resistivity of high -performance fiber-reinforced concretes (HPFRCs) were highlighted in this investigation through an experimental approach. There are four HPFRC mixtures as follows: HPFRC0 (no fiber), HPFRC1 (macro steel fiber, 1.5% by volume), HPFRC2 (micro steel fiber, 1.5% by volume), and HPFRC3 (hybrid fiber, 1.0% by volume macro steel fiber blended with 0.5% by volume micro steel fiber). All HPFRC specimens had an identical size of 40 × 40 × 160 mm3 (width x depth x length). The electrical resistivity of HPFRCs was measured under three temperature levels, including 0oC, 25oC, and 50oC using a chamber machine. The research proved that the electrical resistivity of the studied HPFRCs obviously decreased with increasing of the temperature ranging from 0oC to 50oC. Generally, the temperature exhibited a considerable effect on the electrical resistivities of cement-based composites.

Experimental investigation of the shear response of large-scale fibre-reinforced concrete panels

Although fibre-reinforced concrete has been the subject of extensive research for decades, its mechanical behaviour in shear is still not well understood. Furthermore, hardly any large-scale shear tests on elements with moderate fibre contents have been conducted to date. The present paper addresses this knowledge gap by presenting and discussing the results of an experimental campaign on large-scale fibre-reinforced concrete shear panels. Six panels with dimensions of 2.00 m × 2.00 m × 0.27 m were tested in the Large Universal Shell Element Tester at ETH Zurich by applying homogeneous shear. In four of these experiments, the in-plane shear was combined with homogeneous uniaxial compression by simulating the longitudinal restraint provided by the chords in a girder. Five tests focused on concrete of normal strength with moderate fibre contents and one test studied the behaviour of ultra high-performance fibre-reinforced concrete. The combined application of digital image correlation instrumentation and distributed fibre optical sensing allowed gaining a deeper insight into the structural behaviour of the panels. Overall, the test results showed the high efficiency of the fibres as shear reinforcement in large-scale web elements. However, failure of the panels without any steel reinforcing bars was rather brittle, with only few cracks forming over the element. The provision of a moderate amount of distributed longitudinal bar reinforcement has been found to be highly beneficial to the crack behaviour and thus significantly increase the ductility.

Physicomechanical Behavior of High-Performance Concrete Reinforced with Recycled Steel Fibers from Twisted Cables in the Brittle State—Experimentation and Statistics

This research studied the effect of recycled steel fibers extracted from twisted cable waste on the fresh and hardened states of high-performance concretes. Accordingly, slump, water absorption (WA), compressive strength (CS), flexural strength (FS), and split tensile strength (STS) were measured in the laboratory using mixtures generated by the response surface methodology (RSM). The RSM-based central composite design (CCD) was used to assess the influence of water-to-binder (W/B) ratios from 0.27 to 0.31, length-to-diameter (L/d = 46 to 80) and steel fiber content (SFC) in the range of 19 to 29 kg/m3 on the behavior of high-performance fiber-reinforced concrete (HPFRC). The accuracy and validation of the generated models were evaluated by employing analysis of variance (ANOVA) and optimal parameters. The experimental findings revealed that the use of an L/d ratio of 63, a W/B ratio of approximately 0.28, and an SFC of around 22 kg/m3 resulted in high workability in terms of slump. While a notable increase in compressive strength was observed when employing an L/d ratio of approximately 70, a W/B ratio of around 0.28, and the maximum SFC of 29 kg/m3, as confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis.