Steel Fiber Reinforced Concrete Specimens Research Articles

Comparative analysis of flexural strength prediction in SFRC using frequentist, Bayesian, and Machine Learning approaches

Steel fiber reinforcement significantly enhances the flexural strength of concrete, which is vital for structural integrity. Annex L of the new Eurocode 2 classifies steel fiber-reinforced concrete by its flexural performance, aiding engineers in designing resilient structures. This study investigates the flexural behavior of steel fiber-reinforced concrete (SFRC) using three data-driven methodologies: Frequentist Inference (FI), Bayesian Inference (BI), and Machine Learning (ML). A comprehensive database was constructed from three-point bending tests on SFRC specimens, encompassing various compressive strengths, fiber quantities, and geometric parameters, to identify key factors influencing material properties.The findings indicate that all three methodologies yield comparable predictive capabilities for flexural responses in SFRC. Notably, FI models emphasize the importance of compressive strength and fiber volume fraction, along with fiber properties such as non-dimensional length and tensile strength. BI models enhance predictive stability by integrating prior knowledge and quantifying uncertainty, demonstrating their advantage, particularly in data-scarce situations. Additionally, ML analysis reveals that linear regression (LR) models can achieve accuracy similar to or greater than that of more complex models. This research provides novel insights into the application of BI and ML in concrete technology, emphasizing their potential to enhance predictive modeling. Additionally, it offers practical guidelines for optimizing SFRC design through a case study that compares residual flexural strengths obtained via Bayesian analysis, classifying the material in accordance with Annex L of the new Eurocode 2.

Optimizing Building Rehabilitation through Nondestructive Evaluation of Fire-Damaged Steel-Fiber-Reinforced Concrete.

Fire incidents pose significant threats to the structural integrity of reinforced concrete buildings, often necessitating comprehensive rehabilitation to restore safety and functionality. Effective rehabilitation of fire-damaged structures relies heavily on accurate damage assessment, which can be challenging with traditional invasive methods. This paper explores the impact of severe damage due to fire exposure on the mechanical behavior of steel-fiber-reinforced concrete (SFRC) using nondestructive evaluation (NDE) techniques. After being exposed to direct fire, the SFRC specimens are subjected to fracture testing to assess their mechanical properties. NDE techniques, specifically acoustic emission (AE) and ultrasonic pulse velocity (UPV), are employed to assess fire-induced damage. The primary aim of this study is to reveal that AE parameters-such as amplitude, cumulative hits, and energy-are strongly correlated with mechanical properties and damage of SFRC due to fire. Additionally, AE monitoring is employed to assess structural integrity throughout the loading application. The distribution of AE hits and the changes in specific AE parameters throughout the loading can serve as valuable indicators for differentiating between healthy and thermally damaged concrete. Compared to the well-established relationship between UPV and strength in bending and compression, the sensitivity of AE to fracture events shows its potential for in situ application, providing new characterization capabilities for evaluating the post-fire mechanical performance of SFRC. The test results of this study reveal the ability of the examined NDE methods to establish the optimum rehabilitation procedure to restore the capacity of the fire-damaged SFRC structural members.

Dynamic constitutive modeling of steel fiber reinforced concrete considering damage evolution under high strain rate

This study conducted quasi-static compression and splitting tensile tests on steel fiber reinforced concrete (SFRC), as well as dynamic compression tests using the split Hopkinson pressure bar (SHPB). The mechanical properties of SFRC with varying fiber contents and under different loading strain rates were examined separately. Experimental results indicate that the addition of steel fibers effectively enhances the properties of concrete. The dynamic mechanical performance of SFRC specimens (compressive strength, peak toughness, ultimate toughness, and energy absorption capacity) demonstrated a clear strain enhancement effect. The dynamic stress-strain curves of SFRC reveal the material's good viscoelastic properties. Then, a viscoelastic constitutive model for SFRC considering damage under high strain was proposed, with parameter fitting based on SHPB test results. The constitutive model was applied to the numerical simulation by the user-defined material (UMAT) in ABAQUS. The dynamic stress-strain curves and damage patterns obtained by numerical simulation are basically consistent with the test results. This further demonstrates that the proposed constitutive model effectively describes the dynamic characteristics of SFRC.

Dynamic Splitting Performance and Energy Dissipation of Fiber-Reinforced Concrete under Impact Loading.

In this paper, the influence of different fiber materials on the dynamic splitting mechanical properties of concrete was investigated. Brazil disc dynamic splitting tests were conducted on plain concrete, palm fiber-reinforced concrete, and steel fiber-reinforced concrete specimens using a split Hopkinson pressure bar (SHPB) test device with a 100 mm diameter and a V2512 high-speed digital camera. The Digital Image Correlation (DIC) technique was used to analyze the fracture process and crack propagation behavior of different fiber-reinforced concrete specimens and obtain their dynamic tensile properties and energy dissipation. The experimental results indicate that the addition of fibers can enhance the impact toughness of concrete, reduce the occurrence of failure at the loading end of specimens due to stress concentration, delay the time to failure of specimens, and effectively suppress the expansion of cracks. Steel fibers exhibit a better crack-inhibiting effect on concrete compared to palm fibers. The incident energy for the three types of concrete specimens is roughly the same under the same impact pressure. Compared with plain concrete, the energy absorption rate of palm fiber concrete is decreased, while that of steel fiber concrete is increased. Palm fiber-reinforced concrete and steel fiber-reinforced concrete have lower peak strains than plain concrete under the same loading duration. The addition of steel fibers significantly impedes the internal cracking process of concrete specimens, resulting in a relatively slow growth of damage variables.

Mechanical behavior of steel fiber reinforced concrete at cryogenic temperatures: Characterization with 3D meso-scale modelling

To investigate the mechanical properties of SFRC (Steel Fiber Reinforced Concrete) in low-temperature environments, a 3D mesoscale model approach was employed to simulate the mechanical behavior of SFRC specimens at cryogenic temperatures. The model considers SFRC a multiphase material composed of mortar, aggregate, ITZ (Interface Transition Zone), and steel fiber. Using the mesoscale modelling, the damage pattern, stress-strain curve, load-deformation curve, dissipated energy, strength under compressive and splitting-tensile loadings, strength prediction formula as well as the flexural toughness of SFRC specimens with different steel fiber content at low temperatures were obtained and analyzed. The results show that the compressive/splitting tensile strength significantly increases with the decrease in temperature. The splitting tensile strength, the peak deformation as well, and the dissipated energy increase in the case of a greater steel fiber volume fraction while the improvement effect of fiber content is weaker with the decrease in temperature. A prediction formula that considers the coupling effect of fiber volume fraction and temperature on the tensile strength of concrete was proposed. The effect of steel fiber on compressive strength is not obvious regardless of temperature. The flexural toughness index of SFRC increases significantly with increased steel fiber content but is insensitive to temperature changes.

Characterisation of Steel Fiber Reinforced Concrete: Ductility and Service Life

Plain concrete is a brittle material with low tensile strain and strength capacities. Steel fiber reinforced concrete (SFRC) has gained prominence as an innovative construction material, offering improved tensile and flexural properties over conventional concrete. Singapore Standards, “SS 674: Fiber concrete- Design of fiber concrete structures” just launched recently to offers a comprehensive structure for enhancing comprehension of Fiber-Reinforced Concrete. This study presents a comprehensive characterization of SFRC, focusing on both its mechanical properties particularly residual strength. Following this, a series of experimental works are conducted to assess the residual tensile strength under flexural loading behavior of SFRC specimens. Examining the tensile strength and residual strength of SFRC to assess its material strength and behaviour after being subjected to a load will help engineers comprehend the material's strengths and weaknesses. At 40 kg/m3 fibers content shows an increase of residual strength with a strain hardening behaviour observed as compared to the 20 kg/m3 and 30 kg/m3 fibers content. In conclusion, this study offers a holistic characterisation of SFRC, encompassing mechanical properties with higher residual strength. The outcomes provide scientific understanding and practical insights of SFRC for engineers and practitioners seeking to optimise the use of SFRC to enhance structural longevity and reduce maintenance costs.

Effect of steel fiber on the permeability of freeze-thaw damaged concrete under splitting tensile and compressive loads

This study investigated the effect of steel fibers on the permeability and mechanical properties of freeze-thaw damaged concrete under splitting tensile and compressive loads. A specially designed permeability apparatus is used to investigate the continuous permeability performance of steel fiber reinforced concrete (SFRC) subjected to loads. Results demonstrated that for the concrete without load, the addition of steel fibers exhibits a negative effect on the impermeability performance of the concrete matrix without freeze-thaw damage. The initial permeability of SFRC specimens is between 81.7 % and 180 % higher than that of NC specimens. The addition of steel fibers shows a positive effect on the impermeability of concrete subjected to freeze-thaw cycles. The permeability of SFRC under loads can be categorized into two stages. In the first stage, the concrete matrix is the main water channel. The addition of steel fiber can effectively increase the maximum radial deformation of the first stage and maintain low permeability of concrete in a large radial deformation range. In the second stage, concrete cracks are the main water channels. Both the addition of steel fibers and freeze-thaw cycles can reduce the permeability of the concrete in the second stage. Furthermore, under compressive load, with the increasing of stress level, the permeability of SFRC exhibits a slowly decreasing trend, this is followed by a significant increasing trend. The addition of steel fibers can maintain low permeability performance in a large stress level range, and as the steel fiber content increases, the permeability at peak load gradually decreases. The strain–permeability curves of SFRC under splitting tensile and compressive loads subjected to freeze-thaw cycles are investigated. The permeability of SFRC gradually increases with the increasing of the number of freeze-thaw cycles when the compressive strain exceeds 0.002. However, the opposite trend is observed under splitting tensile load. Notably, the reduction in concrete permeability due to the steel fibers is more significant under splitting tensile load than that under compressive load. Future work might integrate this research with stress-strain constitutive equations and finite element analysis. This will offer a foundational framework for engineering applications aimed at enhancing the permeability of steel fiber concrete under freeze-thaw conditions.

A 3D cohesive‐frictional coupled interface model for mesoscale simulation of steel fibre‐reinforced concrete

AbstractA 3D mesoscale finite element modelling approach is developed for simulating complicated damage and fracture behaviour in steel fibre‐reinforced concrete (SFRC) with explicit modelling of fibre–matrix interfaces. In this approach, a new 3D four‐noded cohesive‐frictional coupled interface element is developed to model the nonlinear interfacial bond‐slip behaviour, supplemented by a kinematic multiple‐point‐constraint (kMPC) algorithm to simulate the wrapping effect of the mortar around the fibres. They are implemented as a user‐defined element (UEL) and a user‐defined MPC subroutine in ABAQUS, respectively. Three cohesive‐frictional constitutive relationships are proposed to describe the nonlinear bond‐slip behaviour of different fibre–matrix compositions. The new approach is validated by single fibre pullout tests, direct tensile tests and three‐point bending tests of SFRC specimens with randomly distributed fibres. The results show that the new approach is capable of effectively capturing typical failure mechanisms in SFRC, such as fibre yielding, matrix failure, and fibre–matrix debonding and slipping.

Microcrack monitoring and fracture evolution of polyolefin and steel fibre concrete beams using integrated acoustic emission and digital image correlation techniques

The use of polymer and steel fibres in plain concrete appears to be an excellent solution for limiting crack propagation and improving the post-ductility performance of concrete structures. Based on this premise, this study investigated the fracture evolution of polyolefin fibre-reinforced concrete (PFRC) and steel fibre-reinforced concrete (SFRC) specimens through the integrated application of two diagnostic techniques, acoustic emission (AE) and digital image correlation (DIC), under three-point bending tests. Based on the processing of AE signals, different AE statistical parameters such as the cumulative number of hits, amplitude distribution, and some representative analysis methods including the b-value method, Ib-value method, and AE intensity analysis methods were selected to analyse the early detection of cracking and post-cracking behaviour in PFRC vs SFRC specimens during mechanical degradation. Simultaneously, the DIC technique was used to validate the fracture evolution of the AE results. Furthermore, to verify the reliability of the AE and DIC results, the damage localisation and fracture evolution of the PFRC versus SFRC specimens were confirmed by integrating the AE fracture energies and DIC outcomes. The tests and analysed results showed that the addition of steel fibres to plain concrete significantly improved the ability to restrict crack propagation and provided higher post-cracking resistance compared to PFRC specimens owing to their stronger fibre–matrix bonding, effective fibre bridging, and crack-arresting mechanism. The present study indicates that the combined AE and DIC techniques are highly effective for the early detection of damage and ductility performance in fibre-reinforced concrete structures.

Residual flexural tensile strength properties of notched concrete beams with high-strength steel fibers

The purpose of this study is to replace the steel bars and barbed wires in reinforced concrete structures, conduct experiments using steel fiber-reinforced concrete (SFRC), and investigate its failure modes. We conduct the experiments by performing the three-point bending test specified in the EN 14651 standard. Based on an analysis of the results obtained worldwide in recent years, we use SFRC specimens fabricated in the structural laboratory of Chungnam University in South Korea and apply the results from other researchers. The residual stresses of 625 SFRC specimens are analyzed based on the high or low strengths of the fibers and categorized according to fiber content and the aspect ratio of the fibers. The contribution of each condition to the residual flexural strength is discussed based on the results of the residual flexural strength after cracking, and it is suggested that more research and calculations are needed for high-strength steel fibers.

Performance of steel fiber reinforced concrete mixed with chloride solution and exposed to high humidity environment

In order to investigate the performance of steel fiber reinforced concrete (SFRC) suffered from chloride attack, the SFRC specimens were prepared using 9 wt% NaCl solution to accelerate the corrosion, and they were also exposed to the high humidity environment (≥90 % RH); meanwhile, the carbonation was also considered. The performance evolution of SFRC suffered from 14 months of in-situ chloride attack was monitored, including compressive strength, flexural property, splitting-tensile property, and so on. The results show that the SFRC specimens showed no deterioration in the mechanical properties after 14 months of chloride attack, while only some corrosion spots were found on the concrete surface, independently of the water to binder ratios and mineral admixtures. The carbonation accelerated the chloride-induced corrosion of steel fibers in the carbonated zone of concrete, but did not result in the reduction in the mechanical properties of SFRC within 14 months of chloride attack.

Mechanical properties of seawater-mixed steel fiber reinforced concrete

In this study, seawater was used for the preparation of steel fiber reinforced concrete (SFRC); furthermore, the mechanical properties of the seawater-SFRC exposed to a high humidity environment—including the cubic compressive strength, axial compressive, and flexural properties—were monitored for 27 months, also considering the carbonation effect. The results revealed that the mechanical properties of the un-carbonized SFRC specimens continued to improve with increasing exposure time, and tended to stabilize after 15 months, even if blended with 20% fly ash or 20% fly ash combined with 40% slag. Moreover, the steel fibers inside the specimens did not show signs of corrosion. For the pre-carbonated SFRC specimens, the mechanical properties also improved gradually over time; however, a decrease in the axial compressive toughness and flexural properties was observed after 15 months of exposure. The carbonation effect reduced the alkalinity of the SFRC and accelerated the corrosion of the steel fibers near the specimen surface, with the thickness of the corroded layer reaching 20–30 mm at 27 months. We found that corrosion of the steel fibers inside the seawater concrete occurred when the pH was less than 10. This study could provide valuable evidence for the potential application of seawater-SFRC.

Experimental and analytical study of the high-strain-rate compressive behavior of SFRC

The compressive behavior of steel-fiber-reinforced-concrete (SFRC) is dependent on the loading rate. This research investigates, experimentally and analytically, the effect of loading rate on the compressive behavior of SFRC designed to be used in prefabricated urban protective furniture. For this purpose, cylinder SFRC specimens were subjected to modified instrumented-drop-weight-impact tests at four dropping heights and quasi-static tests with four different strain rates. The inertia force was analytically obtained and also experimentally measured. The results demonstrate that by increasing the strain rate, elastic modulus, compressive strength, and energy dissipation capacity have increased. Three different models were proposed for predicting each mechanical characteristic, one in the range of quasi-static and the others in the range of impact corresponding to the split Hopkinson pressure bar and drop-weight-impact tests. The experimental dynamic to static ratios obtained for SFRC properties were discussed and compared with those proposed by present study and from other researchers. Three proposed models significantly improve the prediction the dynamic increase factor values in terms of compressive strength, modulus of elasticity and toughness.

Bond Behavior between High-Strength Rebar and Steel-Fiber-Reinforced Concrete under the Influence of the Fraction of Steel Fiber by Volume and High Temperature

Steel-fiber-reinforced concrete (SFRC) is a composite material made by randomly distributing short steel fibers in normal concrete (NC). In this study, central pull-out tests of 32 specimens were performed to investigate the bond behavior between high-strength rebar and SFRC under the influence of the fraction of steel fiber by volume (Vf = 0%, 0.5%, 1.0% and 1.5%) and temperature (T = 20, 200, 400 and 600 °C). The results show that in NC specimens, splitting failure occurs below 400 °C, while split-pullout failure occurs above 600 °C. Split-pullout failure occurs in all SFRC specimens at each tested temperature. The bond strength between rebar and SFRC was found to decay significantly between 400 and 600 °C. The effect of Vf on the improvement in bond strength was more obvious between 400 and 600 °C than between 20 and 400 °C. The positive contribution of steel fibers to bond behavior is the construction of a rigid skeleton with coarse aggregates that can play a bridging role and effectively retard the expansion of concrete cracks. This improves the bond strength between rebar and SFRC at high temperatures. The bond–slip curve can be divided into five stages, namely the initial micro-slide phase, slip phase, splitting failure phase, stress drop phase and residual pull-out phase. A model of the bond–slip relationship between rebar and SFRC considering temperature and Vf was developed by modifying the existing model of the bond–slip relationship between rebar and NC. The model calculation results agree well with those of testing.

Study on the bond properties between steel bar and fiber reinforced concrete after high temperatures

The bond-slip performance between steel bar and normal concrete (NC) and steel fiber reinforced concrete (SFRC) after high temperature were investigated in this paper. The central pull-out test was performed on 40 specimens with specific parameters including the fraction of steel fiber by volume (Vf = 0 %, 0.5 %, 1.0 %, and 1.5 %) and temperature (T = 20 °C, 200 °C, 400 °C, 600 °C, and 800 °C). The results demonstrate that the bond strength increased with the increase of Vf. The increase in bond strength of SFRC specimens compared to NC specimens is more than 66.9 % after 600 °C. As the temperature increases, the bond strength decreases. The bond strength loss after 600 °C compared to room temperature was more than 46.6 % for SFRC and NC specimens. The synergistic effect of steel fibers and aggregates formed a rigid skeleton for bridging cracks, improving the bond strength between steel bar and SFRC. The cumulative initial damage (interface and thermal cracks) generated by temperature reduced the bond strength. An empirical formula for predicting the bond strength was proposed. The bond stiffness decreased with the increase of temperature and increased with the increase of Vf. SFRC specimens with Vf = 1.5 % exhibited insignificant changes in bond toughness after high temperature compared to those with Vf = 1.0 %. The steel fibers significantly improved the bond toughness of SFRC specimens at room temperature. Empirical formulas for predicting bond stiffness and bond toughness were proposed. A prediction model for the bond-slip relationship between steel bar and SFRC after high temperature considering Vf and temperature was proposed. It is found that the established model of the bond-slip relationship agreed well with the experimental results.

Mode-Ι fracture of steel fiber reinforced concrete at low temperatures: Characterization with 3D meso-scale modelling

To investigate the mode Ι fracture behavior of SFRC (Steel Fiber Reinforced Concrete) at low temperatures, 3D meso-scale models of SFRC specimens with different steel fiber volume fractions (Vf = 0.0 %, 0.5 %, 1.0 % and 1.5 %) were developed by means of finite element analysis. The corresponding failure patterns as well as fracture properties were obtained by three-point bending simulations at low temperatures. SFRC is regarded as a multiphase material composed of mortar, aggregate, ITZ (Interface Transition Zone) and steel fiber at the mesoscopic scale. The comparison between simulation results and the test results verifies that the meso-scale numerical model could well describe the mechanical behavior of SFRC. The simulation results show that the fracture energy and unstable fracture toughness of SFRC significantly increase with the increase of fiber volume fraction and the decrease of temperature. The characteristic length of SFRC decreases with decreasing temperature but increases with increasing fiber volume fraction. The initial fracture toughness is less affected by fiber content while increasing with decreasing temperature. The prediction formulas were proposed which could be used to predict the fracture energy, characteristic length and unstable fracture toughness of SFRC at low temperature, respectively.

Experimental study on the influence of polypropylene and steel fiber on flexural behaviours of high strength concrete beams

Many properties of plain concrete are readily enhanced by adding various fibers. Different types of fibers were added to improve its tensile and bending behaviours. In the present experimental study, four different fiber dosages of polypropylene (0.025, 0.050, 0.075, and 0.10%) and steel fiber (0.25, 0.50, 0.75, and 1.00%) considered to determine the optimized content of 0.05% of polypropylene and 0.75% (both by volume of concrete) of steel fiber based on the workability and strength test results. These fiber content were added in controlled concrete of 60 MPa compressive strength to observe the improvements in flexural behaviour. Set of three reinforced concrete beam specimens of dimension 200 × 300 × 2100 mm were casted for considered series: controlled concrete (CC), polypropylene fiber reinforced concrete (PFRC) and steel fiber reinforced concrete (SFRC). Four-point bending test was conducted on all specimens by continuously recording the mid span deflection using liner variable differential transformer (LVDT). Primarily, load vs deflection response was plotted to analyze the improvements in, energy absorption capacity, flexural toughness, ductility and post-peak energy dissipation. The cracking pattern was studied in terms of crack width, spacing and number. Results indicated, increased average load sustaining capacity of CC specimen from 58.4 kN to 70.5 kN and 110.6 kN in PFRC and SFRC respectively at yield point. The magnitude of ultimate load enhanced by 12.1 kN in PFRC and 50.1 kN in SFRC specimens. Normalized flexural toughness values increased by 14.86% and 23.51% in PFRC and SFRC. The total energy absorption capacity of CC samples improved by 689.57 kN-mm due to polypropylene fiber and 2271.89 kN-mm because of steel fiber addition. The CC, PFRC and SFRC series displayed 1892.96 kN-mm, 2184.19 kN-mm and 2956.15 kN-mm of energy dissipation in the post-peak region. Steel fiber inclusion indicated the branching of cracks from the primary cracks.

Experimental study of reinforced concrete beams reinforced with hybrid spiral-hooked end steel fibres under static and impact loads

Discrete short steel fibres were proposed to be mixed with concrete for arresting cracks and enhancing the post-cracking resistance. It has been proven in previous tests that spiral steel fibres possessed markedly higher bonding to concrete matrix, leading to significantly improved performance of steel fibre reinforced concrete (SFRC) in terms of crack controllability, impact resistance, deformability and energy absorption capability. However, at the initial stage of cracking, SFRC reinforced with spiral fibres has relatively lower resistance to crack opening as compared to that reinforced with other types of steel fibres because of spiral shape stretching. To overcome this shortcoming, in the present study, short hooked-end steel fibres that exhibit high pull-out resistance at the crack initiation stage were mixed with spiral steel fibres in the normal-strength concrete matrix. A total volume fraction of 1% of hybrid steel fibres was mixed to cast SFRC specimens. With various mix ratios between spiral and hooked-end fibres considered, five batches of SFRC specimens were tested. Uniaxial compressive tests and four-point bending tests were carried out to compare the mechanical properties of SFRC materials with hybrid fibres while three-point bending tests on SFRC structural beams under static, drop-weight impact and post-impact static loading tests were conducted to investigate the structural performances. An equal dosage of hooked-end and spiral fibres was found to outperform other blend proportions to provide synergetic reinforcement to concrete matrix in terms of post-cracking resistance, energy absorption capacity and post-impact performance.

Residual strength and toughness properties of 3D, 4D and 5D steel fiber-reinforced concrete exposed to high temperatures

Conventional single-hooked (3D) steel fibers are one of the most widely used fibers to improve the strength, ductility and toughness properties of plain concrete. Recently, multi-hook 4D and 5D steel fibers with modified end geometries have been widely used in concrete applications as an alternative to 3D conventional steel fibers. The primary aim of this study was to compare mass loss, compressive and flexural strength, and toughness capacities of 3D, 4D and 5D steel fiber-reinforced concrete (SFRC) at room conditions and after high-temperature effects. Fibers were added to cement mortars at 0.5% and 1.5% by volume. All specimens were exposed to temperature effects of 300, 500 and 800 °C. According to the results obtained, the residual strength and toughness capacities of control and 3D, 4D and 5D SFRC specimens decreases significantly at 500 and 800 °C. However, when compared to control concrete, 3D, 4D and 5D SFRC specimens have higher residual compressive and flexural strength and residual toughness capacity after high-temperature effects. Furthermore, 5D steel fibers are more effective than 3D and 4D steel fibers to enhance the residual compressive and flexural strength and residual toughness capacity of concrete due to superior end geometry and higher tensile strength. In addition, this increase was more pronounced when the fiber volume ratio increased from 0.5% to 1.5%.

Experimental Investigation of Ultrasonic Pulse Velocity (UPV) Test Specimen in Assessing the Strength of Steel Fiber Reinforced Concrete Structure

This study aims to conduct the Ultrasonic Pulse Velocity (UPV) test and compressive strength test of Steel Fiber Reinforced Concrete (SFRC). This paper also examines the correlation of UPV test data and compressive strength test data for SFRC specimens. The experiments were carried out with the same value of the water-cement ratio, superplasticizer but different fiber volumes of steel fiber. Twelve prism sizes 100mm x 100mm x 500mm were casted and 0.5%, 1.0%, and 1.5% of steel fiber reinforced concrete were added and the prisms undergone curing for 7, 14 and 28 days. The highest value of the UPV test at the x-axis is SFRC-0.5%, 6.26 km/s at seven days and 6.8377 km/s at 14 days. The highest value of the UPV test at the y-axis is SFR-0.5%, 6.68 km/s at seven days and 6.34 km/s at 28 days. Nevertheless, the grading is still considered excellent concrete quality based on BS1881. The highest value of compressive strength is SFRC-1.0%, 193.2 MPa at 14 days. The R-squared value for the correlation coefficient between UPV result and the compressive strength result at the x-axis and y-axis is 0.9963 and 0.9966 respectively. The non-linear models show high regression coefficient of R-squared close to 1.00, which means the parameters are strongly correlated. The correlation equation obtained can be used to predict compressive strength based on UPV data for steel fiber volume fraction up to 1.5%. Thus, it can be concluded that percentage of steel fiber added, affect the strength of the tested concrete specimens and the optimized value of steel fiber added is at 1% in this study.