Fibre-reinforced Self-compacting Concrete Research Articles

Bond Behavior of Recycled Tire Steel-Fiber-Reinforced Concrete and Basalt-Fiber-Reinforced Polymer Rebar after Prolonged Seawater Exposure

The integration of basalt-fiber-reinforced polymer (BFRP) rebars into concrete design standards still remains unrealized due to limited knowledge on the performance of the rebars in concrete, particularly in terms of bond durability in harsh conditions. In this work, we investigated the bond durability characteristics of BFRP rebars in fiber-reinforced self-compacting concrete (FRSCC) structures. To this aim, a number of 24 FRSCC pullout specimens reinforced with either BFRP rebar or glass-fiber-reinforced polymer, GFRP, rebar, which is a commonly used type of FRP, were fabricated. Half of these specimens were submerged in simulated seawater for a two-year span, while the other 12 similar specimens were maintained in standard laboratory conditions for comparative purposes. Subsequently, all 24 specimens underwent monotonic and fatigue pull-out tests. The exploration in this study focused on investigating the influence of the environmental condition, reinforcement type, and loading type on the bond stress versus slip relationship, maximum bond stress, and failure mode of the specimens. Based on the results obtained and by adopting the durability approach of industry standards for prediction of the bond retention of FRP-reinforced concrete, the bond strength retention between BFRP/GFRP and FRSCC after 50 years of exposure to seawater was estimated. The outcomes of the study are expected to enhance engineers’ confidence in the use of FRP, especially BFRP, for constructing durable and sustainable reinforced concrete structures in aggressive environments.

Study on the impact resistance of steel fiber-reinforced self-compacting concrete after high temperature

The present study explored the dynamic mechanical properties of steel fiber-reinforced self-compacting concrete (SFRSCC) after a high temperature. The impact test was conducted using a φ80 mm split Hopkinson pressure bar (SHPB) device, with a focus on the factors of influence and the regularity of steel fiber content (0.5 %, 1.0 %, and 1.5 %), impact strain rate (55 s−1, 90 s−1, and 140 s−1), and temperature (20 °C, 300 °C, 600 °C, and 900 °C) on the failure form, dynamic strength, impact toughness, and dynamic increase factor (DIF-σ) of SFRSCC after high-temperature exposure, and the mechanism analysis based on the results of the SEM examination. The impact test results revealed the following: (1) With the increase in the steel fiber (SF) content, the dynamic strength (fp) of the SFRSCC exhibited a further evident growth trend after high temperature compared to that at normal temperature reaching 105 % and the toughness index also increased by more than 20 %. (2) While the effect of SF content on DIF-σ of SFRSCC was not significant under normal temperature conditions after high-temperature exposure, the DIF of SFRSCC can increase by over 40 % with the increase of SF content. In addition, the strain rate effect was also further significant, and the DIF-σ can increased by about 30 % after high-temperature treatment compared to normal temperature. (3) A prediction formula was proposed for DIF-σ of SFRSCC after high temperature, and the results were in good agreement with the results of the impact test. This prediction formula can better provide theoretical data support for disaster prevention and reduction in subsequent projects. The findings of the present study would serve as a valuable reference for subsequent research on the impact resistance of SFRSCC after high-temperature exposure.

Variability Analysis of Compressive and Flexural Performance of Coconut Fibre Reinforced Self-Compacting Concrete

Self-compacting concrete (SCC) is a high-performance material that flows freely and consolidates without segregation or bleeding. This study investigated the effectiveness of incorporating coconut fiber into SCC to improve its strength and toughness. Three mixtures with coconut fiber inclusions of 0.2%, 0.4%, and 0.6% by weight of cement were used. The addition of coconut fiber reduced the workability and passing ability of the concrete, but all mixes met the SCC specification. The CFRSCC with 0.2% had the highest compressive and flexural strengths. The study concluded that adding 0.2% coconut fiber to SCC can increase its strength. The use of natural fibers like coconut can enhance the properties of concrete and could be an alternative to synthetic fibers, especially in regions where natural fibers are locally available and cost-effective.

Impact resistance of micro and macro crimped steel fibre reinforced self-compacting concrete with SCM

This paper aims to investigate the impact resistance of micro and macro crimped steel fibre-reinforced self-compacting concrete (SFRSCC) with the volume fractions of 0.25%, 0.50%, and 0.75%. A total of seven mixtures were investigated with different volume fractions of steel fibres considering in terms of fresh, mechanical properties and impact resistance. The total binder contains 60% cement and 40% supplementary cementitious materials (SCM) with a combination of 30% fly ash and 10% silica fume. The addition of steel fibre decreases the workability of SCC. However, the inclusion of SCM compensates and increases its workability. Mechanical behaviour of micro and macro steel fibre reinforced SCC outperforms the conventional SCC in terms of compressive strength, split tensile strength and flexural strength. The impact resistance of SFRSCC is determined through a modified testing procedure derived from the guidelines provided by ACI 544.2 R. It is observed that the volume fraction of both 0.75% micro and macro steel fibre has improved impact resistance with increase percentage of energy absorption of 180% and 240%. The relationship between UPV and impact test results found that the number of blows can be predicted using the UPV values from the regression equations. The results of the Weibull distribution (WD) and reliability analysis indicate that 80% (τ = 0.8) of the SFRSCC samples are reliable enough to survive 14 blows at first crack and 20 blows at failure crack. The incorporation of crimped steel fibres into the concrete matrix led to the even distribution of impact loading throughout the concrete specimen with the help of steel fibres, thereby improving the impact resistance of SCC.

Effect of fibre diameter and tensile strength on the mechanical, fracture, and fibre distribution properties of eco-friendly high-strength self-compacting concrete

The development of Steel Fibre-Reinforced Self-Compacting Concrete (SFR-SCC) is a complex task with significant practical implications for the construction industry. However, the absence of established design guidelines and recommendations, and the limited availability of design methodologies, present a significant challenge. Achieving the targeted rheological and mechanical properties while simultaneously minimising production costs requires a comprehensive understanding of the optimal blend of fibre type and quantity and the coarse aggregate content. This paper addresses the impact of steel fibre properties on the rheological and fundamental mechanical properties of eco-friendly high-strength self-compacting concrete (HSSCC), using 40% ground granulated blast furnace slag (GGBS) as a cement replacement. The research focused on 30 mm long hooked-end steel fibres with tensile strengths of 1345 MPa and 3070 MPa, and diameters of 0.55 mm and 0.38 mm, respectively. In addition, the study investigated the combined effect of coarse aggregate content and steel fibre type on the performance of eco-friendly HSSCC. The fresh properties of eco-friendly HSSCC were assessed using the slump flow and J-ring tests. Furthermore, mechanical and fracture properties such as compressive strength, splitting tensile strength, elastic modulus, four-point flexural strength, and three-point flexural strength on notched prisms were also evaluated. The distribution and alignment of steel fibres in the HSSCC were assessed using image analysis techniques, which showed that the steel fibre diameters were a crucial factor in the fibre dispersion. The results demonstrated that using steel fibres with higher tensile strength and smaller diameter significantly enhanced the splitting tensile strength, flexural strength, and fracture energy, compared to steel fibres with larger diameters and lower tensile strengths. Additionally, the study indicated that the elastic modulus and fracture energy of eco-friendly HSSCC reinforced with both types of steel fibre are highly dependent on the content of coarse aggregate used. The study highlighted that the coarse aggregate proportion and the steel fibre characteristics were two vital factors that influenced the rheological and mechanical properties of HSSCC and must be considered during the mix design process to optimise the desired properties while also minimising production costs.

Comparative Performance of SF, PPF and Hybrid Fiber-Reinforced Self-Compacting Lightweight Concrete under Fire Exposure

Comparative Performance of SF, PPF and Hybrid Fiber-Reinforced Self-Compacting Lightweight Concrete under Fire Exposure

Flexural performance of V-shaped RC folded plates: The role of plate thickness and fiber hybridization

Reinforced concrete folded plates (RC-FPs) are frequently used in structures such as industrial buildings, hangars, swimming pools, and sports halls due to their high load-bearing capacity, low self-weight, economic advantages, and architectural appearance. However, experimental studies on the reinforced concrete (RC) behavior of these new-generation structural members are very limited. For this purpose, this article investigated the effect of plate thickness and fiber hybridization on the flexural performance of V-shaped RC-FPs produced from self-compacting concrete (SCC). With this study, the experimental moment–curvature tool was used for the first time to evaluate the flexural performance of V-shaped RC-FP. A total of sixteen large-scale V-shaped RC-FP specimens with different plate thicknesses (50, 60, 70, and 80 mm) and fiber hybridization (single, binary, and ternary) were manufactured and subjected to a four-point loading after a 90-day curing period. After the experimental load–deflection and moment–curvature curves were obtained, load-bearing capacity, toughness, curvature ductility, and effective flexural stiffness values were calculated and also showed in the crack patterns for all large-scale V-shaped RC-FPs. The empirical equations with high-precision have been developed using multiple linear regression analysis for predicting the load-bearing capacity, toughness, curvature ductility, and effective flexural stiffness of V-shaped RC-FPs based on the parameters of plate thickness and fiber hybridization. Consequently, the use of hybrid fiber-reinforced SCC in the production of V-shaped RC-FPs exhibited superior properties in terms of flexural performance and crack behavior, as well as allowing for accelerated erection of the roof carrier system, resulting in significantly reducing construction time and costs. Also, fiber reinforcement rather than an increase in plate thickness induced significant increases in the flexural performance values of the V-shaped RC-FPs, while ternary fiber hybridization was the best.

Retrofitting of post-heated R.C. columns using steel fiber reinforced self-compacting concrete jackets

This work aims to examine the effectiveness of using steel fiber-reinforced self-compacting concrete (SFRSCC) jackets in retrofitting RC columns subjected to high temperatures. In order to do that, eleven RC columns were cast and tested under axial loading. One column served as an unheated control column, and ten columns were heated to 400 °C and 600 °C for two hours. Subsequently, eight columns were retrofitted using SFRSCC jackets. The volume fraction of steel fibers and the thickness of the SFRSCC jackets were the main parameters considered for the retrofitting technique. According to the experimental findings, SFRSCC jackets can significantly enhance the structural performance of post-heated columns as evaluated by failure load, stiffness, and toughness. The percentage increase in the failure load, stiffness, and toughness of retrofitted post-heated columns is greatly impacted by the thickness of the SFRSCC jackets. The retrofitted columns with 25 mm and 50 mm SFRSCC jackets increased their failure load by 63.9% and 211.8%, respectively, relative to that of the heated control column at 600 °C. It is obvious that the failure load of the retrofitted columns was not significantly impacted by increasing the volume fraction of steel fiber in the SFRSCC jackets. Finally, a proposed design equation was suggested to predict the failure load of retrofitted post-heated columns with SFRSCC jackets.

Electrical conductivity and heating performance of hybrid steel fiber-reinforced SCC: The role of high-volume fiber and micro fiber length

Recently, it has become very popular to develop electrically conductive concrete composites for active deicing and snow-melting of transportation infrastructure. These composites should have stable electrical conductivity and a uniform heating performance, as well as high mechanical and durability properties, for a sustainable solution. In this context, the main motivation of this study is to develop an electrically conductive hybrid steel fiber reinforced self-compacting concrete (HSFR-SCC) composite for ice and snow removal applications. The electrical conductivity and heating performance of self-compacting concrete (SCC) mixtures having different fiber volumes (1.00, 1.25, and 1.50%) and the combination of macro steel fiber with micro steel fibers having lengths of 13 and 6 mm as single and hybrid were experimentally investigated for the first time. For this purpose, a total of ten SCC mixtures were designed, one of which was non-fiber Control, the others had steel fiber volumes of 1.00, 1.25, and 1.50% and different fiber combinations. Workability (slump-flow, T500 and J-ring) tests on HSFR-SCC mixtures were performed with reference to EFNARC. Then, mechanical (compressive and flexural strengths), electrical resistivity, and heating performance tests of 90-day HSFR-SCC samples were carried out. Before the electrical resistivity and heating performance tests, HSFR-SCC samples were kept in an oven at 105 ± 5 °C for 24 h to measure their most critical state (dry) performance. Moreover, using multiple linear regression analysis, empirical equations and contour plots were developed to predict the electrical resistivity and temperature increase values of HSFR-SCC samples depending on fiber volumes and combinations. Considering the experimental results, electrically conductive HSFR-SCC mixtures with satisfactory workability and high strength were obtained. The addition of various volumes and combinations of steel fiber to SCC significantly improved the electrical conductivity and heating performance of the concrete, while the mixtures with hybrid fiber were the best for all fiber volumes. As for the different micro fibers added to the HSFR-SCC mixtures, the 13 mm length micro steel fiber was much more effective in improving the electrical resistivity and heating performance of the samples compared to the 6 mm length micro steel fiber. Also, it was found that the fiber-reinforced index of electrically conductive HSFR-SCC samples could be 0.87 for effective and efficient electrical conductivity.

Impact and durability properties of alccofine-based hybrid fibre-reinforced self-compacting concrete

Many research works have already been made and are still in progress on metallic fibres, as their incorporation reduces the brittleness of the concrete and improves its resistance to the impact and crack propagation. But the use of such non-metallic fibres may induce corrosion which is a major problem to be addressed from the durability aspect. To overcome this problem, in the present research work, a non-metallic hybrid fibre combination was investigated with synthetic fibres like polypropylene and abaca fibres. Also, rather than using conventional cementitious materials such as silica fume, fly ash, and ground granulated blast furnace slag, a new generation of ultra-fine material namely alccofine was used as a partial replacement for the cement by 15%. Abaca fibre was utilised in a constant addition of 0.5% and blended with polypropylene fibre in a range varying from 0% to 2% with an increment of 0.5%. The fresh properties of self-compacting concrete (SCC) in mono and hybrid fibres combinations were assessed through slump flow, J-ring, and V-funnel tests. Water absorption and sorptivity tests were conducted to ensure the durability of the prepared mix. Further, impact tests were carried out on the prepared cylinder specimens to check the capability of the mix with the non-metallic hybrid combination. The main objective here was to check whether a high-strength durable SCC could be achieved using non-metallic fibres and natural fibres. From the obtained experimental results, it was observed that 15% alccofine as a partial substitute to the cement with the addition of 0.5% of abaca fibre and 2% of polypropylene fibre to SCC performed better than the control SCC.

Performance of hybrid steel fiber-reinforced self-compacting concrete RC beam under flexure

Hybrid steel fiber-reinforced self-compacting concrete (HSFRSCC) has desirable properties for improving the performance of structures. But the literature is sparse on the flexural performance of the reinforced concrete (RC) beam reinforced with hybrid fibers. The impact of the combined action of micro- and hooked-end steel fibers on the flexural performance of the SCC beam to which mineral admixtures and superplasticisers have been added to improve their workability is investigated in this study. In the experiment, beam specimens, reinforced with micro-steel and hooked-end fibers, with a compressive strength of 60 and 80 MPa and of size 150×230×3000 mm were prepared. The results clearly demonstrate that the flexural performance of the SCC beam significantly improved with the addition of hybrid steel fibers. The combination of 0.5% of hooked-end steel fibers and 0.25% of micro-steel fibers offers a better flexural performance than the addition of hybrid fibers in other proportions. Adding hybrid steel fibers in RCSCC beam increases the beam’s load- and moment-carrying capacities by 40.64% and 40%, respectively, compared to the RCSCC beam without hybrid steel fibers. The crack spacing and crack width are also reduced by 16–45% and 25–75%.

The Effect of Fiber Volume Fraction on Fiber Distribution in Steel Fiber Reinforced Self-Compacting Concrete

This paper investigates the effect of fiber volume fraction on fiber distribution in steel fiber reinforced self-compacting concrete (SFRSCC) through experiments and numerical simulations. Three types of SFRSCC beam specimens with different fiber volume fractions (0.3%, 0.6%, and 0.9%) were cut to expose the steel fibers. The number and the orientation angle of the steel fibers on the beam sections were determined by image analysis techniques. Fiber density, fiber segregation coefficient, fiber dispersion coefficient and fiber orientation coefficient were applied to evaluate fiber distribution on the beam sections. Based on the experimental data, numerical models simulating the pouring process of fresh SFRSCC were established to analyze the overall fiber distribution in the specimens. The results show that the distribution state of the fibers on the beam sections is not random and uniform, which is correlated to the fiber volume fraction. Due to the variable rheological properties, a greater fiber volume fraction causes better fiber uniformity, lower fiber segregation and worse fiber alignment on the beam sections. Meanwhile, the numerical results show that the distribution law of fibers along the length direction of the specimens is almost independent of the fiber volume fraction. In addition, increasing the fiber volume fraction results in the increase of the average angle of the fiber orientation in the specimens. The results can provide a reference for optimizing the fiber distribution in the concrete matrix.

A Numerical Method to Study the Fiber Orientation and Distribution of Fiber-Reinforced Self-Compacting Concrete

Steel fiber-reinforced self-compacting concrete (SCFRC) has been developed in recent decades to overcome the weak tensile performance of traditional concretes. As the flexural strength of SCFRC is dependent on the distribution of steel fibers, a numerical model based on Jeffery’s equation was developed in this study for investigating the effects of the concrete flow on the fiber orientation and distribution in SCFRC. This numerical method shows higher computational efficiency than available particle-based methods like SPH and LBM. The influence of casting parameters like casting method, formwork size and casting velocity on the fiber orientation is investigated from the perspective of the flow field of fresh concrete during casting. The simulation results show that the fiber orientation is largely dominated by the concrete flow during the casting process. Importantly, during casting SCFRC beam, fibers tend to be oriented in parallel along the longitudinal direction at the middle section, while they stick up at the end of the formwork due to the upward concrete flow. In addition, the results from parametric studies show that the formwork size and casting method could significantly affect the concrete flow during the casting process, ultimately the orientation of fibers in a SCFRC beam. Furthermore, it indicates that the casting speed needs to be carefully chosen in order to achieve the optimal fiber alignment.

Evaluation of performance of hybrid fiber-reinforced self-compacting concrete using non-destructive testing techniques

Evaluation of performance of hybrid fiber-reinforced self-compacting concrete using non-destructive testing techniques

Improvement of fresh and hardened properties of a sustainable HFRSCC using various powders as multi-blended binders

Hybrid fiber-reinforced self-compacting concrete (HFRSCC) has been very popular in recent years due to its high mechanical, durability and flexural performance. HFRSCC properties are also closely related to its workability properties. Therefore, a high proportion of binder material is required to provide a uniform distribution of the fibers in the matrix. The use of mineral admixtures replaced by cement has a vital importance to improve especially the workability of HFRSCC mixtures, resulting in reduction of CO2 emission because the production of 1 ton Portland cement releases about 1 ton of CO2. For this reason, in this study, the effects of multi-blended (binary, ternary and quaternary) binders containing Portland Cement (PC), fly ash (FA), ground granulated blast furnace slag (BS) and limestone powder (LP) on the workability (Slump-flow, T500, J-ring and V-funnel) and hardened (compressive, splitting tensile and flexural tensile strength) properties of HFRSCC as well as flexural performance for 7, 28 and 90 days are investigated. The first of three group mixtures in this study consists of only control mixture (Control) without fiber and mineral admixture blends (MAB), in second group there are four SCC mixtures with only MAB replaced by cement as binary, ternary, quaternary SCC-MAB and the last group also includes four SCC mixtures with both mineral admixtures same as second group and hybrid fiber (HFRSCC-MAB). The total binder amount, water/binder ratio, fine aggregate/all aggregate ratio and fiber hybridization are kept constant while the mineral admixture type and blending system are variable parameters. According to the test results, among the HFRSCC-MAB blends, the quaternary blend system performed the best in terms of workability, followed by the binary blends containing FA. In addition, when it came to ultimate strengths, hybrid fiber-reinforced samples with ternary blends performed best for compressive strength, while hybrid fiber-reinforced samples with binary blends containing FA performed best for splitting tensile and flexural tensile strengths. Finally, it has been seen that the use of various powders as multi-blended binders is a successful solution to obtain high workability for uniform distribution of fibers in HFRSCC as well as high compressive strength and flexural performance, resulting in economical, eco-friendly and sustainable composite.

Mechanical and Durability Properties of CCD-Optimised Fibre-Reinforced Self-Compacting Concrete

The accelerated advancement of industrialization, urbanization, and technology produces an enormous amount of waste materials that are channelled into the environment, contaminating the soil, water and air. This exceedingly large volume of waste in the planet’s environment has made it challenging and difficult to handle; thus, it is urgent to facilitate alternative methods of waste disposal. Moreover, the consumption of concrete raw materials increases as a consequence of a sudden increase in concrete usage. In this study, printed circuit boards (PCB), cutting waste (e-waste) (0%, 5%, 10%, 15%, 20%) and recycled concrete aggregate (construction and demolition waste) (0%, 20%, 40%, 60%, 80%, 100%) replace the fine and coarse aggregate; this is utilised in the making of self-compacting concrete (SCC). To mitigate the impact of shrinkage and micro-cracks produced during loading, synthetic fibres (polypropylene fibres) (0%, 0.25%, 0.5%, 0.75%, 1%) are incorporated into the dense matrix of concrete. Based on the experiments conducted, it is concluded that the optimum percentages of e-waste, recycled aggregate and synthetic fibres are 10%, 60% and 0.5%, respectively. It is proposed to use response surface methodology for the statistical modelling of fibre-reinforced self-compacting concrete (FRSCC) ingredients, which will diminish the number of experiments conducted during optimisation. Experimental optimisation of ingredients was carried out by determining the workability properties (slump flow, L-Box, V-Funnel and Sieve test), strength properties (compressive, split tensile, flexural at 7, 14, 28 days of curing) and durability properties against chemical exposure (sulphuric and hydrochloric acid attack, sulphate attack at 29 and 90 days of immersion). In the statistical optimisation process, the central composite design (CCD) is utilised, and it is concluded that the optimum percentages of e-waste, recycled aggregate and synthetic fibres are 9.90%, 51.35% and 0.503%, respectively, as these produce a compressive strength (CS) of 47.02 MPa at the end of the 28th day of curing, whereas FRSCC created with experimentally optimised ingredients shows a strength of 46.79 MPa with the use of 60% of recycled aggregate, 10% of e-waste and 0.5% polypropylene fibre. Hence, it is observed that the CCD-optimised ingredients were the optimum dosage of ingredients based on the compressive strength values at 28 days. It is concluded that the FRSCC specimens created with CCD-optimised parameters show better resistance against loading and chemical exposure, as these show minimum weight and strength loss when compared to FRSCC with experimentally optimised parameters.

Optimization of machine learning models for predicting the compressive strength of fiber-reinforced self-compacting concrete

Optimization of machine learning models for predicting the compressive strength of fiber-reinforced self-compacting concrete

Tensile Performance Test Research of Hybrid Steel Fiber-Reinforced Self-Compacting Concrete.

Notched beam specimens were loaded by the three-point bending test device, and the effects of different volume contents and combinations of steel fibers on the tensile properties of hybrid steel fiber-reinforced self-compacting concrete (HSFRSCC) were studied. The failure law and strain field distribution of the specimens were studied by digital image correlation (DIC) technology. Moreover, the curves between the load and crack mouth opening displacement (CMOD) of 18 groups of hybrid steel fiber-reinforced concrete specimens were obtained, and the stress-strain curves of 18 groups of specimens were derived from the load-CMOD curves. The results show that both single and hybrid steel fibers can improve the crack deformation resistance and tensile properties of concrete, but hybrid steel fibers have a more significant improvement effect. Only when the content of steel fiber is more than 0.6% can it have a more obvious postpeak descending section, and hybrid steel fiber has higher postpeak deformation capacity and flexural toughness. The fundamental reason why concrete with hybrid steel fibers has better tensile properties is that micro and macro steel fibers cooperate with each other to resist cracks, improving the toughness of concrete after cracking. Finally, the mechanism of different size and volume content of steel fiber was analyzed from the micro level, which can be used as a reference for the engineering design of HSFRSCC in the future.

Shear strength of functionally graded self-compacting concrete deep beams reinforced with steel and GFRP bars

Glass fiber-reinforced polymer (GFRP) bars are emerging as a potential replacement for steel rebars due to their vulnerability to corrosion. However, the shear behavior of GFRP bars is not well established, especially in functionally graded self-compacting concrete (SCC) deep beams reinforced with hybrid rebars (GFRP and steel). This article experimentally explores the behavior of functionally graded high-strength SCC deep beams having a hybrid of steel and GFRP bars as tension reinforcement. A total of fourteen deep beams were prepared with varying reinforcement ratios and steel fiber volume fractions. There were three groups of deep beams: (i) plain SCC (i.e., no fibers) beams, (ii) fiber-reinforced SCC (FRSCC) beams having 0.6 % and 1.2 % steel fibers, and (iii) functionally graded deep beams. The functional grading was achieved by casting beams in two layers, with the first layer of lower two-thirds depth having steel fibers and the second layer without fibers. The beams were shear deficient and tested in flexure. The shear resistance of functionally graded deep beams was compared with beams having fibers in full depth and without fibers. The test results reveal the significance of the hybrid system of rebars, which is found to effectively improve the structural capacity of concrete beams and increase the load required to initiate cracking. In addition, the mixing of fibers in concrete enhanced the deep beam shear capacity by 15–23 % for 0.6 % fibers and 37–39 % for 1.2 % fibers. The increase in the shear resistance of concrete deep beams was not influenced by the use of hybrid rebars compared to using GFRP bars only. A model is developed for assessing the shear resistance of functionally graded fiber-reinforced concrete deep beams by incorporating the dowel action of hybrid longitudinal reinforcing bars. The study indicates that the dowel action provided by GFRP bars is comparable to the steel bars of the same area.

Development of machine learning methods to predict the compressive strength of fiber-reinforced self-compacting concrete and sensitivity analysis

Fiber-reinforced self-compacting concrete (FRSCC), a great combination of self-compacting concrete (SCC) and fiber, plays a vital role as a potential construction material. Improving the accuracy of FRSCC’ performance prediction methods is critical and challenging to reduce costly experiments and time. Therefore, this study developed and assessed the performance of three machine learning models, including Decision tree, Light Gradient Boosting Machine, and Extreme Gradient Boosting (XGBoost), for predicting the compressive strength (CS) of FRSCC. The models were developed based on 387 data samples with 17 input parameters. Monte Carlo and K-fold cross-validation techniques were used to assess the models' generalizability and predictive performance. The results showed that the XGBoost model has the highest predictive performance and stability, with typical results R2 = 0.992, RMSE = 1.892 MPa, MAE = 1.438 MPa. The sensitivity analysis of the models indicated that cement, coarse aggregate, fine aggregate, water, and sample age significantly influence the CS of FRSCC with inconsistent order. Finally, XGBoost was the most accurate and reliable model based on the final architecture analysis.