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Öğe An investigation on the effect of hybrid fiber reinforced on the flexural behavior of RC beams having different lap-spliced lengths(Ernst & Sohn, 2023) Turk, Kazim; Bassurucu, MahmutThere are only a few studies related to the effect of the hybrid fiber reinforcement on the flexural behavior of full-scale beam specimens having lap-spliced length. Thus, this study will ensure important experimental data about the effect of macro steel fibers blended with micro steel fibers on lap-spliced length. The aim of this study was to investigate the influence of hybrid steel fiber reinforcement on the flexural behavior of full-scale reinforced concrete beams having different lap-spliced bars. A sum of three traditional concrete mixtures including a total of 1% fiber by volume fraction was adopted: control mixture without steel fiber, only macro steel fiber and hybrid steel fiber reinforced mixtures. For this purpose, 18 full-scale beams (200 x 300 x 2000 mm) having three different lap-spliced length (15, 25, and 35o) as tension steel bars were produced and tested under four-point bending to examine flexural behavior, mode of failure, ductility, and energy absorption capacity properties. In conclusion, the hybrid fiber reinforcement caused the highest increase in the load carrying capacity of the beam specimens. Besides, the hybrid fiber reinforced beam specimens exhibited excellent ductility and energy absorption capacity compared to single fiber reinforced beam specimens. On the other hand, it can be addressed that the hybrid fiber reinforced structural elements had a vital important to compensate the application errors and carelessness in steel bar workmanship, inadequate the lap-spliced length as per the codes. It can be emphasized that the lap-spliced length as per the building codes can be reduced in 40% by containing hybrid steel fiber (0.8% macro-0.2% micro) reinforced concrete without a reduction in load carrying capacity, ductility, and energy absorption capacity compared to control beam specimens without fiber.Öğe Durability of Engineered Cementitious Composites Incorporating High-Volume Fly Ash and Limestone Powder(Mdpi, 2022) Turk, Kazim; Kina, Ceren; Nehdi, Moncef L.This study investigates the effects of using limestone powder (LSP) and high-volume fly ash (FA) as partial replacement for silica sand (SS) and portland cement (PC), respectively, on the durability properties of sustainable engineered cementitious composites (ECC). The mixture design of ECC included FA/PC ratio of 1.2, 2.2 and 3.2, while LSP was used at 0%, 50% and 100% of SS by mass for each FA/PC ratio. Freeze-thaw and rapid chloride ions penetrability (RCPT) tests were performed to assess the durability properties of ECC, while the compressive and flexural strength tests were carried out to appraise the mechanical properties. Moreover, mercury intrusion porosimetry (MIP) tests were performed to characterize the pore structure of ECC and to associate porosity with the relative dynamic modulus of elasticity, RCPT and mechanical strengths. It was found that using FA/PC ratio of more than 1.2 worsened both the mechanical and durability properties of ECC. Replacement of LSP for SS enhanced both mechanical strengths and durability characteristics of ECC, owing to refined pore size distribution caused by the microfiller effect. It can be further inferred from MIP test results that the total porosity had a vital effect on the resistance to freezing-thawing cycles and chloride ions penetration in sustainable ECC.Öğe Extreme Learning Machine for Estimation of the Engineering Properties of Self-Compacting Mortar with High-Volume Mineral Admixtures(Springer Int Publ Ag, 2024) Turk, Kazim; Kina, Ceren; Tanyildizi, HarunThe utilization of supplementary cementitious materials obtained from industrial by-products or wastes is one of the most effective ways to minimize the costs as well as environmental impact associated with cement production. This work investigated the effects of the replacement of Portland cement (PC) with (25, 30, 35 and 40%) fly ash (FA) and (5, 10, 15, and 20%) silica fume (SF) by weight as binary and ternary blends on the compressive strength (f(c)) and flexural strength (f(ft)) of self-compacting mortars (SCMs) at 28 and 91 curing days. Extreme learning machine (ELM), support vector regression (SVR), artificial neural network (ANN), and decision tree (DT) models were devised to predict these strengths of SCMs containing high-volume mineral admixture (HVMA). The selected input variables were the number of curing days, water-cementitious material (W/CM), PC, FA, SF, and sand contents, while the f(c) and f(ft) were the output variables. ANOVA results show that the curing time was the most effective parameter for determining both strengths. The results also indicated that ELM achieved superior performance for the prediction of f(c) and f(ft) of SCMs with HVMA compared to SVR, ANN, and DT due to having the highest coefficient of determination values of 0.9802 for both strengths.Öğe Fire resistance of hybrid fiber reinforced SCC: Effect of use of polyvinyl-alcohol or polypropylene with single and binary steel fiber(Techno-Press, 2023) Turk, Kazim; Kina, Ceren; Balalan, EsmaThis study presents the experimental results performed to evaluate the effects of Polyvinyl-alcohol (PVA) and Polypropylene (PP) fibers on the fresh and residual mechanical properties of the hybrid fiber reinforced SCC before and after the exposure of 250 & DEG;C, 500 & DEG;C and 750 & DEG;C temperatures. The compressive and splitting tensile strength, modulus of rupture (MOR), ultrasonic pulse velocity (UPV) as well as toughness and weight loss were investigated at different temperatures. PVA and PP fibers were added into SCC mixtures having only macro steel fiber and also having binary hybridization of both macro and micro steel fiber. The results showed that the use of micro steel fiber replaced by macro steel fiber improved the fresh and hardened properties compared to the use of only macro steel fiber. Moreover, it was emphasized that PVA or PP enhanced the residual flexural performance of SCC, generally, while it negatively influenced the workability, weight loss, UPV and the residual strengths with regards to the use of single steel fiber and binary steel fiber hybridization. Compared to the effect of synthetic fibers, PP had slightly more positive effect in the view of workability while PVA enhanced the residual mechanical properties more.Öğe Forecasting the compressive strength of GGBFS-based geopolymer concrete via ensemble predictive models(Elsevier Sci Ltd, 2023) Kina, Ceren; Tanyildizi, Harun; Turk, KazimThe compressive strength (fc) of the concrete is an important parameter in the structural design. However, the assessment of fc via an experimental program is time-consuming, costly, and needs a labor force. Therefore, the forecasting of fc through different algorithms can accelerate and facilitate this process and also provide guidance for scheduling the progress of the construction. While some studies have explored the use of models for the prediction of fc of concrete, the ensemble models that can predict the fc of GPC with industrial by-products is still lacking. Within this scope, decision tree (DT), Bootstrap aggregating (Bagging), and Least-squares boosting (LSBoost) models were devised to predict fc of ground granulated blast furnace slag (GGBFS)-based geopolymer concrete (GPC). The data points collected to devise a GEP model in the previous study were used and the prediction results of the GEP model were compared with the proposed ensemble models in the current study. The age of the specimen, NaOH solution concentration, natural zeolite (NZ) content, silica fume (SF) content, and GGBFS content were used as input parameters, and fc was used as output parameter. According to ANOVA analysis, the age of the specimen was found as the most influential parameter in the determination of the fc of GGBFS-based GPC. Also, Multiple linear regression equation was proposed to estimate the fc of GGBFS-based GPC with the accuracy of 93%. The most accurate model was introduced through performance metrics and the Taylor diagram. The results proved that the highest accuracy and stable predictions were achieved by the LSBoost model with R-squared value of 98.25% followed by GEP model developed in the previous study, DT and Bagging models. However, it is worth mentioning that due to having a high coefficient of correlation values (>%80), DT and Bagging models also have an acceptable ability for predicting fc of GGBS-based GPC.Öğe Importance of pumice amount in the design of self-compacting lightweight concrete(2024) KARADAĞ, ENES MİRAÇ; Gürocak, Mustafa; Kina, Ceren; Turk, KazimAlthough concrete has high compressive strength values, it has a heavy unit volume and low tensile strength. In this study, the normal-weight aggregate, which takes up the most space in concrete by volume and mass, was partially replaced with pumice aggregate, and macro steel fiber (30 mm) was also added to the mixtures. This experimental work aims to investigate the effect of pumice aggregate amount on the fresh and hardened properties, as well as the flexural performance of the self-compacting lightweight concrete (SCLC). The replacement proportions of pumice aggregate with crushed sand were arranged as 45%, 50%, and 55% of the entire aggregate by weight. Three mixtures, each with 1% macro steel fiber reinforcement and without fiber, were prepared for each mixture scenario. The mix design of these six mixtures was arranged to achieve the self-compacting ability and the workability tests recommended by EFNARC (slump-flow, T50, J-ring) were taken into account. To investigate the mechanical properties (compressive, splitting tensile, and flexural strengths) and flexural toughness of the samples, the specimens were cured in water at 23±2 °C for 28 days. As a result, the unit volume weights of the specimens produced from pumice-substituted mixtures decreased with the increase in the pumice dosage, while the compressive, splitting tensile, and flexural strengths decreased. However, it has been determined that all SCLC mixtures including pumice aggregate provided workability properties in general and had enough compressive strength to be used in the production of structural bearing elements, regardless of fiber content. As a result, the optimum pumice aggregate replacement percentage with crushed sand was found to be 45% and the best flexural performance values of the specimens having macro steel fiber were observed in the ones having 45% pumice aggregate substitution.Öğe Investigation of shear strength of SCC beams with hybrid fiber as experimental and statistical(Yildiz Technical Univ, 2023) Turk, Kazim; Bassurucu, Mahmut; Oztekin, ErolIn this study, the effects of different blending and combination of macro and micro steel fibers on the shear strength, ductility, failure mode and crack propagation of hybrid fiber reinforced self-compacting concrete beams were investigated experimentally and statistically. In the design of concrete, straight steel micro and hooked steel macro fibers were used. For this purpose, twelve 200x200x1000 mm reinforced concrete beam specimens, which had same reinforcing bar details, were produced and tested under four-point bending to investigate ultimate shear strength, displacement ductility, crack patterns, mode of failure, energy absorption capacity and yield stiffness properties. In conclusion, the beam specimens produced from self-compacting concrete (SCC) with hybrid steel fiber prevented the shear failure while all SCC beam specimens containing hybrid steel fiber reached the ultimate bearing capacity with the mode of flexural failure. Also, it can be clearly emphasized that the SCC beam specimens with hybrid steel fiber had higher shear strength, energy absorption capacity and yield stiffness than those of beam specimens containing only macro or micro steel fiber.Öğe Machine Learning Prediction of Residual Mechanical Strength of Hybrid-Fiber-Reinforced Self-consolidating Concrete Exposed to Elevated Temperature(Springer, 2023) Turk, Kazim; Kina, Ceren; Tanyildizi, Harun; Balalan, Esma; Nehdi, Moncef L. L.Establishing the engineering properties of cement-based composites at elevated temperature requires costly, laborious, and time-consuming experimental work. Data-driven models can provide a robust and efficient alternative. In this study, extreme learning machine (ELM), support vector machine (SVM), artificial neural network (ANN), and decision tree (DT) models were trained to predict the residual compressive, splitting tensile, and flexural strengths of hybrid fiber-reinforced self-compacting concrete (HFR-SCC) exposed to high temperatures. Mixtures including macro and micro steel fibers, polyvinyl alcohol (PVA), and polypropylene (PP) were subjected to different temperature levels, leading to an experimental database of 360 specimens. Eleven input parameters including cement, fly ash, water, sand, gravel, fiber type, water reducer, and temperature were deployed. The residual mechanical strengths were targeted as output parameters. ANOVA was used to explore the influence of input parameters. Temperature was found to be the most influential parameter. Dataset consisting of 114 instances was retrieved from pertinent literature and used along with the authors' experimentally generated dataset for residual strength prediction. The experimental results were compared with predictions of ELM, SVM, ANN, and DT. ELM achieved superior performance and can offer a robust tool for predicting the residual mechanical strengths of HFR-SCC upon exposure to high temperature.Öğe Research on bond behavior between steel rebar and self-compacting geopolymer concrete (SCGC) containing recycled aggregate by large-scale beams: The role of different hybrid activator content and precursor materials(Elsevier Sci Ltd, 2025) Utu, Rumeysa; Katlav, Metin; Donmez, Izzeddin; Kina, Ceren; Turk, KazimThis paper aims to experimentally evaluate, for the first time in the literature, the bond strength between steel rebar and self-compacting geopolymer concrete (SCGC) containing 100 % recycled aggregates, considering the effects of different hybrid activator ratios and precursor material combinations, using large-scale reinforced concrete (RC) beams. With this aim, a total of twelve full-scale SCGC beams, each with dimensions of 200 x 300 x 2000 mm, were produced with different hybrid activator ratios ((Na2SiO3 / (Ca(OH)2 + Na2SiO3)= 0.15, 0.20, 0.25) and precursor material combinations (single, binary and ternary) and tested under four-point bending loading after a 90-day curing period. Test outcomes were compared and evaluated based on main structural performance parameters, including crack patterns and propagation, failure modes, load-midspan displacement curves, load-strain behavior, and bond strength. Moreover, the predictive performance of some existing mechanics-based models for predicting bond strength was evaluated for spliced steel rebar in the SCGC beams. According to the experimental outcomes, both the hybrid activator ratio and the precursor material combinations had remarkable effects on the bond behavior of SCGC beams. In general, lower hybrid activator ratios primarily induced flexural cracks concentrated within the pure bending region, while increasing the hybrid activator content led to a greater number of cracks, particularly transforming into inclined (shear) cracks in the shear region. As for the influence of precursor materials, binary blends-the combination of silica fume (SF) and ground granulated blast furnace slag (BS)-consistently provided superior structural performance, characterized by improved crack control, enhanced load-carrying capacity, and higher bond strength. Notably, the 0.50SF+ 0.50BS_0.15 N specimen with a 0.15 hybrid activator ratio achieved the highest peak load of 96.58 kN and the maximum bond strength of 4.31 MPa among all tested specimens. Furthermore, while existing mechanical bond strength models offered moderately accurate predictions for SCGC, they failed to comprehensively account for the unique interaction mechanisms inherent to geopolymer systems. Therefore, this study underscores the importance of optimizing both activator dosage and precursor synergy to ensure reliable predicted bond performance in SCGC. All in all, these results are expected to provide valuable guidance for structural engineers seeking to implement environmentally friendly, durable, and structurally efficient SCGC members in real-world construction applications.Öğe The effect of hybrid fiber and shear stud on the punching performance of flat-slab systems(Elsevier, 2023) Bassurucu, Mahmut; Turk, Kazim; Turgut, PakiIn this paper, for the first time, the binary/ternary hybrid fiber and/or shear stud reinforcement as a measure was used to improve the punching performance of flat-slab systems by innovative selfcompacting concrete (SCC). Because in these slab systems, sudden and brittle punching failure can be seen due to application and design errors, early removal of formwork, changes in the purpose of use of the building, earthquakes, etc. Besides, numerous studies investigated the punching performance of the single fiber and/or shear stud reinforced flat-slab systems, but research into the measures of the hybrid fiber or the combined use of hybrid fiber and shear stud reinforcement, which were the variable parameters of this study, was quite lacking. For this purpose, the half-scale slab-column connection elements were produced from SCC containing different punching measures (binary/ternary hybrid and/or shear stud) and tested to investigate the punching performance of flat-slab systems. In conclusion, it was found that hybrid fiber reinforcement was the best punching measure to improve the punching performance of slabcolumn connection elements with/out shear stud. Besides, 3D graphs were drawn so that designers and researchers could estimate the punching strength and energy absorption capacity for flat-slab systems with/out shear stud based on the parameters of micro fiber type and total volume fraction. On the other hand, empirical formulas were developed to predict the punching strength of binary/ternary hybrid fiber reinforced flat-slab systems with/out shear stud by compressive strength, fiber reinforcement index, the slab useful height, and the punching perimeter parameters.Öğe Workability, flexural response and shrinkage crack restriction of fiber-reinforced SCC: Effects of low coarse aggregate content and micro fiber type(Elsevier Sci Ltd, 2025) Kina, Ceren; Turk, KazimSelf-compacting concrete (SCC) has become increasingly popular due to its beneficial properties, such as reducing labor and construction time, achieving higher quality finish surfaces, and facilitating the construction of heavily congested structural elements. However, the requirement for a greater volume of paste and fine aggregate in the mix design of SCC, compared to ordinary concrete, raises concerns about increased shrinkage. The novelty of this study lies in the use of a low coarse aggregate-to-total aggregate ratio of 0.25, which aims to diminish the beneficial impact of coarse aggregate content on shrinkage performance. This approach seeks to achieve dimensional stability in SCC by incorporating various types and hybrid forms of fiber and allows to investigate their effects on reducing cracks that arise from restraint. In this sense, four fiber types (doublehooked-end steel fiber as macro, short and long straight steel fiber, and PVA synthetic fiber as micro fibers) and their hybridizations (single, binary, ternary, and quaternary) were utilized.Experimental results showed that among the fiber-reinforced SCC mixtures, although all mixtures met the self-compacting criteria, only the binary blend containing 0.8 %macro steel fiber and 0.2 %short micro steel fiber satisfied both the SF3 and VS2/VF2 class limits, while all were classified in PJ1 according to EFNARC. This binary blended sample also showed the highest compressive strength gain, with increases of 24.45 %, 28.89 %, and 20.72 % compared to the control sample at 3, 28, and 90 curing days, respectively. In terms of flexural strength, the ternary blend of 1 %macro steel fiber, 0.8 %long micro steel fiber and 0.5 %PVA demonstrated the greatest enhancement. It showed a 56.8 % increase relative to the control SCC sample, achieving the highest toughness at 101.7 N-m, and displayed significant multiple-cracking behavior among the 90-day samples. Furthermore, under restrained conditions, the quaternary fiber-blended SCC sample achieved the lowest total crack width and shrinkage strain, measuring 149 mu m and 117 mu epsilon, respectively. In conclusion, in a system with a low ratio of coarse aggregate, these cracks can be effectively controlled by incorporating fibers and adopting a hybrid approach, which not only enhances strength, but also ensures that the fresh properties stay within the SCC standards.
