Browsing by Author "Akbulut, Z.F."

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Advancing Hybrid Fiber-Reinforced Concrete: Performance, Crack Resistance Mechanism, and Future Innovations
(Multidisciplinary Digital Publishing Institute (MDPI), 2025) Akbulut, Z.F.; Tawfik, T.A.; Smarzewski, P.; Guler, S.
This research investigates the effects of steel (ST) and synthetic (SYN) fibers on the workability and mechanical properties of HPFRC. It also analyzes their influence on the material’s microstructural characteristics. ST fibers improve tensile strength, fracture toughness, and post-cracking performance owing to their rigidity, mechanical interlocking, and robust adhesion with the matrix. SYN fibers, conversely, mitigate shrinkage-induced micro-cracking, augment ductility, and enhance concrete performance under dynamic stress while exerting negative effects on workability. Hybrid fiber systems, which include ST and SYN fibers, offer synergistic advantages by enhancing fracture management at various scales and augmenting ductility and energy absorption capability. Scanning electron microscopy (SEM) has been crucial in investigating fiber–matrix interactions, elucidating the effects of ST and SYN fibers on hydration, crack-bridging mechanisms, and interfacial bonding. ST fibers establish thick interfacial zones that facilitate effective stress transfer, whereas SYN fibers reduce micro-crack formation and enhance long-term durability. Nonetheless, research deficiencies persist, encompassing optimal hybrid fiber configurations, the enduring performance of fiber-reinforced concrete (FRC), and sustainable fiber substitutes. Future investigations should examine multi-scale reinforcing techniques, intelligent fibers for structural health assessment, and sustainable fiber alternatives. The standardization of testing methodologies and cost–benefit analyses is essential to promote industrial deployment. This review offers a thorough synthesis of the existing knowledge, emphasizing advancements and potential to enhance HPFRC for high-performance and sustainable construction applications. The findings facilitate the development of new, durable, and resilient fiber-reinforced concrete systems by solving current difficulties. © 2025 by the authors.
A Comprehensive Review of Concrete Durability in Freeze-Thaw Conditions: Mechanisms, Prevention, and Mitigation Strategies
(Elsevier Ltd, 2025) Guler, S.; Akbulut, Z.F.
Freeze-thaw (F-T) damage is a critical factor affecting the durability of concrete in cold climates. This study provides a comprehensive review of F-T deterioration mechanisms and evaluates strategies to mitigate such damage. Key internal processes, including hydrostatic and osmotic pressure, salt crystallization, and the micro-ice lens hypothesis, are identified as primary contributors to internal cracking, pore pressure buildup, and crystalline expansion, which lead to material degradation. Critical saturation is highlighted as a crucial parameter in assessing concrete's susceptibility to F-T damage. Among the mitigation strategies, air-entraining agents (AEA) are recognized as the most effective, as they create micro-air voids that accommodate freezing water, thereby reducing internal stresses and minimizing crack formation. Additionally, surface strengthening techniques and fiber reinforcement show promise in enhancing concrete's resilience against F-T cycles by improving its structural integrity and flexibility. Despite the advancements in mitigation strategies, challenges remain, particularly concerning the complex interactions between F-T cycles, de-icing salts, and concrete's material properties. Further research is needed to refine predictive models and develop advanced material modifications to enhance the long-term performance of concrete in F-T environments. This study underscores the necessity for continued investigation to develop more resilient concrete structures, particularly for infrastructure exposed to severe freezing and thawing conditions. © 2025 Institution of Structural Engineers
Corrigendum To “the Effects of Waste Iron Powder and Steel Fiber on the Physical and Mechanical Properties of Geopolymer Mortars Exposed To High Temperatures” [Structures 58 (2023) 105398] (Structures (2023) 58, (S2352012423014868), (10.1016/J.istruc.2023.105398))
(Elsevier Ltd, 2025) Akbulut, Z.F.; Guler, S.; Khan, M.
The authors regret to report an error in the affiliations section of the original article. The correct affiliation for M. Khan is School of Civil Engineering, University College Dublin, Newstead, Belfield, Dublin 4, Ireland. The authors would like to apologise for any inconvenience caused. ____________________________ DOI of Original Article: 10.1016/j.istruc.2023.105398 © 2025 Institution of Structural Engineers
The Coupling Effect of Silica Fume and Basalt Fibers on Workability and Residual Strength Capacities of Traditional Concrete Before and After Freeze–thaw Cycles
(Springer Science and Business Media Deutschland GmbH, 2023) Guler, S.; Akbulut, Z.F.
The combined use of silica fume (SF) and single and hybrid-basalt (BA) fibers can be a prominent option in diminishing the degradations of concrete after freeze–thaw (F–T) effects. This study investigated slump, mass loss (ML), abrasion loss (AL), residual compressive strength (RCS), and residual splitting tensile strength (RSTS) of SF and single- and hybrid-BA fiber-reinforced concrete after F–T cycles. The results demonstrated that although using SF and BA fibers together adversely affected the workability of the mixtures, they significantly improved the samples’ RCS and RSTS capacities. Besides, after F–T cycles, SF alone and with BA fibers are very efficient in reducing the AL of the samples. However, while using SF alone was somewhat effective in reducing the ML losses of the pieces, its use with single- and hybrid-BA fibers remained negligible. Furthermore, the hybrid use of BA fibers is more efficient in recovering concrete samples' workability and AL, RCS, and RSTS capacities than the single use. Compared to room conditions, after the 180 F–T cycles, the AL of the R0 control sample increased by 29.24%, while the SF and BA fiber-added R1–R7 samples ranged from 7.11% to 10.17%. Additionally, after the 180 F–T cycles, while the RSTS capacity of R0 control concrete decreased by 27.06%, the reduction in RSTS capacity of R1–R7 BA fiber-reinforced concrete ranged from 13.42% to 23.63%. This study is expected to constitute an important reference to the literature on how SF pozzolanic admixture and BA fiber additives play a role in improving the behavior of concrete against F–T cycles. © 2023, Wroclaw University of Science and Technology.
Effect of Freeze-Thaw Cycles on Strength and Toughness Properties of New Generation 3d/4d Steel Fiber-Reinforced Concrete
(Elsevier Ltd, 2022) Guler, S.; Akbulut, Z.F.
This study aimed to compare the changes in mass loss, relative dynamic modulus of elasticity (RDME), residual compressive strength (RCS), residual flexural strength (RFS), and residual flexural toughness (RFT) of 3D, 4D and 5D steel fiber-reinforced concrete (SFRC) specimens after freeze-thaw (F-T) cycles. 3D, 4D, and 5D steel fibers were added to the concrete mixes at rates of 0.5% and 1.5% by volume. All specimens were subjected to 100, 200, and 300 F-T cycles. The changes in the microstructural properties of control and 3D, 4D, and 5D SFRC samples after F-T cycles were examined with scanning electron microscope (SEM) analysis. According to the test results, 3D, 4D, and 5D steel fibers did not affect reducing mass loss of concrete after F-T cycles. However, 3D, 4D, and 5D SFRC samples had higher RDME, RCS, RFS, and RFT values than control concrete after F-T cycles. Furthermore, 5D steel fibers were more effective than 3D and 4D steel fibers in improving the residual strength and toughness capacity of concrete after F-T cycles due to their stronger fiber/matrix interface. © 2022
Effect of High-Temperature on the Behavior of Single and Hybrid Glass and Basalt Fiber Added Geopolymer Cement Mortars
(Elsevier Ltd, 2022) Guler, S.; Akbulut, Z.F.
This study aims to investigate the workability, visual appearance and mass loss, compressive, and flexural strength properties of the single and hybrid glass (GL) and basalt (BA) fiber added fly ash (FA)-based geopolymer cement (GPC) mortars after the high-temperature effect. Micro- and macro - GL and BA fibers were added to the GPC mixtures in two different volumetric ratios, 0.5% and 1%. 300, 500, and 800 °C of high temperatures were applied to the GPC mortar samples. After the high-temperature effect, microstructural variations of selected GPC mortar specimens were determined using scanning electron microscope (SEM) analysis tests. As a result of the study, it was seen that the use of GL and BA fiber had a very negative effect on the workability of the mixtures and caused a significant decrease in the spreading diameters. Compared to the control concrete, it was observed that the GPC samples with GL and BA fiber additives had considerably higher (upper 5%) residual compressive and flexural strengths after the high-temperature effect. Furthermore, the hybrid use of GL and BA fibers is somewhat more effective than single GL and BA fibers in increasing the residual compressive and flexural strengths of the GPC mortar samples after the effect of high temperature. In addition, since GL fibers are less agglomerated and exhibit a more homogeneous distribution in blends, they are slightly more effective in improving both workability and residual compressive and flexural strengths of GPC mortar samples compared to BA fibers. © 2022 Elsevier Ltd
Effect of Macro Polypropylene, Polyamide and Steel Fibers on the Residual Properties of Scc at Ambient and Elevated Temperatures
(Elsevier Ltd, 2021) Guler, S.; Akbulut, Z.F.; Siad, H.; Lachemi, M.
This paper considers the effect of equivalent macro size fibers of polypropylene (PP), polyamide (PA) and steel (ST) on the properties of reinforced self-compacting concrete (FRSCC) exposed to normal and elevated temperatures. Different fiber concentrations of 0%, 0.3%, 0.6% and 1% were investigated under temperatures of 20 °C, 300 °C, 500 °C and 800 °C. Mass loss, residual compressive strength (RCS), residual flexural strength (RFS), toughness indices (TI), residual strength factors (RSF) and residual toughness (RT) capacities of FRSCCs were studied at hardened state based on their initial results at ambient curing. Meanwhile, slump-flow diameter, T500 time and L-box parameters were also tested at fresh state. In addition, the microstructural changes due to the use of various fibers and temperatures were examined by scanning electron microscope (SEM) analysis. The effect of macro PA and PP was comparable in terms of their minor influence on the mass loss, RCS and RFS of FRSCC compositions. However, macro PA presented greater contribution than PP in preserving the toughness capacity, particularly in the post-peak stage. Unlike PA and PP, the use of macro ST fibers caused noticeable increments in RFS and RT capacities. The superior outcome of using macro ST was confirmed through its higher effect in mitigating the crack formation of FRSCC, especially under elevated temperatures of 500 °C and 800 °C. © 2021 Elsevier Ltd
The Effects of Single and Hybrid Polypropylene Fibers on the Workability and Residual Strength Properties of Concrete Road Pavements Against Freeze–thaw Cycles
(Institute for Ionics, 2023) Guler, S.; Akbulut, Z.F.
This study mainly examines the slump, mass loss (ML), abrasion loss (AL), residual compressive strength (RCS), and residual splitting tensile strength (RSTS) of concrete reinforced with micro- and macro-polypropylene (PP) fibers after the F–T process. In the blends, micro- and macro-PP fibers were added to the blends at 0.3%, 0.6%, and 1% by volume. In total, 25, 50, 100, and 150 F–T cycles were applied to all samples. The study’s results show that micro- and macro-PP fibers negatively affect the blends' slump values. Besides, PP fibers did not contribute to reducing the ML values of the samples after the F–T process. Moreover, the contribution of the PP fibers in prohibiting the decrease in RCS capacities of specimens after the F–T process is valid up to 0.3% volumetric fiber content. Additionally, PP fibers were more efficient in hindering reductions in AL and RSTS capacities after the F–T process of the specimens. Furthermore, using macro-PP fibers in hybrid form with micro-PP fibers reduced AL and improved RCS and RSTS capacities more than single macro-PP fibers. After 150 F–T processes, the reduction in AL of C0 control concrete was 9.41%, while the declines in AL of C1-C6 samples ranged from 7.56% to 8.92%. In addition, after 150 F–T processes, the decrease in RCS and RSTS loss of C0 control concrete is 25.09% and 28.30%. In contrast, the decline in RCS and RSTS loss of C1-C6 samples varies between 22.94–32.97% and 20.10–25.75%, respectively. © 2023, King Fahd University of Petroleum & Minerals.
Enhanced Freeze-Thaw Resilience of Cement Mortars Through Nano-Sio2 and Single/Hybrid Basalt Fiber Incorporation: Assessing Workability, Strength, Durability
(Elsevier Ltd, 2024) Guler, S.; Akbulut, Z.F.; Siad, H.; Lachemi, M.
This study investigated how freeze-thaw cycles (FTC) impact concrete durability and structural integrity, exploring novel approaches like integrating nanomaterials and fibers into concrete compositions. After subjecting the materials to FTC, the study evaluated mortars enriched with nano-SiO2 (NS) and micro- and macro-basalt (BA) fibers. NS was incorporated by substituting 1 % and 2 % of the cement content. Meanwhile, 24 mm in length macro-BA fibers were added individually or in hybrid compositions with 6 mm micro-BA fibers at 0.5 % and 1 % volumetric ratios. The results revealed significant improvements in both the strength and durability of mortar specimens post-FTC, attributed to the enhancing properties of NS. Its capacity to fill voids and substantial pozzolanic activity notably improved the material's performance. However, adding BA fibers adversely affected mortar workability, causing a decrease in flow diameters (FD) as the fiber ratio increased. Nevertheless, BA fibers effectively maintained specimen integrity post-FTC despite leading to decreased residual compressive (RCS) and flexural strengths (RFS). This reduction was linked to the robust bonding between BA fibers and the matrix, impeding crack propagation post-FTC. Interestingly, combining BA fibers in hybrid configurations improved workability and significantly enhanced residual strength characteristics, surpassing singular applications. For instance, after 180 FTC, the K0 control specimen exhibited a 34.17 % and 34.56 % reduction in RCS and RFS, respectively. In contrast, the K10 specimen with 2 % NS and a hybrid combination of BA fibers at a volumetric ratio of 1 % displayed notably lower reduction rates of 23.69 % and 16.99 %, respectively. © 2024 Elsevier Ltd
Enhancement of Cement Mortar’s Resistance To Hydrochloric Acid Using Hybrid Sst/Dhst Fibers and Silica Fume
(Taylor and Francis Ltd., 2025) Akbulut, Z.F.
This study investigates the durability of cement mortars against hydrochloric (HCl) acid attacks by incorporating silica fume (SF), melt-extracted straight stainless steel (SST), and double-hooked steel (DHST) fibers. The addition of SF increased the mortar viscosity, reducing workability but significantly improving mechanical strength and resistance to HCl degradation. Combining SF with hybrid SST/DHST fibers showed promising results, demonstrating synergistic effects. SF’s pozzolanic activity promoted the formation of calcium-silicate-hydrate (C-S-H) bonds, filling pores, reducing permeability, and enhancing the mortar’s resistance to HCl exposure. Furthermore, hybrid SST/DHST fibers outperformed DHST fibers alone in mitigating micro and macro crack formation. Their combined ability to bridge and restrict crack propagation reinforced the mortar’s structural integrity. In conclusion, incorporating SF and hybrid fibers effectively improves mortar durability against HCl attacks. The findings highlight that the pozzolanic reaction of SF improves the durability of cement-based materials by enhancing the formation of C-S-H, which increases strength and reduces permeability. Additionally, the synergistic effect of hybrid fibers boosts crack resistance by distributing stress evenly and preventing crack propagation, offering valuable insights for optimizing cement mortar formulations in aggressive environments. © 2025 Informa UK Limited, trading as Taylor & Francis Group.
Enhancing Concrete Performance Through Sustainable Utilization of Class-C and Class-F Fly Ash: a Comprehensive Review
(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Akbulut, Z.F.; Yavuz, D.; Tawfik, T.A.; Smarzewski, P.; Guler, S.
Integrating class-C and class-F fly ash (FA) as supplementary cementitious materials (SCMs) in concrete offers a promising pathway for sustainable construction practices. This study explores the pivotal role of FA in reducing carbon dioxide (CO2) emissions and improving concrete’s durability and mechanical properties through a comprehensive life cycle analysis (LCA). By blending FA with cement, significant reductions in CO2 emissions are achieved, alongside enhancements in the workability, compressive strength, and permeability resistance of the concrete matrix. This research elucidates the pozzolanic reaction between FA and calcium hydroxide (CH) during cement hydration, highlighting its contribution to concrete strength and durability. Through a range of comprehensive analysis techniques, including mechanical testing and environmental impact assessment, this study demonstrates the substantial benefits of prioritizing the utilization of class-C and class-F FA in sustainable construction. The findings underscore the industry’s commitment to environmentally conscious practices, promoting structural integrity and reducing ecological impacts. Overall, this research emphasizes class-C and class-F FA as critical components in achieving sustainable construction goals and advancing towards a more environmentally responsible built environment. © 2024 by the authors.
Enhancing the Resilience of Cement Mortar: Investigating Nano-Sio2 Size and Hybrid Fiber Effects on Sulfuric Acid Resistance
(Elsevier Ltd, 2024) Akbulut, Z.F.; Guler, S.
This article explores fortifying cement mortars against severe sulfuric acid (SLA) attacks by studying the impact of nano-SiO2 (NS), macro-steel (ST), and micro-polypropylene (PP) fibers. The aim is to assess their effects on workability, physical attributes, mechanical properties, and durability against SLA attacks when incorporated into mortar blends. Replacing 1 % of cement weight with NS, having average particle diameters of 15 nm (nm) (NS15) and 55 nm (NS55), and utilizing macro-ST and micro-PP fibers at volumes of 0.5 % and 1 % in singular and hybrid forms resulted in significant changes in mortar characteristics. While these additives increased fresh mortar viscosity and negatively affected workability, they substantially boosted mortar strength and durability against SLA attacks. The most substantial improvements were observed using smaller NS particle sizes and employing hybrid ST/PP fibers. The formation of calcium-silicate-hydrate (C-S-H) bonds by NS within the network emerged as a pivotal factor. NS's high pozzolanic activity and void-filling capacity significantly enhanced the mortars' strength and durability against SLA attacks. Furthermore, instead of their singular application, the combined use of ST and PP fibers proved more effective in restraining micro and macro cracks within the mortar matrix. The bridging effect of hybrid ST/PP fibers delayed crack propagation throughout the network, highlighting their superior efficiency against SLA attacks. Overall, these findings hold promise for designing cement-based composites resilient to harsh, acidic environments. Using smaller NS particles and hybrid fiber combinations presents potential pathways to prolong service life in challenging conditions. © 2024 Elsevier Ltd
Examining the Workability, Mechanical, and Thermal Characteristics of Eco-Friendly, Structural Self-Compacting Lightweight Concrete Enhanced With Fly Ash and Silica Fume
(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Akbulut, Z.F.; Yavuz, D.; Tawfik, T.A.; Smarzewski, P.; Guler, S.
This study compares the workability, mechanical, and thermal characteristics of structural self-compacting lightweight concrete (SCLWC) formulations using pumice aggregate (PA), expanded perlite aggregate (EPA), fly ash (FA), and silica fume (SF). FA and SF were used as partial substitutes for cement at a 10% ratio in various mixes, impacting different aspects: According to the obtained results, FA enhanced the workability but SF reduced it, while SF improved the compressive and splitting tensile strengths more than FA. EPA, used as a fine aggregate alongside PA, decreased the workability, compressive strength, and splitting tensile strength compared to the control mix (K0). The thermal properties were altered by FA and SF similarly, while EPA notably reduced the thermal conductivity coefficients. The thermal conductivity coefficients (TCCs) of the K0–K4 SCLWC mixtures ranged from 0.275 to 0.364 W/mK. K0 had a TCC of 0.364 W/mK. With 10% FA, K1 achieved 0.305 W/mK; K2 with 10% SF reached 0.325 W/mK. K3 and K4, using EPA instead of PA, showed significantly lower TCC values: 0.275 W/mK and 0.289 W/mK, respectively. FA and SF improved the thermal conductivity compared to K0, while EPA further reduced the TCC values in K3 and K4 compared to K1 and K2. The compressive strength (CS) values of the K0–K4 SCLWC mixtures at 7 and 28 days reveal notable trends. Using 10% FA in K1 decreased the CS at both 7 days (12.16 MPa) and 28 days (22.36 MPa), attributed to FA’s gradual pozzolanic activity. Conversely, K2 with SF showed increased CS at 7 days (17.88 MPa) and 28 days (29.89 MPa) due to SF’s rapid pozzolanic activity. Incorporating EPA into K3 and K4 reduced the CS values compared to PA, indicating EPA’s lower strength contribution due to its porous structure. © 2024 by the authors.
An Experimental Investigation of Hydraulic and Early and Later-Age Mechanical Properties of Eco-Friendly Porous Concrete Containing Waste Glass Powder and Fly Ash
(Elsevier Ltd, 2024) Yavuz, D.; Akbulut, Z.F.; Guler, S.
Porous concrete (PC) is a special concrete that contains interconnected large voids, unlike traditional concrete. Coarse aggregate and a minimal fine aggregate are used in the PC composition, thus providing more air and water permeability than conventional concrete. Thanks to the high permeability feature of PC, the natural water cycle is preserved, and rainwater meets groundwater. However, since PC is porous due to its cavity structure, its compressive strength is generally lower, and its durability properties are weaker than conventional concrete. Although fly ash (FA) and waste glass powder (WGP) adversely affect the permeability properties of PCs, they can significantly improve their strength and durability properties. This study examined the effects of FA and WGP on PC's hydraulic and mechanical properties. As a result of the study, we obtained FA- and WGP-added PC samples' hardened density (HD), apparent porosity (AP), water permeability coefficient (k), compressive, splitting tensile, and flexural strengths. The image analysis was also used to determine the FA- and WGP-added PC sample's gap sizes. According to the results obtained, the FA and WGP filled the gaps in the interior structure of the PC by showing a filler effect and, as a result, reduced the AP and k values of the PC. However, FA and WGP significantly increased the compressive, splitting tensile and flexural strength capacities of PC, especially in older ages, due to the progression of hydration, thanks to the calcium-silicate-hydrate (C-S-H) bonds they constituted in the PC matrix and their high pozzolanic activities. © 2024 Elsevier Ltd
Experimental Investigation of the Surface Properties of Accidental Stained Carbonate Natural Stones
(Elsevier Ltd, 2022) Akbulut, Z.F.
Marmara White (MW), Bursa Beige (BB), Emprador (EM), and Kütahya Black (KB) natural stones are widely used as kitchen countertops and wet floor covering materials in our country. This study investigated the changes in these natural stones' gloss, roughness, and total color change properties due to the spillage of eight different food, beverage, and cleaning materials. Staining-cleaning cycles were applied to natural stones for 1, 3, and 7 days. In addition, with the help of field emission scanning electron microscopy (FESEM) analysis, the damage caused by these stain effects on the internal structures of these natural stones was investigated. According to the results obtained from the study, after three staining-cleaning cycles, the highest gloss loss was observed in the KB sample at the rate of 97.15 % after the descaler effect, while the minor gloss loss was obtained in the MW sample at the rate of 82.16 %. Furthermore, the highest roughness increase was observed in the KB sample at the rate of 555.1 % after the effect of descaler, while the slightest increase in roughness was obtained in the MW sample at the rate of 395 %. In addition, cooking oil has the most negative effect on natural stones' total color change (ΔE) properties. After three staining-cleaning cycles of the cooking oil effect, ΔE = 20.86 was obtained in the MW sample, while this value was 3.25 in the KB sample. © 2022 The Authors
Porous Concrete Modification With Silica Fume and Ground Granulated Blast Furnace Slag: Hydraulic and Mechanical Properties Before and After Freeze-Thaw Exposure
(Elsevier Ltd, 2024) Yavuz, D.; Akbulut, Z.F.; Guler, S.
This study investigates the effects of incorporating silica fume (SF) and ground granulated blast furnace slag (GBFS), both individually and in hybrid combinations, on various properties of porous concrete (PC) were evaluated under room conditions and after freeze-thaw (F-T) cycles. The hardened density (HD), water permeability coefficient (k), apparent porosity (AP), as well as compressive strength (CS), splitting tensile strength (STS), and flexural strength (FS) at 7, 28, and 120 days. Additionally, the impact of SF and GBFS on the mass loss (ML), residual compressive strength (RCS), residual splitting tensile strength (RSTS), and residual flexural strength (RFS) of PC samples subjected to 30, 60, 120, and 180 freeze-thaw (F-T) cycles was analyzed. The findings revealed that the addition of SF and GBFS decreased the AP and k values of PC samples under room conditions. Furthermore, these materials significantly improved the CS, STS, and FS properties of PC samples, especially at the 28-day and 120-day marks, owing to their enhanced pozzolanic activity over time. SF and GBFS also contributed to higher RCS, RSTS, and RFS values in PC samples after F-T cycles compared to the control samples. This was due to their effective gap-filling properties and the formation of additional calcium-silicate-hydrate (C-S-H) gels within the matrix. Additionally, SF and GBFS led to slightly higher RDME values in the C1-C6 samples than in the control samples following F-T cycles. However, SF and GBFS did not have a significant impact on reducing the ML values of PC samples after F-T cycles. © 2024 Elsevier Ltd
Residual Strength and Toughness Properties of 3d, 4d and 5d Steel Fiber-Reinforced Concrete Exposed To High Temperatures
(Elsevier Ltd, 2022) Guler, S.; Akbulut, Z.F.
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%. © 2022 Elsevier Ltd
The Single and Hybrid Use of Steel and Basalt Fibers on High-Temperature Resistance of Sustainable Ultra-High Performance Geopolymer Cement Mortars
(John Wiley and Sons Inc, 2023) Guler, S.; Akbulut, Z.F.
This paper primarily examines the flowability, physical appearance, mass loss, residual compressive strength (RCS), and residual flexural strength (RFS) properties of steel (ST) and basalt (BA) fiber-added sustainable ultra-high performance geopolymer cement (UHPGPC) mortars exposed to high-temperature effects. According to the results obtained, ST and BA fibers adversely influence the workability properties of UHPGPC mortars and thus significantly reduce the spreading diameters of the mortars. However, ST and BA fibers substantially improve the RCS and RFS capacities of UHPGPC specimens exposed to high temperatures because they have a powerful bonding effect with the matrix and effectually restrict the development of micro- and macro-cracks with their bridging effect. Furthermore, this phenomenon is slightly more effective in hybrid form than using ST and BA fibers. © 2023 fib. International Federation for Structural Concrete.
Structural Self-Compacting Lightweight Concrete: Effects of Fly Ash and Basalt Fibers on Workability, Thermal and Mechanical Properties Under Ambient Conditions and High Temperatures
(Elsevier Ltd, 2025) Akbulut, Z.F.; Guler, S.
In today's concrete technology, the use of pumice aggregate (PA) in the production of lightweight concrete is increasingly gaining popularity. This study investigates PA-based self-compacting lightweight concrete (SCLWC), focusing on the effects of fly ash (FA), and single and hybrid basalt (BA) fibers on its fresh and hardened properties under ambient and high-temperature conditions. Replacing 10 % of Portland cement (PC) with FA significantly enhances workability, as shown by improved slump-flow, L-box, and V-funnel test results. The spherical shape of FA enhances fluidity, aiding mixing and placement. However, the addition of macro-BA fibers reduces workability due to their length and frictional resistance during mixing. The inclusion of micro- and macro-BA fibers improves retained splitting tensile strength (RSTS) and compressive strength (RCS) after exposure to high temperatures, which is crucial for maintaining structural integrity despite reduced workability. FA contributes little to strength gains at 7 and 28 days, but by day 120, significant improvements are observed, indicating increased pozzolanic activity. FA and BA fibers enhance the thermal properties of SCLWC. BA fibers improve durability, while FA reduces the thermal conductivity coefficient (TCC), improving insulation. After exposure to 800°C, the compressive strength (CS) of the K0 control specimen decreased by 77.23 %, while for K1-K5 specimens, the decrease ranged from 69.53 % to 78.29 %. Similarly, the splitting tensile strength (STS) of K0 fell by 74.38 %, while for K1-K5, it varied from 62.76 % to 76.58 %. The TCC of K0 was 0.357 W/mK, while for K1-K5, it ranged from 0.282 to 0.323 W/mK. © 2025 Elsevier Ltd
Synergistic Effects of Polypropylene Fibers and Silica Fume on Structural Lightweight Concrete: Analysis of Workability, Thermal Conductivity, and Strength Properties
(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Akbulut, Z.F.; Kuzielová, E.; Tawfik, T.A.; Smarzewski, P.; Guler, S.
Structural lightweight concrete (SLWC) is crucial for reducing building weight, reducing structural loads, and enhancing energy efficiency through lower thermal conductivity. This study explores the effects of incorporating silica fume (SF), micro-polypropylene (micro-PP), and macro-PP fibers on the workability, thermal properties, and strength of SLWC. SF was added to all mixtures, substituting 10% of the Portland cement (PC), except for the control mixture. Macro-PP fibers were introduced alone or in combination with micro-PP fibers at volumetric ratios of 0.3% and 0.6%. The study evaluated various parameters, including slump, Vebe time, density, water absorption (WA), ultrasonic pulse velocity (UPV), thermal conductivity coefficients (k), compressive strength (CS), and splitting tensile strength (STS) across six different SLWC formulations. The results indicate that while SF negatively impacted the workability of SLWC mortars, it improved CS and STS due to the formation of calcium silicate hydrate (C-S-H) gels from SF’s high pozzolanic activity. Additionally, using micro-PP fibers in combination with macro-PP fibers rather than solely macro-PP fibers enhanced the workability, CS, and STS of the SLWC samples. Although SF had a minor effect on reducing thermal conductivity, the use of macro-PP fibers alone was more effective for improving thermal properties by creating a more porous structure compared to the hybrid use of micro-PP fibers. Moreover, increasing the ratio of micro- and macro-PP fibers from 0.3% to 0.6% resulted in lower CS values but a significant increase in STS values. © 2024 by the authors.