Punching shear strengthening of flat slab using SIFCON

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Tuama, György L. Balázs This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7002488/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Punching shear failure in flat slabs remains one of the most critical issues in reinforced concrete structures due to its sudden and brittle nature. This research investigates the potential of using Slurry Infiltrated Fiber Concrete (SIFCON) as an alternative to traditional punching shear reinforcement in flat slabs cast from normal-strength concrete (NSC). The fiber type was hooked-end steel fiber with a fraction volume of 6%. Five square flat slab specimens were cast; the first specimen was cast using NSC. Four of them were reinforced with maximum flexural steel to ensure failure by punching shear. In two of these slabs, SIFCON was used as a whole slab, but since it is expensive to use SIFCON for entire slabs, in others, SIFCON was used partially over an extended area in a form similar to a plus sign shear reinforcement and full or partial depth to improve the resistance to punching shear. The data demonstrate that SIFCON, when applied strategically, is a highly effective material for increasing punching shear resistance and improving post-punching behavior and ductility. Providing a realistic alternative to standard reinforcement approaches. Flat slab Slurry Infiltrated Fiber CONcrete punching shear steel fibers post-punching behavior Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Flat reinforced-concrete floor plates are increasingly favored in modern construction. By eliminating down-stand beams, the system relies on a simple, level formwork deck, streamlining site operations and accelerating the build. In multi-story projects, the reduced structural depth allows additional floors to be fitted within the same overall height. This efficiency cuts the quantity of façade materials, partition walls, and the length of mechanical, electrical, and plumbing runs, yielding notable savings in both resources and cost (Weerasinghe et al., 2020 ). The main weakness of this type of roof is its failure with punching shear, as when making flat slabs using normal strength concrete (NSC), it is brittle and prone to punching shear failure, which occurs around columns at specific distances, Engineers have outlined several ways to raise the punching-shear strength of flat slabs made with normal-strength concrete. These include thickening the slab, adding column capitals, incorporating drop panels, placing additional shear reinforcement, and introducing advanced materials such as fiber-reinforced polymer (FRP). (Tahmoorian et al., 2021 ; Saleh et al., 2019 ; and Halvoník et al., 2019 ). The cost and constructional intricacy of conventional strengthening techniques can, in many practical situations, offset the principal advantages of flat-slab systems. Consequently, recent research has turned toward material-based solutions that increase punching-shear capacity while preserving ease of execution. Other methods have been used to strengthen plain concrete slabs, using special concrete, some of which are high-performance concrete or fiber-reinforced concrete. These concretes have been used by previous researchers in various ways and placed in different areas, depths, and shapes in flat slabs to perform their intended function. They have led to a noticed improvement in the shear resistance of flat slabs (Nguyen et al., 2011 , Facconi et al., 2016 , Qi et al., 2021 , Brisid et al., 2022 , and Yehia et al., 2023 ). Fibers significantly improve shear resistance, so the use of fiber-reinforced concrete to improve the punching shear resistance of reinforced slabs has been studied by some previous researchers (Zamri et al., 2022 ). In Slurry Infiltrated Fiber Concrete (SIFCON), the steel-fiber volume fraction is unusually high, roughly 4–20% (Tauma and Balázs, 2024). Ordinary fiber-reinforced concrete, by comparison, rarely exceeds about 2% fiber because they are mixed directly with cement, sand, and coarse aggregate, and workability quickly deteriorates (ACI 544 2002). SIFCON sidesteps this issue through a different fabrication route: a dense mat of loose steel fibers is placed in the mold first, and a highly fluid mortar is then infiltrated to occupy the gaps between fibers. This manufacturing sequence yields a composite distinguished by exceptional toughness and markedly enhanced compressive, tensile, shear, and flexural strengths (Metin and Mecbure, 2019, & Tauma and Balázs, 2023). Published work on how best to employ SIFCON for upgrading reinforced-concrete flat slabs is still sparse. In the present investigation, flat-slab specimens were cast in which normal-strength concrete was replaced, either wholly or partially, by SIFCON. Also, SIFCON was used partially over an extended area in a form similar to a plus sign shear reinforcement and full or partial depth to improve the resistance to punching shear. The study gauges how SIFCON replacement alters the slab’s resistance to punching shear by comparing these configurations. 2. Experimental work 2.1 Materials and mix design The materials composition adopted in this study, combining SIFCON and normal concrete (NC), is detailed in Table 1 . For both SIFCON and NC, normal quartz sand with varying particle sizes was utilized as fine aggregate, while coarse aggregate in the range of 4–16 mm was used exclusively for NC. The binding materials comprise Portland cement type CEM I (42.5) along with silica fume. To ensure proper workability of the SIFCON mix, the high-range water-reducing admixture BASF Master Glenium 300 was incorporated. Flexural reinforcement was provided according to the specifications of ACI 318 − 19 (ACI 318, 2019), employing Ø10 mm deformed bars positioned on the tension side of the slabs to promote punching shear as the governing failure mode. In this investigation, steel fibers was hooked-end with volume fraction of 6%. The type of fiber employed is illustrated in Fig. 1 , while Table 2 presents their technical characteristics as reported by the manufacturer. Table 1 NSC and SIFCON optimal mixing proportions for 1 m 3 Cement (kg/m 3 ) Sand (0.4-1) mm (kg/m 3 ) Sand (1–4) mm (kg/m 3 ) Coarse agg. (kg/m 3 ) Silica fume kg/m 3 10% rep. Steel fiber % w/b or w/c ratio SP (by wt. of binder) % Slump flow (mm) (4–8) mm (8–16) mm 370 -- 924 462 462 -- -- 50% -- 100 873 970 -- -- -- 97 6 30% 1.75% 260 Table 2 Technical properties of the steel fibers Fiber type Length (mm) Diameter (mm) Density (kg/m3) Tensile strength (MPa) Hooked-end 35 ± 5% 0.6 ± 5% 7,850 1350 Figure 2 illustrates the proportion of materials used in both NSC and SIFCON mixtures, expressed as a percentage of the total mix weight. A fiber volume content of 6% was selected in this study for the hooked-end fiber, as it was the most appropriate for the dimensions of the molds utilized. The mixing method adopted for the SIFCON mixture was developed based on previous studies and preliminary trials to ensure optimal workability. The mixing process involved initially blending the dry components for 3 minutes. Subsequently, two-thirds of the water, pre-mixed with the superplasticizer, was added and mixed for another 3 minutes. The remaining one-third of the water, also containing superplasticizer, was then introduced, and mixing continued for an additional 2 minutes. 2.2 Casting and testing samples and specimens This investigation involved testing the compressive and flexural strengths of both NSC and SIFCON materials. Compressive strength was evaluated using cubes with dimensions of 150 mm for NSC and 100 mm for SIFCON. Flexural strength was assessed through prism specimens, sized 700 × 700 × 250 mm for NSC and 40 × 40 × 160 mm for SIFCON. For each test type and material, the reported values represent the average of three specimens tested at both 7 and 28 days. The main objective of this study is to examine the structural behavior of flat slabs when using SIFCON in full or in part. The type of fibers are used in SIFCON is hooked-end steel fiber. The experimental program consisted of testing 5 slab specimens; one reference specimen was cast with NSC. 2 NSC-SIFCON hybrid flat slab specimens with flexural reinforcement cast by using SIFCON partially over an extended area in a form similar to a plus sign shear reinforcement and full or partial depth, by using hooked-end steel fiber. 2 SIFCON flat slab specimens cast by using SIFCON entirely with or without flexural reinforcement by using hooked-end steel fiber. In this study, square concrete slabs were utilized as test specimens, each measuring 600 mm on each side with a constant thickness of 60 mm. The specimens were classified according to the SIFCON concrete, the type of fibers used, or the depth of the SIFCON in composite slabs, as presented in Table 3 . Table 3 The symbols of slab and their meanings. Symbol Details N Normal strength concrete (NSC) slab S Slurry infiltrated fiber concrete (SIFCON) slab without flexural reinforcement S + R Slurry infiltrated fiber concrete (SIFCON) slab with flexural reinforcement N-S2+ NSC flat slab – the SIFCON area in a plus sign form with 20 mm depth N-S6+ NSC flat slab – the SIFCON area in a plus sign form with full slab depth 3 flat slab specimens cast by using NSC or SIFCON entirely. Since SIFCON is an expensive material, this study explores strengthening the punching shear by using a similar way of shear reinforcement steel, which is using SIFCON in the shape of a plus, with the width of each arm equal to 100 mm and full depth 60 mm or partial depth 20 mm in the tension side. Figure 3 shows the overall slab geometries and reinforcement layout details. Prior to the casting process, all constituent materials were carefully prepared and proportioned according to the mix volume. The slab specimens, each measuring 600×600×60 mm, were formed using wooden molds supported by external iron frames and placed on a steel base to ensure dimensional stability throughout the casting. Before each pour, molds were thoroughly cleaned, coated with release agent, and leveled on a flat surface. The sequence of casting for various concrete types is illustrated in Fig. 4 . For slabs made with NSC, reinforcement meshes were accurately placed inside the molds, ensuring proper bottom cover. In SIFCON slabs, the steel fibers were introduced in a single batch into the mold before the slurry was poured, allowing the mix to penetrate and encapsulate the fibers. In the case of hybrid slabs, a fine galvanized steel mesh was positioned precisely at the interface between the NSC and SIFCON regions. This mesh was anchored to the bottom reinforcement and held in position from above using a wooden formwork system to control the geometry, as shown in Figs. 4 b. Given the self-consolidating nature and relatively quick setting of SIFCON, the outer region was cast first using NSC, followed shortly by placement of the SIFCON. There were two types of hybrid slabs; in the first one, the SIFCON was cast in the form of a plus sign with the full thickness of the slab and 100 mm wide arms, the SIFCON was cast while the NSC was still fresh. In the second, the SIFCON thickness was only 20 mm on the tension side of the slab, the SIFCON was cast the next day when the NSC had hardened. A chemical adhesive material was placed to bond the old and new concrete to increase the bonding for the second type. Once mixing was complete, the fresh concrete was placed into the molds. The slab specimens were cured under wet coverings saturated with water, while additional samples were cured in a water tank maintained at a temperature of 23 ± 2°C. Upon completion of the 28-day curing period, structural load tests were performed on all slab specimens under monotonically increasing central loading until ultimate failure was reached. The loading protocol utilized a precision-calibrated electro-hydraulic testing machine with a rated capacity of 500 kN, as depicted in Fig. 5 . The load application was controlled to ensure uniform rate progression and avoid dynamic effects. Each slab was simply supported along all four sides over an effective span of 500 mm using a custom-fabricated steel frame integrated within the testing setup. This frame comprised four rigid steel members, precisely welded at right angles to form a closed square support boundary, thereby ensuring consistent edge support and accurate simulation of boundary conditions. Loading was applied using a 60×60 mm steel stub column, rigidly connected to the actuator of the electrical testing system, which was suspended from a fixed steel reaction frame. All tests were conducted under a controlled displacement rate of 0.5 mm/min. To monitor deflection behavior, linear variable differential transducers (LVDTs) were positioned at the slab center and two quarter-span points on opposite sides of the applied load. This incremental loading scheme enabled the acquisition of detailed load-deflection data, facilitating a comprehensive analysis of slab performance. Key response parameters recorded included the cracking load, the ultimate load associated with punching shear or flexural failure, mid-span deflection, and the averaged deflections at the quarter-span points. The ultimate deflection was defined following Kaka et al. (2016) as the deflection corresponding to a post-peak load reduction to 80% of the maximum load. Given the emphasis on the high ductility behavior of SIFCON in this investigation, particular attention was directed to the structural response beyond the peak load. Two critical deflection points in the post-peak regime were identified: one at 80% and the other at 60% of the peak load. These deflection values are referred to herein as u 1 and u 2 , respectively, and were used to assess the residual load-carrying capacity and the contribution of fibers under advanced deformation. 3. Results and discussion 3.1 Mechanical properties In this work, the flexural and compressive strengths of SIFCON and NSC concrete are tested. The cubes and prisms made for this purpose were evaluated for compressive and flexural strength at 7 and 28 days. The NSC and SIFCON are displayed in Table 4 . The findings demonstrate that SIFCON with hooked-end steel fiber has a substantially higher compressive and flexural tensile strength than NSC. The capacity of fibers to limit and stop fracture development, as well as to reduce the rate and direction of crack propagation, can be explained by their increased strength. Table 4 also shows the increases in both compressive and flexural strength for SIFCON relative to the reference NSC at 28 days. Table 4 The mechanical properties results of the NSC and SIFCON. Type of concrete Compressive strength (MPa) Flexural strength (MPa) The percentage increases (%) in 28 days compared to NSC 7 days 28 days 7 days 28 days Compressive strength Flexural strength NSC 31 43 3.7 4.8 -- -- SIFCON 89 118 23.5 32 174 567 3.2 First crack strength The first crack loads, for the various slabs, are summarized in Table 5 . Also, the same table shows deflection of the center and the average deflection of two quarters at the first crack. The results show that using SIFCON increased the first crack strength of the slab. The first crack strength increased for hybrid slabs by 56% for the slab in which the SIFCON was used in the form of a plus with full depth. The highest percentage increase in first crack was reached in the slab made entirely of SIFCON using hooked-end steel fibers. The percentage in the S + R slab reached 342%. The core driver behind SIFCON’s markedly higher first-crack load is its dense fiber network, 6% of the volume of slab. Closely spaced steel filaments intersect every potential crack plane, so the instant a micro-crack forms, the fibers “bridge” it, pick up the tensile force, and spread the strain over a much larger area. This bridging action keeps crack widths microscopic, meaning the member must be subjected to far greater external loads before any visible cracking occurs. Table 5 The first crack load and deflection of the specimens at the first cracks. Specimen P cr (kN) Δ c (mm) Δ q (mm) η f (%) N 11.18 1.23 0.21 -- S 42.72 2.61 2.35 282 S + R 49.43 2.95 2.69 342 N-S2+ 16.92 1.83 1.20 51 N-S6+ 17.43 1.91 1.24 56 Note: P cr = First cracking load; η f = The percentage of improved first crack strength compared to specimen N; Δ cf = Center deflection at first cracking load; Δ qf = Quarters av. deflection at first cracking load. 3.3 Failure mode and crack pattern Figure 6 maps the cracking patterns that developed on the tension face of every slab. Three discrete failure mechanisms were identified: punching shear, flexure, and a coupled punching-shear ⁄ flexural mode. The reference specimen N failed in punching shear: radial cracks nucleated directly beneath the load and spread outward to form a circumferential ring, accompanied by local concrete spalling. A purely flexural response characterized specimens S and N-S2+, where cracks originated at mid-span and propagated diagonally toward the supports. Specimens S + R and N-ST6 + exhibited the mixed mode: load-induced longitudinal cracks first appeared parallel to the reinforcement, then evolved into diagonal and peripheral circular cracks. In hybrid slabs, the initial crack consistently formed along the interface between the SIFCON layer and the surrounding NSC, circled the SIFCON core, and continued outward until the peak load, when the punching-shear cone was fully established. Deflection records underscore the ductility advantages conferred by SIFCON. The reference slab displayed virtually no post-peak deformation 4.82 mm at peak load and 5.33 mm at the u₂ stage revealing a brittle response. In contrast, slabs containing SIFCON showed substantial displacement capacity beyond first cracking. The most pronounced increase occurred in specimen S + R, whose deflection rose from 12.6 mm at peak load to 24.8 mm at u₂ . This post-peak ductility grew with the SIFCON volume fraction. Moreover, hooked-end steel fibers improved energy absorption and postponed failure, reaffirming that a higher fiber dosage markedly enhances both ductility and load-carrying capacity in the later stages of loading. 3.4 Peak load and load-deflection response Table 6 compiles the ultimate (peak) loads, the corresponding mid-span deflections and the average deflection of two quarters at the peak load, together with the percentage gain in peak load relative to the reference slab N. Figure 7 charts the complete load–deflection histories for each specimen. The data confirm that enlarging the SIFCON portion of a slab generally raises its ultimate load. Every specimen containing SIFCON, whether throughout the full depth or only in selected regions, surpassed the reference slab. The greatest strength enhancements were obtained for slab S + R, whose peak loads were 118% higher than those of slab N. Among the hybrid plus-pattern specimens, the best performance was achieved by slab N-S6+, which exceeded the reference slab’s peak load by roughly 36%. Even in cases where the load increase was modest, the presence of SIFCON altered the failure mode from brittle punching to a more desirable ductile flexural response. For hybrid slabs, the gap between u₁ and u₂ widened as the SIFCON layer was deepened. In slabs cast entirely with SIFCON, this deflection gap was the larger in S + R slab, further promoting a switch from punching to flexural failure and greatly enhancing ductility, as observed in specimens S and S + R. Overall, the study demonstrates that even a modest amount of SIFCON, applied as a plus-shaped core throughout the thickness, can deliver substantial strength gains while providing excellent ductility. The difference between the deflection at peak load and u 2 stage reached roughly 12 mm in N-S6 + slab cases. These findings emphasize the promise of SIFCON for flat-slab construction: significant improvements in capacity and toughness can be achieved without increasing slab thickness or adding drop panels or column capitals. Table 6 The peak load and deflection of the specimens at the peak cracks. Specimen P p Δ cp Δ qp η p N 50.18 4.82 2.25 -- S 93.14 7.74 4.25 86 S + R 109.3 12.06 5.25 118 N-S2+ 56.01 8.41 3.21 12 N-S6+ 68.05 11.46 3.32 36 Note: P p = Peak load by (kN); Δ cp and Δ qp = Center and Quarters av. deflection by (mm) at peak load respectively; η p = The percentage of improved peak load compared to specimen N. 3.5 Ductility Ductility, µ, describes the capacity of a structural member to undergo substantial deformation after first yield. In this study, it is expressed as the ratio of the ultimate displacement, Δ u , to the corresponding yield displacement, Δ y , by Eq. (1) and the procedure proposed by Lim and Hong (2016). The ultimate displacement is taken as the deflection recorded when the applied load has fallen to 80% of the specimen’s peak value. To locate the yield point, the load–deflection response is idealized as an elastic–perfectly-plastic curve that (i) passes through the peak load and (ii) has an initial slope equal to the secant stiffness measured at two-thirds of the peak load. The intersection of this idealized line with the actual response defines the yield displacement, following the approach used by Sukontasukkul et al. 2004, Lim and Hong (2016), and Kaka et al. (2016). Because the slabs exhibited continuing deformation after peak load, ductility ratios were evaluated at two ultimate stages u 1 and u 2 to capture the influence of fiber reinforcement on post-peak behavior. The resulting indices, µ 1 and µ 2 , are reported in Table 7 and provide a clearer picture of how fiber type and distribution affect the later stages of the response. \(\:\mu\:=\frac{\varDelta\:u}{\varDelta\:y}\) Eq. (1) Table 7 The ductility results. Specimen P y Δ cy Δ cu1 Δ cu2 µ 1 µ 2 η µ1 η µ2 N 48.90 4.65 5.22 5.30 1.12 1.14 -- -- S 83.44 5.56 8.85 17.54 1.59 3.15 42 176 S + R 93.94 5.40 16.71 24.78 3.09 4.59 176 303 N-S2+ 49.99 6.67 9.1 9.72 1.36 1.46 21 28 N-S6+ 61.00 5.68 16.36 23.51 2.88 4.14 157 263 Note: P y = yield load by (kN); Δ cy = Center deflection by (mm) at yield load; Δ c(u1 and u2) = Center ultimate deflection by (mm) u 1 and u 2 respectively; µ 1 and µ 2 = the ductility 1 and 2 ; η µ1 and η µ2 = The percentage of improved ductility 1 and 2 compared to specimen N. Table 7 demonstrates that embedding SIFCON in the slab markedly elevates its ductility. During the first post-peak phase u 1 ductility increases steadily, while a far more pronounced gain emerges in the second phase u 2 . For hybrid slabs most clearly in specimen N-S6+, where a plus-shaped SIFCON core extends through the full thickness, the greatest benefit appears in the transition between these two stages. After the longitudinal reinforcement fully yields, the SIFCON fibers engage, bridging and confining cracks so effectively that the slab sustains its load-bearing capacity for an extended period and the failure mode shifts from brittle to ductile. These results confirm the study’s key premise: outstanding ductility can be achieved with only a modest volume of SIFCON. 3.6 Inclination of cracks and rotation of slabs After completing the slab tests, the rotation of each slab about the loading zone was recorded, and the specimens were subsequently sectioned longitudinally to delineate the dominant crack patterns Fig. 8 . By mapping cracks on both the top and bottom faces, the punching-cone angle defined as the inclination between the failure surface and the vertical plane, was established. Results show that this angle on the tensile face decreases monotonically with higher SIFCON content. This finding demonstrates that the critical cracks migrate progressively away from the critical punching-shear zone, transforming the failure mode from brittle to ductile. Moreover, the slab’s rotation angle increases with SIFCON incorporation, particularly when larger SIFCON regions are provided. 4. Conclusion This study evaluates the structural performance of flat slabs strengthened either fully with SIFCON or partially through a hybrid system combining SIFCON with normal-strength concrete (NSC). The experimental program measured the compressive and flexural strengths of both SIFCON and NSC, determined ultimate load, deflection, ductility, and rotation, and recorded crack patterns together with crack inclinations. The results highlight the efficiency of adding SIFCON, in boosting punching-shear resistance and improving the behavior of flat slabs, and they confirm the merit of hybrid NSC–SIFCON assemblies in enhancing overall structural performance. Finally, the study presents a series of conclusions that reaffirm the scientific significance of the findings and open new avenues for forthcoming research and practical engineering applications related to the design of slabs subjected to punching-shear forces: On seven and twenty-eight days, the mechanical properties of the two varieties of concrete employed in this study, NSC and SIFCON, were evaluated. At 28 days, SIFCON with hooked-end steel fibers had greater compressive and flexural strengths of 118 and 32 MPa, respectively. Comparing SIFCON to the reference NSC, the gains in compressive strength were 174%. In comparison to the reference NSC, the flexural strength gains for SIFCON was 567%. The slabs made entirely of SIFCON concrete with hooked-end fibers demonstrated a substantial improvement in the initial cracking load. With a 342% improvement above the control NSC slab, the SIFCON slab experienced the greatest rise. However, there was no discernible increase in the initial crack load in hybrid slab construction; the higher increase in these slab was 56%. When compared to the traditional NSC slab, maximum load capacity of the SIFCON flat slab shows a significant improvement. With an 118% increase above the control, the SIFCON slab with hooked-end steel fiber showed the greatest enhancement. Depending on the SIFCON depth, the hybrid slabs demonstrated benefits that 36%. The load–deflection curves showed that all the slabs that used SIFCON entirely or partially had a high ductility and gradual post-peak decline, unlike the NSC slab, which failed sharply. The highest deflection was recorded in the SIFCON slab, which was 24.8 mm, while in the hybrid slabs, the highest deflection was recorded as 23.5 mm in the slab in which the depth of the SIFCON was equal to the depth of the slab. The failure mechanisms of the slabs were different. In a brittle punching-shear mode, specimens made entirely of normal strength concrete NSC showed very little ductility and developed large, steeply inclined cracks at about 32°. On the other hand, the SIFCON slabs broke down in a very ductile way: many tiny cracks spread at shallow angles of roughly 17°, demonstrating the material's exceptional capacity to prevent cracks. The reaction of hybrid NSC–SIFCON slabs was in the middle; cracking was more regularly spaced and happened at moderate inclinations (26°–29°), which was better than plain NSC but still less controlled than in full-SIFCON members. In the total SIFCON specimen S + R slab, the slab's rotation around the load point increased according to its SIFCON share, reaching roughly 4.7°. A considerable improvement in ductility was found in slabs that included SIFCON. The highest ductility index was observed by all SIFCON specimens, demonstrating their remarkable capacity to dissipate energy and withstand significant inelastic deformations before collapse. While the reference NSC slab, which was controlled by a brittle punching shear failure, had the lowest index, hybrid NSC–SIFCON members also showed considerable increases. In order to shed light on fiber efficiency under the most recent loading, this study is also the first to investigate "late stage" ductility at the deflection levels u 1 and u 2 . The ductility amplification factor η µ2 increased by around 303% in the S + R slab and 263% in the N-S6 + slab at the maximal deflection u 2 . Declarations Funding This research received no external funding. Author Contribution W. K. conducted the experimental work, performed the tests, analyzed the results, prepared all figures and tables, and wrote the main manuscript text. B. L. provided the materials, supervised the research process, and contributed to project oversight. All authors reviewed and approved the final manuscript. Acknowledgement The authors would like to express their sincere gratitude to Betonmix Ltd. for generously providing the steel fibers used in this study. Their valuable support and contribution significantly contributed to the successful completion of the experimental work. References ACI Committee 544. (2002). State-of-the-Art report on fiber reinforced concrete (ACI 544.1R-96) . American Concrete Institute. ACI Committee 318. (2019). Building code requirements for structural concrete (ACI 318 – 19) . American Concrete Institute. Brisid, I., Joao, P., Carla, M., & Antonio, P. (2022). 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Procedia Engineering , 14 , 1830–1837. https://doi.org/10.1016/j.proeng.2011.07.230 Yehia, E., Khalil, A. H., Mostafa, E. E., & El-Nazzer, M. A. (2023). Experimental and numerical investigation on punching behavior of ultra-high performance concrete flat slabs. Ain Shams Engineering Journal , 14 (10), 102208. https://doi.org/10.1016/j.asej.2023.102208 Zamri, N. F., Mohamed, R. N., Awalluddin, D., & Abdullah, R. (2022). Experimental evaluation on punching shear resistance of steel fiber reinforced self-compacting concrete flat slabs, Journal of Building Engineering, vol. 52, Art. no. 104441. https// 10.1016/j.jobe.2022.104441 Tauma, W. K., Balázs, G., & L (2023). Impact and blast resistance of slurry infiltrated fiber concrete (SIFCON): a comprehensive review. Concrete Structures Journal , 24 , 129–136. https://doi.org/10.32970/CS.2023.1.18 Tauma, W. K., Balázs, G., & L (2024). Properties of fibers and mortar of slurry infiltrated fiber concrete (SIFCON). 14th Central European Congress on Concrete Engineering. ISPN 978 – 80 , 908943 (1-0), 454–465. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7002488","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":485730359,"identity":"97c5549c-a800-4817-b867-1a4454ce96be","order_by":0,"name":"Wisam K. Tuama","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABRklEQVRIie3OsWrCQBjA8U8OkiUxayRUX+FCwFJs9UG6KIG6XKDODtrlXCquZuortMu1oxAwyz1Ayi2K4NRC2k4i0sbEoUmR0q3D/eFuuMvvvgDIZP8xtN9mAIp6OCjvt9IQqgDt7BYfIwhlB8qBOEcJHAgUSWd4hOBQXb5HvHlZRsbc3JBmTTG4vXh7Yt2JSjDqkXM4Nds5EmiORSLXowgplTFzbQrcsX0uPP/2BSOfXcHZNEfqgQYWiVFKTJ2hEi2NmaVT4d1HyRSdBYCjAlFXWxIPsik7NmhRpD9ud1R0Wxn5/EmgnvxYkBIrebNDlXSWaGMzJbMiaQVavUF4uCdO44SFLtWMj8qYCnvK19eBz1wN88V3UpmEK0Hmfe9udLN8fmX9i4kx78QbKmrGyH1Y9VizisPclF+aJUv7w/cymUwmy/oC6xN6o82NE2QAAAAASUVORK5CYII=","orcid":"","institution":"Budapest University of Technology and Economics","correspondingAuthor":true,"prefix":"","firstName":"Wisam","middleName":"K.","lastName":"Tuama","suffix":""},{"id":485730360,"identity":"2d29fa60-fa6a-4675-9a6f-b31fe3f74513","order_by":1,"name":"György L. Balázs","email":"","orcid":"","institution":"Budapest University of Technology and Economics","correspondingAuthor":false,"prefix":"","firstName":"György","middleName":"L.","lastName":"Balázs","suffix":""}],"badges":[],"createdAt":"2025-06-29 11:53:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7002488/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7002488/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":86961896,"identity":"5a455c45-a3b8-4cb0-96d2-2115a0324e21","added_by":"auto","created_at":"2025-07-17 16:21:14","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":239358,"visible":true,"origin":"","legend":"\u003cp\u003eHooked-end steel fiber, the dimensions are millimeter.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7002488/v1/13005d7cdde851d20e9d385a.png"},{"id":86960663,"identity":"825e364b-b0db-4f93-a46a-e8d7dd6d1aa4","added_by":"auto","created_at":"2025-07-17 16:05:14","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":82234,"visible":true,"origin":"","legend":"\u003cp\u003eMaterials proportion used in NSC and SIFCON mixture (% of total mix weight).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7002488/v1/dbe81375ab787dd30c81dc89.png"},{"id":86960664,"identity":"c00307e6-ccf0-4905-9d62-a97cc1613606","added_by":"auto","created_at":"2025-07-17 16:05:14","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":206753,"visible":true,"origin":"","legend":"\u003cp\u003eSpecimen dimensions and layout: (a) NSC or SIFCON slab with reinforcement details; (b) Hybrid slab with full depth of SIFCON; (c) Hybrid slab with partial depth of SIFCON.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7002488/v1/89fddee244fe09dcc9ffa351.png"},{"id":86960668,"identity":"2e96e071-b66f-4387-aeae-b8d8450c962a","added_by":"auto","created_at":"2025-07-17 16:05:14","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1638656,"visible":true,"origin":"","legend":"\u003cp\u003eThe steps of casting the different types of flat slab concrete (a- NSC slab, b- SIFCON slab and NSC-SIFCON slab).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7002488/v1/9f0453cdc18a199d71048d4e.png"},{"id":86962396,"identity":"de70d594-6a42-4022-bc57-6ed0ce1b7429","added_by":"auto","created_at":"2025-07-17 16:29:14","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":506190,"visible":true,"origin":"","legend":"\u003cp\u003ePunching shear test of slabs.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7002488/v1/c6ff71618afe7de024f2da00.png"},{"id":86961580,"identity":"e4e6ce29-0dbf-44a8-9d7f-406ef94291a2","added_by":"auto","created_at":"2025-07-17 16:13:14","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1812452,"visible":true,"origin":"","legend":"\u003cp\u003eCrack pattern evolution on the tension face and in mid-span cross-sections: (a) Specimen N; (b) Specimen S; (c) Specimen S+R; (d) Specimen N-S2+; (e) Specimen N-S6+.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7002488/v1/e9df1389ccdd4a31dbe86de6.png"},{"id":86961897,"identity":"db54ecee-b3fe-48ba-86b2-7c1999c570b9","added_by":"auto","created_at":"2025-07-17 16:21:14","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":59406,"visible":true,"origin":"","legend":"\u003cp\u003eThe load– center deflection curves of all specimens\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7002488/v1/bd0464837e461b49ebcbea76.png"},{"id":86961899,"identity":"a3b32ce5-a899-4487-8c7a-36705a93aba4","added_by":"auto","created_at":"2025-07-17 16:21:14","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":895278,"visible":true,"origin":"","legend":"\u003cp\u003eInclination of cracks and rotation of slabs: (a) Specimen N; (b) Specimen S; (c) Specimen S+R; (d) Specimen N-S2+; (e) Specimen N-S6+.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7002488/v1/4124bc61110f7c2d5c1d77c9.png"},{"id":88158586,"identity":"db155b1c-1b55-4390-8967-ee74bd1dd43b","added_by":"auto","created_at":"2025-08-02 11:46:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6669705,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7002488/v1/78ea2097-ded5-449f-a5e9-5e82a5fb39c7.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Punching shear strengthening of flat slab using SIFCON","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eFlat reinforced-concrete floor plates are increasingly favored in modern construction. By eliminating down-stand beams, the system relies on a simple, level formwork deck, streamlining site operations and accelerating the build. In multi-story projects, the reduced structural depth allows additional floors to be fitted within the same overall height. This efficiency cuts the quantity of fa\u0026ccedil;ade materials, partition walls, and the length of mechanical, electrical, and plumbing runs, yielding notable savings in both resources and cost (Weerasinghe et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe main weakness of this type of roof is its failure with punching shear, as when making flat slabs using normal strength concrete (NSC), it is brittle and prone to punching shear failure, which occurs around columns at specific distances, Engineers have outlined several ways to raise the punching-shear strength of flat slabs made with normal-strength concrete. These include thickening the slab, adding column capitals, incorporating drop panels, placing additional shear reinforcement, and introducing advanced materials such as fiber-reinforced polymer (FRP). (Tahmoorian et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Saleh et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; and Halvon\u0026iacute;k et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe cost and constructional intricacy of conventional strengthening techniques can, in many practical situations, offset the principal advantages of flat-slab systems. Consequently, recent research has turned toward material-based solutions that increase punching-shear capacity while preserving ease of execution. Other methods have been used to strengthen plain concrete slabs, using special concrete, some of which are high-performance concrete or fiber-reinforced concrete. These concretes have been used by previous researchers in various ways and placed in different areas, depths, and shapes in flat slabs to perform their intended function. They have led to a noticed improvement in the shear resistance of flat slabs (Nguyen et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, Facconi et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2016\u003c/span\u003e, Qi et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, Brisid et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, and Yehia et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Fibers significantly improve shear resistance, so the use of fiber-reinforced concrete to improve the punching shear resistance of reinforced slabs has been studied by some previous researchers (Zamri et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In Slurry Infiltrated Fiber Concrete (SIFCON), the steel-fiber volume fraction is unusually high, roughly 4\u0026ndash;20% (Tauma and Bal\u0026aacute;zs, 2024). Ordinary fiber-reinforced concrete, by comparison, rarely exceeds about 2% fiber because they are mixed directly with cement, sand, and coarse aggregate, and workability quickly deteriorates (ACI 544 2002). SIFCON sidesteps this issue through a different fabrication route: a dense mat of loose steel fibers is placed in the mold first, and a highly fluid mortar is then infiltrated to occupy the gaps between fibers. This manufacturing sequence yields a composite distinguished by exceptional toughness and markedly enhanced compressive, tensile, shear, and flexural strengths (Metin and Mecbure, 2019, \u0026amp; Tauma and Bal\u0026aacute;zs, 2023).\u003c/p\u003e\u003cp\u003ePublished work on how best to employ SIFCON for upgrading reinforced-concrete flat slabs is still sparse. In the present investigation, flat-slab specimens were cast in which normal-strength concrete was replaced, either wholly or partially, by SIFCON. Also, SIFCON was used partially over an extended area in a form similar to a plus sign shear reinforcement and full or partial depth to improve the resistance to punching shear. The study gauges how SIFCON replacement alters the slab\u0026rsquo;s resistance to punching shear by comparing these configurations.\u003c/p\u003e"},{"header":"2. Experimental work","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials and mix design\u003c/h2\u003e\u003cp\u003eThe materials composition adopted in this study, combining SIFCON and normal concrete (NC), is detailed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. For both SIFCON and NC, normal quartz sand with varying particle sizes was utilized as fine aggregate, while coarse aggregate in the range of 4\u0026ndash;16 mm was used exclusively for NC. The binding materials comprise Portland cement type CEM I (42.5) along with silica fume. To ensure proper workability of the SIFCON mix, the high-range water-reducing admixture BASF Master Glenium 300 was incorporated. Flexural reinforcement was provided according to the specifications of ACI 318\u0026thinsp;\u0026minus;\u0026thinsp;19 (ACI 318, 2019), employing \u0026Oslash;10 mm deformed bars positioned on the tension side of the slabs to promote punching shear as the governing failure mode. In this investigation, steel fibers was hooked-end with volume fraction of 6%. The type of fiber employed is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, while Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents their technical characteristics as reported by the manufacturer.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eNSC and SIFCON optimal mixing proportions for 1 m\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"10\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCement (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSand (0.4-1) mm (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSand (1\u0026ndash;4) mm (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eCoarse agg. (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSilica fume kg/m\u003csup\u003e3\u003c/sup\u003e 10% rep.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSteel fiber %\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003ew/b or w/c ratio\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSP (by wt. of binder) %\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSlump flow (mm)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e(4\u0026ndash;8) mm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e(8\u0026ndash;16) mm\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e370\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e--\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e924\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e462\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e462\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e--\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e--\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e50%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e--\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e873\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e970\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e--\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e--\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e--\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e30%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e1.75%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e260\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eTechnical properties of the steel fibers\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFiber type\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLength (mm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDiameter (mm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDensity (kg/m3)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eTensile strength (MPa)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHooked-end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e35\u0026thinsp;\u0026plusmn;\u0026thinsp;5%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.6\u0026thinsp;\u0026plusmn;\u0026thinsp;5%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e7,850\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1350\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eFigure 2\u003c/em\u003e illustrates the proportion of materials used in both NSC and SIFCON mixtures, expressed as a percentage of the total mix weight. A fiber volume content of 6% was selected in this study for the hooked-end fiber, as it was the most appropriate for the dimensions of the molds utilized. The mixing method adopted for the SIFCON mixture was developed based on previous studies and preliminary trials to ensure optimal workability. The mixing process involved initially blending the dry components for 3 minutes. Subsequently, two-thirds of the water, pre-mixed with the superplasticizer, was added and mixed for another 3 minutes. The remaining one-third of the water, also containing superplasticizer, was then introduced, and mixing continued for an additional 2 minutes.\u003c/p\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Casting and testing samples and specimens\u003c/h2\u003e\u003cp\u003eThis investigation involved testing the compressive and flexural strengths of both NSC and SIFCON materials. Compressive strength was evaluated using cubes with dimensions of 150 mm for NSC and 100 mm for SIFCON. Flexural strength was assessed through prism specimens, sized 700 \u0026times; 700 \u0026times; 250 mm for NSC and 40 \u0026times; 40 \u0026times; 160 mm for SIFCON. For each test type and material, the reported values represent the average of three specimens tested at both 7 and 28 days.\u003c/p\u003e\u003cp\u003eThe main objective of this study is to examine the structural behavior of flat slabs when using SIFCON in full or in part. The type of fibers are used in SIFCON is hooked-end steel fiber. The experimental program consisted of testing 5 slab specimens; one reference specimen was cast with NSC. 2 NSC-SIFCON hybrid flat slab specimens with flexural reinforcement cast by using SIFCON partially over an extended area in a form similar to a plus sign shear reinforcement and full or partial depth, by using hooked-end steel fiber. 2 SIFCON flat slab specimens cast by using SIFCON entirely with or without flexural reinforcement by using hooked-end steel fiber. In this study, square concrete slabs were utilized as test specimens, each measuring 600 mm on each side with a constant thickness of 60 mm. The specimens were classified according to the SIFCON concrete, the type of fibers used, or the depth of the SIFCON in composite slabs, as presented in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe symbols of slab and their meanings.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSymbol\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDetails\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eN\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNormal strength concrete (NSC) slab\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSlurry infiltrated fiber concrete (SIFCON) slab without flexural reinforcement\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS\u0026thinsp;+\u0026thinsp;R\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSlurry infiltrated fiber concrete (SIFCON) slab with flexural reinforcement\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eN-S2+\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSC flat slab \u0026ndash; the SIFCON area in a plus sign form with 20 mm depth\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eN-S6+\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSC flat slab \u0026ndash; the SIFCON area in a plus sign form with full slab depth\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e3 flat slab specimens cast by using NSC or SIFCON entirely. Since SIFCON is an expensive material, this study explores strengthening the punching shear by using a similar way of shear reinforcement steel, which is using SIFCON in the shape of a plus, with the width of each arm equal to 100 mm and full depth 60 mm or partial depth 20 mm in the tension side. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the overall slab geometries and reinforcement layout details.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003ePrior to the casting process, all constituent materials were carefully prepared and proportioned according to the mix volume. The slab specimens, each measuring 600\u0026times;600\u0026times;60 mm, were formed using wooden molds supported by external iron frames and placed on a steel base to ensure dimensional stability throughout the casting. Before each pour, molds were thoroughly cleaned, coated with release agent, and leveled on a flat surface.\u003c/p\u003e\u003cp\u003eThe sequence of casting for various concrete types is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e. For slabs made with NSC, reinforcement meshes were accurately placed inside the molds, ensuring proper bottom cover. In SIFCON slabs, the steel fibers were introduced in a single batch into the mold before the slurry was poured, allowing the mix to penetrate and encapsulate the fibers.\u003c/p\u003e\u003cp\u003eIn the case of hybrid slabs, a fine galvanized steel mesh was positioned precisely at the interface between the NSC and SIFCON regions. This mesh was anchored to the bottom reinforcement and held in position from above using a wooden formwork system to control the geometry, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003eb. Given the self-consolidating nature and relatively quick setting of SIFCON, the outer region was cast first using NSC, followed shortly by placement of the SIFCON. There were two types of hybrid slabs; in the first one, the SIFCON was cast in the form of a plus sign with the full thickness of the slab and 100 mm wide arms, the SIFCON was cast while the NSC was still fresh. In the second, the SIFCON thickness was only 20 mm on the tension side of the slab, the SIFCON was cast the next day when the NSC had hardened. A chemical adhesive material was placed to bond the old and new concrete to increase the bonding for the second type.\u003c/p\u003e\u003cp\u003eOnce mixing was complete, the fresh concrete was placed into the molds. The slab specimens were cured under wet coverings saturated with water, while additional samples were cured in a water tank maintained at a temperature of 23\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eUpon completion of the 28-day curing period, structural load tests were performed on all slab specimens under monotonically increasing central loading until ultimate failure was reached. The loading protocol utilized a precision-calibrated electro-hydraulic testing machine with a rated capacity of 500 kN, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The load application was controlled to ensure uniform rate progression and avoid dynamic effects. Each slab was simply supported along all four sides over an effective span of 500 mm using a custom-fabricated steel frame integrated within the testing setup. This frame comprised four rigid steel members, precisely welded at right angles to form a closed square support boundary, thereby ensuring consistent edge support and accurate simulation of boundary conditions.\u003c/p\u003e\u003cp\u003eLoading was applied using a 60\u0026times;60 mm steel stub column, rigidly connected to the actuator of the electrical testing system, which was suspended from a fixed steel reaction frame. All tests were conducted under a controlled displacement rate of 0.5 mm/min. To monitor deflection behavior, linear variable differential transducers (LVDTs) were positioned at the slab center and two quarter-span points on opposite sides of the applied load. This incremental loading scheme enabled the acquisition of detailed load-deflection data, facilitating a comprehensive analysis of slab performance. Key response parameters recorded included the cracking load, the ultimate load associated with punching shear or flexural failure, mid-span deflection, and the averaged deflections at the quarter-span points.\u003c/p\u003e\u003cp\u003eThe ultimate deflection was defined following Kaka et al. (2016) as the deflection corresponding to a post-peak load reduction to 80% of the maximum load. Given the emphasis on the high ductility behavior of SIFCON in this investigation, particular attention was directed to the structural response beyond the peak load. Two critical deflection points in the post-peak regime were identified: one at 80% and the other at 60% of the peak load. These deflection values are referred to herein as \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, respectively, and were used to assess the residual load-carrying capacity and the contribution of fibers under advanced deformation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Mechanical properties\u003c/h2\u003e\n \u003cp\u003eIn this work, the flexural and compressive strengths of SIFCON and NSC concrete are tested. The cubes and prisms made for this purpose were evaluated for compressive and flexural strength at 7 and 28 days. The NSC and SIFCON are displayed in Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. The findings demonstrate that SIFCON with hooked-end steel fiber has a substantially higher compressive and flexural tensile strength than NSC. The capacity of fibers to limit and stop fracture development, as well as to reduce the rate and direction of crack propagation, can be explained by their increased strength.\u003c/p\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e also shows the increases in both compressive and flexural strength for SIFCON relative to the reference NSC at 28 days.\u003c/p\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThe mechanical properties results of the NSC and SIFCON.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eType of concrete\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eCompressive strength (MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eFlexural strength (MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eThe percentage increases (%) in 28 days compared to NSC\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e7 days\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e28 days\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e7 days\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e28 days\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCompressive strength\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFlexural strength\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNSC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSIFCON\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e118\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e174\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e567\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 First crack strength\u003c/h2\u003e\n \u003cp\u003eThe first crack loads, for the various slabs, are summarized in Table \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. Also, the same table shows deflection of the center and the average deflection of two quarters at the first crack. The results show that using SIFCON increased the first crack strength of the slab. The first crack strength increased for hybrid slabs by 56% for the slab in which the SIFCON was used in the form of a plus with full depth. The highest percentage increase in first crack was reached in the slab made entirely of SIFCON using hooked-end steel fibers. The percentage in the S\u0026thinsp;+\u0026thinsp;R slab reached 342%.\u003c/p\u003e\n \u003cp\u003eThe core driver behind SIFCON\u0026rsquo;s markedly higher first-crack load is its dense fiber network, 6% of the volume of slab. Closely spaced steel filaments intersect every potential crack plane, so the instant a micro-crack forms, the fibers \u0026ldquo;bridge\u0026rdquo; it, pick up the tensile force, and spread the strain over a much larger area. This bridging action keeps crack widths microscopic, meaning the member must be subjected to far greater external loads before any visible cracking occurs.\u003c/p\u003e\n \u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThe first crack load and deflection of the specimens at the first cracks.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" style=\"width: 23.9819%;\"\u003e\n \u003cp\u003eSpecimen\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" style=\"width: 19.6833%;\"\u003e\n \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003csub\u003e\u003cem\u003ecr\u003c/em\u003e\u003c/sub\u003e (kN)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e (mm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eq\u003c/em\u003e\u003c/sub\u003e (mm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"left\" class=\"colspec\"\u003e\u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e (%)\u003c/div\u003e\n \u003c/div\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 23.9819%;\"\u003e\n \u003cp\u003eN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 19.6833%;\"\u003e\n \u003cp\u003e11.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 23.9819%;\"\u003e\n \u003cp\u003eS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 19.6833%;\"\u003e\n \u003cp\u003e42.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e282\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 23.9819%;\"\u003e\n \u003cp\u003eS\u0026thinsp;+\u0026thinsp;R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 19.6833%;\"\u003e\n \u003cp\u003e49.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e342\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 23.9819%;\"\u003e\n \u003cp\u003eN-S2+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 19.6833%;\"\u003e\n \u003cp\u003e16.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 23.9819%;\"\u003e\n \u003cp\u003eN-S6+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 19.6833%;\"\u003e\n \u003cp\u003e17.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e56\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003eNote: \u003cem\u003eP\u003c/em\u003e\u003csub\u003e\u003cem\u003ecr\u003c/em\u003e\u003c/sub\u003e = First cracking load; \u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;The percentage of improved first crack strength compared to specimen N; \u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ecf\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;Center deflection at first cracking load; \u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eqf\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;Quarters av. deflection at first cracking load.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Failure mode and crack pattern\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e maps the cracking patterns that developed on the tension face of every slab. Three discrete failure mechanisms were identified: punching shear, flexure, and a coupled punching-shear \u0026frasl; flexural mode. The reference specimen N failed in punching shear: radial cracks nucleated directly beneath the load and spread outward to form a circumferential ring, accompanied by local concrete spalling. A purely flexural response characterized specimens S and N-S2+, where cracks originated at mid-span and propagated diagonally toward the supports. Specimens S\u0026thinsp;+\u0026thinsp;R and N-ST6\u0026thinsp;+\u0026thinsp;exhibited the mixed mode: load-induced longitudinal cracks first appeared parallel to the reinforcement, then evolved into diagonal and peripheral circular cracks. In hybrid slabs, the initial crack consistently formed along the interface between the SIFCON layer and the surrounding NSC, circled the SIFCON core, and continued outward until the peak load, when the punching-shear cone was fully established.\u003c/p\u003e\n \u003cp\u003eDeflection records underscore the ductility advantages conferred by SIFCON. The reference slab displayed virtually no post-peak deformation 4.82 mm at peak load and 5.33 mm at the \u003cem\u003eu₂\u003c/em\u003e stage revealing a brittle response. In contrast, slabs containing SIFCON showed substantial displacement capacity beyond first cracking. The most pronounced increase occurred in specimen S\u0026thinsp;+\u0026thinsp;R, whose deflection rose from 12.6 mm at peak load to 24.8 mm at \u003cem\u003eu₂\u003c/em\u003e. This post-peak ductility grew with the SIFCON volume fraction. Moreover, hooked-end steel fibers improved energy absorption and postponed failure, reaffirming that a higher fiber dosage markedly enhances both ductility and load-carrying capacity in the later stages of loading.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Peak load and load-deflection response\u003c/h2\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e compiles the ultimate (peak) loads, the corresponding mid-span deflections and the average deflection of two quarters at the peak load, together with the percentage gain in peak load relative to the reference slab N. Figure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e charts the complete load\u0026ndash;deflection histories for each specimen. The data confirm that enlarging the SIFCON portion of a slab generally raises its ultimate load. Every specimen containing SIFCON, whether throughout the full depth or only in selected regions, surpassed the reference slab.\u003c/p\u003e\n \u003cp\u003eThe greatest strength enhancements were obtained for slab S\u0026thinsp;+\u0026thinsp;R, whose peak loads were 118% higher than those of slab N. Among the hybrid plus-pattern specimens, the best performance was achieved by slab N-S6+, which exceeded the reference slab\u0026rsquo;s peak load by roughly 36%. Even in cases where the load increase was modest, the presence of SIFCON altered the failure mode from brittle punching to a more desirable ductile flexural response. For hybrid slabs, the gap between \u003cem\u003eu₁\u003c/em\u003e and u₂ widened as the SIFCON layer was deepened. In slabs cast entirely with SIFCON, this deflection gap was the larger in S\u0026thinsp;+\u0026thinsp;R slab, further promoting a switch from punching to flexural failure and greatly enhancing ductility, as observed in specimens S and S\u0026thinsp;+\u0026thinsp;R.\u003c/p\u003e\n \u003cp\u003eOverall, the study demonstrates that even a modest amount of SIFCON, applied as a plus-shaped core throughout the thickness, can deliver substantial strength gains while providing excellent ductility. The difference between the deflection at peak load and \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e stage reached roughly 12 mm in N-S6\u0026thinsp;+\u0026thinsp;slab cases. These findings emphasize the promise of SIFCON for flat-slab construction: significant improvements in capacity and toughness can be achieved without increasing slab thickness or adding drop panels or column capitals.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab6\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThe peak load and deflection of the specimens at the peak cracks.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSpecimen\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ecp\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eqp\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e50.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e93.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e86\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eS\u0026thinsp;+\u0026thinsp;R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e109.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e118\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN-S2+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e56.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN-S6+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e68.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003eNote: \u003cem\u003eP\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e = Peak load by (kN); \u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ecp\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eqp\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;Center and Quarters av. deflection by (mm) at peak load respectively; \u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;The percentage of improved peak load compared to specimen N.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5 Ductility\u003c/h2\u003e\n \u003cp\u003eDuctility, \u0026micro;, describes the capacity of a structural member to undergo substantial deformation after first yield. In this study, it is expressed as the ratio of the ultimate displacement, \u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eu\u003c/em\u003e\u003c/sub\u003e, to the corresponding yield displacement, \u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ey\u003c/em\u003e\u003c/sub\u003e, by Eq.\u0026nbsp;(1) and the procedure proposed by Lim and Hong (2016). The ultimate displacement is taken as the deflection recorded when the applied load has fallen to 80% of the specimen\u0026rsquo;s peak value. To locate the yield point, the load\u0026ndash;deflection response is idealized as an elastic\u0026ndash;perfectly-plastic curve that (i) passes through the peak load and (ii) has an initial slope equal to the secant stiffness measured at two-thirds of the peak load. The intersection of this idealized line with the actual response defines the yield displacement, following the approach used by Sukontasukkul et al. 2004, Lim and Hong (2016), and Kaka et al. (2016).\u003c/p\u003e\n \u003cp\u003eBecause the slabs exhibited continuing deformation after peak load, ductility ratios were evaluated at two ultimate stages \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e to capture the influence of fiber reinforcement on post-peak behavior. The resulting indices, \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, are reported in Table \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e and provide a clearer picture of how fiber type and distribution affect the later stages of the response.\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mu\\:=\\frac{\\varDelta\\:u}{\\varDelta\\:y}\\)\u003c/span\u003e\u003c/span\u003e Eq. (1)\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab7\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThe ductility results.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSpecimen\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003csub\u003ey\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ecy\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ecu1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ecu2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e\u003cem\u003e\u0026micro;1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e\u003cem\u003e\u0026micro;2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e48.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e83.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e176\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eS\u0026thinsp;+\u0026thinsp;R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e93.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e176\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e303\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN-S2+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e49.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e28\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN-S6+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e61.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e157\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e263\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"9\"\u003eNote: \u003cem\u003eP\u003c/em\u003e\u003csub\u003e\u003cem\u003ey\u003c/em\u003e\u003c/sub\u003e = yield load by (kN); \u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ecy\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;Center deflection by (mm) at yield load; \u003cem\u003e\u0026Delta;\u003c/em\u003e\u003csub\u003e\u003cem\u003ec(u1 and u2)\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;Center ultimate deflection by (mm) \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e respectively; \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;the ductility 1 and 2 ; \u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e\u003cem\u003e\u0026micro;1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e\u003cem\u003e\u0026micro;2\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;The percentage of improved ductility 1 and 2 compared to specimen N.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e demonstrates that embedding SIFCON in the slab markedly elevates its ductility. During the first post-peak phase \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e ductility increases steadily, while a far more pronounced gain emerges in the second phase \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e. For hybrid slabs most clearly in specimen N-S6+, where a plus-shaped SIFCON core extends through the full thickness, the greatest benefit appears in the transition between these two stages. After the longitudinal reinforcement fully yields, the SIFCON fibers engage, bridging and confining cracks so effectively that the slab sustains its load-bearing capacity for an extended period and the failure mode shifts from brittle to ductile. These results confirm the study\u0026rsquo;s key premise: outstanding ductility can be achieved with only a modest volume of SIFCON.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.6 Inclination of cracks and rotation of slabs\u003c/h2\u003e\n \u003cp\u003eAfter completing the slab tests, the rotation of each slab about the loading zone was recorded, and the specimens were subsequently sectioned longitudinally to delineate the dominant crack patterns \u003cem\u003eFig.\u0026nbsp;8\u003c/em\u003e. By mapping cracks on both the top and bottom faces, the punching-cone angle defined as the inclination between the failure surface and the vertical plane, was established. Results show that this angle on the tensile face decreases monotonically with higher SIFCON content. This finding demonstrates that the critical cracks migrate progressively away from the critical punching-shear zone, transforming the failure mode from brittle to ductile. Moreover, the slab\u0026rsquo;s rotation angle increases with SIFCON incorporation, particularly when larger SIFCON regions are provided.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study evaluates the structural performance of flat slabs strengthened either fully with SIFCON or partially through a hybrid system combining SIFCON with normal-strength concrete (NSC). The experimental program measured the compressive and flexural strengths of both SIFCON and NSC, determined ultimate load, deflection, ductility, and rotation, and recorded crack patterns together with crack inclinations. The results highlight the efficiency of adding SIFCON, in boosting punching-shear resistance and improving the behavior of flat slabs, and they confirm the merit of hybrid NSC\u0026ndash;SIFCON assemblies in enhancing overall structural performance. Finally, the study presents a series of conclusions that reaffirm the scientific significance of the findings and open new avenues for forthcoming research and practical engineering applications related to the design of slabs subjected to punching-shear forces:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eOn seven and twenty-eight days, the \u003cem\u003emechanical properties\u003c/em\u003e of the two varieties of concrete employed in this study, NSC and SIFCON, were evaluated. At 28 days, SIFCON with hooked-end steel fibers had greater compressive and flexural strengths of 118 and 32 MPa, respectively. Comparing SIFCON to the reference NSC, the gains in compressive strength were 174%. In comparison to the reference NSC, the flexural strength gains for SIFCON was 567%.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe slabs made entirely of SIFCON concrete with hooked-end fibers demonstrated a substantial improvement in the \u003cem\u003einitial cracking\u003c/em\u003e load. With a 342% improvement above the control NSC slab, the SIFCON slab experienced the greatest rise. However, there was no discernible increase in the initial crack load in hybrid slab construction; the higher increase in these slab was 56%.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eWhen compared to the traditional NSC slab, \u003cem\u003emaximum load\u003c/em\u003e capacity of the SIFCON flat slab shows a significant improvement. With an 118% increase above the control, the SIFCON slab with hooked-end steel fiber showed the greatest enhancement. Depending on the SIFCON depth, the hybrid slabs demonstrated benefits that 36%.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe \u003cem\u003eload\u0026ndash;deflection\u003c/em\u003e curves showed that all the slabs that used SIFCON entirely or partially had a high ductility and gradual post-peak decline, unlike the NSC slab, which failed sharply. The highest deflection was recorded in the SIFCON slab, which was 24.8 mm, while in the hybrid slabs, the highest deflection was recorded as 23.5 mm in the slab in which the depth of the SIFCON was equal to the depth of the slab.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe \u003cem\u003efailure mechanisms\u003c/em\u003e of the slabs were different. In a brittle punching-shear mode, specimens made entirely of normal strength concrete NSC showed very little ductility and developed large, steeply inclined cracks at about 32\u0026deg;. On the other hand, the SIFCON slabs broke down in a very ductile way: many tiny cracks spread at shallow angles of roughly 17\u0026deg;, demonstrating the material's exceptional capacity to prevent cracks. The reaction of hybrid NSC\u0026ndash;SIFCON slabs was in the middle; cracking was more regularly spaced and happened at moderate inclinations (26\u0026deg;\u0026ndash;29\u0026deg;), which was better than plain NSC but still less controlled than in full-SIFCON members. In the total SIFCON specimen S\u0026thinsp;+\u0026thinsp;R slab, the slab's rotation around the load point increased according to its SIFCON share, reaching roughly 4.7\u0026deg;.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eA considerable improvement in \u003cem\u003eductility\u003c/em\u003e was found in slabs that included SIFCON. The highest ductility index was observed by all SIFCON specimens, demonstrating their remarkable capacity to dissipate energy and withstand significant inelastic deformations before collapse. While the reference NSC slab, which was controlled by a brittle punching shear failure, had the lowest index, hybrid NSC\u0026ndash;SIFCON members also showed considerable increases. In order to shed light on fiber efficiency under the most recent loading, this study is also the first to investigate \"late stage\" ductility at the deflection levels \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e. The ductility amplification factor \u003cem\u003eη\u003c/em\u003e\u003csub\u003e\u003cem\u003e\u0026micro;2\u003c/em\u003e\u003c/sub\u003e increased by around 303% in the S\u0026thinsp;+\u0026thinsp;R slab and 263% in the N-S6\u0026thinsp;+\u0026thinsp;slab at the maximal deflection \u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis research received no external funding.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eW. K. conducted the experimental work, performed the tests, analyzed the results, prepared all figures and tables, and wrote the main manuscript text. B. L. provided the materials, supervised the research process, and contributed to project oversight. All authors reviewed and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to express their sincere gratitude to Betonmix Ltd. for generously providing the steel fibers used in this study. Their valuable support and contribution significantly contributed to the successful completion of the experimental work.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eACI Committee 544. (2002). \u003cem\u003eState-of-the-Art report on fiber reinforced concrete (ACI 544.1R-96)\u003c/em\u003e. American Concrete Institute.\u003c/li\u003e\n\u003cli\u003eACI Committee 318. (2019). \u003cem\u003eBuilding code requirements for structural concrete (ACI 318\u0026thinsp;\u0026ndash;\u0026thinsp;19)\u003c/em\u003e. American Concrete Institute.\u003c/li\u003e\n\u003cli\u003eBrisid, I., Joao, P., Carla, M., \u0026amp; Antonio, P. (2022). 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Large-scale experiment on the behavior of concrete flat slabs subjected to standard fire. \u003cem\u003eJ Build Eng\u003c/em\u003e, \u003cem\u003e30\u003c/em\u003e, 101255.\u0026nbsp;\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jobe.2020.101255\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eHalvon\u0026iacute;k, J., Kalick\u0026aacute;, J., Majt\u0026aacute;nov\u0026aacute;, L., \u0026amp; Min\u0026aacute;rov\u0026aacute;, M. (2019). Reliability of models aimed at evaluating the punching resistance of flat slabs without transverse reinforcement. \u003cem\u003eEngineering Structures\u003c/em\u003e, \u003cem\u003e188\u003c/em\u003e, 627\u0026ndash;636.\u0026nbsp;\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.engstruct.2019.03.055\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eSaleh, H., Kalfat, R., Abdouka, K., \u0026amp; Al-Mahaidi, R. (2019). Punching shear strengthening of RC slabs using L-CFRP laminates. \u003cem\u003eEngineering Structures\u003c/em\u003e, \u003cem\u003e194\u003c/em\u003e, 274\u0026ndash;289.\u0026nbsp;\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.engstruct.2019.05.050\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eTahmoorian, F., Nemati, S., Sharafi, P., Samali, B., \u0026amp; Khakpour, S. (2021). Punching behavior of foam-filled modular sandwich panels with high-density polyethylene skins. \u003cem\u003eJournal of Building Engineering\u003c/em\u003e, \u003cem\u003e33\u003c/em\u003e, 101634.\u0026nbsp;\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jobe.2020.101634\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eQi, J., Cheng, Z., Zhou, K., Zhu, Y., Wang, J., \u0026amp; Bao, Y. (2021). Experimental and theoretical investigations of UHPC-NC composite slabs subjected to punching shear-flexural failure. \u003cem\u003eJournal of Building Engineering\u003c/em\u003e, \u003cem\u003e44\u003c/em\u003e, 102662.\u0026nbsp;\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jobe.2021.102662\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eNguyen, L., Rovn, M., Tran, T., \u0026amp; Nguyen, K. (2011). Punching shear resistance of steel fiber reinforced concrete flat slabs. \u003cem\u003eProcedia Engineering\u003c/em\u003e, \u003cem\u003e14\u003c/em\u003e, 1830\u0026ndash;1837.\u0026nbsp;\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.proeng.2011.07.230\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eYehia, E., Khalil, A. H., Mostafa, E. E., \u0026amp; El-Nazzer, M. A. (2023). 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Impact and blast resistance of slurry infiltrated fiber concrete (SIFCON): a comprehensive review. \u003cem\u003eConcrete Structures Journal\u003c/em\u003e, \u003cem\u003e24\u003c/em\u003e, 129\u0026ndash;136.\u0026nbsp;\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.32970/CS.2023.1.18\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eTauma, W. K., Bal\u0026aacute;zs, G., \u0026amp; L (2024). Properties of fibers and mortar of slurry infiltrated fiber concrete (SIFCON). 14th Central European Congress on Concrete Engineering. \u003cem\u003eISPN 978\u0026thinsp;\u0026ndash;\u0026thinsp;80\u003c/em\u003e, \u003cem\u003e908943\u003c/em\u003e(1-0), 454\u0026ndash;465.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Flat slab, Slurry Infiltrated Fiber CONcrete, punching shear, steel fibers, post-punching behavior","lastPublishedDoi":"10.21203/rs.3.rs-7002488/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7002488/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePunching shear failure in flat slabs remains one of the most critical issues in reinforced concrete structures due to its sudden and brittle nature. This research investigates the potential of using Slurry Infiltrated Fiber Concrete (SIFCON) as an alternative to traditional punching shear reinforcement in flat slabs cast from normal-strength concrete (NSC). The fiber type was hooked-end steel fiber with a fraction volume of 6%. Five square flat slab specimens were cast; the first specimen was cast using NSC. Four of them were reinforced with maximum flexural steel to ensure failure by punching shear. In two of these slabs, SIFCON was used as a whole slab, but since it is expensive to use SIFCON for entire slabs, in others, SIFCON was used partially over an extended area in a form similar to a plus sign shear reinforcement and full or partial depth to improve the resistance to punching shear. The data demonstrate that SIFCON, when applied strategically, is a highly effective material for increasing punching shear resistance and improving post-punching behavior and ductility. Providing a realistic alternative to standard reinforcement approaches.\u003c/p\u003e","manuscriptTitle":"Punching shear strengthening of flat slab using SIFCON","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-17 16:05:09","doi":"10.21203/rs.3.rs-7002488/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"55911cb1-18d0-4316-8d40-e5a2ea5cc717","owner":[],"postedDate":"July 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-08-02T11:38:46+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-17 16:05:09","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7002488","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7002488","identity":"rs-7002488","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}