https://doi.org/10.14311/APP.2022.33.0001 Acta Polytechnica CTU Proceedings 33:1–7, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague COMPARATIVE FLEXURAL PERFORMANCE OF STEEL FIBRE REINFORCED SELF-COMPACTING CONCRETE (SCFRC) RIBBED SLAB WITH DIFFERENT FIBRE PROVISION AREA Hazrina Ahmada,∗, Mohd Hisbany Mohd Hashimb, Afidah Abu Bakarb, Fariz Aswan Ahmad Zakwana, Ruqayyah Ismaila a Faculty of Civil Engineering, Universiti Teknologi MARA, Cawangan Pulau Pinang, Kampus Permatang Pauh, 13500 Permatang Pauh, Pulau Pinang, Malaysia b Faculty of Civil Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia ∗ corresponding author: hazrina180@uitm.edu.my Abstract. The flexural performance of three SCFRC ribbed slabs with different fibre provision area were investigated in this paper; in both ribs and flange (SFWS), ribs only with additional welded mesh in flange (SFT) and in ribs only (SFR). Short hooked end fibres of 35 mm length of 1% volume fraction was blended with the flowable self-compacting concrete (SCC) were used as the material for the slabs. Slab samples of 2.8 × 1.2 × 0.2 m were constructed and loaded until failure under four- point bending. Investigation was carried out in view of the load bearing capacity, deflection, energy absorption capacity as well as the failure modes. The influence of the steel fibre provision on the strain distribution was also examined. Keywords: Ribbed slab, self-compacting concrete, steel fibres. 1. Introduction Steel fibre reinforced concrete (SFRC) can be applied in structural slabs that usually cater uniformly dis- tributed low and moderate loads owing to the abil- ity of the steel fibres (SF) to reduce brittleness and enhance its mechanical properties. In consideration of the workability and fibre distribution of the fibre concrete used, this study focuses on the utilization of self-compacting fibre reinforced concrete (SCFRC) that is able to be cast in place without any vibration. The flow ability of the SCFRC offer advantage to the construction process that further leads to a reduction of manpower cost and time [1]. At present, the in- clusion of steel fibres is now extended as the main re- inforcing material in slab applications to partially or totally replace conventional reinforcements. A num- ber of studies had been performed utilizing SCFRC material in flat slab [2–7]. However, limited studies were found on literatures concerning a ribbed profiled structure. To date, studies on the application of steel fibres in slab structures with rib profile were still lim- ited to its application in normal steel fibre reinforced concrete with low volume fraction (0.5%) [8–10]. The objective of this research is to experimen- tally determine the ultimate flexural strength, load- deflection curves and the energy absorption capacity of SCFRC ribbed slabs varying in the provision area of the steel fibres (fully and partially steel fibre rein- forced). 2. Experimental program Nine (9) numbers of SCFRC ribbed slabs were cast with 2800 mm length, 1200 mm width and overall thickness of 200 mm. Two ends of the slabs were simply supported on rollers providing clear effective span length of 2600 mm. Two-line loads were ap- plied on the slabs under displacement control of 0.1 mm/sec. Sensitive linear voltage differential trans- ducers (LVDT) were used to measure the displace- ment at the slab centre (rib and flange soffit). Grade C30/37 plain self-compacting concrete (PSCC) mix was used for the fabrication of the ribbed slab samples with the mix proportions shown in Ta- ble 1. The volume fraction of the hooked end steel fibres was 1% which corresponds to 80 kg/m3. Detail properties of the steel fibres is shown in Table 2. The mechanical properties of the PSCC and SCFRC mix used in this research is discussed elsewhere [11]. Similar SCC mix was used for the SCFRC mix in combination with the steel fibres. The SCFRC mix was classified as SF1 [12], thus no vibration was ap- plied during casting of the samples. Details on the variation of the slab samples are listed in Table 3 while Figure 1 presents the steel fibre provision in the slab samples applied in this research. The SCFRC ribbed slab are divided into three categories; i.e. full steel fibre reinforced (SFWS), partially steel fibre re- inforced with welded mesh (SFT) and partially steel fibre reinforced without welded mesh (SFR). Each type of samples also varies in terms of its topping flange thicknesses (80, 100 and 120 mm). 1 https://doi.org/10.14311/APP.2022.33.0001 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en H. Ahmad, M. H. Mohd Hashim, A. Abu Bakar et al. Acta Polytechnica CTU Proceedings Cement CEM I 42.5R Pulverized fly ash 10 mm coarse aggregate Fine aggregate Water w/c Steel fibre content 315 kg/m3 105 kg/m3 830 kg/m3 865 kg/m3 185 kg/m3 0.44 80 kg/m3 Table 1. SCC mix composition. Fibre type Tensile strength (N/mm2) Length L (mm) Diameter df (mm) Fibre aspect ratio L/df Hooked end 1250 35 0.55 65 Table 2. Steel fibre properties. Reinforcement Designation Topping flange thickness (mm) Fully steel fibre reinforced SFWS SFWS80 80 SFWS100 100 SFWS120 120 Partially steel fibre reinforced with BRC SFT SFT80 80 SFT100 100 SFT120 120 Partially steel fibre reinforced without BRC SFR SFT80 80 SFT100 100 SFT120 120 Table 3. SCFRC sample details. � 6)7��3DUWLDO�6)�ZLWK�ZHOGHG�PHVK� 6)5 �3DUWLDO�6)� 6):6 �)XOO�6)� Figure 1. Steel fibre provision area. 2 vol. 33/2022 Steel Fibre Reinforced Self-Compacting Concrete Sample First crack load Pcr (kN) Ultimate load Pult (kN) Displacement at ultimate load δult (mm) Energy absorption at Pult (kNmm) Total energy absorption (kNmm) SFWS80 35.78 57.83 8.75 403.15 1298.91 SFWS100 47.67 60.00 7.8 367.56 1379.22 SFWS120 46.04 74.71 12.47 716.73 1540.65 SFT80 42.89 50.66 3.17 104.23 823.49 SFT100 49.14 51.64 2.97 99.96 1019.92 SFT120 39.53 49.25 7.95 320.01 794.38 SFR80 47.89 55.65 3.17 117.11 482.52 SFR100 44.69 49.3 2.1 66.72 375.83 SFR120 46.26 54.79 2.61 87.46 264.72 Table 4. Flexural test results. 3. Experimental results and discussion 3.1. First crack and ultimate strength of ribbed slabs The presence of the steel fibres significantly influ- ences the first crack occurrence of the SCFRC ribbed slab. The experimental results of the flexural test are presented in Table 4. The first crack load of all SFWS, SFT and SFR samples were found to be ap- proximately double the first crack load of conven- tional ribbed slab sample without any steel fibres. The first crack values used for comparison are 17.59, 21.39 and 21.99 kN for 80, 100 and 120 mm flange thickness, respectively. These results are reported elsewhere [13]. Additionally, the first crack load of all samples was observed to be more than 60% of the ultimate load achieved, proving the ability of the steel fibres to transfer stresses across the cracks within the concrete matrix. Furthermore, the provision of steel fibres also sig- nificantly influences the ultimate strength of the ribbed slab that corresponds to the major crack initi- ation in the ribbed slab samples. The SFWS samples that were fully reinforced with steel fibres achieved the highest ultimate load even with the absence of any conventional reinforcements. Partially reinforced samples (SFT and SFR) however, achieved lower ul- timate loads. This might be due to the faster occur- rence of the major crack in the sample since the steel fibres were only provided in the ribs causing the stress transfer within the matrix to be more rapid. The presence of the welded mesh in the topping flange also showed no significant contribution to the ulti- mate strength of the partially steel fibre reinforced samples as it is not in the tension zone. 3.2. Load-displacement The load-displacement curves for all SCFRC ribbed slab samples are shown in Figure 2. Before the first crack occurrence, the elastic region was steeper for the partially SF reinforced samples (SFT and SFR) in comparison to the SFWS samples that showed a more gradual increment. Beyond the first crack occurrence, only the SFWS samples exhibited displacement-hardening response towards the ulti- mate load displaying the efficiency of the SF to trans- fer the stresses within the cracked samples. This hardening behaviour is in relation to the ex- istence of the SF in the topping flange that played an important role in resisting the formation of the cracks as it propagates from the ribs to the flange section. At this point, some of the steel fibres will be subjected to pull-outs as the loading continues. This displacement-hardening response was less significant in the partially SF reinforced samples (SFT and SFR) even with presence of the welded mesh reinforcement in the topping flange. Beyond the ultimate load, all samples experienced displacement-softening response where the load car- rying capacity gradually decrease as the vertical dis- placement continues to increase further. Gradual softening curves are exhibited by the SFWS and SFT samples reaching up to 32 mm displacement. In contrast, the SFR samples underwent more abrupt softening resulting lower displacement reflecting to a more brittle behaviour of the structure. In view of the topping flange thickness for each type of samples, the increase in the topping flange thickness significantly affects the softening curves. Steeper curves were observed for 120 mm topping flange thicknesses of all ribbed slab samples exhibit- ing a more brittle post-cracking behaviour as the top- ping thickness increases beyond half of the total slab depth (100 mm). This brittleness might be as the result of the topping thickness that enters the tensile zone of the sample reducing the function of the rib section. This finding also agrees well with the previ- ous findings where higher slab thickness resulted in higher brittleness of the section [3, 14]. 3 H. Ahmad, M. H. Mohd Hashim, A. Abu Bakar et al. Acta Polytechnica CTU Proceedings � � �� �� �� �� � � �� �� �� �� �� �� / RD G� �N 1 � 'LVSODFHPHQW��PP� 6):6�� 6):6��� 6):6��� 6)7�� 6)7��� 6)7��� 6)5�� 6)5��� 6)5��� Figure 2. Load-displacement curves. Figure 3. Energy absorption capacity. 3.3. Vertical displacement At ultimate load, the highest displacement was exhib- ited by the SFWS samples at both ultimate load and at final failure of the samples (Table 4). This was followed by the SFT and SFR samples. The SFR samples which are more brittle experienced the low- est vertical displacement at ultimate load as well as at final failure exhibiting a lower level of ductility. Nevertheless, all samples fulfilled the displacement requirement at service load whereas the values are within the allowable limit (L/500) as stated in the Eurocode 2 revealing the capability of the SCFRC samples under flexural load. In view of the topping flange thickness, the lowest displacement at ultimate load was observed in the samples with 100 mm topping flange thickness for all types of samples. This can be related to the location of the neutral axis and the transmission of the stresses between the rib and flange section of the ribbed slab. At final failure, however, the 120 mm samples expe- rienced the lowest displacement that is as the result of the brittle behaviour of the SCFRC ribbed slab as the topping flange thickness increases. 3.4. Energy absorption capacity Steel fibre inclusion enhances the energy absorption capacity of the slab as calculated by the area under the load-displacement curve. Higher volume of steel fibres in concrete resulted in an increase in the energy absorbed by the slab structure. The SFWS samples showed the highest energy absorption capacity at the ultimate load as well as the total energy (see Table 4). The energy absorption capacity is in close relation with the total volume of SF in the slab. The SFWS samples showed higher energy absorption for higher flange thicknesses. However, a contradict trend were observed in the SFT and SFR samples showing the relation towards the provision area of the SF (Fig- ure 3). 4 vol. 33/2022 Steel Fibre Reinforced Self-Compacting Concrete � Figure 4. Strain distribution of SFWS and SFT samples. � �D��6):6� �E��6)7� �F��6)5� Figure 5. Crack pattern of the SCFRC ribbed slab and steel fibres bridging the cracks. 3.5. Strain distribution The neutral axis location of the SCFRC ribbed slab samples can be determined based on the strain distri- bution across the depth of the slab at various stages of loading. For the SFWS samples, only for 80 mm top- ping thickness, the neutral axis falls below the top- ping flange. The neutral axis falls in flange for all other samples, including all SFT and SFR samples. No significant effect of the topping flange on the neu- tral axis location thickness was observed. The strain distribution for the SCFRC ribbed slab samples is presented in Figure 4. The view of the bridging steel fibres is also pre- sented in Figure 5. From the crack openings, it can be observed that most of the steel fibres were in the lon- gitudinal direction that is perpendicular to the crack direction. The steel fibres had effectively bridged the cracks by holding the matrix together and the hooked end shape had assisted in increasing the bonding to the concrete matrix contributing to the structural strength to resist loads. The crack pattern for the partially reinforced sam- ples (SFT and SFR) were different from the SFWS samples whereas it only experienced one major crack 5 H. Ahmad, M. H. Mohd Hashim, A. Abu Bakar et al. Acta Polytechnica CTU Proceedings � Figure 6. SCFRC ribbed slab at final failure. line with very minimal minor cracks across the sam- ple. The crack started at the rib’s soffit and propa- gated to the flange soffit. The SFT samples under- went ductile failure, gradually failing after the ulti- mate load was reached. The SFR samples on the other hand experienced a more rapid crack propaga- tion experiencing a more brittle failure. 3.6. Crack pattern and failure modes Figure 5 showed the crack pattern of the SFWS sam- ples. The first crack of all three SFWS samples was detected within the central region of the ribbed slab located at the external rib soffit. After the occurrence of the first crack, more cracks developed at the external rib’s soffit on both sides of the sample as well at the middle rib soffit. These cracks then continued to propagate to the sides of the rib sections and further to the soffit of the flange as the loading continued. As the cracks continued to widen at the ribs, it could be visually observed from the slow propagating cracks that the steel fibres had effectively bridged the cracks as the loading continued to increase further. The view of the bridging steel fibres is also pre- sented in Figure 5. From the crack openings, it can be observed that most of the steel fibres were in the lon- gitudinal direction that is perpendicular to the crack direction. The steel fibres had effectively bridged the cracks by holding the matrix together and the hooked end shape had assisted in increasing the bonding to the concrete matrix contributing to the structural strength to resist loads. The crack pattern for the partially reinforced sam- ples (SFT and SFR) were different from the SFWS samples whereas it only experienced one major crack line with very minimal minor cracks across the sam- ple. The crack started at the rib’s soffit and propa- gated to the flange soffit. The SFT samples under- went ductile failure, gradually failing after the ulti- mate load was reached. The SFR samples on the other hand experienced a more rapid crack propaga- tion experiencing a more brittle failure. In view of the topping thickness variation, the cracks were observed to be more concentrated on the rib soffit of the SFWS samples with lower flange thick- nesses (80 mm and 100 mm). Consequently, more cracks were observed to be distributed over the flange soffit for the 120 mm topping thickness. At the end of the loading test, all SFWS samples still remained intact, held by the steel fibres in the ribs and topping flange (Figure 6). As for the SFT and SFR samples, all samples except for the sam- ples with 120 mm topping thickness remains intact at final failure with the assistance of the welded mesh and bridging of the fibres in the ribs section. Samples with 120 mm thickness experienced brittle failure, i.e. breaking into two at the end of the loading process. These conditions might be due to the reduced thick- ness of the rib section resulting smaller volume of the steel fibres to bridge the cracks. 4. Conclusion Based on the results, these conclusions can be drawn: 1. All SCFRC ribbed slab underwent flexural failure. The fully SF reinforced samples experienced multi- ple cracks while the partially SF reinforced samples experienced only one major crack, displaying the significant effect of the steel fibre provision under flexural load. 2. The fully SF reinforced samples also achieved the highest ultimate load at higher deflection exhibit- ing higher level of ductility amongst all samples 3. Increase in the flange thickness resulted an increase in the ultimate load for the SFWS samples but shows no significant increase in the SFT samples. Beyond the ultimate load, samples with higher 6 vol. 33/2022 Steel Fibre Reinforced Self-Compacting Concrete flange thickness becomes more brittle resulting in a more rapid strength loss. Overall, based on the experimental results, it can be concluded that the fully steel fibre reinforced sam- ple (SFWS) with the highest flange thickness dis- played a good performance under bending. Acknowledgements Special thanks to the laboratory staffs of the Faculty of Civil Engineering, Universiti Teknologi MARA for their technical support and the Institute of Research Manage- ment and Innovation (IRMI), UiTM for their assistance in managing the research process. This study was funded by the E-science Fund (06-01-01-SF0835) from the Min- istry of Science, Technology and Innovation (MOSTI) of Malaysia. References [1] M. Paja̧k, T. Ponikiewski. Flexural behavior of self-compacting concrete reinforced with different types of steel fibers. Construction and Building Materials 47:397-408, 2013. https: //doi.org/10.1016/j.conbuildmat.2013.05.072. [2] A. Blanco, P. Pujadas, A. de la Fuente, et al. Assessment of the fibre orientation factor in SFRC slabs. 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