INFLUENCE OF CARBON AND STEEL USED IN COMBINATION WITH PARTIAL BEAM

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 13, December 2018, pp , Article ID: IJCIET_09_13_0733 Available online at aeme.com/ijciet/issues.asp?jtype=ijciet&vtype= =9&IType=13 ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed INFLUENCE OF CARBON AND STEEL FIBERS USED IN COMBINATION WITH PARTIAL STIRRUPS ON STRUCTURAL BEHAVIOR OF BEAM Fatimah. H. Naser Al Mamoori* Hydraulic Structures Department, Water Resources Engineering g College, Al Qasim Green University, Hilla, Iraq Ali. H. Naser Al Mamoori Civil Engineering Department, Engineering College, Karbala University, Hilla, Iraq ABSTRACT This paper presents the effect of optimum volume fraction of carbon and/or steel fibers added into reinforced concrete beams without any mineral or chemical admixtures in combinationn with partial shear reinforcement. The size of the beam was fixed at mm. The clear span of the beam 1260 mm. A total of eight shear-deficient beams were tested under two-point loading for the shear span to depth ratio 2.5. Three beams with half amount of stirrups (stirrup spacing 80 mm) added with 1% carbon fiber, 1.5% steel fiber and hybrid fibers (0.5% carbon fiber and 0.75% steel fiber). Whilst, the other three beams tested with a minimum amount of stirrups (maximum spacing between stirrups 180 mm) added with fibers with a same volume fraction of same fibers types mentioned previously. The beam without fibers was taken as the control beam for each group. Results indicates that first cracking load, ultimate load and stiffness increased as the amount of shear reinforcement increased by decreasing the spacing between stirrups with or without fibers. It was also noted that the failure mode was modified from brittle shear failure to flexural-shear failure with or without fibers. The mechanical behavior of beams were improved due to the combined effect of stirrups and fibers; the fibers with steel and hybrid showed better efficiency in improving the shear response. The experimental result gives promising improvement of the load carrying capacity ranged from % to 45.75% and their corresponding mid span deflection at ultimate load ranged from 8.40% to 53.41% as well as controlled cracks propagation for the beams. Additionally, it was observed that addition of fibers changes the mode of failure of the beams from brittle to a more ductile. Key words: Hybrid Fibers, Carbon and Steel Fibers, Shear Strength, Failure Mode, Reinforced Concrete Beam, Stirrups, Composite Effect editor@iaeme.com

2 Influence of Carbon and Steel Fibers Used In Combination with Partial Stirrups On Structural Behavior of Beam Cite this Article: Fatimah. H. Naser Al Mamoori and Ali. H. Naser Al Mamoori, Influence of Carbon and Steel Fibers Used In Combination with Partial Stirrups On Structural Behavior of Beam, International Journal of Civil Engineering and Technology (IJCIET) 9(13), 2018, pp INTRODUCTION The beams usually reinforced with stirrups in order to prevent the brittle and sudden shear failure which is occurred before the full strength achieved. The adding of steel fibers can increase the strength capacity of shear and it can also modify the pattern of cracks; as it's known. If a sufficient amount of steel fibers are added in a reinforced concrete beam, it can increase the post-cracking behavior of the beam due to obstruct the width of cracks; which is led to reducing the cracks width and spacing [1, 2]. Therefore, the steel fibers can be used to replace some of the vertical stirrups in the members, resulting in cost and time savings over the transverse reinforcements. In addition to the stirrups reduction reduces the problems involved with the shear reinforcement congestion. Many researchers focused their works on this matter such as [1-7]; using different types of steel fiber; with or without vertical stirrups. Newly, the synthetic non-metallic fibers have become more attractive due to their effectiveness in improving strength of shear and their lower density and more resistance to corrosion when compared with that of steel fibers only. Therefore, many researchers such as [8-10] have been interested to studying the effect of non-metallic fiber on concrete mechanical properties; but the fibers in these research used with using chemical admixtures in order to improve workability and used usually with lightweight concrete to reduce density or used with cement mortar. Carbon fibers as a non-metallic fiber have high thermal conductivity, excellent resistance of abrasion, good stability of chemical and low density; and it can be used to reduce shrinkage and cracking. These fibers increase concrete mechanical properties such as flexural and tensile strengths, impact resistance and flexural toughness. Carbon fibers also increase dry shrinkage and durability and decreases the electrical resistance [11,12]. These attractive properties of carbon fiber are encouraged to be used as an alternative to the shear reinforcement. For a long time investigators and engineers have shown great interest in using different types of fiber in concrete with different ratios of volume fractions and combinations and their impact on the mechanical properties of concrete, but in Iraq little useful information are available to the civil engineers on general using hybrid fibers(in size or in material) in concrete. And yet, no information about using combination of steel and carbon fibers in concrete without any chemicals or mineral admixtures. 2. OBJECTIVES AND EXPERIMENTAL PROGRAM The first objective of the research is related to using steel and carbon fibers as fiber reinforcement in normal strength concrete without any chemical or mineral admixtures and studying some of mechanical properties of concrete result at different ratio of fiber (0.5%, 0.75%, 1.0%, 1.5% and 2%) separately and combination as a hybrid fibers (HF). The second objective is to study the influence of using these fibers at optimum percent that gotten from the first objective of research (which are 1.5% SF and 1% CF) in combination with minimum stirrups that required for shear reinforcement and with half amount of stirrupson structural behavior of beams. This objective includes testing of eight reinforced concrete beams of (150 mm width 200 mm depth 1400 mm height). A clear cover of concrete 20 mm was kept constant from all sides. Each of the eight beams was editor@iaeme.com

3 Fatimah. H. Naser Al Mamoori and Ali. H. Naser Al Mamoori reinforced with one layer of two longitudinal bars of 10 mm diameter, in addition to longitudinal compression bars (2 Φ 6 mm). Four beams reinforced with minimum stirrups and the other reinforced with half stirrups of 4 mm diameter. Figure 1 and Table 1 give all beam details. Figure 1. Details of Beams Reinforcements (all dimensions are mm) Symbol of Specimen Table 1 Details of Beams Amount of Stirrups % Steel Fiber (SF) S0 Half 0 0 S1 Half 0 1% S2 Half 1.5% 0 S3 Half 0.75% 0.5% S4 Minimum 0 0 S5 Minimum 0 1% S6 Minimum 1.5% 0 S7 Minimum 0.75% 0.5% % Carbon Fiber (CF) 3. MATERIAL PROPERTIESAND MIX PROPORTIONS The cement used known as (Kar) is ordinary Portland cement. The physical and chemical analysis of cement is meeting with the limits of Iraqi Specification IQS No The natural sand of Al-Akaidur within the zone 2 were used in this work; it was satisfied the requirements of the limits of Iraqi Specification No.45/1984. Rounded coarse aggregate from Al-Nebai quarry with maximum aggregate size of 14 mm were used. The limits of chemical and physical properties of this coarse aggregate compliance to the IQS No Turkish production of deformed steel bars (4, 6 and 10) mm in diameter were used in this work. Three symbols of each type were tested according to ASTM A The results of testing steel bars are listed in Table 2.In this work, steel and carbon fiber have the same length approximately; used as fiber reinforcement in normal strength concrete without any chemical editor@iaeme.com

4 Influence of Carbon and Steel Fibers Used In Combination with Partial Stirrups On Structural Behavior of Beam or mineral admixtures as shown in Figure 2. Table 3 listed the properties of fibers used. Drinking water was used for all concrete processes. Table 2 Test Results for the Reinforcement Bars Φ (mm) Measured Diameter Yield (mm) Strength(MPa) Ultimate Strength(MPa) Carbon Fibers (CF) Steel Fibers (SF) Figure 2.Fibers used in the study Table 3 The Manufacturer Properties of Fibers Used Fiber Type Form Length Lf (mm) SF Straight 13 CF Straight 12 Diameter Df (mm) Tensile Strength (MPa) Relative Density Kg/m Melting Point C o According to the literature e researches and after many trail mixes the cement: sand : gravel ratio used is 1 : 2 : 2.4. The water/cement ratio is (0.417) and the amount of cement used was 400 kg/m 3 at different ratio of fiber (0.5%, 0.75%, 1.0%, 1.5% and 2%). The influence of fibers ratio on the concrete properties in term of slump according to ASTM C and compressive strength according to ASTM C39-05 are showed in Figure 3 with keeping all other mix proportions constant. Figure 3 shows that the concrete with carbon fiber has better workability as compared to concrete with steel fiber and the 1.5% of SF and 1% of CF give the optimum performance of concrete in compressive strength with acceptable workability. Therefore, it will be used in casting the eight beams. Figure 3. Relationship Between Compressive Strength, Slump and Fiber Ratio % editor@iaeme.com

5 Fatimah. H. Naser Al Mamoori and Ali. H. Naser Al Mamoori 4. TESTING OF HARDENED CONCRETE For each beam, two cylinder of (150*300) and three cube of (150*150)were cast with concrete according to ASTM C39-05 and BS 1881-part ; respectively. Also, the concrete prisms of ( mm) according to ASTM C78-02 were used to getting flexural tensile strength of concrete f r while the splitting tensile strength f sp of cylinder ( mm) was found according to ASTM C The density of concrete also measured. Figure 4 illustrated all the processes of mixing, casting and curing of beams and other molds for mechanical properties were performed depended on ASTM C Figure 4. Mixing, Casting and Curing of Beams and Accessories All beams were tested under two point load with a length ofspan 1260 mm and 420 mm of shear span as shown in Figure 5. The beams were instrumented with three dial gauges of 50 mm length and0.01 mm accuracy; one at mid-span and the others at third points to reading the deflections. The load was applied at a rate of 150 N/sec. At each load increment 5 kn, the cracks width was measured by crack meter (Elecometer 900) of0.02 mm accuracy; and the propagation of cracks were also marked. Figure 5. Testing of Beams and Instruments Used 5. RESULTS AND DISCUSSION OF EXPERIMENTAL WORK 5.1. Mechanical Properties of Concrete for Beam Some of concrete mechanical properties for eight beams are listed in Table 4. It is obvious from Table 4 that there is only a marginal improvement in compressive strength due to addition of fibers, the percent of increase in cylinder compressive strength were about 6.66%, 10.68% and 8.67% as average for CF, SF and HF fibers; respectively when compared with plain concrete. The plain mix exhibited brittle failure mechanism while the fibrous concrete were quite ductile in the compression test. Hence, the fibers used were very effective in internally confining the concrete. Table 4 Mechanical Properties of Each Beam editor@iaeme.com

6 Influence of Carbon and Steel Fibers Used In Combination with Partial Stirrups On Structural Behavior of Beam Symbol of Specimen f c' MPa f cu MPa f sp MPa f r MPa Density Kg/m 3 S S S S S S S S Splitting tensile strength indicated important increase because of the fibers inclusion. This increase because of the fibers inclusion is attributed to the mechanism of fibers in arresting progression of crack. Where, the fibers presence in concrete prevents the internal microcracks growth and thus participates to an increase of the tensile strength. The percent of increase in splitting tensile strength were 23.22%, 49.37% and 33.85% as average for CF, SF and HF fibers; respectively when compared with plain concrete. For the flexural strength which expressed as the modulus of rupture, the percent of increase were about 31.87%, 73.81% and 45.54% as average for CF, SF and HF fibers; respectively when compared with plain concrete. The carbon fibers concrete, gave no reduction or little in the unit weight while the steel fibers concrete gave slightly higher unit weight with average value increased from 2380 kg/m3 to 2447 kg/m3. The combination of fibers results to reduce unit weight from 2447 kg/m3 to 2424 kg/m The Behavior of Cracking When the tensile stress of concrete in a beam exceeds the specified tensile strength, the cracks forms. Two types of crack occurred in the tested beams; the flexural cracks resulting from the tensile stresses of flexural at the region of the beam cross-section below the neutral axis, and the shear cracks which form as a result of the inclined or principal tensile stresses acting on the web of the beam at the region of combined moment and shear. The first cracking observed of the beam represents the initial significant event that occurs in the direction change of the load-deflection curve and the first cracks for all beams appeared firstly at flexural region. The first cracking load of shear and flexural appears in the beams are listed in Table (5). They are ranged from 12 to 28 kn in flexural region and from 17 to 31 kn for inclined web region depending on the concrete properties, amount of steel stirrups and type of fiber used; which are accelerate or delay the cracking formation. Figure (6) shows the Cracks failure pattern for all beams; the mechanism of cracks development in each beam is differ from other due to different type of fibers and amount of transverse reinforcement (spacing between stirrups) but the mechanism of cracks development is almost same for steel and hybrid fibers in the two groups. Expected difference is observed in width of cracks between the beams in each group; the development width of crack in the beam S0 more than the beams S1, S2 and S3 at the same load level, also, the beam S4 have crack width more than the beams S5, S6 and S7 at all interval loads, this is due to used fibers. The steel fibers more effective to reduce crack than carbon and hybrid fibers in addition to increasing the number of cracks. On the other hand the reducing in spacing between stirrups, decrease the crack width when compared between all beams in two groups. Figure (7) shows the comparison between cracks width at 70% of ultimate load for all beams editor@iaeme.com

7 Fatimah. H. Naser Al Mamoori and Ali. H. Naser Al Mamoori Table 5 Test Result of All Beams Symbol of Specimen 1st Crack Load (kn) Flexure crack Shear crack S S S S S S S S Increase in Maximum Deflection Ultimate (mm) Ultimate Load (kn) Load Over Mid Span Third Span 0% fiber Failure Mode Shear Shear-Flexure Flexure Shear-Flexure Shear-Flexure Shear-Flexure Flexure Flexure Figure 6 Cracking Pattern of Testing Beams Figure 7 Crack Width at service load for All Beams 5.3. Ultimate Shear Strength and Load-Deflection Curves In Table (5), the recorded data includes failure mode, deflections and ultimate loads for all eight beams. In beam S0 with half amount of steel stirrups and without any fibers, Shear editor@iaeme.com

8 Influence of Carbon and Steel Fibers Used In Combination with Partial Stirrups On Structural Behavior of Beam failure was occurred. Flexurall small cracks along the bottom of beam were appeared at 12 kn and micro diagonal shear crack formed from the left side of shear span at 17 kn. With increasing interval load, additional shear and flexural cracks formed at the beam spans, which were propagated and widenedd until shear failure occurred suddenly at the total test load of kn. In beam S1 reinforced by carbon fibers, the beam failed by the diagonal shear crack and the flexure gradually due to the beam S1 continued carrying the load after many cracks of flexural were observed as shown in Figure 8-A. After the load of 55 kn; diagonal cracks from the two sides of the beam propagated toward loading point and the shear-flexure failure happened. The used of 1% of carbon fibers increased the ultimate load capacity by about 14.60% compared with the beam S0 without any fibers. Also, it was observed to more stiffness and more ductile as shown in Figure 8. The ultimate load of beam S2 was more than the beam S1 due to steel fibers which were provided better cracks distribution throughout the beam span, and the failure mode changed from the brittle shear-flexural failure in beam S1 to more ductile of failure which is the flexural failure. The mechanical behavior of beam S2 was improved due to the combined effect of steel fibers and stirrups. rups. The stiffness and deflection of the beams increased when compared to beam S0 without fibers; also, the ultimate load capacity increased by about 36%. The combination of carbon and steel fibers and stirrups has shown a positive effect on the concrete shear strength of beam behavior over reference beam S0 or single fiber (carbon fibers) concrete beam S1 by about 23.25% and 7.54%; respectively. The addition of hybrid fibers has increased shear strength by 23.25% compared to the beam S0. The experimental load versus mid span deflections for the four beams which had half amount of stirrups are shown in Figure 8-A. Figure 8-A: Half Amount of Stirrups Figure 8-B: Minimum Amount of Stirrups Figure 8 Load Versus Deflection For Two Groups of Beams The addition of fibers to concrete beams reinforced with half amount of stirrups in S1, S2 and S3 resulting in increasing of 29.47%, 53.41% and 46.15% in deflection at ultimate load over that of the control beam S0. This may be explained by efficiency of steel fibers in arresting and delaying the propagation and controlling the growth of the cracks within the beams and hence, maintaining the beam integrity throughout the interval between the first crack and ultimate load stage, therefor, the beam could withstand greater loads and deflections before failure.however, the number of crack were more in fiber reinforced concrete beam than in that without steel fiber and appeared ared to be smaller in width as mentioned previously in cracking behavior. In beam specimen S4 that t reinforced with minimum amount of steel stirrups (maximum spacing between stirrups) and without any fibers, the flexural cracks appeared first obviously editor@iaeme.com

9 Fatimah. H. Naser Al Mamoori and Ali. H. Naser Al Mamoori at 19 kn, and after that at about 26 kn the diagonal shear cracks started to appearing. With increasing interval loads more cracks of diagonal in bothshear spans sides of the beam were observed, at load 50 kn the diagonal crack rapidly propagated toward the loading point simultaneously with flexural cracks under two point loads. With increasing the interval loads, the diagonal and flexural cracks spread quickly and become wider. Then the shear- flexural failure happened at a load of kn by partial separate from two sides in diagonal and flexural region at the same time. The beam S5 had similar behavior of beam S4 till the shear cracks appear at 28 kn, after that, each beam continued in carrying applied load with a new slope till shear- flexural mode failure occurred at kn. The ultimate load increased by about 19.26% due to effect of carbon fibers combination with steel stirrups. Also the beam is more stiffness and ductile as compared with beam S4 as shown in Figure 8. The increasing in the beam stiffness S6 compared with the other three beams occurred due to the applied shear force was carried by the steel fibers concrete with the combination steel stirrups which was the more effective in restricted to cracks to grows and widening. The addition of steel fibers in this beam increased the load carrying capacity and shear strength by modifying the failure mode from brittle; shear-flexural failure to ductile; flexural failure. From Tables 5 it can be noted that the beam shear strength B6 is 45.75% higher than that of the beam S4 without fibers. The addition of hybrid fibers (carbon and steel) with the minimum shear reinforcement in concrete beam B7 resulting in increasing of 33.76% in ultimate load over that of the control beam S4. It is clearly that both fibers and stirrups act compositely better than when either of them exist in the beam alone. This may explained as follows: the performance of fibers which act as crack arrestors and therefore provide reactions to the internal concrete arches was enhanced by using stirrup. The fiber contribution assisted the stirrups in carrying the shear force and hence allowed it accommodate commodate more applied load before they yielded a significant increase in the ultimate shear strength. The addition of fibers to concrete beams reinforced with minimum amount of stirrups (maximum spacing between stirrups) in S5, S6 and S7 resulting in increasing of 8.40%, 31.38% and 20.75% in deflection at ultimate load over that of the beam S4 due to the same causes mentioned above. Figure 9 shows that the same amount of fibers are more efficiency in increasing ultimate strength and deflection when be used with minimum amount of stirrups than half amount of them. Figure 9 Load Versus Deflection For All Beams Figure 10 shows the effect ect of increasing shear reinforcement ratio on concrete beam without fibers. Comparison of the slope of the two curves in this figure shows that using of web reinforcement increase the stiffness of beams to a high degree, i.e the difference in editor@iaeme.com

10 Influence of Carbon and Steel Fibers Used In Combination with Partial Stirrups On Structural Behavior of Beam deflection for certain load is large between each two mentioned beams. However the loads that causes failure for beams with minimum reinforcement are much more than for beams with half amount of shear reinforcement. It is also observed that the type of failure at ultimate load is changed from shear failure to shear-flexural failure. Figure 10 Effect of Spacing Between Stirrups 5.4. Deflected Shape of Beams The effect of variations in the amount of steel stirrups in combination with steel, carbon and hybrid (steel and carbon) fibers on the load deflection characteristics of a given reinforced concrete beams of a given section are presented in Figure 11. The curves show that failure is brittle for half amount of stirrups without fibers, i.e., curves S0 and becomes ductile when using fibers or decrease the spacing between stirrups. Figure also shows the deflected shape of beam at service load (70% of ultimate load) and the deflected shape at failure. Figure 11 Distribution of Deflection at Service and Ultimate Load along the Length for All Beams editor@iaeme.com

11 Fatimah. H. Naser Al Mamoori and Ali. H. Naser Al Mamoori At 15 kn, there is slight difference in deflected shape in eight beams as shown in Figure 11. This was due to fact that, in the early stage of loading, the applied load was carried by the concrete only which was the different in the beams because of using different fibers, and before that there was not any activity of the shear reinforcement (stirrups).at 40 kn, the stirrups usually lay to confine the concrete core and lay to resist of the diagonal crackswidening, in addition to the prevented the main steel bars from splitting and kept them in their position; at the same time, the fibers orientation, across the flexural crack restricted its propagation and transmitted the tensile stress uniformly to the concrete around the cracks. This would result in obviously difference between deflected shape of beams at 40 kn. 6. CONCLUSIONS Concrete with hybrid fibers showed the high mechanical properties over reference concrete without fibers or single carbon fibers concrete mixesand gave better efficiency in improving the shear response. The first cracking load, ultimate load and stiffness increased as the amount of shear reinforcement increased by decreasing the spacing between stirrups with or without fibers. A combination of stirrups and fibers can reduce the area of shear reinforcement. The fibers ability in controlling the cracks propagation of the beams was demonstrated by the change of the failure mode from brittle to a more ductile. REFERENCES [1] Cucchiara C, Mendola LL, Papia M. Effectiveness of stirrups and steel fibres as shear reinforcement. Cement Concrete Compos 2004;26: [2] Kwak YK, Eberhard M, Kim WS, Kim J.: Shear strength of steel fibre-reinforced concrete beams without stirrups. ACI Structural Journal, 99(4), (2002). [3] Praveen K., Venkateswara R. S. and Rathish K. P Hybrid Effects of Stirrup Ratio and Steel Fibers on Shear Behaviour of Self-Compacting Concrete. Archives of Civil Engineering, Vol. LXIV, Issue 1, (2018). [4] Daniel d. L. A., Fernanda G. T. N., Romildo D. T. F., and Moacir A. S. d. A. Shear strength of steel fiber-reinforced concrete beams, Acta Scientiarum Technology, Vol. 36, No.3, (2014). [5] Gustavo J. P M. Shear Strength of Beams with Deformed Steel Fibers Evaluating an alternative to minimum transverse reinforcement, Concrete international, (2006). [6] Timothy N., Hiroshi M., Akira D. and Kohei M. Experimental and analytical study on shear capacity in steel fiber and stirrup RC beam, Journal of Structural Engineering JSCE, Vol.56A, 10 pp. (2016). [7] Lana D. S. G., Dênio R. C. O., Bernardo N. M. N., Adelson B. M., Alcebíades N. M., Francisco A. C. S. Experimental analysis of the efficiency of steel fibers on shear strength of beams, Latin American Journal of Solids and Structures, 16 pp. (2018). [8] Pitcha J., Koji M. and Junichiro N. Shear Capacity of Fiber Reinforced Concrete Beams With Various Types and Combinations of Fibers, Journal of JSCE. Vol. 1, (2013). [9] Navas F. O., Navarro-Gregori J., Herdocia G. L., Serna P., Cuenca E. An experimental study on the shear behaviour of reinforced concrete beams with macro-synthetic fibres, Journal of Construction and Building Materials, (2018) editor@iaeme.com

12 Influence of Carbon and Steel Fibers Used In Combination with Partial Stirrups On Structural Behavior of Beam [10] Hamid H. H., Saeed K. R. and Hayder T. A. Effect of Hybrid Fibers on the Mechanical Properties of High Strength Concrete, Tikrit Journal of Engineering Sciences, (2014). [11] M.Yakhlaf,M.Safiuddin, K.A.Soudki.Properties of Freshly Mixed Carbon Fibre Reinforced Self-Consolidating Concrete. Construction and Building Materials, Vol. 46, pp [12] Hassan I. and K.N.Kadhim "Development An Equations For Flow Over Weirs Using MNLR And CFD Simulation Approaches".International Journal of Civil Engineering & Technology (IJCIET), Volume 9, Issue 3, (Feb 2018)