Fiber reinforced concrete is becoming popular in improving the quasi-brittle failure of concrete. Natural fibers such as sisal holds great promise in this regard. It has amazing tensile strength and is renewable. This paper presents the result of an investigation carried out on the effect of sisal fiber on the compressive strength, Split tensile strength, failure mode and Poisson ratio of Sisal Fiber-Reinforced Concrete (SFRC).
A mix proportion of 1:1.92:3.68 and w/c ratio of 0.47 for a target compressive strength of 35 MPa was used. Sisal fiber was added at percentages of 0.5%, 1.0%, 1.5%, and 2.0% by weight of cement. The effect of specimen shape on the compressive strength of sisal fiber-reinforced concrete (SFRC) was reported. The compressive strength of cube (150mm X 150mm) and cylinder (150mm diameter and 300mm height) specimen was determined at 7 and 28 days, while Split tensile strength and Poisson ratio were obtained using cylindrical specimen (150mm diameter and 300mm height).
The result shows that the addition of sisal fiber slightly reduces the compressive strength of concrete, increases its split tensile strength up to 47.167% of the control specimen, arrests crack propagation and reduces its Poisson ratio. The correlation between the compressive strength of cylindrical and cube specimen was established with a ratio ranging between 0.82 - 0.73. The difference in the compressive strength was found to increase with rise in the percentages of sisal fiber. Based on the ratio and mechanical properties, 1.0% sisal fiber content was recommended as the optimum for reinforcing concrete.
Concrete reinforced with fiber is a unique material which has found great relevance in the field of engineering with a wide range of possible applications in construction. It is made by incorporating uniformly distributed and randomly oriented short discrete fibers in a concrete mix. Concrete on its own is brittle with some other undesired properties such as low resistance to crack propagation, low impact and tensile strength [1N. Hidaya, R.N. Mutuku, and J.N. Mwero, "Physical and mechanical experimental investigation of concrete incorporated with polyethylene terephthalate (PET)", Fibers (Basel), vol. 6, no. 8, pp. 31-41.]. The low tensile strength is as a result of internal micro-cracks at the concrete matrix interphase whose rapid propagation under applied stress results in quick failure [2A. Rai, and Y.P. Joshi, "Applications and properties of fibre reinforced concrete", Eng. Res. Appl., vol. 4, no. 1, pp. 123-131.], addition of fibers plays a crucial role in arresting these cracks, reducing its width thus resisting structural deformation [2A. Rai, and Y.P. Joshi, "Applications and properties of fibre reinforced concrete", Eng. Res. Appl., vol. 4, no. 1, pp. 123-131., 3R.N. Nibudey, P.B. Nagarnaik, D.K. Parbat, and A.M. Pande, "Cube and cylinder compressive strengths of waste plastic fiber reinforced concrete", Int. J. Civ. Struct. Eng., vol. 4, no. 2, pp. 174-182.]. It also influences the mechanical strength, ductility and energy absorption of concrete [4S. Sabarinathan, "A study on mechanical properties of sisal fiber reinforced concrete", Int. J. Civ. Eng., pp. 16-20. March].The durability of natural fibers such as sisal in a cement based matrix is greatly enhanced by using low alkali content cement, and modification of the mix by including additives such as silica fume, fly ash and slag. Surface treatment with NaOH and silica fume has also been reported to improve its long-term performance in an alkali medium [5F. Pacheco-Torgal, and S. Jalali, "Cementitious building materials reinforced with vegetable fibres: A review", Constr. Build. Mater., vol. 25, no. 2, pp. 575-581.[http://dx.doi.org/10.1016/j.conbuildmat.2010.07.024] ]. In a study carried out by [6J. Wei, and C. Meyer, "Improving degradation resistance of sisal fiber in concrete through fiber surface treatment", Appl. Surf. Sci., vol. 289, pp. 511-523.[http://dx.doi.org/10.1016/j.apsusc.2013.11.024] ] subjecting sisal fiber to thermal treatment and Na_{2}CO_{3} surface treatment significantly improved the durability and mechanical properties of concrete composite.
Regardless of the numerous additional benefits of including fibers in concrete, concrete is still relied upon for its compressive strength. There are generally two standard test specimen recommended for measuring concrete’s compressive strength viz: cubes and cylinders. The latter is the recommended standard specimen in the United States, Canada, France, Australia and New Zealand while Britain and most African countries adopts the former [7J. Kim, and S. Yi, "Application of size effect to compressive strength of concrete members", Sadhana, vol. 27, no. 4, pp. 467-484.[http://dx.doi.org/10.1007/BF02706995] ] Cubes have a smaller volume space (0.003375mm^{3}) compared to cylinders of the same size (0.005301mm^{3}) and do not require capping for testing as they are rolled over on their sides to get a plane loading surface. In real structures, the cylinder specimen seems more appropriate as they are casted and tested in the same position, unlike cubes that are turned on their sides [8A.J. Hamad, "“Size and shape effect of specimen on the compressive strength of HPLWFC reinforced with glass fibres,” J. King Saud Univ. -", Eng. Sci., vol. 29, no. 4, pp. 373-380.].
Aspect ratio (height to diameter ratio) of test specimen is crucial for confinement effects during loading [8A.J. Hamad, "“Size and shape effect of specimen on the compressive strength of HPLWFC reinforced with glass fibres,” J. King Saud Univ. -", Eng. Sci., vol. 29, no. 4, pp. 373-380.]. The greater the aspect ratio, the more the correction factor as the value of the compressive strength of cubes and cylinder of the same aspect ratio converges [9E.I. Al-Sahawneh, "Size effect and strength correction factors for normal weight concrete specimens under uniaxial compression stress", Contemp. Eng. Sci., vol. 6, no. 2, pp. 57-68.[http://dx.doi.org/10.12988/ces.2013.13006] ]. However, a higher aspect ratio for a single specimen implies lower confinement. Hence a cylinder specimen with an aspect ratio of 2 can resist smaller load compared with that of an aspect ratio of 1, assuming the adopted slope value is close to 45^{o}.
In comparing the compressive strength of cubes and cylinder specimen, BS 1881-120 recommends multiplying the cube compressive strength by a factor of 0.8 to obtain the cylinder compressive strength of plain concrete for an aspect ratio of 1 while ASTM C42-90 recommended a correction factor of 0.87 [9E.I. Al-Sahawneh, "Size effect and strength correction factors for normal weight concrete specimens under uniaxial compression stress", Contemp. Eng. Sci., vol. 6, no. 2, pp. 57-68.[http://dx.doi.org/10.12988/ces.2013.13006] ]. However, this ratio may not always be precise especially when there are additional materials like fibers in the concrete matrix. Most studies on the effect of sisal fiber on the compressive strength of concrete adopt cubes as the test specimen [4S. Sabarinathan, "A study on mechanical properties of sisal fiber reinforced concrete", Int. J. Civ. Eng., pp. 16-20. March,10K.T.S. Radha, and A. B. S. Dadapheer, "Experimental investigation on the propreties of sisal fibre reinforced concrete", Int. Res. J. Eng. Technol., vol. 4, no. 4, .].
The low resistance of crack propagation of concrete is improved significantly by incorporation of fibers. It also improves its tensile strength and deformation. Under axial stress up to about 40% of the compressive strength, the ratio of the transverse and longitudinal strain of normal strength concrete varies between 0.15 and 0.20 [11B. Persson, "Poisson’s ratio of high-performance concrete", Cement Concr. Res., vol. 29, pp. 1647-1653. July[http://dx.doi.org/10.1016/S0008-8846(99)00159-3] ]. At stresses above 60%, microcracks begin to develop in a direction parallel to that of the applied stress. The microcracks result in an increase in the transverse strain as the applied stress increases. Fibers acting as crack arrestors can significantly reduce the propagation of these microcracks, and by extension the transverse strain. Leading to a reduction in Poisson ratio. Few studies [11B. Persson, "Poisson’s ratio of high-performance concrete", Cement Concr. Res., vol. 29, pp. 1647-1653. July[http://dx.doi.org/10.1016/S0008-8846(99)00159-3] -13L. Yan, and N. Chouw, "Dynamic and static properties of flax fibre reinforced polymer tube confined coir fibre reinforced concrete", J. Compos. Mater., vol. 48, no. 13, pp. 1595-1610.[http://dx.doi.org/10.1177/0021998313488154] ] however reports the Poisson ratio of fiber reinforced concrete. Amorphous metallic fibers were reported to lower the horizontal expansion of concrete and reduced its Poisson ratio [14N-H. Dinh, K-K. Choi, and H-S. Kim, "Mechanical properties and modeling of amorphous metallic fiber-reinforced concrete in compression", Int. J. Concr. Struct. Mater., vol. 10, no. 2, pp. 221-236.[http://dx.doi.org/10.1007/s40069-016-0144-9] ]. Similar reduction in Poisson ratio was noticed in steel fiber-reinforced, high-strength, Light weight concrete. The Poisson ratio was reportedly observed to reduce from 0.25 to 0.166 depending on aspect ratio and increasing volume fraction [12J. Gao, W. Sun, and K. Morino, "Mechanical properties of steel fiber-reinforced, high-strength, lightweight concrete", Cement Concr. Compos., vol. 19, no. 4, pp. 307-313.[http://dx.doi.org/10.1016/S0958-9465(97)00023-1] -15R.D. Tolêdo Filho, K. Joseph, K. Ghavami, and G.L. England, "The use of sisal fibre as reinforcement in cement based composites", Rev. Bras. Eng. Agric. Ambient., vol. 3, no. 2, pp. 245-256.[http://dx.doi.org/10.1590/1807-1929/agriambi.v3n2p245-256] ] studied the effect of sisal fibers on the Poisson ratio of cement mortal, it was reported that sisal had no significant effect on the Poisson ratio of cement mortal.
Since limited studies exist on the effect of shape on the compressive strength of Sisal fiber reinforced concrete and its Poisson ratio. This study aims to investigate the effect of shape on the compressive strength of concrete reinforced with sisal fibers using cubes and cylinders. The chosen sizes are believed to give a good representation of what is used in local and international construction industries for testing the compressive strength of concrete. The tensile strength and Poisson ratio of sisal fiber were also investigated.
The tested physical and chemical properties of the cement used in this study are presented in Tables 1 and 2 respectively. The chemical content was obtained using an X-ray fluorescence device. The cement was found to fulfil the physical and chemical requirement of ASTM C 150 for use in making concrete [16ASTMC150, "Standard specification for portland cement", Am. Soc. Test. Mater., vol. 04, no. 2, pp. 1-7.].
Natural River sand with specific gravity and fineness modulus of 2.56 and 2.66 respectively was used in this study. The sand was obtained from Kivaa in Kenya and was within the limits of ASTM C 33 [17ASTMC33, "Standard specification for concrete aggregates", Annu. Book ASTM Stand., vol. 04, no. 02, pp. 1-11.] as shown in Table 3.
The coarse aggregate used in this study was granite obtained from Ruiru in Kenya with a nominal size of 25mm- 9.5mm and specific gravity of 2.70. The grading limits according to ASTM C 33 [17ASTMC33, "Standard specification for concrete aggregates", Annu. Book ASTM Stand., vol. 04, no. 02, pp. 1-11.] are presented in Table 4.
Locally available sisal fiber from Juja in Kenya was used for this research. The tensile strength of sisal was measured using a Hounsfield Tensometer and its properties are presented in Table 5.
MasterRoc MS 610 Silica fume slurry from Ultra-tech Kenya Limited was used in treating the sisal fibers. The fibers were immersed in the slurry for 10mins and left to dry at room temperature for 15 minutes [5F. Pacheco-Torgal, and S. Jalali, "Cementitious building materials reinforced with vegetable fibres: A review", Constr. Build. Mater., vol. 25, no. 2, pp. 575-581.[http://dx.doi.org/10.1016/j.conbuildmat.2010.07.024] ]. The properties of the silica fume slurry are presented in Table 6. Commercially available superplasticiser was used to ensure good workability and compaction. Ordinary water available in the university premises was used for the preparation of the concrete mix and curing of the test samples.
The designed mix used in this study was 1:1.92:3.26 (cement: sand: granite) for a target strength of 35 MPa according to [18ASTMC33, "Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete", Am. Concr. Institute, Farmingt. Hills, MI, USA, pp. 1-10.]. Batching was done by weight and the water-cement ratio was carefully selected to achieve a slump of 100mm, since sisal fiber was expected to affect the workability of the mix, different dosages of superplasticizer were tried to obtain the optimum without bleeding or segregation. The mix was incorporated with sisal fibers at 0.5%, 1.0%, 1.5% and 2.0% of weight of cement labelled respectively as M0.5, M1.0, M1.5 and M2.0.with the control (Plain concrete) as M0.0 Fig. (1). Mix proportion details are as presented in Table 7.
Two specimen shapes (Cubes and cylinders) of respective size 150mm X 150mm according to BS EN 12390-2:2000 [19B. EN12390-3, "Testing hardened concrete - Part 3: Compressive strength of test specimens", British Standard, .] and 150mm diameter and 300mm height as stated in ASTM C39 [20 ASTM C39, “Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens 1,” vol. 04, no. October, pp. 1–7, 2014] were used for each compressive test. Cylinder samples of the aforementioned dimension were also used for split tensile tests. For each mix, three samples were casted in non- absorbent moulds for testing.
Mixing of concrete was done by dry mixing the cement, sand and granite for 3 minutes, after which 80% of water blended with superplasticizer was added to the dry mix. The wet blend was mixed for further 8 minutes before the remaining of water blended with superplasticizer was added to the mix and mixed thoroughly. About 50% of the sisal fiber were then manually added to mix with care being taken to ensure there was no balling of the fibers, mixing was carried out for further 2 minutes before the rest of the fibers was added. The concrete was ready for placing after 2 minutes of mixing. The concrete was placed in the moulds and compacted using a proctor vibrator. Once compacted, a steel float was used for levelling the specimen’s surface. The specimens were left undisturbed in the moulds for 24±3h before demoulding and placed in a curing tank in a curing room with regulated temperature of 21 ^{o}C ±2^{o}C until 7 and 28 days of testing.
Fig .(1) (a) Untreated sisal fiber (b) Sisal fiber treated with silica fume (c) Fresh concrete mix with 2% fiber content |
Fig. (2) (a) Test Samples (M_{2.0}) (b) Servo-Plus Evolution UTM |
One of the most important indicators used in evaluating the performance of fiber reinforced concrete is its compressive strength. The average compressive strength of cube and cylinder specimen at 7 and 28 days are shown in Figs. (3 and 4). The compressive strength was observed to decrease with increase in the amount of sisal fiber added for 7 and 28 days for both specimen shapes (cubes and cylinders). At low fiber content (<0.5%) where the modulus of elasticity of fiber is less than that of the plain matrix (E_{f}/E_{m} < 1), little reduction is expected in the compressive strength. The reduction can be expected to be as high as 25% and 30% respectively for a volume fraction of 2% to 3% [15R.D. Tolêdo Filho, K. Joseph, K. Ghavami, and G.L. England, "The use of sisal fibre as reinforcement in cement based composites", Rev. Bras. Eng. Agric. Ambient., vol. 3, no. 2, pp. 245-256.[http://dx.doi.org/10.1590/1807-1929/agriambi.v3n2p245-256] ]. Percentage reduction of 4.22%, 11.54%, 18.18%, 25.30% and 2.07%, 7.75%, 14.76%, 16.35% were obtained for M0.5, M1.0, M1.5, M2.0 in cubes and cylinders respectively when compared to M0.0 at 28days due to the modulus of elasticity of sisal fiber being less than that of the concrete matrix thus replacing stronger concrete constituent. A similar result was presented by [1N. Hidaya, R.N. Mutuku, and J.N. Mwero, "Physical and mechanical experimental investigation of concrete incorporated with polyethylene terephthalate (PET)", Fibers (Basel), vol. 6, no. 8, pp. 31-41.], although there was an increase in compressive strength with curing time due to further hydration and improved bond between the fibers and concrete matrix.
4S. Sabarinathan, "A study on mechanical properties of sisal fiber reinforced concrete", Int. J. Civ. Eng., pp. 16-20. March24F.F. Wafa, "Properties and applications of fiber reinforced concrete", JKAU Eng. Sci, vol. 2, no. September, pp. 49-63.[http://dx.doi.org/10.4197/Eng.2-1.4] 25Z. Li, X. Wang, and L. Wang, "Properties of hemp fibre reinforced concrete composites", Compos. Part A Appl. Sci. Manuf., vol. 37, no. 3, pp. 497-505.[http://dx.doi.org/10.1016/j.compositesa.2005.01.032] _{f}_{m}26F. de A. Silva, R.D.T. Filho, J. de A. M Filho, and E. de M. R. Fairbairn, "Physical and mechanical properties of durable sisal fiber-cement composites", Constr. Build. Mater., vol. 24, no. 5, pp. 777-785.[http://dx.doi.org/10.1016/j.conbuildmat.2009.10.030] 27M. Donà, "Computational modelling of concrete structures", Proceedings of the euro-c conference on computational modelling of concrete structures., pp. 185-193.
Fig. (3) Compressive strength of sisal fiber-reinforced concrete cubes. |
Fig. (4) Compressive strength of sisal fiber-reinforced concrete cylinders. |
The research was carried out to study the effect shape has on the compressive strength of sisal fiber reinforced concrete. The compressive strength of plain concrete cube was observed to be higher than that of cylinders by 27.97% and 18.04% at 7 and 28days respectively. It could be deduced from the result that cube specimen give higher compressive strength [3R.N. Nibudey, P.B. Nagarnaik, D.K. Parbat, and A.M. Pande, "Cube and cylinder compressive strengths of waste plastic fiber reinforced concrete", Int. J. Civ. Struct. Eng., vol. 4, no. 2, pp. 174-182., 8A.J. Hamad, "“Size and shape effect of specimen on the compressive strength of HPLWFC reinforced with glass fibres,” J. King Saud Univ. -", Eng. Sci., vol. 29, no. 4, pp. 373-380., 28B. Graybeal, and M. Davis, "Cylinder or cube: Strength testing of 80 to 200 mpa (11. 6 to 29 ksi) ultra-high-performance fiber-reinforced concrete", ACI Mater. J., vol. 105, no. 6, pp. 603-609.]. The specimen with the highest sisal fiber content (M2.0) gave a cube compressive strength which was 21.14% and 29.68% greater than that of the cylinders at 7 and 28 days respectively. However, these finding doesn’t agree with that of fiber reinforced ultra-high performance concrete where the compressive strength of cylinder was reportedly higher than cube’s [29Y. Kusumawardaningsih, E. Fehling, and M. Ismail, "UHPC compressive strength test specimens: Cylinder or cube?", Procedia Eng., vol. 125, pp. 1076-1080.].
The ratio of the compressive strength of cylinder specimens (f_{cy}) to the cubes (f_{cc}) was between 0.72 and 0.54, with an average of 0.64 at 7 days as shown in Table 8, while the ratio of the compressive strength of cylinders (f_{cy}) to cubes (f_{cc}) was between 0.82 and 0.73, with a mean ratio of 0.79 at 28 days as depicted in Table 9. The difference in compression strength may be due to the applied axial force tending to align the fibers in certain planes. It tends parallel in cubes while in cylinders, which tend to align perpendicular to the axis of loading where it could help inhibit lateral bursting [30T.Y. Erdogan, "Materials of construction", A Comp. Eval. Plain Steel Fiber Reinf. Concr. Gr. Slabs, Middle East Technical University press, 2001.].
From the decreasing cylinder to cube compressive strength ratio, it can be deduced that sisal fiber incorporation increases the effect specimen shape has on the compressive strength of concrete at both 7 and 28days. The ratio of the 28 days cube compressive strength to that of cylinders was however observed to be between 1.22 and 1.37, with an average of 1.28. The higher f_{cu} is due to the development of tri-axial compression zones in cubes by virtue of the presence of restrained zones during uniaxial compression test which is absent in cylinders with an aspect ratio of 2 [31A.S. Malaikah, "Effect of specimen size and shape on the compressive strength of high strength concrete", Pertanika J. Sci. Technol., vol. 13, no. 1, pp. 87-96.]. M0.5, M1.0, M1.5 gave respective f_{cy}/f_{cc} ratio of 0.80, 0.79 and 0.79 at 28 days which shows that the ratio of f_{cy}/f_{cc} for SFRC was in close agreement with the value 0.8 which was recommended by BS EN 12390-3.
Furthermore, the variation in the effect of sisal on the compressive strength of the cube and cylinder specimen can be discerned after further curing, the disparity in the compressive strength between the two shapes grows with increase in the percentages of sisal fibers at 7 and 28 days as shown in Figs. (4 and 5). Table. 10 shows the standard deviation (S_{d}) and coefficient of variation (C_{V}) between the cube and cylinder for the same fiber content. Both the standard deviation and coefficient of variation increases with rising sisal fiber content at the same curing age. Certainly, incorporation of fibers reduces concrete’s density, raises its water absorption and void. The increase in voids generates more interface zone between sisal and the concrete constituent’s interfaces [32I. Soto Izquierdo, O. Soto Izquierdo, M.A. Ramalho, and A. Taliercio, "Sisal fiber reinforced hollow concrete blocks for structural applications: Testing and modeling", Constr. Build. Mater., vol. 151, pp. 98-112.]. Consequently, SFRC has an increased number of permeable and micro crack regions than plain concrete, which further elucidate on the reduction in the compressive strength. Additionaly, the greater interface zone between the fiber and concrete aggregate impacts more on the restrained zones of concrete under uniaxial compression. The tri-axial compression zones in cube specimen aid its compressive strength, however, cylinders have their unrestrained zone situated away from their ends which is further compromised by the increased interface zone as a result of fiber content. As fiber content increases, the interface zone grows and the compressive strength of cylinders reduces, this explains the increase in the shape effect at higher fiber content. Overall, the incorporation of sisal fiber into concrete reduces its compressive strength and increases the influence shape has on the strength of concrete.
Fig. (5) Relationship between 7 days compressive strength of SFRC of cube and cylinders. |
Fig. (6) Relationship between 28 days compressive strength of SFRC of cube and cylinders. |
The results of the split tensile strength are presented in Table 11. It has long been known that the presence of fibers considerably improves the tensile strength due to the tensile stress transfer capability of the sisal fibers across concrete crack surfaces, known as crack-bridging [33C.E. Chalioris, "Steel fibrous RC beams subjected to cyclic deformations under predominant shear", Eng. Struct., vol. 49, pp. 104-118.]. The 28 days split tensile strength value was higher than those at 7 days due to further hydration and strength gain. At 28 days, a percentage increase of 29.60% and 47.17% was observed in the split tensile strength of M0.5 and M1.0 respectively compared to plain concrete, while on further addition of sisal fiber, M1.5 and M2.0 showed a declining percentage increase of 16.57% and 6.62%. Thus, the split tensile strength of SFRC at each curing age increases up to 1.0% beyond which it drops but remain higher than that of plain concrete.
The least recorded tensile strength for SFRC at 7 and 28 days (2.180 N/mm^{2} and 2.509 N/mm^{2}) was still higher than that of plain concrete (2.073 N/mm^{2} and 2.353 N/mm^{2}) implying that incorporation of sisal increases the tensile strength of concrete for all percentages up to 2.0%.The maximum split tensile strength recorded was 3.463 N/mm^{2} for 1.0% fiber addition, the finding is in close agreement with the target tensile strength of 3.5 N/mm^{2} (for class 30/35). The improvement in the split tensile strength is due to the ability of sisal fiber to impact more ductility in the concrete, Load is transferred to the fibers at the crack site after the formation of cracks, and at this stage different behaviour may be exhibited depending on the strength, volume fraction and aspect ratio of the fiber. At sufficient fiber content, aspect ratio and strength, sisal fibers bridge across the possible cracks as shown in Fig. (7). Thus, sisal fibers acted as porous bridging elements across cracks, permitting the deposition of new hydration products and the subsequent infill/closure of the cracks [15R.D. Tolêdo Filho, K. Joseph, K. Ghavami, and G.L. England, "The use of sisal fibre as reinforcement in cement based composites", Rev. Bras. Eng. Agric. Ambient., vol. 3, no. 2, pp. 245-256.[http://dx.doi.org/10.1590/1807-1929/agriambi.v3n2p245-256] ]. Furthermore, unlike the brittle failure observed in plain concrete, fibrous concrete like SFRC demonstrates a pseudo-ductile tensile behaviour and enhanced energy dissipations capacities [27M. Donà, "Computational modelling of concrete structures", Proceedings of the euro-c conference on computational modelling of concrete structures., pp. 185-193.,34C.E. Karayannis, "Nonlinear analysis and tests of steel–fiber concrete beams in torsion", J Struct Eng Mech, vol. 9, no. 4, pp. 323-338.]. The observed trend in split tensile strengths of SFRC compared favourably with those of previous works [10K.T.S. Radha, and A. B. S. Dadapheer, "Experimental investigation on the propreties of sisal fibre reinforced concrete", Int. Res. J. Eng. Technol., vol. 4, no. 4, .,35P. Sasikumar, and J. Thivya, "An investigation of sisal fibre concrete using quarry dust", Int. J. Innov. Res. Sci. Eng. Technol., vol. 6, no. 4, pp. 5560-5567.].
Fig. (7) Failure modes of concrete cylinder after split tensile test (a) M_{0.0}(b) M_{0.5}(c) M_{1.0}(d) M_{1.5}(e) M_{2.0} |
The increase in the tensile strength and post cracking performance of SFRC as shown in Fig. (8) can be achieved up to a certain fiber content known as critical volume fraction; V_{f,cr} [36P. Sung-Sik, and H. Yaolong, "Tensile Strength Characteristics of Cement Paste Mixed with Fibers", J Korean Geotech. Soc., .-38V. S. P. Shah SP, P. Stroeven, and D. Dalhuisen, "Complete stress-strain curves for steel fiber reinforced concrete in uniaxial tension and compression", Proc. RILEM Symp. Test. test methods fiber Cem. Compos. Constr. Press. Lancaster, pp. 399-408., 33C.E. Chalioris, "Steel fibrous RC beams subjected to cyclic deformations under predominant shear", Eng. Struct., vol. 49, pp. 104-118.].
(1) |
Fig. (8) Failure modes of concrete cylinder and cube specimens after compression. (a) M_{0.0}(b) M_{0.5}(c) M_{1.0}(d) M_{1.5}(e) M_{2.0} |
Where f_{ct} is the tensile strength of plain concrete; n_{1} is the ratio of the average fiber stress to the maximum fiber stress and equals to 1:n_{0} is the fiber orientation factor in the elastic range and equals to 0.405; σ_{_fu} is the ultimate fiber stress. For the tested fibrous concrete mixtures, the ultimate fiber stress equals 399.44 MPa and the tensile strength of plain concrete is 2.353MPa giving a critical volume fraction of 1.45%. Hence, for the post-cracking tensile behaviour of the concrete mixtures with 1.50% and 2.0% volume of fibers, a lower tensile.
Fig. (8) shows the failure mode of cube and cylinder specimen after compression test. The stopping load for all the specimen was set at 40% of the failure load. Cracks were observed to form in the longitudinal direction before the peak stress and propagate in the lateral direction as the applied load increases. Inclined shear failure cracks were formed at the beginning of the softening phase. The crack pattern was columnar for cylinders and non-explosive for cubes. It was noticed that the cracks formed were wider with higher numbers in the specimens without sisal fibers (M0), whereas, they were reduced for SFRC. The least number of cracks was noticed on M2.0. From the split tensile strength and the compressive mode of failure, it could be said that that sisal fiber plays a significant role in arresting crack formation and propagation in concrete.
The improved tensile strength and cracking performance of sisal fiber is important in the shear response of structural elements like concrete beams. The effect of using sisal fiber in concrete is quite similar to that of steel fibers reported by [39K. Watanabe, T. Kimura, and J. Niwa, "Synergetic effect of steel fibers and shear-reinforcing bars on the shear-resistance mechanisms of RC linear members", Constr. Build. Mater., vol. 24, no. 12, pp. 2369-2375.[http://dx.doi.org/10.1016/j.conbuildmat.2010.05.009] ].Thus, fibers like sisal could be promising as a non-conventional reinforcement in shear critical beams by potentially reducing shear reinforcements and altering shear brittle failure into ductile flexural ones [33C.E. Chalioris, "Steel fibrous RC beams subjected to cyclic deformations under predominant shear", Eng. Struct., vol. 49, pp. 104-118.]. Unlike sisal however, steel fibers have already been used to partially reduce steel stirrups especially in sections where high transverse steel ratio with small spacing is required [40Y. Ding, Z. You, and S. Jalali, "The composite effect of steel fibres and stirrups on the shear behaviour of beams using self-consolidating concrete", Eng. Struct., vol. 33, no. 1, pp. 107-117.[http://dx.doi.org/10.1016/j.engstruct.2010.09.023] , 41N. Spinella, "Shear strength of full-scale steel fibre-reinforced concrete beams without stirrups", Comput. Concr., vol. 11, no. 5, pp. 365-382.[http://dx.doi.org/10.12989/cac.2013.11.5.365] ].
The ratio of the transverse strain to the axial strain known as Poisson's Ratio (V_{c}), Fig. (9) shows the variation of Poisson ratio with fiber content at 40% of ultimate stress.
Fig. (9) Poisson ratio of SFRC |
The measured value of Poisson ratio ranged between 0.200 and 0.189. Plain concrete had a Poisson ratio of 0.1995, for normal strength concrete, a value of 0.2 is usually adopted [42N. Ganesan, P.V. Indira, and A. Santhakumar, "Engineering properties of steel fibre reinforced geopolymer concrete", Adv. Concr. Constr., vol. 1, no. 4, pp. 305-318.[http://dx.doi.org/10.12989/acc2013.1.4.305] ]. While SFRC shows a slight decrease in Poisson ratio as the fiber content increased. The reduction in the Poisson ratio demonstrates that the presence of sisal fibers in a concrete matrix arrests deformation, reduces expansion and stretch in the horizontal direction, resulting in less destructive external surface [12J. Gao, W. Sun, and K. Morino, "Mechanical properties of steel fiber-reinforced, high-strength, lightweight concrete", Cement Concr. Compos., vol. 19, no. 4, pp. 307-313.[http://dx.doi.org/10.1016/S0958-9465(97)00023-1] , 14N-H. Dinh, K-K. Choi, and H-S. Kim, "Mechanical properties and modeling of amorphous metallic fiber-reinforced concrete in compression", Int. J. Concr. Struct. Mater., vol. 10, no. 2, pp. 221-236.[http://dx.doi.org/10.1007/s40069-016-0144-9] ]. Similar reduction in poisson ratio of fiber reinforced concrete was reported by [43O.M. Smirnova, A.A. Shubin, and I.V. Potseshkovskaya, "Strength and Deformability Properties of Polyolefin Macrofibers Reinforced Concrete", Int J Appl Eng Res, vol. 12, no. 20, pp. 9397-9404.]. The relationship between Poisson’s ratio and fiber content follows the equation.
(2) |
Where μ_{f} is the Poisson ratio of SFRC; μ_{c} the Poisson ratio of plain concrete and V_{f} is the fiber content.
From this experimental investigation on the effect of specimen shape on the mechanical strength of SFRC, for a constant mix proportion of 1:1.92:3.68 and w/c ratio of 0.47, the following deductions can be drawn. The compressive strength of SFRC reduces with rising sisal fiber content, therefore sisal fiber cannot be used to enhance compressive strength of concrete. Despite the reduced strength, SFRC exhibited the ability to increase post-cracking ductility and energy dissipation. The variation in the compressive strength of SFRC cubes and cylinders increases with curing time and rise in the percentage of sisal fibers. The average ratio of the 28 days compressive strength of SFRC cylinders to cubes is 0.79. Hence, the relationship between cube and cylinder compressive strength presented in British standard can be applied to SFRC. Furthermore, Sisal fiber plays a crucial role in reducing the Poisson ratio of concrete and improving the split tensile strength. Based on the conclusion, an optimum sisal fiber addition of 1.0% is recommended for reinforcing concrete. M1.0 gave the highest split tensile strength, a cylinder to cube ratio in close agreement with that recommended in standards and a cube compressive strength of 33.55 MPa, which didn’t deviate excessively from the target design strength of 35 MPa.
Not applicable.
The authors declare no conflict of interest, financial or otherwise.
The authors will like to appreciate the African Union Commission, under the aegis of Pan African University, Institute for Basic Science, Technology and Innovation (PAUISTI) and AFRICA-ai-JAPAN project for funding this research.
[1] | N. Hidaya, R.N. Mutuku, and J.N. Mwero, "Physical and mechanical experimental investigation of concrete incorporated with polyethylene terephthalate (PET)", Fibers (Basel), vol. 6, no. 8, pp. 31-41. |
[2] | A. Rai, and Y.P. Joshi, "Applications and properties of fibre reinforced concrete", Eng. Res. Appl., vol. 4, no. 1, pp. 123-131. |
[3] | R.N. Nibudey, P.B. Nagarnaik, D.K. Parbat, and A.M. Pande, "Cube and cylinder compressive strengths of waste plastic fiber reinforced concrete", Int. J. Civ. Struct. Eng., vol. 4, no. 2, pp. 174-182. |
[4] | S. Sabarinathan, "A study on mechanical properties of sisal fiber reinforced concrete", Int. J. Civ. Eng., pp. 16-20. March |
[5] | F. Pacheco-Torgal, and S. Jalali, "Cementitious building materials reinforced with vegetable fibres: A review", Constr. Build. Mater., vol. 25, no. 2, pp. 575-581.[http://dx.doi.org/10.1016/j.conbuildmat.2010.07.024] |
[6] | J. Wei, and C. Meyer, "Improving degradation resistance of sisal fiber in concrete through fiber surface treatment", Appl. Surf. Sci., vol. 289, pp. 511-523.[http://dx.doi.org/10.1016/j.apsusc.2013.11.024] |
[7] | J. Kim, and S. Yi, "Application of size effect to compressive strength of concrete members", Sadhana, vol. 27, no. 4, pp. 467-484.[http://dx.doi.org/10.1007/BF02706995] |
[8] | A.J. Hamad, "“Size and shape effect of specimen on the compressive strength of HPLWFC reinforced with glass fibres,” J. King Saud Univ. -", Eng. Sci., vol. 29, no. 4, pp. 373-380. |
[9] | E.I. Al-Sahawneh, "Size effect and strength correction factors for normal weight concrete specimens under uniaxial compression stress", Contemp. Eng. Sci., vol. 6, no. 2, pp. 57-68.[http://dx.doi.org/10.12988/ces.2013.13006] |
[10] | K.T.S. Radha, and A. B. S. Dadapheer, "Experimental investigation on the propreties of sisal fibre reinforced concrete", Int. Res. J. Eng. Technol., vol. 4, no. 4, . |
[11] | B. Persson, "Poisson’s ratio of high-performance concrete", Cement Concr. Res., vol. 29, pp. 1647-1653. July[http://dx.doi.org/10.1016/S0008-8846(99)00159-3] |
[12] | J. Gao, W. Sun, and K. Morino, "Mechanical properties of steel fiber-reinforced, high-strength, lightweight concrete", Cement Concr. Compos., vol. 19, no. 4, pp. 307-313.[http://dx.doi.org/10.1016/S0958-9465(97)00023-1] |
[13] | L. Yan, and N. Chouw, "Dynamic and static properties of flax fibre reinforced polymer tube confined coir fibre reinforced concrete", J. Compos. Mater., vol. 48, no. 13, pp. 1595-1610.[http://dx.doi.org/10.1177/0021998313488154] |
[14] | N-H. Dinh, K-K. Choi, and H-S. Kim, "Mechanical properties and modeling of amorphous metallic fiber-reinforced concrete in compression", Int. J. Concr. Struct. Mater., vol. 10, no. 2, pp. 221-236.[http://dx.doi.org/10.1007/s40069-016-0144-9] |
[15] | R.D. Tolêdo Filho, K. Joseph, K. Ghavami, and G.L. England, "The use of sisal fibre as reinforcement in cement based composites", Rev. Bras. Eng. Agric. Ambient., vol. 3, no. 2, pp. 245-256.[http://dx.doi.org/10.1590/1807-1929/agriambi.v3n2p245-256] |
[16] | ASTMC150, "Standard specification for portland cement", Am. Soc. Test. Mater., vol. 04, no. 2, pp. 1-7. |
[17] | ASTMC33, "Standard specification for concrete aggregates", Annu. Book ASTM Stand., vol. 04, no. 02, pp. 1-11. |
[18] | ASTMC33, "Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete", Am. Concr. Institute, Farmingt. Hills, MI, USA, pp. 1-10. |
[19] | B. EN12390-3, "Testing hardened concrete - Part 3: Compressive strength of test specimens", British Standard, . |
[20] | ASTM C39, “Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens 1,” vol. 04, no. October, pp. 1–7, 2014 |
[21] | B. EN12390, "Testing hardened concrete. Compressive Strength of Test Specimens", Br. Stand. Institution, London, UK, . |
[22] | ASTM C 496, "Standard test method for splitting tensile strength of cylindrical concrete specimens", Annu. B. ASTM Stand., vol. 04, no. 02, pp. 1-5. |
[23] | ASTMC469, "Standard test method for static modulus of elasticity and poisson’s ratio of concrete in compression", ASTM Stand. B., vol. 04, pp. 1-5. |
[24] | F.F. Wafa, "Properties and applications of fiber reinforced concrete", JKAU Eng. Sci, vol. 2, no. September, pp. 49-63.[http://dx.doi.org/10.4197/Eng.2-1.4] |
[25] | Z. Li, X. Wang, and L. Wang, "Properties of hemp fibre reinforced concrete composites", Compos. Part A Appl. Sci. Manuf., vol. 37, no. 3, pp. 497-505.[http://dx.doi.org/10.1016/j.compositesa.2005.01.032] |
[26] | F. de A. Silva, R.D.T. Filho, J. de A. M Filho, and E. de M. R. Fairbairn, "Physical and mechanical properties of durable sisal fiber-cement composites", Constr. Build. Mater., vol. 24, no. 5, pp. 777-785.[http://dx.doi.org/10.1016/j.conbuildmat.2009.10.030] |
[27] | M. Donà, "Computational modelling of concrete structures", Proceedings of the euro-c conference on computational modelling of concrete structures., pp. 185-193. |
[28] | B. Graybeal, and M. Davis, "Cylinder or cube: Strength testing of 80 to 200 mpa (11. 6 to 29 ksi) ultra-high-performance fiber-reinforced concrete", ACI Mater. J., vol. 105, no. 6, pp. 603-609. |
[29] | Y. Kusumawardaningsih, E. Fehling, and M. Ismail, "UHPC compressive strength test specimens: Cylinder or cube?", Procedia Eng., vol. 125, pp. 1076-1080. |
[30] | T.Y. Erdogan, "Materials of construction", A Comp. Eval. Plain Steel Fiber Reinf. Concr. Gr. Slabs, Middle East Technical University press, 2001. |
[31] | A.S. Malaikah, "Effect of specimen size and shape on the compressive strength of high strength concrete", Pertanika J. Sci. Technol., vol. 13, no. 1, pp. 87-96. |
[32] | I. Soto Izquierdo, O. Soto Izquierdo, M.A. Ramalho, and A. Taliercio, "Sisal fiber reinforced hollow concrete blocks for structural applications: Testing and modeling", Constr. Build. Mater., vol. 151, pp. 98-112. |
[33] | C.E. Chalioris, "Steel fibrous RC beams subjected to cyclic deformations under predominant shear", Eng. Struct., vol. 49, pp. 104-118. |
[34] | C.E. Karayannis, "Nonlinear analysis and tests of steel–fiber concrete beams in torsion", J Struct Eng Mech, vol. 9, no. 4, pp. 323-338. |
[35] | P. Sasikumar, and J. Thivya, "An investigation of sisal fibre concrete using quarry dust", Int. J. Innov. Res. Sci. Eng. Technol., vol. 6, no. 4, pp. 5560-5567. |
[36] | P. Sung-Sik, and H. Yaolong, "Tensile Strength Characteristics of Cement Paste Mixed with Fibers", J Korean Geotech. Soc., . |
[37] | T.Y Lim, "Analytical model for tensile behavior of steel–fiber concrete", ACI Mater. J., vol. 84, no. 4, pp. 286-298. |
[38] | V. S. P. Shah SP, P. Stroeven, and D. Dalhuisen, "Complete stress-strain curves for steel fiber reinforced concrete in uniaxial tension and compression", Proc. RILEM Symp. Test. test methods fiber Cem. Compos. Constr. Press. Lancaster, pp. 399-408. |
[39] | K. Watanabe, T. Kimura, and J. Niwa, "Synergetic effect of steel fibers and shear-reinforcing bars on the shear-resistance mechanisms of RC linear members", Constr. Build. Mater., vol. 24, no. 12, pp. 2369-2375.[http://dx.doi.org/10.1016/j.conbuildmat.2010.05.009] |
[40] | Y. Ding, Z. You, and S. Jalali, "The composite effect of steel fibres and stirrups on the shear behaviour of beams using self-consolidating concrete", Eng. Struct., vol. 33, no. 1, pp. 107-117.[http://dx.doi.org/10.1016/j.engstruct.2010.09.023] |
[41] | N. Spinella, "Shear strength of full-scale steel fibre-reinforced concrete beams without stirrups", Comput. Concr., vol. 11, no. 5, pp. 365-382.[http://dx.doi.org/10.12989/cac.2013.11.5.365] |
[42] | N. Ganesan, P.V. Indira, and A. Santhakumar, "Engineering properties of steel fibre reinforced geopolymer concrete", Adv. Concr. Constr., vol. 1, no. 4, pp. 305-318.[http://dx.doi.org/10.12989/acc2013.1.4.305] |
[43] | O.M. Smirnova, A.A. Shubin, and I.V. Potseshkovskaya, "Strength and Deformability Properties of Polyolefin Macrofibers Reinforced Concrete", Int J Appl Eng Res, vol. 12, no. 20, pp. 9397-9404. |