|Year : 2012 | Volume
| Issue : 1 | Page : 63-67
Earthquake-Resistant Performance of Polypropylene Fiber Reinforced Concrete Beam
Department of Civil Engineering, Dr. M.G.R Educational and Research Institute University, Maduravoyal, Chennai, Tamil Nadu, India
|Date of Web Publication||24-Mar-2012|
Department of Civil Engineering, Dr. M.G.R Educational and Research Institute University, Maduravoyal, Chennai, Tamil Nadu
Source of Support: None, Conflict of Interest: None
| Abstract|| |
The cyclic behavior of polypropylene fiber reinforced, plain concrete beams was studied in this research work. The reinforcement and volume ratio of polypropylene fiber were kept constant for all the beams. The beams were same dimensions, and the beams were tested under positive cyclic loading and the results were evaluated with respect to crack strength, ductility, energy absorption capacity, and stiffness behavior. The results showed that polypropylene fiber concrete beams had only slight effect on the stiffness, cracking moment, and ultimate moment. From the test results it was observed that polypropylene fibers were effective in reducing the crack width and crack propagation. Furthermore, it was observed that introduction of polypropylene fiber significantly improves the cracking behavior in terms of a formation of large number of finer cracks. Combining polypropylene fibers and reinforcement improved the behavior of reinforced concrete beams and changed its failure mode. Addition of polypropylene fiber to RCC imported ductility to structural members which is essential for seismic force-resisting structure.
Keywords: Crack, cyclic load, ductility, energy absorption capacity, polypropylene fibers, stiffness
|How to cite this article:|
Arivalagan S. Earthquake-Resistant Performance of Polypropylene Fiber Reinforced Concrete Beam. J Eng Technol 2012;2:63-7
| 1. Introduction|| |
Concrete has acknowledged to be a relatively brittle material when subjected to normal stresses and impact loads, where tensile strength is only approximately one tenth of its compressive strength. The addition of steel reinforcement significantly increases the strength of concrete, but to produce concrete with homogenous tensile properties, the development of micro cracks is a must to suppress. The introduction of fibers was brought in a solution to develop concrete in view of enhancing its flexural and tensile strength, which are a new form of binder that could combine Portland cement in the bonding with cement matrices. Fibers are most generally discontinuous, randomly distributed throughout the cement matrices. The term of "fiber reinforced concrete" (FRC) is made up with cement, various sizes of aggregates, which incorporate with discrete, discontinuous fibers. FRC is an ordinary concrete with randomly distributed short fibers. The main role of the fiber is to bridge the cracks in the matrix and prevent them from extending. Hence, it helps to improve the concrete post-cracking behavior such as ductility, cracking control, and impact resistance. Recent earthquakes in different parts of the world have revealed again the importance of design of reinforced concrete structures with high ductility. Conventional concrete loses its tensile resistance after the formation of multiple cracks. However, fiber concrete can sustain a portion of resistance of cracking of more cycles of loading. For this reason, it must be provided with adequate stiffness and strength to sustain the loads transmitted from beams.
Arivalagan et al.  conducted an experimental investigation on polypropylene fibers reinforced concrete (PPFRC) beams and concluded that while adding fibers in the concrete, marginal increase of strength was observed and this reduces the cracking behavior of the section at the post-yielding state. Alhozaimy et al.  in their research results showed no effect or slight adverse effect on structural properties due to the inclusion of polypropylene fibers. The difference between the results may be related to the difference in PPF parameters and matrix composition. Ganesan et al.  conducted an experimental program to compare the behavior of high-performance concrete (HPC) and steel fiber reinforced high-performance concrete (SFRHPC) flexural members under two point loadings. Results indicate that introduction of steel fibers significantly improves the cracking behavior in terms of a significant increase in first crack load and the formation of a large number of finer cracks. However, only marginal improvement was observed in the case of ultimate load. Addition of steel fibers to HPC imparted high ductility to structural members which is essential for seismic force-resisting structures. Malhotra et al.  conducted research on polypropylene beams and concluded that it is the most widely used in concrete due to its good resistance to acids and alkalis in addition to the cheapness of the raw material compared (on the volume basis) with steel fibers and other alternatives. Pant et al.  conducted research on steel fiber reinforced rectangular concrete beams without web reinforcement. The top reinforcement, aspect ratio and volume fraction of steel fibers are kept constant for all the beams and variable parameter in longitudinal steel at bottom only. From the above tests it was found that the torsional strength is independent of longitudinal reinforcement. Yoon-Keun et al.  conducted 12 tests on reinforced concrete beams with three steel fiber-volume fractions (0, 0.5, and 0.75%), three shear span-depth ratios (2, 3, and 4), and two concrete compressive strengths (31 and 65 MPa). The results demonstrated that the nominal stress at shear cracking and the ultimate shear strength increased with increasing fiber volume, decreasing shear span-depth ratio and increasing concrete compressive strength. As the fiber content increased, the failure mode changed from shear to flexure.
The research in the area of cyclic behavior of polypropylene FRC, plain concrete beams is limited; to keep in view of the above, an attempt was made to study the cycle behavior of concrete beam with polypropylene fiber.
| 2. Experimental Program|| |
2.1. Materials and Mixes
The concrete was produced using ordinary Portland cement conforming to IS 456: 2000. The nominal maximum size of the coarse aggregate was 10 mm. The fine aggregate of zone II and coarse aggregate complied with IS: 383-1970. The properties of polypropylene fiber were used in this study as shown in [Table 1].
The concrete mix proportions were chosen based on the results of trial mixes carried out to optimize the mix proportions and fiber content. The PFC and PPFRC basic mix proportions were based on combined properties including workability, compressive strength, flexural strength, and flexural toughness. Properties of coarse aggregate, fine aggregate, and cement values of a concrete are given in [Table 2]. The volume of fiber content is 0.35% of a volume fraction. The nominal water to cement ratio was 0.50. However, the actual water content varied according to the fiber content to maintain comparable workability as measured from the slump test according to IS 10262-1982.
2.2. Preparation of test beams
A conventional rotary concrete mixer was used. The dry coarse aggregate, cement, and sand were first mixed for about 1 minute before adding the mixing water. The fibers were added slowly to the running mixer, after 3 minutes, to avoid clumping. Mixing was continued for another 2 minutes to achieve uniform distribution of the fiber. Workability of the fresh concrete was assessed using the slump test. The properties of coarse, fine aggregate, and cement are shown in [Table 2]. After casting, the concrete was compacted using a vibrating table. From each mix, three 150-mm cubes and three 150-mm diameter, 300-mm height cylinders were casted for compressive and split tensile strength. The beams and the cubes were cured in normal water available in laboratory until testing at 30 days. The results of tested specimens are shown in [Table 3].
2.3. Test procedure and measurements
The sizes of the test beams were 900 mm length, 150 mm breath, and 150 mm depth. The test beams have a total length of 900 mm and an effective span length of 800 mm between supports. The dimensions and the details for the test beams are shown in [Figure 1], while [Table 3] shows the properties of these beams. All beams were of same dimension and longitudinal reinforcement. The specimens were tested in a universal testing machine of 400 kN capacity. A constant load of 5 kN, which are about 5.5% of the capacity of the beam, was applied to the beam for holding the specimens in a position and to simulate load. A hydraulic load was used to apply a load at the beam as shown in [Figure 1]. A dial gauge with a least count of 0.02 mm was used to measure the beam displacements. The increment of loading was taken as 10 kN. The beam was loaded up to the first increment, then unloaded brought to zero and reloaded to the next increment of load, and this pattern of loading was continued for each increment.
| 3. Results and Discussion|| |
3.1 Cracking strength and ultimate moment
The crack patterns for without reinforcement and with reinforcement beams were nearly similar. As failure was approached, the PPFRC beams developed new cracks between the primary cracks. The new cracks were due to increased ductility. The extension of the cracks through the beam height was lower in case of PPFRC beams compared with RCC beams due to the action of the fibers that restrained the propagation of cracks. [Table 4] shows the actual cracking moment for the tested beams. The presence of the polypropylene fibers (with volume ratio V f = 0.35%) slightly reduced the flexural cracking resistance, and this was observed in case of PPFRC beams. RCC and PPFRC beams are shear failure. PFC beams failed in flexure failure. While adding fiber in RCC, it converts to flexure failure to shear failure. While adding fiber it gives warning before failure and reduces the crack propagation. [Figure 2] shows the cracks patterns of failure for the tested beams. PFC takes less load carrying capacity, comparing to RCC and PPFRC beams. While comparing to RCC beams, PPFRC beams show slightly improved load carrying capacity.
3.2 Deflection behavior
[Table 5] shows the mid span deflection of the tested beams at the different load levels. Beams without fibers (RCC1 and RCC2) show higher flexural rigidity before cracking. After cracking, its rigidity dropped to about 57% due to the rapid progress of cracks through the section height. For FRC beams, the slope of load-deflection relation in the uncracked stage was less than that of RCC beam. However, after cracking the drop was smaller than that of RCC beams.
3.3 Energy absorption Capacity
The energy absorption capacity of specimens was calculated as the area under the load deflection plots of the each cycle load. For PPFRC specimens with 0.35% fibers, its energy absorption capacity was about 2.45 times higher than that of RCC without fibers shown in [Table 6].
|Table 6: Energy absorption capacity, stiffness degradation and ductility factor|
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3.4 Ductility and stiffness behavior
The ductility and stiffness factor values are given in [Table 6]. From these, it is observed that ductility factor increases in the FRC beams when compared with conventional reinforced concrete specimens, and this is due to the tensile property of fibers.
The gradient of the load-deflection relationship is an indication of beam stiffness. It may be seen in [Figure 3] that prior to cracking, the stiffness of the beams remained practically the same for the entire set in this study. PPFRC beam demonstrated slightly higher post-cracking stiffness than the corresponding RCC beam. The post-cracking stiffness has been found to decrease in PFC beam specimens. The effect of the amount of compression reinforcement or the spacing of stirrups in the flexural zone has practically no influence on beam stiffness. While comparing to plain fiber beam, RCC beam gives higher stiffness.
|Figure 3: Cyclic load deflection (a) Load deflection-PPFRC1, (b) Load deflection-PPFRC2, (c) Load deflection-RCC1, (d) Load deflection- RCC2, (e) Load deflection-PFC1, (f) Load deflection-PFC2|
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| 4. Conclusion|| |
Based on the test results, the following conclusions can be obtained:
- The inclusion of polypropylene fibers into plain and reinforced concrete beams reduced the crack propagation and significantly improved the steel tensile stress of the concrete beams.
- Energy absorption capacity and ductility have improved considerably when fiber content increased which makes PPFRC beams highly suitable for seismic force-resistant structures.
- Inclusion of polypropylene fiber in to concrete, the rate of stiffness delay in the PPFRC beam After cracking.
| 5. Acknowledgments|| |
This research work is a Post Doctoral Research work of the author. Authors wish to express gratitude and sincere appreciations to the President, Dr. M.G.R. Educational and Research Institute (Dr. M.G.R Deemed University), Chennai, Tamil Nadu, India, for giving research fund assistance and full co-operation to this research. The authors are very grateful for the assistance rendered by the Civil Engineering Laboratory Technical Staff and University students at various stages of this investigation.
| References|| |
|1.||S. Arivalagan, and T. S. Thandavamoorthy, "Flexural Behaviour of Reinforced and Plain Concrete Beams made with Polypropylene Fibers", Proceedings of International Conference on Advances in Materials and Techniques for Infrastructure Development (AMTID 2011) NIT Calicut, India, September-28-30, pp. 159-165, 2011. |
|2.||M. Alhozaimy, P. Soroushian, and F. Mirza, "Mechanical properties of polypropylene fiber reinforced concrete and the effects of pozzolanic materials", Cement & Concrete Composites, Vol. 18, No. 2, pp. 85-92, 1996. |
|3.||N. Ganesan, P. V. Indira, and R. Abraham, "Behaviour of Steel Fibre Reinforced High Performance Concrete Members under Flexure", IE(I) Journal, Vol. 88, pp. 20-23,2007. |
|4.||V. M. Malhotra, G. G. Carette, and A. Bilodeau, "Mechanical properties and durability of polypropylene fiber reinforced high-volume fly ash concrete for shotcrete applications", ACI Materials Journal, Vol. 91, No. 5, pp. 478-486,1994. |
|5.||A. S. Pant, and S. R. Parekar, "Steel Fiber Reinforced Concrete Beams Under Bending, Shear And Torsion Without Web Reinforcement", International Journal ofRecent Trends in Engineering, Vol. 1, No. 6, pp.86-88, 2009. |
|6.||K. Yoon-Keun, M. O. Eberhard, K. Woo-Suk, and K. Jubum, "Shear Strength of Steel Fiber-Reinforced Concrete Beams without Stirrups", American Concrete Institute, Vol.99, No.4, pp. 530-538, 2002. |
| Authors|| |
Arivalagan S. Post-doctoral fellow, Professor and HOD, Department of Civil Engineering, Dr. M.G.R. Educational and Research Institute University. Chennai, Tamil Nadu, India. Author has published more than 25 International and National journal and Conference papers. Area of research interest is Steel and Concrete structures. Author has completed his post-doctoral research work in Dr. M.G.R University along with Anna University of Technology- Trichirappalli and in Association with University of Malaya, Malayisa (paper publication).
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]