The use of miscanthus (Giganteus) as a plant fiber in concrete production

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1 Scientific Research and Essays Vol. 6(1), pp , July, 011 Available online at DOI: /SRE ISSN Academic Journals Full Length Research Paper The use of miscanthus (Giganteus) as a plant fiber in concrete production Hicran Acikel Selcuk University, Faculty of Engineering and Architecture, Engineering, (TR-00) Konya, Turkey. hicranacikel@gmail.com Accepted May, 011 In this study, it was intended to study the useability of miscanthus, an energy plant in the production of concrete as a plant fiber in the city of Konya which is an agricultural city. It was thought that the concrete that is used in the production of structural elements can be strengthened and produced lighter by the use of miscanthus. The aggregates that are used in the experiments are supplied from Gocu village of Konya. Concrete specimen are produced in three types, namely cubic, cylindirical and beam. A total of 0 experiment specimens are produced from 1 different mixtures, out of these specimens, 105 are cubical with dimensions of cm, 6 are cylindrical with dimensions of 15 0 cm, and 7 are beam. The granulometry of the aggregate was kept constant, and the concrete was produced with a water-cement ratio of 0.5, having, 50 and 00 kg/m cement dosages, and with various fiber ratios and styles (grinded, cut and as reinforcement). The produced specimens were kept in water for 8 days. For each different mixture, two cubic specimens are tested for compression on the 7 th day, and on the 8 th day, compression, splitting and bending tests are performed on three cubical, cylindrical and beam specimens, respectively. Moreover, the unit weight and consistency of fresh concrete, unit weight of hardened concrete and water absorption ratio are determined for every mixture. According to the results obtained from the experiments carried out, using grinded miscanthus as a concrete admixture has increased the strength of concrete in compression, tension and bending by to 8, 9 to 5 and to 9%, respectively. When miscanthus was embedded into the beams as reinforcement, around to 6% increase was observed in the bending strength of the beams. Key words: Using of fiber in concrete, vegetable (plant) fiber, miscanthusxgiganteus. INTRODUCTION Presently, the production of structural elements using fiber concrete is becoming rather popular. In particular, the reinforcement of the materials which have less tensile strength than their compressive strength, with fibers goes back to hundreds of years ago. The first example to this is the fabrication of bricks composed of soil and hays by burning them under the sun light. Afterward, pipes with asbestos became the most common practice. Following the use of asbestos fibers, in time, steel, fiber-glass, carbon, cellulose, nylon and polypropylene fibers are utilized. Other than these fibers, plant fibers are also being used. However, the use of miscanthus (an energy plant), as a fiber has not been discussed in the literature. Plant fibers used in some countries includes Manila hemp, sisal hemp, coir, cotton and Indian hemp. In Turkey, plant fibers have not yet been used. Plant fibers, are abundant in tropical countries, especially in Brazil (Savastano et al., 1998; Savastano and Agopyan, 1997). The main purpose of using fibers is reducing the fragility of material, thus, increasing its ductility. This property is very important since it increases the energy absorption capacity, hence, the earthquake resistance (Agopyan and John, 199). Pacheco-Torgal and Jalali (010) have been discussed in their paper, the use of vegetable fibres as reinforcement in cement based materials. Filho et al. (009) presented an experimental research on the durability performance of compression molded sisal fiber cement mortar laminates (SFRML). In order to produce a matrix totally free of calcium hydroxide (CH), the Portland cement (PC) was replaced by calcined clay

2 Acikel 661 Table 1. Results of unit weight, specific gravity and water absorption. Aggregate Compact unit Loose unit weight Dried specific Dried specific gravity of Normal dried specific Water absorption weight kg/m kg/m gravity kg/m saturated dry surface kg/m gravity kg/m % Fine aggregate (0 to mm) Coarse aggregate ( to 16 mm) (metakaolin and calcined waste crushed clay brick) and a material with enhanced performance was obtained. As a result, it was indicated that the newly developed CH-free matrix avoided the fiber embrittlement process keeping the toughness in time even after 100 cycles of wetting and drying. Filho et al. (009) in another study, also examined developing the sisal fiber cement composites reinforced with long unidirectional aligned fibers and characterizing their physical mechanical behavior. Agopyan et al. (005), in their research, have been presented the approach which is directed towards the development of alternative binders, with controlled free lime, using ground granulated blast furnace slag in order to improve the durability of vegetable fibres. Ramakrishna and Sundararajan (005) have studied on the durability of natural fibres and the effect of corroded fibres on the strength of mortar. Silva et al., 008), have studied the monotonic tensile behavior of a high performance natural fiber in their paper. Andersons et al. (005), have studied the flax fibre strength distribution and efficient experimental methods for its determination. In their study, elementary flax fibres of different gauge lengths were tested by single fibre tension in order to obtain the stress strain response and strength and failure strain distributions. The applicability of single fibre fragmentation test for flax fibre failure strain and strength characterization was considered. It was shown that fibre fragmentation test could be used to determine the fibre length effect on mean fibre strength and limit strain. Alawar et al. (009) have investigated the effect of different treatment process on the data palm fiber (DPF) in their study. In this research, it was aimed to investigate the usability of miscanthus in concrete production as a plant fiber. Miscanthus is an energy plant and grown in Konya, a city of agriculture. The reason for using miscanthus as a plant fiber is that it can be grown in the weather conditions of the city of Konya, Turkey. Miscanthus used in the experiments was fairly easily obtained from the fields in the campus area which are controlled by the Agricultural Engineering Faculty at Selcuk University, Konya. Since miscanthus is easily cultivated, its price is quite low. It was targeted to obtain low cost and high quality in this experimental study. EXPERIMENTAL STUDIES The materials used in the experiments The aggregate used in the experiments were supplied from the town of Göçü located around Konya. The experiments of the aggregate were carried out according to the code of Turkish Standards (TS). These included the specific gravity and water absorption experiments according to TS 56, compact unit weight and loose unit weight experiments according to TS 59 and granulometry experiments according to TS 10 (Table 1 and Figure 1). The aggregate had a fineness modulus of k =.16 and a specific gravity of 560 kg/m. The aggregate had a compact unit weight of 1710 kg/m and a loose unit weight of 165 kg/m. The water absorption rates of the sand and gravel were.8 and 0.65%, respectively. In the concrete mixtures, Portland Cement, PÇ.5 with a specific gravity of 150 kg/m and produced by Konya Cement Industry Co., was used. The water in the mixtures was supplied from Selcuk University s campus water network. The miscanthus used as a plant fiber was supplied with a diameter to 8 mm and a length of 60 to 80 mm, and was added into the mixtures by grinding and/or cutting at suitable lengths (Figure ). It had a density of 70 kg/m and a water absorption rate of 110%. The strain and stress at failure of miscanthus were.% and 95 to 118 MPa, respectively (Acaroğlu, 000). Concrete experiments Three types of concrete specimens were produced. A total of 0 experimental specimens were produced from 1 different mixtures, 105 of these specimens were cubical with dimensions of cm, 6 were cylindrical with dimensions of 15 0 cm, and 7 were beam with dimension of cm. The granulometry of the aggregate was kept constant, and the concrete was produced with a water-cement ratio of 0.5 having, 50 and 00 kg/m cement dosages, and with various fiber ratios and styles (grinded, cut and as reinforcement). The produced specimens were kept in water for 8 days. For each type of mixtures, in compliance with TS 11 (Turkish Standards), two cubic specimens at 7 th day, and three cubic specimens at 8 th day were subjected to compression tests; in compliance with TS 19, three cylindrical specimens were subjected to splitting tests at 8 th day; and in compliance with TS 85, three beam specimens were subjected to bending tests at 8 th day. Additionally, the unit weight of fresh concrete according to TS 91, the consistency of fresh concrete according to TS 871, and the specific weight and water absorption rate of

3 Under the sieve (%) 66 Sci. Res. Essays Diameter of particle (mm) A A B B C C Mixture Mixture Figure 1. Granulometric curve of natural aggregate and TS 80 reference curves. Figure. The plant of miscanthus hardened concrete according to TS 6 were determined for all the mixtures. EXPERIMENTAL RESULTS The unit weight of fresh concrete, the results of the specific weight, the water absorption rate, the compressive strength, the splitting strength and the bending strength tests of hardened concrete and the properties of the mixtures were all presented in Table. The values given in the table were the average of the values obtained from the tests of three specimens. The compression strength value for 7 day was the average of the strengths of two experimental specimens. The strengths of specimens with and without fibers were compared by means of the compression strength tests performed with cubic specimens. As a result of this comparison, it was determined that the addition of % grinded fiber into the mixture caused around to 6% increase in the compressive strengths of cubic specimens with 00 and 50 kg/m cement dosages. Similarly, in the case of adding % grinded fiber into the mixture, it was found out that the compressive strengths increased around 8 to 10%. The compressive strengths of the mixtures increased up to 6% for specimens having kg/m cement dosage and % grinded fiber, when compared to the strengths of mixtures without

4 Acikel 66 Table. The properties of experimental mixtures and the results of the experiments. Mixture Label 1 Cement dosage kg/m Fiber rate and type 00 without fiber Specimen label The unit weight of fresh concrete kg/m The specific weight of hardened concrete kg/m The water absorption rate of hardened concrete % Compression strength (f ck) ( cm cubic) Mpa for 8 day Splitting strength Mpa Bending strength MPa Ort. Ort. ort ort S a Ort. S a f ck Ort. f ck y e y e (%) grinded (%) cut (%) grinded and cut (%) cut

5 66 Sci. Res. Essays Table. Contd without fiber (%) grinded (%) cut (%) grinded (%) cut

6 Acikel 665 Table. Contd without fiber (%) grinded (%) cut (%) grinded (%) cut

7 666 Sci. Res. Essays Table. Contd fiber embedded as reinforceme nt fiber embedded as reinforceme nt fiber embedded as reinforceme nt fibers. When the fiber concentration was increased further to % for the specimens with kg/m cement dosage, the rate of increase was 8%. Increasing the fiber percentage of the cubic specimens from to % had affected the increase in the compressive strength positively. It was observed that, generally, the addition of cut miscanthus into the cubic concrete specimens decreases the compressive strength. This was due to that the cut miscanthus plant in the mixture absorbed up to 70% water, then, kept it in its body and deformed. Also, due to the smooth fiber surface, the insufficient bond between the concrete and fiber caused the strength to decrease. This effect was also confirmed by increasing the amount of added cut plant fiber from to % decreased the compressive strengths of cubic concrete specimens. However, when a % mixture of grinded plant fibers were added into the cubic specimens with high cement dosages, the compressive strength increased up to 8%. On the other hand, the increase was not considerable in the case of adding % mixed plant fiber. Increases in the cement dosage changed the effect of fiber. In the cylinder splitting experiments performed using cylinder specimens, the splitting strengths of concrete specimens with and without fiber were compared. For the cylindrical specimens mixed with % grinded fiber, the splitting strength increased around 9.5 to 16% compared to that of the specimens without fibers. When % grinded fiber was added into specimens with kg/m cement dosage, the increase was as much as 5%. There was no considerable increase in the splitting strength of cylindrical specimens with cut fibers. When % grinded and % cut fibers were added together into the specimens, there was a little increase in the splitting strength. In the bending experiments performed with beam specimens, it was determined that % grinded plant fiber added into the mixture caused to 9% increase in the flexural strength. When the rate of grinded fiber added into the mixture increased to %, the increase became 5 to 9%. It

8 Acikel 667 was observed that addition of cut fibers into the beam specimens decreased the flexural strength. The rate of decrease was higher when the amount of added cut fibers was increased. Addition of cut and grinded fibers together had an unfavorable effect, as well. The plant fibers embedded into the beam specimens as reinforcement increased the flexural strength around to 6%. Since the miscanthus plant absorbed so much water, the amount of water in the mix had to be increased. However, increasing amount of water is not an appropriate solution since it will reduce the strength of concrete. In the mean time, being the surface of the plant fiber smooth instead of rough, bonding between the fiber embedded as a reinforcement into the beams and the concrete was prevented and it slipped from the concrete. For this reason, the increase in the flexural strength was limited. Similarly, the cut fiber did not bond well with the concrete and there were crystallizations at the contact surface between the fiber and the mixture. Thus, there was a decrease in the flexural strength. As a result of the unit weight tests of the specimens, it was determined that concrete specimens which had 00 and 50 kg/m cement dosages and grinded fiber, could be produced lighter than those without fiber. RESULTS According to the results from the experiments carried out, the miscanthus added into the concrete in a grinded manner, increased the compressive and tensile strengths of concrete to 8% and 9 to 5%, respectively. The miscanthus embedded into the beam specimens as reinforcement increased the flexural strength to 6%. However, the fiber used in a cut manner had an unfavorable effect. Since the miscanthus can be cultivated easily in the climatic conditions of the city of Konya, it has low cost. Additionally, it had a favorable effect in the concrete properties and increased the tensile and compressive strengths of concrete. As a result of these, the target of the low cost and high quality was realized. For future studies, the additional usage purposes of miscanthus and similar plants should be studied. Moreover, it would be interesting to study the effect of miscanthus on the ductility and energy absorption capacity of structural members made of concrete into which miscanthus is added in a grinded manner. REFERENCES Acaroğlu M (000). Energy from Biomass, Selcuk University, Graduate school of Natural and Applied Sciences (Text Book). Agopyan V, John VM (199). Durability Evaluation for Vegetable Fibre Reinforced Materials, Building Res. Inf., 0(): -5. Agopyan V, Savastano Jr. H, John VM, Cincotto MA (005). Developments on vegetable fibre cement based materials in Sa o Paulo, Brazil: an overview, 005, Cement Concrete Composites 7: Alawar A, Hamed AM, Al-Kaabi K (009). Characterization of treated date palm tree fiber as composite reinforcement, 009, Composites: Part B, 0: Andersons J, Sparnins E, Joffe R, Wallström L (005). Strength distribution of elementary flax fibres, Comp. Sci. Technol., 65: Filho RDT, Silva FA, Fairbairn EMR, Filho JAM (009). Durability of Compression Molded Sisal Fiber Reinforced Mortar Laminates, Construction and Building Materials : Pacheco-Torgal F, Jalali S (010). Cementitious Building Materials Reinforced With Vegetable Fibres: A Review, Construction and Building Materials, doi: /j.conbuildmat Ramakrishna G, Sundararajan T (005). Studies on the durability of natural fibres and the effect of corroded fibres on the strength of mortar, Cement Concrete Composites 7: Savastano Jr H, Agopyan V (1997). Transition Zone Studies of Vegetable Fibre-Cement Paste Composites, Cem. Concr. Comp.,1: Savastano Jr H, Agopyan V, Nolasco AM, Pimentel L (1998). Plant Fibre Reinforced Cement Components for Roofing, Construct. Buildings Mater., 1: -8. Silva FA, Chawla N, Filho RDT (008). Tensile behavior of high performance natural (sisal) fibers, Comp. Sci. Technol., 68: 8-.