Determination of Tensile Property of Bamboo for Using as Potential Reinforcement in the Concrete

Transcription

1 International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol: 11 No: Determination of Tensile Property of Bamboo for Using as Potential Reinforcement in the Concrete Md Ahsan Sabbir 1, S.M. Ashfaqul Hoq 2, and Saiada Fuadi Fancy 3 Abstract This research was undertaken to investigate the possibility of using bamboo as a potential reinforcement in the concrete beam to compensate the low tensile property of the concrete. Even though steel reinforcement is a very suitable material for complementing concrete s low tensile strength, considering the cost, some parts of the world people build their houses by using only concrete or mud-brick which is very vulnerable. To overcome these problems, bamboo may be the alternative materials to substitute the reinforcing bar in concrete for less important structures by investigating the physical properties of this type of natural reinforcement. To evaluate these properties, tension test was conducted on bamboo specimen. First three samples of finished bamboo were tested in natural condition (without treatment). Then five samples of finished bamboo were tested with GI wire spiral at the ends for improved gripping. From this test, the tensile strength, proof strength and modulus of elasticity were determined from stress-strain curve for bamboo reinforcement and satisfactory results are obtained in terms of tensile strength and stress-strain characteristics of bamboo for using as reinforcement in the concrete. Index Term Bamboo, Stress, Strain, Tension test, Tension test grip. 1. INTRODUCTION One of the properties that would make bamboo a good substitute to steel in reinforced concrete is its strength. The strength of bamboo is greater than many timber products which are advantageous, but it is quite less than the tensile strength of steel. Bamboo is easily accessible as it is available in almost every tropical and subtropical regions, this lowers the cost of construction and increases the strength of the buildings that would otherwise be unreinforced. Tension test is the most basic type of mechanical test. It is easy to perform and relatively inexpensive compared to other tests. The stressstrain characteristics of bamboo have been derived from the results of this tension test. in connection with this. The mechanical properties vary with height and age of the bamboo culm. Research findings indicate that the strength of bamboo increases with age. The optimum strength value occurs between 2.5 and 4 years. The strength decreases at a later age [1]. Amada et al. (1997) investigated the mechanical and physical properties of bamboo. They conducted a thorough investigation into the structure and purposes of the nodes, which they found to strengthen the bamboo culm [2]. Lo et al. (2004) gave a detailed description of the mechanical properties of bamboo in their study. They found that the physical, as well as mechanical attributes vary with respect to diameter, length, age, type, position along culms, and moisture content of bamboo [3]. Amada and Untao (2001) studied the fracture properties of bamboo. In contradiction to other studies, this study states that the tensile strength of bamboo fibers almost corresponds to that of steel [4]. Ghavami (1995) discussed the mechanical properties of bamboo, specifically pertaining to bamboo in concrete. This study showed that the ultimate strength of a concrete beam reinforced with bamboo is approximately 4 times when compared with un-reinforced concrete [5]. 3. SAMPLE PREPARATION First a bamboo was divided into two pieces length wise with the carpenter s tools like hammer, chisel etc. Each of the two halves was further divided into three pieces. It was then rounded to shape of a rod as shown in the Fig. 1, Fig. 2, Fig. 3 and Fig OBJECTIVES OF THE RESEARCH Whereas the mechanical properties and behavior of steel reinforcement have been thoroughly studied and well documented, there exists no comprehensive data describing bamboo reinforcement. Therefore, the aim of this study is to provide a preliminary contribution toward the collection of the mechanical properties and behaviors of bamboo reinforcement. Some of the previous researches are mentioned Fig. 1. Bamboo splitting into two pieces Fig. 2. Half bamboos splitting into three pieces.

2 International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol: 11 No: finished bamboo and bamboo twig specimen was placed in such a way that strain measurement and the corresponding load can be taken. Fig. 3. Preparation of sample bamboo by using fem Fig. 4. Prepared bamboo sample as reinforcement 7. RESULTS OF TENSION The tensile tests were conducted for several samples of both bamboo and bamboo twig specimens. Their failure pattern, ultimate and yield strength will be discussed in the following section. Tension tests were performed for specimens with different conditions of gripping. 4. GRIPPING OF BAMBOO REINFORCEMENT Proper gripping is an important factor for tensile test. Bamboo is relatively soft materials than the materials used for gripping purpose in UTM. At the time of tension tests, early failure was observed at the gripping end as shown in the Fig. 5, possibly due to high stress developed from lateral compression. Moreover, the surface of the bamboo specimen is very slippery and therefore the samples in some case experienced slip at the time of tension test. To solve these gripping problem GI wires (2mm diameter) were wringed spirally at both ends of the specimen. The application of GI spiral around the ends of bamboo specimen has been shown in Fig. 6. Fig. 7. Finished bamboo under tension test 7.1 RESULTS OF TENSION TESTS FOR BAMBOO SPECIMENS (NORMAL BAMBOO SURFACE AT GRIP AREA) Fig. 5. of the sample at grip during tension test 5. PREPARATION OF SPECIMENS Fig. 6. Bamboo specimen with GI spiral 3 samples of finished bamboo without GI spiral and 5 samples of finished bamboo with GI spiral were taken for tensile test each having the following criteriai. Each specimen contained at least 3 knots. ii. Any form of imperfection (fracture, void, decay, etc) was avoided. iii. Any undulation was trimmed off. iv. Diameter was measured at four different locations and then the average diameter was calculated. 6. TEST SETUP For tension test, Universal testing Machine was used. The specimen (finished bamboo) under tension test has been shown in Fig. 7.To derives the stress-strain characteristics, the According to the test, the splitting end grip failure was observed for sample-1 as shown in the Fig. 8. The splitting failure initiated at the gripping area and finally smashed. Therefore, it can be opined that if failure at grip could have been avoided, the specimen would take more load. The sample experienced failure at knot as shown in the Fig. 9 and no failure was observed at the grip and hence the specimen carried higher load. The third sample experienced failure similar to sample-1 as shown in the Fig. 10. The failure loads of these samples are shown in Table I. Fig. 8. Splitting and grip failure (sample-1)

3 International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol: 11 No: specimen was typical splitting without any slip at the grip location as shown in the Fig. 11. The split is parallel to the grain and propagates through the knot and finally failure occurs more than one location. The failure patterns of other four samples are similar to sample no-1 as shown in the Fig. 12 to Fig. 15. The failure loads of these samples are shown in Table II. From these results it can be said that the tensile strength is nearly uniform and failure pattern is very similar for bamboo specimens where failure at grip was avoided. The tensile strength of bamboo specimens with prepared ends (to avoid grip failure) is always higher than the corresponding bamboo specimens without prepared ends (failure at grip). Fig. 9. at knot(sample-2) Fig. 11. Typical splitting failure of bamboo reinforcement (sample-1) Fig. 10. Splitting and grip failure (sample-3) Table I Results of tension test for bamboo reinforcement Specimen No. Avg. Stress at type Splitting and failure at grip at node Splitting and failure at grip 7.2 RESULTS OF TENSION TESTS FOR BAMBOO SPECIMENS (BAMBOO SURFACE WITH GI WIRE AT GRIP AREA) During tension tests of bamboo reinforcement, an attempt was made to avoid failure at the grip by wrapping the ends by GI wire. According to the test, the failure pattern of bamboo Fig. 12. Typical splitting failure of bamboo reinforcement (sample-2) Fig. 13. Typical splitting failure of bamboo reinforcement (sample-3)

4 International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol: 11 No: Fig. 14. Typical splitting failure of bamboo reinforcement (sample-4) Fig. 16. Stress- strain curve of bamboo samples D Y Fig. 15. Typical splitting failure of bamboo reinforcement (sample-5) Table II Results of tension test of bamboo reinforcement without grip failure Specimen Avg. Stress at type No Splitting Splitting Splitting Splitting Splitting 7.3 STRESS STRAIN RELATION Stress-strain data are shown for sample-1 and sample-2 in the Table III and Table IV. The gage length was taken between 203 mm and 254 mm for all the samples. The stress-strain curve for sample-1 and sample-2 is shown in Fig. 16. From this curve, the yield strength has been calculated by offset method. The offset is the horizontal distance between the initial tangent line and any line running parallel to it. The value of the offset for a given material is usually expressed this way: Yield Strength, 0.1% Offset. 0.1% Offset means 0.1% of the fundamental extension units of inches per inch, or 0.001in./in. along the X-axis. Now using that as the origin, a line (C-D) parallel to the initial tangent line was drawn. It is noted that the line C-D intersects the stress- strain curve at a certain point Y shown in the Fig. 17. The ordinate of this point (the amount of stress in psi) is the yield strength at 0.1% Offset C Fig. 17. Stress- strain curve of bamboo samples 2.9 Table III Stress-strain data for bamboo (sample-1) Stress (Mpa) Displacement (mm) Strain( X 10-3 ) (mm/mm)

5 International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol: 11 No: Table IV Stress-strain data for bamboo (sample-2) Stress Displacement (mm) Strain( X 10-3 ) (mm/mm) much lower than the steel reinforcement. Therefore, the deflection will be higher considering the steel reinforcement. A comprehensive study could be made by involving both experimental and finite element study to understand the behavior of bamboo more accurately. For further research of natural reinforcement, the tensile property of bamboo twig and cane can be investigated. REFERENCES [1] Amada, S. and Untao, S., Fracture Properties of Bamboo, Composites Part B. Vol. 32, 2001, pp [2] Amada, S., Lchikawa, Y., Munekata, T., Nagase, Y. and Shimizu, H., Fiber Texture and Mechanical Graded Structure of Bamboo, Composites Part B, Vol.288,1997, pp [3] Lo, Cuo, Leung, The Effect of Fiber Density on Strength Capacity of Bamboo, Materials Letter, vol. 58,2004, pp [4] Amada, S. and Untao, S. (2001), Fracture Properties of Bamboo, Composites Part B. Vol. 32, pp [5] Ghavami, K. (1995), Ultimate Behavior of Bamboo-Reinforced Lightweight Concrete Beams, Cement & Concrete Composites, Vol. 17, pp Therefore, from this method, the yield strength fy = 109 MPa. To be on the conservative side the value of fy = The modulus of elasticity was found to be MPa. 8. CONCLUSION Based on the experimental studies presented in this paper, the following conclusions can be drawn: (i) If tension tests are conducted without specimen end preparation, actual results may not be found due to smashing at the grip location especially for bamboo twig specimen but if the grip is prepared by using GI wire then no smashing and slippage occurs at that location. Without end preparation, the strength is considerably low because of premature failure at the grip. (ii) In general, sample failure was accompanied by tension failure for bamboo specimens. (iii) In case of specimens with ends wounded by G.I wire, the tensile strength failure was observed is nearly uniform and their failure pattern is also similar as splitting parallel to the grain. The average tensile strength with prepared ends (wounded with G.I wire) has been found to be higher than the specimens without prepared ends. This reduced strength is due to the premature failure at the grip. (iv) Bamboo specimen shows some nonlinearity before its failure. (v) The modulus of elasticity, E of bamboo is found to be