The article evalautes the properties of bamboo and the effectiveness of bamboo fibers in concrete.
Dr. S. Kavitha, Professor, Jain University, Bangalore

In most of the developing countries, demand for steel for use as a reinforcing material is increasing day by day. However, when steel is in short supply, one can consider bamboo as an alternative material for reinforcement. It is available in plenty, and due to its strength, it can be used as a reliable reinforcing material. What’s more, as a natural product, bamboo has the capacity to withstand wind pressures due to its hollow tubular structure.

Structure of a bamboo CulmFigure 1: Structure of a bamboo Culm

Bamboo fiber reinforced concrete is a composite material. It comprises of natural bamboo fibers of different lengths and diameters with different fractions. As a carbon sequestrant, bamboo will capture the carbon in the concrete.

Bamboo fibers are natural plant fibers that are environment friendly, sustainable, cost less, have less density, an extraordinary growth rate, high strength, a is a good CO2 sequestrant. Like glass fiber, it is lightweight, biodegradable, and inexpensive. Bamboo has wooded stems, which when young are called shoots and when the plant is completely mature they are called culms.

Different ages of raw bambooFigure 2: Different ages of raw bamboo

The culm or stem grows above the ground and below are the roots called rhizome. A bamboo culm yields up to 15km of a pole and diameter of 30cm approximately in its entire life. These features make bamboo a traditionally popular construction material and its growing use as a composite reinforced material.

Bamboo cleaved into stripsFigure 3: Bamboo cleaved into strips

1.156mm diameter of bamboo fiber of aspect ratio (l/d) =40Figure 4: 1.156mm diameter of bamboo fiber of aspect ratio (l/d) =40

Scanning electron microscopic test
SEM image of bamboo fiberof diameter 700μFigure 5: SEM image of bamboo fiberof diameter 700μ

SEM image of bamboo fiber of diameter of 1.156mmFigure 6: SEM image of bamboo fiber of diameter of 1.156mm

From the SEM studies of the above the images with higher resolution and contrast, examining features like important measurements like fiber diameters are 1.156mm and 700 μ and orientation observed is continuous longitudinal stands with no flaws and pores. So the quality check of fibers is of great importance.

Research was conducted for mix proportioning of M30 grade of concrete according to the IS codes. The fibers are blended arbitrarily in the concrete mix with the percentages of materials of the FRC. The qualities of the fibers and ingredients impact the consequences of FRC.

In the present examinations, tests led on BFRC to assess the bamboo fibers length to diameter ratio.Various ages of bamboo are gathered and mechanical methodis used to separate the fibers. After the extraction of fibers,SEM test is conducted to estimate the diameter, bamboo fibers microstructure to study the failure analysis.

The two unique diameters of 700 μ (microns), 1.156 mm were selected and are treated with the anti-termite solution to which was added at the fixed rate of 0.5% to 1.5 % (0.5, 0.75, 1, 1.25, 1.5) with an increment of 0.25% of the powder weight. Then cubes, cylinders, and beams are casted from the concrete mix of M30 Grade and fibers where the workability tests are conducted for arriving at the fresh properties of the BFRC, and curing was done for 7,14,28 days. Research facility tests are directed to assess the hardened properties of the concrete and aspect ratio (l/d ratio) based on strength increment and, further more, the viability of utilization of bamboo fiber in concrete.

Fresh state concrete properties
Experiments to evaluate the workability properties for the mix with the addition of fiber content 0, 0.5%, 1.0%, 1.5% and 2.0% of 1.156mm and 700μ. Results confirm to recommended values as per IS: 456-2000 even after the addition of fibers till 1% of adding of fibers. As increment in the fiber content, slump flow decreases linearly.

Casting of specimensFigure 7 & 8: Casting of specimens

Table 1 Workability of fresh BFRC D1 (Diameter 700 μ)
Sl No Description NC PM1 PM2 PM3 PM4 Recommended slump as per IS:456-2000
Min Max
1 Slump flow (mm) 95 90 85 79 68 50 100

Table 2 Workability of fresh BFRC D2 (Diameter 1.156 mm)
Sl No Description NC PM1 PM2 PM3 PM4 Recommended slump as per IS:456-2000
Min Max
1 Slump flow (mm) 99 95 90 85 80 50 100
Concrete properties at hardened state
The basic concrete hardened properties are evaluated by conducting various tests evaluated as below:

Compressive strength
Table 3 & 4 indicates compressive strength of bamboo fiber reinforced concrete cubes of size 150mmx150mmx150mm using fibers of diameters (D1) 700 μ and (D2) 1.156 mm for M30 grade of concrete for 28 days for the aspect ratio of 30, 40 and 50.it is shown that the diameters 700μ and 1.156 mmfibers at 1% aspect ratio (l/d) of 40 gave the maximum compressive strength. The diameter 1.156 mm fibers at 1% gave the maximum compressive strength of 41N/mm2 with an aspect ratio (l/d) of 40 when mixed with concrete. Both the diameters of fibers showing the decrement in the strength at the 1.25% addition of fibers.

Table 3 Compression strength test results at 28 days of BFRC D1(Diameter 700 μ)
Sl. No Percentage of fibers Compression strength (N/mm2) at 28 days
(l/d) 30 (l/d) 40 (l/d) 50
1 0% 30.9 30 30.2
2 0.5% 31.5 33.9 32.6
3 0.75 % 31.8 35.7 32.8
4 1% 32.52 35.44 33.2
5 1.25% 31.9 32.9 31.6
Compression strength test outcomes at 28 days of BFRC (Diameter=700μ)Figure 9: Compression strength test outcomes at 28 days of BFRC (Diameter=700μ)

Table 4 Compression strength test outcomes at 28 days of BFRC D2 (Diameter 1.156mm)
Sl. No Percentage of fibers Compression strength (N/mm2) at 28 days
(l/d) = 30 (l/d) =40 (l/d) =50
1 0% 30.1 32.8 30.6
2 0.5% 30.8 33.7 31.1
3 0.75 % 32.3 36.8 34.2
4 1% 33.6 41 35.1
5 1.25% 34.9 38.9 38.1
Compression strength test outcomes at 28 days of BFRC (Diameter=1.156mm)Figure 10: Compression strength test outcomes at 28 days of BFRC (Diameter=1.156mm)

Splitting tensile strength
Splitting tensile strength of BFRC cylinders of size 150mmx300mm using two different diameters (D1) 700 μ and (D2) 1.156 mm for M30 grade of concrete for 28 days for the aspect ratio of 30, 40 and 50. It is shown that the diameter of 1.156 mmfibers at 1% gave the maximum split tensile strength of 4.8N/mm2 with an aspect ratio (l/d) of 40 when mixed with concrete. Both the diameters of fibers showing the lesser decrement in the strength at the 1.25% addition of fibers.

Table 5 Splitting tensile strength test outcomes at 28 days of BFRC of D1 (Diameter 700μ)
Sl. No Percentage of fibers Splitting tensile strength(N/Mm2) At 28 Days
(l/d) 30 (l/d) 40 (l/d) 50
1 0% 2.67 2.67 2.68
2 0.5% 2.7 3.0 3.4
3 0.75 % 3.1 3.3 3.5
4 1% 3.3 3.9 3.5
5 1.25% 3.29 3.68 3.79
Splitting tensile strengthat 28 days of BFRC (Diameter1=700μ)Figure 11: Splitting tensile strengthat 28 days of BFRC (Diameter1=700μ)

Table 6 Splitting tensile strength results at 28 days of BFRC of D2 (Diameter 1.156mm)
Sl. No Percentage of fibers splitting tensile strength(N/mm2) at 28 days
(l/d) = 30 (l/d) =40 (l/d) =50
1 0% 2.68 2.67 2.67
2 0.5% 2.98 3.1 3.
3 0.75 % 3.7 4.1 3.9
4 1% 3.81 4.8 4.2
5 1.25% 3.92 4.3 3.9
Splitting tensile strength at 28 days of BFRC [Diameter2=1.156mm]Figure 12: Splitting tensile strength at 28 days of BFRC [Diameter2=1.156mm]

Flexural strength
The flexural strength of BFRC beam of size 150mmx150mmx1200mm using two different diameters (D1) 700 μ and (D2) 1.156 mm for M30 grade of concrete for 28 days for the aspect ratio of 30, 40 and 50.It is shown that the diameter of 1.156 mm fibers at 1% gave the maximum split tensile strength of 8.5 N/mm2 with an aspect ratio (l/d) of 40 when mixed with concrete. Both the diameters of fibers show the very less decrement in the strength, at the 1.25% addition of fibers.

Table 7 Flexural strength test results at 28 days of BFRC D1=700μ

Sl. No

Percentage of fibers

flexural strength(N/mm2) at 28 days
(l/d) 30 (l/d) 40 (l/d) 50
1 0% 4.68 4.68 4.68
2 0.5% 4.8 5.1 5.3
3 0.75 % 5 5.4 5.8
4 1% 5.3 5.9 6.1
5 1.25% 5.2 5.79 5.98
Strength in flexure at28 days of BFRC (Diameter 700μ)Figure 13: Strength in flexure at28 days of BFRC (Diameter 700μ)

Table 8 Flexural strength test results at 28 days of BFRCof  D2=1.156mm
Sl. No Percentage of fibers flexural strength(N/mm2)at 28 days
(l/d) 30 (l/d) 40 (l/d) 50
1 0% 4.68 4.68 4.68
2 0.5% 5.1 6.8 7.1
3 0.75 % 6.23 7.02 7.6
4 1% 6.9 7.25 7.9
5 1.25% 7.1 7.5 8.5
Flexural strength at 28 days of BFRC Diameter1.156mm)Figure 14: Flexural strength at 28 days of BFRC (Diameter1.156mm)

Conclusion
The research concluded that bamboo fiber is an inventive, eco-friendly fiber which when added in concrete enhances the tensile and flexural properties, to deliver high strength concrete. As a natural plant fiber its costs very less and has a lower density.

The bamboo fibers extracted by mechanical methods were selected and SEM test was carried out to study the diameters of the fibers, orientation of the longitudinal strands, pore sizes of fibers, and micro structure, to assess the failure.

The FRC with fibers of different diameters, 700μ and 1.156mm was extracted using mechanical methods with various aspect ratios of 30,40,50 gave tremendous results when compared with normal concrete.

The length/diameter ratio of bamboo fibers is evaluated as 40 based on the strength parameters and the optimum dosage of bamboo fiber addition is 1%. It is also concluded that bamboo is a sustainable fiber.

About the Author
Dr. (Prof) S.Kavitha has 15 years of industrial and teaching experience and has been conducting research on sustainable materials and earthquake resistant structures. She has published more than 40 articles and has two patents.
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