Table of Content for Bamboo Reinforced Concrete-
- Introduction
- Bamboo as Reinforcement Material in Concrete
- Strength
- Durability
- Other Uses of Bamboo in Construction
- Limitations of Bamboo
- Bamboo Reinforced Concrete
- Beams
- Slabs
- Columns
- Behaviour of Bamboo in Bending Stress
- Sustainability
- Future for Bamboo Reinforced Concrete
1. Introduction
Cement and steel are two of the most used materials in the current infrastructure industry. The production of both of these materials involve complex processes and requires a huge initial investment. Moreover, the production of these two materials need power and degrades the environment. An alternative is required in developing countries where a power crisis prevails.
The above-said problem has led to various researches to find the economical, environment-friendly, easy to produce and locally available material. Bamboo is one such alternative that satisfies all the shortfalls of steel. The bamboo uses 50 times lesser energy than steel for the same amount of production.
The bamboo is a type of perennial grass that grows naturally and has sufficient strength to support light loads. It is found in diverse environmental conditions across the globe. Bamboo is an ideal material to be used in low-cost projects where the structure has a lower strength requirement.
The bamboo grows taller and rapidly as compared to other plants. Their structure is hollow cylindrical with nodes. The use of bamboo minimises energy consumption, pollution, consumption of fossil fuels and promote renewable resource usage.
2. Bamboo as Reinforcement Material in Concrete
2.1 Strength
The bamboo has a high strength to weight ratio that makes it suitable to be used as a construction material. It has strength comparable to hardwood.
Bamboo is orthotropic in nature. They have high strength in the direction parallel to the fibres and low strength perpendicular to the fibres respectively.
The physical and mechanical properties of bamboo vary with the moisture content present. Higher moisture content results in weaker strength and higher weight. Generally, the moisture content should be lesser than 15%. Only well-dried and treated bamboo should be used for structure and reinforcing works.
The following table compares the bamboo with concrete and mild steel-
Bamboo may have tensile strength as high as 370 MPa. In some cases, they can be used as tension members replacing steel. The tensile strength to weight ratio of bamboo is six times greater than that of steel. However, it should not be confused as bamboo has a higher tensile strength than steel.
Bamboo outperforms steel and concrete when compared in terms of Young’s Modulus and density. The following graph shows the performance of other materials in comparison to bamboo.
The stress strain curve for bamboo shows its’ brittle nature-
2.2 Durability
An untreated bamboo may last up to 2-6 years and up to 1 year when exposed to water. Moreover, it is susceptible to termite attack and rot (fungus) if left untreated. The curing of bamboo, when cut at the grove, reduces the starch content and makes it lesser prone to the insect attack. On the spot, curing can be done by smoke, immersion or heating.
The moisture present in bamboo affects durability. Higher the moisture, lesser is durability. The bamboo can be dried in open air, greenhouse or heating.
The durability also depends on the method of preservation used.
2.3 Other Uses of Bamboo in Construction
Bamboo is used as a building material for scaffolding, pedestrian bridge, building construction, and reinforcing material.
In China and India, bamboo has been extensively used for suspension bridge constructions since ages. Japan commonly uses bamboo for fencing, grates and gutters, fountains and decorative works. In the Philippines, Nipa Hut is a type of hut made of bamboo.
Bamboo flooring and furniture is also available in the market.
What uncommon/innovative use of bamboo have you seen? Let me know in the comment below.
3. Limitations of Bamboo-
3.1 Insect Attack-
Termite and beetle attack make bamboo lesser durable. Due to shell structure, a small deterioration equal to shell thickness can lead to considerable change in strength. Insecticide like boric acid can be used on bamboo.
3.2 Swelling & Shrinkage
Swelling and shrinking are one of the biggest limitations of bamboo. The change in the size of bamboo due to moisture variation and/or temperature leads to a weaker bond between concrete and bamboo leading to failure in pull-out condition.
When untreated bamboo is used as reinforcing material, it absorbs curing water and expands. Post curing period the bamboo shrinks to its original size and leaves the void between itself and concrete. This limitation can be overcome if bamboo is treated with water-repellent material.
3.3 Low Fire Resistivity
Bamboo is very much prone to fire. However, it can be made somewhat fire-resistive by applying fire retardant like borax.
3.4 Lower Strength compared to Steel
Nowadays, high yield strength steel bars are in use which have yield strength as much as 30 times of bamboo. Thus, for similar loading condition bamboo to be used is 30 times of steel that will make the structure bulky.
3.5 Unsuitability for the Earthquake Resistant Structures
Bamboo is brittle in nature and cannot be used as reinforcing material in the earthquake-resistant structure.
4. Bamboo Reinforced Concrete
As the demand for low-cost alternatives of steel is increasing the research in this field is also increasing. Bamboo has been tried and tested as reinforcing material in concrete and has given satisfactory results but still bamboo reinforced concrete is still in the early stage of research before being used at a large scale.
4.1 Beams-
Researches have shown that for the beam of size 3.4m x 0.12m x 0.3m (free span- 3m) when reinforced with 3% bamboo increased ultimate applied load by 400% as compared to beam without reinforcement.
4.2 Slabs-
In, Brazil bamboo reinforced slabs are being made successfully. Half bamboo diaphragms connected with bamboo rod close to the diaphragms passing through bamboo diameter is used in the slab. The formwork used is the permanent type. This arrangement of bamboo prevents the shear failure of the slab and also provides sufficient bond.
The absence of the connector rod leads to shear failure as diaphragm alone is insufficient to sustain the shear stress.
4.3 Columns-
When 0.3m diameter circular columns reinforced with 3% bamboo (with bonding agent) and permanent bamboo formwork were tested, the results of such column were similar to the steel column of the same size. Thus, it can be said that the bamboo reinforced columns are as good as steel-reinforced columns.
4.4 Behaviour of Bamboo in Bending Stress-
The behaviour of bamboo reinforced concrete is still a matter of research as the failure occurs mostly due to tensile failure of concrete and bamboo even when the beams were over reinforced. The problem arises due to imperfect bond between the concrete and the bamboo.
5. Sustainability-
The industrial processes have become more eco-friendly with a focus on reducing pollution and preserving the environment. The bamboo provides a sustainable alternative.
The production of 1 ton of cement and 1 ton of steel emits more than 1 ton and 2 tons of carbon dioxide respectively. The production of 1 ton of bamboo consumes more than 1 ton of carbon dioxide.
6. Future of Bamboo Reinforced Concrete
In Singapore, to make a composite material bamboo has been combined with thermoset polymer resin under pressure. The said material has given satisfactory results. The tensile strength is around 400 MPa, compressive strength 100-120 MPa, bending strength 200 MPa and modulus of elasticity 50 GPa. Moreover, the process is carbon dioxide negative.
The Maharashtra Public Works Department have included bamboo in State Schedule Rates for 2020-21. This step will further help in popularising the bamboo as a construction material.
To read about researches mentioned above in detail, visit here and here.
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