Bamboo as a Construction Material
Throughout the world's tropical and the sub-tropical regions, bamboo gain a long and well established tradition as a building material. Bamboos are employed for different form of construction, especially in the housing construction in the rural areas.
|Fig.1. Two Restaurant in The state of Morelos Built with Bamboo|
When compared to other building materials like brick, cement or concrete, bamboo is a versatile material that is renewable, easily available, stronger and less in weight. The construction procedure with bamboo is simple to carry out employing by simple tools. The correct detailing and structural design of bamboo in construction will bring the bamboo building resilient to wind and earthquake.
The use of bamboo as a construction material has been carried out for centuries, but the idea of using bamboo as a reinforcing material was initiated by Clemson's Study that was conducted in the Clemson Agricultural College. The details from the study and an overall analysis is updated in this article.
Selection of Bamboo For Reinforcement in Concrete
|Fig.2.Selecting The Bamboo From the Nature|
There are certain factors that are taken into consideration while selecting bamboo in a whole, irrespective of the purpose it is employed, that is for internal or external structural works. A general and minimum quality level have to be acquired by bamboo when used in construction. They are mentioned below.
- Colour of Bamboo : Use bamboo that have a pronounced brown colour. The brown colour will ensure that the plant is minimum three years old.
- Diameter of the culm: When selecting bamboo, always select the bamboo with large diameter.
- Seasoning: The bamboo that are well seasoned should be used for taking the culms.
- Best Harvesting Season: The spring season or early summer is not suitable for harvesting the bamboo for construction purpose (reinforcing). The spring season will make the bamboo to gain higher moisture content within their fibers.
Preparation of Bamboo for Reinforcing
- Sizing: Splints (split culms) are generally more desirable than whole culms as reinforcement. Larger culms should be split into splints approximately 3/4 inch wide. Whole culms less than 3/4 inch in diameter can be used without splitting.
|Fig.2:Sizing and Spacing of Bamboo Reinforcement used in slabs and walls|
- Splitting : Splitting of the bamboo can he done by separating the base with a sharp knife and then pulling a dulled blade through the culm. The dull blade will force the stem to split open; this is more desirable than cutting the bamboo since splitting will result in continuous fibers and a nearly straight section. Table II shows the approximate net area provided by whole culms and by 3/4-inch-wide splints, as well as the cross-sectional properties of standard deformed steel bars and wire mesh.
|Fig.3: Splitted Bamboo|
- Seasoning: When possible, the bamboo should be cut and allowed to dry and season for three to four weeks before using. The culms must be supported at regular spacing to reduce warping.
|Fig.4: Bamboo Seasoning|
- Bending: Bamboo can be permanently bent if heat, either dry or wet, is applied while applying pressure. This procedure can be used for forming splints into C-shaped stirrups and for putting hooks on reinforcement for additional anchorage.
|Fig.5: Bamboo Bending|
- Waterproof Coatings: When seasoned bamboo, either split or whole, is used as reinforcement, it should receive a waterproof coating to reduce swelling when in contact with concrete. Without some type of coating, bamboo will swell before the concrete has developed sufficient strength to prevent cracking and the member may be damaged, especially if more than 4 percent bamboo is used. The type of coating will depend on the materials available. A brush coat or dip coat of asphalt emulsion is preferable. Native latex, coal tar, paint, dilute varnish, and water-glass (sodium silicate) are other suitable coatings. In any case, only a thin coating should be applied; a thick coating will lubricate the surface and weaken the bond with the concrete.
|Fig.6: Bamboo Treatment Pool|
Water Absorption and Bonding Strength of Bamboo Reinforced Concrete
|Fig.7.Bamboo Reinforced Wall Panels|
Water absorption is a primary factor and property of bamboo that will govern the use of a specific species of bamboo for reinforcing concrete or for any external structural works. So making bamboo highly impermeable requires certain treatment. These treatment is carried out by the considering the following factors:
- The adhesion property of the treatment agent applied with bamboo
- The water repelling nature of the treating agent material
- The rough surface given to the bamboo after treatment.
Among different species of bamboo that are available, the Dendrocalamus gigantes which is known as DG and the species Bambusa Vulgaris Hard called as BVS are the ones that have less water absorption rate. The figure below shows the water absorption rate for different species of bamboo:
|Fig.8. The Water absorption rate for different bamboo species with time|
The figure-5, below shows the average bond stress -displacement for the beam that is reinforced with bamboo that is treated with eopxy glued stone connectors. Sufficient bonding is enhanced with sufficient roughness in the bamboo surface like the provision of ribs in the steel reinforcement. This roughness in the case of bamboo can be obtained with other methods like:
- Bamboo rolling with the wire
- Getting Rugosity to the bamboo surface through pressing of treated bamboo road against sand
- Coating with petrol products
Fig.9: Bond stress v/s deflection graph for beam reinforced with bamboo treated with epoxy.