The world timber demand is increasing at a rapid rate but the timber supply is depleting. It’s been found through research that bamboo can suitably replace timber and other materials in construction and other works. Industrially treated bamboo has shown great potential for production of composite materials and components which are cost-effective and can be successfully utilized for structural and non-structural applications in construction. Bamboo is one of the oldest traditional building materials used by mankind.
The bamboo culm, or stem, has been made into an extended diversity of products ranging from domestic household products to industrial applications. Examples of bamboo products are food containers, handicrafts, toys, furniture, flooring, pulp and paper, boats, charcoal, musical instruments and weapons. Bamboo is quite common for bridges, scaffolding and housing, but it is usually used as a temporary exterior structural material. In many overly populated regions of the tropics, certain bamboos supply the one suitable material that is sufficiently cheap and plentiful to meet the extensive need for economical housing. It has been used in bicycles, windmills, scales etc. Its uses are broad and plentiful.
With the advancement of science and technology and the tight supply of timber, new methods are needed for the processing of bamboo to make it more durable and more usable in terms of building materials. Studies have been carried out on the basic properties and on processing of bamboo into various kinds of composite products. Bamboo has several unique advantages like ability to grow fast with a high yield and also it matures quickly. Additionally bamboo can be grown abundantly and that too at a lower cost which makes it more economical
Processing of Bamboo and Treatment of Bamboo:
It has been found that bamboo panel composites have great potential due to their better strength, dimensional stability and other characteristics. Main characteristic features, which make bamboo as a potential building material, are its high tensile strength and very good weight to strength ratio. It can be easily worked upon by simple tools and machines. The strength-weight ratio of bamboo also supports its use as a highly resilient material against forces created by high velocity winds and earthquakes. Above all bamboo is renewable raw material resource from agro-forestry and if properly treated and industrially processed, components made by bamboo can have a reasonable life of 30 to 40 years. Though natural durability of bamboo varies according to species and the types of treatments, varied uses and applications in building construction have established bamboo as an environment-friendly, energy-efficient and cost-effective construction material.
Through several technologies mat based composites from bamboo have been developed like Bamboo Mat Board (BMB), Bamboo Mat Veneer Composite (BMVC) and Bamboo Mat Corrugated Sheets (BMCS).
The mat composites are manufactured by hot pressing the woven strips of bamboo. Thin bamboo strips called as “slivers” of width 0.6 to 1.0mm are manually woven into a mat of different sizes and patterns of which herringbone is the most common pattern in which the slivers are at an angle of 450 with respect to the edges of the mat. Then the mats are dipped in Phenol formaldehyde resin which is a chemical preservative to enhance resistance against decay and termites, later they are dried and 2 to 5 mats are assembled and hot pressed to the required thickness.
For BMVC mats wood veneers are placed in-between the layers of bamboo mats. The property of BMVC mainly depends on the properties of the inter-leaved wood veneers.
2.1 Preservation and Treatment:
As bamboo has less natural durability it requires chemical treatment for longer life. Bamboos have low natural durability (1 to 3 years) against attacks by fungi and insects. They are very difficult to be treated by normal preservative methods in dry condition since their outer and to some extent inner membranes are impermeable to liquids. The treatment of bamboo is, therefore, best carried out in green conditions. The following are methods used for bamboo preservation as per IS 401-2001-“code of practice for timber preservation” and IS 9096-1979-“code for practice for preservation of bamboo for structural purposes”:
Types of Preservatives:
· Coal Tar Creosote -This is a fraction of coal tar distillate with a boiling point range above 200°C and is widely used admixed with fuel oil in the ratio of 50:50. The fuel oil ensures stability to creosote against evaporation and bleeding from the treated bamboos. Creosote has high performance; it is non-corrosive and provides good protection from termites.
· Copper Chrome Arsenic Composition - A typical composition of this preservative comprises of coppersulphate, arsenic pentoxide and sodium or potassium dichromate in proportion of 3: 1:4.
· Copper Chrome Boric Composition: A typical composition of the preservative comprises boric acid, copper sulphate and sodium or potassium dischromate in the proportion of 1: 5: 3: 4.
· Copper Chrome Zinc Arsenic Composition - A typical composition of this preservative comprises 28 parts of arsenic acid 25 parts of sodium arsenate, 17 parts of sodium dichromate and 30 parts of zinc sulphate.
· Chromated Zinc Chloride - This consist of zinc-chloride and sodium or potassium dichromate in the ratio of 81.5: 18.5.
· Boric Acid Borax - This has been used successfully against lyctus borers. A mixture of 2:5 percent of each is found more suitable.
Methods of Treatment:
· Surface Application: this is done by brushing, spraying or dipping of timber in preservative solution for the required period.
· Soaking process: the debarked timber is submerged in the preservative solution for sufficient period till the desired absorption is obtained.
· Hot & Cold process: timber is preserved in the solution and then heated to temperature of about 900C and maintained at this temperature for suitable period and then cooled until required absorption is obtained.
· Boucherie process: it makes use of water soluble preservatives and hydraulic pressure.
· Pressure process: it can be employed to any type of preservative and is used where maximum absorption of the preservative is required.
Bamboo as Construction Material:
Through research it has been found that some species of bamboo have ultimate tensile strength same as that of mild steel at yield point and this coupled with other merits boosts the usage of bamboo as construction material.
Bamboo is a versatile material because of its high strength-to-weight ratio, easy workability and availability. Bamboo needs to be chemically treated due to their low natural durability. It can be used in different ways for roof structure as purlins, rafters and reapers, for flooring, doors and windows, walling, ceiling, man-hole covers etc.
1.1 Bamboo Trusses:
The bamboo has strength comparable to that of teak and sal. An experiment with the construction and testing of a 4m span truss made of round bamboo and different jointing techniques for web-chord connections gave results that were matching with the strength of timber.
1.2 Bamboo Roofs Skeleton:
It consists of bamboo truss or rafters over which solid bamboo purlins are laid and lashed to the rafter by means of G.I.wire. A mesh of halved bamboo is made and is lashed to the purlins to cover the roof.
1.3 Bamboo walling/ceiling:
As the bamboo material is light in weight it is more advantageous in earthquake prone areas as its chances of falling are very less and even if it falls it can be re-erected easily with less human and property loss with least efforts and minimum cost. Bamboo walls can be constructed in different modes like
· Whole stem, halved or strips of bamboo can nailed to one or both the sides of the bamboo frame
· Split
· Bamboo strips nailed to bamboo frame or posts for interior walling
· Cement or lime plastering can be done on the mud covering for better appearance and hygiene.
It has been found that the bamboo in the vertical position is more durable than in horizontal direction. For partition walls only single layer of bamboo strips are used.
1.4 Bamboo Doors and Windows:
Bamboo frames can replace timber frames appropriate to function. Bamboo mat shutters fixed to bamboo frame or a panel of bamboo board fixed to the frame which is hinged to the wall can be used as door. Small framed openings hinged to the top in the wall can serve as windows.
1.5 Bamboo Flooring:
Bamboo can be used as flooring material due to its better wear and tear resistance and its resilience properties. Whole culms act as frame work and the floor covering is done using split bamboo, bamboo boards, mats etc by means of wire lashing these to the frame.
1.6 Reed Boards:
Reed boards are made by flat pressing the reed at high temperatures. These reed boards are used in elements like flooring, walls, ceiling and roofing. They can also be used for partitions, doors, windows etc.
1.7 Scaffolding:
Bamboo poles lashed together have been used as scaffolding in high rise structures due to their strength and resilience. The timber planks can be replaced with bamboo culms and these can be lashed to the vertical culms.
Strength Properties of Bamboo:
Experimentally it has been found that the ultimate tensile strength of some species of bamboo is comparable to that of mild steel and it varies from 140N/mm2- 280N/mm2. This together with other properties has made Bamboo a more visible option as a construction material.
It has also been found that bamboo acts very well in buckling but due to low stresses than compared to steel and due to it not being straight it may not be very good.
Further, it has been established that in seismic zones the failure of bamboo is very less as the maximum absorption of the energy is at the joints. Cellulose is the main component present in bamboo which is the main source of mechanical properties of bamboo.
Some specific properties of Bamboo are as given below:
Specific gravity - 0.575 to 0.655
Average weight - 0.625kg/m
Modulus of rupture - 610 to 1600kg/cm2
Modulus of Elasticity - 1.5 to 2.0 x105kg/cm2
Ultimate compressive stress- 794 to 864kg/cm2
Safe working stress in compression - 105kg/cm2
Safe working stress in tension - 160 to 350kg/cm2
Safe working stress in shear- 115 to 180kg/cm2
Bond stress - 5.6kg/cm2
Conclusion:
Scientific studies have shown that Bamboo can satisfy the various structural requirements and also due to its technical performance Bamboo can be used as a construction material for various structural components. The important advantages which make Bamboo a more suitable material are:
· It is economical and helps achieve cost effective construction.
· Bamboo is a fast growing species and it is a renewable resource which can be cultivated in most types of soil.
· The designs of the components being simple, there is no need of highly skilled labour.
· The dependency on the natural forests for wood will be reduced thus contributing to the protection of the environment.
· As it can grow in many types of soil, bamboo cultivation is suitable for rehabilitation of degraded forests and other waste lands thus converting them into fertile lands to some extent.
· Creation of employment opportunities especially for the rural people as the Bamboo mats have to be manually woven before making them into Bamboo Mat Boards, Bamboo Mat Veneer Composites and Bamboo Mat Corrugated Sheets.
· Thus due to all the above aspects there will be overall welfare of the society, particularly of the economically weaker section.
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