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.
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”:
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.
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.
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.
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 mats can be fastened to the bamboo posts or mats can be woven, mud can also be applied to both sides of such mats. 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.
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.
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.
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.
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.