BAMBOO AND ITS RELEVANCE AS A SUSTAINABLE BUILDING MATERIAL

Surya Ramesh. S, Lecturer in Architecture,

Government Engineering College, Thrissur-680 009,Kerala, INDIA

ar_suryas@yahoo.com

Abstract

Bamboo is among the oldest building materials known to man. There are a wide range of uses for bamboo- from making mats and artifacts to building footbridges and pavilions. Technological innovations show new ways to tap its potential. Building industry is looking forward to new research and development in the field of sustainable building materials, and bamboo, being the fastest growing plant and having excellent strength and flexibility is among the top in the list. This paper explores the anatomy and structural properties of bamboo, some of its uses as a structural member in building construction and a few methods of preservation of bamboo. There are two case studies in which bamboo has been put to structural use. The paper concludes by emphasizing the relevance of bamboo as a material of the future, especially in India which owns one of the world’s richest resources of bamboo.

Bamboo plant

Throughout the world there are about 500 different species and hundreds of subspecies of bamboo i.e. almost 1500 varieties. For thousands of years, bamboo has benefited people in Asia, Africa and South America. The uses of bamboo are numerous. It is a building material with the strength of steel; it is used to make furniture, weapons writing and musical instruments, fuel, food and medical products. Even the first rocket was a bamboo tube stuffed with gunpowder. (bambouhabitat.com).

Bamboo grows naturally in the tropical world extending to temperate climates. Bamboo does not have a central trunk as in trees. It grows from rhizomes or rootstalks which are horizontal stems of the plant usually found underground, often sending out roots and shoots from its nodes. Rhizome gives rise to a shoot that grows into a culm, the woody stem of bamboo. Such culms grow close together as a clump. Young shoots are protected by a series of sheaths, covered with tiny sharp hairs, which will fall off as the shoot grows into a mature culm. Most bamboos are hollow. In the hollow inner area, some horizontal partitions called "diaphragms" can be seen. On the outside, these partitions are denoted by a ring around the culm. A diaphragm and the ring on the outside together form a "node". Branches grow from these nodes. The part between two nodes is called an "internode". The internodes of most bamboos are hollow; that is, they have a "cavity". The wall of the culm is called simply the "culm wall".

Characterized by the type of rhizome and the formation of upright canes there are three main groups of bamboo. The first group is called monopodial bamboos. They form long and thin extensions of the rhizome whose buds produce single shoots at regular intervals. The sympodial

bamboos constitute the second group. They have short, thick rootstocks the tips of which produce the canes. The third group is called climbing bamboos. They can grow very irregularly and may form impenetrable thickets. The main areas of distribution are the tropics. 64 % of the bamboo species are native to Southeast Asia. 33% grows in Latin America, and the rest in Africa and Oceania. Bamboo grows at sea-level and can be found at altitudes of up to 3800m. Most bamboo species grow at temperatures from -28°C to +50°C. Bamboos grow mainly on sandy loam to loamy clay soils. They prefer well drained soils but grow also in wet and even marshy locations. They do not tolerate saline soils. (Dr. Jules Janssen, INBAR 2000)

Figure 1. Anatomy of Bamboo Intermode (Wan Tarmeze Wan Ariffin, IEM, University Of Birmingham-2005)

Bamboo- A sustainable building material.

Bamboo is the fastest growing grass in the world. The species Phyllostachys Edullis can grow upto 120cm/day. Some varieties grow so large it is called timber bamboo- 120 feet high and 13" diameter. Thick bamboo poles are 2-3 times stronger than comparable size of wood timber. Bamboo can be harvested in 7 years versus 10-50 years for softwoods and hardwoods, yielding up to 20 times more than wood. A sixty foot tree cut for the market takes 60 years to replace. Asixty foot bamboo cut for market takes 59 days to replace. Being a naturally growing material, no energy is used in its ‘production’. It is non-polluting in its growth. One bamboo clump can produce 200 poles in the five years it takes one tree to reach maturity. Bamboo can be sustainably harvested and replenished with virtually no impact to the environment. (Martin Coto, 2007)

Figure 2. Growth rate of Bamboo (Texas Bamboo Society, 2009)

Engineering Properties

Bamboo has a strength/weight ratio of 897. (The strength/weight ratio of timber and mild steel are 880 and 544 respectively). It also possesses excellent flexibility. The fibers of the bamboo run axial. In the outer zone they are highly elastic vascular bundles, that have a high tensile strength, higher than that of steel, but it is not possible to construct connections that can transfer these tensile strengths. Bamboo shrinks more than wood when it loses water. Bamboo shrinks in the cross section ca. 10-16 %, in the wall thickness ca. 15-17 %. The fire resistance is very good because of the high content of silicate acid. Filled up with water, it can stand a temperature of 400° C while the water boils inside. The enormous elasticity of bamboo makes it to a very good building material for earth-quake-endangered areas. (Exhibition and international Workshop on Bamboo- Thailand 2005/06).

Another advantage of bamboo is its light weight. It can be transported and worked easily, the use of cranes is mostly unnecessary. The table shows a comparison of some engineering properties of bamboo with other materials.

Table 1. Comparison of Engineering Properties of Bamboo and other materials

Material Density Kg/m3

Compressive strength Kg/cm2

Tensile Strength Kg/cm2

Stiffness Factor

Energy Index

Concrete 2400 200 weak 10 24Mild steel 7800 4250 3700 27 146.25Timber 600 532 500 18 40Bamboo 600 645 Upto 4000 33 2.50

The stress limit to which a material can be taken without losing the ability to return to its original size or shape is called stiffness limit. Stiffness Factor = Stiffness limit/Density. In applications where a material has to undergo violent cycles of stress-applied and released-stiffness factor indicates the utility of the chosen material.

Energy index indicates the comparative energy expenditure to carry the same field load. The table shows the extremely low expenditure of energy in bamboo production to carry the same field stress as other materials. These figures of energy indices obtained from Dr. Jules Janssen’s paper ‘Mechanical Properties of Bamboos’, International workshop, 1985, China, have been drawn from energy intensive bamboo farming in the West, which would become almost negligible under Indian conditions. (Vinoo Kaley, 1998).

The tissues of bamboo enable the culm to take the weight of the foliage when it sways under strong winds. Strips of bamboo taken from different cross sectional locations of the culm possess different strengths, and also the strength increases from the core to the periphery. The bending stress of bamboo strips taken from core edge and periphery edge are 950 Kg/cm2 and 2535 Kg/cm2 respectively, and tensile stress is 1480 Kg/cm2 and 3180 Kg/cm2 respectively. Similarly they become stronger in compression and fatter towards the base of the culm. But the tensile strength is more towards the top of the culm.

Planting, cutting and seasoning

Bamboo can usually be seen growing in natural forests, homesteads and plantations. In many parts of the world, the largest stock of bamboo still grows in natural forests, the primary habitat of bamboo. Historically, the people living in and around a forest had the customary right to harvest the bamboo growing in that forest for their use and in pursuit of their livelihood. But growing bamboo on a commercial basis requires more skill on plantation management. The

management of a new plantation starts with a market survey to identify the end uses to help select the appropriate bamboo species, as well as to determine the quantity requirement, the selection of appropriate species and the selection of a site. The local climate also forms a factor in species selection. The site has to be selected with regard to soil quality, water, transport, labor force, etc., and there has to be a species-site matching.

The plantation work starts with clearing the site off shrubs and other unwanted vegetation, and the construction of access roads and sheds. Planting material (plants, cuttings or offsets) may be obtained from a bamboo forest, another plantation or a nursery. It is advisable to obtain planting material from different sources to insure against the possibility of losing the entire plantation to gregarious flowering. Obtaining the daily labor requirement for a new plantation is the next step.

A bamboo grove or plantation can not only be looked at as the production site of a building and engineering material; but it is also a haven for the living. Many birds build their nests on bamboo. It also acts as a means of erosion control, riverbank protection, landslide prevention and land rehabilitation. At intervals of two to four years up to 30 % of the mature poles are removed from the cluster. The remaining canes not only support the young shoots but also maintain the full power of the rhizomes. Two to five year old bamboo poles are considered most suitable for building and other purposes. The correct seasons for felling are autumn and winter in the subtropics and the dry season in the tropics. This reduces attack by beetles because the insects are less active. Felling is best carried out using a machete or similar tool. After felling the branches have to be carefully removed so that the outer skin of the cane is not damaged. Bamboo poles should be stored horizontally and frequently supported so that they can neither sag nor bend. They should be protected against sun, rain and soil moisture. (Dr. Jules Janssen, INBAR 2000).

Preservation

Natural durability and service life of bamboo is very short compared to other timber varieties, mainly due to its hollowness. The skin of bamboo is built of silica and wax. It protects the bamboo to a great extent, but sudden drop in moisture content causes the skin to crack, thus permitting entry of termites. If the cross sectional exposure and branching points of a whole bamboo can be sealed after bringing down the moisture gradually to a safe 12%, its life can be increased to a good extent. The main agents of decay in bamboo are fungi, beetles and termites. It is the starch in the bamboo that makes it attractive to fungi and beetles.

Durability of untreated bamboo approximately is as follows- 1-3 years in the open and in contact with soil; 4-6 years under cover and free from contact with the soil; and 10-15 years under very good storage/use conditions.

Preservation can improve these periods considerably. But bamboo is not made up in a way that facilitates preservative treatment. The outer skin, with its high silica content, resists insects and also prevents preservative from entering the culm. The inside is covered with a waxy layer that is impermeable as well. So, a preservative can enter only through the conducting vessels, which are not more than ten percent of the cross-section. They close forever within 24 hours after harvest, which means that preservation has to be carried out within this short time limit. (Dr. Jules Janssen, INBAR 2000).

Natural methods of preservation

1. Fell only mature bamboos, and fell during the dry part of the year.2. After felling, keep the culm upside down with foliage intact in a sunny place. This

exhausts the starch in the body with photosynthesis.

3. Soaking and seasoning involves the culms immediately on felling to be immersed in stagnant or running water for three months to leach out the sugars. After removal from water the wet bamboos are air-dried under shade for two weeks to bring the moisture to 12%. Split bamboo seasons faster.

4. Rotating bamboo skin on light fire after applying castor seed oil is another method.5. Smoking, treatment of the culms over fire, is effective against fungi and insects. Lime-

washing protects it against fungal attack.

Figure 3. Preservation by Smoking

Chemical Preservation

If bamboo is to be used in modern industry or in large-scale projects for housing or other buildings, chemical methods of preservation are unavoidable. It is better to avoid preservatives with chemicals like arsenic as they pose a risk to the environment as well as to the health of those handling them. Effective and safe chemicals are based on the element boron, such as copper-chrome-boron (CCB). Chemicals like boric acid, borax and boron are cheap and effective.

Immediately after felling the stem with foliage and branches intact is made to stand vertically up in a drum in a sunlit area. A solution of desired strength of active chemicals is poured into the drum up to 30cm depth. The nutritive juice in veins of bamboo gets used up in photosynthesis and chemical solution fills up the space.

In Modified Boucherie process method, the preservative is passed under pressure through the culm vessels till it comes out at the other end of the culm. This can be applied only to fresh bamboo, within 24 hours after the harvest. As the preservative is passed through the vessels, the remaining 90% of the cross section does not get any contact with the preservative.

The preservative liquid is kept in a closed drum, which is connected to one end of the bamboo with rubber tubes and sleeves tightly clamped around the end of the bamboo. An air pump provides the pressure. Air in the upper part of the sleeve has to be removed; otherwise, the upper part of the culm will remain unpreserved, resulting in badly treated culms. At first, sap will start dripping from the lower end without preservative in it. As the process continues, the concentration of preservative in the sap will increase. The process has to be continued till the whole length of bamboo gets sufficient quantity of preservative. To determine end of process, the concentration of the solution dripping from the lower end must be checked. If it nearly equals the concentration of the preservative in the tank, the process is complete. The liquid passing out of the culm may be recycled after cleaning and adding chemicals to achieve the

original concentration. After treatment, the culms must be stored under shade to dry. Dyeing lends colour to bamboo and acts as a preservative.

.Figure 4. Boucherie process

Structural Applications of Bamboo

The extensive use of bamboo in Asia has been recorded in a large number of documents, both ancient and modern. Although there is evidence that bamboo was equally important to some ancient cultures in the Americas (bamboo housing components that are about 4500 years old have been found in Ecuador), documentation of the ways and means by which it was put to use is sparse. (Jorge A. Gutiérrez, 2000). Bamboo scaffolding is a rich tradition in many Asian countries such as China, India and Thailand. Bamboo scaffolding is well known for its capacity to resist hurricanes.

The various methods of jointing in bamboo have been studied and researched extensively. Bridges built from bamboo instead of steel could provide a cheaper, more environmentally sustainable engineering solution. Bamboo as a building material for bridges has applications ranging from a few bamboo poles placed across a ditch to the twin suspended framed truss spanning a 30 - 50 m wide river.

The advantages of using bamboo as a reinforcing material in concrete are: (a) the high tensile strength and (b) the low price. The common tensile stress in steel reinforcement is 160 N/mm2

and in bamboo 20 N/mm2, a ratio of 8 to 1. The mass per volume of steel is 7850 kg/m 3 and of bamboo is about 500-700 kg/m3, a ratio of 16 to 1. Evidently, bamboo will be cheaper because the price of bamboo per weight will be less than half that of steel. But there is no bonding between the bamboo and the concrete; this is never a problem with steel reinforcement. Concrete will shrink during the hardening process and this result in a firm bond of the concrete around the steel reinforcing bars. But bamboo will absorb water as soon as the concrete is poured around it. When the concrete hardens and dries, bamboo will dry as well and shrink. The shrinkage of bamboo can be four times that of concrete. Clearly, this will completely break down any bonding between bamboo and concrete, and the result will be that bamboo cannot act

as reinforcement in concrete. But bamboo reinforced cement mortar is a good alternative as the second case study shows.

Case studies

ZERI Pavilion and Foot bridge, Colombia by architect Simon Velez The ZERI organisation (Zero Emission Research Initiative) pavilion, which was build for the EXPO 2000 in Hannover, is one of the largest bamboo structures in the world. The bamboo canes are connected using thread rods and concrete/mortar injections. This new technology allows realizing impressive constructions and great spans. Simon Veléz´s project is a circular bamboo structure, or more precise a ten-sided polygon 40 meters in diameter with a peripheral overhang seven meters wide, so not only the interior of the open pavilion but also the construction is protected from rain. The building rests on two concentric courses of 20 supporting wooden pilars measuring 8 to 14 meters height. The pavilion provides 2,150m²floor-area on two levels (1,650m² at ground level and 500m² on first floor galllery).

Figure 5. Prototype of the ZERI Pavilion (www.zeri.org/case_studies.htm)

Figure 6. Foot bridge by architect Simon Velez in Colombia

Inspiration- Architects’ office, Kerala

Office building of area 2750 Sft. Thin RCC columns and ferro-cement beams form the structural grid. The infill floor, walls and roof of the building are constructed using bamboo reinforced plaster or micro-steel reinforced mortar bamboo composite. The temperature difference between the exterior and the interior averages 4-5 degrees on a hot summer day. The dead load of the composite is 1500 N/m2 and the live load is taken as 4000 N/m2. The building is also analyzed for wind and earthquake loads. All bamboo used on the building has been given

preservative treatment of CCB. Also Liquid Organic Solvent Preservative (LOSP) cold dip treatment for in-situ bamboo is suggested. It is a non-hazardous trichlorophenol formulation which can be used to replace water soluble preservatives. Bamboo replaces almost 80% of structural cement and steel, the self weight of the building is reduced by around 50% in comparison to a conventional building of the same nature.(Inspiration, 2002).

Figure 7. Inspiration office

Prefab Bamboo panels

Industrial processes such as prefabricated bamboo panels need to be developed if bamboo is to contribute towards housing the one billion homeless people in the world. It must also be mentioned that industries provide large-scale employment.

Figure 8. Houses constructed using prefabricated bamboo panels

Conclusion

As a building material the relevance of bamboo is undeniable. With the right kind of research, the potential of bamboo can be used more efficiently. As a renewable and sustainable resource, bamboo should be grown on industrial basis thus generating more jobs and also providing

solutions for mass housing problems. Thus undoubtedly structural bamboo can become the material of the future. Acknowledgements

Architect Latha Raman, Inspiration, CochinArchitect Prasad Jonathan

References

International Bamboo Building Design Competition, Bamboo Technologies.com, Haiku HI, USA, 2007

Jorge A. Gutiérrez, International Network for Bamboo and Rattan, LANAMME, “Structural Adequacy of Traditional Bamboo Housing in Latin America” 2000

Jules J.A. Janssen, Designing and Building with Bamboo, Technical Report 20, International Network for Bamboo and Rattan, 2000

Kaley Vinoo, ‘Venu Bharati’, 1998

Wan Tarmeze Wan Ariffin, IEM, University Of Birmingham, 2005

www.texasbamboosociety.net

www.zeri.org/case_studies.htm