The authors are particularly grateful to the International Network for Bamboo and Rattan (INBAR) for the technical assistance provided during preparation and editing. Appendices 1 to 5 have been reproduced from the publication "INBAR Technical Report No. 3" by Satish Kumar, K. S. Shukla, lndra Dev and P. B. Dobriyal, with the kind permission of the Indian Council of Forestry Research and Education (ICFRE), INBAR and the International Development Research entre (IDRC).

Special thanks are extended to Mr M. W. Parkes, the former DFID Senior Architectural and Planning Adviser, and Mr M. Mutter, the present Adviser, without whose support and guidance this book could not have been published.

Preface

Bamboo is one of the oldest and most versatile building materials with many applications in the field of construction, particularly in developing countries, It is strong and lightweight and can often be used without processing or finishing. In spite of these clear advantages, the use of bamboo has been largely restricted to temporary structures and lower grade buildings due to limited natural durability, difficulties in jointing, a lack of structural design data and exclusion from building codes.

The diminishing wood resource and restrictions imposed on felling in natural forests, particularly in the tropics, have focused world attention on the need to identify a substitute material which should be renew-able, environmentally friendly and widely available. In view of its rapid growth (exceeding most fast growing woods), a ready adaptability to most climatic and edaphic conditions and properties superior to most juvenile fast growing wood, bamboo emerges as a very suitable alternative. However, in order to fully exploit the potential of bamboo, development effort should be directed at the key areas of preservation, jointing, structural design and codification. In addition, socio-economic, appropriateness and technical studies will be essential to identify factors which govern current bamboo usage, and those which will influence its use in the future. Once these issues have been addressed, bamboo will be ideally placed to become a principal engineering and construction material for the twenty first century and beyond.

1. Introduction

Bamboo has a long and well established tradition as a building material throughout the world’s tropical and sub-tropical regions. It is widely used for many forms of construction, in particular for housing in rural areas. Bamboo is a renewable and versatile resource, characterised by high strength and low weight, and is easily worked using simple tools. As such, bamboo constructions are easy to build, resilient to wind and even earthquake forces (given the correct detailing) and readily repairable in the event of damage. Associ-ated products (bamboo based panels and bamboo reinforced concrete, for example) also find applications in the construction process.

There are however a number of important considera-tions which currently limit the use of bamboo as a universally applicable construction material:

Durability: bamboo is subject to attack by fungi and insects. For this reason, untreated bamboo struc-tures are viewed as temporary with an expected life of no more than five years

Jointing: although many traditional joint types exist, their structural efficiency is low (Herbert et al. 1979). Considerable research has been directed at the development of more effective jointing methods.

Flammability: bamboo structures do not behave well in fires, and the cost of treatment, where avail-able, is relatively high.

Lack of design guidance and codification: the engineering design of bamboo structures has not yet been fully addressed.

The aim of this publication is to offer a general intro-duction to bamboo as a construction material, with the key areas of preservation and jointing addressed in more detail.

A range of chemical and non-chemical treatment methods is discussed and appropriate preservative formulations and treatment schedules are presented. Consideration is given to environmental and health and safety issues, and areas requiring further research are highlighted.

The section on jointing attempts to summarise and illustrate the many different joint types and connection methods that have been devised, from traditional techniques to recent developments. It is hoped that this accumulated knowledge will inspire further work in this area.

2. Protection of bamboo

Natural durability As with all timbers, the service life of bamboo is governed by its exposure position and durability, which together dictate the rate of attack by biological agents. In general it has been found that untreated bamboo has an average life of l-3 years where it is directly exposed to soil and atmosphere. When used under cover, the life expectancy of bamboo increases to 4-7 years. Under very favourable circumstances, the service life of bamboo can be as high as 10-I 5 years, for example when used for rafters and internal framing.

The chemical constituents of bamboo are known to vary greatly depending on species, position within the culm and the age of the culm. In very general terms bamboo consists of 50-70% hemicellulose, 30% pentosans, and 20-25% lignin (Tamolang et al. 1980, Chen et al. 1985). 90% of the hemicellulose is xylan with a structure intermediate between hardwood and softwood xylans (Higuchi, 1980). The structure of the lignin present in bamboo is unique, and undergoes changes during the elongation and ageing of the culm (Itoh et al. 1981). Bamboo is known to be rich in silica (0.5-4%), but almost the entire silica content is located in the epidermis layers, with hardly any silica in the rest of the wall. Bamboo also has minor amounts of resins, waxes and tannins. However, none of these have sufficient toxicity to impart much natural durability to the culms. Laboratory tests have indicated that bamboo is more prone to both soft rot and white rot attack than to brown rot (Liese, 1959).

The natural durability of bamboo varies according to species. For example, Dendrocalamus strictus is known to be less resistant to termites than Dendroca-Iamus longispathus. Although the culms of a few bamboos, notably Guadua angustifolia, appear to have a relatively high resistance to wood eating insects and decay fungi, they are all susceptible to biodegradation. Variation in durability has also been observed along the length of the culm and through the thickness of the wall. The lower portion of the culm is considered more durable, while the inner part of the wall deteriorates faster than the outer harder portion. This is probably related to the anatomical and chemical nature of the woody cells.

Because of the lack of any toxic constituents, bamboo forms a ready food source for a variety of organisms. The presence of considerable quantities of starch in green or dry bamboo makes it more attractive to such organisms, especially stain fungi and borer beetles (Beeson, 1941, Gardener, 1945, Mathew et al. 1990, Gnanaharan et al. 1993). The most serious borers of felled bamboo are Lyctus and three species of Dinoderus (celluris, minutes, brevis), which attack bamboo rich with starch (Casin et al. 1970, Sandhu, 1975). They cause immense damage during drying, storage, and subsequent use. Carpenter bees and termites also attack bamboo (Beeson, 1938, Sensarma et al. 1957). Bamboo is susceptible to attack by marine organisms and, when used in sea water, can be destroyed in less than a year (Anon, 1945),

Protection of plantations Only a limited amount of research has been carried out into insect pests of standing bamboo. However, some defoliators (Mathur, 1943), bamboo stem beetles (Roonwal, 1977), weevil borers (Chatterjee et al. 1964) and sap suckers (Singh, 1988) have occasionally been observed.

Defoliators can be controlled by spraying with 0.2% fenitrothion or 0.1% carbaryl in water with a sticker. Silvicultural controls work better with weevils, while sap suckers can be controlled by spraying kerosene oil in soap emulsion or folian spray with 0.04% dimacron/ rogor or 0.2% fenitrothion.

Dangers from fungal attack are low in plantations, but vigilance is necessary during normal silvicultural practices in the event that some protection or control is needed (hilohanan et al. 1990).

Protection pre- and post-harvesting In bamboo, soluble sugars form the principal nutrients for degrading organisms. Therefore, if these can be by non-chemical removed from the culms, the risk of decay is signifi-methods cantly reduced. A number of methods for lowering the sugar content have been adopted:

Felling during low sugar content season

Felling of mature bamboo

Post-harvesting transpiration

Water soaking

These methods are outlined below.

Fell i ng of bamboo during low sugar Sugar content season content in almost all plants varies according to season. In India, for example, it is higher in spring than in winter (Joseph, 1958). It is therefore advisable to harvest bamboo during the winter months.

Felling of mature bamboo when sugar Sugar content is low content in bamboo varies with age and is lowest during the first year. However, the usefulness of very young bamboos is limited due to their low strength and yield.

Post-havesting transpiration of bamboo culm Sugar content in bamboo can also be reduced by keeping culms upright or leaning them against trees for a few days, with the branches and leaves intact. Parenchyma cells in plants continue to live for some time, even after felling. During this period, the stored food materials are utilised and thus the sugar content of the bamboo is lowered.

Water soaking of bamboo The soaking method is commonly used in many Asian and African countries and consists of submerging freshly cut culms for 4-12 weeks in stagnant or running water, or mud (Sulthoni, 1987). Generally, stones are placed on top of the bamboo to keep it submerged during the soaking period.

During the process of soaking, the starch content of the parenchyma cells of the culm is reduced by dilution. As a result it is claimed that the bamboo is more resistant to wood borers. It is important to realise that treatment using this method does not confer added protection to the bamboo. It merely reduces the inherent susceptibil-ity of the material.

Comments The best likely protection will result from a combination of the above methods, for example harvesting mature culms during the winter months, leaving them upright for a few days after harvesting and then soaking them in water for 4-l 2 weeks.

Efforts have also been made to correlate the natural durability of bamboo with phases of the moon (Kirkpatrick et al. 1958), but any connection appears to be more myth than scientific fact.

Protection pre- and post-harvesting by chemical methods Pilot-scale trials for short term protection of bamboo were carried out at three different mills under different climatic conditions in India by the Forest Research Institute, Dehra Dun. Stacks of bamboo were prepared following the pattern adopted by individual mills in a crisscross arrangement, and were treated by the same chemicals found effective in laboratory trials with minor variation in chemical ratio. The material was assessed after different storage periods, both with and without prophylactic treatment, for incidence of fungal and borer attack (Table 1, Kumar et al. 1985).

The use of PCPs is under constant review from a health, safety and environmental stand-point. Note that the efficacy of boric acid/borax (relatively safe chemicals) is comparable with that of PCP formulations.

Laboratory and field trials have shown that losses from fungi and insects can be significantly reduced if proper treatment is carried out at the time of stacking, even under open storage. It should be noted that pest attack of stored bamboo can be sporadic. For instance, with beetle attack of reed bamboo, harvesting season and mode of transportation (by water or road) are not important, but maturity of the culms is the key element.

For long term storage of bamboo in the open, it is recommended that the stacks are raised on specially prepared ground to prevent termite attack. The stacks should be profusely treated during different stages of stack forming (i.e. at 3, 4, 5 and 6 metres height) and can be covered with treated bamboo mats or grass thatch. However, coverings produced from non-biological materials can offer improved protection as they are less likely to harbour a reservoir of infection.

For protection of structural bamboo (if stored outside), repetition of the treatment after four to six months is recommended. Such bamboo can be treated with any of the compositions listed in Appendix 2.

In all cases, treatment must be carried out in a safe and responsible manner. For example, the use of fine spray nozzles can result in more than 50% preserva-tive loss and heavy pollution of the environment.

3. Preservation of bamboo

Bamboo is subject to attack by micro-organisms and insects in almost any construction application. Unfortu-nately, like most lignocellulosic materials, bamboo has very low resistance to biological degrading agents The service life is therefore mainly determined by the rate of attack.

A variety of methods to improve the durability of bamboo have, however, been developed. Several of these techniques are described here with the aim of providing helpful guidelines to users.

Non-chemical (traditional) methods of preservation Non-chemical methods of preservation, otherwise known as traditional methods are widely used by villagers and can be undertaken without the use of any special or sophisticated plant and equipment or significant increase in costs. Typical traditional methods include:

Smoking

Whitewashing

Elevated construction

Smoking method Traditionally, bamboo culms are placed above fire-places inside the house so that the smoke and heat rises up and both dries and blackens the culms. It is possible that the process produces some toxic agents that provide a degree of protection. Alternatively, the heat generated by the fire could possibly destroy or reduce the starch content of the parenchyma cells by pyrolysis.

Whi tewashing method Bamboo culms and bamboo mats for housing construction are often painted with slaked lime. This is carried out mainly to enhance the appearance, but there is also an expectation that the process will prolong the life of the bamboo structure by preventing moisture entering the culms. It is possible that water or moisture absorption is delayed or in some cases

prevented which will provide a higher resistance to fungal attack. However, there remains a question as to whether the bamboo can be weakened over time by such an alkaline treatment.

In Indonesia, bamboo mats are tarred and later sprinkled with a layer of sand. When this is dry, up to four coats of whitewash are applied. Plastering is also a common practice, using cow dung mixed with either lime or mortar (see WaIl s in Chapter 5).

Elevated const r uctio n method The elevated construction method is designed to prevent the bamboo coming into direct contact with the ground by placing the bamboo posts on stones or pre-constructed cement walls (see Foundations in Chapter 5). In this way the bamboo can be kept dry, thereby reducing deterioration due to fungal attack. Good air circulation throughout the structure is also necessary. Furthermore, treatment of the bamboo with water repellent formulations reduces the hygroscopic properties with the effect that moulds are discouraged.

In addition, careful attention to construction detailing will help to enhance the service life of the building (see Detail in g for durabi li ty in Chapter 5).

Comments Undoubtedly traditionally treated bamboo culms show increased resistance to insect and fungal attack when compared to freshly cut bamboo culms. However, because of the low natural resistance of bamboo to biological deterioration, the methods do not provide durability of product or structure in the long term and therefore offer no real cost saving benefits.

Chemical treatment methods Bamboo culms have a number of important chemical and anatomical differences from hardwoods and softwoods. These differences have a significant influence on the efficacy of treatments applied to bamboo. Three major anatomical differences that influence the penetration of preservative solution between bamboo culms and hardwoods and softwoods can be identified:

The ray cells in hardwoods and softwoods are linked to form a radial transport system. These structures are absent from bamboo where there are no cells to facilitate an easy movement of liquids in the radial direction.

The vessels, which run axially between the inter-nodes, are isolated from each other by parenchyma cells. The vessels branch extensively within the node region of the culms. There is a gradation in vessel size - small at the periphery of the culm and larger in the centre.

The outside wall of the culm is lined with epidermal cells. The inner layer of cells is heavily lignified and appears thicker. The outermost cells of the culm have a waxy coating and the inside of the culm is composed of numerous sclerenchyma cells.

This anatomy and structure mean that there is very little opportunity for radial movement of liquids. Therefore, preservative penetration pathways exist only at the cut culm ends and, to a lesser extent, at the scars around the nodes.

The penetration of liquids into the culm takes place through the vessels in the axial direction, from end to end. To ensure a satisfactory treatment process for the bamboo it is necessary for the treatment solution to diffuse from the vessels into the surrounding fibres and parenchyma cells. The vessels only account for about 5-1 0% of the barn boo cross section. Thus even when the vessels are filled to saturation point, the bamboo can still be vulnerable to fungal or insect attack if the preservative does not diffuse sufficiently into the main tissue of the culm.

When compared to traditional methods, the use of chemicals for the preservative treatment of bamboo is more effective in providing protection against biological deterioration. However, chemical preservatives are invariably toxic and due care and attention should be exercised whenever they are used (see Chapter 4, Health, safety and envi ro nment al aspects of preserv a- tive treat ment) .

The following chemical treatment techniques are described below:

Butt treatment

Open tank method for cold soaking

Boucherie method

Modified Boucherie method

Pressure treatment

l-lot and cold bath process

Glue line treatment

The types of preservative suited to these methods of application are listed in Appendices 2-4. The applica-tion of fire retardant treatments is also addressed.

Butt treafmenf The butt ends of freshly cut culms, with the branches and leaves intact, are placed in a drum containing the preservative. The continued transpiration of the leaves draws the chemical solution into the vessels of the culm. The method is used for the treatment of shorter culms with a high moisture content (green or freshly cut). The treatment process is very slow and often the vessels do not take up enough of the liquid to preserve, by diffusion, the surrounding fibres and parenchyma cells. The preservative in the barrel must be replenished regularly in order to maintain the desired level. When the treatment has been completed, care should be taken in the disposal of the contami-nated foliage.

Butt treatment is usually applied to bamboo posts. Such posts are often used for fruit supporting sticks in banana plantations.

Open tank method for coId soaking The open tank treatment method (figures 1 and 2) is economical, simple and provides good effective protection for bamboo. Culms, which have been prepared to size, are submerged in a solution of a water-soluble preservative for a period of several days. The solution enters the culm through the ends and sides by means of diffusion.

Immature bamboo culms can be penetrated by preservative solution more easily than mature culms. This is probably largely due to the increased lignifica-tion present in mature culms.

Also, penetration is easier with dried culms than with freshly cut (green) culms. Green culms are difficult to treat because they are likely to have a moisture content in excess of 100%. As a result there will be little or no room for additional liquid within the culm. Preservative concentration should therefore be higher when green culms are being treated. Following soaking, the culms should be wrapped to enable further diffusion of the preservative.

Since the inner skin of the culm is slightly more permeable than the outer skin, split culms can be treated more effectively than round culms. Some success in the treatment of bamboo has been obtained by punching the internode region of the culms. Admit-tedly, this operation is probably not practicable on a commercial basis. Mechanical scratching of the outer skin of the culm can help to speed up the penetration, especially where slow diffusing preservatives are used.

The time of treatment can be reduced considerably by using the hot dipping or the hot and cold method (see Hot and col d bath process). A double treatment can also be applied although this technique is fraught with commercial and technical difficulties that effectively prevent its use in practice.

Boucherie method The Boucherie method requires the culms to be in a green condition. The water-transporting part of the culm can be penetrated completely and the treatment itself is applied by an inexpensive installation.

Preservative is fed by gravity from a container placed at a higher level than the culm through pipes into its base end (figure 3). The culms are fastened to the tubes by rubber sheaths and clamps. It is also possible to hang the culm vertically and to scratch the inner wall of the top internode in order to use it as a reservoir for treatment. The treatment is terminated when the solution at the dripping end shows a sufficiently high concentration of chemicals.

The duration and success of the treatment process depends on the type of preservative, its adhesion and precipitation, and the swelling influences on the cell wall. Preservatives with high adhesion can stop flowing through the culm in a relatively short period of time, blocking the vessels and pits. Also, if the moisture content of the culm is too low, water is withdrawn from the preservative solution causing precipitation and blocking the vessels. The best results are therefore obtained during or shortly after the rainy season, using younger culms with a higher moisture content.

Allowing the bamboo to dry slowly in the shade for a period of at least two weeks after treatment ensures that the solution diffuses into all of the tissue surrounding the vessels

Modified Boucherie method The basic Boucherie method has been improved by the introduction of pneumatic pressure over the preservative fluid in a reservoir, for example by using an air pump (A. Purushotham et al. 1953) or electric pump. The preservative is forced axially through the culm by the air pressure in the reservoir. In this way the time of treatment can be reduced from several days to 3-8 hours. In other respects the process is similar to that for the basic Boucherie method.

The modified Boucherie apparatus is illustrated in figure 4. A detailed manual on the operation of the modified Boucherie apparatus has been prepared by the Environmental Bamboo Foundation in Bali, Indonesia.

Pressure treatment method Pressure treatment, using either creosote or water- borne preservatives, offers the best method of preser-vation for bamboo culms. The applied pressure ranges from around 0.5-l .5N/mm 2 (5-15 bar) and as such requires special plant and equipment. Accordingly, costs are high, but a service life of up to 15 years can be expected from adequately treated bamboo when used in the open and in contact with the ground.

In order to achieve sufficient chemical penetration and absorption, the culms must be air dried prior to treatment. Also, since the inner skin of the culm is slightly more permeable than the outer skin, split culms can be treated more effectively than in the round.

Hot and cold bath process When pressure treatment facilities are not available the hot and cold bath process offers an acceptable alternative. The bamboo is submerged in a tank of preservative which is then heated, either directly over a fire or indirectly by means of steel coils in the tank. The bath temperature is raised to about 90°C held at that temperature for about 30 minutes and then allowed to cool.

When using preservatives which can precipitate when heated, it is best to pre-heat the bamboo in a suitable liquid, such as water, and then transfer the hot bamboo into a separate tank containing cold preservative. In order to assist the effectiveness of the treatment, the impermeable diaphragm of the nodes should be cleanly bored through, thus providing uninterrupted access throughout the culm for the preservative.

When the treatment process has been completed, the bamboo should be allowed to dry slowly to allow further diffusion of the preservative to take place.

Glue line treatment Glue line treatment is specific to the manufacture of bamboo mat board and involves adding preservatives to the glue during manufacture. This process is also more economical than using adhesives of a higher solid content. Additives which have been shown to provide effective preservative treatment without impairing the bond strength of the mat board include 1% Chlordane or 1% sodium octaborate tetrahydrate with a 1:2 diluted PF solution containing 17% solid content (Padmanabhan et al. 1994).

Fire retardant treatment Fire presents a potential hazard in any form of con- struction, but the risk is especially high in bamboo buildings. The combination of bamboo and matting, and the tendency of the internodes to burst causes rapid fire spread. The danger is increased when the joint lashings are destroyed, which can cause cata-strophic collapse of the building.

It is, however, possible to treat bamboo with a combi-nation of preservative and fire retardant chemicals. The process is normally carried out by pressure treatment. A commonly used chemical composition is shown below:

The cost of fire retardant treatment is generally high and is therefore often considered inappropriate. The importance of finding a suitable and cost effective treatment, which will provide combined protection against bio-degrade and fire, is a necessary area for further research. Boron based retardants offer a possible solution, with the added advantage of being relatively safe to use.

Drying of bamboo Green bamboo can have a moisture content of 100-150%, depending on the species, area of growth and felling season. The chemical composition of bamboo results in a comparatively higher hygroscopic-ity than wood. Additional problems in the drying of bamboo occur because the material lacks an efficient radial transport system and possesses a waxy coating. Therefore, the major pathway for the loss of moisture is from the ends of the culms (Sekhar et al. 1964, Laxmana, 1985).

The liability to biological degradation and to deforma-tion owing to excessive shrinkage (which occurs even above the fibre saturation point) necessitates quick drying of bamboo.

Kiln drying At the present level of drying technology, kiln drying of round bamboo is not feasible. Even mild drying conditions can increase the incidence of cracking and collapse (Rehman et al. 1947). Split bamboo can, however, be kiln dried.

Air drying Air drying takes 6-12 weeks, depending on the initial moisture content and wall thickness. Collapse can be a major problem in some species, owing to excessive and non-uniform shrinkage of the culm. However, problems are mostly seen in drying of immature culms.

Air drying of split bamboo does not pose any problems, even in direct sunlight. Split bamboo standing upright dries faster than when stacked horizontally. Round bamboo can also be dried standing upright or in stacks, using bamboo crossers of appropriate diameter.

Developmental needs While chemical treatment has proved to prolong the serviceable life of bamboo by making the material more resistant to decay caused by fungal and insect attack, it is nevertheless the subject of continued research and investigation in order to find the best and safest forms of application, and at the same time to improve cost effectiveness. Future benefits for bamboo could emerge from the results of bio-genetic research. In the meantime the current lack of management expertise and commercial energy required to achieve the maximum benefits from the existing technology is depriving many regions and indigenous communities of significant improvements to their standards of living.

In addition to the design and support of new research programmes, the governments concerned, together with appropriate institutions, must take the lead role in establishing the necessary technical, commercial and economic framework for the wider use of treated bamboo through:

The advancement of developments through international co-operation

The introduction of building legislation

The formulation of health and safety regulations

The use of technically and commercially trained management teams to assess the best treatment process for the locality or region

The provision and/or establishment of suitable and safe treatment facilities

The promotion of education, training and appropri-ate marketing techniques

4. Health, safety and environmental aspects of preservative treatment

The methods of preservative treatment described under non-chemical (traditional) techniques in Chapter 3 are considered very safe and pose little threat to health or risk of environmental pollution. However, these benefits are offset by the limited scope of such methods for extending the service life of bamboo.

Chemical preservation methods employ substances toxic to fungi and insects which are also invariably toxic to mammals Nevertheless, the preservatives listed in Appendix 2 (under constant review by various pollution control agencies) have good safety records when used correctly. Formulations containing arsenic and chro-mium have been rigorously tested for leaching in laboratory and under service conditions, and meet current safety standards. Such formulations make complexes with wood substances and are rendered safe, and are therefore unlikely to present any toxicity threat. Rather, the danger with such chemicals arises from the formulation and impregnation process itself. Slight carelessness in handling of either the chemicals or freshly treated materials can pose serious risks to humans and animals alike. Proper safety garments such as gloves, aprons and eye protection glasses should be worn, and any spillage of chemicals should be immediately attended to. Freshly treated material should be stored under cover during drying to avoid rain leaching of chemicals. A useful reference book covering these issues has been issued by UNEP (Anon, 1994).

Boric-acid, borax and Cu/Zn naphthenates/abietates are among the safest preservatives and are in use world-wide. Many new chemicals considered to be environmentally safe such as Tebuconazole, IPBC (3-iodo 2-propanyl butyl carbamate), chloro-thalonil, isothiozolones and synthetic pyrethroides are under Boric-acid, borax and Cu/Zn naphthenates/abietates are among the safest preservatives and are in use world-wide. Many new chemicals considered to be environmentally safe such as Tebuconazole, IPBC (3-iodo 2-propanyl butyl carbamate), chloro-thalonil, isothiozolones and synthetic pyrethroides are under

Pollution hazards exist at formulation as well as impregnation sites. It is suggested that premixed and ready-to-use formulations should be used to minimise the risks and that necessary safety precautions as specified by the manufacturers should be rigorously followed. Treatment effluents, if generated on a large scale, should be adequately treated before disposal.

Disposal of preservative treated bamboo after pro-longed service can present a problem. In some countries, it is not considered a hazardous waste, but in others it has to be brought to special dumping sites.

5. Construction methods

The majority of bamboo construction relates to rural community needs in developing countries. As such, domestic housing predominates and, in accordance with their rural origins, these buildings are often simple in design and construction relying on a living tradition of local skills and methods. Other common types of construction include farm and school buildings and bridges.

Further applications of bamboo relevant to construction include its use as scaffolding, water piping, and as shuttering and reinforcement for concrete. In addition, the potential number of construction applications has been increased by the recent development of a variety of bamboo based panels.

Domestic housing and small buildings There is a long-standing tradition of bamboo construc- tion, dating back many hundreds of years. Different cultures have found in this material an economical system of building, offering sound yet light and easily replaceable forms of shelter. The methods, activities and tools are often simple, straightforward accessible to even the young and unskilled 1995).

Bamboo can be used to make all the components of small buildings, both structural and non-structural, with the exception of fireplaces and chimneys. It is, how-ever, often used in conjunction with other materials, cost and availability permitting.

A typical building comprises the following elements:

Foundations

Floors

Walls

Roof

Doors and windows

Water pipes

Bamboo building construction is characterised by a structural frame approach similar to that applied in traditional timber frame design and construction. In this case, the floor, wall and roof elements are intercon-nected and often one dependent on the other for overall stability. A recent study by Arce (1995) has highlighted the need to control lateral deformations inherent in some traditional forms of building.

The adequacy and suitability of the building for occupancy will also depend to a large extent on good detailing, for example to help prevent water and moisture ingress, fungal attack and vermin infestation.

All of the above features are dealt with in the following sections.

Foundations The types of bamboo foundation identified are:

Bamboo in direct ground contact

Bamboo on rock or preformed concrete footings

Bamboo incorporated into concrete footings

Composite bamboo/concrete columns

Bamboo reinforced concrete

Bamboo piles

Bamboo in direct ground contact Bamboo, either on the surface or buried, can decay within six months to two years. Preservative treatment is therefore recommended. For strength and stability, large diameter thick walled sections of bamboo with closely spaced nodes should be used. Where these are not available, smaller sections can be tied together.

Bamboo on rock or preformed concrete footings Ideally, where bamboo is being used for bearings it should be placed out of ground contact on footings of either rock or preformed concrete (see figure 5). As above, the largest and stiffest sections of bamboo should be used.

Bamboo incorporated info concrete footings The third approach is to incorporate the bamboo directly into the concrete footing. This can take the form of single posts or strip footings (figures 6 and 7).

Composite bamboo/concrete columns An innovative development involves the casting of a concrete extension to a bamboo post using a plastic tube of the same diameter (Janssen, 1995). The result is a bamboo post with an integral, durable foundation (figure 8).

Bamboo reinforced concrete Bamboo reinforced concrete slabs offer another solution, although this type of construction has its own specific problems. These are dealt with in more detail in Chapter 7.

Bamboo pi/es Bamboo piles have been used successfully to stabilise soft soils and reduce building settlement. In the example cited (Stulz, 1983), treated split bamboo piles 8m long and 80 to 90mm in diameter were filled with coconut coir strands wrapped with jute. The sections were then tied with wire. After installation of the piles at 2m centres by drop hammer, the area was covered with a 2.5m surcharge of sandy material (see figure 9).

Floors The floor of a bamboo building may be at ground level, and therefore consist only of compacted earth, with or without a covering of bamboo matting. However, the preferred solution is to raise the floor above the ground creating a stilt type of construction. This improves comfort and hygiene and can provide a covered storage area below the floor. A minimum ground to floor distance of 500mm is recommended to allow for inspection (Janssen, 1995). When the floor is elevated, it becomes an integral part of the structural framework of the building. The floor will comprise:

structural bamboo elements

bamboo decking

Floor structure Floors normally consist of bamboo beams fixed to strip footings or to foundation posts. The beams therefore run around the perimeter of the building. Where the beams are fixed to posts, careful attention to jointing is required (see Chapter 8, Jointing techniques). Beams and columns are generally around 1 00mm in diameter.

Bamboo joists then span in the shortest direction across the perimeter beams. The joists are often laid on the beams without fixing, but some form of mechanical connection is recommended. Depending on the form of floor decking, secondary joists, often taking the form of split culms, may be required. Joist diameters are in the order of 70mm. Joist centres are typically 300 to 400mm, or up to 500mm if secondary joists are used (figures 10 and 11).

Floor decking Bamboo floor decking can take one of the following forms:

Small bamboo culms

Split bamboo

Flattened bamboo (bamboo boards)

Bamboo mats

Bamboo panels

Bamboo parquettes

Small bamboo culms: small diameter culms are tied or nailed directly to the joists (figure 12).

Split bamboo: bamboo culms are split along their length into strips several centimetres wide. They can be fixed directly to the joists in the case of tying or nailing, or a timber batten can be fixed to the joist beforehand to facilitate nailing (figure 13).

Fla ttened bamboo (bamboo boards): these are formed by splitting green bamboo culms, removing the diaphragms then unrolling and flattening them. The resulting board is laid across the joists and fixed by nailing or tying (figure 14).

The surface finish of these three types of floor deck is, understandably, uneven and difficult to clean. They can be screeded with cement mortar for reasons of hygiene and comfort.

Bamboo mats: these are formed by weaving thin strips of bamboo. Strips vary in size from 20 x 2mm to 2 x i mm, depending on the intricacy of the pattern. Some examples are shown in figure 15.

Mats should not be fixed by direct nailing, but are held in place by bamboo strips or timber battens tied or nailed over the top (figure 16). This is one of the easiest types of traditional floor to keep clean.

Bamboo panels: layers of woven mats or strips, laid at right angles, are bonded together into boards (see Bamboo based panels in Chapter 7), which are then nailed to the joists.

Bamboo parque tte: thin slivers or mats of bamboo are formed into multi-layered tiles and laid on treated bamboo or wooden strips fixed to compacted earth or a concrete sub-floor.

Walls The most extensive use of bamboo in construction is for walls and partitions. The major elements of a bamboo wall (posts and beams) generally constitute part of the structural framework. As such they are required to carry the self-weight of the building and also loadings imposed by the occupants, the weather and, occasionally, earthquakes. To this end, efficient and adequate jointing is of primary importance (see Chapter 8, Jointing techniques).

An infill between framing members is required to complete the wall. The purpose of the infill is to protect against rain, wind and animals, to offer privacy and to provide in-plane bracing to ensure the overall stability of the structure when subjected to horizontal forces. The infill should also be designed to allow for light and ventilation. Not least is its architectural and aesthetic function.

This infill can take many forms:

Whole or halved vertical or horizontal bamboo culms, with or without bamboo mats

Split or flattened bamboo, with mats and/or plaster

Bajareque

Wattle (wattle and daub, lath and plaster, quincha)

Woven bamboo, with or without plaster

Bamboo panels

Whole or halved bamboo culms The preferred orientation is vertical as this increases the shear resistance of the wall and is also better for drying after rain. Vertical members can be driven directly into the ground or fixed back to beams by tying with or without facing battens (figure 17). Halved culms can be fixed in the same way, either as a single or double ply construction, or anchored between horizon-tal halved culms (figure 18). Woven bamboo mats can be attached to one or both faces using tied or nailed bamboo battens.

Split or flattened bamboo Split or flattened bamboo (see also Floors) can be fixed vertically to intermediate bamboo members tied to or mortised into the posts, or fixed horizontally directly to the posts. Boards can be stretched or covered by wire mesh to provide a suitable surface for plastering. Closely woven matting can also be applied to the board surface, with or without plaster.

Bajareque This is a type of construction commonly employed in Latin America. It consists of horizontal bamboo strips tied or nailed to both sides of the posts. The cavity is then filled with mud or mud and stones, producing a relatively massive form of construction (figure 19).

Wattle wattle and daub, lath and plaster, quincha Common in parts of India, Peru and Chile, this com- prises coarsely woven panels of bamboo strips (vertical weft and horizontal warp), plastered on both sides (figure 20).

Woven bamboo Coarsely woven panels similar to those for wattle but with closer wefts can be used with or without plaster (figure 21).

The plaster can be made from any combination of mud, clay, and sand, stabilised with lime, cowdung, cement and organic fibres. The surface can be finished with a lime wash to give a typical stucco appearance (Jagadeesh and Ganapathy, 1995).

Preservatives may be added (Satish Kumar et al. 1994), but due attention should be paid to health, safety and environmental matters.

Bamboo panels Panels have been developed specifically for use in walls and partitions and have the advantage of imparting greater structural rigidity to the construction (see Bamboo based panels in Chapter 7).

Bamboo has also been used as a reinforcement for stabilised or rammed mud walls (Mishra, 1988). However, difficulties exist in achieving an adequate bond between the mud and bamboo to ensure composite action.

Roofs The roof of a building is arguably its most important component - this is what defines a construction as a shelter. As such, it is required to offer protection against extremes of weather including rain, sun and wind, and to provide clear, usable space beneath its canopy. Above all, it must be strong enough to resist the considerable forces generated by wind and roof coverings. In this respect bamboo is ideal as a roofing material - it is strong, resilient and light-weight.

The bamboo structure of a roof can comprise "cut’ components - purlins, rafters and laths or battens, or triangulated (trussed) assemblies. Bamboo, in a variety of forms, is also used as a roof covering and for ceilings.

Roof structure Tradit ional roof construcfion: The simplest form of roof comprises a bamboo ridge purlin and eaves beams, supported on the perimeter posts. Halved culms are then laid convex side down, edge to edge, spanning from the ridge to the eaves. A second layer, convex side up, is then laid to cover the joints (figure 22). The maximum overall span using this method is about 3 metres.

A variation on this is the use of whole culms, suitably spaced to accept battens for tiles or thatch (see Roof covering). To extend the span, a central post can be used. Beyond this, the options are almost infinite. A selection of cross sections is shown in figure 23. Efficient jointing of components is a key consideration (see Chapter 8, Jointing techniques).

Trusses: Trusses offer a number of advantages over traditional forms of construction, including more economic and efficient use of materials, the ability to span larger distances, the use of shorter components (counteracting effects of bow, crook and taper) and the use of prefabrication.

Much research and development has been carried out in this area. This work has highlighted the relative weakness of the joints and also of the bamboo in compression perpendicular to its length. In addition, much of the deflection of a loaded truss has been found to be due to deformation at the joints (Janssen, 1995, Punhani et al. 1989, Tular et a/. 1984) (see Chapter 8, Jointing techniques).

As with cut roofs, truss configurations are many and various. The King-post and Fink are the simplest, readily spanning 4m using traditional jointing (figures 24 and 25). Culm diameters typically range from 40-l 00mm. Janssen (1995) has achieved an 8m span using improved jointing (figure 26).

The pitch of the truss should be at least 30° in areas of high rainfall (Narayanamurty et al. 1972). Truss spacings are consistent with the use of bamboo purlins (2-3m).

Needless to say, for both cut and trussed types of roof, the applied loads must be considered and, for trusses in particular, the design justified by test. In-plane stability is another primary consideration; this is usually provided by diagonal bracing members.

Roof covering Bamboo roof coverings can form an integral part of the structure, as in the case of overlapping halved culms. More often, they are non-structural in function. Exam-ples include:

Bamboo tiles

Bamboo shingles

Bamboo mats

Corrugated bamboo roofing sheets

Plastered bamboo

Bamboo files: these can take the form of halved, internodal culm sections, fixed to battens and over-lapped in a similar manner to the full length halved culms (figure 27). Roofs covered in this manner are susceptible to leakage (Mathur et al. 1964).

Bamboo shingles: shingles, measuring 30-40mm wide x internodal length (400-600mm) are cut from green culms, 70mm or more in diameter and then air dried. The shingles are hooked onto bamboo battens (maximum spacing 150mm - Narayanamurty et al. 1972) by means of a tongue cut into the underside (figure 28). Three laps are required to make a roof watertight, requiring some 200 shingles per square metre. Nailing may need to be considered if high winds are Ii kely.

Bamboo mats: a layer of bitumen is sandwiched between two mats forming a semi-rigid panel. The mats can be fixed to rafters at 200-250mm centres (figure 29). A bituminous or rubberised weatherproof coating is then applied to the finished roof (Damodaran et al. 1991).

Corrugated bamboo roofing sheets: PF resin is applied to a bamboo mats to form a five layer set which is then hot pressed between corrugated platens. UF resin bonded sheets overlaid with PF resin impregnated paper have also been produced. These products are strong and lightweight with good insulation properties.

Plastered bamboo: a cement plaster, with or without the addition of organic fibres, is traditionally applied to bamboo roofs in South America.

Other typical roof coverings include:

Reed thatch

Corrugated iron sheeting

Plain clay tiles

Clay or concrete pan tiles

The weights of roof coverings vary considerably (20kg/m 2 for bamboo tiles and shingles, 42kg/m 2 for reed thatch, t 3kg/m 2 for corrugated iron and 71 kg/m 2 for clay tiles - Herbert et al. 1979) and this must be reflected in the strength of the roof structure.

Ceilings The provision of a ceiling can help to reduce heat radiation into the occupied space and also induce a cooling airstream through the roofspace. However, these advantages are often offset by the need to disperse smoke from cooking fires, the reduction in headroom and reduced air circulation within the occupied space. Whether or not a ceiling is installed is therefore dependent upon local needs and customs.

Ceilings can be made from small, closely spaced culms, split or flattened bamboo, bamboo boards or bamboo mats in a manner similar to that for floors (see Floors). Woven mat ceilings are sometimes applied as sarking to the topside of the rafters or purlins, separated from the roof covering by battens.

Doors and windows In traditional types of bamboo building, doors and windows are usually very simple in form and operation. Bamboo doors can be side hinged or sliding, comprising a bamboo frame with an infill of woven bamboo or small diameter culms (figures 30 and 31).

In higher grade buildings, wooden doors are common. Doors and shutters comprising bamboo mat board as panelling, or as flush skins for hollow core doors (figure 32) offer another solution (Ganapathy and Zoolagud, 1993).

Bamboo windows are generally left unglazed and can have bamboo bars, or a sash with woven bamboo infill. The sash can be side hinged or sliding (figure 33), or, more commonly, top hinged to keep out direct sunlight and rain. At night, windows are closed to protect against insects and animals. Hinges are formed from simple bindings, or connecting bamboo elements.

As with doors, in higher grade buildings windows are more commonly made of wood and are often glazed.

Water pipes and gutters Whole bamboo culms, with the diaphragms removed, can be used as water pipes either below or above ground.

Below ground: the system is usually gravity fed. To ensure watertight connections, the ends of the culms can be reamed and fitted into short sections of metal, pvc or bamboo pipe and suitably caulked (figure 34). To control insect attack, the trench can be treated with insecticide before the pipes are laid.

The development of water piping in Tanzania (Lipangile, 1985) presents possibilities for the wider use of bamboo as piping for the supply of drinking water. In this particular process, the bamboo pipes are coated internally and externally with an approved bituminous paint. The exterior of the pipes can also be treated with a hot bituminous coating which gives sound protection against exterior attack. The pipes are then buried in trenches treated with insecticides which fix in the ground. It has been shown that the life of bamboo pipes can be simply extended by ensuring that the bore is full and that the water carried is clean. It is reported that the bamboo pipes treated in the above manner have given good service for ten years.

Above ground: again, the system is usually gravity fed with pipes supported on bamboo trestles. Joints can simply be formed by tapering or scarfing the ends of the culms to enable the sections to be fitted together end to end (figure 35). Watertight connections can be achieved as for pipes below ground.

Halved culms, with the diaphragms removed, can be used as eaves gutters and drainage troughs (see Detailing for durabi/i ty) .

Detailing for durability In addition to structural and functional considerations, the suitability and durability of any construction will depend to a large extent on good detailing. Protection against wetting and vermin infestation are two such factors with particular relevance to bamboo buildings.

We tting Inhibiting wetting is the first defence against decay. Wetting is caused by direct rain, flooding and, to a lesser extent, washing and cooking water.

To prevent wetting of the interior, water can be ducted away using bamboo pipes and troughs (see Water pipes and gutters). To protect the foundation posts against flooding, local effects caused by roof run-off can be minimised by ensuring good eaves and gable overhangs, and perhaps guttering to discharge the water some distance from the building. The provision of good overhangs will also help to protect the walls from direct rain. The effects of more generalised flooding can be countered by building above the ground on a graded site and using stone or concrete footings.

The life of foundation posts can be further shortened by splashing rainwater. Janssen (1995) proposes inter-changeable post ends as a possible solution to this problem (figure 36).

Vermin infestation Bamboo constructions by their nature feature hollow members and overlapping joints, forming cavities which can provide ideal nesting areas for rodents. This problem can be largely overcome by careful detailing. In general, open beam, joist, rafter and purlin ends should be plugged. More specifically, relating to different constructional details, the following points should be observed:

Floors: wall cladding should not extend past the end of the joists - this creates a concealed area between the beams and floor deck (figure 37).

Walls: walls should preferably not be of cavity con-struction. If two layers of bamboo are used (halved culms, boards or mats, or any combination of these), they should be fiied closely together.

Roofs: cavities will inevitably result where rafters cross ridge purlins and eaves beams. Here, the solution is to ensure good visibility and regular inspection.

Ceilings: access to the roof space via a closeable hatch should be provided for inspection purposes. Where the ceiling takes the form of sarking, it should extend past the wall (figure 38).

6. Other types of construction

While domestic housing and small buildings account for the majority of bamboo construction, applications extend to other areas often less constrained by scale and convention. Bridges and scaffolding fall into this category.

Bridges A bridge can be defined as an elevated structure supported at intervals for carrying traffic across obstacles (valleys and rivers, for example). In general terms, therefore, the range of types, spans and capacities is almost infinite. Bamboo bridges, however, are generally of trestle construction and of limited span for carrying only light (usually pedestrian) traffic. Simple trussed constructions have also been built and have been shown capable of supporting substantial loads.

Some examples of bamboo bridges are described below:

Footbridge (figure 39): this bridge consists of simple cross-braced frames with the walkway formed at the crutch. Culms of 50-75mm diameter are bound with bamboo lashings. The bridge is suited to rivers with muddy or sandy bottoms where the height above the bed does not exceed 5m (Royal Engineers Training Memorandum, 1945). A typical crossing might be 20m.

Handcart bridge (figure 40): this is a more elaborate construction with abutments and pilings. The abut-ments are formed from pairs of culms staked to the ground. The piles, culms of 80-120mm diameter, are cut to a point at the thinner end and driven in with a sledgehammer. A pair of horizontal culms form the pile cap and diagonal braces stabilise the assembly. The projecting pile ends act as handrails. To form the roadway, three longitudinal bamboo beams of 100mm diameter are lashed to the caps and tied together at the centre of each bay with a cross-member.

Closely spaced culms laid transversely and covered with split bamboo form the deck. A kerb is laid along each edge of the deck and secured to the outer beams by torsion lashing (twisting the lashings with a cane or stick). This ties the deck assembly together.

A bridge of this type can support 200kg per metre length, for example people carrying loads on their backs or propelling small handcarts (Trojani, 1930).

light traffic bridge (figure 41): this is a heavier duty version of the handcart bridge. It features four piles per bay and double abutments. The bay size remains the same (about 3m) but the piles are at closer centres (nominally 750mm). Bracing is also increased with the addition of two diagonal tie members. The roadway comprises paired beams, rather than singles, decked in a similar manner to the handcart bridge. This bridge can support 500kg per metre length, for example herds of cattle or animal-drawn wagons with four people plus loads (Trojani, 1930).

Simple truss (flying buttressed) bridge (figure 42): this bridge is designed to cross deep, narrow rivers. It will clear-span about 4m and relies on triangulation to carry the loads back to the abutments, The scissors frame is made from culms of 100-I 20mm diameter, stabilised with diagonal members. The roadway and deck are made in a similar manner to that for the handcart bridge, and the bridge will carry similar loads (Janssen, 1985).

Py/on bridge (figure 43): Prefabricated bamboo pylons, or towers, are set at intervals across the bed of a shallow river using an aerial ropeway. The pylons can then be decked in situ or by using prefabricated sections of walkway (Janssen, 1982).

Queen post truss bridge (figure 44): using compound members (four culms per chord) and a combination of wire lashing and steel pins, a 15m span prototype bridge was constructed comprising two modified queen post trusses. The bridge supported a load of 1.6 tonnes with only slight damage to the deck and some of the pinned joints (Kumpe, 1937).

Scaffolding Bamboo scaffolding is widely used throughout South and South East Asia and also South America as a temporary structure for supporting working platforms in building construction and maintenance. There appears to be no height limit - 40 storeys is not uncommon - but for taller constructions wooden posts are often used as the main supports (Fu, 1979).

Usually, two layers of scaffolding are used. The outer layer provides the main strength and stability and is fixed to the building at intervals. The inner layer provides the means of supporting walkways (timber boards or bamboo culms) and accessing the face of the building. The distance between components is dictated by practical considerations such as the effective reach of the s&folder. The strength and stability of the scaffold is judged to be adequate if individual components and joints can support the weight of the scaffolder. Joints are typically made with bamboo strips.

The main advantages of bamboo scaffolding when compared with steel are its lightness and low cost. It is also readily tailored to suit the shape of a building. A typical arrangement is shown in figure 45.

7. Other applications relevant to construction

Bamboo reinforced The use of bamboo as concrete reinforcement is concrete one of the more broadly covered topics relating to bamboo in construction and considerable research effort continues to be directed at this subject.

There are several good reasons why bamboo might be considered as reinforcement for concrete:

4 It is of low cost compared with steel

+ It is readily available

+ Its strength to weight ratio compares favourably with

steel

However, bamboo exhibits certain characteristics which limit its effectiveness as concrete reinforcement. The more important considerations are summarised below:

Bond If seasoned (dry) bamboo is used as reinforcement, when the concrete is poured it will absorb water and swell. Later, as the concrete dries, the bamboo will shrink and the bond will be broken. If unseasoned (green) bamboo is used, it will lose water and shrink as the concrete dries and again the bond will be broken.

The bond can be improved in a number of ways:

Mature culms (at least 3 years old) should be used.

Bamboo strips rather than whole culms should be used as the inner surface develops a better bond than the outer surface. Also, culms with prominent and numerous nodes offer improved bonding (figure 46).

Moisture related movement can be inhibited by the use of a brushed bitumen coating which acts as moisture barrier. If the coating is too thick, it can create a shear zone which will in itself reduce the bond.

Sand, nails and thin rope can be used in conjunction with the bitumen coating to improve the bond.

Thin strips of bamboo with the inner layer removed, plaited into a cable, exhibit improved characteristics (figure 47).

Low modulus of The relatively low modulus of elasticity can cause elasticity problems in respect of the following:

Cracking and deflection: a bamboo reinforced element will crack and deflect perhaps 50% more than a steel reinforced element of equivalent section.

Quantity of reinforcement: ten times more bamboo is required than in an equivalent steel reinforced section, i.e. 5% of the cross sectional area compared with 0.5% for steel.

Durabi lity Concrete is very alkaline and will attack the bamboo reinforcement. tile is known about its likely long term performance. In addition, cracking can allow water ingress which will cause further deterioration.

In general, while bamboo can be used to reinforce beams and suspended slabs, it is perhaps more suited to use in floor slabs, roads and lightly loaded elements such as partition walls where cracking, or even failure, would not be so critical.

Bamboo based panels The earliest bamboo panel was made in China during the First World War. To date, some 28 different panel types have been developed, mostly in Asia, but investigations into construction applications have only recently been carried out (Ganapathy et al. 1995). Bamboo based panels have proved suitable for structural as well as non-structural applications, in both low and high grade building work. Specific end uses include floors, walls, partitions, doors, ceilings and roofs, and by virtue of their inherent rigidity and enhanced durability (through preservative treatment), such panels can offer significant advantages over the use of bamboo in its natural state. The various types of panel product can be broadly classified as follows:

Processed strips, laths or slivers

Processed, peeled veneers

Strands, particles or fibres reconstituted into panels

Combinations of one or more of the above

Combinations of one or more of the above with wood, other lignoceliulosic materials and inorganic substances

The two most common panel types, for which product standards have been formulated in countries where they are commercially produced, are:

Bamboo mat board (bamboo mat plywood)

Bamboo strip board (bamboo strip plywood)

Bamboo mat board (bamboo mat plywood): as the name suggests, these boards are formed from bonded layers of mats (see figure 15), woven from mechani-cally or manually cut slivers of uniform size (8-16mm wide x 0.8-I .2mm thick). After drying to a moisture content of 8-16%, adhesive is applied to the mats by spreader or by dipping. Several layers are then either cold pressed (urea-formaldehydes) or hot pressed (phenol-formaidehydes) to produce the board. The boards are finished by sanding and then trimmed to size.

To increase durability, preservative chemicals are generally incorporated in the adhesive, but better results can be achieved by treating the mats them-selves (Padmanabhan et al. 1994). To improve theappearance of the board, slivers bleached and dyed prior to weaving. can be sanded,

The number of layers and board thickness will vary according to end use. 2 to 7 layers are common, varying in thickness from 1 to 10mm, with the thinner boards used for panelling and the thicker boards for concrete formwork. Products of this type have also been used for roof cladding, barrel vaulting, grain silos and as webs in I- or box-beams spanning up to 9m (Damodaran et al. 1991) .

Using a similar process, researchers in China have developed a bamboo curtain plywood laminated with resin impregnated paper, or BCPLRIP, panel with properties equivalent to those for plywood and also suitable for use as concrete formwork (Zhao et al. 1992).

Bamboo strip board (bamboo strip plywood): in its simplest form, common to South America where bamboos do not split so easily, this is made by gluing together cross-banded flattened bamboo or bamboo strips (Janssen, 1995).

The process, however, lends itself well to improved methods of processing and production. With the outer surface and nodal projections removed, culms are split then softened by soaking and heating at 130-I 45°C. The pieces are flattened, the inner surface is scraped and they are then dried by heat and pressure to 8% moisture content. The subsequent manufacturing process is much the same as for conventional ply-woods (Guisheng, 1987). The strips are planed and edged, spread with PF adhesive, assembled into cross-banded panels and then hot pressed. The resulting boards are finished by sanding and trimming. Typical applications include floor decking and walling. The product has good strength and stiffness properties and a high degree of resistance to abrasion and weathering. (Ganapathy et al. 1995)

It is now possible to obtain automated processing and production machinery for the manufacture of high quality laminated bamboo flooring following the principles outlined above. The material compares favourably with other panel products in terms of mechanical performance and is also highly decorative (Chin Yung Machine Works, 1995).

Bamboo mat board, coated with a PF film or overlaid with suitable materials, offers a stable and durable alternative to plywood for concrete shuttering and formwork.

8. Jointing techniques

Effective jointing is fundamental to the structural integrity of a framed construction. Furthermore, the suitability of a material for use in framing is largely dependent upon the ease with which joints can be formed.

Because of its round, tubular form, jointing of two or more bamboo members requires a different approach to that adopted for, say, solid timber. Despite its relatively high strength, bamboo is susceptible to crushing, particularly of open ends. It is also character-ised by a tendency to split; the use of nails, pegs, notches or mortises can therefore result in consider-able reductions in strength. Connections must also cope with variations in diameter, wall thickness and straightness.

Clearly, these limitations have not presented an obstacle to the use of bamboo in traditional forms of construction. However, the building of structurally efficient, more durable and possibly larger and more economical bamboo structures will depend to a large extent on improvements and developments in jointing technology.

Traditional joints Traditional jointing methods rely principally on lashing or tying, with or without pegs or dowels. The basic joint types are:

Spliced joints

Orthogonal joints

Angled joints

Through joints

Spliced joins Two (or more) culms are joined in line to form longer members. Splicing is usually carried out in one of four ways:

Full-lapping: Full section culms are overlapped by at least one internode and tied together in two or three places. For greater strength, bamboo or hardwood dowels can also be used. One disadvantage of this joint is that it quite bulky (figure 48).

catnapping: Culms to be joined should be of similar diameter and cut longitudinally to half depth over at least one internode length. The components are fixed as for the full lap joint (figure 49).

Butt joint with side plates: Culms of similar diameter are laid end to end. Side plates, made from quarter-round culms of slightly larger diameter and two or more internodes long, are fixed over the joint by tying and, usually, dowelling (figure 50).

Sleeves and inserts: short lengths of bamboo of appropriate diameter are used either externally or internally to join two culms together (figure 51).

Variations on the basic splice joints described above are shown in figure 52.

Orfhogonal joints These are the commonest types of joint, where two or more members meet or cross at right angles. The basic configurations are:

Butt joint

Crossover joint

Butt joint: The simplest form of butt joint comprises a horizontal member supported directly on top of a vertical member. Typical examples would be roof eaves beams on posts or floor beams on intermediate posts. The top of the post can be cut to form a saddle to ensure secure seating of the beam and good load transfer (figure 53). The saddle should be close to a node to reduce the risk of splitting. A variation on the saddle involves the cutting of a long, integral tongue which is bent right over the transverse member and tied back (figure 54). Other details include square notched ends, side plates and tenons (figure 55).

The saddle detail can also be applied to horizontal framing (figure 56)). Variations include the double joint (figure 57) and the double bent joint (figure 58).

For the single butt joint, improved stiffness can be achieved by the use of a hardwood tenon and key (figure 59). The ends of the horizontal members can be cut to form horns or integral tenons to be located in corresponding mortises in the post (figure 60). How-ever, for both these methods, splitting is a risk. Bamboo inserts also offer a solution, but this requires the cutting of an even larger hole in the vertical member (figure 61).

Crossover joint: these are formed when two or more members cross at right angles. In the horizontal plane, the function of the joint is mainly to locate the members and to provide a degree of lateral stability. Examples would include joist to beam connections which can be effected simply by tying. Where the crossover is in the vertical plane, the joint could be loadbearing, as in the connection of floor beams to posts. Simple tying is an option, although improved stability can be achieved by supporting the beam either on the stump of a branch at a node (figure 62) or on a short length of culm tied independently to the post. The tendency to slip can be reduced by insetting the supporting piece into the post, or by dowelling (figure 63).

reduced by insetting the supporting piece into the post, or by dowelling (figure 63).

Fixing methods: Most types of joint rely mainly on tying or lashing, with or without the use of pegs or dowels. Ties can be made from split bamboo, coir rope, palm fibre rope, iron wire (preferably galvanised) or tape. In the case of butt joints, the ties can be passed through a predrilled hole (figure 56) or around hardwood or bamboo pegs or dowels inserted into preformed holes. Pegs are driven from one side, usually at an angle to increase strength (figure 65); dowels pass right through the member, usually at right angles (figure 66). Crossover joints can similarly be dowelled and tied.

Angled joints Angled joints are formed where two or more members meet or cross other than at right angles. For butt joints, the ends of the member can be shaped to fit in much the same way as an orthogonal saddle joint. Horns (integral tenons) might also be used but fabrication is time consuming. Examples would include web mem-bers in trusses (figure 67). Angled crossovers can be dealt with in much the same way as orthogonal crossovers, for example the diagonal bracing in the plane of a roof.

Through joints Members of differing diameters can be joined by passing the smaller through a hole drilled in the larger. The joint is secured by a dowel passing through both members (figure 68). Applications for this type of joint might include partitions, doors and window framing.

Improved traditional joints The mechanical performance of traditional bamboo joints can be improved by the adoption of the following procedures:

Form joints at or near nodes: nodes are more resistant to splitting than internodes. It is therefore good practice to make joints as close to nodes as possible. For example, in the simple saddle joint, the saddle should be formed directly above a node.

Minimise on holes: it is generally accepted that holes, cuts and notches will reduce the ultimate strength of a bamboo culm. If a hole is made in a culm (for a peg, dowel, mortise, inset support or insert) this should be as close as possible to the node, paying particular attention to the direction of the applied force. Further-more, whenever possible holes should be round or radiused rather than square cut as these are less likely to propagate splits.

Use seasoned culms: seasoned rather than green bamboo should be used for two reasons. Firstly, bamboo shrinks on drying and this will generally cause joints to loosen. Secondly, drying splits can form which could further weaken the assembly (Narayanamurty et al. 1972).

Reinforce against splitting and crushing: tight binding, especially with wire, can in itself offer good resistance to splitting. In trusses, the use of quarter-round bamboo bearing plates reduces the risk of crushing of the chords by the compression webs (Janssen, 1995).

Improve durability: preservative treatment of the bamboo and protection from wetting by good detailing will increase the life of the joint. The use of wire is in many cases preferable to bamboo lashings or rope as it is not subject to insect attack.

Recent developments By building on traditional methods and exploiting the strengths and advantages of bamboo, a number of jointing techniques have been developed which offer more structurally efficient solutions to jointing problems. However, their adoption and suitability will depend to a large extent on the cost and availability of materials, equipment and skilled labour.

Gusset plates: plywood or solid timber side plates, applied to joint assemblies in trusses for example, and fixed with either bolts or bamboo pegs, show improved stiffness and strength when compared with traditional jointing methods (Janssen, 1995, Punhani et al. 1989) (figure 69).

lTCR joint: this is a simple joint developed by the lnstituto Tecnologico in Costa Rica and a variation on the gusset principle. It comprises a plywood insert glued into slots sawn into the ends of the bamboo elements to be joined (figure 70). During curing, the assembly can be readily clamped together using Jubilee clips. A disadvantage of this jointing method is that the ends of the culms remain open. It is also difficult to achieve good and consistent quality glued joints in the field.

Arce joint: this technique, developed by Dr Arce of ITCR, relies on the use of wooden inserts to reinforce the end of the bamboo and to form the joint. Rectangu-lar blocks, possibly cut from plantation thinnings, are turned down at one end to fit inside the culm, which can be reamed to a uniform diameter. Slots are sawn into the culm in order to accommodate slight variations in size. The blocks, when glued in place, can be connected using conventional wood fixings (e.g. nails and screws), perhaps in combination with steel plates (figure 71).

Filled joint: this is a modification of the Arce joint, developed by Morisco and Mardjono (1 995). The inner surfaces of the culms to be joined are cleaned with a wire brush. A gap filling resin is used to bond a wooden plug inside the culms. Holes can then be drilled and the assembly bolted together. Cement mortar can be used in place of a timber plug, in which case the bolts are placed before the mortar is poured. Either system can be used in conjunction with steel or plywood gusset plates (figure 72).

Das clamp: steel bands with integral bolt eyes are fitted around bamboo sections. The action of bolting two or more elements together tightens the clamps around the culms (figure 73). Additional steel straps can be used if required. This method, designed by the Bhagalpur College of Engineering in India, would be best suited to connections in one plane, e.g. trusses.

Herbert shear pin connector: In this method, developed at the UK Building Research Establishment, bamboo elements are bolted together at sections reinforced with thin gauge steel sleeves. The sleeves are fixed using a series of small diameter pins (pop rivets were found to be more effective than screws and nails) which act to transfer the load to the bamboo (figure 74). Although strong, the joint is bulky and laterally unstable as in-plane connections are not possible. Other methods of fixing suggested include binding, rather than pinning, and the use of sleeves with integral teeth.

Gutierrez joint: this technique is interesting because it exploits the compressive and bending strength of bamboo but does not require it to transmit shear or tensile forces. This is achieved by passing a steel bar through the centre of the element and welding a steel plate at both ends (figure 75). The protruding-ends of the steel bars can then be welded together to make a joint.

Steel or plastic insert connectors: angled joints can be formed by tightening bamboo elements with slotted ends around prefabricated tubular steel connectors using Jubilee clips (figure 76). Expanding plastic inserts have been used for straight connections (figure 77).

The following jointing methods would not truly consti-tute new developments but should nevertheless be noted:

Nails and screws: the fixing of small elements to larger elements (e.g. floor decking to joists) or the assembly of joint components using splice plates can be effected by the use of nails and screws but, with few exceptions (some Guadua and Chusquea species - McClure, 1953), this requires pre-drilling due to the tendency of the bamboo to split. Nailed joints also have a tendency to loosen, making for inefficient load transfer and high deformations (Arce, 1 991).

Steel straps: to help resist wind uplift forces, steel straps can be used in conjunction with nails to anchor major components, for example trusses to posts. The straps, if tightly applied, will help to counteract the effects of splitting.

9. Design considerations

The use of bamboo as an engineering material is limited from the point of view of design by two major considerations:

The formulation of structural design guidance is governed to a large extent by practical, engineering experience. In the case of bamboo, information from this source is somewhat limited.

Basic mechanical properties have been dealt with by many authors, but, unlike timber, bamboo properties do not relate well to species because of the dependency on other factors, such as geo-graphical location and age (Arce, 1993).

Considerable effort continues to be directed at the derivation of mechanical properties, but perhaps with insufficient regard to applications in the field. Janssen (1995), however, has conducted his research with the field practitioner in mind and, as such, his design approach is very simple. Accordingly, it is possibly best suited to simple constructions.

Janssen has shown that a relationship exists between density and permissible stress which forms the basis of the following table:

-For example, if green bamboo has a density of 600kg/m 3 , the allowable stress in bending would be 0.015 x 600 = 9N/mm 2 . As these are long-term stresses, Janssen suggests they may be increased by 25% for live, or medium-term loading, and by 50% for short-term loading.

Other studies relate to specific species, or groups of species. Rajput et al. (1994) considered sixteen species and derived minimum long-term safe working stresses for the green condition as summarised in the tables below:

Although densities are not detailed, assuming 600kg/m 3 , the values for group C compare quite well with those from Janssen (9 and 6.6 N/mm 2 for bending and compression respectively).

Another study conducted by Chandrakeetthy (1995) in relation to temporary bamboo structures deals exclu-sively with Bambusa vuigaris. The recommended design values of 16.7N/mm 2 in bending and 1 5.2N/mm 2 in compression (in the green condition) are considerably higher than those for either Rajput (Group C, within which B. vu lgaris falls) or Janssen.

Codification, along similar lines to timber, can be seen as the next important step towards the promotion and wider acceptance of bamboo as a valid building material. This will provide an objective and coherent approach to bamboo design, taking into account not only its more favourable qualities but also its limitations.

10. Tools

A major advantage of bamboo is its ability to be worked by hand using very simple tools. If, however, the commercial potential of bamboo as an engineering material is to be realised, then there will be a need to develop efficient handling, machining and production methods.

Hand tools It is possible to build in bamboo with nothing more than a machete, but a few basic tools will greatly increase the scope and effectiveness of the construction process. The tools listed below will enable the prepara-tion and assembly of most bamboo elements used in building. While this subject has been addressed recently in an INBAR initiative (Gnanaharan, 1995), the list draws almost exclusively on McClure (1953, a reference which has lost little of its relevance or value over the last 40 years.

Production machinery Machines for specific applications are already avail able, for example the production of high quality bamboo floor boarding. Some of the more basic machining operations could, however, be equally applicable to many other end uses. Typical machines which are now readily available include:

11. Bamboo species suitable for construction

Approximately 1250 species of bamboo have been identified to date (FAO, 1978). While many species find applications in construction, their use will be dictated by availability in sufficient quantity, suitability for different end uses and local custom.

The following table, based on data compiled by McClure (1953), gives an indication of species suited to certain applications. It should be emphasised, how-ever, that other species can be used, subject to an understanding of their relevant properties. Further information is given in Appendix 6.

12. Useful contact addresses

The following alphabetical list, which represents people and organisations with extensive knowledge and experience of bamboo, may be helpful if further information is required.

Agence Cooperation et Amenagement (ACA)

6 Rue Clisson

75013 Paris

France

Dr. Oscar Arce

Construction Engineering Dept.

lnstituto Technologico de Costa Rica

P.O. Box 159 - Cartago

Costa Rica

Bouwcentrum International Education (BIE)

700 Weena

P.O. Box 299

3000 AG Rotterdam

The Netherlands

Ms. Linda Garland

P.O. Box 196

Ubud

Bali 80571

Indonesia

Prof. K. G havami

Centre for Science and Technology

Pontificia Universidade Catolica do Rio de Janeiro

PUC - Rio de Janeiro

Brazil

Dr. Jorge A. Gutierrez

Proyecto National de Bambu

Aptdo Aereo 45 40

San Jose

Costa Rica

INADES - Documentation

African Inst. for Economic and Social Development

15, Avenue Jean-Mermoz, Cocody

P.O. Box 8

Abidjan

Ivory Coast

lnternational Network for Bamboo and Rattan

(INBAR)

17 Jor Bagh

New Delhi - 1 10 003

India

Dr. Jules J. A. Janssen

Technische Universiteit (Eindhoven)

Den Dolech 2, Postbus 513

5600 MB Eindhoven

The Netherlands

Eur. Ing. Lionel Jayanetti

TRADA Technology Ltd

Hughenden Valley

High Wycombe

Buckinghamshire HP1 4 4ND

Harutsugu Kashiwagi

Fuji Bamboo Garden

Nagaizumi-Cho, Sunto Gun

Shizuoka-Ken, 411

Japan

Dr. Kodira Kushalapa

Indian Plywood Industries Research and Training

Institute

P.B. No. 2273, Tumkur Road

Bangalore 560 022

India

Dr. Prof. Walter Liese

University of Hamburg

Leuschnerstr. 91

D-21 031 Hamburg

Germany

Arq. Oscar Hidalgo Lopez

Centro de Inv. del Bambu

Univ. Nac. de Colombia

Aptdo Aereo 54118

Bogota

Colombia

Fu Maoyi

Xiao Jiang Hua

Subtropical Forestry Research Institute

The Chinese Academy of Forestry

Fuyang, Zhejiang

China

Dr. Abdul Latif Mohmod

Forest Research Institute Malaysia

Kepong, Selangor, 52109

Kuala Lumpur

Malaysia

Mrs. Maria C. T. A. Rigter

Bamboo Development Corporation

Lindengracht 197L

1015 KG Amsterdam

The Netherlands

Dr. R. M. Singhal

Forest Research Institute

Indian Council of Forestry Research and Education

P.O. New Forest

Dehra Dun 248006

India

Stichtings Technische Ontwikkeling

Ontwikkelings Landen (TOOL)

Entrepot Dok 68A/69A

1010 AD Amsterdam

The Netherlands

University of Leuven

Post Graduate Centre of Human Settlements

Kastcel Aren berg

3030 Leuven - Heverlec

Belgium

Dr. Feiizardo Virtucio

Philippine Bamboo Research & Development Project

ERDB

College, Los Banos, Laguna 4031

Philippines

Dr. Masatoshi Watanabe

Kamigamo Exp. Forest

Kamigamo, Kita-ku, Kyoto

Japan

Dr. Elisabeth Widjala

Herbarium Bogoriense

National Biological Institute

Bogor

Indonesia

K. M. Wong

Forestry Department

Bandar Seri, Begawan 2067

Brunei

Ms. Zhang Xinping

Bamboo Information Centre

The Chinese Academy of Forestry

Wan Shou Shan

Beijing 100091

China

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Appendix 1

PRACTICAL GUIDELINES FOR THE PRESERVATIVE TREATMENT BAMBOO

Steps in the treatment of bamboo strips

Preparation of material

a) Cut mature culms at least three years old.

b) Make strips using appropriate tools (see Chapter 10, Tools, figures 78 and 79). Treatment of strips

a) When strips have a high moisture content and there is insufficient time for seasoning, treat the strips by steeping or diffusion process.

b) When strips are dry, treat strips by either cold soaking, open-tank or pressure

process.

Steps in the treatment of freshly felled whole round bamboo

Preparation of material

a) Cut mature culms at least three years old. These should be cut at least 30cm above the ground. Keep the branches and leaves on.

b) Cut the top of the culm at a position above which it is unsuitable for the purpose

for which it is being treated.

Treatment with preservatives

Treat the culm by the modified Boucherie process using water-borne preserva-tive solutions.

b) Branches should be cut immediately after the treatment is completed. If this is not done, a part of the preservative is likely to be drawn into the branches due to the evaporation of moisture through the leaves.

c) Treated bamboo should then be stored under shade to facilitate further diffusion and fixation of the preservative.

d) Cutting and boring carried out on treated bamboo is likely to expose untreated surfaces. Therefore, such surfaces should be brushed, sprayed or flooded with the same preservative solution.

C. Steps in the treatment of round bamboo of short lengths

Preparation of bamboo posts

Cut culms that are at least 2-3 years old.

b) Cut culms to the required length. It is best if the top node is at least 8-10cm below the top of the post. Cut posts from the lower two-thirds of the culms, since the upper part of the culm usually splits during seasoning.

c) Knock out all nodes except for the top one with an iron bar, then bore 6mm diameter holes for fastening wire to the post at the appropriate height. It may not be possible to knock out all nodes (due to irregular shape, or smaller internal diameter due to greater wall thickness, or the nature of the bamboo species in which case, bore 6mm holes as given in figures Al and A2 (a&b) in such a way that the holes remain on the upper side of the post when grouted in the ground. Culms intended for use as tent poles or scaffolding should also be bored in the above manner, keeping the bore position just above the node when grouted.

Treatment with preservatives

When bamboo is of sufficiently high moisture content, preferably almost green:

Treat the bamboo with water soluble preservatives by the diffusion process.

ii) Drain out the preservative from the tank after achieving the requirements of treatment.

iii) Take out the treated bamboo from the preservative tank and leave them upright over a fixed support to allow the preservative to drip out from the bamboo culms. Collect the left-over preservatives for safe disposal.

iv) Stack the bamboo under shade and allow to air dry. When bamboo is partially dry and there is sufficient time for drying:

Stack the material for air drying, as green bamboo or bamboo with high moisture content will not absorb preservative solution. First, place two or more bamboos across each block and then place the material cross-wise. Season the material for 4-5 weeks in dry weather and 8-10 weeks in wet weather, or until the material reaches a moisture content of 1520%.

ii) Give prophylactic treatment, either by dipping or spraying, to prevent stain/fungus/powder-post beetle attack during drying.

iii) The material can be treated when dry. This can be done by either cold soaking, hot and cold bath treatment or pressure processes.

iv) After draining the cylinder, take out the treated material and keep it upright, resting on some fixed support, so as to allow the preservative to drain out. Collect and safely dispose of left-over preservative.

Appendix 2

LIST OF POSSIBLE PRESERVATIVES FOR TREATMENT OF BAMBOO
Note: The use of certain chemicals is restricted or banned in some countries.

a) Coal tar creosote and fuel oil (5050) by weight. In high termite-infested areas, it is possible to add 1% dieldrin. Coal tar creosote should meet the relevant standard specification for preservation purposes (Bureau of Indian Standards, 1961).

b) Copper-chrome-arsenic composition containing copper sulphate (CuSO4H2 O), sodium or potassium dichromate (Na2 Cr2 O7,2H2 or K2 Cr2 O7, and arsenic pentoxide (As2 O 5 2H2 0) in the proportion of 3:4:1 (Bureau of Indian Standards, 1981 b). In some countries, CCA of different formulations are also used.

c) Borated-copper-chrome-arsenic (SBOR) composition conforming search Institute, Dehra Dun composition (Patent pending). to Forest Re-d) Acid-copper-chrome composition containing copper sulphate (CuS04 2H2 0) 50 parts, sodium dichromate (Na2 Cr2 O 7 2H2 O) 47.5 parts, chromic acid (CrO 3 ) 1.68 parts (equivalent to 2.5 parts of sodium dichromate) (Bureau of Indian Standards, 1981 a).

e) Copper-chrome-boron composition containing boric acid (H3BO3), copper sulphate (CuSO 4 5H2 O) and sodium or potassium dichromate (Na2 Cr2 O 7 2H2 O) or (K2 Cr2 O 7 ) in the proportions of 1.5:3:4 (Bureau of Indian Standards, 1981c).

f) Ammoniacal-copper-arsenite composition containing copper-sulphate, arsenic trioxide dissolved in ammonia (Dev et a/. 1990).

g) Boric acid:borax (1: 1.54).

h) Copper naphthenate/abietate and zinc naphthenate/abietate containing 0.5% copper or 1% zinc.

Appendix 3

PRESERVATIVES, RETENTION, SUGGESTED CONCENTRATIONS OF TREATMENT SOLUTIONS AND METHODS OF TREATMENT OF BAMBOO FOR STRUCTURAL PURPOSE S*

* A code of practice for preservation of bamboo for structural purposes (IS:9096) was for-mulated by FRI, Dehra Dun and Bureau of Indian Standards, New Delhi. This Appendix incorporates some new additions.

+ Letters refer to list of preservatives given in Appendix 2.

Appendix 4

PRESERVATIVES, RETENTION, SUGGESTED CONCENTRATIONS OF TREATMENT SOLUTIONS AND MET HODS OF TREATMENT FOR BAMBOO FOR NON-STRUCTURAL PURPOSE *

* A code of practice for preservation of bamboo for non-structural purposes (IS 1902) was formulated in 1961 by FRI, Dehra Dun and Bureau of Indian Standards, New Delhi. This

appendix incorporates some new additions.

+ Letters refer to list of preservatives given in Appendix 2.

Appendix 5

STANDARD METHODS FOR DETERMINING PENETRATION OF PRESERVATIVES

/Vote: The following methods are suited with the capacity to conduct the tests. to specialist institutes and organizations

Method for determining penetration of arsenic-containing preservatives
Reagents

Solution I: Dissolve 3.5g ammonium 9ml concentrated nitric acid. molybdate in 90ml distilled water; then add

Solution 2: Dissolve 0.079 benzidine dihydrochloride acid and add the solution to 90ml distilled water. in 10ml concentrated acetic

Solution 3: Dissolve 30g stannous chloride in 1 00ml of 1 :I hydrochloric acid (one part concentrated hydrochloric acid added to one part distilled water).

Best results are obtained with freshly prepared solutions. Agitate the solution until all chemicals are dissolved. Solution 1 is clear and colourless; solution 2 (benzidine is difficult to dissolve) is clear and light violet in colour; solution 3 is colourless or slightly turbid. Solution 1 must be prepared for each day’s testing; solutions 2 and 3 will keep in clean, glass-stoppered, brown-glass bottles for one week.

Method of application

Solution 1 is first applied by dipping the boring or cross section in a flat glass dish containing the solution or pouring the solution over the cross-section or boring. The entire wood surface must be saturated. After waiting two minutes, shake off the excess solution and allow to dry for about one minute.

Solution 2 is next applied in the same manner as solution 1. After waiting two minutes, shake off excess solution and allow to dry for about one minute.

Solution 3 is applied last by pouring the solution on the cross-section or boring, beginning at the untreated part. The entire wood surface will immediately turn bluish; hence, it is necessary to wait several minutes for the reaction to bring about the maximum colour contrast. Untreated portions will fade to a bright red or reddish orange, while treated portions will be light bluish-green to dark bluish- green. Usually the colour differences are more distinct when the specimens are observed at arm’s length. After about one hour, the stain fades; the colours can then be renewed by another application of solution 3.

Method for determining penetration of boron-containing preservatives
Reagents

Solution 1: Extract clear solution. turmeric with 90gm ethyl alcohol. Decant or filter to

Solution 2: Dilute 20ml of concentrated hydrochloric acid diluted to 100mI with ethyl alcohol and then saturate with salicylic acid (about 13g per 1 00ml).

Procedure

A smooth surface showsthe results of the spot test better than a The surface must be dry; otherwise, the test will not be satisfactory. rough surface.

Solution I is treated. The applied, surface preferably by being treated 1 spraying, or with is then allowed a a dropper, to the surface few minutes to dry. to be

Solution 2 is then applied in a similar manner to the areas that have been coloured yellow by the application of solution 1. The colour changes should be observed carefully and will show up a few minutes after application of the second solution. In the presence of boron, the yellow colour of the turmeric solution is turned red.

After reagent application, placing bamboo in a warm oven accelerates and intensifies the colour reaction to better differentiate between treated and untreated bamboo.

Method for determining penetration of copper-containing preservatives
Reagent

Dissolve 0.5g Chrome and dilute to 100ml.

Procedure

Spray the solution over split borings or freshly cut deep blue colour reveals the presence of copper. surfaces of treated bamboo. A

Method for determining penetration of chromium
Reagent

Dissolve water. 0.5g diphenyl carbazide in 50ml of isopropyl alcohol and 50mI distilled

Procedure

The boring or cross-section of bamboo to be tested shall be reasonably dry, dipped into or sprayed with the solution of diphenyl carbazide. The treated wood quickly turns purple, while the untreated wood retains nearly its original colour.

Method for determining penetration of zinc-containing preservatives
Reagents

1 g of potassium ferricyanide in 1 00ml of water.

1 g of potassium iodide in 1 00ml of water.

Starch indicator solution. Make a paste of 1 gm of soluble starch in about 5ml of distilled water, add 100ml of distilled water and boil for one minute with constant stirring. Cool. This solution is subject to decomposition, and should therefore not be used for longer than three days before a new batch is prepared.

Method of application

The boring or cross-section of bamboo to be tested should be reasonably dry. Mix 10ml each of the three stock solutions and pour into a good atomiser. Spray the boring or cross-section of wood evenly. The reaction between the zinc chloride and the spraying solution will cause the treated wood to turn a deep blue instantly, while the untreated part will retain its original colour. This method is a positive test. Should the colour fade, repeat the process.

Appendix 6

TABULAR DATABASE OF SOME BAMBOOS USED IN CONSTRUCTION

’ The following tabular database contains information relating to some of the more useful species of bamboo suited to construction. The layout is designed to enable ready access to relevant data including vernacular as well as scien- tific names, regional distribution and applications. The identification numbers allocated to each species in Table 6.1 are referred to for convenience in the subsequent tables. The database is by no means fully comprehensive, but should rather be treated as a template or model to which additional information may be added as appropriate.