Guadua Bamboo
The plant and its origin
This variety was initially identified as belonging to the Bambusas until 1822 when the German botanist Karl S. Kunth determined that it constituted a genus in itself and identified it as Guadua, thus maintaining the word used by the indigenous communities.
Guadua is the most important bamboo genus in America, endemic to this continent and made up of about 30 species. The Guadua angustifolia, native to Colombia, is the most important of these thanks to its extraordinary physical-mechanical properties and the progress in the silvicultural and structural study that has been carried out in the country in recent years. Although it is found in its natural state from Ecuador to Venezuela and between 0 and 2,000 m. above sea level, the optimum development of the plants is between 500 and 1,500 m., with temperatures of 17º to 26º C, rainfall of 1,200 to 2,500 mm/year, relative humidity of 80-90% and soils with moderate fertility and good drainage, characteristics of the central region of the Andes, known as the Colombian coffee axis.
Guadua forests
The groups of these Bamboos form the so-called Guaduales, spectacular forests where it is generally possible to enter because they are not particularly dense and that give rise to very dynamic and highly specialized ecosystems. There is a great amount of life inside, with a multitude of plants, mammals, birds and reptiles associated with them.
These formations are very important even in distant areas because among their main functions they are water flow regulators, absorbing water when there is excess and gradually releasing it to prevent possible flooding, prevent soil erosion and deforestation thanks to their underground branches, contribute a large amount of biomass to the land and are one of the largest environmental CO2 fixers on the planet with records of between 100 and 150 tons per hectare in each life cycle, from 4 to 5 years.
Growing and cutting
The bamboo does not increase its diameter with the passage of time, but emerges from the soil with its diameter determined, being a monocotyledonous it lacks cambium tissue so it does not get fat like trees….
Depending on the type of soil and climatic conditions these diameters can be up to 22-25 cm. although they are usually between 8 and 13 cm.
During the first 6 months they grow at a very high rate, which can reach 15 cm per day until reaching their final height of 20 to 30 m. During the following years the plant will contribute biomass to the soil, fixing environmental CO2 and developing its woody structure.
After about 4 years the stem is considered to have the ideal maturity for use as a structural material and is cut. If this is done well, a rhizomatic energy transfer mechanism begins in the plant and a new culmo begins to be generated, so that new production is guaranteed. In addition, regular and controlled exploitation favours the development of Guadual as a whole and stimulates its natural regeneration.
It is estimated that the ideal composition of canes in a guadual is 10% of shoots, 30% in young stems, and 60% in mature canes, with a density of 4,000 to 8,000 stems per hectare. The estimated productivity for a Guadua forest is between 1,200 and 1,400 stems per hectare/year, which makes it a totally effective alternative to wood for the production of structural laminates, panels, floors, etc…
Guadua canes
The Guadua stems, with their more than 20 m. high, are cut into standard 6 m. long canes, and according to their original position in the plant, 3 different sections are established.
The reeds obtained from the highest section, called Sobrebasa, have thin walls but maintain a high fiber content. They are used for auxiliary furniture, beams and strips.
The intermediate sections or Basas are slender and very light in relation to their enormous strength, maintain the outer diameter very well and are very fibrous so they are the most used parts in construction, especially in the manufacture of beams and composite trusses.
The pieces of the lower part are called Strains, they have a great wall thickness, short internodes and due to their high compressive strength they are perfect for column construction.
Origin preservation treatment
To prevent the bamboo from being attacked by xylophagous insects and to prevent fungal growth, the canes are immersed for 4-6 days in a solution of borax and boric acid at a ratio of 1:1 and a concentration of 4-6%.
Before introducing the reeds in the dissolution, all the internodes of the reeds are perforated, on the one hand this facilitates the immersion because it allows the air to escape from the inside of the reeds and the reed stops acting as a float, and on the other hand it allows the entry of the mixture into the different sections of the reed, thus ensuring a correct preservation because the bamboo is much more permeable from the inside.
When drilling the diaphragms it could be thought that we are reducing the load capacity of the cane, to determine this possible failure, several studies have been carried out at the Universidad Tecnológica de Pereira in tensile tests with perforated and unperforated stems and in the tests only a decrease in resistance of around 2% can be observed, very little significant in comparison with the great benefits provided by this preservation technique.
The preservation by Immersion in Pentaborate is considered friendly because its functionality does not depend on a toxic but on salts, a natural and innocuous product at these concentrations.
The mixture prevents the proliferation of insects without using poison thanks to the intrinsic structure of these borax salts, (hard and angular) so that if a xylophage attacks the cane, these small sharp stones pierce its stomach preventing the insect from continuing with its life cycle. As an added advantage, all materials treated in this way have fire-resistant properties thanks to borax.
Properties
Among the characteristics of the Guadua is its extraordinary firmness to compression and a good resistance to the parallel cut, this added to the great flexibility that presents turn the Guadua cane into a tool especially interesting for the bioconstruction, where this catalogued as structural material seismic-resistant.
The high percentage of fibre present in its structure and the high content of silica in its outer face make this species present the amazing characteristics of resistance and flexibility that characterize it.
Thanks to the morphology of the Guadua, the diameter of the canes of this variety is very constant, with a maximum reduction or taper value of about 5 mm/m.
The wall thickness is generally quite thick, although it can vary between the different sections chosen. In the vines can reach more than 3 cm, (used in pillars or where a lot of work is received by compression) while in the bases can be between 0.8 and 2 cm, as the internal number of fibers is the same these pieces are perfect for working on beams and straps.
The minimum straightness or curvature that they present is totally assured because although in the plantation always some can appear with curves, our canes are perfectly straight thanks to a careful selection in origin (the pieces of this variety are not straightened with heat as it is done in China).
Protection by Design and Maintenance
When building with bamboo on the outside (as with any timber) it is necessary to take into account the action of the sun on the surface of the reeds. Ultraviolet rays are highly damaging as they dry and damage the surface and can even “desquamate” it.
For structural applications of Bamboo, whenever possible it is preferable to prevent the sun from shining directly on the canes by protecting the structure by design, including eaves in the project and not leaving the ends exposed.
Another important protection to take into account is to avoid direct contact with sources of moisture because, although the Guadua includes a complete treatment against fungi and xylophages, the great variations of humidity inside can end up producing cracks. This is avoided in the structures by adding footings or any other element that lifts the piece and allows rainwater to drain away.
In Colombia it is said that the houses of Guadua must include “a big hat and good boots”.
Independently of this protection, to keep the bamboo nourished, in good condition and with a healthy appearance we use oils like the ones used for outdoor furniture, nowadays in the market there are many products that fulfill their function with dignity, the most important thing we must take into account is to let the cane breathe while keeping the pore open (unlike varnishes or synthetic paints), which offers a high protection against UV rays being waterproof, and to maintain a certain elasticity to avoid cracking with possible variations in shape in the cane. By using this type of oil, maintenance is very simple (new annual or biannual applications, without the need to remove the old material).
It is common for some cracks to appear in the bamboo, always longitudinal, which do not pose any structural problem as the properties of bamboo remain practically unchanged. If it is necessary to hide these cracks, either for aesthetic reasons or to facilitate the cleaning of the structure itself, the ideal is to cover them with the same flexible putties used in wood, since it is usual that with an increase in humidity the openings close again.