RICE HUSK WALLS
Extracted from Chapter V: The New Techniques of Construction With Bamboo In Colombia
Referred to in the Vancouver Sun, 18th November 2006
JER Envirotech (Delta BC) also SE Asia and elsewhere
5.1 Introduction. Many years passed before a great architect from Manizales, one of the coffee regions of Colombia, started to implement new and advanced methods of construction with bamboo and other local timber materials. Simon Velez used bamboo in a way that nobody had before; he expanded bamboo eaves providing maximum capacity and resistance using contemporary materials such as reinforced concrete, steel and fibers. In this chapter I classify and analyze some of his master works, which are considered in Colombia and around the world to be a revolutionary in the use of traditional materials and for introducing new technologies of construction.
In this study one important source of information has been the work of Prof. Oscar Hidalgo, another of several architects who has developed new techniques of bamboo construction. The new techniques he developed are for prefabricated and in-situ use, and some of these I will describe in detail in this chapter.
Another important contribution to this chapter is the recognized work of Prof. Carlos Vergara who died five years ago. His work focused on the employment of rice husk waste, and much of his later research was given to me by his own hand to develop and use in my work, which was enriched by his formulas and important new applications in the techniques of building with bamboo.
The following is a selection form the work of the above-mentioned great architects which represents the most important achievements in the area of alternative bamboo technologies.
The most representative examples of bamboo walls in the modern and improved methods of construction, are mixes of both styles; the Bahareque walls are made out of almost the same materials as the traditional ones, with a variation in the finishing, a mix of low-cost painting components: lime, "marmolina" and water. Even though the following examples of low-cost wall are not made with bamboo, their structural support is.
5.2.1. Rice Husk Walls
Large quantities of rice husk are produced as waste material when the grain is processed, leading to serious pollution problems. In the 60's, Prof. Carlos Vergara from Valle University started to test its utility with different materials, making slabs with sawdust using the ashes of rice husk as a component of Zorel cement. Later, in the 70's, it was used raw as a light filler material in concrete slabs (Los Fundadores residential compound, Cali 28.000 M2), Subsequently a house in a middle income neighborhood and a country house were built with cement panels containing raw rice husk. Then Prof. Vergara tested rice husk with other waste materials which led him to the concept of Rice Husk Walls or Porous Walls (Muros Esponjosos).
The basic recyclable elements are:
If it is possible to get fly ash from the combustion of coal from industrial plants, it could be used by mixing it in ball mills to diminish the quantity of cement up to 50%. (Figs. 5.01.- 5.02).
- Treated rice husk from rice mills.
- Treated sawdust, a by-product of saw mills.
- Waste coal, resulting from incomplete combustion of coal in ovens and boilers.
- Hydrated lime, cement and water.
The rice husk and the sawdust are treated in a solution of lime in water (5%) for 24 hours, or else rice husk and sawdust are mixed with lime and water then dried out for use.
188.8.131.52. The mixing.
The approximate volume resultant from the mixing is 1/4 M3
- 1 cement sack (50 Kg)
- 1/2 hydrated lime sack
- 21/2 waste coal sacks
- 21/2 saw dust sacks
- 4 rice husk sacks
- 40 L of water
If it is possible to get fly ash, 1/2 of the cement sack is replaced by 1/2 of fly ash and 21/2 burned and powdered rice husk sacks.
184.108.40.206. Physical characteristics.
220.127.116.11. Process of production.
- Resistance to compression and flex tension currently being tested.
- weight: 600 and 900 Kg/M3
- Excellent thermic and acoustic insulator
- Seismic resistant due to elastic and plastic characteristics of the material
- Hygroscopic, therefore it is necessary to waterproof the exteriors
The components of the material are mixed dry; as in any concrete, water is added and the mix stirred again. The mix is poured in a mold, which will have convenient measurements to make blocks or panels. The panels are of 0.90 m*0.45 m-0.10 m.
18.104.22.168. Process of assembly.
First the bamboo structure must be completely finished in order to make the walls. When blocks or panels are used, these are glued on their edges to the bamboo posts and beams with plaster getting the adherence by barbed wire, which is nailed to the bamboo structure. The panels are straightened, to avoid lateral movement.
If the wall is made in situ it is necessary to place the mold on each side of the bamboo posts and make the plaster cast without vibration to avoid its disintegration; it is necessary to compact the material until it adjusts itself without leaving empty spots. Molds could be disassembled after 24 hours.
22.214.171.124. Comparative analysis.
The physical characteristics of the material and its components offer a comparative advantage to traditional construction systems.
a. The light weight (600 to 900 Kg/M3) gives simplicity and affordability to the structure and foundation.
b. As in any concrete, its load capacity varies according to the mixing dosage, but by the proved tests, a mix with 200 Kg. of cement/M3 gives appropriate characteristics for its use for walls with a slimness = 30
c. It is a good thermic insulator.
d. Its absorption coefficient from 8% to 10% forces the protection of the surfaces exposed to rain with a waterproof coat or at least with a first coat of cement; however, because its surface could be even enough it would not need to be applied with the traditional plaster. A flat finishing could be accomplished, if wanted, with a coat of cement of minimum thickness and then plaster and paint.
e. The ductility of the material makes it resistant to cracking; the same characteristic makes it resistant to seismic movements.
f. Because it is porous, it has good qualities as an acoustic insulator.
g. To add plastic elements, like carboximetil cellulose at 0.5% or povinilic alcohol at 10% in the water, allow the immediate dismolding after pouring the mix into the mold of the prefabricated wall, without collapsing, up to a height of 10 times the thickness of the wall.
h. Qualified labor is needed only in the leveling and plumbing of the bamboo structure and molding; the rest of the activities are carried out with unskilled laborers. This is an ideal system for self-help construction programs.
i. Electrical and hydraulic installations are made before pouring the walls, to avoid their opening and restoration
j. The low-cost of the rice husk walls is based on the bamboo structure and the recycling of waste products. The major costs are in the small amount of cement and in transport.
****************************** continued ............
126.96.36.199. Rice Husk Walls.
- Its lightness makes walls very easy to handle, creating labor savings , since one man can carry two panels at the same time.
- The lightness also saves money in foundations, because the quantity of steel is not the same as in the traditional brick or concrete wall.
- Because of its porosity, this kind of wall has great thermal and acoustical insulation properties.
- High compression resistance.
- The rice husk panels can be cut easily with a saw, allowing many possibilities for shapes and forms when bamboo braces and beams are embedded into the wall.
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