Steel-reinforced concrete is the most common building material in the world, and developing countries use close to 90% of the cement and 80% of the steel consumed by the global construction sector. However, very few developing countries have the ability to produce their own steel or cement. Out of 54 African nations, for instance, only two are producing steel.
But, according to Future Cities Laboratories, steel is not irreplaceable. There is a material alternative that grows in the tropical zone of our planet, an area that coincides closely with the developing world: bamboo.
Bamboo has been in construction for many years. Given its outstanding tensile properties, replacing steel reinforcement in reinforced concrete structural concrete with bamboo should of high interest.
Bamboo reinforced concrete construction follows same design, mix proportions and construction techniques as used for steel reinforced.
Selection of bamboo for reinforcement can be done based on these factors:
- Color and Age – Employ bamboo having an evident brown color. This shows the age of bamboo to be at least 3 years
- Diameter – Use the one with long large culms
- Harvesting – Try to avoid those bamboos that are cut either during spring or summer seasons.
- Species – Among 1500 species of bamboo, the best one must checked, tested to satisfy the requirement as a reinforcing material.
Positives attributes of bamboos:
- The rapid growth and maturity rate of bamboo,
- aesthetics, and
- its strength properties,
- low cost,
These attributes of bamboos make it worth investigating as a substitute structural material for steel. However, the tensile strength property which is the main requirement of a reinforcing material is seen appreciable for bamboo, compared with other materials including steel. The structure of bamboo from its origin gives this property. The hollow tubular structure has high resistance against wind forces when it is in natural habitat.
PROPERTIES AND AVAILABILITY OF BAMBOOS IN NIGERIA
Bamboo is commonly available in almost all the states of Southern region of Nigeria except for Bayelsa State and Lagos State where the distribution is considered to be relatively low. The states with the abundance of bamboo occurrence are identified to be Abia, Anambra, Akwa Ibom, Cross River, Delta, Edo, Ebonyi, Enugu, Imo, Ogun, Oyo, Osun, Ondo, and Rivers States. Also, the report of RMRDC (2004) indicates that at least ten (10) per cent of the natural vegetation in these states is dominated by bamboo, with the existing bamboo clumps showing substantial gregarious growth that is continuous over large areas. In states like Bayelsa, Benue, Ekiti, Kogi, Kwara, Lagos and Nassarawa States, the distribution of bamboo was observed to be frequent, indicating that between six (6) to nine (9) per cent of the natural vegetation is occupied by bamboo. Several bamboo clumps were also reported in Niger, Plateau and Taraba States as well as within the Federal Capital Territory (FCT). However, there are 12 North Western and North-Eastern states where the bamboo occurrence is rare. These states include Adamawa, Bauchi, Borno, Gombe, Kano, Kaduna, Katsina, Kebbi, Sokoto, Jigawa, Yobe, and Zamfara State.
Bamboos from Nigeria can be said to be very poor in tension giving a tensile strength of
31N/mm²- 94N/mm²; Yield stress of 0N/mm² – 50.19N/mm² and a tensile force value of 3kN –
19kN. The ductility of steel allows it to undergo plastic deformation and necking before breaking. Bamboo undergoes brittle failure. i.e., it breaks sharply without plastic deformation.
According to tensile strength test carried out by Ogunbiyi, Moses A. (2015), on bamboos grown
in Nigeria the result are tabulated below:
|High Yield Steel Bar||Mild Steel Bar||Bamboo|
|Sample Size||Tensile Strength (N/mm2)||Breaking elongation (%)||Tensile Strength (N/mm2)||Breaking elongation (%)||Tensile Strength (N/mm2)||Breaking elongation (%)|
Bamboo with slimmer tubes has a higher compressive strength value than bamboos with larger tubes as regard to their cross-section. Bamboo with slimmer tubes possesses better material properties because larger tubes of bamboo usually have a disadvantage of having a minor part of the outer skin that is highly resistant to tension. Hence, compressive strength is affected by the portion of lignin inside the culms and the large portion of cellulose influences buckling and the tensile strength because it represents the building substance of the bamboo fabrics.
The natural form of bamboo is biodegradable and renewable in nature and also in concrete within 3 – 6 months if not treated. An untreated bamboo affects the bonding strength in the following manner:
- By pushing the concrete away, by the swelling of bamboo material
- It can shrink which can further lead to the segregation of concrete
- By the formation of voids within the concrete
- By formation of cracks as the products of void formation
- It is not good enough to oppose the seismic force
- Coating of other materials is required before using it.
There are few concerns about bamboo before declaring whether it can be used as a substitute of steel in concrete or not.
- The mechanical properties of bamboo. According to the researchers, the modulus of elasticity of bamboo in tension is about 1/10th of steel; which means, the bamboo reinforced structures are prone to have higher deflection, wider cracks and lower load or moment bearing capacity than the steel has.
- The dimensional changes of bamboo due to moisture, temperature, and load relative to concrete is different. That is bamboo swells and pushes concrete due to water absorption when curing begins. But, as it dries, it shrinks back and hence creates some void between concrete and bamboo interface. Along with this, the differential thermal expansivity and Poisson’s ratio make it vulnerable to cracking of the concrete during the service life.
- Like timber, bamboo is vulnerable to environmental degradation and insect attacks. Its durability depends on the types of species, ages, conservation condition, treatment, and so on.
Though according to some research, the bonding of bamboo with concrete can be enhanced using some adhesives, like epoxy, the technique is an expensive method. Similarly, the durability of the bamboo can be enhanced by using treatment procedure, but that too depends on numbers of other aspects, like age, chemicals, etc. Though all the above-mentioned constraints are met, every aspect of construction needs a thorough inspection.
IMPROVING DURABILITY OF BAMBOO MATERIAL
Its property of being a natural product make it more exposed to environmental agents and insects. A remedy against this is to undergo bamboo curing. The curing process enables the treatment of humidity content and the starch within it, which is the main reason for insect attraction. The curing is effective only if the chosen bamboo is right one. As mentioned in the selection of bamboo. The curing of bamboo can be done either by:
- Curing on spot
- Immersion process
- By heating
- Smoke Curing
The treatment must be done when the bamboo is in a dry state so that the penetration undergoes in the right way. The preservation treatment done on bamboo to take care of durability factor should have no effect on the chemical composition. The treatment itself should last, without being washed away under high water conditions if any. Durability is a major concern for bamboo material. The physical and chemical properties of bamboo are found high with low content of humidity within it. This low content would keep away molds in bamboos.
Secondly, treatment with bitumen or other suitable materials and introduction of nails at specific interval on the bamboos culms can cater for most of the limitations.
Bamboo is good for low-cost housing, especially where they are readily available. It can be used for concrete beams not exceeding 4metres, as discussed by Dr. Ikponmwosa from the Department of Civil and Environmental Engineering on the use of Bamboo with Vanguard Nigeria in 2012.
In some cases, the bamboo must first be sliced into strips like the size of a rebar but square –
10mm x 10mm or 10mm x 12mm. They are then dried and treated with bitumen or other suitable materials.
Bamboo from Nigeria cannot be employed as a main structural member in building and other engineering works, but can be used as portioning wall, ceiling, roof and other areas of engineering construction that is not heavy load bearing, as concluded by Ogunbiyi M.A. et al on the Comparative Analysis of the Tensile Strength of Bamboo and Reinforcement Steel bars as Structural Member in Building Construction published in 2015
K. Ghavami, ―Bamboo as reinforcement in structuralconcrete elements: cement and concrete compositespp. 637-649, http:// www.sciencedirect.com . 2004
Global journal of researches in engineering, vol 16 issue 3 version 1.0 2016 “analysis of Tensile Strength of Bamboo Reinforced Polyester Composite by O By Omholua, Anthony Omokhudu, Ujam. A. J & Uviesherhe Okiemute Edijana -Nnamdi Azikiwe University”
Moses Ogunbiyi- “Comparative Analysis Of The Tensile Strength OBamboo And Reinforcement
Steel Bars As Structural Member In Building Construction” 2015
Akash Parashar (Quora.com) Devendra kumar (Quora.com) Pramod Ray (Quora.com)