Bamboo reinforced concrete construction follows same design, mix proportions and construction techniques as used for steel reinforced. Just steel reinforcement is replaced with bamboo reinforcement. Properties of bamboo reinforcement, mix proportion of concrete, design and construction technique with bamboo reinforced concrete is discussed in this article.
Nature’s material, bamboo has been widely used for many purposes. Mainly as a strength bearing material. It is used for building shelters from an earlier time.
Bamboo has used for scaffolding works, formwork supporting stands and many in building construction works. These are limited to medium-large projects.
Even though existence of bamboo has been found from centuries, bamboo as reinforcement material is an innovation in the civil engineering construction field. This innovation was based on Clemson’s study that has been conducted in the Clemson Agricultural College.
Bamboo is a biodegradable and renewable in nature. It is energy efficient as it is of natural origin and environmentally sustainable in nature. These properties have forced to use this in the construction field for centuries.
The details on how bamboo is efficient in replacement for steel reinforcement in concrete are discussed in the following sections.
Significance of Bamboo Reinforced Concrete
The steel as a reinforcing material is a demand that is increasing day by day in most of the developing countries. There is situations when the production is not found enough to face the demand for steel.
Hence it is essential to have an alternative that is worth compared to steel. Bamboo is found in abundant, they are resilient and hence these can face the demand as a reinforcing material and become an ideal replacement for steel.
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. Working on the weak points of bamboo and bringing up an innovation of bamboo as a structural steel replacement, would be a great alternative.
Bamboo as Reinforcement for Concrete Construction
The material used as a reinforcement in concrete should show all the essential properties to make the element structurally active under load. In the case of steel, we manufacture steel to the desired proportion and test for the basic strength values as a quality check.
Similarly, the process must be done for bamboo too. Bamboo is found in nature, they have in different species. Each species differs in their characteristics, texture, thickness and strength. Hence it is essential to know which species is best for reinforcing and which is not.
Selection of Bamboo for Reinforced Concrete Construction
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.
Material Properties of Bamboo for Reinforced Concrete
Bamboo is by its origin an orthotropic material. It posses fibers within it. It gains high strength along the fibers and low strength in the transverse direction.
The bamboo has a structure of a composite material with cellulose fibers aligned across the length. It has high thick fibers near to the outer length of the bamboo, which is the main reason why they resist huge wind forces.
Fig.1: Schematic Diagram of a Bamboo with centroid axis ‘Z’ and height ‘L’
Figure-1 shows a schematic diagram of a bamboo sample. The node that is seen in the bamboo are represented by n. It is subjected to a lateral load ‘p’ causing a maximum moment at the support. It forms a cantilever arrangement.
Water Absorption Property of Bamboo
The main requirement of bamboo when used in reinforcement is the concern for water absorption. The water absorption capacity was studied in various species. Among which Dendrocalamus giganteus, known simply as DG and Bambusa vulgaris hard, BVS are the ones which absorbed less water. The rate of water absorption can also be reduced by certain treatment.
Fig. Water Absorption Rate of different bamboo species with time
To increase its effectiveness in impermeability certain treatment has been carried out. The treatment substance in incorporated in the bamboo material should consider three primary factors:
- The materials adhesion property towards bamboo and concrete
- The formation of rough surface on the bamboo for perfect bonding
- The water repelling property of the treatment substance
Bamboo Strength towards Bonding
As in the case of steel rebar with ribs in it, which facilitate proper bonding with the concrete, bamboo too should have proper adhesion with the concrete.
The bonding strength is based on this adhesive property of cement and the compressive forces that are formed on the surface of the reinforcing bars. An untreated bamboo affects the bonding strength in the following manner:
a) By pushing the concrete away, by the swelling of bamboo material
b) By the formation of voids within the concrete
c) By formation of cracks as the products of void formation
Fig. The Action of an untreated Bamboo as a Reinforcing Material
These problems are well faced by a proper bamboo treatment.
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.
Fig. A beam Bamboo Reinforcement after 15 years exposed to open air
Fig. A column steel reinforcement bars after 10 years exposed within a closer area
Bamboo reinforcement is found more durable than steel if it has undergone proper treatments.
Bamboo Reinforced Concrete Design Principles
Design of bamboo reinforced concrete is similar to design of steel reinforced concrete. The mechanical properties of bamboo reinforcement to be used for design can be assumed as per table below.
Table: Mechanical Properties of Bamboo Reinforcement
| Mechanical Property | Symbol | Value (psi) |
Ultimate compressive strength
|
—
|
8,000
|
Allowable compressive stress
|
s
|
4,000
|
Ultimate tensile strength
|
—
|
18,000
|
Allowable tensile stress
|
s
|
4,000
|
Allowable bond stress
|
u
|
50
|
Modulus of elasticity
|
E
|
2.5×106
|
Procedure and equations for the design of steel reinforced concrete can be used for the design of bamboo reinforced concrete by using the mechanical properties of bamboo reinforcement in place of steel reinforcement in the calculation.
Bamboo in flexural members such as beams and slabs develops some cracking under normal service loads due to its low modulus of elasticity. If such cracks in bamboo is not tolerable for structural members, then the structural design can be carried then steel reinforced designs or designs based on unreinforced sections are required.
Bonding between concrete and bamboo as reinforcement is must for design. Split bamboo provides better bonding with concrete than whole culms when used as reinforcement. Bamboo should be split and provided in more compact reinforcement layers for better bonding with concrete.
Concrete Mix Proportions for Bamboo Reinforced Concrete
Water-cement ratio plays an important role in strength and durability of reinforced concrete. Bamboo being a natural building material has the property of absorbing water as discussed earlier. The absorption of water causes swelling of bamboo.
Thus, concrete mix proportion for bamboo reinforced concrete must have water-cement ratio as low as possible. It should also be considered to use concrete with high early-strength cement to minimize cracks caused by swelling of bamboo.
The mix design of concrete can be as per the strength requirement for structure, as per structural design. Since use of reinforcement has no effect on compressive strength requirement of concrete, bamboo reinforced concrete mix proportion can be same as steel reinforced concrete mix design.
Bamboo Reinforced Concrete Construction
The methods used for construction of steel reinforced concrete can be used for bamboo reinforced concrete. It is just the replacement of steel with bamboo reinforcement. All other process for bamboo reinforced concrete construction remain same as conventional concrete construction.
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