Stanley Amalaha
4 November 2009
OVER the years bamboo, a vegetative fibre which grows in many parts of Nigeria, has been used mainly for temporary structures like fencing of buildings, in rural areas, while in Urban areas it is predominantly used on construction sites as support during concreting.
With the ground breaking research carried out recently by Professor Funso Alphonsus Falade, Head of Civil & Environmental Engineering, University of Lagos, bamboo will now play a greater role in the nation's structural/civil engineering. Said
Prof Falade,"Concrete surpasses the other construction materials with respect to flexibility of shape, strength, durability and response to its environment and economy. It is strong in compression but weak in tension. Its tensile strength is about 10% of its compressive strength. When concrete structures are subjected to tensile stresses, reinforcement is provided in the form of steel, synthetic and glass fibres to withstand the stresses.
Generally, in developing countries, including Nigeria, steel reinforcement is commonly embedded in concrete to take tensile stresses which plain concrete is incapable of resisting. In reinforced concrete structures, civil structural engineers design concrete to carry compressive stress while reinforcement is designed to carry the tensile stress. The transfer of stress from concrete to steel is made possible through effective bond between concrete and the reinforcement".
On cost effectiveness,hehas this to say: "Among the components of reinforced concrete structural elements, reinforcement is the most unstable material in terms of cost. A large proportion of the quantity of reinforcement that we use is imported and, therefore, foreign exchange - dependent. The cost has been increasing consistently over the years to the extent that the material is no longer affordable to the low and medium income groups.
In 1993, for example, the cost per ton of steel reinforcement was N24, 000.00. It was N31, 500.00 in 1995 while in 1996 the price was N37, 500.00. A decade later the cost of steel reinforcement has assumed an alarming proportion. For instance, in 2006, the average cost per tonne was N135, 000.00, it rose to N165, 000.00 in 2007 and in 2008 it hovered between N185, 000.00 and N260.000.00 per tonne. This trend underscores the need for alternative materials as partial or total replacement of steel in concrete."
About the use of bamboo as reinforcement, the don who studied Civil Engineering at The University of Lagos, and Moscow Institute of Civil Engineering Russia, had this to say: "Bamboo is a natural fibre and widely available in Nigeria. It grows in natural vegetation among thick forest and in riverine areas. It is used in its natural form in rural areas as columns (nakedly or as composite with mud).
The culms - a term used for the stem of bamboo in its natural form are also used as flooring material, roof trusses and wall in temporary structures. In urban areas, they are predominantly used on construction sites as temporary support to formwork during concrete work and scaffolding during plastering and painting works".
According to him, there are seven species of bamboo in Nigeria. Among the species, bambusa vulgaris constitutes 80%. Its ability to sustain appreciable load on construction sites led to the preliminary investigation to determine its engineering properties and the possibility of using it as reinforcement in concrete. There are over 1250 species of Bamboo around the world. There is need for researchers to identify the bamboo species within their localities and determine their engineering properties for effective utilisation.
Asked long he has researched on Bamboo,the don asserted. All my PH.D works centered on the use of Bbmboo.The pioneer work on the utilisation of bamboo as reinforcement in concrete in Nigeria started at University of Lagos in 1993 when I developed my Ph.D research work on the topic. The focus of the research was to assess the possibility of using bamboo as reinforcement in concrete for low-cost housing in the desire to alleviate stress being experienced by the citizenry as a result of high cost of steel reinforcement.
The research work was supervised by Professor T.A. I. Akeju. The project was executed in two phases: The first phase focused on determination of the properties of bamboo and the appropriate splint size that would be used to ensure optimum utilisation of bamboo in concrete.
The results showed a maximum tensile strength of 133.54N/mm2 for bamboo as opposed to steel reinforcement which has values of 250N/mm2 and 410N/mm2 for mild steel and high yield reinforcement respectively. The result further showed that bamboo splints of smaller sections are more ductile than those of medium and larger sections. The thickness of the bamboo culm determined the thickness of the splints since a square section is preferred".
"In the 2nd phase of the investigation, the bahaviours of bamboo reinforced beams were studied. The deformation of the samples of the beams under load was observed; the strengths of the samples were evaluated and compared with both unreinforced and steel reinforced concrete.
Bamboo has high rate of water absorption. Because of that the surface of the bamboo splints was coated with bitumen and in order to compensate for the smoothless of the bitumen surface, the surface was sandblasted.
The influence of bitumen coating to reduce the absorption of the mixing water and sandblasting on the surface of the splints to improve the bond characteristics of bamboo were evaluated. A designed mix of 0.55:1:1.86.4.34 (water: cement: sand: granite chips) with varying reinforcement volume fractions for bamboo and steel in beams. The beam specimens were cured in water and tested at 7, 14 21, 28 and 90 days".
On the outcome of the result, Falade said: "The results showed that the inclusion of bamboo splints in concrete beams increased the load carrying capacity of the beam but not proportionately. The strength was observed to improve by up to 134.65% above the strength of unreinforced beams at 28-day curing.
For the same section and percentage reinforcement, the failure load of mild steel reinforced beam was approximately 1.5times that of its equivalent bamboo reinforced beams. It was also found that bamboo splints imparted post-cracking strength to concrete beams. The results further showed that bamboo deteriorates in concrete with age which manifest in reduction of strength after 28th curing age".
The question then arose as to what could be responsible for the decrease in strength. According to him, the answer bordered on the study of the anatomy of bamboo. Dr. Toyin Ogundipe (now Professor and Dean, School of Postgraduate Studies University of Lagos), provided necessary facilities to study the internal structure of bamboo before embedding it in concrete and after its retrieval from concrete specimens.
The results revealed that the reduction in strength could be attributed to deterioration of bamboo due to weakening effect of the fibres of bamboo. The application of appropriate thickness of bitumen coating improved the performance of the bamboo splints. Low water/cement ratio is also required for optimum utilization of bamboo as reinforcement in concrete.
We have also developed and designed equations for the determination of the appropriate size and quantity of splints that would be required to resist applied load to any structural member says the distinguished researcher".
Prof. Falade further highlighted the results of the cost analysis, based on the cost equations that they developed: The result showed that the replacement of steel with bamboo splints reduced the volume of concrete by 2.54% while the reduction was 0.65% for steel reinforced beam. The cost of bamboo reinforced beams of the same section and comparable strength with steel reinforced section was found to be 22.82% cheaper.
"We used stress-strain relationship of bamboo reinforced concrete beam section to evaluate the maximum allowable percentage of bamboo in concrete. This was found to be 5.20% against 4% percent for steel reinforcement in concrete. Further research investigations showed that bamboo has limitation as reinforcement in concrete and that it can only be successfully used in beams with maximum span of 4.0m and under a maximum load of 60% of its moment of resistance. Also bamboo is not suitable as reinforcement in columns. The load-carrying capacity of bamboo reinforced columns was lower than that of unreinforced columns".He said.
On the way forward, the Professor commented: "My next research is to design and construct a prototype building in which bamboo will serve as key reinforcing material in slabs and beams within the already defined limits".
He further recommended the following for quality structural design:
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