Abstract: Constructionindustry acts as an important role in the world and it consumes more materialand energy to fulfil the all needs. Concrete and steel are the most commonmaterials use in construction industry and price of steel is increasing day byday. So alternative materials should be found to face that problem and reducethe cost of construction. Using timber in construction is new trend andresearchers are trying to find the suitability of using timber materials likebamboo and palmyrah as reinforcement in concrete. In this paper a study wascarried out to find an approach to design a hybrid reinforced concrete slab byphysical modelling and finite element modelling using Midas software.

Bamboo isselected to use as reinforcement with steel because it is rapid growing andeasily available material. Bamboo has higher strength compare with other timbermaterials and has higher strength to weight ratio.  Due to its brittle nature it can’t fullyreplace to steel and properties of bamboo also vary with its age and species.

Still now there are no any code practice to design hybrid reinforcement elementand because of that designers are avoid using timber for reinforcement inconcrete.       Keywords:  Bamboo;Concrete; Reinforcement; Hybrid reinforcement  1.   IntroductionResearchersare trying to find suitable replacement for conventional materials of buildingconstruction for sustainable development.

Need of construction activitiesincrease day by day with increase in population. Provide a structure withacceptable cost and prevent environmental degradation by construction processare the responsibilities of people involved in construction industry. Concreteand steel are most commonly used materials in construction and it consumes highpercentage cost of total budget. In reinforced concrete structures steel actsas very important role to solve the problems in concrete.

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Concrete is verystrong in compression and have high durability. But the problem is it is weakin tension. So steel is used with concrete to solve the problem because steelis strong in tension. That’s why steel has higher demand in the world and itcauses to increase the cost of steel.

Researchersfound that timber like bamboo, palmyrah are good replacement material for steeland many researches also carried out on this subject. But they found manyproblems in using timber as reinforcement material and gave a solution toovercome some of these problems. Use timber as a part of the reinforcement withsteel (hybrid reinforcement) in concrete is best solution to get rid of thedisadvantages in using timber. In this case, bamboo is selected asreinforcement material with steel because it reaches its full growth in a fewmonths and has higher tensile strength compare with other timber materials.Itis already reported that bamboo can be used as reinforcement material inconcrete for light weight elements. It is because of the brittle nature ofbamboo, low stiffness and low compressive bearing capacity. Water absorption ofbamboo is one of the major problems and it causes to swelling and shrinkage ofbamboo in concrete.

Study on effect of water absorption of bamboo in concreteand treatment methods were already investigated by researchers (Munasinghe, 2015).Some coating is used to prevent the water absorption of bamboo in concrete andvarnish is one of the best water repellent for this. Bonding strength isanother important factor in concrete and bond between bamboo and concrete isrelatively low compare with that of steel and to improve the bond betweenbamboo and concrete bamboo should be treated (Alireza Javadian a, 2016).     2 Bamboo as a construction materialMany years ago, study on the use ofbamboo as reinforcement to replace steel material was started (Lopez, 2003). Before that bamboowas used to some construction work like scaffolding, shuttering and dwelling. Evenconcrete is generally the most economical material of construction and willprovide long life and low maintenance costs, it can’t withstand the tension. Sothat reinforcement is provided to solve this problem and steel is the bestsolution because it is strong in tension.

But due to the economical problem andhigh energy consumption there is a need to find a suitable alternative forsteel. Bamboo has been used as a construction material due to its specificproperties like low weight, high tensile strength and biodegradable. There aremany species of bamboo are growing in the world and there was a report that inSri Lanka 14 species of bamboo was growing (Senerathne, 1956).Bamboo is not a tree and it is a rapidgrowing grass type.

It was selected as reinforcement in concrete because of itshigh tensile strength. It can reach strength of 370 MPa (Ghavami K. , 1995) and it makes bambooas an attractive alternative material in tensile loading elements. Many researcheswere already conducted to find the mechanical properties of bamboo and Table 1shows a summary of these details which they found strength and stiffnessproperties of bamboo (Dias, Munasinghe, & Baskaran, 2015). Table1: Properties of Bamboo   Ratio of tensile strength to weight is six times greaterthan that of steel (Ghavami & Hombeeck, 1981). Researchers foundthat modulus elasticity of bamboo is very low compare with concrete and itcan’t contribute to the flexural stiffness of the reinforce element. And alsoit is consider approximately 1/15 of that of steel (Nayak, Bajaj, Jain, Khandelwal, & Tiwari, 2013).

 Bamboo is one of the sustainable construction materialsand no need any fuel energy to produce it. But the problem is properties ofbamboo vary with its age and location. Properties of bamboo mainly depend onnature of growth and growing is depended on climate condition and soil type.  It is reported that bamboo reaches its maximumstrength between 2.5-4 years of its age and also its strength decreases at alater age (Amada & Untao, 2001). Colour of bamboouse to identify the suitability of using construction material and Brown colourtrunk is indicate that the tree is at least three years old. Properties of bamboo vary with species and generallydendrocallamus gianteus is one of the most usable and high strength species.

Ithas tensile strength of 120 MPa and compressive strength of 55 MPa. Because ofthe low density of bamboo which is about 700 kg/m3, strength toweight ratio is much higher than that of steel and concrete. Density of steelis 7800 kg/m3 and that of concrete is 2400 kg/m3 (Baba, 2009). A Material selection method was developed atCambridge University from the relationship between modulus elasticity E anddensity q. In Figure 1, the line presenting the equation C= E1/2 qfor bamboo. The materials situated above the line have a better performancethan bamboo and materials which are situated below the line have worseperformance than bamboo.

It shows that only palm trees and balas are in thesame range as bamboo and steel, concrete are situated far below the line (Wegst, Shercliff, & Ashby, 1993).     Figure1: Performance of bamboo and other materials, inrelation to their E and qDurability of bamboo depends on its age, type of speciesand curing condition. It can easily attack by insects and it will increase withthe amount of starch plus humidity content.

Some treatments are help to reducethe starch such as heating and immersion. In past years many of the concretestructures were deteriorated because of corrosion of the steel. But that problemis avoided when using the bamboo as reinforcement in concrete. There a researchwas conducted to check the durability of concrete with steel structure andconcrete with bamboo structure. A reinforced concrete column after 10 yearsservice which was a part of tunnel structure of Rio’s Metro and bambooreinforced concrete beam which has 15 years of service life were tested andresults also compared.

The condition of these elements is sown in Figure 2 and3 (Ghavami & Hombeeck, 1981).    Figure2: Condition of bamboo reinforced beam   Figure3: Condition of reinforced column It shows that steel was severely corroded and need to bereplaced. But they found that the bamboo reinforce beam was satisfactorycondition.

That bamboo bars were treated to getting strong bond and prevent theattack from insects. But there are some disadvantages in using bamboo asreinforcement in concrete such as water absorption and shrinkage of bambooelement. Study on these properties of bamboo was conducted by many researchersand they recommended suitable treatment methods to solve these problems. 2.1 Water absorption of bamboo Generally water absorption of timber is very high andit causes severe problem in concrete when it used as reinforcement. Manyresearches were conducted on properties of bamboo to absorb water. Volume ofbamboo is changed when it absorbed water from concrete. That volumetric changecauses to induced stresses and it will develop crack in concrete.

Swelling andshrinkage of bamboo create several problems in concrete and it is also one ofthe major problems in using bamboo as reinforcement in concrete instead ofsteel.  Reinforcing bamboo absorbs water from concrete whenit’s poured and curing. At the time it expands like shown in Figure 4(a).

Thenconcrete was pushed away from reinforcement bars due to swelling of bambooshown in Figure 4(b). After curing process bamboo starts to loss moisture andshrinks back to initial condition. Swelling and shrinkage of bamboo cause todevelop crack in concrete as shown in Figure 4(c) (Ghavami & Zielinski, 1988).    Figure4: Behavior of bamboo reinforcement in concreteCoeffient of thermal expansion of bamboo is as lowas that of concrete and shrinkage of bamboo is higher than that of concrete.

These differential properties of concrete and bamboo are also seriouslimitation in use of bamboo as reinforcement. To find the water absorptioncapacity of bamboo, a test was carried out on 63 treated and untreated bamboosamples which are getting from top and bottom part of the trunk of the tree.These samples were submerged in to the water for 96 hours and weighted. Sand sealerwith single coat, sand sealer with double coats, varnish with single coat,varnish with double coat, black oil with single and double coat were used totreat the bamboo samples and results were compared. Untreated bamboo samplesshown higher amount of absorption and varnish coating have the potential tolimit water absorption to 8% by mass and limiting the volume change of bambooelement (Dias, Munasinghe, & Baskaran, 2015). 2.

2 bonding strength of bamboo  In a reinforced concrete element bonding between concreteand reinforcement bars is important factor and if the bonding is weak whenapply the load then concrete element goes to failure. So it is very importantto ensure that the bonding strength is adequate to withstand the loading when bamboois used as reinforcement to replace the steel. Some studies were conducted onthis chapter and they found that water-repellent treatment needs to improve thebonding between bamboo segment and concrete. Several types of coating wereapplied on the bamboo segments and series of pull out test were conducted tofind out the bonding behavior of bamboo with concrete.

Sand was also adds ontop of the coating for some samples to increase the friction. But in this studythey found that bond strength of bamboo with no coating is comparable to coatedreinforcement. And there were no any significant difference in using fine sandand coarse sand to increase the friction (Javadian, Wielopolski, Smith, & Hebel). In a study they found that Sikadur 32-Gel is the bestproduct which used to prevent the corrosion of reinforcing bars, it hasincreased the bonding strength of treated bamboo segments (Ghavami K. , 2005).

Environmental factors such astemperature variation, moisture content, pH value of concrete and surfacetexture are also related to the boding strength. When apply protective coatinglike water proofing to control the water absorption it should be applied as athin layer. Otherwise it affects the bonding between concrete and bamboosegment. Bamboo has higher bonding capacity compare with palmyrahstrips because it has nodes along the length of the trunk.    2.3 Hybrid reinforcement  Concrete has lower ductility and it breaks without anywarning signs. Because of that the reinforcing material which use in concreteshould have higher ductile behavior. Steel has high ductile behavior and itincreases the ductile behavior of concrete when using as reinforcement.

Generally timber materials are in brittle nature and bamboo also brittle naturematerial. When using bamboo alones in concrete as reinforcement failure ofelement   may breaks suddenly withoutwarning signs. Hybrid reinforcement arrangement is the best solution to solvethat problem. So using steel and bamboo in a proper proportion is help to reacha effective usage of timber in concrete element.     3 ConclusionsBamboo material is one of thebest solutions to face the increasing demand of steel and it has to promote andresearches should be try to make people aware about the use of bamboo as reinforcement in concrete. Even thereis some limitation in using bamboo as reinforcement in concrete; there areseveral methods to solve these problems. By suitable chemical treatment attackfrom insects can prevented.

To improve the bonding strength and to avoid thehigher amount of water absorption many coating materials can be used. But stillthere is a problem that no one getting idea to use bamboo in concrete becausethere are no any guidelines or specific method to do the design. So it is the importantthing and needed thing that find an approach to design a hybrid reinforcementconcrete element.  4 Acknowledgements I would like to express my gratitude to my researchsupervisor, senior lecturer Dr.K.Baskaran and Department of Civil Engineering,University of Moratuwa to give the financial support. And also I would like tothank my friends who giving support to continue the research.