Flexural behaviour of hybrid fiber reinforced concrete beamusing BFRP bars

The corrosion of rebar is one of the main problem in the construction industry. A lot of amount is spent on the repair work every year but none of them is that effective. Therefore, the recent studies are being conducting on the FRP rebar due to the brittle nature and the bonding performance. We have also used PVA fiber in concrete to increase the strength of the concrete. we are using Hybrid beams in which we have replaced the corner rebar with BFRP bars because of their superior corrosion effect and the strength to weight ratio. We used four point loading test on these hybrid reinforced beams to find the flexural behaviour by which we can predict the performance. 0.25% PVA fiber reinforced concrete showed the optimum results.


Introduction
Fiber-reinforced polymer is an alternative construction material and has been used as a substitute for steel in the construction industry for several decades. However, there are several weaknesses of FRP rebars, which are needed to be enhanced because of which the usage of the material is limited in civil infrastructures to reduce these disadvantages of using FRP, the concept of hybridization is introduced. The introduction of a hybrid structure includes cost-effectiveness. As there are some of the disadvantages in Fiber Reinforced concrete structures, so to improve these properties, a new model has been introduced and are being studied. The researchers have explained that the hybrid rebars are composed of many different fibers, the behaviour are mostly similar to that of steel rebars. The ductility of RC beams reinforced with 2 steel and 2 FRP rebars was also similar to that of steel RC beams. In all reinforced concrete structures, the corner steel bars that get corroded in the structure are mentioned (Qu and Zhang): 1 exposure of oxygen & water, 2) resistance is less towards spalling than in other Cross sectional parts and 3) high carbonation rates. Then the corrosion from the outer side of steel bars spreads to the inner side of the reinforcement. The most commonly used FRP bar along with Steel is a Glass Fiber-reinforced polymer rebar it has a good and successful alternative that has various advantages than that of the traditional reinforcement method, which gives a longer service life. The BFRP rebar is a structural ribbed reinforcing bar product of excessive power and corrosion-resistant glass fiber which are impregnated and sure by an exceptionally long-lasting polymeric epoxy resin.
Infeature houses are ideal for any harsh and corrosive environments. BFRP rebar is much lighter in weight than the same strength of steel rebar. It is very much less complicated to handle and in maximum cases, only one truck of steel is enough to bear the load for a whole project. Many researchers have tested the flexural conduct of hybrid BFRP/steel R C beams. The maximum load carrying capacity, crack width, and deflections were predicted in many research papers by experimental, numerical, etc methods. The use of steel reinforcement with FRP reinforcement in combinations increases the flexural strength of the beams. The ratio of reinforcement is the main factor that explains the ultimate moment of the beams, however, axial stiffness value between the BFRP & Steel bars have some effect on the flexural ability. The load deflection reaction of hybrid BFRP/steel RC beams may be classified into 3 parts. In the 2nd & 3rd part, flexural stiffness will increase with change in reinforcement ratio. The steel reinforcements enhance the ductility of the hybrid RC beams. The researchers have not only replaced the steel rebars in reinforced concrete structures with FRP rebars to improve the properties of the members of a structure. There were many experiments conducted on hybrid reinforced beams in recent times. Tan tested the many RC beams with Aramid FRP & steel rebars are found that once the usage from Aramid FRP bars becomes not extra than one-1/2 of whole reinforcement, the hybrid Aramid FRP-metal strengthened RC beams have average serviceability. The Researchers have tested many Reinforced beams with BFRP and steel rebars. Silarbi has tested beams reinforced with Carbon FRP and steel bars and many other researchers have conducted various tests on hybrid reinforced beams. All these experiments lead to a conclusion that the tensile strength factor of the steel reinforcement reaches the maximum yield strength while the stress in FRP RC beam reaches a minute percentage of its ultimate value. Now a days the impact of association of Fiber Reinforced Polymer bars and steel bars on the durability of members are studied. The researches have determined that using Fiber Reinforced Polymer rebars close to the corner of the tensile area and steel rebars used in middle or center of the tensile area offer the most advantage for the structure durability. They have also taken the consideration of different types of arrangements. There are many different types of arrangement like single layer in this type of arrangement all rebars are placed at the bottom of member in a single line with a definite distance between each rebar where there is maximum tensile strength that can be exerted. The next type of arrangement of reinforcement is double layer reinforcement in this type the reinforcement bars are arranged in two layers in different ways such as one layer of steel rebars and another with FRP rebars, by alternate steel and FRP rebars the bars can be arranged many possible ways of arrangement. They can also be arranged in a bundle form only a few researchers have conducted the test on this arrangement in this the researchers have tied either 1steel, 1FRP or 2FRP or 2 steel or all bars are tied at one place the placement of bars also plays a very vital role in the strength of the structure. Not only does the arrangement of steel rebars play a major role in the strength of the building but also the stirrups are very important. The angle of the hook also helps to increase the strength. Stirrups are mostly used are steel in the experimental as FRP bars cannot be bent so steel is used as it makes the work easy.

Material
In this project, we have used OPC 53 grade Cement as a binder for the fine and coarse aggregates which give strength to the concrete and used PVA fibers in concrete, and partially replaced steel rebars with Basalt fiber rebars for the reinforcement of concrete. The material used is shown in the figure.

Cement
We have used OPC 53 grade cement in this experiment which is used as the binder

Aggregate
We have used Fine aggregate and coarse aggregate which helps to strengthen the concrete.

Conplast SP 430
It is a plasticizer used to reduce the amount of water and increases the workability when the fiber is added to the concrete.

PVA Fibers
Polyvinyl alcohol fibers used are manufactured evenly so that they are dispersed uniformly throughout the mix. We have used 12mm length PVA fibers in concrete to increase the strength.

BFRP rebars
Basalt Fiber Reinforced Polymer (BFRP) rebars manufactured from a single rock from a carefully chosen quarry. They made directly without any additional admixtures as they contain high acidity. Therefore, they melted to liquid form and made into fibers then several fibers are combined using adhesive and made into rebars. The BFRP rebars shown in the Figure.

Mixing of Concrete
We have mixed the material with a mixing machine. The Material has been mixed thoroughly.

Casting of Specimen
We have used the moulds and placed the reinforcement in the mould with a cover of 25mm on all the sides. Then the concrete is placed in the mould Figure 5. Then we used an electric needle vibrator to vibrate the concrete in mould figure 6.

Curing of the Specimen
Once the Specimen is casted, we have waited for one day so that the concrete gets hardened. Then we have used a curing compound for the curing of concrete with a thick coating so that all parts of specimens cover.

Experimental Procedure
In this experiment, we have casted 7 Beams in which 2 beams are control beams and the rest 6 beams are hybrid beams with different percentages of PVA fibers. I have tested these beams using 4-point load testing machine. Then I have connected the Load deflection gauge to the beam. One is placed at the centre and another one is placed at the support. The experiment setup is shown in figure 8.

Load-deflection
We have applied 4-point load on the specimen as shown in the experimental setup. When the load is applied then the beam is deflected the deflection is calculated using the LDT which is connected at the bottom. The loaddeflection curve is shown below of different Samples.

Comparative Study
We are studying the comparison of the behaviour of the load-deflection with the help of graphs and the comparison is mentioned in the following graph. Figure 15. Comparative study of ductility Factor

Ductility Factor
The ability of a material that can stretch to the maximum before the material failed is known as ductility. The ductility is calculated using the experiment and is tabulated below . Ductility Factors of the Beams. Table 3. Ductility Factor of beam

Flexural Behaviour of reinforced concrete beams.
The HFRP beam is placed on the testing machine on which the load is applied. The flexural behaviour is studied using the ultimate load and ultimate moment.