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This study is about using the Fiber Reinforced Polymer for strengthening RC beams mixed with sea sand that contains high chloride. This study focused on the investigation of the crack patterns behavior of RC beam mixed with sea sand and strengthened with Glass Fiber Reinforced Polymer (GFRP) plate as well as to study the flexural strength performance of such beam. Using sea sand as fine aggregate affects the bars in the concrete and cause corrosion to the steel bars. Moreover, the corrosion of steel bars affects the strength performance of concrete and cause cracking at the tension face of the concrete beam. To address this problem GFRP plate is introduced to be placed at the tension face of the concrete beam as strengthening material. Three samples of beams used in this study which are control beam, normal sand beam strengthened with GFRP plate, and sea sand beam strengthened with GFRP with beam length of 1600 mm and GFRP plate thickness of 1.2 mm and length of 1400 mm. All of these beams are tested using four point bending test which were subjected to static load. The results of this study showed that the strength capacity of RC beam mixed with sea sand and strengthened with GFRP plate is 5.5 % more than the strength capacity of the control beam without strengthening. Also it showed that better stiffness of the strengthened beams may cause lower cracks spacing.
The use of fiber reinforced polymer (FRP) has become a very popular all over the world in civil and structure engineering applications due to its great advantages such as high corrosion resistance, greatly improving the stiffness and strength of an existing structural element with minimal effects to the surrounding environment, and high strength-to-weight ratio. A several failure modes of such plated beams are flexural failure by FRP fracture, flexural failure by crushing of compressive concrete, shear failure, plate end interfacial debonding, cracking pattern, and intermediate crack induced interfacial debonding (Aram, Czaderski, & Motavalli, 2008).
The control of cracking in reinforced concrete beams are usually achieved by limiting the stress increment in the bonded reinforcement and ensuring that the bonded reinforcement is suitably distributed, but this way of cracking control is not good enough for reinforced concrete beams that contains high chlorides which permits the corrosion to the bonded reinforcement and induce low flexural strength and shear strength and cause reinforced concrete beams to be cracked. In such matter glass fiber reinforcement (GFRP) is another method for cracking control in reinforced concrete beams that contains high chlorides.
Sea sand is totally contains of chloride contamination -chlorine ion- which gradually eats into the concrete and steel bars of the building's structure. This experiment investigated the strength performance of RC beam mixed with sea sand bonded with the GFRP plate as well as evaluating the cracking patterns of such plate.
Problem Statement of Study
Over the years much of the corrosion of reinforced concrete structures can be attributed to chloride contamination, carbonation, alkali silica reactivity (ASR), or a combination of these factors. So, in order to reduce the environmental degradation effects, to resist several and different applied loads on the reinforced concrete beams, and to maintain strength and long-term sustainable service life for the existing reinforced concrete structures strengthening such beams may be needed by using an appropriate method.
Several studies have been carried out to eliminate and reduce the effects of environmental degradation by different methods. Electrochemical Chloride Extraction (ECE) from steel-reinforced concrete specimens contaminated by ''artificial'' sea-water is used whereby chloride ions are removed from chloride contaminated concrete through ion migration (Fajardo, Escadeillas, & Arliguie, 2006).
Moreover, the glass fiber reinforced polymers is used for the strengthening of reinforced concrete members. So that the structure elements will regain strength and restoration option to stop corrosion and extend the service life of existing reinforced concrete structures (Saleh Hamed, 1998).
Salt sand contains high chlorides which permits the corrosion to the bonded reinforcement and induce low flexural strength and shear strength and cause reinforced concrete beams to be cracked where glass fiber reinforced polymer plays a very important role in addressing this failure mode of the reinforced concrete structure. Therefore, this study focused on the performance of flexural strength and the behavior of cracking patterns of salt sand reinforced concrete beam when it's externally bonded with Glass Fiber Reinforced Polymer (GFRP) plate.
Objectives of the Study
This experiment is conducted:
To investigate the flexural strength performance of RC beam mixed with salt sand and strengthened with glass fiber reinforcement polymer (GFRP) plate.
To evaluate the behavior of cracking pattern of RC beam mixed with salt sand and strengthened by glass fiber reinforcement polymer (GFRP) plate.
Significance of the Study
Study on this area especially in term of using salt sand as fine aggregate in mixing concrete is still not very common due to the high contents of chloride ions in salt sand that may cause serious problems to the structure elements. However, this study is a significant in term of using sea sand rather than river sand due to the shortage of river sand.
Besides that, this study is a beneficial to the workplace at the tropical environment by contributing awareness and understanding about the cracking behavior and performance of concrete structures exposed to high chloride ions and strengthened with GFRP plate.
Moreover, this experiment contributed a very useful and sample knowledge and understanding about the use and performance of RC beams mixed with salt sand bonded with GFRP plate. In additional, better understanding of the failure modes especially on cracking pattern is gained form this experiment.
Scope and Limitation of the Study
In this experiment, the main purpose is to investigate the flexural strength behavior of RC beam mixed with salt sand and strengthened with GFRP plate and cracking pattern behavior. Thus, this study is limited only to the data obtained from the laboratory work (lab testing), as well as the information and data collected from literatures that have been cited (journals and articles).
The work for this study was carried out at the heavy structure laboratory at the Faculty of Civil Engineering at Universiti Teknologi MARA Shah Alam. Three samples of RC beams (control RC beam, RC beam bonded with GFRP, and RC beam mixed with salt sand and bonded with GFRP) size of 1600 x 100 x 150 mm and three cubes prepared at the laboratory of structure at UiTM, Faculty of Civil Engineering, Shah Alam. All beams subjected to static.
Tests on compression for concrete and sieve analysis where carried at the Concrete Laboratory of the Faculty of Civil Engineering UiTM, Shah Alam.
GFRP plate with length of 1400 mm and thickness of 1.2 mm utilized as an external reinforcement for RC beam for flexural strengthening and for bond load test with epoxy as an adhesive.
Salt sand is used as fine aggregate on the concrete mix. All beams subjected to four point bending test for flexural studies to determine the load carrying capacity, load deflection behavior and cracking behavior.
It is a well-known fact that the primary function of the fiber reinforced polymer in a reinforced concrete structures is to act as crack arresters and crack closers, to ensure that distributed and not localized cracking takes place during loading, and to stabilize the distributed cracking. Thus, compared with plain reinforced concrete without strengthening, reinforced concrete strengthened with fiber reinforced polymer has higher flexural loading capacity.
The strengthening of reinforced concrete structures using externally bonded fiber reinforced polymer (FRP) systems has gained wide spread acceptance in recent years. This strengthening technique is particularly attractive for RC structures in marine environments since fiber reinforced polymer (FRP) composites are noncorrosive. In addition, externally bonded fiber reinforced polymer (FRP) composites can act as a protective layer to internal reinforcement and concrete and prevent such as chloride ion penetration and that of other aggressive agents (Dai, Yokota, Iwanami, & Kato, 2010).
The performance of the interface between FRP and concrete is one of the key factors affecting the behavior of the strengthened structure, and has been widely studied using simple shear tests on FRP plate/sheet-to-concrete bonded joints. While a great deal of research is now available on the behavior of these bonded joints, no closed-form analytical solution has been presented which is capable of predicting the entire debonding propagation process (Yuan, Teng, Seracino, Wu, & Yao, 2004).
Sea Sand Concrete
Sea sand concrete is a kind of concrete in which sea sand use as fine aggregate, which is large-scale application in the coastal areas in recent years (Guoliang, Junzhe, Jianbin, & Zhimin, 2011).
The sea sand solves the problem of river sand shortage, coupled with cheaper price; most of the ready-mixed concrete companies are willing to use salted sea sand instead of river sand. Many companies even are using sea sand without any treatments (Guoliang et al., 2011).
The biggest difference between sea sand and river sand is their salt content. Strictly sea sand can be used as concrete fine aggregates, for which some studies has been used that successfully. In China, the conception of desalinating sea sand is officially proposed in 1997. Sea sand has now been classified as natural sand in Sand for building (Bing Quan Sun, May, 2011).
By measuring the strength of sea sand concrete with fly ash, finding out the law of strength for the sea sand concrete by the presence of fly ash (Guoliang et al., 2011).On the other hand, in this experiment, fly ash did not apply only using glass fiber reinforcement polymer (GFRP) as an external reinforcement to strengthen the sea sand reinforced concrete beam.
Concrete beams that are mixed with sea sand are weakened by the chloride ion and their load-deflection curves as well as stiffness and ductility are reduced in different degree. But other beams that are mixed with desalinated sea sand are reduced not obviously (Heng Lin Lv, March, 2011).
Chloride Contains in Sea Sand
The use of sea sand in the concrete affects the structure elements. Since the sea sand contain chlorine ion (chemical element cl.) which cause cracking in the concrete which will allow the water and air to infiltrate down to the steel bars that definitely will cause corrosion to the steel bars.
The degradation of steel reinforced concrete structures due to exposure to chlorides either from deicing salts or from marine environments is regarded as the principal cause of premature deterioration in such concrete. This type of corrosion, called ''pitting'', causes the formation of anodes at sites of breakdown of the passive film of oxide that would otherwise confer protection on steel in an oxygenated alkaline environment. These local anodes cause the formation of expansive corrosion products that induce cracks and then breakage of the concrete around the steel. Electrochemical chloride extraction (ECE) is a curative method for treating reinforced concrete about to suffer or already suffering from chloride induced reinforcement corrosion. In this process, negatively charged chloride ions (Cl) are carried away from the coating concrete by the application of a current between the steel, which acts as a cathode, and a temporary external anode placed on the concrete surface. This ECE treatment was investigated in several studies in the 1970s (Fajardo et al., 2006)
Resulting from these selected studies reveal that cracking due to the high temperatures of the concrete, increases in permeability and loss bonding of the reinforcement was the major drawbacks.
Glass Fiber Reinforced Polymer
Glass fiber reinforced polymers (GFRP) plates are being increasingly used in rehabilitation and retrofitting of concrete structures as an alternative to steel in concrete due to their high strength-to-weight ratio and corrosion and fatigue resistance. Ease of handling and application at site are added advantages. Glass fibers are of different types such as E-glass, S-2 Glass, AR-Glass, A-Glass, C-Glass, D-Glass and R-Glass depending on their properties and chemical composition.
Of the different types of glass fibers, E-Glass is mostly used for reinforcement due to its high strength and electrical resistivity. Glass fibers have high strength and temperature resistance, but it is the low cost that makes GFRP the most popular FRP reinforcement in civil engineering applications (Mukherjee & Arwikar, 2007)
Glass fiber-reinforced polymer (GFRP) composites are currently being used as alternatives to traditional steel reinforcement in concrete mixed with fine aggregate that contains high chloride, or in concrete structures exposed to aggressive environments, such environments could contain sea water, deicing agents or other chemicals that limit the lifetime of steel reinforcement. In glass fiber reinforced polymer (GFRP) composites, a polymer matrix holds the glass fibers together and provides a degree of protection from damage due to handling and aggressive environments. GFRP reinforcement bars are currently made by pultrusion like processes in which the fibers are aligned in the longitudinal direction of the bar as shown in Figure 2.1, resulting in highly anisotropic elastic and strength properties. The durability of bond properties of GFRP bars, known to be highly influenced by the surface geometry of the bar and transverse properties of the composite material have not been investigated to a great extent in realistic loading situations (Bakis, Boothby, & Jia, 2007)
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Figure 2. GFRP (scale = mm) (Bakis et al., 2007)
For the case of FRP-strengthened flexural structures under bending and shearing, Saadatmanesh and Ehsani, (2007), performed a parametric study to examine the effect of different design material properties and quantities on the strength of glass FRP retrofitted beams. As a result, various kinds of failure modes, such as interfacial debonding and FRP sheet rupture were observed. Generally, the use of fiber composite plates such as glass FRP eliminates the possibility of corrosion at the epoxy-plate interface and reduces the chance of bond failure.
Behavior of FRP-to-Concrete in RC Beam
The existing applications of FRP reinforcement in buildings, bridges and tunnel linings have demonstrated that the FRP bonding technique is remarkably efficient. Due to the fact that structural strengthening is achieved by the interfacial stress transfer from FRP plates to concrete matrix through the adhesive layer, in the recent years, many efforts have been made to study the interfacial bonding/debonding behaviours.
External bonding of fiber reinforced polymer (FRP) plates or sheets has emerged as a popular method for the strengthening or retrofitting of reinforced concrete (RC) structures. In this strengthening method, the performance of the FRP-to-concrete interface in providing an effective stress transfer is of crucial importance. Indeed, a number of failure modes in FRP strengthened RC members are directly caused by interfacial debonding between the FRP and the concrete. The performance of the interface between FRP and concrete is one of the key factors affecting the behavior of the strengthened structure, and has been widely studied using simple shear tests on FRP plate/sheet to concrete bonded joints (Yuan et al., 2004).
Existing studies have been shown that beams bonded externally with GFRP and subjected to wet and dry exposure under sea water resulted in33% reduction in strength (Mukherjee & Arwikar, 2007).
The strengthening of reinforced concrete structures using externally bonded fiber reinforced polymer FRP systems has gained widespread acceptance in recent years. This strengthening technique is particularly attractive for RC structures in marine environments since FRP composites are noncorrosive. In addition, externally bonded FRP composites can act as a protective layer to internal reinforcement and concrete and prevent such as chloride ion penetration and that of other aggressive agents. However, a significant obstacle to the wider adoption of externally bonded FRP systems in marine RC structures is uncertainty regarding the long-term performance (Dai et al., 2010).
RC elements generally fail because of the crushing of compressed concrete and/or yielding of the internal steel reinforcement. FRP materials show a linear elastic behavior up to failure, but in general their high strength is not achieved when they are used as external reinforcement, because the strengthened elements often fail due to a mechanism that is known as debonding. This failure mode depends on the bond behavior at the concrete FRP reinforcement interface and generally happens with the detachment of a more or less thick concrete cover. Location of failure along the beam and thickness of concrete detached depend mainly on cracking pattern, internal steel reinforcement percentage, presence of steel stirrups, loading scheme, and interaction between shear and normal bond stresses along the interfaces (F, 2010).
Existing studies suggest that the main failure mode of FRP-to-concrete joints in shear tests is concrete failure under shear, occurring generally at a few millimeters from the concrete-to-adhesive interface. The ultimate load (i.e. the maximum transferable load) of the joint therefore depends strongly on concrete strength. In addition, the plate-to-concrete member width ratio also has a significant effect. A very important aspect of the behavior of these bonded joints is that there exists an effective bond length beyond which an extension of the bond length cannot increase the ultimate load (Yuan et al., 2004).
Ritchie et al, (1991) investigated the magnitude of increases of strength and stiffness of beams provided by the externally bonded GFRP and CFRP plates. As a result, the research demonstrated that bonded plates of fiber reinforced polymer were indeed a viable method of enhancing the strength and stiffness of a reinforced concrete beam. All strengthened beams showed a fairly substantial increased in stiffness and strength compared to a working load of control beams. The stiffness increased in the range of 17 to 99% relative to the working load range. The strength increased ranging from 19 to 99% over the working load and increased between 20 to 97% at ultimate (Ritchie, P. A., Thomas, D. A., 1991).
An investigation done by Ritchie et al (1991) showed that GFRP bonded plate were viable method of improving the stiffness and strength of strengthened reinforced concrete beam. As a result, the increased compared to the control beam was in the range of 17% to beyond 90%. One Carbon and one glass FRP strengthened beam exhibited flexural failure where internal steel yielded followed by plate fracture in the constant moment region (Ritchie, P. A., Thomas, D. A., 1991).
Debonding Failure Modes
When a reinforced concrete beam with an externally bonded FRP plate is subjected to flexural loading, high tensile and bond shear stresses develop in the concrete near the adhesive layer. In general, debonding of the FRP plate from the concrete is due to these high stresses.
From the experimental observations done by other researcher (Wu & Yin, 2003), there are two typical final failure modes, the macroscopic interfacial debonding of FRP-concrete interface and the rupture of FRP sheets. The macroscopic interfacial debonding also has three types of fracturing behaviors. The first type of debonding, as presented in Figure 2.2 (a), happens within epoxy adhesive layer, which is mainly due to weak or imperfect bond. The second type of debonding is micro diagonal cracks that occur in interfacial concrete finally connect together and lead to the delamination of FRP sheets, as shown in Figure 2.2 (b). In this case, it is assumed that the bond strength of adhesive layer is relatively high. In both of these cases, only one dominant flexural crack locally occurs at mid span from which the debonding initiates and propagates, no matter if the interfacial debonding happens within adhesive layer or through interfacial concrete. The third type of debonding is schematically shown in Figure 2.2 (c), in which a secondary diagonal shear or flexural crack occurs beside the first flexural concrete crack at mid-span. Then, the debonding starts to propagate from the root of the secondary diagonally shear or flexural crack. On the other hand, for the beams ended with FRP rupture failure, there are also two representative Cracking behaviors: (1) one dominant flexural crack at mid-spa with some micro diagonal cracks nearby, as shown in Figure 2.2 (d), and (2) multiple flexural cracks distributed along the bond interface, as shown in Figure 2.2 (e). In most situations, FRP rupture happens near the mid-span. The load capacity is apparently higher for the beams of FRP rupture failure than those of debonding failure (Wu & Yin, 2003)
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Figure 2.2 Cracking behaviors and final failure modes (Wu & Yin, 2003)
As a result, there are two types of debonding failure. The first type is mid-span debonding which initiates at flexural or shear cracks in the mid-span of a concrete element and propagates towards the ends of the plate. The second debonding failure type is plate end debonding which starts at the ends of the plate and propagates along the beam.
(Wu and Niu (2006) developed a methodology to predict the debonding failure load and the influence of concrete flexural crack spacing on interfacial shear stress distribution in RC beams based on linear elastic beam theory. In order to investigate the flexural strengthening effect of externally bonded FRP sheets, a series of tests were performed by Wu et al (2003) from which the structural responses of FRP strengthened beams with different strength of concrete, interfacial bond conditions and amounts of bonded FRP sheets were studied. Various kinds of failure modes, such as interfacial debonding and FRP sheet rupture were observed.
Intermediate Cracking (IC) Debonding Failure
One of the failure modes, referred to as intermediate crack induced debonding (IC debonding), involves debonding which initiates at a major crack and propagates along the FRP-to-concrete interface. In RC beams flexurally-strengthened with a tension face FRP plate/sheet, IC (intermediate crack) debonding may arise at a major flexural crack or flexural-shear crack. In RC beams shear-strengthened with FRP plates/sheets bonded to the sides, IC debonding can arise as a result of a shear crack. In IC debonding, the interface is dominated by shear stresses, so the debonding failure is also referred to as Mode II fracture in the context of fracture mechanics. In RC beams bonded with a tension face plate, debonding is also likely at the plate ends where debonding is due to a combination of high shear stresses and high normal stresses.In IC debonding failures, the stress state of the interface is similar to that in a shear test specimen in which a plate is bonded to a concrete prism and is subject to tension as shown in Figure 2.3 (Yuan et al., 2004).
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Figure 2.3 Intermediate flexural crack induced interfacial debonding (Smith & Teng, 2002)
Experimental Cracking Behavior
The cracking behaviour of RC elements externally bonded with composite materials is very complex. In addition to the stress transfer between steel bar and concrete, the transfer between the external laminate and the concrete, depending on the bond law at the interface, has to be introduced. The development of cracks is progressive and the crack number increases as the load increases until a stabilisedcracking condition is reached. When an external reinforcement is applied, the developmentof cracking is modified because of theadditional stresses transferred to the tensile concrete bythe laminate. The number of cracks and crack spacingchange depending on the bond behaviour at the concrete-laminate interface. Typically the bond behaviourbetween concrete and laminate is stiffer compared to thatbetween steel and concrete, allowing the transfer of highstresses along a very short length. For RC elements the average crack width, wm, is usually evaluated neglecting contribution of concrete strain in tension and can be expressed as follows: wm = É›sm _ srm , where É›sm is the mean steel strain and srm the mean crackspacing (Ceroni & Pecce, 2007).
Considering the evolution of cracks during the loading history of beams, the crack pattern observed at the service load corresponds to a stabilized cracking situation, because no more cracks formed until the failure when cracking became irregular. It is clear that the service load is not the same for all the beams and that crack width is higher for higher values of service load. In general no relevant difference in crack spacing wasobserved for the unstrengthened and all the strengthenedbeams; only at failure condition the beams externally reinforcedwere characterized by a smaller crack spacing with acrack pattern more irregular due to local debonding at theconcrete-laminate interface as shown in Figure 2.4 a and b (Ceroni & Pecce, 2007).
Figure 2.4: Cracking pattern: (a) unstrengthened beam, D; (b) strengthened
Beams (Ceroni & Pecce, 2007).
Crack growth mechanism
In heterogeneous materials such as concrete, sandstone, and rock, the weakest link is generally represented by the interfacial zone between two dissimilar materials. For normal weight concrete specifically, the bond zone between (mortar or cement) matrix and aggregate particles is considered to be the weakest element in the material structure. However, it seems that not only does the strength of the interface play a dominant role in crack initiation, but more meaningfully, the combination of stress and strength also. In fact, the material is most likely to fail at the point with the highest stress relative to its strength. At the interface between matrix and aggregate, the two dissimilar materials meet but retain their considerably different identities in Young's moduli. This results in stress concentrations (Chiaia, van Mier, & Vervuurt, 1998).
Combined with the relatively low strength, this zone becomes of major importance for crack initiation and propagation. After an entropic stage of diffused microcrack nucleation at interfaces, these zones, together with pre-existing microdefects, become "attractors" for the subsequent macrocrack development. The overall material response is highly dependent on the distribution of these attractors and on their tendency to connect and coalesce. The process from microcracking to macrocracking is thus characterized by interfacial cracks growing through the matrix and joining into macrocracks as shown in Figure 2.5. The macrocracks remain discontinuous during a very long time. In the softening stage, the crack faces are still connected by the so-called crack face bridges . These bridges (Figure 2.5) provide for stress transfer, and explain the long stable tail of the tensile softening curve (Chiaia et al., 1998)
Figure 2.5: Image processing on crack bridging pattern (a, b, c) (Chiaia et al., 1998)
Figure 2.6: Bridging in the matrix of the phosphorous-slag concrete (Chiaia et al., 1998)
The crack development of concrete beams mixed with sea sand in indoor natural environment or in artificial climate environment can be seen in Figure 2.7 and Figure 2.8. It can be seen that The crack distribution of RC beams and common beams when compression failure is basically the same. The crack distribution of RC beams with the same mix proportion is different between artificial climate environment and indoor natural environment, especially for concrete beams mixed with desalinated sea sand. Because of high temperature and high humidity and salt rain and infrared lamp and etc, the degradation of mechanical performance and compressive strength is accelerated. As a result, the prime rigidity and cracking load of the tested beams is increased in artificial climate environment rather than in indoor natural environment. The influence of cracking load about environment is reduced by the sea sand desalination technology (Heng Lin Lv, March, 2011).
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Figure 2.7: Crack development in indoor natural environment (Heng Lin Lv, March, 2011)
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Figure 2.8: Crack development in artificial climate environment (Heng Lin Lv, March, 2011)
Gap of Study
Mohd Hisbany Bin Mohd Hashim, 2010 Studied the flexural behavior of RC member strengthened with CFRP plate and fabric and also the interfacial bonding of the CFRP-concrete system exposed to tropical climate.
Additionally, Wu, & Yao, 2004 investigated the debonding propagation process of RC beam bonded with FRP
This study will investigate the cracking behavior of RC beam mixed with sea sand and strengthened with Glass Fiber Reinforced Polymer(GFRP)
This experiment is conducted to investigate the cracking behavior of RC beam mixed with sea sand and strengthened with GFRP plate as well as the flexural strength performance of such beam. This experiment is classified as laboratory studies which required three different research methodologies which are collection of the materials, Preparation of the RC beam bonded with GFRP, and then the testing of the specimens. Stages are shown in Figure 3.1.
Figure 3.1: Research Methodology Process
Materials and dimension
Several materials is used in conducting this experiment which is three concrete specimens with dimension of 1600 x 150 x 100 mm (length, height and width respectively) subjected to four point loads (P), GFRP plate of 1400mm length and 1.20 mm thick is externally bonded on the bottom tension surface of the specimen through epoxy adhesive, as shown in Figure.3.2, and salt sand is used as fine aggregate. In additional to that 2T12 mm as bottom reinforcement bars and links diameter of R6-300 is used as shown in Figure.3.3.
500 A 500 500 RC beam
Adhesive layer GFRP 150
100 50 A 50
Figure 3.2: Specimen dimension (All units in mm)
Figure 3.3: Section A-A
Sampling & Concreting
Framework of three samples of RC beams - control RC beam, RC beam bonded with GFRP, and RC beam mixed with salt sand and bonded with GFRP is prepared as shown in Figure 3.4 and twelve cubes prepared and designed according to the code of practice (BS 8110) with characteristic strength of 50 N/mm2. Those three samples are used to test the properties of concrete which include flexural strength capacity, and cracking pattern.
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Figure 3.4: RC beam Framework
Concreting was the next step after sampling the concrete. Three processes involved in concreting, which were mixing the concrete, pouring the concrete into the formwork as shown in Figure 3.5 and curing the specimen.
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Figure 3.5: pouring the concrete into the formwork
The weight of sand, water, coarse aggregate, and cement are calculated- designed as according to BS1881- and recorded in design mix sheet as shown in Table 3.1
Per m3 (to nearst 5 kg)
Table 3.1 concrete mix design quantities
Curing process conducted after the concrete poured. Curing process of the three beams are done by using water retaining method by covering the specimen with wet rugs as shown in Figure 3.6 while the concrete cubes is cured by using curing tank for the period of 7 and 28 days as shown in Figure 3.7.
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Figure 3.6: Water retaining method Figure 3.7: Curing water tank method
Bonding GFRP Plate to RC Beam
Fiber Reinforced Polymer (FRP) plate bonded to the tension faces of concrete structures to provide additional flexural strength by using epoxy as an adhesive as shown in Figure 3.8.
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Figure 3.8: GFRP bonded to RC beam
The specimen used left aside for 28 days to achieve the required strength. After that, the specimen was ready for instrumentation and experimental set-up. Some measuring devices and instruments used to measure the parameters. The instruments and devices that used in conducting this experiment are strain gauges, displacement transducer, load cell, and data logger.
Strain gauge is a device used to measure deformation (strain) of the specimen. The strain gauge is properly glued to the surface of the specimen by using special glue after the surface of reinforcement bars has been cleaned from the dust by using acid acetate and cotton cloth. Concrete strain gauge is used in this experiment as shown in Figure 3.9.
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Figure 3.9: Concrete strain gauge at the face of RC beam.
Linear Variable Differential Transducer (LVDT)
Linear variable differential transducer (LVDT) used to measure the displacement of specimen during testing. It is constructed with two secondary coils placed symmetrically on either side of a primary coil contained within the hollow cylindrical shaft as shown in figure 3.10.
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Figure 3.10: LVDT set up.
Load cell is a transducer, which converts force into a measurable electrical output. There are many types of load cells which are hydraulic load cell, Pneumatic load cells, and strain gauge load cells. In this experiment, a strain gauge load cell was used to concert the load acting on them into electrical signals. The gauges themselves were bonded onto beams that deforms when weight is applied. All gauges were wired with compensation adjustment as shown in Figure 3.11.
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Figure 3.11: Load Cell
Data logger is a device that reads various types of electrical signals and store data in its internal memory to be downloaded into a computer. It converts the electrical signals from instruments (strain gauges and LVDT) to strain (µÎµ) and deflection (in mm) as shown in Figure 3.12.
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Figure 3.12: Data Logger
Flexural strength is the ability to resist an applied bending force. A determination of the flexural strength is frequently necessary as part of the design of concrete mixtures to check compliance with established specifications or to provide information necessary to design of an engineering structure. In the flexural-strength test, a test load applied to the sides of a tested beam. During flexural-strength test, four bending points were used as shown in Figure 3.13 and Figure 3.14.
500 P 500 P 500
All Units: mm
50 1400 (GFRP) 50
Side elevation Strain gauge location
Figure 3.13: RC Beam test set-up
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Figure 3.14: RC beam test set up at the laboratory