REINFORCED CONCRETE BEAMS STRENGHTENED WITH NEAR SURFACE MOUNTED CARBON FIBER REINFORCED POLYMER (CFRP) ROD UNDER SALTWATER EXPOSURE Amiruddin Mishad
Mohd Hisbany Mohd Hashim
Senior Lecturer, Msc, Assoc. Prof., PhD, Prof., PhD, Faculty of Civil Engineering, Faculty of Civil Engineering, Faculty of Civil Engineering, Universiti Teknologi MARA, Malaysia Universiti Teknologi MARA, Malaysia Universiti Teknologi MARA, Malaysia Telephone number : +60355436189 Telephone number :+60355436423 Telephone number :+60355435263
[email protected] [email protected]
edu.my Mohd Norazizi Herry Marpi
Graduate Student, BSc., Faculty of Civil Engineering, Universiti Teknologi MARA, Malaysia Telephone number :+60109694996
Polymer (GFRP) has become the staple in the building industry in the mid-1930. Besides that, the development of Fiber Reinforced Concrete (FRP) for commercial use was being extensively research in 1930's while carbon fiber production began in late 1950 but not been used widely. Then, today Carbon Fiber Reinforced Concrete Polymer (CFRP) has been one of the demanding reinforcement in the industries.
ABSTRACT The existing structure such as building and bridge may require rehabilitation and strengthening to overcome defect and environment deterioration. Nowadays, Fiber Reinforced Polymer (FRP) becomes very popular in construction industry for repairing and strengthening structure because it has high tensile strength, long lasting, high durability, high corrosion resistance, low maintenance and lighter weight. This research studies the flexural performance of reinforced concrete beams strengthened with Carbon FRP rod. Three numbers of beam samples with dimension of 125mm x 300mm x 1800mm were prepared and mark as control beam, second beam and third beam. Control beam and second beam were cured at normal environment condition, while third beam were cured in saltwater solution for 28 days. All beams were tested using four point bending test, 30% of maximum load from control beam applied to second and the third beam to determine the pre-crack for the beam. Second and third beam were strengthened with CFRP rod using near surface mounted (NSM) method. The flexural strength for concrete beam for second beam is higher compared to control beam and third beam. Normal environment condition and saltwater solution did not give significant bad effect for the flexural performance of the beam.
Three reinforcement concrete beams were produced with the same mixture to check the flexural behaviour. The first reinforcement concrete was tested until the maximum bending then the other two reinforcement concrete were checked the behaviour until 30 percent of pre cracked load. The Reinforcement Concrete (RC) beams with 30 percent of cracking were strengthened with Carbon Fiber Reinforce Polymer (CFRP) using Near Surface Mounted (NSM) method. One of the beam was undergone process with air cured while the other one was cured with salt water solution. After that, the flexural behaviour were tested again. In addition, the results of the experiment were compared with the theoretical result. This paper describes use of experimental analysis in an attempt to identify the behaviour of the reinforced concrete beam. The work has been aimed at investigating on the behaviour of the reinforced concrete beam at their maximum flexural strength and providing the engineer with design information essential for the improvement of new and old structure of buildings.
Keywords Fiber Reinforced Polymer (FRP), Carbon Fiber Reinforced Polymer (CFRP), Near Surface Mounted (NSM), Four Point Bending Test, Normal Environment Condition, and Saltwater Solution.
2. LITERATURE REVIEW Fiber Reinforced Polymer (FRP) is a composite material made of a polymer matrix reinforced with fibers, normally it consist of carbon, glass, basalt or aramid with their different strength as shown in Figure 1. The polymer used usually a vinylester, epoxy or polyester thermosetting plastic and phenol formaldehyde resins. FRP rods are very useful in many types of construction especially building that required to enhance the strength such as old building. In addition, new building such as there were mistake in design causing the concrete cracks and not gain full strength also may require FRP for strengthening. FRP rods also able to solve the corrosion problem in steel due to its characteristic of high resistance to corrosion, structure that exposed to the marine
1. INTRODUCTION Fiber Reinforced Polymer (FRP) is a composite material made of a polymer matrix reinforced with fibers, it's an extremely strong, light, flexible, corrosion resistance and also high impact of resistance. Fiber Reinforce Polymer (FRP) is made of either carbon fiber, glass fiber, or aramid fiber. Polymer is usually an epoxy, vinyl ester, polyester thermosetting plastic and phenol formaldehyde resins are still in use. History says, Bakelite is the first Fiber Reinforce Polymer (FRP) and was develop by Belgian born chemist Leo Baekeland in New York in 1907, it was the first plastic made from synthetic component. Glass Fiber Reinforced 1
chloride such as sea walls and coastal construction that exposed to salt fog mainly using FRP rods as an additive reinforcement.
Figure 2: Example deformation of steel reinforcement bar at dock (Grace et. al., 2005)
3. EXPERIMENTAL PROGRAM 3.1 Carbon Fiber Reinforced Polymer According to  and , reinforced concrete beams were strengthened with CFRP rod using Near Surface Mounted (NSM) method and its arrangement bars shown in Figure 3. CFRP has properties of light weight, longer life time, high elastic modulus and fatigue strength. Therefore, CFRP had been used in the research project as internal strengthening material. In this study, the cross sectional area of CFRP rod used is 11mm with 1500mm in length. The modulus elasticity is 165Gpa.
Figure 1: Stress –Strain Curves of Typical Reinforcing Bars (ACI 440, 2006) According to Hisbany et. al. , corrosion due to chloride is not suitable for ‘Patch repair’ technique for treating corrosion because to remove all the penetrated chloride is costly and difficult, chloride that remains on the adjacent side of the affected area will initiate new corrosion circuit. In addition, cracks are formed as the steel reinforcement is corrodes and swells therefore the introduction of FRP in the industry is very worthy in order to solve the problem moreover FRP ability to resist corrosion and enhance performance of the structure give an advantages to the client since the cost may be reduce. Therefore, numerous numbers of researches are conducted on the use FRP in the structural element such as beam and column. Beam was strengthened using NSM system before tested using four point bending test. NSM system is conducted with the FRP bars were inserted into a grooves that is made in the surface of the concrete with a concrete saw. Then, the grooves were filled with epoxy adhesive to bond the FRP to the concrete. While, according to Lorenzis and Nanni , NSM strengthens the flexural members by installing FRP composite material in longitudinal position near the concrete cover.
(All dimensions are in mm)
Figure 3: The arrangement and cross-sectional area and dimension for CFRP bar
3.2 Specimen In this test program, three (3) samples of beams had been used and the first sample was the normal Reinforced Concrete (RC) beam acted as as control for this experiment. The second sample, reinforced concrete that was undergone air cured process for twenty eight (28) days then strengthened using Carbon Fiber Reinforced Polymers (CFRP) rod.While the third sample, reinforced concrete was immerged into salt water for twenty eight (28) days and strengthened using Carbon Fiber Reinforced Polymer (CFRP) rod.Three (3) samples of the beams had same size which was 125mm x 300mm and 1800mm in length as shown in Figure 4.
Sea wall, bridges and building at coastal area are types of structure that exposed to the salt water or sea water. Generally, concrete structure is partially exposed to a sea water or salt water which mainly lower structure was immerged in sea water while the upper structure was exposed to the environment. Salt water or mostly known as sea water contains magnesium chloride, sulphate ions and hydrogen carbonation ions that will cause the concrete to crack at certain degree and times. The major effect of salt water to concrete structure is causing a corrosion to steel reinforcement bar inside concrete structure as stated in Figure 2. The chloride and sulphate ions in salt water was weaken the nominal cover of concrete which protects steel from corrosion. Consequently, salt water was soaked into the concrete and the corrosion process begins on the steel reinforcement bar. Corrosion of steel reinforcement bar is the main causes of concrete structure deterioration. According to Grace et. al., , salt water can causes concrete structure suffered strength and stiffness deterioration due to corrosions cause by salt water. The steel reinforcement reduces in cross sectional area which then effect the strength of concrete. Hence, bond between reinforcement and concrete is really important because high quality of concrete structure is having good strength and stiffness.
Figure 4: The example of reinforced concrete beam dimension
Tables 1 and 2 shows the result of ultimate load capacity obtained from the experimental study is 113.14kN for control beam which was lower than the two beams. However, beam was undergone air cured process was higher than beam immerged into salt water. The result recorded that the value of the ultimate load capacity for the beam undergoes curing process is 120.95kN. CFRP bar gave improvement to the beam because the ability to resist tension more than steel while under the load application.
3.3 Flexural Strength Figure 4 is flexural strength tests were conducted on all specimens after 28 days of air cured or immerged into salt water. Before testing is conducted, all the specimens were painted in white colour to increase the visibility of crack during the process of test. All the specimens were tested using the same testing procedure. The 250kN Universal Testing Machine at heavy Structure Laboratory,UiTM Shah Alam was used to conduct the testing as shown in Figure 5.
The beam immerged into salt water achieved the ultimate strength at 118.36kN. Where, it is 4.6% higher than control beam. The differences of the ultimate load occur due to a few factors which are the ability of the CFRP bar to resist tension, amount of the material consumption, the age of the samples and the compaction of the materials during the casting of the sample. These factors lead to such result obtained from each sample. In addition, by theory the result of maximum load should be 100kN. The testing shows that the maximum loads are different from the theoretical. The different ratios for the control beams over theory is 1.1314, while the beam curing and beam immerged into salt water are 1.2095 and 1.1836 respectively.
Figure 5: Experimental setups for four point flexural strength test
Table 1: Percentage difference of ultimate load for each sample of beam
4. RESULT AND DISCUSSION 4.1 Load Displacement Relationship Of Beam Flexural test implemented after Reinforced Concrete (RC) Beam specimens reached 28 days to achieve the compressive strength of the concrete. The objectives of this study were to determine the maximum flexural strength, behaviour of Reinforced Concrete (RC) beam strengthened using Carbon Fiber Reinforce Polymer (CFRP) and maximum flexural strength of RC beam that immerged into salt water. The beam transferred the subjected load from the structure to the column and footing. Based on the calculation, the reinforced concrete beam fully failed at 100kN of applied load and the maximum load applied in the laboratory was about 250kN. The RC beam sustained the applied load until reach it limits. When the applied load reaches the limit, RC beam failed either in bending or shear. These tests affected the displacement and strains of reinforced concrete beam due to the vertical load applied is shown Figure 6. Increases of applied caused yielded of steel bar and increased on cracking load was considerable. Besides that, the deflection and strain increase due to increment of applied load.
Ultimate load, kN
Different % of sample to control beam
Different % sample to beam (air cured)
Beam (air cured)
Beam (immerged into salt water)
Table 2: The comparison between load ultimate and load theory Maximum Load, kN
Load Ultimate Load Theory
Beam (air cured)
Beam (immerged into salt water)
4.2 Crack Pattern Of Flexural Strenghtened With NSM Rod
All the beam samples experienced the nearly same mode of failure as stated in Figure 7. The first mode was occurred due to bending which concrete crushing at the top fiber cross section after
Figure 6: The graph of load (kN) vs displacement (mm) of all sample beams 3
yielding of the tension steel reinforcement. The second mode occurred due to shear failure, a crack from mid span to support shows that the shear cracks develop on the beam travelled inclined until the ends of the beam. The peeling failure of concrete also occurred when the beam was undergone the near failure applied load. The first cracks start with the flexural cracks and after a while the critical shear crack formed.
Furthermore, in terms of failure mode, the beam with CFRP bars experienced the shear, flexural and crack failure. Following conclusion are drawn based on the performance and analysis of the control beam and other two sample beam which strengthen with CFRP bars after undergoes curing process and the beam strengthen with CFRP bars after has been immerged into salt water from the experimental results.
Flexural failure for the beam always occurs at the mid span of the beam. Flexural cracks on the sides of a beam started at the tension face and was extended, at most, up to the neutral axis. For this experiment, the first crack was occurs at mid span of the beam before it developing and move further towards support. Crack widths was greatest at the tension face and will reduce with distance from that face. The flexural failure for second and third beam occurs when less bond between CFRP rod and concrete.
The beams strengthened with CFRP bars gave higher ultimate capacity then control beam which is 120.95kN and 118.36kN.The beam was undergone air cured process has higher ultimate capacity which is 2.14 % than beam was immerged into salt water. The beam was undergone the air cured process then strengthened using CFRP bars has higher strength, ductility and durability compared with the control beam and the other sample beam.The Control beam and other beam samples have two modes of failures that are flexural and shear failures.
In this experiment, shear failure occurred when the beam reach near failure load. When the load applied increase, the micro crack was increase in size and form large crack. Shear crack occur from the support and move upward to the loading point at the top of the beam. For the second and third beam, shear failure happen when the debonding between CFRP rod and concrete occurred before the beam achieve the failure mode.As the main material of this beam was only plain concrete, the bond between the concrete and CFRP was only by using epoxy. Hence, the beam achieved the failure load after the debonding occurred between concrete and CFRP.
6. ACKNOWLEDGMENTS This work was supported in part by LESTARI under Grant Nos. 600-RMI/DANA 5/3/LESTARI (2/2016).The authors wish to express their appreciation to Universiti Teknologi MARA, providing the facilities assistance for successfully accomplishment of this research study.
7. REFERENCES  ACI Committee 440 (2006), “Guide for the design and construction of structural concrete reinforced with FRP bars”, ACI 440.1R-06, American Concrete Institute, Farmington Hills, MI., USA.  Mohd Hashim et. al. (2013). Jurnal Teknologi Full Paper Structural Performance and Ductility of Fiber Reinforced Polymer Concrete Bonding System Under Tropical Climates, 3(2013) 21–29.
 Suki, Nauwal, Mohd Hisbany, Mohd Hashim, and Afidah Abu Bakar (2014). Flexural Performance Of RC Beams Under Tropical Climate Effect, (2014) 9-13.
 De Lorenzis L and Nanni A. (2002). Bond between NSM fiber-reinforced polymer rods and concrete in structural strengthening, (2002) ACI Struct J.
 Grace, N. F., & Singh, S. B. (2005). Durability evaluation of carbon fiber-reinforced polymer strengthened concrete beams: experimental study and design. ACI Structural Journal 102 (1), 40, 2005.
Beam in air curing
 BS EN 1992-1-1:2004, Eurocode 2: Design of Concrete Structures (Part 1-1: General Rule and Rules for Building), CEN, April 16, 2004.  BS EN 1992-1-2:2004, Eurocode 2: Design of Concrete Structures (Part 1-2: General Rules Structural Fire Design), CEN, July 8, 2005. c)
Beam in saltwater solution
Figure 7: Modes of failure of all beams
5. CONCLUSION The results shows that beam strengthen with CFRP bars play an essential role to increase the capacity of tensile strength. Based on experimental result, the load capacity of the beam could up to 120kN. Therefore, this study proves that both of the beam which was undergone air cured process then strengthen using CFRP bars and the beam immerged into salt water and strengthen using CFRP bars can increase the tensile strength drastically. 4