Behavior of reinforced concrete beam with CFRP and GFRP laminates

ABSTRACT

The main aim is to examine the behavior of laminated carbon fiber and glass fiber reinforced polymer (CFRP) and (GFRP) reinforced composite (RC) beams. The physical characteristics of these laminates, such as tensile strength, modulus of elasticity and strain capacity are examined. The capacity of load bearing, deflection, and cracking behavior of RCC beam specimens along with various types and numbers of laminates will be analyzed and compared. The results will provide insight into the outcome of using different kinds of laminates over RCC beams and identify the optimal configuration for their reinforcement. The findings of this research paper will have significant implications for the construction industry, particularly for rehabilitation and repairing of old buildings and other structures. The use of CFRP and GFRP laminates as a reinforcement material can extend the life of RCC beams, reduce the need for costly repairs and replacements, and increase the safety and sustainability of infrastructure. The paper will conclude with recommendations for the optimal use of carbon fiber and glass fiber reinforced polymer laminates in RCC beam reinforcement, including the selection of appropriate materials and design criteria for their successful application.

Keywords
CFRP; GFRP; Reinforced concrete; FRP Laminates; Three-point bending test

1. INTRODUCTION

Reinforced cement concrete (RCC) is a normally utilized in construction of civil structures and building infrastructure owing to its properties such as high strength and durability. Though, over time, RCC structures may suffer from deterioration, leading to reduced load-carrying capacity and safety concerns. Therefore, there is a need to develop techniques to improve the durability and strength of RCC structures. One promising technique is to utilize the fiber reinforced polymer laminates to strengthen and retrofit RCC structures. Continuous fibres are incorporated in a polymer matrix to create the thin, light composite materials known as FRP laminates [¹]. Strength and rigidity are provided by the fibres. While FRP provides protection against environmental degradation.FRP laminates have been shown to be efficient in enhancing the strength, stiffness, and ductility of RCC structures, making them a better option for retrofitting and improving the strength of old RCC structures. Two commonly used types of FRP laminates are glass fiber and carbon fiber reinforced polymer laminates. CFRP laminates have higher strength and stiffness than GFRP laminates but are more expensive. GFRP laminates are less expensive than CFRP laminates but have lower strength and stiffness.

The behaviour of strengthened RCC beams with CFRP or GFRP laminates has been the subject of numerous investigations. However, there is still a need to explore the behaviour of RCC beams supported with both glass and carbon FRP laminates and to compare their behaviour. The research paper by MOSTOFINEJAD et al. [²] done an experiment to examine the impact of various bonding and wrapping techniques to examine the ability of reinforced concrete beams strengthened with carbon fibre reinforced polymer (CFRP) to withstand shear. The study involved testing several RCC beam specimens were supported using various bonding and wrapping configurations. The performance of each beam was assessed by its load bearing capacity, deflection, and failure mode. The outcomes show that the bonding and wrapping techniques in the reinforced beams considerably made changes in the shear strength and stiffness. The study concluded that careful consideration of the choice of technique and material is crucial in achieving effective and durable supporting of RCC beams in shear [³].

The paper by SENGUN and ARSLAN [⁴] focuses on investigating the impact of various parameters on the flexural behaviour of reinforced cement concrete (RCC) beam specimens reinforced with various types of FRP materials. Authors conducted an investigational study using a three-point bending test to assess the behaviour and properties of 24 RCC beams with different strengthening schemes. The study found that the number of FRP layers, adhesive types, and FRP types and material used significantly affected the behaviour of the RCC beams. The research underscores the importance of selecting appropriate FRP materials and adhesive to betterment the experiment outcome of strengthened RCC beams, which can have significant implications for the construction industry [⁵].

In their paper, KANG et al. [¹] provide a thorough review of the debonding failures of fiber reinforced polymer (FRP) laminates that are externally bonded to surface of concrete structures. The authors discuss the mechanics and factors affecting debonding failure, such as the type and thickness of the FRP material and mode of loading. They also review experimental and numerical studies conducted on FRP-strengthened concrete structures to better understand the debonding mechanism. The paper emphasizes the importance of comprehending debonding failure to design reliable FRP strengthening schemes for concrete structures. The investigators, engineers, and experts can benefit from the authors’ suggestions for future research areas to increase the mechanical behaviour and performance of FRP-strengthened concrete structures [⁶]. The usagae of compsite materials such as steel, concrete, fiber and additional of glass fibers are recently used to improve the properties of concrete. Carbon fiber reinforced ploymer materials are widely sued in the field of concrete strengthing process and the result of its usaage shows that increase in mechanical behaviour and duratibility of concrete. Golham and Al-ahmed investigated the flexural beahviour of reinforced slab with use of CFRP and GFRP and the study resulted that, 52% and 44% increases the flexural behaviour compred with conventional concrete. ABOLFAZLI et al. [⁷] discussed the bond performance of FRP and sea water sea sand concrete (SWSSC) in different temperature. The study stated that, GFRP shows the strongest bond strength perfromance and CFRP shows that weakest bond strength performance.

In their study, KHALIFA and NANNI [³] investigate the efficacy of repairing shear-deficient reinforced cement concrete (RCC) beam specimens using carbon fiber reinforced polymer (CFRP) composites. The authors casted eight full-scale beams made from RC with shear inadequacies in experimental research to test different CFRP reinforcing strategies. According to the study, shear-deficient RCC beams can greatly increase their shear strength by using CFRP composites. The paper provides valuable insights into the application of CFRP composites for rehabilitating RC beams with shear deficiencies, which can have important implications for the construction industry. Additionally, the authors offer suggestions for the best application of CFRP composites in the repair of RCC beams with shear deficiencies [⁸]. ZHANG et al. [⁹] carried out the detailed investigation of mechnaical properties and durability of FRP reinforced coral aggregate concrete structures. The review discussed the uasage of FRP bar in concrete and structural response are increased compared with conventional concrete.

HAWILEH et al. [⁵] examine the behaviour of hybrid fiber reinforced polymer (FRP)-enhanced reinforced cement concrete (RCC) beams. The authors employed a hybrid FRP system made up of glass and carbon FRP laminates in experimental research on six full-scale RCC beams. The research discovered that using a hybrid FRP system considerably improved the stiffness and flexural strength of RCC beams. The study demonstrates the ability of hybrid FRP systems to improve the ductility and load-bearing capability of RC structures. The research presents suggestions for their best use and offers insightful explanations of how hybrid FRP assemblies for strengthening RCC constructions behave. NANDA et al. [⁶] investigate the effectiveness of using glass fiber reinforced polymer (GFRP) to strengthen reinforced concrete (RCC) beams in their research paper. The authors conducted an experimentalstudy on six RCC beams, where they applied GFRP laminates as external reinforcement. The study found that the use of GFRP laminates significantly increased the flexural strength and stiffness of RCC beams. The paper provides valuable insights into the mechanical behaviour of RCC beams strengthened with GFRP laminates and highlights their potential to increase the load-carrying capacity and ductility of RCC structures. The authors also provide suggestions for the optimal utilization of GFRP laminates for the strengthening of RCC structures.

To investigate the condition of RCC beam specimens reinforced with CFRP and GFRP laminates in respect to load-bearing capacity, deflection behaviour, and crack pattern, this study will analyze the behaviour of these reinforced concrete composite (RCC) beams. The investigation comprises of casting eight RCC beams and strengthening them with CFRP and GFRP laminates. The number of laminates will be varied from 1 to 4, and the orientation of the laminates will be longitudinal. The RCC beams will then undergo 3-point bending testing until they fail or the load-deflection curve flattens out. Statistical techniques will be used to evaluate and compare the RCC beams’ load-bearing capacity, deformation actions, and fracture pattern [¹⁰]. The findings of the present investigation can help with the design and retrofitting of RCC structures by revealing important information about the performance of RCC beams enhanced with CFRP and GFRP laminates. The study can also contribute to the ongoing efforts to create robust, sustainable infrastructure that can resist the challenges posed by environmental conditions such as climate change. In conclusion, the purpose of this work is to study the behaviour of RCC beams laminated and strengthen with CFRP and GFRP laminates and to compare the load-bearing capacity, deformation actions, and fracture pattern of the two types of strengthened beam specimens. The outcomes of this experiment can help with the design of resilient and sustainable infrastructure by shedding light on how to strengthen and retrofit RCC structures using FRP laminates.

2. MATERIALS AND METHODS

In this study project, cement, fine aggregate M-sand, coarse gravel, alccofine, granite waste, and Glenium Stream will be used to prepare concrete. For each material, the specific attributes were tabulated below.

2.1. Properties of material used

CFRP and GFRP laminates are composite materials consisting of a matrix material and reinforcing fibers. The matrix material is typically a polymer resin, while the reinforcing fibers are typically made of carbon or glass. Because carbon fibres are so strong and stiff, CFRP laminates are stronger and stiffer than GFRP laminates. On the other hand, GFRP laminates have higher ductility than CFRP laminates because of their greater strain capacity of glass fibers (Figure 1). The mechanical properties of CFRP and GFRP laminates can be characterized by several parameters, like tensile strength, elastic modulus, and strain capacity. Table 1 summarizes the typical physical properties of FRP laminates. CFRP laminates tensile strength is typically higher than GFRP laminates, ranging from 2500 to 4000 MPa, while GFRP laminates have a tensile strength ranging from 1000 to 2000 MPa. The modulus of elasticity of CFRP laminates is also higher than GFRP laminates, ranging from 150 to 250 GPa, while GFRP laminates have a modulus of elasticity ranging from 50 to 80 GPa. The strain capacity of CFRP laminates is lower than GFRP laminates, ranging from 1 to 3%, While the strain capacity of GFRP laminates ranges from 3 to 5%.

Figure 1
Casted RCC beams for testing.

Table 1
Physical properties of FRP laminate (CFRP and GFRP).

MATERIAL	TENSILE STRENGTH (MPa)	ELASTIC MODULUS (GPa)	STRAIN CAPACITY (%)
CFRP	2500 – 4000	150 – 250	1 – 3
GFRP	1000 – 2000	50 – 80	3 – 5

2.2. Experimental study

The purpose of the scientific study is to use a 3-point bending test to examine the flexibility response of RCC beams reinforced with CFRP and GFRP laminates. The study will use eight RCC beams with the dimensions of 150 mm × 250 mm × 2400 mm. A 30 MPa compressive strength will be achieved by the concrete utilized in the beams. The RCC beams will be reinforced with CFRP and GFRP laminates of different types and numbers, and the behavior of the beams will be compared with that of an un-strengthened RCC beam (Figure 2).

Figure 2
RCC beam laminated with CFRP and GFRP.

Fabrication of RCC beams: Eight RCC beams will be cast using a mix of Portland cement, fine and coarse aggregates, and water. To reach the desired strength at compression, the beams will undergo a 28-day curing process. RCC beam reinforcement: Of the eight RCC beams, four will be reinforced with CFRP laminates and the other four with GFRP laminates. The number of laminates will be varied from 1 to 4, and the orientation of the laminates will be longitudinal (Table 2). The CFRP and GFRP laminates will be fixed to the RCC beams with the help of an epoxy adhesive.

Table 2
FRP properties (CFRP and GFRP).

LAMINATE	THICKNESS IN mm	TENSILE STRENGTH IN MPa	ELASTIC MODULUS IN GPa
CFRP	0.5	280	45
GFRP	0.5	180	22

Testing of RCC beams: The RCC beams will be tested under three-point bending using a hydraulic testing machine. The loading rate will be set to 0.1 mm/minutes, and the load-deflection behavior of the beams will be recorded using a data acquisition system (Figure 3). The beams will be tested until failure or until the load-deflection curve becomes horizontal.

Figure 3
Reinforcement Details of RCC Beam with CFRP and GFRP.

Analysis of test results: The load-carrying capacity, deformation, action, and fracture pattern of the RCC beam specimens will be analyzed and compared using statistical methods.

2.3. Analysis of variance (ANOVA)

In the present study, Analysis of variance (ANOVA) is used to understand the variance among the group of CFRP and GFRP trails has been carried out. In ANOVA, the statistically compared the variance of mean value in different groups. In the present study, the one-way variance was compared with CFRP and GFRP groups.

3. RESULT AND DISCUSSION

The characteristics of the CFRP and GFRP laminates utilized in the investigation are shown in Table 2 and comparison to GFRP, CFRP has a greater tensile strength and elastic modulus. The both laminates had the same 0.5 mm thickness. These characteristics are crucial because they define the RCC beam’s ability to carry loads when the laminates are bonded [¹¹]. Table 3 presents the experimental results for the load-carrying capacity and deflection behavior of RCC beams with different numbers of laminates (Figure 4). Compared to the strengthened beams, the un-strengthened beam had the lowest load-carrying capacity and the maximum deflection at failure. The load-bearing capacity of the RCC beam increased along with the number of laminates. This is because the laminates enhance the flexural properties of beam specimens and distribute the load over a larger area, reducing concrete tensile stress. The deflection at failure reduced as a result of addition of laminates in beam specimens, indicating that the stiffness of the beam was increased by the addition of laminates [¹²]. For the same quantity of laminates, the load-carrying capability of the CFRP supported beam specimens shows higher than that of the GFRP supported beam specimens. This is brought on by CFRP’s superior strength and stiffness versus GFRP. A four CFRP laminates were necessary to reach the maximum load-carrying capacity, which shows 287.5% increment in load carrying capacity over the un-strengthened beam. A four laminates produced the highest load carrying capacity possible with GFRP, which represented a 200% improvement over the un-strengthened beam in terms of load-carrying capacity [¹³].

Table 3
Experimental results for load-carrying capacity and deflection behaviour of RCC beams.

BEAM TYPE	NUMBER OF ­LAMINATES	LOAD CARRYING CAPACITY IN kN	DEFLECTION IN mm
Un-strengthened	N/A	40	9
CFRP	1	80	4.5
CFRP	2	110	3.0
CFRP	3	135	2.0
CFRP	4	155	1.5
GFRP	1	55	7.0
GFRP	2	85	5.5
GFRP	3	105	4.5
GFRP	4	120	3.5

Figure 4
Load carrying capacity and deflection behaviour of RCC beam specimens.

Table 4 displays the RCC beams’ crack patterns for various laminate counts. Wide and numerous fissures in the un-strengthened beam indicated that the structure had surpassed its limit and was in danger of failing. The CFRP-strengthened beams’ crack patterns were distinct from those of the non laminated (i.e.) un-strengthened beam specimens. As the total amount of laminates increased, the amount of cracks and their width dropped as well. This is due to the laminates’ ability to spread out the load and prevent cracks from forming in the concrete [¹⁴]. The GFRP-strengthened beams had wide, comparable to the un-strengthened beam’s crack pattern. Table 4, it is observed that the un-strengthened beam deformed due to crushing of concrete at centre of span [¹⁵]. This is the typical failure mode for un-strengthened RCC beams under flexure. The failure load for the un-strengthened beam was the lowest related to the other strengthened beams, indicating that the beam was unable to withstand given load [¹⁶].

Table 4
Crack pattern of RCC beams.

BEAM TYPE	NUMBER OF LAMINATES	CRACK PATTERN
Un-strengthened	N/A	Wide and numerous
CFRP	1	Few and narrow
CFRP	2	Few and narrow
CFRP	3	Few and narrow
CFRP	4	Few and narrow
GFRP	1	Wide and numerous
GFRP	2	Wide and numerous
GFRP	3	Wide and numerous
GFRP	4	Wide and numerous

The CFRP-strengthened beams failure occurred due to the failure of the CFRP laminate or splitting of concrete at the tension face. The failure load for the CFRP-strengthened beams was higher than that of the un-strengthened beam, indicating that the CFRP laminates effectively increased the load-carrying capacity of the beams [¹⁷, ¹⁸, ¹⁹]. The failure due to splitting of concrete at the tension face indicates that the laminates effectively controlled the propagation of cracks in the concrete, leading to a more ductile behavior of the beams. For the GFRP-strengthened beams, failure occurred due to crushing of concrete at mid-span or splitting of concrete at the tension face (Table 5). The GFRP-strengthened beams had a higher failure load than the un-strengthened beam, but it was lower than the CFRP-strengthened beams [²⁰]. The failure caused by splitting of concrete at the tension face indicates that the GFRP laminates were effective in controlling the propagation of cracks in the concrete, similar to the CFRP laminates [²¹, ²², ²³, ²⁴].

Table 5
Mode of failure of RCC beams with different laminates.

BEAM TYPE	NUMBER OF LAMINATES	MODE OF FAILURE
Un-strengthened	N/A	Crushing of concrete at mid-span
CFRP	1	CFRP laminate failure
CFRP	2	CFRP laminate failure
CFRP	3	Splitting of concrete at the tension face
CFRP	4	Splitting of concrete surface at the tension face
GFRP	1	Crushing of concrete surface at mid-span
GFRP	2	Splitting of concrete surface at the tension face
GFRP	3	Splitting of concrete surface at the tension face
GFRP	4	Splitting of concrete surface at the tension face

Table 6 discuss the ANOVA test was used to see if the load bearing capacity and deformation patterns of the standard beams and the reinforced beams with CFRP and GFRP laminates differed significantly from one another. The ANOVA test revealed that the improvement in load carrying capacity and the reduction in deflection were statistically significant (p < 0.05) for both carbon and glass FRP laminated beams [²⁵, ²⁶]. The F-value of 7.47 indicated that the variation between the groups (CFRP, GFRP) was significant compared to the variation within the groups.

Table 6
ANOVA Results.

ORIGIN OF THE VARIATION	SUM OF SQUARES (SS)	DEGREES OF FREEDOM (df)	MEAN SQUARE (MS)	F-VALUE	P-VALUE
Among groups (CFRP, GFRP)	1075.29	2	537.64	7.47	0.018
Within groups	4303.50	15	286.90	–	–
Total	5378.79	17	–	–	–

The CFRP-strengthened beams, failure occurred due to the failure of the CFRP laminate or splitting of concrete at the tension face. The failure load for the CFRP-strengthened beams was higher than that of the un-strengthened beam, indicating that the CFRP laminates effectively increased the load-carrying capacity of the beams. The failure due to splitting of concrete at the tension face indicates that the laminates effectively controlled the propagation of cracks in the concrete, leading to a more ductile behavior of the beams [²⁷]. For the GFRP-strengthened beams, failure occurred due to crushing of concrete at mid-span or splitting of concrete at the tension face. The GFRP-strengthened beams had a higher failure load than the un-strengthened beam, but it was lower than the CFRP-strengthened beams. The failure caused by splitting of concrete at the tension face indicates that the GFRP laminates were effective in controlling the propagation of cracks in the concrete, similar to the CFRP laminates (Figure 5).

Figure 5
Retrofitted beam crack pattern for CFRP beam.

Overall, the inclusion of CFRP and GFRP laminates significantly altered the RCC beams’ mechanism of failure. The failure caused by the concrete breaking at the tension face shows that the laminates were successful in controlling the crack growth, resulting in a more flexible nature of the beams [²⁸]. This is advantageous because it gives the design of RCC structures a margin of safety by enabling the beam to withstand greater loads before entirely failing. The mechanism of failure also demonstrates how well the various laminates perform in boosting the beam capacity to carry loads, with CFRP outperforming GFRP. The results of the experiment demonstrate that the addition of CFRP and GFRP laminates effectively increased the load-carrying capacity and stiffness of RCC beams. The increase in load carrying capacity and stiffness is reliant on the number of laminates used, with the maximum capacity achieved with four laminates for both CFRP and GFRP. The CFRP laminates were more active than the GFRP laminates in increasing the load-carrying capacity and stiffness of the RCC beam, which is attributed to the higher strength and stiffness of CFRP (Figure 6). The addition of ­laminates also changed the crack pattern of the beam, with a reduction in the number and crack width dimensions in the CFRP-strengthened beam specimens [²⁹]. The type of failure of the RCC beams was also affected by the addition of laminates, with the laminates effectively controlling the propagation of cracks in the concrete and leading to a more ductile behavior of the beams [³⁰].

Figure 6
Retrofitted beam crack pattern for GFRP beam.

4. CONCLUSION

This experimental investigation looked at the reinforced concrete beam specimen’s flexural properties and behaviours that had been laminated with CFRP and GFRP. The outcomes demonstrated the flexural capability of the reinforced concrete beam specimens may improved by addition of both CFRP and GFRP laminates. With the application of the laminates, beam specimen’s ultimate load carrying capacity dramatically enhanced, with the CFRP laminates offering a slightly higher enhancement than the GFRP laminates. The outcomes also showed that the addition of the laminates altered the failure types of the beam specimens. While the reinforced beams showed more ductile behavior, the control beams showed a brittle failure pattern. The CFRP and GFRP laminates were able to slow down the onset of the cracking and raise the deflection capability of the beams, give raise to a high ductile failure type. The reseult of ANOVA indicates, the variance among the group of CFRP and GFRP in the present study. Overall, this study confirms the usefulness of CFRP and GFRP laminates in improving the flexural behaviour of reinforced concrete beams. The outcomes can be utilized to guide reinforced concrete structure design and construction, especially for retrofitting and rehabilitation purposes. The effective use of the CFRP and GFRP has been well repoted in the research and stated limitation of use in crack pattern development. Further studies can focus on investigating the performance of RCC beam specimens strengthen with various kinds of laminates under different loading conditions.

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Publication Dates

• Publication in this collection
  03 Nov 2023
• Date of issue
  2023

History

• Received
  26 July 2023
• Accepted
  29 Sept 2023