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Experimental investigation of RC beams strengthened with externally bonded BFRP composites

  • Ali K. Al-Asadi EMAIL logo , Salih K. Alrebeh and Waleed Kh. Hadi
Published/Copyright: February 23, 2024
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Open Engineering
From the journal Open Engineering Volume 14 Issue 1

Abstract

Objectives

The goal of this article is to examine the behavior of reinforced concrete (RC) rays that strengthen superficially the basalt fiber-reinforced polymer (BFRP) fabrics. We found out that one ray without BFRP and seven rays enveloped within numerous lay-up arrangements. The importance of the study is to improve the flexural capacity of rays, using fiber-reinforced polymer procedure and examine the over-reinforcement technique.

Methods

Interestingly, we have examined under two-point loading, one BFRP fabric sheet flexure.

Results

Loads corresponding to the first crack/delamination and ultimate failure of the beams have been verified. Moreover, we have recognized the types of failure and load contrasted with deflection graphs that have been strategized at outstanding ray locations.

Novelty

Our investigation has unraveled the increased flexural strength of the strengthened RC rays after using coating. Additionally, we have applied pressure to the BFRP fabrics on both sides of the beams. Moreover, we have improved performance with flexural strength, ductility, and failure. Our results are novel and show that the flexural capacity of the wrapped RC rays increases by 46.6%. The ductility increased by 84%, and unfortunately, we had failed the FRB and the concrete had crushed.

Keywords: strengthening basalt fiber-reinforced polymer; reinforcement concrete RC beams; rays; externally bonded; flexural behavior; ductility

1 Introduction

Production of novel fiber-reinforced polymer (FRP) is gaining increased attention worldwide [1,2,3,4,5,6,7]. Basalt fiber-reinforced polymer (BFRP) is a novel kind of inorganic fiber that is robust and armored. As the name suggests, basalt fiber is composed of pure natural basalt, which is less expensive than carbon fibers. Basalt fiber is unique because of its high strength, good durability, remarkable fire resistance and electrical insulation, and resistance to acid, alkali, and chemical corrosion [8,9,10]. A considerable number of research works have investigated fiber. Nevertheless, some of it has been performed on the consolidation of reinforced concrete (RC) beams/girders using lightly joined BFRP laminates/sheets.

Other researchers have examined the mechanical and basalt fibers' stability and concluded that they display durable stability weathering. Moreover, it showed high-temperature criteria as associated with glass or carbon fibers [11]. Likewise, basalt fibers originate from volcanic rock [12]. Fabric, along with other forms, might be used as clearly combined combinations for consolidation and recovery of various structural components. The superficially fused FRP combinations in solidification beams in flexure reach the limit of their presence with the fibers involved in the longitudinal route. According to Sim et al. and Lihua et al., BFRP is noticeably devoted when used as a flexural hardening agent for RC beams. The modifications fortified RC rays with variable numbers of layers positioned to one direction BFRP sheets and learned that a higher number of layers of BFRP augmented beams with final measurements. Nevertheless, these experiments found that if sparse distance is selected, failure by interfacial deboning can arise, which is unwanted.

Fiore et al. [13] have indicated that based on the mechanical properties of BFRP, the load capacity of the structural element has improved. Additionally, owing to the high compressive properties of BFRP, RC components have a greater strength capability based on the experimental study completed. According to Pawłowski and Szumigała [14], the RC beam increased by BFRP acted as linearly as possible for failure. According to Shen et al. [15], the central assumptions have been reported that the RC box beam repaired with BFRP reduces the progress of concrete flaws. Moreover, the toughness and natural frequency of the renovated beam were increased by 16.6 and 8.0%, respectively, in comparison to the naked ray.

According to the experimental work of Qin et al. [16], the application of a two-point load has twisted severely pre-cracked RC beams braced with BFRP sheets to their intact state.

According to the experimental studies conducted by other researchers [17,18], pre-cracks in the concrete had no effect on the RC ray enhanced by BFRP. The cost of structural element remediation is nearly equal to the cost of permutation, so the process would become cost-effective. Ma et al. [19] reported that the flexural capacity of RC specimens strengthened with BFRP sheets can be significantly improved, and the BFRP sheets can limit the crack propagation of concrete structures and improve their ductility [20].

Several researchers have documented the use of BFRP sheets in the seismic solidification of building and bridge structures. Lu et al. [21,22,23] conducted a training on the seismic earthquake-damaged concrete edge joints covered with BFRP. Only a few studies on the use of BFRPs in concrete beams for flexural strengthening are available [24]. As a consequence, analysis of the use of BFRP materials for flexural RC beams is considered necessary. As a matter of fact, this article offers a presentation test of RC beams reinforced with basalt fabrics as a composite.

2 Experimental program

The current study uses a trial to extrapolate the structural behavior of RC beams by wrapping those beams in BFRP fabric. Different BFRP wrapping patterns were used to achieve the aim of this work. Eight RC beams were prepared and tested. One of these beams was used as a reference beam (without using BFRP fabric). The strategy for testing the RC beams was by applying the two-point loading. All the beams have the same dimensions. The material qualifications are presented in the following sub-sections.

2.1 Material properties

2.1.1 Ordinary Portland cement

A Portland cement CEM I 42.5R based on Turkish qualifications TS EN 197 [25] was used in this work to manufacture self-compacting concrete (SCC) for comparison purposes.

2.1.2 Fly ash (FA)

Class F. FA was utilized for fixing the RC specimens, as shown in Figure 1. Furthermore, FA is a very beneficial material, which has a spherical microstructure and affords high flow ability. It was delivered by warm air control Ceyhan Sugözü Turkish herb [26].

Figure 1 FA picture that was employed in the fixing RC.
Figure 1

FA picture that was employed in the fixing RC.

2.1.3 Aggregates

The local coarse aggregate was used with a nominal size of 10 mm, while the river sand and fine crushed stone were used as the fine aggregate with a maximum size and specific gravity of 2.6. Figure 2 shows the aggregate used in the mix design of all samples, while Figure 3 shows the volumetric pitches of the rough and fine collections.

Figure 2 Aggregates used in the mix design. (a) Coarse aggregate. (b) Fine aggregate. (C) Fine crushed stone.
Figure 2

Aggregates used in the mix design. (a) Coarse aggregate. (b) Fine aggregate. (C) Fine crushed stone.

Figure 3 Gradients of volume for rough and small smash aggregate.
Figure 3

Gradients of volume for rough and small smash aggregate.

2.1.4 Superplasticizer

Figures 3 and 4 show that sulfonated naphthalene formaldehyde has a declining additive specific gravity of 19. The superplasticizer was transformed across the mixing process in order to improve the assortment’s workability. Superplasticizer was purchased from a neighborhood provider; all information is shown in Table 1.

Figure 4 Superplasticizer used in our study.
Figure 4

Superplasticizer used in our study.

Table 1

Characteristics of superplasticizer

Belongings Superplasticizer
Term Viscocrete 30
Color Dark brown
State Liquid
Specific gravity (kg/l) 1.07
Chemical composition Modified polycarboxylic-type polymer
Amount 1–2% (% binder content)

2.1.5 BFRP fabrics and resin

In this study, the RC beams were strengthened using unidirectional BFRP fabric. This type of fabric was chosen because of its fire resistance, availability, smooth consistency, resilience, low price, and high tensile as compared to fabric. The mechanical features of the fabric are displayed in Table 2. More details of the epoxy used, Master Brace 4500 epoxy resin, were linked to the BFRP fabric on the exterior concrete side. According to the company, the epoxy resin had a compressive strength greater than 60 MPa, a bending strength greater than 50 MPa, and a bond strength greater than 3 MPa. The necessary amount of epoxy (A + B) is added in a 3:1 ratio. Figure 5 displays epoxy resin that connects to BFRP sheets. The procedural text determined upon the presentation of the bonding agent to the ray examination samples. The mechanical characteristics of the used epoxy resin have been described in detail by an independent group of scientists [27].

Table 2

Dimensions and properties of basalt fiber fabric

Tensile strength (MPa) Tensile modulus of elasticity (GPa) Elongation (%) Thickness (mm) Area weight (g/m2)
2,100 105 2.6 0.3 300
Figure 5 Epoxy resin used for bonding and BFRP sheets.
Figure 5

Epoxy resin used for bonding and BFRP sheets.

3 Specimen preparation

The theoretical capacity of beams depends on external reinforcement. The dimensions and system of steel reinforcement for all specimens were similar. The dimensions of each specimen were 100 mm × 150 mm × 1,000 mm. In addition to the 8 mm stirrups that measure 75 mm from center to center, the specimens' system of reinforcing bars consists of four longitudinal steel bars, two of which have a diameter of 10 mm at the tension zone, and the other two bars have a diameter of 8 mm at the compression zone. For 8 and 10 mm steel bars, respectively, the produce asset of reinforcement bars is 550 and 485 MPa, and the ultimate strength is 640 and 595 MPa. The concrete cover for all beams was 25 mm. Figure 6 shows the beam dimensions and reinforcement facts.

Figure 6 Dimensions and reinforcement of RC beam.
Figure 6

Dimensions and reinforcement of RC beam.

4 Mixture casting and curing condition

4.1 Mix design

The preparation of SCC has differed from that of conventional concrete due to the difference in placing and filling manner. SCC was chosen for use in experimental investigations since it included FA. SCC improves concrete-to-concrete interaction and eliminates the need for a compression process. In addition, FA is a very advantageous material, has a sphere-shaped microstructure, and offers excellent fluidity. Supplemental materials were also used to make SCC with the required fresh properties, such as superplasticizers and crushed stones. Table 3 shows the mixing ratio of SCC [28].

Table 3

Mixing ratio and concrete properties [28]

Cement (kg/m3) FA (kg/m3) Coarse aggregate (kg/m3) River sand (kg/m3) Crushed sand (kg/m3) Water (kg/m3) Superplasticizer (kg/m3) f c ′ (MPa) Density (kg/m3)
275 285 710 651 217 188.1 2.77 41.0 2338.27

4.2 Casting and curing condition

Table 3 shows the weighted quantities of required materials needed for the two batches. First, the fine and coarse aggregates were mixed in dry conditions for 2 min. Then, the binder materials containing cement, FA, and crushed sand were added with half the amount of the water and mixed for 1 min. Finally, the remaining water and superplasticizers were pre-mixed and poured into the mixture with another 2 min of mixing to consist of the mixture contents. After the mixing procedure was complete, the concrete was poured into the molds immediately without compaction. The steps of casting and curing are illustrated in Figure 7. The beams are covered and left for 24 h in the casting room. After completion of concrete casting, all tested beams were cured in a water tank at laboratory temperature for 28 days. Before starting the test procedure, the compressive strength test was made for six cylinders (100 mm × 200 mm).

Figure 7 Steps casting and curing.
Figure 7

Steps casting and curing.

5 Surface and wrapping preparation

  1. Preparing the concrete surface,

  2. Preparing BFRP, and

  3. Impregnating and applying the BFRP fabric.

As shown in Figure 8, a concrete mincer with a rotating disk was served to form the concrete surface by expelling a laitance layer and concrete crumpling. Beams’ lower sides were rotated with a radius of about 0.5 in. [29] to evade the concentration stress, which led to premature rupture of the BFRP sheets in accordance with ACI 440.2R [30].

Figure 8 Configuration steps of the preparation surface RC beams to increase the adherence of BFRP by epoxy.
Figure 8

Configuration steps of the preparation surface RC beams to increase the adherence of BFRP by epoxy.

6 Wrapping of BFRP fabrics

Wet lay-up technique (ACI 440 2008) was used to construct the BFRP laminate system [31,34,35].

To complete the implementation of the research, the test was performed for eight RCs.

The first BFRP free beam sheet was categorized as B1 and presented in Figure 9.

Figure 9 The control beam B1.
Figure 9

The control beam B1.

The second beam, known as B2 (Figure 10), had a single layer of BFRP textiles covering it entirely at the lowest point and at a height of 25 mm on both sides from the bottom.

Figure 10 Beam B2 specifics of covering with BFRP sheets.
Figure 10

Beam B2 specifics of covering with BFRP sheets.

The third beam, designated as B3, was entirely covered with BFRP fabrics at the lowest part and 75 mm high at both edges from the lowest part in one layer. It is shown in Figure 11.

Figure 11 Beam B3 covers the BFRP sheets.
Figure 11

Beam B3 covers the BFRP sheets.

The fourth beam, designated as B4, was coated completely with BFRP fabrics at the bottom portion and 105 mm high at both sides from the bottom in one layer (Figure 12).

Figure 12 Beam B4 details of covering with BFRP sheets.
Figure 12

Beam B4 details of covering with BFRP sheets.

The fifth beam, designated as B5, was covered completely with BFRP sheets just at the lowest part in one layer (Figure 13).

Figure 13 Beam B5 covers with BFRP sheets.
Figure 13

Beam B5 covers with BFRP sheets.

The sixth beam, designated as B5, was wrapped BFRP with three stirrups in the flexural zone; the distance between stirrups is 10 cm (Figure 14).

Figure 14 Beam B6 covers BFRP sheets.
Figure 14

Beam B6 covers BFRP sheets.

The seventh beam, designated as B7, was covered completely with BFRP fabrics at the lowest portion, plus stirrups in the flexural zone in one layer (Figure 15).

Figure 15 Beam B7 covers with BFRP sheets.
Figure 15

Beam B7 covers with BFRP sheets.

The eighth beam, designated as B7, was covered completely with BFRP sheets except for the upper surface part in one layer (Figure 16).

Figure 16 Beam B8 covers with BFRP sheets.
Figure 16

Beam B8 covers with BFRP sheets.

All samples were kept for 1 week air curing at a temperature of 27 ± 2°C before starting the test.

7 Flexural test setup and instrumentation

RC beams, both with and without BFRP fabrics, every single sample, were investigated under a static two-point load. For the assessment process, an INSTRON testing machine, as demonstrated in Figure 8, was utilized, which includes a hydraulic with a load size of 250 kN with a closed-loop servo-hydraulic testing system digital controller (Figure 17).

Figure 17 The flexure test setup.
Figure 17

The flexure test setup.

Finally, the beam was removed from the test equipment, and the concrete surface was examined at various angles; these tests were performed at Gaziantep University’s College of Engineering in Gaziantep, Turkey.

8 Results and discussion of RC beams

The visuals of load vs mid-span deflection and the collapse shapes of all samples are included in the results. The reinforced beam’s increased load-bearing capability, ductility, and crack pattern are investigated. Finally, the outcomes of the tests are reached and employed to compare the efficacy of BFRP laminates.

8.1 Relationships and failure modes of load–deflection

We studied the failure mode of each RC beam. Generally, the strengthened RC beam failure involved flexural cracks, crushing concrete, and BFRP rupture (Figure 18).

Figure 18 Load vs deflection for all beams.
Figure 18

Load vs deflection for all beams.

Beam (B1): To assess the behavior of the strengthened RC beams, the results of the unstrengthen control beam were used as a benchmark. The data were utilized to draw the load versus mid-span deflection curve, as shown in Figure 18. The ultimate load of 53.1 kN that corresponds to a deflection of 5.81 mm of the control beam is recorded. The failure deflection value was 15.82 mm. The beam failed in a typical flexural mode in which the reinforcement bars were deformed, followed by the crushing of the concrete on the upper surface of the beam in the middle section. The failure was mild, and there was adequate warning of impending failure,

Beam (B2): The RC beam strengthened was covered completely with BFRP sheets at the lower section and 25 mm height at both edges from the bottom in one layer has been tested to fail. From the test, as shown in Figure 18, the load versus mid-span deflection records were obtained. The obtained ultimate load was 72.82 kN, which corresponds to 13.76 mm vertical deflection. The recorded deflection value in the middle area of the failure was 13.94 mm. The percentage increase within the flexural capacity was 37%. The percentage decrease in ultimate and failure ductility values was 81 and 29%, respectively. The beam failed in a typical flexural mode in which the reinforcement bars were deformed, followed by the crushing of the concrete on the upper surface of the beam in the middle section. The mode of failure was sudden, accompanied by the crushing of the compression concrete zone and a partial debonding of the BFRP.

Beam (B3): The RC beam strengthened was covered completely with BFRP sheets at the lower section and 75 mm height at both edges from the bottom in one layer has been tested to fail. The load versus mid-span deflection records were obtained from the test and presented in Figure 18. The obtained ultimate load was 76.55 kN that corresponds to a deviation of 14.58 mm. The deflection value in the middle area of the failure was 16.39 mm. The percentage increase within the flexural capacity was 44%. The percent reduction in ultimate and failure ductility values was 85 and 23%, respectively. The beam failed in a typical flexural mode in which the reinforcement bars were deformed, followed by the crushing of the concrete on the upper surface of the beam in the middle section. The mode of failure was sudden, with partial debonding of the BFRP sheet, which failed due to concrete crushing in the compression zone and some tearing-off of BFRP.

Beam (B4): The RC beam strengthened was covered completely with BFRP sheets at the lower section and 105 mm height at both edges from the bottom in one layer has been tested to fail. The load versus mid-span deflection records were obtained from the test, as shown in Figure 18. The obtained ultimate load was 80.55 kN that corresponds to a deflection of 18.53 mm. The deflection value in the middle area of the failure was 19.17 mm. The percentage increase within the flexural capacity was 52%. The percentage decrease in ultimate and failure ductility values was 89 and 28%, respectively. The beam failed by yielding the reinforcement rebar, tearing off the BFRP, and concrete crushing in the compression zone. The failure occurred with little obvious sign of impending collapse before the element failure.

Beam (B5): The RC beam strengthened was covered completely with BFRP sheets just at the lower section in one layer and was tested to fail. The load versus mid-span deflection records were found from the test, as shown in Figure 18. The obtained ultimate load was recorded to a value of 72.56 kN, which corresponds to a deflection of 9 mm. The deflection value of the mid-span at failure was recorded as a value of 14 mm. The percentage increase in the flexural capacity was recorded to a value of 36%. The percentage decline in the ultimate and failure ductility values was equal to 17 and 32%, respectively. The yielding of the reinforcement rebar caused the beam failure, followed by BFRP debonding and failed due to concrete crushing in the compression zone, and the failure was relatively sudden and without warning.

Beam (B6): The strengthened RC beam was wrapped by BFRP fabrics as stirrups in the flexural zone portion in one layer was tested to fail. The load versus mid-span deflection records were gained from the test, as shown in Figure 18. The obtained ultimate load was recorded to a value of 58.28 kN, which corresponds to a deflection of 6.49 mm. The value of mid-span deflection at failure was recorded to a value of 16.20 mm. The percentage increase in the flexural capacity was recorded to a value of 9.4%. The percentage decline in the ultimate and failure ductility readings was equal to 5 and 0.2%, respectively. The yielding of the reinforcement rebar caused the beam failure, followed due to concrete crushing in the compression zone; the failure was not as mild as for the unstrengthen element but could not be described as “sudden.”

Beam (B7): The strengthened RC beam was covered with BFRP fabrics just at the bottom with stirrups in the flexural zone portion in one wrap and was tested to fail. The load versus mid-span deflection records were gained from the test, as shown in Figure 18. The obtained ultimate load was recorded to a value of 73.56 kN, which corresponds to a deflection of 9.10 mm. The value of mid-span deflection at failure was recorded to a value of 14.25 mm. The percentage increase in the flexural capacity was recorded to a value of 38.53%. The percentage decline in the ultimate and failure ductility readings was equal to 19 and 33%, respectively. The yielding of the reinforcement rebar caused the beam failure, followed by BFRP debonding and concrete crushing in the compression zone. The failure happened suddenly and without warning.

Beam (B8): The RC beam enforced was wrapped at the bottom and two sides completely with one layer of BFRP fabric was tested to fail. The load versus mid-span deflection records were gained from the test, as shown in Figure 18. The ultimate load obtained was recorded to a value of 82.55 kN, which corresponds to a deflection of 15 mm. The value of mid-span deflection at failure was recorded as 16.64 mm. The percentage increase in the flexural capacity was equal to 56%. The percentage decrease in the ultimate and failure ductility readings was equal to 44 and 45%, respectively. The failure occurred suddenly, and there was no warning of impending failure from the deflections of cracking patterns. The destruction of BFRP and concrete crushing in the compression zone as.

When the fail modes of the various strengthened beams are compared in Table 4, it can be observed that the strengthened RC beams by one-wrap BFRP fabrics had the superior failure mode. The failure of these beams is due to BFRP wrap falling-out, indicating that the ultimate capacity of the BFRP wraps had been reached and the strengthening system was completely used [35].

Table 4

Brief of ultimate loadings and failure modes

Sample P cr (kN) P y (kN) P u (kN) P u / P uc
Control B1 19 50.48 53.1 —
B2 29 64.74 72.82 1.37
B3 44 66.35 76.55 1.44
B4 63 72.70 80.55 1.51
B5 31 66.55 72.56 1.36
B6 35 55.59 58.28 1.09
B7 43 67.58 73.56 1.38
B8b — 73.92 82.54 1.55

8.2 Ductility

The most widely used methods for calculating ductility from data are divided into two methods. The first one was the deflection ductility index ( μ ∆ ) , which is represented in equation (1) [32]

(1) μ ∆ = ∆ u ∆ y .

A similar behavior was also observed. Attari et al. [33] also noticed that all of the strengthened specimens showed lower ductility than the control specimens.

The second method of estimating ductility was the energy ductility index ( μ E ) by using equation (2) [32]

(2) μ E = E u E y .

Tables 5 and 6 summarize the measured ductility indications for total tested specimens.

Table 5

Brief of the deflection and ductility results

Sample Deflection at yield (mm) Deflection at ultimate (mm) Deflection at failure (mm) Ductility index
μ ∆ Increase % μ E
Control B1 4.71 6.01 15.79 1.27 — 1.4
B2 5.75 13.25 13.85 2.30 81 3.5
B3 6.27 14.84 16.27 2.36 85 3.3
B4 7.50 18.09 19.05 2.41 89 4.4
B5 6.11 9.12 13.91 1.49 17 1.69
B6 4.81 6.49 16.20 1.34 5 1.5
B7 6.19 9.45 14.03 1.52 19 1.75
B8 8.69 16.02 16.25 1.84 49 4.01
Table 6

Summary of the failure deflection index ( I f )

Specimen I f = ∆ f / ∆ y I f / I fc a Decrease %
Control B1 3.35 1 —
B2 2.44 0.71 29
B3 2.59 0.77 23
B4 2.54 0.75 25
B5 2.27 0.67 33
B6 3.36 1 0.5
B7 2.26 0.67 33
B8 1.86 0.55 45

a I fc is the failure index of the control beam.

Table 5 shows that beam B6 had a maximum ductility of 5%, while beam B4 had a minimum ductility of 89% in RC beam ductility compared with the un-strengthened beam. Generally, the ductility decreased with increasing amounts of strengthening.

Table 6 shows that the failure deflection index at beam B6 had a maximum of 0.5%, while the minimum failure index at beam B8 was 45% compared with the un-strengthened beam.

8.3 Crack patterns

As can be seen from the results presented, crack propagation in strengthened elements differs significantly from that of normally reinforced elements. This is to be expected as strengthened elements can be considerably stiffer than their non-strengthened counterparts, which understandably affects their behavior under loading.

Beam B1 control specimen has been loaded in a four-point bend test setup as described previously. The beams have been loaded with equal force on the two load points until the beams are deformed. The damage in the beams started with bending cracks in the central region of the beam, as shown in Figure 19. The first crack was observed at 19 kN. As load reached 52 kN, more cracks were observed. Almost all cracks were vertical. Near top and bottom edge sub-cracks were generated connecting to the main crack. The first crack generated was between the left point load and the beam center. The second crack was just inside the right point load. The third and fourth cracks generated were between the center point of the beam and the right point load. The fifth crack was just outside of the right point load. The sixth crack was between the third and fourth cracks. Major cracking was observed at 53.1 kN, and the beam stopped taking load after this point.

Figure 19 Crack pattern for beam B1.
Figure 19

Crack pattern for beam B1.

Beam B2, when load was applied on the beam, the first crack was observed at 29 kN. Spalling started at 52 kN load. The crackling sound of laminates was observed at 29 and 57 kN. Again, spalling was observed at 67 kN, as shown in Figure 20. Laminate failed at 72.82 kN by interfacial debonding. Loading was stopped after laminate failure.

Figure 20 Crack pattern for beam B2.
Figure 20

Crack pattern for beam B2.

Beam B3, when loading was started new crack was observed at 44 kN. The crackling sound was there at 69, 71, and 72 kN. Spalling started at 75 kN. Also, crackling sound was there in fibers at 75 kN as well. BFRP failed at 76.55 kN load, making the sound like a blast. Partial peeling off and partial debonding failure were observed, as shown in Figure 21.

Figure 21 Crack pattern for beam B3.
Figure 21

Crack pattern for beam B3.

Beam B4, when the load was applied on the beam, the first crackling was shown at 63 kN, and after that, again at 69, 71, and 76 kN, sound of the BFRP sheet was heard. Concrete crushing in compression at the top, as shown in Figure 22. The beam stopped taking further load at 80.55 kN. As compared to laminates, sheets did not fail over large area; only debonding was there in the bottom center. Debonding was not throughout the width of the beam. An increase in load-carrying capacity was observed as the beam with BFRP failed at 80.55 kN.

Figure 22 Crack pattern for beam B4.
Figure 22

Crack pattern for beam B4.

Beam B5, the first crack, was observed at 31 kN. As load reached 58 kN, more cracks were observed. Almost all cracks were vertical; near the top and bottom edge sub-cracks were generated connecting to the main crack. Major cracking was observed at 69 kN. The beam stopped taking load at 72.56 kN. Partial debonding failure was observed in the tension zone, as shown in Figure 23.

Figure 23 Crack pattern for beam B5.
Figure 23

Crack pattern for beam B5.

Beam B6 shows similar behavior as beam B1. Therefore, steel was yielded in the specimen. The damage in the beams started with bending cracks in the central region of the beam, as shown in Figure 24; first crack was observed at 35 kN. As load reached 55 kN, more cracks were observed. Almost all cracks were vertical, and near the top and bottom edge sub-cracks were generated connecting to the main crack. The beam stopped taking load at 58.28 kN.

Figure 24 Crack pattern for beam B6.
Figure 24

Crack pattern for beam B6.

Beam B7, the first crack, was observed at 43 kN. As load reached 54 kN, more cracks were observed. Almost all cracks were vertical, and near the top and bottom edge sub-cracks were generated connecting to the main crack. Major cracking was observed at 63 kN. The beam stopped taking load at 73.56 kN, as shown in Figure 25.

Figure 25 Crack pattern for beam B7.
Figure 25

Crack pattern for beam B7.

Beam B8, U shape wrapped therefore no cracks could not be observed. The crackling sound was heard when loading was applied. The beam failed by flexural failure, rupture of BFRP, and crushing of concrete at the loaded point as shown in Figure 26. The beam stopped taking further load at 88.55 kN. The failure sound heard like a blast.

Figure 26 Crack pattern for beam B8.
Figure 26

Crack pattern for beam B8.

As can be seen from the results presented, crack propagation in strengthened elements differs significantly from that of normally reinforced elements. This is to be expected as strengthened elements can be considerably stiffer than their non-strengthened counterparts, which understandably affects their behavior under loading. The reason for this is that the presence of the basalt fiber composites helps to better distribute the tensile forces at the soffit of the element, which results in a reduction of the width and length of cracks that would normally be expected in an un-strengthened element. Due to debonding total utilization of the strength of the BFRP sheet was not achieved.

9 Conclusions

BFRP is considered a green material and has been illustrated to be a proper material for developing the infrastructure sustainability of RC members. This study has pointed out the need to enhance the knowledge of RC beams after strengthening by basalt fiber fabric. From the experimental test results presented, the following general conclusions can be drawn:

  • The flexural capacity of the wrapped RC beams increases in percentage varied from 9.4 to 56% over the unwrapped beam.

  • By comparing between the strengthened beams and un-strengthened beams, the percentage decline in the ductility varies from 5 to 89%.

  • RC beams wrapped with a sheet of BFRP fabrics failed by FRP failure, taking into consideration that this FRP strengthening approach was completely used to its highest capacity.

  • Excessive deformation occurs, and failure of the BFRP composites takes place. It should be noted that not all fibers may reach the ultimate limit state at the same time, which can result in a more gradual release of the stored elastic energy. This took place during the failure of beam B8, where distinct sounds of fibers snapping were noted before ultimate failure was reached.

  • The adhesive bond between the fiber and the concrete substrate fails, resulting in a peeling off of the fiber composite sheet or plate along part or all of its length. This normally initiates at the end of the sheet or plate but, in some cases, can start elsewhere and propagate in two directions until failure occurs. Additionally, it is often the case that a delamination failure, as it propagates along the length of the beam, will become a tearing-off type failure. This occurs when the delaminating fiber composite sheet encounters a crack that is severe enough to allow the concrete cover to be torn away from the soffit of the beam, while remaining attached to the sheet. An example of this type of failure can be seen in B2, B3, B4, and B5.

  • When an element is over-reinforced and/or over-strengthened in tension, the development of high compressive stresses in the compressive concrete zone results in a sudden, sometimes “crushing,” compressive failure of the concrete. In fact, the internal steel reinforcement has not normally even reached its yield point. An example of this type of crushing failure can be seen in all specimens.

  • Crack propagation of crack widths for elements with externally bonded basalt fiber composites was investigated. It had already been shown that the occurrence of surface cracking in strengthened elements varied considerably from that of their unstrengthen counterparts. The main differences for strengthened elements can be summarized as follows and are attributable to the ability of the BFRP composites to better distribute the stress in the element soffit, resulting in a more consistent crack distribution: There is a higher number of surface cracks. Both the maximum and average crack lengths are shorter.

Acknowledgements

We acknowledge Dr. Minen Al-Kafajy for English observation and valued comments.

  1. Conflict of interest: Authors state no conflict of interest.

  2. Data availability statement: Data available within the article or its supplementary materials. The authors confirm that the data supporting the findings of this study are available within the article [and/or] its supplementary materials.

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Received: 2023-07-16
Revised: 2023-10-19
Accepted: 2023-10-30
Published Online: 2024-02-23

© 2024 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/eng-2022-0548
Keywords for this article
strengthening basalt fiber-reinforced polymer; reinforcement concrete RC beams; rays; externally bonded; flexural behavior; ductility
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BY 4.0

Articles in the same Issue

  1. Regular Articles
  2. Methodology of automated quality management
  3. Influence of vibratory conveyor design parameters on the trough motion and the self-synchronization of inertial vibrators
  4. Application of finite element method in industrial design, example of an electric motorcycle design project
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  57. Experimental study of improving hot mix asphalt reinforced with carbon fibers
  58. Asphalt binder modified with recycled tyre rubber
  59. Thermal performance of radiant floor cooling with phase change material for energy-efficient buildings
  60. Surveying the prediction of risks in cryptocurrency investments using recurrent neural networks
  61. A deep reinforcement learning framework to modify LQR for an active vibration control applied to 2D building models
  62. Evaluation of mechanically stabilized earth retaining walls for different soil–structure interaction methods: A review
  63. Assessment of heat transfer in a triangular duct with different configurations of ribs using computational fluid dynamics
  64. Sulfate removal from wastewater by using waste material as an adsorbent
  65. Experimental investigation on strengthening lap joints subjected to bending in glulam timber beams using CFRP sheets
  66. A study of the vibrations of a rotor bearing suspended by a hybrid spring system of shape memory alloys
  67. Stability analysis of Hub dam under rapid drawdown
  68. Developing ANFIS-FMEA model for assessment and prioritization of potential trouble factors in Iraqi building projects
  69. Numerical and experimental comparison study of piled raft foundation
  70. Effect of asphalt modified with waste engine oil on the durability properties of hot asphalt mixtures with reclaimed asphalt pavement
  71. Hydraulic model for flood inundation in Diyala River Basin using HEC-RAS, PMP, and neural network
  72. Numerical study on discharge capacity of piano key side weir with various ratios of the crest length to the width
  73. The optimal allocation of thyristor-controlled series compensators for enhancement HVAC transmission lines Iraqi super grid by using seeker optimization algorithm
  74. Numerical and experimental study of the impact on aerodynamic characteristics of the NACA0012 airfoil
  75. Effect of nano-TiO2 on physical and rheological properties of asphalt cement
  76. Performance evolution of novel palm leaf powder used for enhancing hot mix asphalt
  77. Performance analysis, evaluation, and improvement of selected unsignalized intersection using SIDRA software – Case study
  78. Flexural behavior of RC beams externally reinforced with CFRP composites using various strategies
  79. Influence of fiber types on the properties of the artificial cold-bonded lightweight aggregates
  80. Experimental investigation of RC beams strengthened with externally bonded BFRP composites
  81. Generalized RKM methods for solving fifth-order quasi-linear fractional partial differential equation
  82. An experimental and numerical study investigating sediment transport position in the bed of sewer pipes in Karbala
  83. Role of individual component failure in the performance of a 1-out-of-3 cold standby system: A Markov model approach
  84. Implementation for the cases (5, 4) and (5, 4)/(2, 0)
  85. Center group actions and related concepts
  86. Experimental investigation of the effect of horizontal construction joints on the behavior of deep beams
  87. Deletion of a vertex in even sum domination
  88. Deep learning techniques in concrete powder mix designing
  89. Effect of loading type in concrete deep beam with strut reinforcement
  90. Studying the effect of using CFRP warping on strength of husk rice concrete columns
  91. Parametric analysis of the influence of climatic factors on the formation of traditional buildings in the city of Al Najaf
  92. Suitability location for landfill using a fuzzy-GIS model: A case study in Hillah, Iraq
  93. Hybrid approach for cost estimation of sustainable building projects using artificial neural networks
  94. Assessment of indirect tensile stress and tensile–strength ratio and creep compliance in HMA mixes with micro-silica and PMB
  95. Density functional theory to study stopping power of proton in water, lung, bladder, and intestine
  96. A review of single flow, flow boiling, and coating microchannel studies
  97. Effect of GFRP bar length on the flexural behavior of hybrid concrete beams strengthened with NSM bars
  98. Exploring the impact of parameters on flow boiling heat transfer in microchannels and coated microtubes: A comprehensive review
  99. Crumb rubber modification for enhanced rutting resistance in asphalt mixtures
  100. Special Issue: AESMT-6
  101. Design of a new sorting colors system based on PLC, TIA portal, and factory I/O programs
  102. Forecasting empirical formula for suspended sediment load prediction at upstream of Al-Kufa barrage, Kufa City, Iraq
  103. Optimization and characterization of sustainable geopolymer mortars based on palygorskite clay, water glass, and sodium hydroxide
  104. Sediment transport modelling upstream of Al Kufa Barrage
  105. Study of energy loss, range, and stopping time for proton in germanium and copper materials
  106. Effect of internal and external recycle ratios on the nutrient removal efficiency of anaerobic/anoxic/oxic (VIP) wastewater treatment plant
  107. Enhancing structural behaviour of polypropylene fibre concrete columns longitudinally reinforced with fibreglass bars
  108. Sustainable road paving: Enhancing concrete paver blocks with zeolite-enhanced cement
  109. Evaluation of the operational performance of Karbala waste water treatment plant under variable flow using GPS-X model
  110. Design and simulation of photonic crystal fiber for highly sensitive chemical sensing applications
  111. Optimization and design of a new column sequencing for crude oil distillation at Basrah refinery
  112. Inductive 3D numerical modelling of the tibia bone using MRI to examine von Mises stress and overall deformation
  113. An image encryption method based on modified elliptic curve Diffie-Hellman key exchange protocol and Hill Cipher
  114. Experimental investigation of generating superheated steam using a parabolic dish with a cylindrical cavity receiver: A case study
  115. Effect of surface roughness on the interface behavior of clayey soils
  116. Investigated of the optical properties for SiO2 by using Lorentz model
  117. Measurements of induced vibrations due to steel pipe pile driving in Al-Fao soil: Effect of partial end closure
  118. Experimental and numerical studies of ballistic resistance of hybrid sandwich composite body armor
  119. Evaluation of clay layer presence on shallow foundation settlement in dry sand under an earthquake
  120. Optimal design of mechanical performances of asphalt mixtures comprising nano-clay additives
  121. Advancing seismic performance: Isolators, TMDs, and multi-level strategies in reinforced concrete buildings
  122. Predicted evaporation in Basrah using artificial neural networks
  123. Energy management system for a small town to enhance quality of life
  124. Numerical study on entropy minimization in pipes with helical airfoil and CuO nanoparticle integration
  125. Equations and methodologies of inlet drainage system discharge coefficients: A review
  126. Thermal buckling analysis for hybrid and composite laminated plate by using new displacement function
  127. Investigation into the mechanical and thermal properties of lightweight mortar using commercial beads or recycled expanded polystyrene
  128. Experimental and theoretical analysis of single-jet column and concrete column using double-jet grouting technique applied at Al-Rashdia site
  129. The impact of incorporating waste materials on the mechanical and physical characteristics of tile adhesive materials
  130. Seismic resilience: Innovations in structural engineering for earthquake-prone areas
  131. Automatic human identification using fingerprint images based on Gabor filter and SIFT features fusion
  132. Performance of GRKM-method for solving classes of ordinary and partial differential equations of sixth-orders
  133. Visible light-boosted photodegradation activity of Ag–AgVO3/Zn0.5Mn0.5Fe2O4 supported heterojunctions for effective degradation of organic contaminates
  134. Production of sustainable concrete with treated cement kiln dust and iron slag waste aggregate
  135. Key effects on the structural behavior of fiber-reinforced lightweight concrete-ribbed slabs: A review
  136. A comparative analysis of the energy dissipation efficiency of various piano key weir types
  137. Special Issue: Transport 2022 - Part II
  138. Variability in road surface temperature in urban road network – A case study making use of mobile measurements
  139. Special Issue: BCEE5-2023
  140. Evaluation of reclaimed asphalt mixtures rejuvenated with waste engine oil to resist rutting deformation
  141. Assessment of potential resistance to moisture damage and fatigue cracks of asphalt mixture modified with ground granulated blast furnace slag
  142. Investigating seismic response in adjacent structures: A study on the impact of buildings’ orientation and distance considering soil–structure interaction
  143. Improvement of porosity of mortar using polyethylene glycol pre-polymer-impregnated mortar
  144. Three-dimensional analysis of steel beam-column bolted connections
  145. Assessment of agricultural drought in Iraq employing Landsat and MODIS imagery
  146. Performance evaluation of grouted porous asphalt concrete
  147. Optimization of local modified metakaolin-based geopolymer concrete by Taguchi method
  148. Effect of waste tire products on some characteristics of roller-compacted concrete
  149. Studying the lateral displacement of retaining wall supporting sandy soil under dynamic loads
  150. Seismic performance evaluation of concrete buttress dram (Dynamic linear analysis)
  151. Behavior of soil reinforced with micropiles
  152. Possibility of production high strength lightweight concrete containing organic waste aggregate and recycled steel fibers
  153. An investigation of self-sensing and mechanical properties of smart engineered cementitious composites reinforced with functional materials
  154. Forecasting changes in precipitation and temperatures of a regional watershed in Northern Iraq using LARS-WG model
  155. Experimental investigation of dynamic soil properties for modeling energy-absorbing layers
  156. Numerical investigation of the effect of longitudinal steel reinforcement ratio on the ductility of concrete beams
  157. An experimental study on the tensile properties of reinforced asphalt pavement
  158. Self-sensing behavior of hot asphalt mixture with steel fiber-based additive
  159. Behavior of ultra-high-performance concrete deep beams reinforced by basalt fibers
  160. Optimizing asphalt binder performance with various PET types
  161. Investigation of the hydraulic characteristics and homogeneity of the microstructure of the air voids in the sustainable rigid pavement
  162. Enhanced biogas production from municipal solid waste via digestion with cow manure: A case study
  163. Special Issue: AESMT-7 - Part I
  164. Preparation and investigation of cobalt nanoparticles by laser ablation: Structure, linear, and nonlinear optical properties
  165. Seismic analysis of RC building with plan irregularity in Baghdad/Iraq to obtain the optimal behavior
  166. The effect of urban environment on large-scale path loss model’s main parameters for mmWave 5G mobile network in Iraq
  167. Formatting a questionnaire for the quality control of river bank roads
  168. Vibration suppression of smart composite beam using model predictive controller
  169. Machine learning-based compressive strength estimation in nanomaterial-modified lightweight concrete
  170. In-depth analysis of critical factors affecting Iraqi construction projects performance
  171. Behavior of container berth structure under the influence of environmental and operational loads
  172. Energy absorption and impact response of ballistic resistance laminate
  173. Effect of water-absorbent polymer balls in internal curing on punching shear behavior of bubble slabs
  174. Effect of surface roughness on interface shear strength parameters of sandy soils
  175. Evaluating the interaction for embedded H-steel section in normal concrete under monotonic and repeated loads
  176. Estimation of the settlement of pile head using ANN and multivariate linear regression based on the results of load transfer method
  177. Enhancing communication: Deep learning for Arabic sign language translation
  178. A review of recent studies of both heat pipe and evaporative cooling in passive heat recovery
  179. Effect of nano-silica on the mechanical properties of LWC
  180. An experimental study of some mechanical properties and absorption for polymer-modified cement mortar modified with superplasticizer
  181. Digital beamforming enhancement with LSTM-based deep learning for millimeter wave transmission
  182. Developing an efficient planning process for heritage buildings maintenance in Iraq
  183. Design and optimization of two-stage controller for three-phase multi-converter/multi-machine electric vehicle
  184. Evaluation of microstructure and mechanical properties of Al1050/Al2O3/Gr composite processed by forming operation ECAP
  185. Calculations of mass stopping power and range of protons in organic compounds (CH3OH, CH2O, and CO2) at energy range of 0.01–1,000 MeV
  186. Investigation of in vitro behavior of composite coating hydroxyapatite-nano silver on 316L stainless steel substrate by electrophoretic technic for biomedical tools
  187. A review: Enhancing tribological properties of journal bearings composite materials
  188. Improvements in the randomness and security of digital currency using the photon sponge hash function through Maiorana–McFarland S-box replacement
  189. Design a new scheme for image security using a deep learning technique of hierarchical parameters
  190. Special Issue: ICES 2023
  191. Comparative geotechnical analysis for ultimate bearing capacity of precast concrete piles using cone resistance measurements
  192. Visualizing sustainable rainwater harvesting: A case study of Karbala Province
  193. Geogrid reinforcement for improving bearing capacity and stability of square foundations
  194. Evaluation of the effluent concentrations of Karbala wastewater treatment plant using reliability analysis
  195. Adsorbent made with inexpensive, local resources
  196. Effect of drain pipes on seepage and slope stability through a zoned earth dam
  197. Sediment accumulation in an 8 inch sewer pipe for a sample of various particles obtained from the streets of Karbala city, Iraq
  198. Special Issue: IETAS 2024 - Part I
  199. Analyzing the impact of transfer learning on explanation accuracy in deep learning-based ECG recognition systems
  200. Effect of scale factor on the dynamic response of frame foundations
  201. Improving multi-object detection and tracking with deep learning, DeepSORT, and frame cancellation techniques
  202. The impact of using prestressed CFRP bars on the development of flexural strength
  203. Assessment of surface hardness and impact strength of denture base resins reinforced with silver–titanium dioxide and silver–zirconium dioxide nanoparticles: In vitro study
  204. A data augmentation approach to enhance breast cancer detection using generative adversarial and artificial neural networks
  205. Modification of the 5D Lorenz chaotic map with fuzzy numbers for video encryption in cloud computing
  206. Special Issue: 51st KKBN - Part I
  207. Evaluation of static bending caused damage of glass-fiber composite structure using terahertz inspection
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