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Bond-slip behavior between fiber reinforced concrete and CFRP composites
Ain Shams Engineering Journal 10 (2019) 359–367
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Civil Engineering
Bond-slip behavior between fiber reinforced concrete and CFRP composites Mohammad A. Alhassan a,⇑, Rajai Z. Al Rousan a, Esmail A. Al Shuqari b a b
Civil Engineering, Civil Engineering Department, Jordan University of Science and Technology (JUST), Irbid, Jordan Civil Engineering Department, Jordan University of Science and Technology (JUST), Irbid, Jordan
a r t i c l e
i n f o
Article history: Received 23 November 2017 Revised 26 September 2018 Accepted 11 March 2019 Available online 27 March 2019 Keywords: Structural synthetic fibers DSSF Bond-slip behavior CFRP Anchorage
a b s t r a c t The influence of discontinuous structural synthetic fibers (DSSF) on the bond-slip behavior between concrete and carbon fiber reinforced polymer (CFRP) composites was investigated using a double-shear pull-off test. The tested blocks were divided into three groups depending on the DSSF content. The CFRP composites were bonded to the blocks (with and without a CFRP anchoring strip) in three lengths (Lf): 50, 75, and 100 mm. For each Lf, three widths (bf) were used: 50, 75, and 100 mm. The results showed that: addition of DSSF to concrete slightly enhances the bond strength with CFRP composites, the pull-off force and slip increase with the increase in the CFRP bond length and width, and the use of CFRP anchorage strip improves the bond characteristics. The failure mode and bonding interface showed that as the DSSF increases, more concrete was attached to the peeled CFRP composite indicating that the concrete surface gets stronger. Ó 2019 The Authors. Published by Elsevier B.V. on behalf of Faculty of Engineering, Ain Shams University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ncnd/4.0/).
1. Introduction Concrete is the most broadly utilized material for structures since many decades. However, concrete is a brittle material with a low tensile strength and strain capacities. There have been enduring efforts to help overcome these disadvantages using many techniques. Fiber reinforced concrete (FRC) is a concrete incorporating relatively short, discrete, discontinuous fibers. There are various types of fibers that can be added to concrete, including: steel, carbon, plastic, synthetic and glass fibers. Among all types, steel and synthetic fibers are most commonly used for enhancing the mechanical properties of concrete [1]. Synthetic fibers are noncorrosive, alkali resistant, easy to apply, and added in small amounts because of their low density. Addition of discontinuous structural synthetic fibers (DSSF) reduces the concrete’s tendency for cracking and supplies it with crack-arresting and toughness characteristics [2–8]. ⇑ Corresponding author. E-mail addresses: [email protected] (M.A. Alhassan), [email protected]. jo (R.Z. Al Rousan), [email protected] (E.A. Al Shuqari). Peer review under responsibility of Ain Shams University.
Recently, carbon fiber reinforced polymer (CFRP) composites have been widely used for repairing and strengthening reinforced-concrete damaged members due to several advantages such as their high corrosion resistance, high strength, light weight, and ease of installation [9–11]. External bonding of CFRP onto the faces of the structural elements is the most common strengthening technique. The bond between the CFRP composites and concrete is considered as the key design factor. Therefore, systematic design of externally bonded CFRP composites requires a realistic understanding of the behavior of CFRP composites-concrete bonding interface [12,13]. Recent research studies reported that the effect of the bond between normal weight concrete and CFRP composites on the failure of adhesively bonded joints depends on many factors including the concrete compressive and/or tensile strengths [14,15], CFRP bonding length and width [13,16–18], adhesive properties [19], CFRP stiffness and thickness composition [20,21], surface preparation and roughness [22,23], type of CFRP sheets [20,24], and anchorage system [25,26]. Majority of the studies acknowledged that the failure modes in CFRP-strengthened reinforced concrete members are caused by de-bonding of the CFRP composites from the concrete surface. Retrofitting of structural elements using CFRP composites in a form of strips or sheets significantly improve their strength and ductility without adding stiffness to the elements. The high modulus of elasticity and strength of CFRP makes it suitable for applications as confinement
Production and hosting by Elsevier https://doi.org/10.1016/j.asej.2019.03.001 2090-4479/Ó 2019 The Authors. Published by Elsevier B.V. on behalf of Faculty of Engineering, Ain Shams University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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for reinforced concrete columns and beams to improve their strength and ductility [27–29]. The main objectives of this research are to evaluate the impact of DSSF on the bond-slip behavior between CFRP composites and concrete considering the effects of three major parameters including: percentage of DSSF, CFRP composites bonding length and width, and the use of CFRP anchorage strip. A total of 108 concrete blocks (150x150x100 mm) were prepared and then bonded to CFRP sheets using a primer resin epoxy at three length (Lf) of 50, 75, and 100 mm. For each Lf, three different widths (bf) were used: 50, 75, and 100 mm. The concrete blocks were bonded to the CFRP sheets with and without CFRP anchorage strip. Finally, the specimens were subjected to double shear pull-off tests using a universal testing machine to determine the bond-slip relationship. 2. Experimental program 2.1. Test specimens The specimens include three groups; each contains 36 concrete blocks depending on the DSSF content (0, 3, and 5 kg/m3) equivalent to fiber volume fractions of 0%, 0.33%, and 0.55%, respectively. Addition of more than 0.55% of DSSF to concrete imposes serious workability and finishing problems, and therefore it was selected as the maximum feasible DSSF ratio in terms of workability to evaluate its influence on the performance. Addition of 0.33% DSSF ratio is feasible in terms of workability, but the enhancement may not be significant. The blocks were prepared and cured in a limesaturated water for 28 days and then bonded to CFRP sheets at different length and width using a special epoxy. In some blocks the end of the main CFRP sheets received CFRP anchorage sheets adhered perpendicular to the free-end of the main CFRP sheets at two parallel sides of the concrete blocks with a constant width by length of 25 150 mm, respectively. Parameters of investigation and designation of test specimens are summarized in Table 1.
Table 1 Parameters of investigation and designation of specimens. Designation
DSSF content
Bond length (Lf) (mm)
Bond width (bf) (mm)
0–50–50–N 0–50–75–N 0–50–100–N 0–75–50–N 0–75–75–N 0–75–100–N 0–100–50–N 0–100–75–N 0–100–100–N 3–50–50–N 3–50–75–N 3–50–100–N 3–75–50–N 3–75–75–N 3–75–100–N 3–100–50–N 3–100–75–N 3–100–100–N 5–50–50–N 5–50–75–N 5–50–100–N 5–75–50–N 5–75–75–N 5–75–100–N 5–100–50–N 5–100–75–N 5–100–100–N
0
50
50 75 100 50 75 100 50 75 100 50 75 100 50 75 100 50 75 100 50 75 100 50 75 100 50 75 100
75 100
3 kg/m3 (0.33%)
50
75
100
5 kg/m3 (0.55%)
50
75
100
Notes: All of the above specimens were made with and without CFRP anchorage sheet. The first number in the designation indicates the DSSF content in kg/m3, followed by the CFRP sheet length, then the width and the last letter N means no CFRP anchorage sheet (if Y, it means CFRP anchorage is used). Two specimens were made from each type.
2.2. Material properties 2.2.1. Concrete mixture Ordinary Type I Portland cement was used in the preparation of all mixtures. Crushed limestone coarse aggregates were used with a maximum aggregate size of 12.5 mm, a specific gravity (SG) of 2.62, and absorption of 2.3%. The SG, fineness modulus, and absorption of the fine aggregates were 2.65, 2.69, and 1.9%, respectively. 2.2.2. Discontinuous structural synthetic fiber (DSSF) The used type of DSSF is macro synthetic fiber with mono-fiber configuration, composed of polypropylene and polyethylene blends and manufactured with high strength and high modulus. It is 40 mm long with an aspect ratio of 90 (Fig. 1) and specifically engineered to provide high post-crack control performance. It is a user-friendly fiber reinforcement which is easy and safe to use. The main properties of DSSF include: SG of 0.92, no absorption, elastic modulus of 9.5 GPa, tensile strength of 620 MPa, melting point of 160 °C, ignition point of 590 °C, has high alkali, acid, and salt resistance.
Fig. 1. Sample of the used DSSF.
resin that was used to attach both the CFRP sheets strips and the anchorage strip is composed of part A (base component) and part B (hardener). 2.3. Mix design
2.2.3. Carbon fiber reinforced polymer (CFRP) sheets and bonding resin Unidirectional high strength CFRP sheets were used and attached to the concrete blocks using a primer epoxy resin to form CFRP composites. The used CFRP sheets have 0.166 mm-thickness and 500 mm width that can be cut into desired lengths. The tensile strength, elastic modulus, and elongation at break of the CFRP sheets are 4900 MPa, 230 GPa, and 2.1%, respectively. The primer
A concrete mixture (Table 2) was designed with the following proportions by weight: 0.42:1:2.23:2.25, for the water, cement, coarse aggregates, and fine aggregates, respectively. Superplasticizer was used as a percent of the cement weight to improve the workability and to provide a slump of about 75 mm. The mixing was performed using a tilting drum mixer with a capacity of
M.A. Alhassan et al. / Ain Shams Engineering Journal 10 (2019) 359–367 Table 2 Mix design proportions. Ingredient
Quantity (kg/m3)
Cement Water w/c Super- plasticizer Coarse aggregate Fine aggregate
400 205 0.51 8 890 900
0.15 m3. The volume of each batch was 0.09 m3 sufficient to cast 18 specimens and six (100 200 mm) cylinders. At the beginning, the inner surface of the mixer was wetted, then all of the coarse aggregates with portion of the water were added while the mixer is running. After that, the successive addition of fine aggregates, cement, and water were added gradually. The last amount of water was added to the mixture together with the super-plasticizer. The required dosage of DSSF was the last ingredient to be added, and it was distributed manually while the mixer is running. After introducing the DSSF, the ingredients were mixed for about 5 min before pouring to ensure uniform DSSF distribution. The slump val-
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ues for all batches were in the range of 60–90 mm. The concrete blocks were casted into wooden molds with inner dimensions of (150 150 100 mm) and compacted appropriately with an electrical vibrator. Twenty-four hours after casting, all specimens were de-molded and then placed in a curing tank with lime-saturated water for 28 days. The average compressive and splitting tensile strengths were 54.3 and 3.64 MPa for the mixture with 0% DSSF, 52 and 3.97 MPa for the mixture with 0.33% DSSF, and 51.6 and 4.27 MPa for the mixture with 0.55% DSSF. Compared with the mixture without DSSF, the results indicate that the DSSF has minor influence on the compressive strength, but leads to noticeable increase in the splitting tensile strength of about 9% and 17% for the 0.33% and 0.55% DSSF, respectively. 2.4. Bonding of CFRP sheets to the concrete blocks The CFRP sheets were bonded to the concrete blocks with and without CFRP anchorage strip using a primer resin. To provide the maximum possible bonding, the bonding surfaces of the concrete blocks were leveled, roughened, and brushed with steel wire cup brush. Then the surfaces of the concrete blocks were cleaned
Fig. 2. Pull-off test setup.
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Table 3 Average test results for all specimens. CFRP anchorage (mm)
Lf (mm)
bf (mm)
0% DSSF Pult (kN)
Slip (mm)
Toughness (kNmm)
Pult (kN)
Slip (mm)
Toughness (kNmm)
Pult (kN)
Slip (mm)
Toughness (kNmm)
0 0 0 0 0 0 0 0 0 25 25 25 25 25 25 25 25 25
50 50 50 75 75 75 100 100 100 50 50 50 75 75 75 100 100 100
50 75 100 50 75 100 50 75 100 50 75 100 50 75 100 50 75 100
13.6 19.3 22.4 18.5 24.6 28.0 22.8 29.2 33.3 15.9 23.1 26.8 22.1 29.7 33.3 27.2 34.4 39.4
0.053 0.068 0.077 0.065 0.081 0.092 0.079 0.095 0.109 0.082 0.105 0.119 0.101 0.127 0.143 0.122 0.147 0.169
0.55 1.01 1.32 0.93 1.54 1.98 1.38 2.12 2.79 1.01 1.88 2.47 1.72 2.92 3.67 2.56 3.91 5.14
14.4 20.4 23.7 19.6 26.0 29.6 24.2 30.9 35.3 17.0 24.7 28.6 23.6 31.8 35.6 29.1 36.8 42.1
0.055 0.070 0.080 0.068 0.084 0.095 0.082 0.098 0.113 0.088 0.113 0.128 0.108 0.136 0.153 0.131 0.158 0.181
0.61 1.10 1.45 1.02 1.68 2.17 1.51 2.33 3.05 1.16 2.15 2.82 1.97 3.34 4.20 2.93 4.48 5.89
14.9 21.1 24.5 20.3 26.9 30.7 25.0 31.9 36.5 17.9 26.0 30.1 24.8 33.4 37.4 30.6 38.69 44.28
0.056 0.071 0.081 0.069 0.086 0.097 0.083 0.100 0.115 0.092 0.118 0.134 0.114 0.143 0.161 0.137 0.166 0.190
0.64 1.16 1.52 1.07 1.77 2.28 1.60 2.45 3.22 1.28 2.37 3.12 2.18 3.69 4.64 3.24 4.95 6.51
0.33% DSSF
0.55% DSSF
Fig. 3. Typical bond failure modes for the specimens without CFRP anchorage strip.
Fig. 4. Typical bond failure modes for the specimens with CFRP anchorage strip.
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Fig. 5. Pull-off force versus slip for various DSSF dosages and different CFRP sheet length and width.
using air vacuum cleaner to remove any dust and lose particles. After that, the surfaces were dried and maintained free of contaminants by wrapping with plastic sheets. Before application of the
primer resin, the area where the CFRP sheet is to be attached was marked and the remaining area was covered using plastering tape to keep it free of epoxy. The top 25 mm of the specimens were
Fig. 6. Pull-off force versus slip: (a) effect of CFRP bond length (b) effect of CFRP bond width.
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left un-bonded to prevent stress concentration. After that, the CFRP sheets were cut into strips with various lengths and widths to cover the required area at the surface of the specimens. Then, the epoxy compound was prepared by mixing part A and B using low-speed electric drill for at least 3 min to have a homogenous mix. Next, a layer of epoxy was spread uniformly over the marked area on the surface of the blocks and the CFRP strips were placed onto the resin and rolled along the fiber direction using a plastic roller until the resin was distributed over the whole fiber surface and ensuring that all the entrapped air bubbles were removed. Then, the second layer of epoxy resin was applied over the CFRP strips surfaces. For the anchorage system, the anchorage CFRP strip was adhered perpendicular to the free-end of the main CFRP strips after twenty-four hours. Finally, the specimens were left in the laboratory until testing. 2.5. Double shear pull-off test setup The specimens were subjected to double shear pull-off test using a universal testing machine as shown in Fig. 2. Using a universal testing machine, the pulling-off force was applied to a steel U-shaped arm connected to an aluminum cylinder that raps the CFRP middle part causing shear failure of the CFRP composite. The concrete blocks were fixed to the bottom platen of the machine using special fasteners. The tests were conducted under displacement control condition with a loading rate of 0.3 mm/ min. Two linear variable displacement transducers (LVDT) were placed at both sides of the specimen to obtain the force-slip relationship. To obtain the load-slip relationship between the CFRP composites and blocks, the LVDTs were attached between two points; one located at the top of the CFRP strips and another point located on the bottom of concrete specimen surface. All load and displacement measurements were collected using a data acquisition system. 3. Results and discussion The experimental results are presented in this section and discussed in terms of pull-off force versus slip relationships and failure mode considering the effect of the DSSF dosage, CFRP bond length, CFRP bond width, and the anchorage strip. Summary of the test results for all specimens is provided in Table 3.
between the CFRP composites and concrete was brittle and the duration of the de-bonding process was mainly dependent on the CFRP bond length and width, dosage of DSSF, and CFRP anchorage strip. 3.2. Influence of the DSSF dosage Table 3 presents the ultimate pull-off force, ultimate slip, and toughness results for all specimens with the various parameters. The pull-off force and corresponding slip results were plotted as shown Fig. 5 considering the various DSSF dosages and different CFRP sheet length and width. Table 3 and Fig. 5 clearly show that addition of DSSF increases both the pull-off force and slip for the various CFRP sheet length and width. For the specimens without CFRP anchorage strip, addition of 0.33% and 0.55% DSSF increased the pull-off force by about 6% and 10% with respect to the control specimens without DSSF. The corresponding increase in the bond slippage 4% and 5.5%, respectively. The results of the specimens with CFRP anchorage strip were discussed independently in Section 3.5. 3.3. Influence of the CFRP bond length and width The influence of bond length on the pull-off force and slip was evaluated through comparing the results of identical blocks having three different CFRP sheet bond lengths of 50, 75, and 100 mm for a given CFRP sheet width and a given DSSF dosage. As expected, the pull-off force and slip increase with the increase in the CFRP bond length as shown in Table 3 and Fig. 6(a), however the increase was not proportional. In other words, for a similar width, CFRP bond lengths of 75 and 100 mm means that the area of the CFRP sheet is 1.5 and 2.0 times. Almost for the various DSSF dosages, when the CFRP bond length increased from 50 mm to 75 mm and 100 mm, the pull-off force increased by about 36% and 68% for bf = 50 mm, 27% and 51% for bf = 75 mm; and 25% and 49% for bf = 100 mm as shown in Fig. 7. To assess the effect of the bond width independently, the results of the blocks with three different CFRP sheet bond widths of 50, 75, and 100 mm were compared for a given CFRP sheet length and a given DSSF dosage as shown in Fig. 8. Both the pull-off force and slip increase non-proportionally with the increase in the CFRP bond width as shown in Table 3 and Fig. 8. When the CFRP bond width increased from 50 mm to 75 mm and 100 mm, the pull-off force
3.1. Failure mode of the bond interface Majority of previous studies reported that the mode of failure of the CFRP-composites can be one of the following: (a) failure in the concrete while the CFRP-composite remains attached, (b) debonding of the CFRP composite, or (c) rupture of the CFRP sheet [13–15,17,18,20,21]. In this study, all the tested specimens experienced a failure mode similar to (b) where a thin layer of concrete at different thicknesses remained attached to the surface of the CFRP composite. It was noticed that the amount of peeled concrete clearly depends on the DSSF dosage. The thickness and area of peeled concrete increase as the dosage of DSSF increases as can be seen in the typical photos in Fig. 3. This could be attributed to that the DSSF increase the tensile strength of the concrete blocks resulting in a stronger bonding interface. The influence of the CFRP anchorage strip was evaluated through comparing the companion specimens with and without the CFRP anchorage strip. |More peeled concrete spread under the CFRP anchorage strip as shown in Fig. 4. This indicates that the use of a CFRP anchorage strip at the end of the main CFRP sheet is very effective and desirable. It alleviates the stress-concentration at the end of the CFRP composite at which de-bonding is usually initiated. The de-bonding failure
Fig. 7. Normalized ultimate load capacity versus CFRP sheet length.
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through increasing the sheet length only or vice versa, the increase in the pull-off force will be less than 50% if the CFRP bonding area is increased by 50%, and also will be less than 100% if the CFRP bonding area is doubled. For a similar total area, the CFRP composite that has larger bonding length results in almost similar pull-off strength as the CFRP composite with larger bonding width. 3.4. Influence of the CFRP anchorage strip
Fig. 8. Normalized ultimate load capacity versus CFRP sheet width.
increased by about 42% and 65% for Lf = 50 mm, 33% and 51% for Lf = 75 mm; and 28% and 46% for Lf = 100 mm. Following nearly a similar trend as the pull-off force, when the CFRP bond width increased from 50 mm to 75 mm and 100 mm, the ultimate slip increased by about 27% and 45% for Lf = 50 mm, 25% and 41% for Lf = 75 mm; and 20% and 38% for Lf = 100 mm. The obtained results indicate that whether the CFRP sheet bonding area is increased
To study the effect of CFRP anchorage strip, the bond load-slip curves shown in Table 3 and Fig. 9 for the three DSSF dosages (0%, 0.33%, and 0.55%) were compared. The results indicate that using an anchorage CFRP strip attached perpendicular to the free end of the CFRP sheets (Fig. 9) significantly enhances the bond strength and corresponding slip. The average increase in the pulloff force and corresponding slip at failure for the specimens with anchorage strip with respect to those without was 19% and 55% for specimens with 0% DSSF (Fig. 9(a)), 20% and 60% for specimens with 0.33% DSSF (Fig. 9(b)), and 22% and 65% for specimens with 0.55% DSSF (Fig. 9(b)), respectively. The results reveal that the use of an anchorage strip improves the performance of the CFRP composite and leads to about 20% increase in the pull-off strength. 3.5. Toughness characteristics In general, toughness indicates the ability of a member to absorb energy and plastically deforms without failure. The tough-
Fig. 9. Pull-off force versus slip for tested specimens due to anchorage strip of (0 and 25 mm) (a) 0% DSSF (b) 0.33% DSSF (c) 0.55% DSSF.
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ness values listed in Table 3 were calculated as the entire area under the load-slip curves. With respect to the blocks without DSSF, the results show that addition of DSSF at dosages of 0.33% and 0.55% improves the toughness by 10% and 16% for 0.33%, respectively. Table 3 also shows that for the various DSSF dosages, the toughness increased when Lf increased from 50 mm to 75 mm and 100 mm by about 67% and 149% for bf = 50 mm; 53% and 111% for bf = 75 mm; and 50% and 111% for bf = 100 mm, respectively. On the other hand, it can be stated that, when bf increased from 50 mm to 75 mm and 100 mm, the toughness increased by about 81% and 138% for Lf = 50 mm; 65% and 113% for Lf = 75 mm; and 54% and 102% for Lf = 100 mm, respectively. These results indicates that the toughness approximately increases by 50% and 100% when the CFRP sheet is increased by 50% or 100% through increasing the bonding length or width. Finally, the toughness results confirm the effectiveness of the CFRP anchorage strip that enhanced the toughness significantly with an average of 85%, 94% and 103% for 0%, 0.33% and 0.55% of DSSF dosages, respectively. 4. Conclusions Based on the experimental tested results, the following conclusions are drawn: 1. The use of DSSF in concrete is advantageous to the bond-slip behavior between concrete and CFRP composites. Addition of DSSF at 0.33% and 0.55% by volume resulted in increase in the bond strength of about 6% and 10%, respectively with respect to plain concrete. These results are confirmed also with the failure modes that showed more concrete attached to the surface of the peeled CFRP composite as the DSSF dosage increased. 2. Both the pull-off force and slip increase non-proportionally with the increase in the CFRP bond length or width (Lf or bf). For bf = 75 mm or 100 mm, increasing Lf by 50% and 100% results in an increase in the bond strength of approximately 25% and 50%. For bf = 50 mm, increasing Lf by 50% and 100% results in an increase in the bond strength of approximately 35% and 70%. 3. Almost similar enhancement would be achieved if bf is increased by 50% and 100% for a constant Lf indicating that both Lf and bf have the same influence for equivalent CFRP area. 4. The toughness approximately increases by 50% and 100% when the CFRP sheet is increased by 50% or 100% through increasing Lf or bf. 5. For all of the used CFRP sheet lengths and widths, the use of 25 mm CFRP anchorage strip attached perpendicular at the end of the main CFRP sheet was very effective and enhanced the bond strength by about 20%. It also enhances the toughness significantly.
Acknowledgement This work was fully supported by a grant from the Deanship of Research at Jordan University of Science and Technology (Project No. 2016/356). This support is gratefully acknowledged. References [1] ACI Committee 544, Design consideration for steel fiber reinforced concrete. ACI, 1999; web. 8, sep 2012. [2] Oh BH, Kim JC, Choi YC. Fracture behavior of concrete members reinforced with structural synthetic fibers. Eng Fract Mech 2007;74(1):243–57. [3] Jiabiao J, Loh S, Gasho T. Synthetic structure fibers for toughness and crack control of concrete. 29th conference on our world in concrete & structures. Singapore, vol. 25, no. 1. p. 26–33.
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Mohammad A. Alhassan Dr. Alhassan earned his bachelor and masters’ degrees in structural engineering in 2000 and 2003 from the Jordan University of Science and Technology (JUST). He earned his PhD degree in Civil Engineering from the University of Illinois at Chicago (UIC) in 2007. He started as an assistant professor at Purdue University-Fort Wayne (IPFW) in 2008 and promoted with tenure to associate professor in 2012. He then joined JUST in 2016 as an associate professor of civil engineering. His main research areas include: structural analysis and simulations, CFRP composites, fiber reinforced concrete, and seismic design.
M.A. Alhassan et al. / Ain Shams Engineering Journal 10 (2019) 359–367 Rajai Z. Al Rousan Dr. Al-Rousan is currently working as an associate professor at the Department of Civil Engineering at the Jordan University of Science and Technology. Dr. Al-Rousan received his Bachelor and M. S of Science in Civil Engineering in 2000 and 2003, respectively, from the Jordan University of Science and Technology, Jordan, and his Ph.D. in Civil Engineering from the University of Illinois at Chicago, USA in 2008. His field of expertise is Structural Engineering with emphasis on structural design of buildings and bridges, damage assessment, concrete materials, and strengthening of structural elements with CFRP.
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Esmail A. Al Shuqari Engineer AlShuqari is currently a masters’ of civil engineering student at the Jordan University of Science and Technology. He received his bachelor degree in civil engineering from Albaath University in-Yaman in 2012. He has very experience in concrete mixing and laboratory testing. He is expected to complete his masters’ degree in December 2017.
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Civil Engineering
Bond-slip behavior between fiber reinforced concrete and CFRP composites Mohammad A. Alhassan a,⇑, Rajai Z. Al Rousan a, Esmail A. Al Shuqari b a b
Civil Engineering, Civil Engineering Department, Jordan University of Science and Technology (JUST), Irbid, Jordan Civil Engineering Department, Jordan University of Science and Technology (JUST), Irbid, Jordan
a r t i c l e
i n f o
Article history: Received 23 November 2017 Revised 26 September 2018 Accepted 11 March 2019 Available online 27 March 2019 Keywords: Structural synthetic fibers DSSF Bond-slip behavior CFRP Anchorage
a b s t r a c t The influence of discontinuous structural synthetic fibers (DSSF) on the bond-slip behavior between concrete and carbon fiber reinforced polymer (CFRP) composites was investigated using a double-shear pull-off test. The tested blocks were divided into three groups depending on the DSSF content. The CFRP composites were bonded to the blocks (with and without a CFRP anchoring strip) in three lengths (Lf): 50, 75, and 100 mm. For each Lf, three widths (bf) were used: 50, 75, and 100 mm. The results showed that: addition of DSSF to concrete slightly enhances the bond strength with CFRP composites, the pull-off force and slip increase with the increase in the CFRP bond length and width, and the use of CFRP anchorage strip improves the bond characteristics. The failure mode and bonding interface showed that as the DSSF increases, more concrete was attached to the peeled CFRP composite indicating that the concrete surface gets stronger. Ó 2019 The Authors. Published by Elsevier B.V. on behalf of Faculty of Engineering, Ain Shams University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ncnd/4.0/).
1. Introduction Concrete is the most broadly utilized material for structures since many decades. However, concrete is a brittle material with a low tensile strength and strain capacities. There have been enduring efforts to help overcome these disadvantages using many techniques. Fiber reinforced concrete (FRC) is a concrete incorporating relatively short, discrete, discontinuous fibers. There are various types of fibers that can be added to concrete, including: steel, carbon, plastic, synthetic and glass fibers. Among all types, steel and synthetic fibers are most commonly used for enhancing the mechanical properties of concrete [1]. Synthetic fibers are noncorrosive, alkali resistant, easy to apply, and added in small amounts because of their low density. Addition of discontinuous structural synthetic fibers (DSSF) reduces the concrete’s tendency for cracking and supplies it with crack-arresting and toughness characteristics [2–8]. ⇑ Corresponding author. E-mail addresses: [email protected] (M.A. Alhassan), [email protected]. jo (R.Z. Al Rousan), [email protected] (E.A. Al Shuqari). Peer review under responsibility of Ain Shams University.
Recently, carbon fiber reinforced polymer (CFRP) composites have been widely used for repairing and strengthening reinforced-concrete damaged members due to several advantages such as their high corrosion resistance, high strength, light weight, and ease of installation [9–11]. External bonding of CFRP onto the faces of the structural elements is the most common strengthening technique. The bond between the CFRP composites and concrete is considered as the key design factor. Therefore, systematic design of externally bonded CFRP composites requires a realistic understanding of the behavior of CFRP composites-concrete bonding interface [12,13]. Recent research studies reported that the effect of the bond between normal weight concrete and CFRP composites on the failure of adhesively bonded joints depends on many factors including the concrete compressive and/or tensile strengths [14,15], CFRP bonding length and width [13,16–18], adhesive properties [19], CFRP stiffness and thickness composition [20,21], surface preparation and roughness [22,23], type of CFRP sheets [20,24], and anchorage system [25,26]. Majority of the studies acknowledged that the failure modes in CFRP-strengthened reinforced concrete members are caused by de-bonding of the CFRP composites from the concrete surface. Retrofitting of structural elements using CFRP composites in a form of strips or sheets significantly improve their strength and ductility without adding stiffness to the elements. The high modulus of elasticity and strength of CFRP makes it suitable for applications as confinement
Production and hosting by Elsevier https://doi.org/10.1016/j.asej.2019.03.001 2090-4479/Ó 2019 The Authors. Published by Elsevier B.V. on behalf of Faculty of Engineering, Ain Shams University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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for reinforced concrete columns and beams to improve their strength and ductility [27–29]. The main objectives of this research are to evaluate the impact of DSSF on the bond-slip behavior between CFRP composites and concrete considering the effects of three major parameters including: percentage of DSSF, CFRP composites bonding length and width, and the use of CFRP anchorage strip. A total of 108 concrete blocks (150x150x100 mm) were prepared and then bonded to CFRP sheets using a primer resin epoxy at three length (Lf) of 50, 75, and 100 mm. For each Lf, three different widths (bf) were used: 50, 75, and 100 mm. The concrete blocks were bonded to the CFRP sheets with and without CFRP anchorage strip. Finally, the specimens were subjected to double shear pull-off tests using a universal testing machine to determine the bond-slip relationship. 2. Experimental program 2.1. Test specimens The specimens include three groups; each contains 36 concrete blocks depending on the DSSF content (0, 3, and 5 kg/m3) equivalent to fiber volume fractions of 0%, 0.33%, and 0.55%, respectively. Addition of more than 0.55% of DSSF to concrete imposes serious workability and finishing problems, and therefore it was selected as the maximum feasible DSSF ratio in terms of workability to evaluate its influence on the performance. Addition of 0.33% DSSF ratio is feasible in terms of workability, but the enhancement may not be significant. The blocks were prepared and cured in a limesaturated water for 28 days and then bonded to CFRP sheets at different length and width using a special epoxy. In some blocks the end of the main CFRP sheets received CFRP anchorage sheets adhered perpendicular to the free-end of the main CFRP sheets at two parallel sides of the concrete blocks with a constant width by length of 25 150 mm, respectively. Parameters of investigation and designation of test specimens are summarized in Table 1.
Table 1 Parameters of investigation and designation of specimens. Designation
DSSF content
Bond length (Lf) (mm)
Bond width (bf) (mm)
0–50–50–N 0–50–75–N 0–50–100–N 0–75–50–N 0–75–75–N 0–75–100–N 0–100–50–N 0–100–75–N 0–100–100–N 3–50–50–N 3–50–75–N 3–50–100–N 3–75–50–N 3–75–75–N 3–75–100–N 3–100–50–N 3–100–75–N 3–100–100–N 5–50–50–N 5–50–75–N 5–50–100–N 5–75–50–N 5–75–75–N 5–75–100–N 5–100–50–N 5–100–75–N 5–100–100–N
0
50
50 75 100 50 75 100 50 75 100 50 75 100 50 75 100 50 75 100 50 75 100 50 75 100 50 75 100
75 100
3 kg/m3 (0.33%)
50
75
100
5 kg/m3 (0.55%)
50
75
100
Notes: All of the above specimens were made with and without CFRP anchorage sheet. The first number in the designation indicates the DSSF content in kg/m3, followed by the CFRP sheet length, then the width and the last letter N means no CFRP anchorage sheet (if Y, it means CFRP anchorage is used). Two specimens were made from each type.
2.2. Material properties 2.2.1. Concrete mixture Ordinary Type I Portland cement was used in the preparation of all mixtures. Crushed limestone coarse aggregates were used with a maximum aggregate size of 12.5 mm, a specific gravity (SG) of 2.62, and absorption of 2.3%. The SG, fineness modulus, and absorption of the fine aggregates were 2.65, 2.69, and 1.9%, respectively. 2.2.2. Discontinuous structural synthetic fiber (DSSF) The used type of DSSF is macro synthetic fiber with mono-fiber configuration, composed of polypropylene and polyethylene blends and manufactured with high strength and high modulus. It is 40 mm long with an aspect ratio of 90 (Fig. 1) and specifically engineered to provide high post-crack control performance. It is a user-friendly fiber reinforcement which is easy and safe to use. The main properties of DSSF include: SG of 0.92, no absorption, elastic modulus of 9.5 GPa, tensile strength of 620 MPa, melting point of 160 °C, ignition point of 590 °C, has high alkali, acid, and salt resistance.
Fig. 1. Sample of the used DSSF.
resin that was used to attach both the CFRP sheets strips and the anchorage strip is composed of part A (base component) and part B (hardener). 2.3. Mix design
2.2.3. Carbon fiber reinforced polymer (CFRP) sheets and bonding resin Unidirectional high strength CFRP sheets were used and attached to the concrete blocks using a primer epoxy resin to form CFRP composites. The used CFRP sheets have 0.166 mm-thickness and 500 mm width that can be cut into desired lengths. The tensile strength, elastic modulus, and elongation at break of the CFRP sheets are 4900 MPa, 230 GPa, and 2.1%, respectively. The primer
A concrete mixture (Table 2) was designed with the following proportions by weight: 0.42:1:2.23:2.25, for the water, cement, coarse aggregates, and fine aggregates, respectively. Superplasticizer was used as a percent of the cement weight to improve the workability and to provide a slump of about 75 mm. The mixing was performed using a tilting drum mixer with a capacity of
M.A. Alhassan et al. / Ain Shams Engineering Journal 10 (2019) 359–367 Table 2 Mix design proportions. Ingredient
Quantity (kg/m3)
Cement Water w/c Super- plasticizer Coarse aggregate Fine aggregate
400 205 0.51 8 890 900
0.15 m3. The volume of each batch was 0.09 m3 sufficient to cast 18 specimens and six (100 200 mm) cylinders. At the beginning, the inner surface of the mixer was wetted, then all of the coarse aggregates with portion of the water were added while the mixer is running. After that, the successive addition of fine aggregates, cement, and water were added gradually. The last amount of water was added to the mixture together with the super-plasticizer. The required dosage of DSSF was the last ingredient to be added, and it was distributed manually while the mixer is running. After introducing the DSSF, the ingredients were mixed for about 5 min before pouring to ensure uniform DSSF distribution. The slump val-
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ues for all batches were in the range of 60–90 mm. The concrete blocks were casted into wooden molds with inner dimensions of (150 150 100 mm) and compacted appropriately with an electrical vibrator. Twenty-four hours after casting, all specimens were de-molded and then placed in a curing tank with lime-saturated water for 28 days. The average compressive and splitting tensile strengths were 54.3 and 3.64 MPa for the mixture with 0% DSSF, 52 and 3.97 MPa for the mixture with 0.33% DSSF, and 51.6 and 4.27 MPa for the mixture with 0.55% DSSF. Compared with the mixture without DSSF, the results indicate that the DSSF has minor influence on the compressive strength, but leads to noticeable increase in the splitting tensile strength of about 9% and 17% for the 0.33% and 0.55% DSSF, respectively. 2.4. Bonding of CFRP sheets to the concrete blocks The CFRP sheets were bonded to the concrete blocks with and without CFRP anchorage strip using a primer resin. To provide the maximum possible bonding, the bonding surfaces of the concrete blocks were leveled, roughened, and brushed with steel wire cup brush. Then the surfaces of the concrete blocks were cleaned
Fig. 2. Pull-off test setup.
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Table 3 Average test results for all specimens. CFRP anchorage (mm)
Lf (mm)
bf (mm)
0% DSSF Pult (kN)
Slip (mm)
Toughness (kNmm)
Pult (kN)
Slip (mm)
Toughness (kNmm)
Pult (kN)
Slip (mm)
Toughness (kNmm)
0 0 0 0 0 0 0 0 0 25 25 25 25 25 25 25 25 25
50 50 50 75 75 75 100 100 100 50 50 50 75 75 75 100 100 100
50 75 100 50 75 100 50 75 100 50 75 100 50 75 100 50 75 100
13.6 19.3 22.4 18.5 24.6 28.0 22.8 29.2 33.3 15.9 23.1 26.8 22.1 29.7 33.3 27.2 34.4 39.4
0.053 0.068 0.077 0.065 0.081 0.092 0.079 0.095 0.109 0.082 0.105 0.119 0.101 0.127 0.143 0.122 0.147 0.169
0.55 1.01 1.32 0.93 1.54 1.98 1.38 2.12 2.79 1.01 1.88 2.47 1.72 2.92 3.67 2.56 3.91 5.14
14.4 20.4 23.7 19.6 26.0 29.6 24.2 30.9 35.3 17.0 24.7 28.6 23.6 31.8 35.6 29.1 36.8 42.1
0.055 0.070 0.080 0.068 0.084 0.095 0.082 0.098 0.113 0.088 0.113 0.128 0.108 0.136 0.153 0.131 0.158 0.181
0.61 1.10 1.45 1.02 1.68 2.17 1.51 2.33 3.05 1.16 2.15 2.82 1.97 3.34 4.20 2.93 4.48 5.89
14.9 21.1 24.5 20.3 26.9 30.7 25.0 31.9 36.5 17.9 26.0 30.1 24.8 33.4 37.4 30.6 38.69 44.28
0.056 0.071 0.081 0.069 0.086 0.097 0.083 0.100 0.115 0.092 0.118 0.134 0.114 0.143 0.161 0.137 0.166 0.190
0.64 1.16 1.52 1.07 1.77 2.28 1.60 2.45 3.22 1.28 2.37 3.12 2.18 3.69 4.64 3.24 4.95 6.51
0.33% DSSF
0.55% DSSF
Fig. 3. Typical bond failure modes for the specimens without CFRP anchorage strip.
Fig. 4. Typical bond failure modes for the specimens with CFRP anchorage strip.
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Fig. 5. Pull-off force versus slip for various DSSF dosages and different CFRP sheet length and width.
using air vacuum cleaner to remove any dust and lose particles. After that, the surfaces were dried and maintained free of contaminants by wrapping with plastic sheets. Before application of the
primer resin, the area where the CFRP sheet is to be attached was marked and the remaining area was covered using plastering tape to keep it free of epoxy. The top 25 mm of the specimens were
Fig. 6. Pull-off force versus slip: (a) effect of CFRP bond length (b) effect of CFRP bond width.
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left un-bonded to prevent stress concentration. After that, the CFRP sheets were cut into strips with various lengths and widths to cover the required area at the surface of the specimens. Then, the epoxy compound was prepared by mixing part A and B using low-speed electric drill for at least 3 min to have a homogenous mix. Next, a layer of epoxy was spread uniformly over the marked area on the surface of the blocks and the CFRP strips were placed onto the resin and rolled along the fiber direction using a plastic roller until the resin was distributed over the whole fiber surface and ensuring that all the entrapped air bubbles were removed. Then, the second layer of epoxy resin was applied over the CFRP strips surfaces. For the anchorage system, the anchorage CFRP strip was adhered perpendicular to the free-end of the main CFRP strips after twenty-four hours. Finally, the specimens were left in the laboratory until testing. 2.5. Double shear pull-off test setup The specimens were subjected to double shear pull-off test using a universal testing machine as shown in Fig. 2. Using a universal testing machine, the pulling-off force was applied to a steel U-shaped arm connected to an aluminum cylinder that raps the CFRP middle part causing shear failure of the CFRP composite. The concrete blocks were fixed to the bottom platen of the machine using special fasteners. The tests were conducted under displacement control condition with a loading rate of 0.3 mm/ min. Two linear variable displacement transducers (LVDT) were placed at both sides of the specimen to obtain the force-slip relationship. To obtain the load-slip relationship between the CFRP composites and blocks, the LVDTs were attached between two points; one located at the top of the CFRP strips and another point located on the bottom of concrete specimen surface. All load and displacement measurements were collected using a data acquisition system. 3. Results and discussion The experimental results are presented in this section and discussed in terms of pull-off force versus slip relationships and failure mode considering the effect of the DSSF dosage, CFRP bond length, CFRP bond width, and the anchorage strip. Summary of the test results for all specimens is provided in Table 3.
between the CFRP composites and concrete was brittle and the duration of the de-bonding process was mainly dependent on the CFRP bond length and width, dosage of DSSF, and CFRP anchorage strip. 3.2. Influence of the DSSF dosage Table 3 presents the ultimate pull-off force, ultimate slip, and toughness results for all specimens with the various parameters. The pull-off force and corresponding slip results were plotted as shown Fig. 5 considering the various DSSF dosages and different CFRP sheet length and width. Table 3 and Fig. 5 clearly show that addition of DSSF increases both the pull-off force and slip for the various CFRP sheet length and width. For the specimens without CFRP anchorage strip, addition of 0.33% and 0.55% DSSF increased the pull-off force by about 6% and 10% with respect to the control specimens without DSSF. The corresponding increase in the bond slippage 4% and 5.5%, respectively. The results of the specimens with CFRP anchorage strip were discussed independently in Section 3.5. 3.3. Influence of the CFRP bond length and width The influence of bond length on the pull-off force and slip was evaluated through comparing the results of identical blocks having three different CFRP sheet bond lengths of 50, 75, and 100 mm for a given CFRP sheet width and a given DSSF dosage. As expected, the pull-off force and slip increase with the increase in the CFRP bond length as shown in Table 3 and Fig. 6(a), however the increase was not proportional. In other words, for a similar width, CFRP bond lengths of 75 and 100 mm means that the area of the CFRP sheet is 1.5 and 2.0 times. Almost for the various DSSF dosages, when the CFRP bond length increased from 50 mm to 75 mm and 100 mm, the pull-off force increased by about 36% and 68% for bf = 50 mm, 27% and 51% for bf = 75 mm; and 25% and 49% for bf = 100 mm as shown in Fig. 7. To assess the effect of the bond width independently, the results of the blocks with three different CFRP sheet bond widths of 50, 75, and 100 mm were compared for a given CFRP sheet length and a given DSSF dosage as shown in Fig. 8. Both the pull-off force and slip increase non-proportionally with the increase in the CFRP bond width as shown in Table 3 and Fig. 8. When the CFRP bond width increased from 50 mm to 75 mm and 100 mm, the pull-off force
3.1. Failure mode of the bond interface Majority of previous studies reported that the mode of failure of the CFRP-composites can be one of the following: (a) failure in the concrete while the CFRP-composite remains attached, (b) debonding of the CFRP composite, or (c) rupture of the CFRP sheet [13–15,17,18,20,21]. In this study, all the tested specimens experienced a failure mode similar to (b) where a thin layer of concrete at different thicknesses remained attached to the surface of the CFRP composite. It was noticed that the amount of peeled concrete clearly depends on the DSSF dosage. The thickness and area of peeled concrete increase as the dosage of DSSF increases as can be seen in the typical photos in Fig. 3. This could be attributed to that the DSSF increase the tensile strength of the concrete blocks resulting in a stronger bonding interface. The influence of the CFRP anchorage strip was evaluated through comparing the companion specimens with and without the CFRP anchorage strip. |More peeled concrete spread under the CFRP anchorage strip as shown in Fig. 4. This indicates that the use of a CFRP anchorage strip at the end of the main CFRP sheet is very effective and desirable. It alleviates the stress-concentration at the end of the CFRP composite at which de-bonding is usually initiated. The de-bonding failure
Fig. 7. Normalized ultimate load capacity versus CFRP sheet length.
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through increasing the sheet length only or vice versa, the increase in the pull-off force will be less than 50% if the CFRP bonding area is increased by 50%, and also will be less than 100% if the CFRP bonding area is doubled. For a similar total area, the CFRP composite that has larger bonding length results in almost similar pull-off strength as the CFRP composite with larger bonding width. 3.4. Influence of the CFRP anchorage strip
Fig. 8. Normalized ultimate load capacity versus CFRP sheet width.
increased by about 42% and 65% for Lf = 50 mm, 33% and 51% for Lf = 75 mm; and 28% and 46% for Lf = 100 mm. Following nearly a similar trend as the pull-off force, when the CFRP bond width increased from 50 mm to 75 mm and 100 mm, the ultimate slip increased by about 27% and 45% for Lf = 50 mm, 25% and 41% for Lf = 75 mm; and 20% and 38% for Lf = 100 mm. The obtained results indicate that whether the CFRP sheet bonding area is increased
To study the effect of CFRP anchorage strip, the bond load-slip curves shown in Table 3 and Fig. 9 for the three DSSF dosages (0%, 0.33%, and 0.55%) were compared. The results indicate that using an anchorage CFRP strip attached perpendicular to the free end of the CFRP sheets (Fig. 9) significantly enhances the bond strength and corresponding slip. The average increase in the pulloff force and corresponding slip at failure for the specimens with anchorage strip with respect to those without was 19% and 55% for specimens with 0% DSSF (Fig. 9(a)), 20% and 60% for specimens with 0.33% DSSF (Fig. 9(b)), and 22% and 65% for specimens with 0.55% DSSF (Fig. 9(b)), respectively. The results reveal that the use of an anchorage strip improves the performance of the CFRP composite and leads to about 20% increase in the pull-off strength. 3.5. Toughness characteristics In general, toughness indicates the ability of a member to absorb energy and plastically deforms without failure. The tough-
Fig. 9. Pull-off force versus slip for tested specimens due to anchorage strip of (0 and 25 mm) (a) 0% DSSF (b) 0.33% DSSF (c) 0.55% DSSF.
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ness values listed in Table 3 were calculated as the entire area under the load-slip curves. With respect to the blocks without DSSF, the results show that addition of DSSF at dosages of 0.33% and 0.55% improves the toughness by 10% and 16% for 0.33%, respectively. Table 3 also shows that for the various DSSF dosages, the toughness increased when Lf increased from 50 mm to 75 mm and 100 mm by about 67% and 149% for bf = 50 mm; 53% and 111% for bf = 75 mm; and 50% and 111% for bf = 100 mm, respectively. On the other hand, it can be stated that, when bf increased from 50 mm to 75 mm and 100 mm, the toughness increased by about 81% and 138% for Lf = 50 mm; 65% and 113% for Lf = 75 mm; and 54% and 102% for Lf = 100 mm, respectively. These results indicates that the toughness approximately increases by 50% and 100% when the CFRP sheet is increased by 50% or 100% through increasing the bonding length or width. Finally, the toughness results confirm the effectiveness of the CFRP anchorage strip that enhanced the toughness significantly with an average of 85%, 94% and 103% for 0%, 0.33% and 0.55% of DSSF dosages, respectively. 4. Conclusions Based on the experimental tested results, the following conclusions are drawn: 1. The use of DSSF in concrete is advantageous to the bond-slip behavior between concrete and CFRP composites. Addition of DSSF at 0.33% and 0.55% by volume resulted in increase in the bond strength of about 6% and 10%, respectively with respect to plain concrete. These results are confirmed also with the failure modes that showed more concrete attached to the surface of the peeled CFRP composite as the DSSF dosage increased. 2. Both the pull-off force and slip increase non-proportionally with the increase in the CFRP bond length or width (Lf or bf). For bf = 75 mm or 100 mm, increasing Lf by 50% and 100% results in an increase in the bond strength of approximately 25% and 50%. For bf = 50 mm, increasing Lf by 50% and 100% results in an increase in the bond strength of approximately 35% and 70%. 3. Almost similar enhancement would be achieved if bf is increased by 50% and 100% for a constant Lf indicating that both Lf and bf have the same influence for equivalent CFRP area. 4. The toughness approximately increases by 50% and 100% when the CFRP sheet is increased by 50% or 100% through increasing Lf or bf. 5. For all of the used CFRP sheet lengths and widths, the use of 25 mm CFRP anchorage strip attached perpendicular at the end of the main CFRP sheet was very effective and enhanced the bond strength by about 20%. It also enhances the toughness significantly.
Acknowledgement This work was fully supported by a grant from the Deanship of Research at Jordan University of Science and Technology (Project No. 2016/356). This support is gratefully acknowledged. References [1] ACI Committee 544, Design consideration for steel fiber reinforced concrete. ACI, 1999; web. 8, sep 2012. [2] Oh BH, Kim JC, Choi YC. Fracture behavior of concrete members reinforced with structural synthetic fibers. Eng Fract Mech 2007;74(1):243–57. [3] Jiabiao J, Loh S, Gasho T. Synthetic structure fibers for toughness and crack control of concrete. 29th conference on our world in concrete & structures. Singapore, vol. 25, no. 1. p. 26–33.
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Mohammad A. Alhassan Dr. Alhassan earned his bachelor and masters’ degrees in structural engineering in 2000 and 2003 from the Jordan University of Science and Technology (JUST). He earned his PhD degree in Civil Engineering from the University of Illinois at Chicago (UIC) in 2007. He started as an assistant professor at Purdue University-Fort Wayne (IPFW) in 2008 and promoted with tenure to associate professor in 2012. He then joined JUST in 2016 as an associate professor of civil engineering. His main research areas include: structural analysis and simulations, CFRP composites, fiber reinforced concrete, and seismic design.
M.A. Alhassan et al. / Ain Shams Engineering Journal 10 (2019) 359–367 Rajai Z. Al Rousan Dr. Al-Rousan is currently working as an associate professor at the Department of Civil Engineering at the Jordan University of Science and Technology. Dr. Al-Rousan received his Bachelor and M. S of Science in Civil Engineering in 2000 and 2003, respectively, from the Jordan University of Science and Technology, Jordan, and his Ph.D. in Civil Engineering from the University of Illinois at Chicago, USA in 2008. His field of expertise is Structural Engineering with emphasis on structural design of buildings and bridges, damage assessment, concrete materials, and strengthening of structural elements with CFRP.
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Esmail A. Al Shuqari Engineer AlShuqari is currently a masters’ of civil engineering student at the Jordan University of Science and Technology. He received his bachelor degree in civil engineering from Albaath University in-Yaman in 2012. He has very experience in concrete mixing and laboratory testing. He is expected to complete his masters’ degree in December 2017.