strengthening of corroded reinforced concrete … · ahmed m. gomaa, manar a. ahmed, ehab m. lotfy,...

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 10, Issue 09, September 2019, pp. 295-305, Article ID: IJCIET_10_09_031

Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=9

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication

STRENGTHENING OF CORRODED

REINFORCED CONCRETE BEAMS EXPOSED

TO TORSIONAL AND FLEXURAL STRESSES

Ahmed M. Gomaa, Manar A. Ahmed, Ehab M. Lotfy, Erfan A. Latef

Civil Engineering Department, Faculty of Engineering,

Suez Canal University, Ismailia, Egypt

ABSTRACT

Corrosion of steel reinforcement is one of the main durability threating problems

for reinforced concrete infrastructures worldwide. In this paper, an experimental

study is performed to investigate the effects of corrosion of steel reinforcement on

behavior of beams with three different percentage of corrosion (2.5%, 5%, and 7.5%),

the experimental study investigates the effects of using carbon fiber reinforced

polymer (CFRP) and glass fiber reinforced polymer (GFRP) for strengthening

corroded reinforced concrete beams with 5% corrosion only. Eighteen beams are

divided into three sets, each set consists of one beam specimen is neither corroded nor

strengthened to serve as reference, three beams are corroded to serve as corroded

control, and the remaining two beams are corroded and strengthened with CFRP or

GFR for each. All beam specimens are 100×200×2000 mm with main steel

reinforcement 2Ø 12. Accelerated corrosion pool is used for the accelerated corrosion

process. The results show that the load carrying capacity and torsional moment of the

beam is higher, but deflection and angle of twist is lower for control beams compared

to corroded beams. Strengthening beams with CFRP is more effective than

strengthening beams with GFRP. The number of cracks developed is more in case of

control beams compared to corroded beams, but as the rate of corrosion increases the

crack width increases in corroded beams compared to control beams.

Keywords: CFRP, GFRP, Flexure, Torsion, Strengthening, Corrosion

Cite this Article: Ahmed M. Gomaa, Manar A. Ahmed, Ehab M. Lotfy,

Erfan A. Latef, Strengthening of Corroded Reinforced Concrete Beams Exposed to

Torsional and Flexural Stresses. International Journal of Civil Engineering and

Technology 10(9), 2019, pp. 295-305.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=9

1. INTRODUCTION

Over the last few years interest in the rehabilitation and repair of Reinforced Concrete (RC)

structures has increased, as the premature degradation of RC structures exposed to severe

environmental conditions and excessive mechanical loading has become an increasingly

serious problem. The strengthening of existing structures is of great importance especially in



earthquake prone areas, and the efficiency of various techniques for the improvement of their

structural performance has been examined in previous studies [1-5].

Corrosion of reinforcement in concrete is considered to be one of the most common

reasons for the deterioration of reinforced concrete (RC) [6]. In 2000, the US State

Department spent an estimated $5 billion to remediate concrete bridges, which were directly

affected by corrosion of reinforcing steel bars [7]. Similar costs are spent in Europe and

Canada to maintain their bridge infrastructure in service. In the United Kingdom (UK) alone,

it has been estimated that the cost of repairing corrosion-damaged RC bridges is about £616.5

million [8]. In the United States, the situation is even worse as the annual estimated direct cost

of replacing or repairing corrosion-damaged bridges is $8.3 billion [9]. Other countries in

North America and Europe are faced with the same challenge, so emphasizing the global

significance of the issue. To efficiently rehabilitate corrosion-damaged reinforced concrete

structures, the residual strength and failure mechanism of the deteriorated structure must be

determined. For this purpose, several studies have been reported in the literature. Most of the

studies in the literature focused on flexural and bond strength of corroded beams [10-12].

Models have been developed by many researchers to determine the residual flexural/bond

strength of corroded beams [13-15]. However, there are only a few studies related to the

torsional strength of corroded beams. In the last two decades, the use of fiber-reinforced

polymer (FRP) reinforcement for retrofitting RC structures has become a field of much

research interest. FRP have several advantages over classic strengthening techniques, such as

design flexibility, ease of use, and corrosion resistance.

2. METHODS

Eighteen reinforced concrete beams with dimension of 100mm x 200mm in cross section and

2000mm in length have been casted. The behavior of reinforced concrete beams of 2.5%,

5.0%, and 7.5% corrosion is studied under two types of loading; flexural and torsional. Table

(1) illustrates the test matrix of beams that are used for the testing. Fig (1) to fig (3) illustrate

the reinforcement of beams, shape and strengthening method. The beams are tested under the

effect of 4 points loading by compression machine in flexure, two cantilever steel beams are

used to create a mechanism for testing beam under torsion, see fig (5), and a dial gauge is

used to measure the deflection in beams. Fig (4) illustrates locations of loading points and dial

gauge, Fig (5) illustrates the mechanism created for testing beam under torsion; a bracket is

formed by attaching I-beam section around the concrete beam to act as lever arm to apply the

torsional moment, a long steel wide flange I-beam is diagonally laid down resting on hinged

end supports on top of the lever arms. The nomenclature used for the beams is as follows in

table (1)

Table 1 Test Matrix

Beam Notation corrosion Corrosion

direction

Repaired loading

B-F-N-1 0%

0%

0%

longitudinal

longitudinal

transverse

control

control

control

flexure N=None(0%mass loss)

L=Low(2.5%mass

loss)

M=Mild(5%mass loss)

H=High(7.5%mass

loss)

G=GFRP

C=CFRP

F=Flexure

B-T-N-1 torsion

B-T-N-2 torsion

B-F-L-1 2.5% longitudinal Unrepaired flexure

B-F-M-1 5% longitudinal Unrepaired flexure

B-F-H-1 7.5% longitudinal Unrepaired flexure

B-F-M-G-1 5% longitudinal repaired flexure

B-F-M-C-1 5% longitudinal repaired flexure

B-T-L-1 2.5% longitudinal unrepaired torsion

Strengthening of Corroded Reinforced Concrete Beams Exposed to Torsional and Flexural Stresses


Figure 1. Flexure sets

Figure 2. Torsional longitudinal sets Figure 3. Torsional transverse sets

Figure 4. Sketch illustrates locations of points loading and dial gauge

B-T-M-1 5% longitudinal unrepaired torsion T=Torsion

B-T-H-1 7.5% longitudinal unrepaired torsion

B-T-M-G-1 5% longitudinal repaired torsion

B-T-M-C-1 5% longitudinal repaired torsion

B-T-L-2 5% transverse unrepaired torsion

B-T-M-2 5% transverse unrepaired torsion

B-T-H- 2 7.5% transverse unrepaired torsion

B-T-M-G-2 5% transverse repaired torsion

B-T-M-C-2 5% transverse repaired torsion



Figure 5. Schematic of torsion test setup

2.1. Accelerated Corrosion Technique

After 28 days of curing, eighteen beams are subjected to accelerated corrosion by impressing

a direct current into the bars through power supplies; one power supply for each two beams.

The reinforcing bar acted as an anode and the stainless steel bar acted as a cathode in this

artificial corrosion cell. The schematic diagram showing the details of the connection between

the reinforcing bars, the stainless-steel tube and the power supply are shown in Figs (6) and

(7). This technique involves the use of chloride salts in the concrete to activate the corrosion

process. The amount of chloride salt (NaCl) was range from 3.5-5%. The direct current was

impressed through the reinforcing bars at a constant current density. A current density of 200

μA/cm2 is selected, based on a study done by El-Maaddawy and Soudki (2003).

Figure 6. Corrosion pool

2.2. Time Required For Calculating Different Percentage of Corrosion

Faraday’s Law is used to determine the time required to reach the desired mass loss:

Where: m = mass loss (g)

I = corrosion current (A)

t = corrosion time (s)

a = atomic weight (56 g for iron)

Z = valence of the corroding metal (2 for iron)

F = Faraday’s constant (96,500 A.s.)

Figure 7. Details of accelerated corrosion

circuit



2.3. Preparing strengthened Specimens

Strengthening by using (CFRP) and (GFRP) is performed as follows; preparing and cleaning

the surface as shown in fig (14), two components of epoxy are mixed according to

recommendations on epoxy data sheet, applying the epoxy on the surface of the beam, and

CFRP &GFRP sheets are installed over the concrete surface in the strengthening zones as

shown in fig (15).

Figure 8. Smoothing the surface

Figure 9.Placing CFRP and GFRP in strengthening zones

3. RESULTS

Beams are tested up to failure for every sets. The failure modes and the crack patterns

occurred for all tested beams have been studied. Table (2) shows the cracking and ultimate

loads (Pcr and Pu), the corresponding deflections at middle span (Δcr and Δu), cracking and

ultimate Moments (Mcr and Mu), the corresponding angle of twist (Ψcr, Ψu), and failure

type.



Table 2 Values of crack and ultimate load, torsional moment, deflection, angle of twist, and

failure type

3.1. Crack pattern and failures modes

Fig (10) to fig (27) show the failure modes and the crack patterns occurred for tested beams

exposed to flexure and torsion stresses. It is observed that all un-strengthened beams failed in

shear mode; the cracks for all un-strengthened beams are inclined.

Beam Pcr Δcr Pu Δu Failure

type KN mm KN mm

B-F-N-1 23 6 60 15

Sh

ear

B-F-L-1 21 3 51 17

B-F-M-1 20 3 45 19

B-F-H-1 20 4 41 21

B-F-M-G-1 24 4 47 14

B-F-M-C-1 27 2 64 13

Beam Mcr Ψcr Mu Ψu Failure

type KN.m Rad/m KN.m Rad/m

B-T-N-1 6.5 9 8.5 15

Sh

ear

B-T-L-1 6.2 10 7.6 16

B-T-M-1 6.2 13 6.8 18

B-T-H-1 5.8 14 6.2 23

B-T-M-G-1 7 11 8 15

B-T-M-C-1 8.9 13 9.5 16

B-T-N-2 7 10 8.5 16

B-T-L-2 6.8 13 7 17

B-T-M-2 6 10 6.3 21

B-T-H-2 4.9 7 5.8 25

B-T-M-G-2 6.5 11 7.4 20

B-T-M-C-2 8 12 9.6 14



3.2. Load–deflection curves & torsional moment-angle of twist curves

Deflection (mm) is measured vs load (KN). Fig (28) shows the load-deflection curves for

beams exposed to flexure stress, fig (29) shows the torsional moment-angle of twist curves for

beams exposed to torsional stress with longitudinal steel corrosion, and fig (30) shows the

torsional moment-angle of twist curves for beams exposed to torsional stress with transverse

steel corrosion. All beams are compared for torsional moment and first crack load, as shown

in fig (31) to fig (33). Comparisons are also made at ultimate torsional moment and load, as

per fig (34) to fig (36).

Figure 28. Load-deflection curves for flexure tested beam Figure 29. Torsional moment-angle of twist curves (longitudinal steel corrosion) beam



Figure 30. Torsional moment-angle of twist curves (transverse steel corrosion)

Figure 31. Load at first crack

F Figure 34. Ultimate Load

Figure 32. Torsional moment at first crack (longitudinal steel corrosion)

Figure 33. Torsional moment at first crack

(transverse steel corrosion)

Figure 36. Ultimate torsional moment (transverse

steel corrosion)

Figure 35. Ultimate torsional moment

(longitudinal steel corrosion)



4. DISCUSSION

4.1. Flexure beams set

For the beam corroded by 2.5%, the ultimate load decreases by 15 % and the ultimate

deflection increases by 13% compared to the control beam. While for beam corroded by 5%,

the decrease in ultimate load is 25 % and the increase in ultimate deflection is 26% compared

to control beam. For beam corroded by 7.5%, ultimate load decreases by 31 % and ultimate

deflection increases by 40% compared to control beam. These results indicate that, as the rate

of corrosion increases the drop in ultimate load decreases, while the rate of deflection increase

is approximately the same.

For flexure sets the beam strengthened by CFRP, the increase in ultimate load is 42 % and the

decrease in ultimate deflection is 31% compared to beam corroded by 5%, but in case of

strengthening beam by GFRP the ultimate load increases by 4 % and the ultimate deflection

decreases by 26% compared to beam corroded by 5%. It was observed that the ultimate load

of the beam strengthened by CFRP is higher by 36%, and the ultimate deflection is lower by

15% than strengthening beam by GFRP. and this indicate that strengthening by CFRP shows

tendency to carry more load compared to GFRP.

4.2. Torsional beams set (corrosion in longitudinal steel)

For beam corroded by 2.5%, the decrease in ultimate torsional moment is 11 % and the

increase in ultimate angle of twist is 6% compared to control beam, while for beam corroded

by 5%, the decrease in ultimate torsional moment is 20% and the increase in ultimate angle of

twist is 20% compared to control beam. The decrease in ultimate torsional moment for beam

corroded by 7.5% is 27 % and the increase in ultimate angle of twist is 53% compared to

control beam. This indicates that, as the rate of corrosion increases the drop in ultimate

torsional moment slightly decreases and there is a significant increase in deflection.

For beam corroded by 5%, strengthening the beam with CFRP increases ultimate torsional

moment by 39 % and decreases ultimate angle of twist by 12% compared to beam without

strengthening, but in case of strengthening beam by GFRP the ultimate torsional moment

increases by 17 % and ultimate angle of twist decreases by 17%. It was observed that the

ultimate torsional moment of the beam strengthened by CFRP is higher by 18%, and the

ultimate angle of twist is lower by 6% compared to beam strengthened by GFRP, this

indicates that strengthening by CFRP shows tendency to carry more load compared to GFRP.

4.3. Torsional beams set (corrosion in transverse steel)

Corrosion of transverse steel by 2.5% decreases the ultimate torsional moment by 18 % and

increases ultimate angle of twist by 6% compared to control beam, and corrosion by 5%

decreases ultimate torsional moment by 26% and increases ultimate angle of twist by 31%

compared to control beam, while 7.5% corrosion decreases ultimate torsional moment by 32

% and increases ultimate angle of twist by 56% compared to control beam, this indicates that,

as the rate of corrosion increases the drop in ultimate torsional moment slightly decreases and

there is a significant increase in deflection.

Strengthening beam by CFRP increases ultimate torsional moment by 52 % and decreases

ultimate angle of twist by 33% compared to beam corroded by 5%, but in case of

strengthening beam by GFRP the ultimate torsional moment increases by 17 % and ultimate

angle of twist decreases by 5% compared to beam corroded by 5%. It was observed that the

ultimate torsional moment of beam strengthened by CFRP is higher by 29%, and ultimate

angle of twist is lower by 30% compared to beam strengthened by GFRP, and this indicates

that strengthening by CFRP shows tendency to carry more load compared to GFRP.

Corrosion of transverse reinforcement is more critical than corrosion of longitudinal

reinforcement on ultimate torsional moment and angle of twist.



All strengthened specimens show limited deformation and cracks before failure of concrete.

5. CONCLUSION

The following conclusions are made based on the results of this study:

The load carrying capacity and torsional moment of the beam is higher, but deflection and

angle of twist is lower for control beams with respect to corroded beams (2.5%, 5%, and

7.5%).

Strengthening corroded beams with CFRP is more effective than strengthening beams with

GFRP for both flexural and torsional loading.

The ultimate deflection and ultimate angle of twist for beam strengthened with CFRP is less

compared to beams strengthened with GFRP.

The number of cracks developed is more in case of control beams compared to corroded

beams, but as the rate of corrosion increases the crack width increases in corroded beams than

in control beams.

Corrosion of transverse reinforcement is more effective than corrosion of longitudinal

reinforcement on ultimate torsional moment and angle of twist.

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strengthening of corroded reinforced concrete … · ahmed m. gomaa, manar a. ahmed, ehab m. lotfy,...

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