STRENGTHENING OF CORRODED REINFORCED CONCRETE BEAMS ... · To efficiently rehabilitate...
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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
Ahmed M. Gomaa, Manar A. Ahmed, Ehab M. Lotfy, Erfan A. Latef
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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
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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
Ahmed M. Gomaa, Manar A. Ahmed, Ehab M. Lotfy, Erfan A. Latef
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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
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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.
Ahmed M. Gomaa, Manar A. Ahmed, Ehab M. Lotfy, Erfan A. Latef
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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
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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
Ahmed M. Gomaa, Manar A. Ahmed, Ehab M. Lotfy, Erfan A. Latef
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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)
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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.
Ahmed M. Gomaa, Manar A. Ahmed, Ehab M. Lotfy, Erfan A. Latef
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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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