20320140502006 2

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN
0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME

INTERNATIONAL JOURNAL OF CIVIL
ENGINEERING AND TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 5, Issue 2, February (2014), pp. 52-70
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2014): 3.7120 (Calculated by GISI)
www.jifactor.com

IJCIET
©IAEME

STRENGTHENING REINFORCED CONCRETE ONE WAY SLABS BY
OVERLAY TECHNIQUE & USING CFRP
Samir A.AL Mashhadi
University of Babylon, College of Engineering
Ahmed Hassan Hadi
University of Babylon, College of Engineering

Abstract
The objective of this research is to study the behavior of reinforced concrete one way slabs,
that strengthened with concrete overlay with and without externally bonded Carbon Fiber Reinforced
Polymer (CFRP) sheets. The experimental results showed that increasing in concrete overlay
thickness from 25mm to 50mm caused an increase in the first cracking load value, this increasing
ranged about (33% to 100%) while for ultimate load was about (31% to 88%) in compared with
control slab specimens. The increasing in compressive strength of the concrete overlay did not give a
considerable increase in the first crack loading and ultimate loading. It was obtained that using the
bonding materials gave higher ultimate loading, low deflection and low concrete strain in compared
with specimens without bonding materials. From results the bonding materials can be arranged
according to bonding. The specimens strengthened with suggested combined strengthening system
(concrete overlay plus CFRP sheets) showed the best results which gave an increase 164% in
ultimate load and 167% in first crack loading when compared with the corresponding control
specimens.
1.

INTRODUCTION

Reinforced concrete is the most frequently applied structural material. That is explainable
with its easy use, its advantageous mechanical properties which develop after hardening. The
commonly held view, that concrete is a durable, maintenance-free construction material has been
changed in recent years. Several examples can be shown where concrete did not perform as well as it
was expected. These are the results of the insufficient consideration of durability during the design
process, the inadequate execution and the maintenance. Therefore, repair or strengthening of a
concrete structure may become necessary:
52


To increase live-load capacity, example of a bridge subject to increased vehicle loads or a
building the use of which is to change from residential to commercial.
To add reinforcement to a member that has been under designed or wrongly constructed.
To improve seismic resistance, either by providing more confinement to increase the strain
capacity of the concrete, or by improving continuity between members.
To replace or supplement reinforcement, example damaged by impact or lost due to
corrosion.
To improve continuity, example across joints between precast members (Ibrahim and
Mahmood, 2009).
In the past, reinforced concrete slabs were strengthened by conventional methods such as
concrete overlay as shown in figure 1, span shortening and externally bonded steel reinforcement.
Today there are several types of Carbon Fiber Reinforcement Polymer (CFRP) strengthening
systems and techniques available to strengthen reinforced concrete slabs. The suitability of each
system depends on the type of structure that shall be strengthened. Therefore, it is essential for
engineers to understand the consequences of the design choice in terms of efficiency and failure
mechanism for different systems before further attempts are carried out (Tan, 2003).

Concrete

Bonding Material

Existing concrete slab

Figure 1: Conventional concrete overlay

2. SPECIMEN DETAILS
The experimental study consisted of testing twenty-one reinforced concrete one way slabs
under one point loading. All slabs were 1200mm long, and had 250mm wide, 100mm high cross
section. The flexural reinforcement of these slabs consisted of 3-Ø8mm in the main direction and
Ø4mm@100mm in the transverse direction. The flexural reinforcement ratio is 0.68 % which is
below the maximum reinforcement ratio allowed under the current ACI 318-05 Code.
The flexural reinforcement of overlay slabs consisted of 3-Ø4mm in the main direction which
represent the minimum steel reinforcement and Ø4mm@100mm in the transverse direction. The
concrete overlay used was 25 or 50mm thickness.
Figure 2 shows the cross section and the reinforcement details for the bare slab and concrete
overlay.

53


3. SPECIMENS IDENTIFICATION AND STRENGTHENING SCHEMES
In order to identify the test specimens with different variables and strengthening schemes, the
following designation system is used:
Type of loading: P: Positive bending (i.e. placed concrete overlay in compression zone) and
N: Negative bending (i.e. placed concrete overlay in tension zone).
Type of bonding materials between the hard concrete (bare slab) and the fresh (concrete
overlay): QM: Quickmast 108, SBR: SBR, OPC: Ordinary Portland Cement and
WT: Without bonding material.
Thickness of concrete overlay: 25: Thickness of overlay 25mm and 50: thickness of overlay
50 mm.
Reinforcement of concrete overlay: R: reinforced concrete overlay and P: Plain concrete
overlay.
Nominal compressive strength of concrete overlay: C25: 25MPa, C40: 40MPa and C70:
70MPa.
Number of CFRP sheets: 0: No CFRP, 1: one sheet and 2: two sheets.
Table 1 illustrates the specimen identification system used based on the specimen
identification pattern described above.

Figure 2: Cross –section of test specimens
4. STRENGTHENING SCHEMES
Six of the reinforced concrete slabs were strengthening by externally bonded CFRP placed in
the tension zone. The slab specimens P-QM 25 R-C25-1 and P-QM 50 R-C25-1 were strengthened
with one CFRP sheets bonded on bare slabs while the slab specimens P-QM 25 R-C25-2 and P-QM
50 R-C25-2 were strengthened with two CFRP sheets bonded on bare slab and the slab specimens N54


QM 25 R-C25-2 and N-QM 50 R-C25-2 were strengthened with two CFRP sheets bonded on
concrete overlay slab, as shown in Figure 3.
Table 1: Specimen Identification and Strengthening Schemes
Overlay
Overlay
Type of Thickness
Type of
reinforcement
Specimen
bonding of overlay
fc′
loading
description
material
(mm)
(MPa)
Control 1
Nil
Nil
Nil
Nil
Nil
Control 2
Nil
Nil
Nil
Nil
Nil
P-QM 25
25
Reinforced
25
Positive Quickmast
R-C25-0
P-QM 50
Positive Quickmast
50
Reinforced
25
R-C25-0
P-QM 25
25
Reinforced
40
Positive Quickmast
R-C40-0
P-QM 50
50
Reinforced
40
Positive Quickmast
R-C40-0
P-QM 25
25
Reinforced
70
Positive Quickmast
R-C70-0
P-QM 50
Positive Quickmast
50
Reinforced
70
R-C70-0
P-WT 50
Positive
Without
50
Reinforced
25
R-C25-0
P-SBR 50
Positive
SBR
50
Reinforced
25
R-C25-0
P-OPC 50
Positive
Cement
50
Reinforced
25
R-C25-0
P-QM 25
Positive Quickmast
25
Plain
25
P-C25-0
P-QM 50
50
Plain
25
Positive Quickmast
P-C25-0
N-QM 25
Negative Quickmast
25
Reinforced
25
R-C25-0
N-QM 50
Negative Quickmast
50
Reinforced
25
R-C25-0
P-QM 25
25
Reinforced
25
Positive Quickmast
R-C25-1
P-QM 50
Positive Quickmast
50
Reinforced
25
R-C25-1
P-QM 25
Positive Quickmast
25
Reinforced
25
R-C25-2
P-QM 50
Positive Quickmast
50
Reinforced
25
R-C25-2
N-QM 25
Negative Quickmast
25
Reinforced
25
R-C25-2
N-QM 50
Negative Quickmast
50
Reinforced
25
R-C25-2
55

CFRP
amount
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
2
2
2
2


Figure 3: Schematic representation of CFRP strengthening schemes
All stirrups of CFRP of length 1200 mm, width 80 mm and thickness 0.131mm comprising
an equivalent steel area 75mm2.

5. MATERIALS
5.1 Cement
Ordinary Portland Cement (Type I) of Tasluja-Bazian mark was used in casting all the
specimens. Test results indicate that the adopted cement conforms to Iraqi specifications (I.O.S.
NO.5/1984) .OPC was used as bonding additive (bonding old concrete with new concrete) by
scattering water on the surface of the bare slab and scattering dry OPC as a slurry coat.
5. 2 Fine Aggregate (Sٍ nd)
a
Natural sand from Al-Akhaider region was used as a fine aggregate in this research. Results
indicate that the fine aggregate grading and the sulphate content are within the requirements of the
Iraqi specification No.45/l984.
5.3 Coarse Aggregate (Gravel)
Locally available rounded gravel of (19mm) and (10mm) maximum size were used. For high
strength concrete, it was used crushed gravel with a maximum size of (10mm). Results indicate that
the Coarse Aggregate grading and the sulphate content are within the requirements of the Iraqi
specification No.45/l984.

56


5.4 High Range Water Reducing Admixture (HRWRA)
A chemical admixture based on modified polycarboxylic ether, which is known commercially
(Glenium 51) was used in producing HSC as a high range water-reducing admixture.
5.5 Mixing Water
Ordinary clean tap water was used for casting and curing all the specimens.
5.6 Carbon Fiber Reinforced Polymer (CFRP)
The mechanical properties of CFRP sheets used here is taken from manufacturing
specifications (Sika, 2005).
5.7 Steel Reinforcing Bars
For all slabs specimens, two size of steel reinforcing bars were used (Ø8mm and Ø4mm).
5.8 Impregnation resin
Sikadur-330 (impregnation resin) was used in this work for the bonding of CFRP sheet.
5.9 Quickmast 108
Quickmast 108 is a two components, solvent free epoxy resin bonding agent, supplied in preweighed packs containing base and hardener. The surface of the bare slab was grinded using an
electrical hand grinder to expose the aggregate and to obtain a clean sound surface and painted by
Quickmast 108.
5.10 Styrene- Butadiene- Rubber (SBR) admixture
SBR is used as bonding additive (bonding old concrete with new concrete) when used as a
slurry coats in the following proportions: 1 SBR: 1 clean water: 3 OPC (by volume).
5.11 Concrete Mix
All bare slabs that used with control mix proportions of materials; 1:1.8:2.5 (cement: sand:
gravel), and water/cement ratio is 0.5 (by weight).
Concrete overlay that used with three types of compressive strength:
•

25 MPa cylinder compressive strength, the mix proportions were: 1:1.91:2.08 (cement: sand:
gravel), and water/cement ratio is 0.48 (by weight). Concrete mix was designed according to
the American mix design method ACI 211 (Neville, 1995) to have compressive strength 25
MPa at age of 28 days with maximum rounded aggregate size (10mm) and the slump is
60mm (from seven experimental mixes).
• 40 MPa cylinder compressive strength, the mix proportions were: 1:1.34:1.61 (cement: sand:
gravel), water/cement ratio was 0.35 (by weight) and superplasticizer of 0.44% quantity by
weight of cement was used.
• 70 MPa cylinder compressive strength, the mix proportions were: 1:1.134:1.93 (cement:
sand: gravel), water/cement ratio is 0.28 (all by weight) and superplasticizer of 1.4 %
quantity by weight of cement was used. Mix proportions and details for all mixes are shown
in Table 2.

57


Table 2: Details of Mixes Used in Slabs
S.P, %
Sand
Gravel
w/c
weight of
3
3
kg/m
kg/m
ratio
cement

Slab
group

Cement
content
kg/m3

Bare
slab

370

777

1023

---

fc′25

417

797

867

fc′40

540

725

fc′70

550

635

f c′

Slump
(mm)

MPa

0.50

55

22.9

---

0.48

60

25.7

867

0.44

0.35

60

40.6

1085

1.4

0.28

150

73.7*

where:
f c′ : Average cylinder 150×300mm compressive strength.
* Average cube 100×100×100mm compressive strength.

5.12 Test Setup
After curing, the slabs specimens were transported to the Structural Laboratory of Babylon
Technical Institute to test them under one point loading up to failure.
All slab specimens were tested in one point loading. slab specimens were tested as simply
supported over 1050mm span in 1000 kN capacity hydraulic machine. Each slab specimen was
supported and loaded by rollers. Forces were distributed through steel bearing plate 250mm in
length to cover the entire slab width. To observe crack development, slab specimens were painted
white with emulsion paint before testing. Cracks were traced by pencil. Figure 4 shows the test
setup. Deflection of the slab specimens was measured at mid-span using a dial gage with travel
distance of 30mm and accuracy of 0.01mm. An ELE mechanical strain gage having an accuracy of
0.002mm was used to measure the concrete strains. Demec discs were calibrated using an
accompanying special ruler. Arrangement and distribution of these Demec discs are shown in
Figure 5.
6. EXPERIMENTAL RESULTS
6.1 Compressive Strength
The compressive strength test results are obtained from the average of three concrete cubes
cast with two concrete slab specimens except slab specimen P-WT 50 R-C25-0 cast with three cubes
and tested at the same age of the slab specimens, as presented in Table 3.
6.2 Flexural Strength (Modules of Rupture)
The results of flexural tensile strength test of the concrete specimens (prisms
100×100×400mm) were tested at the same age of the slab are given in Table 4.
6.3 First Cracking Loads
In specimens series P-QM 25 R-C25-0 to P-WT 50 R-C25-0 strengthening of RC slab by
adding concrete overlay showed better enhancement in first cracking loads when compared with
control slab specimens 1 and 2 as shown in Table 5.

58


Figure 4: Test setup for slab specimens

Figure 5: Arrangement of fixed demec steel disks

59


Table 3: Measured Values of Compressive Strength at the same age of the slab
Slab specimen
Control 1
Control 2
P-QM 25 R-C25-0
P-QM 50 R-C25-0
P-QM 25 R-C40-0
P-QM 50 R-C40-0
P-QM 25 R-C70-0
P-QM 50 R-C70-0
P-WT 50 R-C25-0
P-SBR 50 R-C25-0
P-OPC 50 R-C25-0
P-QM 25 P-C25-0
P-QM 50 P-C25-0
N-QM 25 R-C25-0
N-QM 50 R-C25-0
P-QM 25 R-C25-1
P-QM 50 R-C25-1
P-QM 25 R-C25-2
P-QM 50 R-C25-2
N-QM 25 R-C25-2
N-QM 50 R-C25-2

Bare slab compressive strength
MPa
Cube
Cylinder

Overlay
compressive strength MPa
Cube
Cylinder

35.3

28.2

---

---

34.3

27.4

35.8

28.6

35.1

28.1

51.7

41.4

35.7

28.6

75.2

---

34.8

27.8

35.7

28.6

34.8

27.8

36.0

28.8

37.0

29.6

36.3

29

36.4

29.1

34.3

27.4

33.4

26.7

38.2

30.6

33.3

26.6

38.9

31.1

31.2

25.0

35.9

28.7

Table 4: The Flexure Strength Results for Bare and Overlay Slabs
Slab specimen

Measured

fr

MPa

Measured

fr

MPa

for bare slab

for overlay

4.4

---

5.1

5.3

4.4

5.6

4.32

7.5

5.3

4.5

4.3

5.1

4.0

5.2

4.4

4.8

4.4

5.2

3.9

5.1

4.2

5.0

Control 1
Control 2
P-QM 25 R-C25-0
P-QM 50 R-C25-0
P-QM 25 R-C40-0
P-QM 50 R-C40-0
P-QM 25 R-C70-0
P-QM 50 R-C70-0
P-WT 50 R-C25-0
P-SBR 50 R-C25-0
P-OPC 50 R-C25-0
P-QM 25 P-C25-0
P-QM 50 P-C25-0
N-QM 25 R-C25-0
N-QM 50 R-C25-0
P-QM 25 R-C25-1
P-QM 50 R-C25-1
P-QM 25 R-C25-2
P-QM 50 R-C25-2
N-QM 25 R-C25-2
N-QM 50 R-C25-2

60


Table 5: First Cracking Load for The Tested Slabs
First
Increase in cracking
Specimen
cracking load , kN
load ,%
Control 1
7.5
N/A
Control 2
7.5
N/A
P-QM 25 R-C25-0
10
33
P-QM 50 R-C25-0
15
100
P-QM 25 R-C40-0
12.5
67
P-QM 50 R-C40-0
15
100
P-QM 25 R-C70-0
12.5
67
P-QM 50 R-C70-0
15
100
P-QM 50 P-C25-0
12.5
67
N-QM 50 R-C25-0
10
33
P-SBR 50 R-C25-0
15
100
P-OPC 50 R-C25-0
17.5
134
P-WT 50 R-C25-0
17.5
134
N-QM 25 R-C25-0
7.5
N/A
P-QM 25 P-C25-0
7.5
N/A
P-QM 25 R-C25-1
12.5
67
P-QM 25 R-C25-2
15
100
P-QM 50 R-C25-1
17.5
134
P-QM 50 R-C25-2
20
167
N-QM 25 R-C25-2
17.5
134
6.4 Cracking Patterns
The control slab specimens 1 and 2 were tested in order to compare between them and the
other that strengthened. The appearance of flexural cracks was first at 7.5 kN under the point load
region. Flexural cracks formed and widened as loading proceeded.
At 12.5 kN loading, new flexural cracks formed and wide speared along the mid-span.
Further flexural cracks occurred near the quarter-span of the specimens as the load increased to 20
kN.
At 27.5 kN loading, no new cracks are appeared and that means the specimens is controlled
by yielding of steel, as shown in Plate 1.
The first crack in strengthened slab specimens P-QM 25 R-C25-0, (which was strengthened
by 28.6 MPa compressive strength reinforced concrete overlay of 25mm thickness bonded by
quickmast 108) was observed in mid-span region at loading of 10 kN. As the load was increased to
17.5 kN new cracks formed within the quarter-span of the specimens. The cracks stretched to the
overlay at the loading of 25 kN and no separation had been occurred between the overlay and the
bare slab. Finally, typical flexural failure occurred at loading of 38.4 kN as shown in plate 2.
The slab specimens P-SBR 50 R-C25-0 was strengthened by adding 28.8 MPa compressive
strength reinforced concrete 50mm overlay thickness and the bonding material SBR placed between
bar slab and the concrete overlay. The first cracking was observed at the load of 15 kN within midspan region. As the loading increased the cracks increased and widened, the separation had occurred
between the concrete overlay and the slab at the load of 40 kN as shown in Plate 3
The first crack in strengthened slab specimens P-QM 25 R-C25-1, (which was strengthened
by adding 32.5 MPa compressive strength reinforced concrete overlay of 25mm thickness and
strengthened with one strip of CERP) was observed at load 12.5 kN under point load region. The
formation of flexural cracks (that occurred as a result of the yielding of embedded steel
61


reinforcement) was at loading 45 kN. The spacemen failed by debonding failure which occerred at
load 52.5 kN as shown in Plate 4.

(a): bottom view

(b): side view
Plate 1: Cracking pattern for slab control 1

(a): bottom view

(b): side view

Plate 2: Cracking pattern for slab P-QM 25 R-C25-0
62


(a): bottom view

(b): side view
Plate 3: Cracking pattern for slab P-SBR 50 R-C25-0

(a): bottom view

(b): side view
Plate 4: Cracking pattern for slab P-QM 25 R-C25-1

63


6.5 Load-Deflection Curves
The structural behavior of tested slab specimens are represented here by their load versus
mid-span deflection as shown in Figures 6 to 14
For the unstrengthened control specimens (control 1 and 2) a large increase in deflection was
noticed in the third stage, while the applied load changed little, as shown in Figure 6.
Figures 7 to 8 show the behavior of the flexural slab specimens with different thickness of
concrete overlay. It is shown from these Figures that the values of the maximum deflection of the
specimens with concrete overlay (25 or 50mm) are smaller than the deflection for control slabs 1 and
2. The specimens with concrete overlay (25 or 50mm) have greater stiffness to resist the applied load
and as the thickness of the concrete overlay increased the resistance of the section will increase
accordingly.
90

Control 1
Control 2

80

Applied load (kN)

70
60
50
40
30
20
10
0
0

2

4

6

8

10

12

14

Midspan deflection (mm)

Figure 6: Load vs. deflection for control slabs 1 and 2

90

Control 1
Control 2
P-QM 25 R-C25-0
P-QM 50 R-C25-0

80

Applied load (kN)

70
60
50
40
30
20
10
0
0

2

4

6

8

10

12

14


Figure 7: Load vs. deflection for slabs with different thickness concrete overlay and compressive
strength 25 Mpa

64

90
Control 1
Control 2
P-QM 25 R-C40-0
P-QM 50 R-C40-0

Applied load (kN)

80
70
60
50
40
30
20
10
0
0

2

4

6

8

10

12

14


strength 40 MPa
90
Control 1
Control 2
P-QM 25 R-C70-0
P-QM 50 R-C70-0

80
Applied load (kN)

70
60
50
40
30
20
10
0
0

2

4

6

8

10

12

14


strength 70 MPa
The specimens P-WT 50 R-C25-0, P-OPC 50 R-C25-0 and P-SBR 50 R-C25-0 failed
suddenly and did not reach the third stage because these specimens failed in shear interface between
the bare slab and concrete overlay as show in figure 10, while P-QM 50 R-C25-0 showed high
ductility and did not fail in shear interface.
Figures 11 to 14 show the effect of CFRP strengthening on the flexural behavior of the slab
specimens. The deflection of the slabs that strengthened with CFRP sheets was lower than the
deflection of the corresponding control slabs 1 and 2. That is due to increasing the reinforcement by
adding CFRP sheets.

65

90

Control 1
Control2
P-QM 50 R-C25-0
P-SBR 50 R-C25-0
P-OPC 50 R-C25-0
P- WT 50 R-C25-0

80

A
pplied load (kN
)

70
60
50
40
30
20
10
0
0

2

4

6

8

10

12

14

Mids pane de fle ction (mm)

Figure 10: Load vs. deflection for slabs with different bonding Materials
90

Control 1
Control 2
P-QM 25 R-C25-0
P-QM 25 R-C25-1
P-QM 25 R-C25-2

Applied load (kN)

80
70
60
50
40
30
20
10
0
0

2

4

6

8

10

12

14

Midspane deflection (mm)

Figure 11: Load vs. deflection for slabs with positive loading, different CFRP amount and concrete
overlay thickness 25mm
90
Control 1
Control 2
P-QM 50 R-C25-0
P-QM 50 R-C25-1
P-QM 50 R-C25-2

80

A
pplied load (kN
)

70
60
50
40
30
20
10
0
0

2

4

6

8

10

12

14


Figure 12: Load vs. deflection for slabs with positive loading, different CFRP amount and concrete
66


90

Control 1

80

Control 2

Applied load (kN)

70

N-QM 25 R-C25-0

60

N-QM 25 R-C25-2

50
40
30
20
10
0
0

2

4

6

8

10

12

14

Midspane de flection (mm)

Figure 13: Load vs. deflection for slabs with negative loading, different CFRP amount and concrete

90

Control 1
Control 2
N-QM 50 R-C25-0
N-QM 50 R-C25-2

80

Applied load (kN)

70
60
50
40
30
20
10
0
0

2

4

6

8

10

12

14


Figure 14: Load vs. deflection for slabs with negative loading, different CFRP amount and concrete

6. CONCRETE STRAINS
The distribution of concrete strains at mid-span section of the tested slab specimens was
measured by using ten, twelve and fourteen Demec discs over the depth (100, 125 and 150mm)
respectively of each slab. The concrete strain distribution over the depth of all the tested slabs at
different load levels as shown in Figures 15 to 17.

67


Distance from soffit (mm)

150
Load 5 kN
Load 10 kN
Load 17.5 kN
Load 22.5 kN
Load 27.5 kN

125
100
75
50
25
0
-0.002

-0.001

0

0.001

0.002

0.003

0.004

0.005

Strain (mm/mm)

Figure 15: Concrete strain distribution for control slab 1


150
Load 5 kN
Load 10 kN

125

Load 15 kN
Load 20 kN
Load 30 KN

100
75
50
25
0
-0.002

-0.001

0

0.001

0.002

0.003

0.004

0.005

Strain (mm/mm)

Figure 16: Concrete strain distribution for slab P-QM 50 R-C25-0


150
Load 17.5 KN
Load 27.5 KN
Load 40 KN
Load 55 KN

125
100

Load 60 KN
75
50
25
0
-0.002

-0.001

0

0.001

0.002

0.003

0.004

0.005

Strain (mm/mm)

Figure 17: Concrete strain distribution for slab P-QM 50 R-C25-1
68


7. CONCLUSIONS AND RECOMMENDATIONS
Based on the results of this work, the following conclusions are obtained:
1. Increasing the thickness of concrete overlay that placed in compression zone (positive
bending) (25 or 50mm) caused an increase in the first cracking load about (33% to 100%) and
(31% to 88%) in ultimate load when compared with the control specimens.
2. Placing the concrete overlay with 50mm thickness at the tension zone (negative bending)
shows a small increase in ultimate load when compared with the of 25mm thickness, while a
considerable increase in first crack loading appear.
3. No considerable effect on the first cracking load and ultimate load when increasing the
compressive strength of concrete overlay, except improving the durability.
4. The bonding materials that used between fresh concrete overlay and bare slab do not affect
on the first crack loading, but there is a considerable increase in the ultimate load capacity.
The materials that give increasing in ultimate load arranged downward as follows: Quickmast
108, SBR and Ordinary Portland Cement.
5. For the cased study it was observed that the deflection values decrease by using the bonding
materials between the bare slab and the concrete overlay, these values are arranged upward as
follows: Quickmast 108, SBR and Ordinary Portland Cement.
6. The slab specimens strengthened by adding plain concrete overlay failed suddenly, exhibited
no ductility and also gave lower ultimate load capacity when compare with the corresponding
slabs strengthened with reinforced concrete overlay.
7. The slabs strengthened with suggested combined (concrete overlay plus CFRP sheets)
showed the best results which gave an increase in the first cracking load and ultimate load
167% and 164% respectively when compared with the corresponding control specimens.
8. Further studies focus on repairing of reinforced concrete one way slabs by adding concrete
overlay and/or CFRP can be investigated with different predamaged ratios.

8. REFERENCES
[1]

[2]
[3]
[4]

[5]
[6]
[7]
[8]
[9]

American Concrete Institute, ACI Committee 318, (2005), "Building Code Requirements for
Structural Concrete (ACI 318-05) and Commentary (ACI 318R-05)", American Concrete
Institute, Farmington Hills, MI.
ACI Committee 441 Report, (1997), "High Strength Concrete Columns State-of-the-Art",
ACI Structural Journal, Vol.94, No.3, pp. 323-335.
British standards Institution, (1989), "Method for Determination of Compressive Strength of
Concrete Cubes", B.S.1881:Part 116:, pp.3.
Ibrahim and Mohamed Sh.Mahmood, (2009), "Finite Element Modling of Reinforced
Concrete Beams with FRP Laminates", European Journal of Scientific Research ISSN 1450216X Vol. NO. 4, pp 526-541.
Iraqi Specification, No.5/1984, "Portland cement".
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Approach”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4,
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69


[10] Javaid Ahmad, Dr. Javed Ahmad Bhat and Umer Salam, “Behavior of Timber Beams
Provided with Flexural as Well as Shear Reinforcement in the Form of CFRP Strips”,
International Journal of Advanced Research in Engineering & Technology (IJARET),
Volume 4, Issue 6, 2013, pp. 153 - 165, ISSN Print: 0976-6480, ISSN Online: 0976-6499.
[11] Shaikh Zahoor Khalid and S.B. Shinde, “Seismic Response of FRP Strengthened RC Frame”,
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[12] Sika (2005), "Sikadur 30-Adhesive for Bonding Reinforcement", Technical Data Sheet,
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[13] Sika (2005), "Sikadur 330-Two Part Epoxy Impregnation Resin", Technical Data Sheet,
Edition 2, (web site: www.sika.co.id).
[14] Asst. Prof. Mr. Samir A. Al-Mashhadi, Asst. Prof. Dr. Ghalib M. Habeeb and Abbas Kadhim
Mushchil, “Control of Shrinkage Cracking in End Restrained Reinforced Concrete Walls”,
International Journal of Civil Engineering & Technology (IJCIET), Volume 5, Issue 1, 2013,
pp. 89 - 110, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
[15] Javaid Ahmad and Dr. Javed Ahmad Bhat, “Ductility of Timber Beams Strengthened using
CFRP Plates”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4,
Issue 5, 2013, pp. 42 - 54, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
[16] Sika (2005), "SikaWrap230C-Woven carbon fiber fabric for Structural Strengthening",
Technical Data Sheet, Edition 2, (web site: www.sika.co.id).
[17] Tan, K., Y., (2003),” Evaluation of Externally Bonded CFRP Systems for the Strengthening
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