REHABILITATION OF NORMAL AND REACTIVE POWDER REINFORCED CONCRETE BEAMS USING EPOXY INJECTION TECHNIQUE

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 7, Issue 3, May–June 2016, pp. 31–42, Article ID: IJCIET_07_03_004

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

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REHABILITATION OF NORMAL AND

REACTIVE POWDER REINFORCED

CONCRETE BEAMS USING EPOXY

INJECTION TECHNIQUE

Assistant Professor Aamer Najim Abbas

Al-Mustansiriya University, Iraq

Assistant Professor Ali Sabah Ahmed


Assistant Professor Saad Khalaf Mohaisen


ABSTRACT

The present study outlines behavior of normal and reactive powder

concrete beams repaired with epoxy resin. Such type of epoxy technique made

for cracks width less than (0.05) mm. For this purpose, four reinforced

concrete beams were casted and tested to maintain failure and deformations.

Two amounts of tensile reinforcement ratios and concrete types were used in

this study. The load-deflection behavior, ultimate capacity, mode of failure,

stiffness and toughness were studied.

Cite this Article: Aamer Najim Abbas, Ali Sabah Ahmed and Saad Khalaf

Mohaisen, Rehabilitation of Normal and Reactive Powder Reinforced

Concrete Beams Using Epoxy Injection Technique, International Journal of

Civil Engineering and Technology, 7(3), 2016, pp. 31–42.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=3

INTRODUCTION

Rehabilitation is considered one of the important branches of structural engineering

because of its great importance in extending the life of the damaged buildings as a

result of age, bad use of the building, an explosion in the building (or nearby

buildings) or as a result of accidental incidents.

The main goal of rehabilitation is to restore the strength of concrete member

before rehabilitation, the rehabilitation process is useful if the above targets are

achieved.

Methods of rehabilitation vary according to the type of damage done on the

structure(1)(2)

, since there are some cases required removing of structural member and

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType

Aamer Najim Abbas, Ali Sabah Ahmed and Saad Khalaf Mohaisen


replace it with a new one(3)

, or is sufficient to remove the damaged part of concrete

member and grouting with a new special concrete(4)

. In other cases, the damaged

structural member needs to repair by gluing steel strip or carbon fiber sheets (5)(6)(7)(8)

.

When the damage of concrete member is in the form of cracks not exceeding

(0.05)mm in width, it is restoring to the injection method of epoxy to connect the two

sides of cracked concrete.

There are many researchers studied the injection technique method as one of most

important type of rehabilitation. M. Kunieda et.al(9)

studied the behavior of repaired

concrete beams by using epoxy injection technique, they concluded that the flexural

strength and fracture energy of repaired specimens were more than those of the

original specimens.

The performance of epoxy for cracks injection in concrete has been studied by

Anwar shah et.al(10)

, three beams each having (4600x300x225) mm3 as a dimensions

of (length x depth x width) respectively were examined, they found that the

performance of epoxy for cracks injection was effective in restoring the strength of

beams.

V. Bhikshma et.al(11)

used three different types of epoxy resin for repairing the

reinforced concrete beams. Six standard size beams (1500x230x150) mm3 as a

dimensions of (length x depth x width) respectively for M50 grade of concrete were

distress in flexure by applying two points load by taking (90%) of the ultimate load,

then these distressed beams were repaired and reloaded up to the failure. The flexural

strength increased significantly up to about (15%) and deflection were smaller in

reinforced concrete beams repaired with epoxy resin in compare with the reference

specimen.

EXPERIMENTAL PROGRAM

Beams Geometry

All beams were geometrically similar, having dimensions (1200x250x180) mm3 as a

dimensions of (length x depth x width) respectively and loaded through two points

load, the distance between the two points load is (350 mm). The beams are simply

supported and the distance from c/c of` supports was (1050 mm).

Beams Reinforcement

Two different longitudinal bottom reinforcement ratios were used (2ɸ16 and 3ɸ16),

the longitudinal top bars and shear reinforcement are kept constant (2ɸ12) and

(ɸ10@100mm) respectively. The tensile strength of deformed bars are (422MPa) and

(385 MPa) for longitudinal and shear reinforcement respectively tested according to

ASTM A615(12)

.

Compressive Strength

Cubical (150x150x150) mm3 specimens were used to test the compressive strength of

concrete. The compressive test was done according to ASTM C39(13)

and B.S 1881(14)

by using a computerized compression machine. The Table (1) below show the

compressive strength values of each specimen.

Rehabilitation of Normal and Reactive Powder Reinforced Concrete Beams Using Epoxy

Injection Technique


Table 1 Characteristics of the Tested Beams

Specimens Type of Concrete Flexural

Reinforcement

Shear

Reinforcement

Compressive

Strength (MPa)

B1 Normal concrete 2Ø12 top

2 Ø16 bottom

Ø10@100mm

29

B2 Normal concrete 2Ø12 top

3 Ø16 bottom

Ø10@100mm 29.7

B3 Reactive powder

concrete

2Ø12 top

2 Ø16 bottom

Ø10@100mm 93

B4 Reactive powder

concrete

2Ø12 top

3 Ø16 bottom

Ø10@100mm 90

Mix Proportions

Table (2) shows the mix proportions were used in tested beams.

Table 2 Mix Proportions

Nominal

Concrete

Strength

(MPa)

Cement

(Kg/m3)

Sand Kg/m3

Passing Through

600Microne Sieve

Gravel Kg/m3

Passing

Through

4.75mm Sieve

Size

w/c

Ratio

SP

Ltr/m3

Silica

Fume

(Kg/m3)

30 415 535 1250 0.44 - -

92 800 900 1000 0.30 7 72

Technical Properties of Epoxy

Table (3) below contains the technical properties of epoxy resin (quick mast 105) , it

is the product of Ayla company.

Table 3 Technical Properties of Epoxy Resin

No. Property Result

1 Compressive strength >72 N/mm2 w days w2 c

2 Flexural strength >60 N/mm2 w2 c

3 Tensile strength >25 N/mm2

4 Pot Life 60 minutes w2 c

5 Specific Gravity 1.1

6 Viscosity 10poise w2 c

7 Min. application Temperature c



INJECTION PROCEDURES

The following procedures were followed after primary test:

Cleaning the surface of beams from dust and removing the sharp edges.

Mixing a small quantity of epoxy adhesive (quick mast 341), then applied in (2-3)

mm thick layer to the back and sides of each nipples flange.

Placing each nipple centrally over the drilled hole using a locating rod, the spacing

between nipples enough to fill the crack. This will allow the injected resin to spread

from the injection point and will therefore leak from adjacent nipples, at the same

time as it reaches the base of the cracks.

Sealing the surface of the crack between the nipples with (quick mast 341), (20-30)

mm wide, (2-3) mm thick.

In case the crack extends on both sides, nipples should be fixed to the other face of

concrete member.

Mixing the Two components of the (quick mast 105) until uniform color is achieved.

Pouring the mix resin in to the injection equipment (pressure 4 bars) and start with the

lowest point. The injections continue until mixed resin appears and leaks out the

nipple above.

EXPERIMENTAL RESULTS AND DISCUSSIONS

Load Deflection Behavior

According to the Figures (1, 2, 3 and 4), there are three main stages along the load –

deflection curve. These stages are:

First linear stage: starts at the beginning of loading application until the appearance

of first crack, at this stage the specimens return to the original manner if the load has

been removed.

Second linear stage: starts beyond first crack until yielding of flexural reinforcement,

the specimens cannot return the original manner when removing the load because the

elongation of steel bar and lack of bonding between the elongated bar with concrete.

Third non-linear stage: starts at the yielding of steel bar till failure.

Through an extensive observation, the increasing of deflection with load application is

less in the early stages of loading than in the advanced stages. Also, it observed that

the increments of deflection of reactive powder concrete beams is more than the

normal concrete one (original and repaired beams), this leads to that the normal

concrete beams have a ductility more than the reactive powder concrete beams.


Injection Technique


Figure 1 Load-deflection Curve of Original and Repaired Beam (B1)


0

20

40

60

80

100

120

140

160

180

200

0 1 2 3 4

Loa

d (

kN)

Deflection (mm)

B1 Repaired

B1 Original

0

50

100

150

200

250

0 0.5 1 1.5 2 2.5 3

Loa

d (

kN)

Deflection (mm)

B2 Repaired

B2 Original





ULTIMATE AND CRACKING CAPACITY

The ultimate and cracking loads of tested beams are shown in Table (4). The strength

ratio (ratio of the ultimate strength of original specimens to that of the repaired

specimens) is also shown in the same table.

In case of normal strength concrete beams, the ultimate strength of repaired

specimens is more than the original one by about (1.3 and 3.8)% in beams (B1) and

(B2) respectively, unlike the reactive powder concrete beams where the ultimate

strength of repaired beams is less than the original beams by about (1.4 and 1.2)% in

0

50

100

150

200

250

300

350

400

0 1 2 3 4

Loa

d (

kN)

Deflection (mm)

B3 Repaired

B3 Origional

0

50

100

150

200

250

300

350

400

450

0 1 2 3 4 5 6

Loa

d (

kN)

Deflection (mm)

B4 Repaired

B4 Origional


Injection Technique


beams (B3) and (B4) respectively, this difference belong to the difference between the

compressive strength of concrete and the epoxy resin, where the compressive strength

of reactive powder concrete more than the epoxy resin one, so using these materials

does not contribute to some extent to restore the original beam capacity.

Table (4) also shows that the strength ratio of normal concrete beams is more than

the strength ratio of reactive powder concrete beams.

Through the studying the behavior of beams during load application, it is clear

that the first cracking load of original specimens less than the first cracking load of

repaired specimens by about (8.5, 12, 3.5 and 3.8) % of beams (B1, B2, B3 and B4)

respectively, this is due to a good tensile strength of the epoxy resin which used in

injection.

Table 4 Load Characteristics of Tested Beams

Sample

No.

First

cracking

load

Ultimate

load

% of

improvement

in F.C load

% of improvement

in U.L

Strength

ratio

60 182.5 8.5% 1.3% 0.98

65 185

75 210 12% 3.8% 0.96

84 218

127.5 365 3.5% -1.4% 1.02

132 355

180 390 3.8% -1.2% 1.01

187 385

B1', B2', B3' and B4' refer to the repaired beams.

FAILURE MODE

The Figures (5 to 12) show that all the tested specimens (original and repaired) failed

in shear. First cracking occurs at mid-span where the applied moment exceeds the

cracking moment (Mcr) causing reduction in stiffness. Then, the diagonal cracks start

to improve near support towards the top surface of specimen with an angle between

(30-40)o. In general, the ductility of original beams is more than the ductility of

repaired beams.

Figure 5 Failure Pattern of Beam (B1)



Figure 6 Failure Pattern of Beam (B1')


]



Injection Technique








STIFFNESS

Stiffness values can be defined as the slope of the line that connects maximum load

carrying capacity point to the origin of load-deflection curve.

In general, there is a decrease in stiffness values after rehabilitation process, see

Table (5). The values of reduction in stiffness is (3.1, 1, 7.75 and 3.1)% in beams

(B1', B2', B3' and B4') in comparison with original beams (B1, B2, B3 and B4)

respectively. The reason of this reduction is due to the decrease of stiffness as a

results of cracks or yielding of reinforcement bars before repairing then weakness of

bond between steel bars and concrete.

Table 5 Stiffness Values of Tested Beams

Sample

No. B1 B1' B2 B2' B3 B3' B4 B4'

Stiffness

Values 67.84 65.74 117.69 116.57 80.1 73.89 88.67 85.98

Differences

(%) 3.1 1 7.75 3.1

ENERGY ABSORPTION

The toughness (energy absorption) of a material is defined as the capacity of a

material to absorb energy in the plastic domain up to rupture (15)

. The method of

determining the toughness from the area under load–deflection curves. This area gives

an insight of the amount of energy absorption that the member can support up to

failure.

In order to analyze the influence of the rehabilitation on the specimens toughness,

the area under load-deflection curves were calculated numerically. Table (6) shows

the experimental results from the load-deflection curves as well as the determined

toughness coefficients values.


Injection Technique


In general, the observed values can be justified by the following mechanism: for a

particular steel-bar reinforcement percentage and compressive strength the depth of

the neutral axis decreases for reactive powder concrete repaired beams, this behavior

give rise to an increase of the deflection of beams because the decreasing of effective

moment of inertia of repaired specimens leading to increase the toughness of repaired

specimens. Reversed behavior can be observed in case of normal concrete groups, the

decreasing of effective moment of inertia less than the decreasing in reactive powder

concrete beams, and then decreasing the toughness of repaired specimens.

Table 5 Toughness Coefficients Values of Tested Beams

Specimen No. B1 B1' B2 B2' B3 B3' B4 B4'

Toughness

(Energy Absorption)

Coefficient

kN.mm 327.4 316.4 850.9 616.2 1306.4 1442.3 264.5 315.5

CONCLUSIONS

The following conclusions can be drawn from the test results and discussions:

The epoxy injection technique restored the original strength.

Using epoxy injection method delayed the appearance of first crack.

All tested specimens (original and repaired) have the same failure pattern.

There is a reduction in stiffness of tested specimens after repairing with epoxy resin.

The energy absorption of reactive powder concrete specimens increased when using

the epoxy resin as a repairing method. Unlike the normal strength concrete

specimens, the value of energy absorption was decreased as a result of repairing

work.

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