DETERMINATION OF THE APPROPRIATE CONTENT OF CALCIUM NITRITE AS A CORROSION INHIBITOR IN REINFORCED CONCRETE docx

LOGO
“DETERMINATION OF THE
APPROPRIATE CONTENT OF CALCIUM
NITRITE AS A CORROSION INHIBITOR IN
REINFORCED CONCRETE”
“DETERMINATION OF THE
APPROPRIATE CONTENT OF CALCIUM
NITRITE AS A CORROSION INHIBITOR IN
REINFORCED CONCRETE”
Dr. Le Quang Hung
State bureau for Construction quality inspection, Viet Nam
Dr. Nguyen Nam Thang
Institute for Building Science and Technology, Viet Nam
Contents
GENERAL
1
RESEARCH RESULTS
3
CONCLUSION
4
MATERIALS AND
RESEARCH METHODOLOGY
2
General
Overview of reinforced concrete corrosion
under the effect of chloride ion
The reaction of corrosive process occurs as below:
Anode: Fe  Fe
2+
+ 2e
Cathode: O

2
+ 2H
2
O + 4e 2 4 OH
-
The reinforced concrete structure is corroded very
fast under the effect of chloride ion in marine
environment
The strongly agressivity rate of chloride ion is the
main reason causing corrosion, especially in the
tropical climate of Vietnam.
Han River port
Vung Tau port
Anode
Cathode
Cl
-
Concrete
Steel
Cua Cam port
General
Principial protection methods:
Calcium nitrite (CN) is used as the most effective
inhibitors in preventing reinforced concrete from
corrosion.
 Primary protection: Compressive strength, water tightness,
width of crack, thickness cover of concrete - protecting layer.
Secondary protection:
Coating surface of structure: Painting
Electrochemistry: Cathodic protection

Corrosion inhibitors: NO
2
-
containing derivatives such as
calcium nitrite, sodium nitrite are often used.
General
The inhibition mechanism of CN
A. Oxidation of FeO to form Fe
2
O
3
B. The adsorption on steel surface to tighten passive membrane
C. Covering around FeO defected sites
D. NO
2
-
ion can cover in new particle Fe
2+
fast
General
Question:
Which is the most appropriate ratio
[Cl
-
]/[NO
2
-
] ?
Cement
River sand

Crush stone
Admixture
Corrosion
inhibitor
Materials
Material and research methodology
Hoang Thanh PCB 30
Nghi Son PCB 40
Sikament R4
Module Mn = 2,5
(Lo river)
Dmax = 20mm
(Kien Khe field
)
30% of solid calcium
nitrite solution
Material and research methodology
1.Extract of
cement water
Testing samples
2. Reinforced
concrete
samples
1. Extract of cement
water
Reference extract of
cement water (H
0
)
Extract of Cement

water with Cl
-
Extract of Cement
water with CN and
Cl
-
Material and research methodology
Extract of cement water
•water/cement = 0,6
• Cl
-
: 1,2kg; 2,4kg vµ 6kg
• [Cl]/ [NO
2
-
] = 1,6 - 2,6
Material and research methodology
2. Reinfored concrete
 Samples with CN and Cl
-
inside concrete grade 20, 30
and 50
Testing environment: wet
and dry cycles,
measurement of corrosion
rates at the time of: 0, 3, 6, 9,
12, 18 and 24 months.
Steel reinforcement: 10 diameter
Concrete grade M20, M30, M50,
Protection thickness layer: 3,5cm

Cl
-
: 1,2kg; 2,4kg và 6kg/m
3
[Cl] / [NO
2
-
] = 1,6-2,6
Wet and dry cycle:
- 3 days in water
- 4 days for drying.
Research results
0
0.01
0.02
0.03
0.04
0.05
0.06
0 3 6 9 12
Time (months)
Corrosion rate (mm/year)
H0: CW H1: CW+1,2kg ion Cl
H8: CW+2,4kg ion Cl H15: CW+ 6,0kg ion Cl
Figure 1. Steel corrosion rate in extracte of
cement water containing Cl
-
1. Case of extract of cement water
Image 1: Steel sample in cement water extract
containing Cl

-
H
0
H
1
H
8
H
15
0
0.01
0.02
0.03
0.04
0.05
0.06
0 3 6 9 12
Time (months)
Corrosion rate (mm/year)
H1:CW+1,2kg ion Cl
H2:CW+[Cl/NO2=2,6]
H3:CW+[Cl/NO2=2,4]
H4:CW+[Cl/NO2=2,2]
H5:CW+[Cl/NO2=2,0]
H6:CW+[Cl/NO2=1,8]
H7:CW+[Cl/NO2=1,6]
Figure 2. Corrosion inhibition ability of CN in
extract of cement water (1,2kg Cl
-
)

Research results
H
1
H
2
H
3
H
4
H
5
H
6
H
7
Image 2: Steel sample in extract of cement
water containing CN and 1,2kg Cl
-
)
Research results
0
0.01
0.02
0.03
0.04
0.05
0.06
0 3 6 9 12
Time (months)
Corrosion Rate (mm/year)

H8: CW+2,4kg ion Cl
H9: CW+[Cl/NO2=2,6]
H10: CW+[Cl/NO2=2,4]
H11: CW+[Cl/NO2=2,2]
H12:CW+[Cl/NO2=2,0]
H13:CW+[Cl/NO2=1,8]
H14:CW+[Cl/NO2=1,6]
Figure 3. Corrosion inhibition ability of CN in
extract of cement water (2,4kg Cl
-
)
H
8
H
9
H
10
H
11
H
12
H
13
H
14
Image 3. Steel sample in extract of
cement water containing (CN and 2,4 kg
Cl
-
)

Research results
0
0.01
0.02
0.03
0.04
0.05
0.06
0 3 6 9 12
Time (months)
Corrosion rate (mm/ year)
H15: CW+6,0kg ion Cl
H16:CW+[Cl/NO2=2,6]
H17:CW+[Cl/NO2=2,4]
H18:CW+[Cl/NO2=2,2]
H19:CW+[Cl/NO2=2,0]
H20:CW+[Cl/NO2=1,8]
H21:CW+[Cl/NO2=1,6]
Figure 4. Corrosion inhibition ability of CN in cement
water extract of (6 kg Cl
-
)
H
1
5
H
1
6
H
1

7
H
1
8
H
19
H
2
0
H
2
1
Image 4: Steel sample in cement water extract
containing (CN and 6,0 kg Cl
-
)
Effectiveness of corrosion inhibition in
extract of cement water containing Cl
-
:
• In H
0
extract, steel is maintained in passive state
and not corroded
• The extract containing Cl
-
: corrosion rate is
continuously increased with the time and with Cl
-
ratios.

• At [Cl
-
]/[NO
2
-
]  2,2; corrosion rate was very
small
Research results
Research results
2. Case of reinforced concrete
B
01
B
1
B
8
B
15
Image 5: Reinforcement in concrete grade
M20containing different contents of Cl-
Figure 5. Steel corrosion rate in concrete grade
M20 containing different contents of Cl-
0
0.01
0.02
0.03
0.04
0 3 6 9 12 15 18 21 24
Time (months)
Corrosion rate (mm/ year)

B01: Reference sample M20
B1: 1,2kg Cl
B8: 2,4kg ion Cl
B15: 6,0kg ion Cl
0
0.01
0.02
0.03
0.04
0 3 6 9 12 15 18 21 24
Time (months)
Corrosion rate (mm/year)
B02: M30
B22: 1,2kg Cl
B29: 2,4kg ion Cl
B36: 6,0kg ion Cl
Figure 6. Steel corrosion rate in concrete grade
M30 containing different contents of Cl-
Research results
B
0-2
B
22
B
29
B
36
Image 6: Reinforcement in concrete grade
M30 containing different contents of Cl-
0

0.01
0.02
0.03
0.04
0 3 6 9 12 15 18 21 24
Time (months)
Corrosion rate (mm/year)
B03
:
M50
B61: 1,2kg Cl
B68: 2,4kg ion Cl
B75: 6,0kg ion Cl
Figure 7. Steel corrosion rate in concrete grade
M50 containing different contents of Cl-
Research results
B
0-3
B
61
B
68
B
75
Image 7: Reinforcement in concrete grade
M50 containing different contents of Cl-
Research results
0
0.01
0.02

0.03
0.04
0 3 6 9 12 15 18 21 24
Time (months)
Corrosion rate (mm/year)
B1: 1,2kg Cl
B2: [Cl/NO2=2,6]
B3: [Cl/NO2=2,4]
B4: [Cl/NO2=2,2]
B5: [Cl/NO2=2,0]
B6: [Cl/NO2=1,8]
B7: [Cl/NO2=1,6]
Figure 8. Steel corrosion rate in concrete grade
M30 containing of Cl and CN
B
1
B
2
B
3
B
4
B
5
B
6
B
7
Image 8: Reinforcement in concrete grade
M30 containing Cl- and CN

0
0.01
0.02
0.03
0.04
0 3 6 9 12 15 18 21 24
Time (months)
Corrosion rate (mm/year)
B8: 2,4kg Cl
B9: [Cl/NO2=2,6]
B10: [Cl/NO2=2,4]
B11: [Cl/NO2=2,2]
B12: [Cl/NO2=2,0]
B13: [Cl/NO2=1,8]
B14: [Cl/NO2=1,6]
Figure 9. Corrosion inhibition ability of CN in
concrete grade M20 containing 2,4 kg Cl-/ m3
Research results
B
8
B
9
B
10
B
11
B
12
B
13

B
14
Image 9: Reinforcement in concrete grade
M20 containing CN and 2,4 kg ion Cl-
Research results
0
0.01
0.02
0.03
0.04
0 3 6 9 12 15 18 21 24
Time (months)
Corrosion rate (mm/ year)
B15: 6,0kg Cl
B16: [Cl/NO2=2,6]
B17: [Cl/NO2=2,4]
B18: [Cl/NO2=2,2]
B19: [Cl/NO2=2,0]
B20: [Cl/NO2=1,8]
B21: [Cl/NO2=1,6]
Figure 10. Corrosion inhibition ability of CN in
concrete grade M20 containing 6 kg Cl-/ m3
B
15
B
16
B
17
B
18

Image 10: Reinforcement in concrete grade M20
containing CN and 6,0kg ion Cl
-
0
0.01
0.02
0.03
0.04
0 3 6 9
12
15 18
21 24
Time (months)
Corrosion rate (mm/year)
B22: 1,2kg Cl
B23: [Cl/NO2=2,6]
B24: [Cl/NO2=2,4]
B25: [Cl/NO2=2,2]
B26: [Cl/NO2=2,0]
B27: [Cl/NO2=1,8]
B28: [Cl/NO2=1,6]
Figure 11. Corrosion inhibition ability of CN in
concrete grade M30 containing 1,2 kg Cl-/ m3
B
22
B
23
B
24
B

25
B
26
B
27
B
28
Image 11: Reinforcement in concrete grade
M30 containing CN and 1,2kg ion Cl
-
/m
3
Research results
Research results
0
0.01
0.02
0.03
0.04
0 3 6 9 12 15 18 21 24
Time (months)
Corr
osio
n
rate
(mm
/yea
r)
B29: 2,4kg Cl
B30: [Cl/NO2=2,6]

B31: [Cl/NO2=2,4]
B32: [Cl/NO2=2,2]
B33: [Cl/NO2=2,0]
B34: [Cl/NO2=1,8]
B35: [Cl/NO2=1,6]
Figure 12. Corrosion inhibition ability of CN in
concrete grade M30 containing 2,4 kg Cl-/ m3
0
0.01
0.02
0.03
0.04
0 3 6 9 12 15 18 21 24
Time (months)
Corrosion rate (mm/year)
B61: 1,2kg Cl
B62: [Cl/NO2=2,6]
B63: [Cl/NO2=2,4]
B64: [Cl/NO2=2,2]
B65: [Cl/NO2=2,0]
B66: [Cl/NO2=1,8]
B67: [Cl/NO2=1,6]
Figure 13. Corrosion inhibition ability of CN in
concrete grade M50 containing 1,2 kg Cl-/ m3
Research results
Effectiveness of corrosion inhibitor in concrete
containing Cl
-
:
Reinforcement corrosion for concrete containing Cl

-
: Cl
-
will penetrate and destroy the passive membrane, this
process happens quite slow after a certain period until
corrosion appeared.
 In the samples with same concrete grade, the steel
corrosion is increasing by the time and by Cl
-
content;
 Higher concrete grade, lower corrosion
Effective content of CN is defined as [Cl
-
]/[NO
2
-
] @ 2.
Conclusion
1. CN is an effective inhibitor to enable
minimizing steel corrosion in concrete
2. Determine the appropriate content of calcium nitrite as
1
Extract of Cement water :
-W/C = 0,6; pH = 12,2
-[Cl
-
]: 1,2kg; 2,4kg and 6kg /m
3
[Cl
-

]/ [NO
2
-
] D 2,2
2
Concrete grade M20, M30,M50:
-Thickness of protective layer: 3,5cm
-[Cl
-
]: 1,2kg; 2,4kg and 6kg /m
3
[Cl
-
]/ [NO
2
-
] D 2,0