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

Overview of reinforced concrete corrosion under the effect of chloride ion The reaction of corrosive process occurs as below: Anode: Fe Fe2++ 2e Cathode: O2+ 2H2O + 4e 2 4 OH -The reinfo

“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

Overview of reinforced concrete corrosion

under the effect of chloride ion

The reaction of corrosive process occurs as below: Anode: Fe Fe2++ 2e

Cathode: O2+ 2H2O + 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

Cl

-Concrete SteelCua 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: NO2 - containing derivatives such as calcium nitrite, sodium nitrite are often used.

The inhibition mechanism of CN

A Oxidation of FeO to form Fe2O3 B The adsorption on steel surface to tighten passive membrane

Question:

Which is the most appropriate ratio [Cl - ]/[NO 2 - ] ?

Material and research methodology

1 Extract of

cement water

Testing samples

2 Reinforced concrete

samples

-Material and research methodology

Extract of cement water

•water/cement = 0,6

• Cl-: 1,2kg; 2,4kg vµ 6kg

• [Cl]/ [NO2 -] = 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,

Cl-: 1,2kg; 2,4kg và 6kg/m3

[Cl] / [NO2-] = 1,6-2,6 Wet and dry cycle:

- 3 days in water

- 4 days for drying.

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 -

H0 H1 H8 H15

Figure 2 Corrosion inhibition ability of CN in

extract of cement water (1,2kg Cl - )

Research results

H1 H2 H3 H4 H5 H6 H7

Image 2: Steel sample in extract of cement water containing CN and 1,2kg Cl - )

Figure 3 Corrosion inhibition ability of CN in

extract of cement water (2,4kg Cl - )

H8 H9 H10 H11 H12 H13 H14

Image 3 Steel sample in extract of cement water containing (CN and 2,4 kg

Cl - )

Effectiveness of corrosion inhibition in extract of cement water containing Cl - :

and not corroded

-ratios.

small

Research results

2 Case of reinforced concrete

B01 B

Image 5: Reinforcement in concrete grade M20containing different contents of Cl-

Figure 5 Steel corrosion rate in concrete grade

M20 containing different contents of

Figure 6 Steel corrosion rate in concrete grade

M30 containing different contents of

Figure 7 Steel corrosion rate in concrete grade

M50 containing different contents of

Cl-Research results

B0-3 B61 B68 B75

Image 7: Reinforcement in concrete grade M50 containing different contents of Cl-

Figure 9 Corrosion inhibition ability of CN in

concrete grade M20 containing 2,4 kg Cl-/ m3

Figure 10 Corrosion inhibition ability of CN in

concrete grade M20 containing 6 kg Cl-/ m3

B15 B16 B17 B18

Image 10: Reinforcement in concrete grade M20 containing CN and 6,0kg ion Cl -

Figure 11 Corrosion inhibition ability of CN in

concrete grade M30 containing 1,2 kg Cl-/ m3

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

Research results

Effectiveness of corrosion inhibitor in concrete

-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

Higher concrete grade, lower corrosion