International Journal of Civil Engineering and Technology (IJCIET)

Volume 8, Issue 9, September 2017, pp. 564–571, Article ID: IJCIET_08_09_064

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

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INITIATION TIME OF CORROSION IN

REINFORCED CONCRETE STRUCTURES
EXPOSED TO CHLORIDE IN MARINE
ENVIRONMENT
Dao Van Dinh
Dr., University of Transport and Communications, Hanoi, VietNam

ABSTRACT
Chloride-induced corrosion of steel in concrete structures exposed to marine
environment has been identified as one of the main causes of durability deterioration
and decreased service lives. The initiation period is a key element in predicting the
service life of reinforced concrete structures. This paper proposes a mathematical
model to predict the initial phrase of steel corrosion in reinforced concrete structures
in the marine environment.
Key words: Reinforced Concrete, Chloride, diffusion coefficient, Initiation time of
corrosion.
Cite this Article: Dao Van Dinh, Initiation Time of Corrosion in Reinforced Concrete
Structures Exposed to Chloride in Marine Environment. International Journal of Civil
Engineering and Technology, 8(9), 2017, pp. 564–571.
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1. INTRODUCTION
The service life of reinforced concrete structures due to Chloride-induced corrosion of steel is
the time from construction to corrosion of steel (due to chloride), which causes damage to the
structures.
A simple definition is of ACI Committee 365 is acceptable: Service life is the period of
time after installation (or in the case of concrete, placement) during which all the properties
exceed the minimum acceptable values when routinely maintained [6]. Theo AASHTO
LRFD-2014: Service life is the period of time that the bridge is expected to be in operation[7].
Service life (of buildings, structures or materials) is the time from when the building until
any limit state is not satisfied, it is possible to maintenance, replacement to extend service life
as shown in Figure 1.

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 Initiation Time of Corrosion in Reinforced Concrete Structures Exposed to Chloride in
Marine Environment

Figure 1 Definition service life and extend the service life of reinforced concrete structures exposed to
chloride

Most of the published service life models associated with corrosion of reinforcing steel in
concrete have followed a simplified model that was first introduced by Tuutti (1980) [5],
wherein the mechanism of corrosion is considered as a two-stage process as Eq 1.

t = t1 + t2
(1)
Where: t1 –Initiation period of corrosion;
t2 –Propagation period of corrosion;
The first stage is the necessary time so that chloride ions penetrate and concentrate on
reinforcement surface with “concentration threshold causing corrosion”, while the second
stage is started from the end of the first stage to the time the concrete cover layer is entirely
cracked due corrosion or the cross-section area of reinforcement is reduced to the disability of
bearing capacity of the structure.
This paper proposes prediction the corrosion initiation, which fact is some parameters will
change to the time.

2. PREDICTION OF CORROSION INITIATION

The penetration of chloride ions into the concrete which causes the corrosion of reinforcement
is described as follows: (1) Chloride ions in the surrounding environment build-up on the
concrete surface; (2) Chloride ions penetrate into concrete; (3) Chloride ion concentration
build-up on the surface of reinforcement; (4) When chloride ion concentration at the surface
of reinforcement reaches “ threshold concentration causing corrosion-Cth”, the corrosion
process begins occuring; (5) The corrosion products expand the concrete volume and cause
the tensile stress in concrete cover; (6) Concrete is weak in tension, therefore, the concrete
cracks either vertically or horizontally to form a delamination between reinforcing bars; (7)
Cracks cause delaminations or spalls, which leads to a degradation of the structure’s
appearance, function, and safety, and finally leads to the end of service life or requires repairs;
(8) The loss of steek as a result of corrosion reaches unsafe strength limit state

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 Dao Van Dinh

Prediction of corrosion initiation will be based on the diffusion of chloride ions. Beacause
there are the differences in concentrations, chloride ions from structural surface will diffuse
through the concrete into the reinforcement surface. This period ends when the concentration
of chloride ions in reinforced surface reaches a critical threshold concentration (Cth) breaking
the passive layer on the surface of steel, then, corrosion phase starts.
The prediction model corrosion initiation period will be based on the equation of Fick’s
second law.

One-Dimension Calculations (Walls and Slabs)

Fick’s second law of diffusion is given in equation 2:
C ( x, t )  2 C ( x, t )
=D (2)
t x 2

Where: C(x,t) = concentration of diffusing substance at depth x and time t;

t = time;
D = diffusion coefficient;
x = depth coordinate from the concrete surface into the concrete;
Case D is constant over time and Surface chloride content is constant, solve equation 2 we
have :
 x 
C ( x, t ) = C0 + ( Cs − C0 ) 1 − erf  (3)
 2 D.t 

Where: Cs Chloride ions concentration at concrete surface; C0 initial uniform chloride

concentration in the concrete.

Two-Dimension Calculations (Beams and Columns)

C ( x, y, t )   2C ( x, y, t )  2C ( x, y, t ) 
= D +  (4)
t  x 2 y 2 

When C(x,t) = Cth or C(x,y,t)= Cth, steel corrosion in concrete will be started.
After solving the differential equations 1 and 3, we have the initiation period of corrosion.
In fact, both D and Cs change over time, therefore, the above equations must be solved by the
numerical methods.

2.1. The Parameters of Model

The parameters of model were divided into three categories: structural parameters, material
parameters and environmental parameters:
• Clear concrete cover (L);
• Chloride ions diffusion coefficent (D);
• Chloride ions concentration at concrete surface (Cs);
• Critical threshold concentration (Cth);

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 Initiation Time of Corrosion in Reinforced Concrete Structures Exposed to Chloride in
Marine Environment

2.1.1. Chloride diffusion Coefficient (D)

Chloride diffusion coefficient D depends on the structure of grout used in concrete and other
elements such as concrete‘s composition, environmental temperature and humidity . In
concrete, cement hydration reaction process occurs for a long time and this hydration reaction
gradually fills the pore system. Consequently, chloride diffusion coefficient tends to decrease
by time. The equation 5 gives apparent diffusion coefficient Dapp.
w cr
Dapp = D28 . exp(−0,165SF ). f (t ). f (T ). f ( H ) + Dcr (5)
scr

D28 the chloride diffusion coefficient of concrete at the 28 days of age, SF- the level of
silica fume in the concrete; f(t),f(T),f(H) the impact factors of aged concrete, temperature,
relative humidity to chloride diffusion coefficient in concrete.
( −12,06 + 2,4 w / c )
D28 = 10 (m2 / s ) [4] (6)

(In case of experimental data, D28 will be taken according to experimental data)
m m
t   28 
f (t ) =  28   f (t = 25) =   [8] (7)
 t   365* 25 

m = 0, 2 + 0, 4( FA / 50 + SG / 70) [8] (8)

U  1 1 
f (T ) = exp   −  [3] (9)
 R  Tref T  

1
f (H ) = [3] (10)
  1 − H 4 
1 +   
  1 − H c  

Where: w/c- the water-cementitious materials ratio;t age of concrete (years); FA và SG

the level of fly ash or slag in the mixture; U activation energy of the diffusion process (
35.000 J/mol); R -gas constant (8,314472 JK−1mol−1 ); T absolute temperature (K); Tref
=273K; H relative humidity, Hc=75%; wcr - crack width (mm); scr- distance between the
cracks; Dcr- the chloride diffusion coefficient in the crack –Boulfiza proposed Dcr=5.10-10 m2/s
[2];

2.1.2. Surface Chloride Concentration

The concentration of chlorine on the concrete surface exposed to a marine environment
depends on the geographic location of the sea as well as the distance above the sea level. Life
365 divides into 4 zones as follows [1]: (1) Marine splash zone, (2) Marine spray zone; (3)
Within 800 m of the ocean; (4) Within 1.5 km of the ocean.

 Cs , max
 kt if t 

Cs ( t ) =  k
C C (11)
s , max if t 
s , max

 k

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 Dao Van Dinh

Table 1 Build-up Rates and maximum concentration of surface chloride

Region Build-up Rate Cs,max
(%/ year) (%/)
Intertidal zone instantaneous 0.8
Marine spray zone 0.10 1.0
Within 800 m of the ocean 0.04 0.6
Within 1500 m of the ocean 0.02 0.6

2.1.3. Chloride Threshold Concentration (Cth)

Based on the results of ACI Committee 365[1], the threshold concentration as follows: for the
reinforced concrete often Cth = 0:05% by weight of concrete; for the prestressed concrete Cth
= 0.012% by weight of concrete.
Cth adjusted additives such as corrosion inhibitors solution of Ca(NO2)2 or depending on
the type of steel.

2.2. Algorithm Diagram of Model

Figure 2 Programming algorithm for prediction of Initiation period of corrosion

2.3. Investigation of the Influence of Parameters

2.3.1. Effect of the Concrete Cover
Thickness of concrete cover is an important parameter affecting the initiation period of
corrosion. Figure 3 shows the impact survey of the thickness of concrete cover to the
Initiation period of corrosion. (Examples with some parameters does not change: w/c=0.35;
T=20oC; H=80%; Cs=0.6%, Build-up Rate 0.04% year; C0=0%)

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 Initiation Time of Corrosion in Reinforced Concrete Structures Exposed to Chloride in
Marine Environment

Figure 3 The relationship between concrete cover and corrosion initiation stage

2.3.2. Effect of the Concrete Material

Figure 4 shows the impact survey of the ratio of water/cement (w/c) to the Initiation period of
corrosion. (Examples with some parameters does not change: thickness of concrete cover is
50mm; T=20oC; H=80%; Cs=0.6%, Build-up Rate 0.04% year)

Figure 4 The relationship between ratio w/c and corrosion initiation stage

Figure 5 shows the impact survey of the percentage of Silica Fume to the Initiation period
of corrosion. (Examples with the parameters does not change: thickness of concrete cover is
50mm; w/c=0.30; T=20oC; H=80%; Cs=0.6%, Build-up Rate 0.04% year)

Figure 5 The relationship between percentage of Silica Fume and corrosion initiation stage

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 Dao Van Dinh

Figure 6 shows the impact survey of content of CNI to the Initiation period of corrosion.
(Examples with some parameters does not change: thickness of concrete cover is 50mm;
w/c=0.30; T=20oC; H=80%; Cs=0.6%, Build-up Rate 0.04% year)

Figure 6 The relationship between content of CNI and corrosion initiation stage

3. CONCLUSIONS
The thickness of concrete cover strongly influences the initiation period of corrosion
;however, this layer mustn’t be too thick because it might affect to structural performance and
economic aspects of the construction. (the preferred thickness is about 30 to 100 mm)
The low ratio between water and cement not only reduces the diffusion coefficient of
chlorine ion but also reduces the creep and shrinkage. Despite the benefits of keeping this
ratio low, it is necessary to add some additives to this mixture in order to increase the
plasticity in concrete mixing process.
Besides choosing the appropriate thickness of the concrete’s protection cover and the right
ratio between water and cement, silica fume and corrosion inhibitors (CNI) should be
considered to be added to the mixture in order to increase time of initial phase of corrosion.

REFERENCES
[1] ACI Committe 365 (2014), Life-365- Service Life Prediction Model- and Computer
Program for Predicting the Service Life and Life-Cycle Cost of Reinforced Concrete
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[2] M. Boulfiza, K. Sakai và N. & Yoshida Banthia, H. ( 2003), "Predic-tion of chlrode ions
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[3] A. Saetta, Scotta, R., and Vitaliani, R. (1993), "Analysis of chloride diffusion into
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[5] K. Tuutti (1980), Service life of structures with regard to corrosion of embedded steel,
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[7] AASHTO (2014), AASHTO LRFD Bridge Design specifications, chủ biên, American
Association of State Highway and Transportation Officials.

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 Initiation Time of Corrosion in Reinforced Concrete Structures Exposed to Chloride in
Marine Environment

[8] P.B. Bamforth (1999), "The derivation of input data for modelling chloride ingress from
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