Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016

29

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures

 

 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

CONDITION ASSESSMENT OF REINFORCED CONCRETE 

ELEMENTS EXPOSED TO CARBONATION 

 

Samindi Samarakoon

 (1)

, Jan Sælensminde 

(2)

, Cecilie Myklebust Helle 

(1)

  

 

(1) University of Stavanger, Stavanger, Norway 

(2)

 

Betec AS, Bergen, Norway 

 

 

 

 

 

 

Abstract 

Onshore reinforced concrete structures are vulnerable to deterioration due to carbonation. 

Condition assessment is a vital task, which helps to determine the reliability of structural 

elements over the remaining service life. This study assesses the condition of reinforced 

concrete structural elements (i.e. consoles) which are 53 years into their service life. The 

reinforced concrete consoles, exhibiting no visible signs of corrosion, were chosen to measure 

carbonation depths. In addition, non-destructive testing method: half-cell potential 

measurements were taken over the surfaces of the consoles. A full-probabilistic service life 

prediction model was used to calculate the expected service life, and a comparison was made 

based on the actual carbonation depth measurements. 

 

 

1.

 

Introduction 

 

Condition assessment of the existing reinforced concrete structures is an important task in the 

planning of maintenance and modification activities. Reinforcement corrosion can be 

considered as one of the potential mechanisms which affect the durability of reinforced 

concrete structures. There are many reasons for the corrosion of steel reinforcement, with 

carbonation and chloride-induced corrosion being dominant mechanisms among them. 

Therefore, it is important to choose the dominant phenomenon based on the exposure 

condition of the structure. Hence, in this study, the diffusion of CO

2

 is considered as the 

dominant transport mechanism for the corrosion in steel reinforcement of residential 

buildings. 

 

Deterministic and probabilistic models have been developed for service life design, to predict 

the time to initiate corrosion and the time to propagate corrosion. However, the probability 

based models can help to make more realistic decisions than deterministic models. Therefore, 

in this study, the full probability based model given in fib_bulletin_34 [1] is used to calculate 

---

30

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures

 

 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

the probability of corrosion initiation. In addition, there are various proactive and reactive 

approaches developed for controlling the condition of reinforced concrete structures, such as 

measuring carbonation depths, using non-destructive testing methods (i.e. Half-Cell Potential 

(HCP) measurements), visual inspection, etc.  In this, study, potential mapping has been 

carried out over the surface of three consoles, and carbonation depths were measured at 

selected locations. Moreover, this manuscript discusses a case study of three reinforced 

concrete consoles in a residential building. In addition, it determines the probability of 

corrosion initiation using the DuraCrete [2, 3] model and compares it with HCP data. 

Moreover, the measured carbonation depths are compared with calculated average 

carbonation depths. 

  

 

2.

 

 Modelling of reinforcement corrosion due to carbonation 

 

Carbonation is a chemical process, in which the carbon dioxide in air diffuses into the 

concrete, dissolves in the pore solution, and reacts with calcium hydroxide, forming insoluble 

calcium carbonate and water. This results in a reduced pH-value of the concrete, which is one 

reason for initiating the corrosion of steel reinforcement. The level of damage due to the 

corrosion of embedded steel in a concrete structure over time can be described using Tuutti’s 

model [4]. Essentially, the model categorizes the service life of a structure into the corrosion 

initiation period and the corrosion propagation period. This manuscript focuses on the 

corrosion initiation phase. 

 

Many researchers have used Fick’s second law to model the carbonation to the un-cracked 

concrete, considering diffusion as the dominant transport mechanism. In this paper, the 

DuraCrete [2, 3] model, derived using Fick’s second law, is adopted to include environmental 

and material parameters, as given in Eq. (1). 

 

*w(t)                                 

(1) 

X

c 

(t): carbonation depth (mm) 

k

e

:

 

environmental function (-) 

k

c

: execution parameter (-) 

k

t

: regression parameter (-) 

R

ACC, 0

-1

: inverse effective carbonation resistance ((mm

2

/year)/(kg/m

3

)) 

t

: error term ((mm

2

/year)/(kg/m

3

)) 

C

s

: CO

2

 concentration of the ambient environment (kg/m

3

) 

w(t): weather function (-), where w(t)=(t

0

/t)

w

, where t

0

: time of reference (years), w: weather 

exponent (-) 

t: time (years) 

 

Time to initiate corrosion (T

i

), when X

c

(t)= X

cover 

(concrete cover) is given in Eq. (2). 

---