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

102

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 

 

 

Figure 8. Crack width evolution and J

corr

 (FS:front side ; TS:top side) 

As shown in [Figure 9-a], two groups of the position of the cracks near the steel surface are 

observed oriented close to 40° and 120° according to the graduated circle (see [Figure 5-a]). 

Two mains cracks seem to be displayed. Two sets of crack lengths could be identified, the 

first one is between 2 and 3cm and the second one is between 1 and 2cm in [Figure 9-b]. The 

lengths tend to fluctuate because of the distribution of the aggregates which influences the 

crack path. The graph in [Figure 9-c] corresponds to crack widths and shows the observed 

general trend. The crack widths are around 0.1 and 0.3mm.

 

The thickness of corrosion products is measured by Scanning Electron Microscopy and the 

perimeter represents the length of the shape of the rebar according to the corrosion volume. 

The minimum thickness of corrosion products varies from 50 to 57μm and the maximum 

thickness varies from 257 to 314μm (see Table 1). The highest thickness is located in the 

upper part of the steel rebar. This ‘expected’ difference could result from the distance between 

the counter electrode and the steel surface area. The closer they get, the more the corrosion is 

forced. The crack width located on the top side is wider than the one located on the front side 

because the penetration path of the chloride ions to reach the steel surface area is the shortest. 

Comparing the internal measurements ‘crack orientations’ and the widths measured on the 

sliced samples to the external observations (corrosion products spots on the front side of the 

samples), the surface observations do not reflect the internal corrosion state at the 

steel/concrete interface.  

                

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103

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 

 

 

 

Figure 9. Quantitative results of internal cracks– a) angular position, b) length and c) width 

Table 1 : Thickness of the corrosion products layers and corresponding visual distribution of 

evidences on the front side 

Slices 

Maximum thickness of the 

corrosion products layers 

(μm) 

Minimum thickness of the 

corrosion products layers 

(μm) 

Perimeter of the corrosion 

products layers Max/Min 

(μm) 

P-008-21d-T10  

257 

57 

2 617 / 5 233 

P-008-21d-T13 

314 

63 

5 233 / 5 233 

P-008-21d-T16 

257 

50 

5 233 / 10 467 

 

4.

 

Conclusions 

 

In this work, cracks due to the corrosion of the steel reinforcement in concrete specimens 

have been investigated using an accelerated corrosion test. This work exposes the finalized 

methodology associated with the experimental program. The following preliminary results 

can be drawn: 

 

There are three stages in the corrosion process: during the first stage, the increase of 

polarization resistance may be explained by the development of resistive iron oxides 

(passivation layer). The second stage could highlight the loss of the resistance of the 

set due to respectively the concrete cracking and the decohesion between the steel and 

concrete surface area. Regarding the third stage, the observed effect may be attributed 

to the fact that the properties of corrosion layers remain unchanged. Then, the value of 

the voltage at the end of the test certainly reflects the resistance of both cracked 

concrete cover and iron oxide layer. After 7 days, an active corrosion is not clearly 

(a) (b) 

(c) 

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104

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 

 

observed and this could be explained by the fact that chloride ions have not reached 

the steel/concrete interface.  

 

The crack orientation, length and width are coherent for the same specimen corroded 

for 21 days. This result has to be confirmed after achieving the measurements for the 

other specimens.  

 

The corrosion-product spots on the surface of the samples do not reflect the internal 

corrosion state at the steel/concrete interface of the specimen.  

Some of the experimental results such as the thickness and the display of the oxide layer will 

be used as input data for the numerical modelling. The other experimental results associated 

to the crack patterns will allow a comparison between the experience and the

 

modelling. To 

improve the modelling of the corrosion product layer in the numerical simulation, an 

experimental test is in progress to characterize mechanical properties of these products. 

 

 

References 

 

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