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