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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 4
Effect of red mud addition on the corrosion parameters of reinforced concrete evaluated by
electrochemical methods
surements in the wet and dry states (0%). Due a larger network of
capillary pores, the reference samples presented a higher absorp-
tion capacity (capillary suction) and greater difficulty in losing this
moisture (lower porosity) than the other samples.
The tests were interrupted when the “unsafe potential” was
reached in samples in the dry state. For a better view, these results
are presented in Figure 5. As can be seen, the reinforcing bars in
specimens containing red mud took longer to depassivate than the
reference samples, regardless of the amount of red mud added.
These results indicate only the onset of the corrosion process,
without, however, presenting quantitative information about the
phenomenon. Although they reached the end of test more quickly,
the specimens that reached the unsafe potential continued to be
subjected to wetting and drying cycles for up to 180 days, when the
last samples (10%) reached this potential. Thus, it was possible to
calculate the corrosion rate of all the samples according to equa-
tion (A). The results are shown in Figure 6.
According to these results, the higher the content of red mud the
lower the corrosion rate, which reached stability between 20 wt%
and 30 wt% of red mud content. This behavior may be due to three
isolated factors or to their combination: i) increasing alkalinity in the
region near the steel-concrete interface; and/or ii) greater anchor-
ing of chloride ions due to the presence of sodium aluminosilicates,
which prevent the free movement of these ions and make them un-
available to start the corrosion process, as discussed with respect
to the results of the chloride migration test; and/or iii) according
to MCCARTER apud SANTOS [13], larger pores (existing in the
specimens containing red mud) lose water more easily than the
small and tortuous pores that are present in the reference sample.
Figure 5 – Rebar corrosion onset period
as a function of red mud content
Figure 6 – Corrosion rate of steel bars
embedded in reinforced concrete specimens,
calculated after the corrosion potential
test, as a function of red mud content
Figure 7 – Electrical resistivity of concrete
specimens containing red mud,
as a function of age
Figure 4 – Evolution of the corrosion potential
of rebars embedded in reinforced concrete
specimens containing red mud, as a function
of age