Page 8 - Open-Access-Nov-2020

TECHNICAL PAPER

If the corrosion rate is not constant, then it has been identified phenomenon, which can mislead many of the apparently straight
that the propagation period can be modelled by considering forward deductions. In large structures, the measurement of the
an increase or a decrease of the corrosion rate with the time. corrosion rate entails a set of difficulties due to the spraying of
This enables to have an expression with “two linear periods or a the applied current along the bars to a distance, which changes
bi-linear model” (Figure 12). with the concrete resistivity and the level of corrosion in the
measurement region. It is necessary to confine the current
= 1 + 2 = 1 + 2 (11) below the auxiliary electrode, which needs sophisticated
1 2
equipement with control of the external guard ring. The
Where t p is the propagation period showing two lineal simultaneous inherent measurement of the corrosion potential
trends t p1 and t p2 , P corr1 and P corr2 are the loss in bar diameter and the resistivity are helpful for the correct interpretation of the
or “accumulated corrosion” in each of the two propagation measurements. Providing a correct value of the corrosion rate
sub-period, V corr1 and V corr2 are the corresponding corrosion rates is obtained on site, its application for predicting the evolution
in each sub-periods. of the loss in bar diameter needs the consideration on whether
the attack is homogeneous or localized and whether the future
The change in the slope of the corrosion penetration (Figure 12) evolution will evolve with the same corrosion rate or not. That
may be originated by different phenomena, in general due to is which is the averaged annual value as a function of the local
the cracking of the cover due to the expansion of the oxides. climate conditions.
When parallel cracks are developed, for example in submerged
conditions, the chlorides may arrive in greater quantity to 5. REFERENCES
the bar surface and then, the corrosion rate would increase.
If however, the concrete is exposed to the atmosphere, the [1] Tuutti, K., (1982). “Corrosion of steel in concrete”, Swedish
generation of parallel cracks may induce a shorter time of Cement and Concrete Research Institute, Stockholm.
wetness because the region of the crack, may dry quicker than [2] Elsener, B., Andrade, C., Gulikers, J., Polder, R., Raupach,
the bulk concrete and the crack would have a shorter wetness M. (2003). “RILEM TC 154-EMC: Electrochemical
period and the corrosion rate would decrease. Nevertheless, this techniques for measuring metallic corrosion Half-
decrease would depend on the time by year that the cracked Cell Potential Measurements – Potential Mapping on
zone is exposed to the rain. If the wetness period by year is long,
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Gulikers, J.; Weidert, R.; and Raupach, M.; (2000),
4. FINAL COMMENTS “Test methods for onsite measurement of resistivity
of concrete”, RILEM TC 154-EMC: Electrochemical
The on-site corrosion measurements in concrete structures
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the measurement using correct equipments, but mainly for the and Structure, Vol. 33, pp. 603-611.
interpretation of test data. The corrosion evolution is a complex [4] Andrade, C., Alonso, C., Gulikers, J., Polder, R., Cigna,
R., Vennesland, Ø, Salta, M., Raharinaivo, A., Elsener, B.
C
(2004). “RILEM TC 154-EMC: Electrochemical Techniques
for Measuring Metallic Corrosion. Recommendations Test
methods for on-site corrosion rate measurement of steel
A
reinforcement in concrete by means of the polarization
resistance method”, Materials and Structures, Vol. 37,
Pcorr (mm) B [5] Vennesland Ø., Raupach M., Andrade, C., (2007).
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“Recommendation of Rilem TC 154-EMC: Electrochemical
techniques for measuring corrosion in concrete-
Measurements with embedded probes”, Materials and
Structures, Vol. 40, pp. 745-758.
t p1 t ip2
time [6] ASTM G59. (2014). “Standard Test Method for Conducting
initiation Propagation Potentiodynamic Polarization Resistance Measurements”.
Figure 12: Linear progression of corrosion depth (line A) and the two [7] ASTM C876. (2015). “Standard Test Method for Corrosion
possibilities of “two-step (bi-lineal)” corrosion propagation models
(line B with a lowering of the corrosion rate in the second step and line Potentials of Uncoated Reinforcing Steel in Concrete”,
C with an increase of it in time) West Conshohocken, PA: ASTM International.

14 THE INDIAN CONCRETE JOURNAL | NOVEMBER 2020