The Scientific World Journal / 2014 / Article / Tab 3

Review Article

Monitoring Corrosion of Steel Bars in Reinforced Concrete Structures

Table 3

Several recent corrosion studies.

ReferenceStudy performedSignificant observationsComments

Pour-Ghaz et al., 2009 [7]Presented a tool for the interpretation of the results of half-cell potential measurement. It relates half-cell potential values to the probability of corrosion through concrete resistivity, cover thickness, temperature and anode to cathode ratio. A model is developed by solving Laplace’s equation, relating corrosion current with average potential on the surface, potential difference on the concrete surface, temperature, resistivity, and concrete cover.In concrete with low resistivity potential distribution on surface represents potential at steel concrete interface.
For better results interpretation of potential readings can be done in accordance with resistivity.
With the increase in concrete cover difference between surface and interface potential increases.
More realistic results can be obtained by considering availability of oxygen and increasing the test points.
More experimental validation of the model is required to increase the confidence.

Song and Saraswathy, 2007 [6]Reviewed several electrochemical and nondestructive testing methods for the assessment of corrosion in concrete structures.Combining several techniques can provide more information about corrosion state of steel bars.
An integrated monitoring system for new and existing concrete structures can reduce inspection cost.
Presented methods are useful to monitor corrosion in concrete structures and all these reviewed methods can be used to develop more accurate and better techniques for monitoring corrosion.

Ahmad, 2003 [3]Reviewed mechanism of corrosion, corrosion monitoring techniques, and methodologies to predict the remaining service life of structures.
Observed that corrosion rate is affected by pH of electrolyte, availability of oxygen, capillary water, and concentration of FE2+ in the concrete near the reinforcement.
Information regarding corrosion state required three parameters half-cell potential, concrete resistivity, and corrosion current density.Presented all the aspects of corrosion, and may be useful for understanding the corrosion theory, progress of corrosion, factors affecting corrosion, monitoring techniques and for predicting service live of structures.

Bjegovic et al., 2000 [2]Described different corrosion monitoring techniques such as half-cell potential measurement, macrocell current measurement, linear polarization method, Geocor 6, electrochemical impedance spectroscopy, Galvanostatic pulse method, and scanning reference electrode method.Nondestructive methods for measuring corrosion are advantageous as measurements can be done over entire structure, provide fast results, and are inexpensive.Presented overview of several nondestructive methods with their relative advantages and disadvantages based on experiences and interpretation of results. It is a useful study covering almost all the present corrosion measuring techniques.

Carino, 1999 [4]Presented an overview of corrosion process and nondestructive evaluation techniques such as half-cell potential method, concrete resistivity test, and the linear polarization method. Corrosion rate in a concrete structure is governed by several parameters such as moisture content, availability of oxygen, and temperature. So, for better results it is necessary to repeat corrosion rate measurement in regular time interval.A useful review has been presented by considering the behavior of electrolytic cells.

So and Millard, 2007 [8]Presented Galvanostatic pulse transient technique for evaluating the corrosion rate in reinforced concrete structures and also presented the advantages of this technique over linear polarization (LPR) method.Corrosion rates calculated from Galvanostatic pulse transient technique are generally higher than those evaluated from LPR technique.It is a useful study presenting a relatively more reliable technique for measuring corrosion rate in RC structures.

Pradhan and Bhattacharjee, 2009 [9]Discussed results of a study conducted on concrete specimens with different cement, steel, and varying water/cement ratios. Specimens are subjected to 3% sodium chloride solution and half-cell potential measurements were carried out to evaluate corrosion activity. Critical chloride content causing corrosion initiation is influenced by steel type, cement type, and w/c ratio.
Found half-cell potential as a parameter indicating rebar corrosion initiation in chloride contaminated concrete.
It has been observed from this study that corrosion initiation time is influenced by the rate of ingress of chloride ions and depassivation of protective passive film.

Hussain and Ishida, 2012 [1]Performed multivariable laboratory experiments to evaluate effect of oxygen on reinforcement corrosion under different environmental conditions and also explained half-cell potential measurement in different conditions such as submerged exposure condition and under cyclic wetting—drying exposure.It was observed that oxygen is an influencing factor for corrosion only for concretes placed completely under water.Results of this analysis can be used for calibrating half-cell potential measurements performed under water.

Cairns and Melville, 2003 [10]Performed nondestructive electrochemical measurements of corrosion to evaluate effect of protective coatings on the reliability of these tests.It has been observed from results that half-cell potential measurements were not affected significantly by coating.Useful study to evaluate reliability of corrosion monitoring techniques.

Elsener, 2001 [11]Discussed about application and limitations of half-cell potential mapping for assessing reinforced concrete structures to evaluate repair work.
Repairs include replacement of chloride contaminated concrete, electrochemical chloride removal, electrochemical realkalization and application of corrosion inhibitors.
For interpretation of half-cell potential readings, it requires precise understanding of corrosion protection mechanisms and good knowledge and experience in half cell potential mapping.A useful study explaining half-cell potential mapping and effect of corrosion repairing over the results provided by half-cell potential method.

Parthiban et al., 2006 [12]Carried out simultaneous potential measurements on different points on concrete slab, using computer based I/O cards and also developed software based on ASTM C-876 for interpretation of measured values.Among the various electrochemical methods potential measurement has been the mostly used field technique for detecting corrosion activity in steel.
Manually measuring half-cell potential values is a tedious job on a large structure, so an automatic system to evaluate the half-cell potential values is present.
An automated useful method to evaluate half-cell potential at different points on a large structure simultaneously is present.   
This method can reduce time required to evaluate potential values at different points for monitoring the corrosion.

Moon and Shin, 2006 [13]Studied corrosion evaluation of the steel bars embedded in underwater concrete. Performed accelerated corrosion tests on three series of reinforced underwater concrete with different admixtures in different conditions. It has been observed that specimens casted in seawater develop early corrosion of steel bars.
Among all the specimens, in OPC manufactured concrete corrosion rate is fastest and exceeds threshold value earlier than other specimens.
Mineral admixtures are more effective in delaying the development of corrosion in underwater concrete.
A careful study on antiwashout underwater concrete to evaluate effect of different admixtures on corrosion of steel bars.

Poursaee and Hansson, 2009 [14]Described pitfalls in assessment of chloride induced corrosion through electrochemical methods.
Factors influencing the results of electrochemical processes are found to make more measurements in short period to reduce the costs, choosing appropriate electrochemical method, and laboratory tests are usually conducted on young and immature concrete.
Results of electrochemical assessment may not represent actual condition of rebars.Explained the pitfalls in electrochemical assessment of chloride induced corrosion of steel, which can be utilized to regulate the results of measurements.

Soleymani and Ismail, 2004 [15]Performed a study to estimate the corrosion activity of steel bars embedded in two types of concrete specimens, ordinary and high performance, applying different corrosion measurement methods. Methods applied are half-cell potential, linear polarization method, Tafel plot, and other chloride content methods.Results indicated that all these method would assess the same level of corrosion in only 24% of specimens.Presented a useful comparison between different corrosion measurement methods. This study can be used by researchers to select better corrosion monitoring technique.

Ahn and Reddy, 2001 [16]Performed accelerated corrosion test to evaluate durability of marine concrete structures subjected to fatigue loading with different water cement ratios. Ultimate strength testing followed by half-cell potential measurement and crack investigations has been performed.Deterioration is faster under fatigue loading than static loading.
Durability decreased with increase in water cement ratio.
Presents significant findings about the effect of fatigue loading and water cement ratio over the durability and life of the structures.

Elsener, 2002 [17]Studied effect of conductivity and cover depth on potential and macrocell current distribution.
Also, discussed consequences of monitoring corrosion through half-cell potential mapping and polarization measurement technique on locally corroded rebars.
Low electrolyte conductivity and cover make it possible to locate anode of the macrocell by potential measurements.Discussed about influence of macrocell corrosion on corrosion monitoring.

Alhozaimy et al., 2012 [18]Performed laboratory experiments to evaluate half-cell potential, corrosion current, and concrete resistivity over chloride contaminated concrete specimens, to investigate the phenomenon of high corrosion at intersection of steel rebars in the wall footing. Observed that experimental measurements are higher at intersection of steel bars in comparison with the areas between them. This high corrosion rate is found to be due to coupled effects of corrosive binding wire materials, electrical connectivity, reduction in centre to centre spacing of steel rebars, and poor concrete microstructures.Phenomenon reported in this paper is new and interesting. More and extensive research is required to understand the effect of all factors influencing the corrosion at intersection of steel rebars.

Duong et al., 2013 [19]Performed half-cell potential and corrosion current density test on concrete specimens to monitor corrosion activity. This corrosion activity had been monitored to evaluate the effect of leaching on carbonation and corrosion initiation of steel bars.Observed that with the increase in leaching exposure carbonation depth also increases.
Replacing cement partially with fly ash reduces the resistance against carbonation and leaching.
Presents the performance of half-cell potential measurement and corrosion current density to detect corrosion due to leaching activity. It has been observed that suitable test methods are required.

Sadowski, 2010 [20]Describes linear polarization and four point Wenner resistivity methods to evaluate corrosion rate without making a direct connection to the reinforcement.Observed that short circuit influence of embedded steel can be used to evaluate the rate of corrosion on the surface of the bars.More validation of methods is required on concrete with wider range of resistivity.

Jung et al., 2003 [21]Half-cell potential and linear polarization measurements have been performed for one year to evaluate the parameters affecting the corrosion rate. Measurements have been made to predict the remaining service life of land concrete affected from steel corrosion. Quantitative polarization method provides more precise results than those of half-cell potential method in evaluating the corrosion activity. Comparison between methods helps researchers to select better techniques for evaluating residual service life of structures.

Lai et al., 2013 [22]Presented a new technique to investigate corrosion of steel bars in concrete using ground penetrating radar (GPR) and modified half-cell potential method. Attempted to measure potential difference with two moving probes and making no connection with steel bars.Results show that both GPR and modified HCP methods can measure electrochemical corrosion process. More researches are required to relate laboratory results with real time structures

Leelalerkiet et al., 2004 [23]Performed half-cell potential measurements to estimate corrosion of reinforcing steel bars embedded in concrete slabs under cyclic wet and dry exposures. Influence of void over potential distribution and current distribution has also been investigated. Observed from results that half-cell potential is marginal successful
In the void specimens half-cell potential values required compensation for more reliable results.
Useful study to demonstrate corrosion estimation in both intact and void specimens.

Faber and Sorensen, 2002 [24]Discussed the application of half-cell potential measurements to evaluate the probability of corrosion and repair after 50 years. This is explained on a corroded concrete structure.It has been observed that half-cell potential measurements may be utilized to update the probability of corrosion.Provided a study on the utilization of half-cell potential method.

Hussain, 2011 [25]Investigated underwater half-cell corrosion potential in submerged RC structures and compares with various other relative humidity conditions. Half-cell potential values for submerged underwater RC structures are not representing actual corrosion rate and these values are required to be calibrated using the experiment results of this research. This study enables researches to perform underwater corrosion measurement for evaluating condition of submerged RC structures.

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