Suitability of Various Measurement Techniques for Assessing Corrosion in Cracked Concrete

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Title: Suitability of Various Measurement Techniques for Assessing Corrosion in Cracked Concrete

Author(s): Mike B. Otieno, Mark G. Alexander, and Hans D. Beushausen

Publication: Materials Journal

Volume: 107

Issue: 5

Appears on pages(s): 481-489

Keywords: chloride-induced corrosion; corrosion assessment; cracked concrete; nondestructive testing

Date: 9/1/2010

Abstract:
This paper presents a critical evaluation of results from three corrosion assessment methods used in an experimental study to investigate the influence of cracks on the rate of chloride-induced corrosion. The objective was to determine the suitability and reliability of the corrosion assessment methods for application in cracked concrete. Beam specimens (100 x 100 x 500 mm [3.9 x 3.9 x 19.7 in.]) with crack widths of 0.7 and 0.4 mm (0.028 and 0.016 in.), as well as incipient cracks, were made using two binder types (100% CEM I ordinary portland cement [OPC]) and 50/50 OPC/ slag blend), two water-binder ratios (w/b) (0.40 and 0.55) and a constant cover of 40 mm (1.6 in.) to steel reinforcing. The specimens were subjected to repeated cycles of 3-day wetting with 5% NaCl, and 4-day air drying for 32 weeks. Half-cell potential (HCP), resistivity (Wenner probe), and corrosion rate (coulostatic) measurements were taken at the end of each 3-day wetting period. Chloride conductivity tests were also performed on companion cube specimens at 28 and 90 days. No significant differences in resistivity values were noted between cracked and uncracked specimens, despite the fact that the corrosion rate increased with increasing crack width. The insensitivity of resistivity measurements to the presence of cracks was attributed to the fact that measurements were taken after every 3-day wetting period, when the specimens would have been saturated with salt solution. The chloride conductivity and resistivity measurements gave a similar indication of the corrosion rates. HCP and corrosion rate measurements showed a good correlation, and they gave a clear indication of corrosion in cracked reinforced concrete (RC) specimens, although for practical applications, HCP measurements need to be complemented with other corrosion assessment techniques. For the resistivity assessment technique—in addition to concrete quality and magnitude of resistivity—correction factors are required to relate the resistivity of uncracked concrete to corrosion characteristics of cracked concrete. A methodology for the application of correction factors is proposed.