United States Department of Transportation
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An evaluation of new inhibitors for rebar corrosion in concrete.
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2003-01-01
[PDF-2.75 MB]
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Edition:Final report;Nov. 1997Dec. 2002.
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Abstract:The corrosion of reinforcing steel in concrete is estimated to affect more than 50% of the 575,000 bridges in the United States. One approach to mitigating this problem is to use corrosion-inhibitive compounds admixed into the concrete paste. This study sought to examine the corrosion inhibition performance of a series of compounds admixed into high-quality concrete and to delineate the effects of these compounds on the concrete with regard to the corrosion process. A series of eight compounds were admixed into Type A4 concrete. The compounds tested were aminoethylethanolamine, aminothiophenol, di-sodium Beta-glycerophosphate, calcium nitrite, di-n-butyl sulfoxide, lithium nitrate, sodium metasilicate, and nitrilotriphosphonic acid. Concrete blocks were cast, into which were placed 0.009-in.-diameter 1040 steel wires. The corrosion rate was assessed via a resistance change measurement (RCM) of these wires over time using a temperature-corrected four-point resistance measurement. The time-to-open circuit for the wires was also monitored. RCM was compared to (1) electrochemical impedance spectroscopy results of tests conducted in a simulated pore solution, and (2) chloride permeability measurements of the concrete as per ASTM C 1202. The effect of the admixtures on the compressive strength and density of the concrete was also assessed. RCM and time-to-open circuit results showed that four test inhibitors had equal or better corrosion prevention at 2 years of testing compared to a widely used commercial mix (DCI). These test inhibitors included di-sodium Beta-glycerophosphate (0.283 mol/cu ft and 0.815 mol/cu ft), aminoethylethanolamine (0.815 mol/cu ft), lithium nitrate (0.815 mol/cu ft), and sodium metasilicate (0.815 mol/cu ft). After 100 weeks, 33% to 44% of the wires were active in concrete admixed with these test compounds, whereas only 25% of the wires were active in concrete admixed with DCI. This research has also shown that the performance of a corrosion inhibitor in high-quality concrete is a function of numerous interrelated factors that are not predicted from any single laboratory test. These tests provide promising results for alternative inhibitive admixtures for standard Type A4 concrete. It is recommended that additional tests be conducted on concrete mixtures containing slag and fly ash using multiple concentrations of the four most promising inhibitors. Further testing may lead to the implementation of a better corrosion-inhibiting admixture, thus increasing the service life of bridges.
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