ABSTRACT

Multiple methods are employed to control and remediate rebar corrosion in new and existing concrete structures and they make up the tool box available to engineers to extend structure life. Methods for extending concrete structure life range from changes in concrete cement chemistry to the use of corrosion inhibitor systems such as pozzolonic cement, surface sealers, corrosion inhibitor admixtures, cathodic protection and surface applied corrosion inhibitors. Most of these methods are covered in ASTM1, AASHTO2 and state departments of transportation (DOT) specification except for surface-applied corrosion inhibitors.. The recent publication of a Unified Facilities Guide Specification (09 97 23.17) ”Corrosion Inhibitor Coating of Concrete Surfaces” has now given a specification for the use of surface-applied corrosion inhibitors and is reviewed along with supporting performance data. 3 The value of corrosion control and remediation systems are examined with respect to the measurement and calculation of structure life extension.

INTRODUCTION

Reinforcing steel (rebar) corrosion is the primary cause of deterioration and limitation of functional life of reinforced concrete structures. A number of specifications for the construction of new structures have been created aimed at reducing the probability of rebar going into a corrosion active condition. New concrete has a high alkalinity expressed as a pH of 13 and uncoated rebar will be in a corrosion passive state as long as the cement pH stays above 11. Penetration into the cement micro pores by chloride ions from deicing salt and maritime exposure and carbon dioxide results in the cement at the rebar level going in to a corrosion active state due to carbonation reducing cement pH and chlorides reacting with the rebar passive film.

Concrete cement porosity can be reduced by addition of silica fume and fly ash to the concrete mix. Reduction in porosity is measured by the rate of chloride ion migration in the cement as described in ASTM C1202 4. Lowering the rate of chloride ion migration in cement can be used to forecast the time for the chloride content at rebar level to reach a corrosion active condition. The forecast though does not take into account the impact of surface cracks furnishing routes for chloride penetration and the effect on cement pH from addition of silica fume or fly ash by reaction with cement alkaline components.

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