CONCRETE RESISTIVITY - ITS ROLE IN CORROSION: FROM REBARS TO STRAY CURRENTS ROM DC TROLLEYS

摘要

Corrosion engineers and scientists working in the area of reinforced concrete structures soon learn that structural durability is measured by more than concrete compressive strength. One concrete property that is often included in non-destructive measures of a concrete's ability to provide successful service is resistivity. A number of published reports and guidelines discuss how measured resistivity values relate to the expected risk of embedded reinforcement corrosion. Concrete is also used as a stray current barrier where direct current (DC) trolleys and streetcars cross or parallel buried metal piping. Several methods to measure concrete resistivity are critiqued, with their respective advantages and weaknesses discussed. The affects on concrete resistivity of both chemical and mineral admixtures are presented. This paper discusses how ionic chemical admixtures may reduce a concrete's resistivity, but not its chloride ion permeability. Also addressed are how replacing cement with mineral admixtures can increase the concrete's electrical resistivity, but may also produce drying or autogenous shrinkage and resulting cracks. Applications of low resistivity acrylic gels to effectively seal concrete cracks and cold joints will also be presented. The paper includes an overview of the surprisingly complex cement pore structure and how those intricacies affect both resistivity and corrosion processes and how corrosion practitioners can use them to their advantage.