Investigations Into the Effect of Coatings on Water Distribution in Concrete Using Multi-ring Electrodes

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Title: Investigations Into the Effect of Coatings on Water Distribution in Concrete Using Multi-ring Electrodes

Author(s): P. Schie, L. W. Breot. And M. Raupach

Publication: Special Publication

Volume: 151

Issue:

Appears on pages(s): 119-134

Keywords: bridges (structures); carbonation; chlorides; coatings; concretes; corrosion; durability; moisture; protective coatings; repairs; Structural Research

Date: 7/1/1994

Abstract:
In recent years, corrosion of the reinforcement caused by chlorides, carbonation of the concrete, or low quality of the concrete cover has caused serious damage to concrete bridges. Apart from other measures, one possible means of repairing damage at the concrete surface due to reinforcement corrosion is to apply a coating to the concrete surface to reduce the water content of the concrete. If the coating has a sufficient high-penetration resistance against water and if no water enters the concrete from other sources, the water content of the concrete will remain low after the application of the coating, or the concrete will dry out slowly, provided that water can evaporate through the coating or through the opposite concrete surface. A multi-ring electrode method for determining the water distribution within the concrete near the reinforcement and the steel surface has been developed at the Institute of Building Materials Research in Aachen, Germany. The electrode is used to determine AC resistance between nine noble metal rings, allowing the water content to be estimated at eight different distances from the concrete surface. To estimate the effect of different types of coatings, time-dependent changes in resistance following wetting of coated and uncoated concrete surfaces were monitored. Fundamental laboratory investigations of the influence of concrete compositions, carbonation, and chloride application were also carried out.