Evaluation of Cover Concrete by Analysis of Chloride Diffusion Coefficients

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Title: Evaluation of Cover Concrete by Analysis of Chloride Diffusion Coefficients

Author(s): O. Cascudo, H. Carasek, M.-P. Yssorche-Cubaynes, A.N. Lopes, and J.-P. Ollivier

Publication: Special Publication

Volume: 229

Issue:

Appears on pages(s): 135-150

Keywords: carbonation; chlorides; concrete cover; effective diffusion coefficient; migration test; wall effect

Date: 9/1/2005

Abstract:
The concrete cover has different characteristics when compared to the concrete confined within the structural elements. Such differences come from the absorption produced by the formwork, from the water evaporation typically pronounced in outer concrete layers, from the wall effect, etc. On account of these factors, it is expected that the concrete cover has worse characteristics in comparison to those of the inner concrete and that this aspect influences the durability as well as the performance of concrete structures. Therefore, the present work aims to evaluate the differences existing between the concrete cover and the inner concrete, taking account the analysis of chloride effective diffusion coefficients (Def) measured in two layers of a beam prototype of reinforced concrete. The study comprises two different concretes cast with W/C 0.40 and 0.55, without curing. Def of two year old specimens were experimentally obtained by means of a migration test, by determining the coefficients in two different depths: in the concrete cover, with a test specimen of 2.0 cm thick, and in a region deeper than 6.0 cm. Contrarily to the expected, the main results showed that Def values in the concrete cover were about 10% of those measured in the inner concrete. The partial carbonation of the concrete cover was the major cause to explain the reduction in chloride movement within the cover layer, since it reduces the paste total porosity.