Modelling Chloride Ingress in Concrete: A Comparative Study of Laboratory and Field Experience

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Title: Modelling Chloride Ingress in Concrete: A Comparative Study of Laboratory and Field Experience

Author(s): T. Callanan and M. Richardson

Publication: Special Publication

Volume: 212

Issue:

Appears on pages(s): 389-408

Keywords: chloride diffusivity; durability design; fly ash; performance-based specification

Date: 6/1/2003

Abstract:
Performance-based specifications for concrete exposed to chlorides may involve the determination of long-term material parameters by relatively short-term laboratory tests. The first generation of chloride environment durability models are likely to be based on diffusion theory, despite the fact that chloride ingress is both by absorption and diffusion. This paper compares chloride resistance values from laboratory experiments and from field trials, derived solely on diffusion-based modelling. Concrete prisms were exposed to sodium chloride solutions in laboratory tests for a period of 12 months. The trials included both continuous immersion and cyclical wetting and drying cycles. Chloride values were determined at 3, 6 and 12 months. Material variables included normal portland cement, fly ash, crushed limestone aggregate, natural sand, and natural gravels. Diffusion coefficients were derived through best-fit curves based on Crank’s error function solution of Fick’s second law of diffusion. It was found that the laboratory test diffusion coefficients diminished significantly with increase in test duration and stabilised between 6 and 12 months, by which time they yielded values of a similar order of magnitude to those from the structures in service. The coefficients for gravel aggregate con- crete specimens were more variable than those for crushed rock aggregate concretes and could exceed the in-service values by a factor of at least two. The beneficial influence of fly ash was reflected in the results.