Field Study of the Penetration of Chlorides and Other Ions Into a High Quality Concrete Marine Bridge Column


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Title: Field Study of the Penetration of Chlorides and Other Ions Into a High Quality Concrete Marine Bridge Column

Author(s): P. Sandberg and L. Tang

Publication: Special Publication

Volume: 145


Appears on pages(s): 557-572

Keywords: bridge columns; chlorides; concrete cores; corrosion; diffusion; durability; field tests; harbor structures; microcracking; permeability; seawater; service life; Materials Research

Date: 5/1/1994

The transport of ions related to the penetration of chlorides into concrete has been studied in the field by drilling 100-mm concrete cores from a marine bridge column. A 4-year-old concrete column in Sweden was selected. The concrete was of high quality (i.e., frost- and sulfate-resistant, with a low-heat, low-alkali portland cement with a maximum water-cement ratio of 0.40) according to new Swedish recommendations. Concrete cores were drilled from the submerged, splash, and atmospheric zones. Selective rinding from the concrete surface (profile grinding) revealed concentration profiles of acid-soluble chlorides, carbonates, sulfates, and water-soluble alkalies. Selected parts of the concrete surface were examined by SEM and thin-section microscopy for microstructural studies. Laboratory estimates of chloride diffusivities were carried out on 6-month-old laboratory concrete of similar mix proportions, and also on unexposed parts of drilled concrete cores. Chloride diffusivities obtained from laboratory exposure were then compared with the values obtained from the field concentration profiles, from both the bridge column and a field station, using Fick's second law of diffusion. Maximum chloride diffusivities calculated from the field profiles after 4 years of exposure were more than ten times lower than those obtained from the same concrete in the laboratory. Clearly, there are important mechanistic problems associated with laboratory procedures, resulting in serious misjudgments, if such laboratory tests are used for linear extrapolation of the service life for marine concretes.