Title:
Chloride Diffusion, Microstructure, and Mineralogy of Concrete after 15 Years of Exposure in Tidal Environment
Author(s):
Tarek Uddin Mohammed, Toru Yamaji, and Hidenori Hamada
Publication:
Materials Journal
Volume:
99
Issue:
3
Appears on pages(s):
256-263
Keywords:
fly ash; ordinary portland cement; slag
DOI:
10.14359/11971
Date:
5/1/2002
Abstract:
A detailed investigation on the chloride diffusion, microstructure, and mineralogy of 15-year-old concrete specimens 150 mm in diameter and 300 mm in height was carried out. The specimens were exposed to a tidal environment. The cement types were ordinary portland cement (OPC), slag cements of Types A, B, and C (SCA, SCB, and SCC), and Type B fly ash cement (FACB). The water-cement ratio (w/c) was 0.45. Compressive strength, carbonation depths, pulse velocity, water- and acid-soluble chloride profiles, microstructure, and mineralogy of concrete were evaluated. Chloride diffusion as well as chloride binding ability of concrete with the variation of cement types is sequenced as OPC>FACB>SCA>SCB>SCC. Improvement of the microstructure of concrete at the outer region of the specimens due to the reaction between seawater and hydration products is clearly observed. It blocks chlorides at the outer regions and chloride profiles drop to a negligible value very sharply at a short distance inside concrete, especially for SCC and SCB. Friedel’s salt is observed, irrespective of the cement types; however, it is limited to the outer region for slag cement. Magnesium hydroxide is observed at the outer regions for OPC and FACB only. Ettringite is formed at the outer regions, irrespective of the cement types; however, for FACB, it infiltrates to a depth more than 45 mm from the surface.