Sea Salts and Alkalinity of Concrete


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Title: Sea Salts and Alkalinity of Concrete

Author(s): O. E. Gjorv and O. Vennesland

Publication: Journal Proceedings

Volume: 73

Issue: 9

Appears on pages(s): 512-516

Keywords: alkalinity: chlorides; concretes; corrosion; corrsion resistance; hydration--aqueous phase: marine atmospheres;pH; portland cements; reinforcing steels: salt water: sea water: sodium chloride.

Date: 9/1/1976

Investigations indicate that large amounts of sea salts can penetrate even high quality concrete. Several questions have been raised as to what effect this may have on the alkalinity or the pH of the liquid phase in concrete. The pH should never drop below a level of about 11.5 to provide good corrosion protection for embedded steel, and the higher the pH, the higher the amounts of chlorides that can be tolerated without resulting corrosion. Experiments were undertaken to determine the effect of sea salt on the pH of saturated solutions of Ca(OH)c and extracts of hydrated portland cement. The results indicate that the effect of sea salt depends very much on the reserve basisity present, i.e., the amount of constituents present that can maintain the high alkalinity. When there was no reserve basisity salt concentrations of only 2 to 6 percent caused a sharp drop in pH down to about 10. When a reserve basisity in the form of solid material was present, however, salt concentrations of up to 20 percent could be tolerated without re-ducing the pH to more than about 12. This demonstrates the importance of using cement with a high reserve basisity in concrete exposed to marine en-vironments. Reductions of pH due to the presence of NaCl have frequently been reported in the literature, but the resent results indicate that this may be due to the effect of the alkaline error of the pH A electrode used.