Aspects of Chloride Ion Determination in Concrete

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Title: Aspects of Chloride Ion Determination in Concrete

Author(s): M. N. Haque and O. A. Kayyali

Publication: Materials Journal

Volume: 92

Issue: 5

Appears on pages(s): 532-541

Keywords: chlorides; concretes; corrosion; fly ash; Materials Research

DOI: 10.14359/893

Date: 9/1/1993

Abstract:
Two methods were used to determine the free and water-soluble chloride ion concentrations in concretes of differing strength that were exposed to penetrating sodium chloride solutions of 5000, 10,000, and 20,000 ppm Cl - ion concentration. The first method analyzed the pore solution expressed from specimens, and the second analyzed the decanted solution of pulverized samples. Results of this study suggest that the testing method utilizing the decanted solutions of concretes overestimates the CL- concentration, and gives erroneously high values for O*H - concentrations. It can be inferred that the expressed pore solution method provides the more accurate measure of free ion concentrations. This paper stresses that a very important distinction needs to be made between free, water-soluble, and total chloride concentration in concretes to make a reasonable estimate of the threshold of corrosion propagation and predict the service life of concrete structures. Concretes manufactured using fly ash give highly differing values of free and water-soluble chlorides when tested. Accordingly, in some cases, a rapid determination of chloride levels in concrete may not be very rapid. Concretes made with superplasticizers seem to give a comparatively higher concentration of Cl - ions in tests made with the expressed pore solution. A tentative plan of action has been put forward to explain the results of this investigation. The authors tentatively put forward their theory concerning the mechanism of action that might cause this discrepancy.


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