Investigations on the Threshold Value of the Critical Chloride Content


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Title: Investigations on the Threshold Value of the Critical Chloride Content

Author(s): W. Breit and P. SchieBl

Publication: Special Publication

Volume: 170


Appears on pages(s): 363-378

Keywords: Chlorides; corrosion; diffusion; tests.

Date: 7/1/1997

Electrochemical tests on mortar electrodes in alkaline chloride solutions were carried out to determine the critical chloride content depending on the mortar composition (type of cement, cement content, water-cement ratio and concrete additions). Sodium chloride, with varying chloride concentrations (between c(NaC1) = 14 and 508 mmol*L-1), was used to initiate corrosion. Depassivation times of the mortar electrodes as well as corresponding total and free chloride contents were determined. By means of macrocell corrosion tests without polarisation and at a constant concentration of the test-solution of c(NaC1) = 282 mmol*L-1, the diffusion process of the chloride and the chloride binding (dependent on the age of the test amples) were investigated in order to obtain reference values for the depassivation time of the steel. Potentiostatic tests with constant polarisation at USHE = +500 mV in alkaline chloride solutions of different concentrations were carried out for 11 different mortar mixtures to determine the critical corrosion-initiating chloride content. A linear relation between corrosion-initiating free and total chloride content was found. A minimum critical chloride content of 0.25 wt.-% relative to cement was determined.