An investigation of experimental methods used to determine free and total chloride contents

• Published in: Cement and concrete research 1996-09, Vol.26 (9), p.1443-1449
• Main Authors: Glass, G.K., Wang, Y., Buenfeld, N.R.
• Format: Article
• Language: English
• Subjects: Analysis of cement phases and constituents; Applied sciences; Buildings. Public works; Cement concrete constituents; Cements; Exact sciences and technology; Materials; Miscellaneous; Properties of anhydrous and hydrated cement, test methods
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/0008-8846(96)00115-9

The free chloride content in cement pastes may be assessed by analysing the pore solution expressed under pressure using a pore press, or achieving an equilibrium between a known external solution and the pore solution, while the total chloride content is commonly determined using acid soluble extraction. A comparison of these techniques indicates that loosely bound chloride is released during pore solution expression under pressure and this may result in a significant overestimation of the free chloride content. Chloride binding relationships determined in this manner may produce errors when used in modelling chloride transport as the expressed pore solution concentration can be significantly greater than that in the contaminating solution. Furthermore acid soluble extraction may underestimate the total chloride content. The use of ultrasonic treatment to accelerate the achievement of equilibrium also results in the release of loosely bound chloride which in turn limits the chloride taken up by such samples.