Potentiometric Determination of Free Chloride in Cement Paste – an Alternative Method for Low-Budget Laboratories

Abstract

Corrosion of rebar in concrete is commonly associated with, and to a large degree influenced by, the free chloride concentration in the pore water. The amount of chloride in concrete is important because chloride can promote corrosion of steel reinforcement when moisture and oxygen are present. A potentiometric procedure that makes use of direct measurement with a chloride ion selective electrode has been developed to analyze free chloride in the pore water extracted from cement paste.¹⁶ The accuracy and reliability of this analytical technique has been checked against a certified reference material, Merck sodium chloride solution. Confidence levels (CL_0.95), of 0.03 and relative standard deviations of 0.2 % for chloride were determined for ordinary Portland cement (OPC) chloride binding capacity.

Keywords: OPC, free chloride, potentiometry