Chloride ion detection through the voltage response of a galvanic pair

Abstract

Chloride ion ingress into reinforced concrete structures is one of the primary causes of concrete degradation. Real-time monitoring of concrete structures for the ingress of chloride ions is therefore of paramount importance towards the achievement of durable and sustainable structures. It is therefore important that the chloride ion detection method used must be accurate and reliable. This paper will endeavour to show how embedded 316L stainless steel and EN3b mild steel galvanic electrode pairs will react to chloride ions present in the concrete pore solution. Through practical experimentation the correlation between the chloride ion concentration in the pore solution and galvanic voltage measurements between the electrode pairs was explored. An experimental setup was proposed, based on concrete samples with inbuilt fluid containment vessels holding sodium chloride solution, which was allowed to permeate through the pore structure of the concrete over a defined period of time. At particular time intervals core samples were taken at different depths in concrete samples, and the chloride ion content was determined with depth of penetration through titration on the extracted material. The chloride ion content results from titration tests were compared to the measured galvanic voltages. Within certain limits there was good correlation between the chloride ion concentration and the measured voltage readings across the galvanic electrode pair. Galvanic voltage measurements provide a relevant technique for the detection of chloride ions in concrete and in the design of a chloride ion sensory system. Validation testing was also carried out, where samples with known salt concentrations were prepared against which the results obtained could be compared.