In situ measurement of chloride ion concentration in concrete: integral solution for sustainable construction

Abstract

Chloride ions are one of the major contributors to degradation of reinforcement-concrete. The presence of these ions initiate pitting corrosion in the reinforcement steel and ultimately results in the failure of the construction. Thus, the chloride ion concentration inside concrete is a crucial parameter to predict the service life of a structure. Potentiometric measurement is the state-of-the-art technique to measure chloride ion concentration in concrete. Despite promising results, this technique is limited to lab-scale measurements because drift in the reference potential causes flawed data. This work is focused on omitting or improving the reference electrode to obtain a reliable and drift free data for long- term measurements. First, a dynamic electrochemical technique, to remove the need for a reference electrode, is treated. An alternative to the potentiometric measurement (zero current technique) is chronopotentiometry, which is a dynamic electrochemical approach. It is proposed as a reference free technique. The response does not depend on the absolute reference potential and any metal wire can be used as a pseudo-reference electrode. Second, an alternative for a long-term reference electrode, i.e. Kynol based activated carbon (AC) pseudo-reference electrode, is treated. The that activated carbon has a huge double layer capacitance (in the order of tens of Farad per gram) and has a better material stability in concrete environment. The high double layer capacitance countervails any small changes in adsorption/desorption reaction (non-faradaic) which would cause a change in its electrode potential. Along with the chloride ion concentration, the corrosion status of steel is an additional aspect for determining the structural deterioration. A rigorous corrosion sensor which indicates the active or passive state of corrosion is presented. The time constant of a decaying potential, after a current pulse is interrupted, gives the status of corrosion of reinforcement steel. Overall this work demonstrates some solutions to the challenges in the measurement of chloride ion in concrete, especially when using a long-term embedded reference electrode. This will help in building a new type of chloride sensor system for concrete based on dynamic electrochemical measurement with embedded corrosion sensors and a better pseudo-reference electrode.