Abstract
This paper reports on the advantages and drawbacks of available test methods for the determination of chloride content in cementitious materials in general, and the application of Ag/AgCl chloride sensors in particular. The main factors that affect the reliability of a chloride sensor are presented. The thermodynamic behaviour of silver in the presence or absence of chloride ions is described and kinetic restrictions are addressed. The parameters that can affect the activity of chloride ions in the medium and/or the rate of ion exchange and dissolution/precipitation processes at the sensor’s surface are also considered. In this regard, the contribution of morphology and microstructure of the AgCl layer, binding of chloride ions and the compactness of hydration products around the chloride sensor are highlighted. The important parameters for a reliable sensor’s response are discussed and the possible causes of inaccuracies are evaluated.
Highlights
Chloride ions are among the primary causes of steel corrosion in reinforced concrete structures.Determination of the chloride content in the concrete cover and near the steel reinforcement is needed for evaluating the risk of corrosion
One of the first documented attempts for non-destructive determination of the chloride content in cementitious materials was reported in the early 1990s, when Ag/AgCl chloride sensors were embedded in mortar specimens [1]
The performance of embedded chloride sensor in cementitious materials depends on the physical condition of the interfaces (Ag/AgCl/cement paste) at the sensor’s surface as well as the pore solution composition
Summary
Chloride ions are among the primary causes of steel corrosion in reinforced concrete structures. The performance of embedded chloride sensor in cementitious materials depends on the physical condition of the interfaces (Ag/AgCl/cement paste) at the sensor’s surface as well as the pore solution composition. When the chloride sensor is embedded in cementitious materials (Figure 1c), the microstructure of these cementitious materials is important for the electrochemical reactions relevant to the sensor’s response (Figure 1d,e) This is mainly in view of pore solution composition and compactness of hydration products at the interface between sensor and cementitious materials. The slag cement paste is considered because it contains a high amount of water soluble sulphates, and sulphide ions [4]
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