Throwing Power of Embedded Anodes for the Galvanic Cathodic Protection of Steel in Concrete

The chloride-induced corrosion of steel reinforcement is one of the main causes of deterioration of reinforced concrete structures. Cathodic protection (CP) of steel in concrete is a widely accepted repair technique to reduce, or completely stop, reinforcement corrosion. One possible method of cathodic protection is through the use of embedded galvanic (sacrificial) anodes, consisting of a zinc metal core surrounded by a precast alkali-activated cementitious mortar. The design of a CP system based on embedded galvanic anodes is based on the required amount of zinc material and the throwing power of the anode (i.e., radius around the anode in which the steel achieves sufficient protection). In this research, the protection of steel reinforcement in concrete surrounding an embedded galvanic anode was evaluated through depolarisation measurements with internal and external reference electrodes. Based on these measurements, the throwing power of the galvanic anode was determined, taking into account the 100 mV depolarisation criterium (cf. EN ISO 12696:2016). Additionally, the influence of the degree of chloride contamination of the concrete and relative humidity and temperature of the environment on the throwing power was evaluated. The results show a strong influence of chloride contamination on the throwing power of the galvanic anodes, in the sense that a higher chloride concentration in the concrete matrix leads to a reduction in the throwing power. This reduction can be related to the more negative potential of corroding steel reinforcement compared to passive steel, thus leading to a lower driving potential for the galvanic reaction. Especially when the chloride concentration is higher than 1 m% vs. cement mass, the throwing power is greatly reduced. Additionally, it was found that a higher relative humidity (RH) of the environment (and consequently, a higher RH of the concrete) resulted in a higher throwing power.

Cathodic protection of steel in concrete – experience and overview of 30 years application

This paper presents an overview of 30 years' experience with cathodic protection of steel in concrete in The Netherlands. Principles and practical aspects of CP and its design and installation are presented. Three phases have passed from the late 1980s until present: pioneering, development and maturity. In the first period CP was mainly applied to precast elements corroding due to mixedin chlorides. The parties involved worked together to draw up a Technical Guideline. In the second period, application to bridges came up, including post-tensioned structures, which was then innovative. Furthermore, galvanic anode systems were introduced. In the third period, CP became a fully accepted method of securing durability and safety. Renewed collaboration led to a database that allowed analysis of various aspects of CP system working life, including shortcomings in early systems. Major successes and lessons learned will be presented. Technical and non-technical developments are highlighted and some recent innovative CP components and systems are discussed.