Corrosion protection of embedded steel bars in concrete

^* Corresponding author: g.green@mapei.co.za

Abstract

The design and construction of structures is a responsible decision, based on sound engineering principles, and virtuous and cautious consideration should be paramount. This presentation is based on the results of two different field studies to protect and ensure longevity of structural reinforced steel in structural concrete.1) Application of sacrificial anodes for the galvanic cathodic protection of reinforced steel.2) Application of a cementitious polymer based elastic coating as a viable corrosion protection system against aggressive elements. The use of these materials allows the protection and increases durability of reinforcement steel in concrete, from premature degradation caused by carbonation and chloride attack, ensuring an extended life span.Sacrificial anodes for galvanic cathodic protection are composed of zinc in conjunction with electrolytic gels that, thanks to electrochemical processes, once connected with the reinforcement steel, lower the potential of corrosion to the reinforcement steel themselves. Thus, allowing the prolongation of corrosive events in structures which need to be repaired whilst preventing degradation, if correctly applied, in new structures.Furthermore, in such protection systems, a polymer-modified cementitious membrane is used, with superior elastic and crack bridge properties in environmental exposure temperatures of up to -20°C, thus protecting the concrete from penetration of carbon dioxide and chloride attack.Due to an in-depth laboratory study in combination with live field tests, this paper will highlight that a 2-mm thick protection layer can effectively counteract the penetration of CO2 for over 50 years, and is comparable to a concrete cover thickness of 54 mm of concrete, at a w/c ratio of 0,5. With regards to chloride attack, studies confirm that 2,5 mm of coating equals 30 mm of concrete cover at a w/c ratio of 0,452.