Cathodic Protection of Steel in Concrete by Paul M. Chess, John P. Broomfield
By Paul M. Chess, John P. Broomfield
Cathodic safeguard of metal in Concrete offers the main entire precis of the electrochemical suggestions for treating metal corrosion up to now. It comprises an exam of the reasons of corrosion and its accelerating cost and describes review tools.
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The electrochemical reaction at the anode surface generates acid products. It has been suggested that excessive evolution of acid causing softening of the concrete surface has been responsible for the failure of some anode systems. However, this is unlikely be a major problem provided that the anode system is properly selected and maintained (Gower and El-Belbol, 1996). 6 NEED FOR AND LIMITATIONS ON PATCH REPAIRS IN CASES WHERE CATHODIC PROTECTION IS TO BE USED The cathodic protection current cannot pass through an air gap and is normally transmitted to the reinforcement via the pore solution of concrete or mortar materials.
It was noted that a sulphate resisting cement was always less effective than a Portland cement. 4 Aggregate type and other additives In general the higher the strength of the aggregate the more likely it is to be resistant to the passage of ions. But this is not always so. For example, granite aggregate has been used for several major projects because of its high strength, but concrete made with this material has been found to provide relatively poor diffusion resistance results. This is probably because of microcracks in the aggregate.
The first consists of changes in appearance, such as discoloration with local blemishes and staining. The second stage affects surface texture and is marked by cracking. The third stage of deterioration is disruption with major spalling of concrete. Signs of poor compaction of concrete, stains or discoloration, cracking, spalling, pop-outs, erosion and softening of concrete should be observed and recorded. The position and orientation of cracks must be considered in relation to loadings and restraint to shrinkage and thermal movement.