Laboratory investigation of electrochemical chloride extraction from concrete with penetrated chloride

摘要

Chloride extraction of concrete is a short-term electrochemical treatment against corrosion of reinforcing steel. The aim is to remove chloride ions from the concrete cover in order to reinstate passive behaviour. Physically sound concrete is left in place. To make this method more predictable and reliable, a laboratory study was carried out. Concrete specimens with penetrated chloride were subjected to electrochemical chloride extraction. The influence on chloride extraction was studied of: cement type (Portland, blast furnace slag), water-cement-ratio, cover to the reinforcement, steel geometry, amount of charge passed and type of electrolyte. Additionally, some potential 'killing' factors and the effect of the treatment on corrosion pits were studied. Chloride profiles before and after treatment were measured. The durability of the final situation is predicted from calculation of the redistribution by diffusion of the remaining chloride ions. For various cement types and cover depths, the minimum amount of electrical charge was determined to obtain corrosion protection for at least 10 years. The presence of bending cracks in the specimens or tie wires close to the concrete surface did not have a significant effect on the extraction result. The test results suggest that active corrosion pits are extinguished by the treatment.