In recent years, electrochemical methods for the repair of reinforced and prestressed concrete structures have been successfully tested in several countries, including Portugal. This project marked the first practical case of a desalination treatment successfully applied to a road viaduct in Sines. 

The viaduct, a prestressed reinforced concrete structure built in the early 1980s, extends along a curve for 155 meters, featuring a continuous box section with interior longitudinal prestressed beams. It is supported by five massive reinforced concrete piers of varying heights and two abutments. 

Intervention goal

Before the current rehabilitation intervention, a diagnostic study and rehabilitation project were carried out. This study identified the main cause of the concrete deterioration as the high chloride content at the level of the reinforcement, resulting from the marine environment surrounding the structure, combined with insufficient concrete cover. As a result, the reinforcement was undergoing corrosion-induced deterioration. 

Technique used

To substantially extend the structure's service life, APS approved the complementary electrochemical desalination treatment. This allowed for a reduced removal of contaminated concrete and eliminated the root cause of the structure’s degradation. 

Results

The electrochemical desalination treatment, using the Norcure method, was successfully completed on approximately 1,600 m2 of the deck. Over a period of six months, the chloride content was reduced to the desired level. The desalination process was monitored in real time and controlled by computerized current transformers, providing continuous critical data throughout the process. 

The total area of 1,600 m² in phases, each lasting five weeks. A significant reduction in chloride content was achieved, with levels near the reinforcement reaching approximately 0.2% by weight of cement, compared to initial levels of around 0.6%. 

As part of the performance evaluation conducted on June 30, 2008, the structure was generally in good condition, showing low levels of deterioration. The electrochemical desalination treatment of the viaduct proved to be effective, meeting expectations in terms of results, safety in use, and elimination of the cause of concrete degradation.