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ELECTROCHEMICALLY BASED TECHNIQUES FOR ASSESSING AND PREVENTING CORROSION OF STEEL IN CONCRETE

Objective

STEEL IN REINFORCED AND POST TENSIONED CONCRETE STRUCTURES IS PROTECTED AGAINST CORROSION BY THE ALKALINITY OF THE SURROUNDING CONCRETE. THIS PROVIDES PASSIVATION OF THE STEEL SURFACE. DETERIORATION OF PASSIVATION CAN BE CAUSED EITHER BY CARBON UPTAKE FROM CO2 IONS OF ATMOSPHERIC ORIGIN OR BY CHLORIDE CONTAMINATION ARISING E.G. FROM DE-ICING AGENTS USED TO PREVENT FROST DAMAGE. THE PROJECT WILL CONCENTRATE ON CATHODIC PROTECTION RESEARCH TO DEVELOP A METHOD OF LONG TERM CORROSION PROTECTION FOR STEEL REINFORCEMENT WHOSE PASSIVATION HAS DETERIORATED.

In this project, the use of cathodic protection (CP) for reinforced structures and the function and lifetime of a polymeric anode have been investigated.

A carbon filled polymeric anode, the FEREX-100, has been developed to meet the special requirements of cathodic protection for reinforced concrete structures, and studied in detail. The deterioration mechanisms of the anode material and of the surrounding concrete were investigated. The anode showed long term stability, a reliable lifetime, and a good electrochemical integrity to concrete. These characteristics of the anode have been realised during 5 years in field application.

The passage of current through concrete causes ions to move by electromigration and changes the chemistry near the anode and at the surface of the protected steel. Quantitative knowledge of electromigration has been obtained in the laboratory. A large number of laboratory model tests and analysis of samples drilled from field installations have confirmed that with the small current used in practical CP, the migration effects are relatively small.

Knowledge has been gathered on the protection criteria for cathodic protected steel in concrete. It was confirmed that even under very unfavourable conditions CP is effective in stopping corrosion of steel in concrete and, most importantly, CP will restore passivating conditions at the steel surface. The maintenance of this condition requires even smaller currents than was previously thought necessary and modified protection criteria are recommended. The spread of protection can also improve with time.

Information on the effect of seasonal variations of temperature and humidity on CP has been obtained from more than 4 years of measurements from an instrumental field installation.

Embeddable sensors for measurements of concrete resistivity, potential and some chemical properties of concrete have been investigated. A new type of embeddable reference electrode, based on manganese dioxid e, has been developed. Experience of more than 4 years of field use and many laboratory studies have confirmed its superiority over currently used electrodes.

Dual purpose probes for corrosion monitoring and resistivity measurements have been developed. The use of a new cathode based on titanium has improved their performance.

Engineering aspects of the practical installation of CP have been investigated. Most installations require the anodes to be placed in a concrete overlay, often sprayed onto the surface. Several large scale installations have been constructed.
THE WORK IS DIVIDED INTO 4 AREAS :

A) DESIGNING OF A MODEL ALLOWING FOR THE DETERMINATION OF THE OPTIMUM POTENTIAL SHIFT TO BE APPLIED TO THE CONCRETE
B) DESIGNING OF LONG TERM STABLE POLYMERIC ANODES TO PROLONG CATHODIC PROTECTION
C) DEVELOPMENT OF ELECTROCHEMICALLY BASED SENSORS FOR LONG TERM USE IN CONCRETE. THESE SENSORS WILL MONITOR CHANGES IN THE PROTECTION QUALITYD) DEVELOPMENT OF REHABILITATION AND REPAIR TECHNIQUES BASED ON CATHODIC PROTECTION
THE OVERALL AIM IS TO DEVELOP APPROPRIATE MATERIALS AND DESIGNS, MORE RELIABLE PROTECTION, CRITERIA, ADEQUATE CONSTRUCTION TECHNIQUES AND CONTROL METHODS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Dyckerhoff & Widmann AG
Address
Erdinger Landstraße 81
81829 München
Germany

Participants (3)

ATV Korrosionscentralen
Denmark
Address

2600 Glostrup
FEDERAL INSTITUTE FOR MATERIAL RESEARCH AND TESTING
Germany
Address
87,Unter Der Eichen 87
12205 Berlin
Raychem Ltd
United Kingdom
Address
Faraday Road
SN3 5HH Swindon