Pr Vassie

FACTORS INFLUENCING ELECTROCHEMICAL REMOVAL OF CHLORIDE FROM CONCRETE

Electrochemical chloride removal was studied using prisms made from concrete containing various levels of chlorides derived from sodium chloride added during mixing. The amount of chloride removed during the treatment was assessed by analysing the anolyte. Chloride removal increased with increasing applied potential, number of reinforcing bars at a particular depth and initial chloride content of the concrete. A greater percentage of chloride was removed from prisms where the thickness of the chloride bearing layer of concrete was less than the depth of cover to the reinforcement. Where the thickness of the chloride bearing layer exceeded the cover to the reinforcement, the use of an external cathode significantly increased the total amount of chloride removed. Chloride removal from a face remote from the source of the chloride contamination (soffit desalination) was shown to be feasible.

INFLUENCE OF CATHODE-TO-ANODE AREA RATIO AND SEPARATION DISTANCE ON GALVANIC CORROSION CURRENTS OF STEEL IN CONCRETE CONTAINING CHLORIDES

Abstract Corrosion of steel embedded in concrete was modelled using a 4m long beam containing a bar in seven segments, one mild steel and six stainless steel, which could be electrically connected or isolated by external switches. The concrete mix was dosed with 3% Cl to initiate corrosion. The current flowing between the mild steel and the stainless steel was monitored using a zero resistance ammeter for a range of connections to investigate the influence of the ratio of cathode anode area and cathode-anode separation. It was found that the current increased with increasing cathode anode area ratio but the rate of increase decreased with increasing cathode anode ratio. The current decreased with increasing separation between the anode and cathode although the cathode elements most distant from the anode contributed a significant current.

Assessing the sustainability of methods of repairing concrete bridges subjected to reinforcement corrosion

Sustainability should be at the heart of all decision making, according to the UK government. The construction industry has a key role in delivering this objective because its products impinge on many facets of human activity and the environment, and also because it consumes vast amounts of resources each year. The repair and maintenance of concrete bridges suffering from reinforcement corrosion remains a significant problem in the UK. Many methods of treatment are available but the challenge facing engineers is how to select options that are demonstrably sustainable. Because sustainability is a relatively new Subject and the information required to Study it quantitatively is not currently available, either because the measurements have not been made or because the data has not been compiled into an accessible form, a pseudoquantitative method has been developed which can be used to appraise sustainability. The paper describes the background to the method and discusses its application to three commonly used bridge maintenance strategies: silane application, concrete repair and cathodic protection.