Development of improved galvanic anodes for the protection of steel in concrete.

摘要

Corrosion in reinforced concrete is a major problem affecting modern infrastructure. If left untreated, severe damage may occur, rendering the structure aesthetically unpleasing and structurally deficient. It is estimated that nearly 15% of all bridges in the U.S. are deemed to be structurally inadequate and are in dire need for major repairs. The toll of corrosion on the economy can be enormous; in a recent study it was estimated that the indirect cost of corrosion is equivalent to 6% of the U.S. Gross Domestic Product. It is therefore imperative that new and improved remedial measures be developed. In Canada, the problem is equally dire; it is estimated corrosion affecting Canadian reinforced concrete infrastructure will cost approximately ;There exist many alternatives in corrosion remedial measures, some of which are undesired and costly. Depending on the circumstance, the degree of corrosion and the importance of the structure, some remedial measures may be preferable to others. However, the cost and effectiveness of the remedial work do not always reach the desired level of protection. In fact, one of the most common remedial practices is known as concrete patch repair and it often accelerates corrosion activity in adjacent non-treated concrete. This phenomenon is known as 'ring anode' effect. The cause of corrosion acceleration is due to electrochemical incompatibilities between the repaired concrete and existing concrete.;Discrete sacrificial anodes are designed to prevent or reduce the corrosion caused by the ring anode effect. Sacrificial anodes function by attaching a more susceptible metal (typically zinc) to the steel reinforcement, which in theory should render the steel into a cathode, thus protecting it from corrosion. Sacrificial anodes are an attractive remedial alternative primarily due to their low maintenance, low cost, and long life expectancy.;Sacrificial Anode A is a new generation protocol discrete anode, intended to provide maximum protection to nearby steel. Presently, sacrificial anodes that are commercially available only provide corrosion prevention or low corrosion control. The maximum protection as deemed by National Association of Corrosion Engineers (NACE) International is cathodic protection and it occurs once the steel has been polarized to levels above 100 mV. At this level, corrosion is virtually, if not completely, halted.;Corrosion of steel reinforcement in concrete is an electro-chemical process. The harmful by-product of oxidizing iron is known as rust. This rust is several times larger in volume than steel and results in the deterioration of concrete due to extreme tensile pressures. Chloride induced corrosion is very common in coastal regions or areas where de-icing salts are used. Once the chlorides have penetrated to the steel reinforcement surface, the chlorides enter into a chemical reaction in which the natural passive film encasing the steel reinforcement is broken down. Without the passive film the rebar is free to corrode.;The primary objective of this research is to test the performance of the new Sacrificial Anode A and compare its performance to sacrificial anodes already available on the market. Reinforced concrete slab specimens, were equipped with the different sacrificial anodes and were then exposed to various environmental and chloride conditions. The specimens were monitored for half-cell potentials, current density output, and potential decay. After several months exposed to these conditions, results show Sacrificial Anode A, was able to consistently out-perform the other sacrificial anodes. Cathodic levels were reached on several occasions with polarization of the steel reaching well above 100 mV. Results also indicated that Sacrificial Anode A was able to generate current densities well into the 2 to 20 mA/m2 range required for maximum protection.