The use of steel in concrete has increased massively in the last century, and it is now one of the most commonly used building materials on earth (second to water in usage by mankind). The biggest durability problem with structures of this material is corrosion of the steel reinforcement. The cause of this corrosion that is most difficult to remedy is the presence of chloride in the concrete, which allows the steel to corrode at a rapid rate. Because of the huge economic significance of this problem over the last 50 years, there has been almost continuous research in many countries to categorise the problem.