Numerical simulation of potential distribution due to the corrosion of reinforcement in concrete structures

Corrosion of the reinforcement is one of the causes of reducing service-life of concrete structures. The methodologies used for making a decision on the repair or the replacement of damaged elements require in situ measurements for locating corroding areas. This paper is focussed on the results of the application of half-cell potential mapping for locating corroding areas on reinforced concrete pipeline and on six concrete columns. For reinforced concrete pipelines the validity of the half-cell potential measurements was confirmed by using finite-element calculations based on the distribution of the electrical field in soil. For the reinforced concrete columns, it was observed that the value of the half-cell potential can be inaccurate for locating corroding zones, when steel-concrete interface is cracked or when concrete cover is delaminated due to the expansion of corrosion products. This means that highly corroding areas are not always detected by this method. The occurrence of cracking and delamination in reinforced concrete structures was also studied by using a finite-element approach. It is shown that the absolute values of potential of steel in concrete depend on the delamination of concrete cover. So, the value of half cell potential should not be used as an indicator of corrosion. On the contrary, the potential gradient is a good indicator for locating corroding reinforcement in crack-free concrete surface. Some additional finite-element calculations were carried out to study the influence of concrete conductivity, cover thickness and delamination size on the size of concrete surface influenced by corrosion. So, this size increases with concrete cover thickness.