Evaluation of Corrosion Progress Using Multichannel Iron Wire Electrodes Embedded in Cement Test Block

Abstract

Eight thin iron wires were embedded in a cement test block to evaluate the corrosion behavior during the carbonization of cement by the CO₂ gas absorption. The gas supplied to the chamber containing the cement test block was subsequently changed as air, CO₂, and air. Electric resistance measurement of thin wires revealed that the iron kept passivated during supplying of air and uncorroded during the CO₂ supply to promote carbonization and began to be corroded from the surface side when the air was resupplied after carbonization due to the existence of oxygen in the air as an oxidizing agent. A series of two-electrode impedance between the selected two iron wires were measured as a function of depth from the surface. The impedance of all electrodes dropped considerably several hours after the CO₂ supply. That was caused by the difference in the immersion potential of iron wires as a function of depth, i.e., pH transition from alkaline to neutral range. As a result, iron wires were polarized when electrically connected to each other during the progress of carbonization. When the carbonization was completed, each iron wire showed the impedance response corresponding to the corrosion condition depending on the depth.