This paper proposes the use of a 1-dimensional (1-D) electromechanical impedance model to extract proper design guidelines when selecting patch-size and frequency range for corrosion detection in reinforced concrete structures using the electromechanical impedance (EMI) technique. The theoretical results show that the sensitivity mainly lies in the peak frequencies of the impedance spectrum, while outside resonant frequencies the sensitivity levels are low, and are prone to natural variation. If the mechanical impedance ratio between the host structure and patch is too large, the peaks and thereby the sensitivity decreases. This can be counteracted by increasing the patch thickness. Tests were carried out in reinforced concrete structures, where lead zirconate titanate (PZT) patches were attached to the rebars. Patches measuring 10 × 10 mm in length and width, with thicknesses of 0.3, 0.5 and 1.5 mm, were used. The results show that only the 10 × 10 × 1.5 mm patch, was able to generate a clear peak in the 50 kHz to 400 kHz impedance spectrum. Furthermore, a reinforced concrete structure with the 1.5 mm patch attached was induced significant corrosion damages, resulting in cracking of the structure. Due to this, a leftward shift of the main peak, and creation of new peaks in the spectrum was observed.

This paper investigates the use of reinforced concrete (RC) battery for powering future Wireless Sensor Nodes (WSN) for internet of things (IoT) -monitoring the corrosion process in tunnels. Results obtained from a realworld immersed tunnel, which has hundreds of electrochemical based corrosion sensors embedded into the reinforced concrete structure, show that sufficient energy can be extracted from these electrochemical sensors to perform wireless transmissions of the corrosion potential to a base-station. With an open circuit potential of 975 mV, the maximum output power that can be extracted is 12.4 µW, while the minimum measured output power is 1 µW. The results also show that power of 8.82 µW, with an open circuit potential of 727 mV, can directly be extracted from the reinforcement steel itself. This makes it possible for the energy source to have a long lifetime, since the steel volume can work as a large battery anode. If the steel reinforcement (anode) is protected by an impressed cathodic protection system (CP) the induced galvanic corrosion-rate is minimum to non-exisiting.Furthermore, performed calculations show that harvesting energy from the corrosion sensors will induce a galvanic corrosion rate of 11 µm/year under continious usage, while a transimission of the corrosion data once every second month, only induces a (galvanic) corrosion rate of 1.83 µm/year. This indicates that there is no risk to the structural integrity when aplying the energy source.