Concrete skin detects cracking and chemical leaks

When concrete chemical and nuclear containment structures begin to crack or corrode, facility engineers need an instant warning. One way to monitor structural integrity of concrete is to measure its electrical impedance, which changes when the material cracks. However, this strategy suffers sensitivity issues. An international team instead is proposing to monitor both cracking and chemical leakage of concrete structures by measuring the electrical impedance of a multilayer coating applied to the structure’s surface (Struct. Health Monit. 2016, DOI: 10.1177/1475921716670574). Researchers led by Aku Seppänen of the University of Eastern Finland and Mohammad Pour-Ghaz of North Carolina State University made the sensing skin from silver, latex, and copper. Silver paint’s impedance is sensitive to cracking, whereas copper paint’s impedance is sensitive to both cracking and chloride ions, which can corrode the reinforcing steel placed in concrete. The latex layer separates and insulates the two metal layers. The team showed that imaging the skin’s two conductive layers using electrical impedance tomography signaled the presence of chloride from a salt solution as well as cracks in a concrete specimen after force was applied.